Background: Patellar complications are a consequential cause of failure of primary total knee arthroplasty (TKA). The purpose of this study was to evaluate the association of demographic and patient factors with the long-term risk of patellar complications as a function of time in a very large cohort of primary TKAs performed with patellar resurfacing.

Methods: We identified 27,192 primary TKAs utilizing cemented all-polyethylene patellar components that were performed at a single institution from 1977 through 2015. We evaluated the risk of any aseptic patellar complication and any aseptic patellar reoperation or revision, subanalyzed risks of reoperation or revision for loosening, maltracking/instability, and wear, and evaluated the risk of clinical diagnosis of patellar fracture and clunk/crepitus. The mean age at TKA was 68 years (range, 18 to 99 years); 57% of the patients were female. The mean body mass index (BMI) was 32 kg/m2. The primary diagnosis was osteoarthritis in 83%, and 70% of the TKAs were posterior-stabilized. Median follow-up was 7 years (range, 2 to 40 years). Risk factors for each outcome were evaluated with Cox regression models.

Results: Nine hundred and seventy-seven knees with all-polyethylene patellae developed patellar complications. Survivorship free from any aseptic patellar complication was 93.3% at 20 years. Twenty-year survivorship free from any aseptic patellar reoperation was 97.3% and free from any aseptic patellar revision was 97.4%. Fifteen-year survivorship for the same end points for procedures performed from 2000 to 2015 was 95.7%, 99.2% and 99.3% respectively, representing substantial improvements compared with implants placed before 2000. Univariate analysis demonstrated that male sex (hazard ratio [HR], 1.4), an age of <65 years (HR, 1.3), and a BMI of ≥30 kg/m2 (HR, 1.2) were associated with increased risk of patellar complications (all p ≤0.01). Posterior-stabilized designs were associated with fewer patellar reoperations and revisions overall (HR, 0.4 and 0.4; p < 0.001) but higher risk of patellar clunk/crepitus (HR, 14.1; p < 0.001).

Conclusions: The 20-year survivorship free from any aseptic patellar complication in this series of cemented all-polyethylene patellae was 93%. Important risk factors for any aseptic patellar complication were male sex, an age of <65 years, a BMI of ≥30 kg/m2, and a patella implanted before 2000.

Level Of Evidence: Prognostic Level IV. See Instructions for Authors for a complete description of levels of evidence.

Unlabelled: We identified patient and surgeon factors associated with patellar component failure in a series of 8530 TKAs performed in 5640 patients using the same posterior cruciate ligament-retaining TKA with all-polyethylene patellar components between January 1983 and December 2003. Patellar failure was defined as loosening, fracture, or patellar revision. All infections were excluded. Statistical analysis using Kaplan-Meier and Cox regression was used to determine the risk of patellar failure. Followup averaged 7.0 years (range, 2-22 years). Patellar component loosening occurred in 4.8% of TKAs (409 knees). Patellar fracture was identified in 5.2% of TKA (444 knees). Twenty-five patellae were revised (0.3%). TKA performed with a lateral release and patients with a body mass index of greater than 30 kg/m(2) were at the greatest risk of patellar loosening and fracture, respectively. Male gender, preoperative varus alignment of greater than 5 degrees , and large patellar component size also predicted a higher risk of patellar fracture. Medial patellar component position, tibial component thickness of greater than 12 mm, preoperative valgus alignment of 10 degrees or more, and preoperative flexion of 100 degrees or more predicted patellar loosening. An awareness of these factors that predict patellar failure after TKA may help determine the relative indications for TKA and influence surgical technique, especially when using this prosthesis.

Level Of Evidence: Level IV, prognostic study. See the Guidelines for Authors for a complete description of levels of evidence.

Patellar complications are a source of poor total knee arthroplasty (TKA) outcomes that can require re-operation or prosthetic revision. Complications can occur with or without patellar resurfacing. The objective of this work is to answer six questions. (1) Have risk factors been identified, and can they help to prevent patellar complications? Patellar complications are associated with valgus, obesity, lateral retinacular release, and a thin patella. Selecting a prosthetic trochlea that will ensure proper patellar tracking is important. Resurfacing is an option if patellar thickness is greater than 12mm. (2) What is the best management of patellar fracture? The answer depends on two factors: (a) is the extensor apparatus disrupted? and (b) is the patellar implant loose? When either factor is present, revision surgery is needed (extensor apparatus reconstruction, prosthetic implant removal). When neither factor is present, non-operative treatment is the rule. (3) What is the best management of patellar instability? Rotational malalignment should be sought. In the event of femoral and/or tibial rotational malalignment, revision surgery should be considered. If not performed, options consist of medial patello-femoral ligament reconstruction and/or medialization tibial tuberosity osteotomy. (4) What is the best management of patellar clunk syndrome? When physiotherapy fails, arthroscopic resection can be considered. Recurrence can be treated by open resection, despite the higher risk of complications with this method. (5) What is the best management of anterior knee pain? The patient should be evaluated for causes amenable to treatment (fracture, instability, clunk, osteonecrosis, bony impingement on the prosthetic trochlea). If patellar resurfacing was performed, loosening should be considered. Otherwise, secondary resurfacing is appropriate only after convincingly ruling out other causes of pain. A painstaking evaluation is mandatory before repeat surgery for anterior knee pain: surgery is not in order in the 10% to 15% of cases that have no identifiable explanation. (6) What can be done to treat patellar defects? Available options include re-implantation (with bone grafting, cement, a biconvex implant, or a metallic frame), bone grafting without re-implantation, patellar reconstruction, patellectomy (best avoided due to the resulting loss of strength), osteotomy, and extensor apparatus allograft reconstruction.

Level Of Evidence: V, expert opinion.

Background: Whether to resurface the patella during total knee arthroplasty (TKA) remains debated. One often cited reason for not resurfacing is inadequate patellar thickness. The aim of this study was to describe the implant survivorships, reoperations, complications and clinical outcomes in patients who underwent patellar resurfacing of a thin native patella.

Methods: From 2000 to 2010, 7,477 patients underwent primary TKA with patellar resurfacing and had an intraoperatively, caliper-measured patella thickness at our institution. Of these, 200 (2.7%) had a preresection patellar thickness of ≤19 millimeters (mm). Mean preresection thickness was 18 mm (range, 12-19). Mean age was 69 years, mean body mass index was 31 kg/m, and 93% of the patients were women. Median follow-up was 10 years (range, 2-20).

Results: At 10 years, survivorships free of any patella revision, patella-related reoperation, and periprosthetic patella fracture were 98%, 98%, and 99%, respectively. There were 3 patella revisions (1 aseptic loosening, 2 periprosthetic joint infections). There were 2 additional patella-related reoperations for patellar clunk. There were 3 nonoperatively managed periprosthetic patella fractures. Radiographically, all nonrevised knees had well-fixed patellae. Knee society scores improved from mean 36 points (interquartile range [IQR] 24-49) preoperatively to mean 81 points (IQR 77-81) at 10-year follow-up.

Conclusion: Resurfacing the thin native patella was associated with high survivorship free of patellar revision at 10-year follow-up. Nevertheless, there was 1 case of patellar loosening and 3 periprosthetic patella fractures. These risks must be weighed against the known higher incidence of revision when the thin native patella is left unresurfaced.

Despite advances in surgical technique and implant design, complications involving the extensor mechanism and patellofemoral joint after total knee arthroplasty (TKA) continue to be the most common cause of pain and the most commonly cited reason for revision surgery. Periprosthetic patellar fractures occur in 1.19% of all reported cases after TKA, with a clear correlation with resurfacing of the patella. In 88.32% of the cases reported the fracture is not associated with a traumatic event and it is identified at the follow-up examination during the first 2 years after knee replacement. Predisposing factors for fracture include lateral release, excessive bone removal, peg fixation and cementation, improper patellar tracking and prosthesis malpositioning. More than 50% of fractures are associated with a loose implant which complicates the fracture management. Non-operative treatment seems to offer acceptable functional results and pain relief, especially in cases of minimal displacement and stable implant fixation. However, when surgical reconstruction is undertaken, open reduction and internal fixation with tension band or cerclage wiring should not be the first choice of treatment as the rate of failure and subsequent non-union may be as high as 90%.

Background: Periprosthetic knee fractures (PPKFs) following total knee arthroplasty (TKA) are uncommon, but potentially serious injuries. We analyze the risk and risk factors for a PPKF in standard primary TKA patients who have osteoarthritis and a minimally (cruciate-retaining TKAs without a femoral box cut) or posterior-stabilized TKA. In addition, we report the risk for patients who have other underlying knee disorders and/or a higher level of TKA constraint.

Methods: All primary TKAs were identified from the Danish National Patient Register and the Danish Knee Arthroplasty Register using data between 1997 and 2022. Subsequent fractures were identified through the International Classification of Diseases diagnosis code, Nordic Medico-Statistical Committee procedure code, or indication for revision TKA.

Results: We included 120,642 standard primary TKA patients who had 1,659 PPKFs. The cumulated proportions were 0.4% (95% confidence interval (CI) 0.3 to 0.4) at 2 years 0.8% (0.7 to 0.8) at 5 years. At 10 years, the cumulated proportion was 1.7% (1.6 to 1.8), with 1.3% in the femur, 0.2% in the patella, and 0.2% in the tibia. Significant risk factors were (hazard ratio [HR] [95% CI]); ipsilateral hip arthroplasty (2.3 [2.0 to 2.6]); women (2.1 [1.8 to 2.4]), osteoporosis (1.4 [1.2 to 1.7]); age 80+ (1.4 [1.3 to 1.6]), uncemented TKA (1.3 (1.1 to 1.5) and Charlson Comorbidity Index score 3+ (1.4 [1.1 to 1.8]). An additional 22,624 primary TKA patients who had other underlying knee disorders and/or a higher level of implant constraint were included with 633 PPKFs. The 10-year cumulated proportions were 8.3% (95% CI 6.9 to 9.8) when the underlying disorder was a previous fracture, 2.8% (2.2 to 3.5) for rheumatic disorders, and 5.2% (2.6 to 10.6) for osteonecrosis. In patients who had condylar constrained knees, it was 6.9% (5.1 to 9.4), and 12.4% (8.0 to 16.04) for hinges.

Conclusions: In standard primary TKA patients, the 10-year cumulated proportion of PPKFs was 1.7%, and ipsilateral hip arthroplasty, women, osteoporosis, advanced age, uncemented TKA and higher Charlson Comorbidity Index increased the risk. Higher risks were observed in non-osteoarthritis patients and/or patients who had a higher level of TKA constraint.

Periprosthetic patella fractures are a rare complication that can lead to severe disability following total knee arthroplasty (TKA). There are several factors that increase the risk of this injury, including patient comorbidities, anatomic considerations, and surgical technique. With these factors limiting healing ability in the area, periprosthetic patellar fractures can pose a major challenge to treat, with potentially lasting morbidity for affected patients. These fractures can occur at any time following TKA and are classified based on their associated implant stability and disruption of the extensor mechanism using the Ortiguera and Berry classification system. Each of the three types of fractures can be managed in their own unique way; however, outcomes remain poor, and the complication rates remain high regardless of fracture type. This article provides an overview of the current literature and the recommended management of periprosthetic patella fractures.

Patellar resurfacing may be associated with improvement in certain patient-reported outcome scores such as KOOS-Pain, QoL, and Sports. However, such improvement is inconsistent and remains substantially disputed. In contrast, despite their relatively low incidence, potential complications of patellar resurfacing include but are not limited to loss of bone stock, increased future revision complexity,
patellar fracture, avascular necrosis, and extensor mechanism violation, which may be catastrophic in the setting of primary elective TKA.

Patellofemoral complications are common after total knee replacement (TKR). Leaving the patellar unsurfaced after TKR may lead to complications such as anterior knee pain, and re-operation to surface it. Complications after patellar resurfacing include patellar fracture, aseptic loosening, patellar instability, polyethylene wear, patellar clunk and osteonecrosis. Historically, patellar complications account for one of the larger proportions of causes of failure in TKR, however, with contemporary implant designs, complication rates have decreased. Most remaining failures relate to patellofemoral tracking. Understanding the causes of patellofemoral maltracking is essential to prevent these complications as well as manage them when they occur.

Total knee arthroplasty (TKA) is one of the most successful procedures in orthopedic surgery. Nevertheless, postoperative patellofemoral complications remain a challenging problem, affecting a substantial proportion of patients. Complications involving the patellofemoral joint (PFJ) can occur in both resurfaced and nonresurfaced patellae. Types of PFJ complications include anterior knee pain, maltracking, fracture, avascular necrosis and patellar clunk. The causes of patellofemoral complications can be categorized into patient-, surgeon- and implant-related factors. Patient characteristics such as female sex, young age, depression and increased body mass index have been linked with increased complications. Important technical considerations to avoid complications include achieving appropriate rotational alignment of the femoral and tibial components, maintaining joint line height, medializing the patellar button and avoiding “overstuffing” the PFJ. Component design features such as conformity, shape and depth of the femoral trochlea have also been shown to be important. Although the cause of patellofemoral complications after TKA may sometimes be unknown, it remains important to minimize errors that can lead to these complications.

Background: Little data exist on the influence of patellar thickness on postoperative motion or complications after total knee arthroplasty (TKA). This study addresses the following questions: Is postoperative motion influenced by change in composite patellar thickness? Is change in patellar thickness associated with more complications? And do more complications occur in the knees with a patellar bone remnant (<12 mm) and a native patellar thickness <18 mm?

Methods: In total, 3655 TKAs were performed by 3 surgeons over a 28-year interval. All knees had caliper measurement of patellar thickness before the patellar cut, after implantation of the component and postoperative motion recorded in the database 1 or 2 years after TKA.

Results: Patellar composite thickness was the same (1034 knees), thicker (1617 knees), and thinner (1004 knees). A significant but weak relationship was identified between the change in patellar thickness and motion (P < .01, ρ = -0.046); an increase in "composite patellar thickness" of 10 mm would result in a 3° loss of knee motion. Significant differences were identified between change in thickness and manipulations (P < .05), ruptures (P = .01), and patellar clunk/crepitus (P < .01). Examining knees with bone remnant thicknesses (<12 mm/≥12 mm), there was no difference in fractures (P = .26). No extensor ruptures occurred in knees with remnant thickness <12 mm. Comparing knees with native bone thickness (≤18 mm/>18 mm), significant differences were found in fractures (P < .01) and patellar radiolucencies (P = .01).

Conclusion: As this data does not demonstrate a strong tendency toward losing motion when the patellar thickness is increased, the authors recommend avoiding compromise of the patellar bone stock and tendon insertion. When native patellar bone is thin (<18 mm), we recommend maintaining 12 mm of patellar bone stock and accept the increase in composite thickness.

Purpose: Patellar thickness is a concern in total knee replacement with patellar resurfacing because of the risk of patellar fracture or implant loosening. The aim of this study was to evaluate if patellar thickness is related to clinical outcome in the absence of patellar fracture or implant loosening.

Methods: Early results of 169 patients who underwent total knee replacement with patellar resurfacing were reviewed to assess the effect of patellar thickness on clinical outcome. The mean follow-up was 13 months. The range of motion, Knee Society Score, Function Score and WOMAC Score were assessed preoperatively, at day 0, 6 months and 1 year. Radiographs were assessed for patellar fracture or implant loosening.

Results: Thirty-one percent of all patients had preoperative thickness <21 mm. Seven percent had <12 mm residual thickness after patellar cut, all were female. Twenty-three percent had ≥1 mm increase of thickness after surgery. Radiographs did not show any patellar fracture or implant loosening. However, preoperative patellar thickness <21 mm had poorer gain in range of motion at 1 year. Preoperative range of motion had greater influence on postoperative range of motion than preoperative patellar thickness. Residual thickness <12 mm had lower gain in WOMAC score at 1 year and an increase in thickness ≥1 mm postoperatively was associated with lower gain in WOMAC score at 6 months.

Conclusions: Early results of patellar resurfacing with preoperative thickness <21 mm or residual thickness <12 mm were found to be inferior even in the absence of patellar fracture or implant loosening. Conservative cutting resulting in 1 mm increase in thickness was also found to have inferior clinical results.

Level Of Evidence: II.

With patellar thickness averaging 24.0 mm and 21.9 mm in Singapore men and women undergoing total knee arthroplasty, achievement of precut thickness is difficult if the recommended residual bony thickness of 15 mm is maintained. We retrospectively compared the clinical outcome of 56 patellae resurfaced 12 mm (mean residual thickness, 13.7 mm). Both groups were comparable in terms of demographic characteristics, presentation, precut patellar thickness, and operative details (P> .05). Knee scores (P= .627), extensor mechanism function (P= .625), and postoperative range of motion (P= .344) were comparable. Differences in the overall (P= .167) and patellar (P= .061) complication rates as determined by chi-square test on the SPSS 10.0 program were not significant, although there were 4 patella-related complications in group 2. Increased patella-related complications may be associated with an excessive patellar composite of the patellofemoral articulation. A residual patellar thickness of <12 mm did not appear to affect the clinical outcome in this series.

Unlabelled: Anthropometric patellar dimensions can influence implant design and surgical techniques in patellar resurfacing for TKA. We measured anthropometric patellar dimensions in 752 osteoarthritic knees (713 in females and 39 in males) treated with TKA in 466 Korean patients and compared them with reported dimensions for Western patients. We investigated the effects of postoperative overall thickness deviations, residual bony thickness after bone resection, and postoperative deviations of component center positions from median ridge positions versus clinical and radiographic outcomes evaluated 1 year after surgery. Korean patients undergoing TKA had thinner and smaller patellae than Western patients. We found no associations between preoperative to postoperative overall thickness differences and clinical and radiographic outcomes and no differences between knees with a residual bony thickness 12 mm or greater and knees with a residual thickness less than 12 mm, with the exception of WOMAC pain scores. We found no associations between postoperative deviations of component center position and clinical or radiographic outcomes. Our findings indicate bone resection for patellar resurfacing can be flexible without jeopardizing clinical outcome.

Level Of Evidence: Level IV, prognostic study. See the Guidelines for Authors for a complete description of levels of evidence.

Patellar complications are a source of poor total knee arthroplasty (TKA) outcomes that can require re-operation or prosthetic revision. Complications can occur with or without patellar resurfacing. The objective of this work is to answer six questions. (1) Have risk factors been identified, and can they help to prevent patellar complications? Patellar complications are associated with valgus, obesity, lateral retinacular release, and a thin patella. Selecting a prosthetic trochlea that will ensure proper patellar tracking is important. Resurfacing is an option if patellar thickness is greater than 12mm. (2) What is the best management of patellar fracture? The answer depends on two factors: (a) is the extensor apparatus disrupted? and (b) is the patellar implant loose? When either factor is present, revision surgery is needed (extensor apparatus reconstruction, prosthetic implant removal). When neither factor is present, non-operative treatment is the rule. (3) What is the best management of patellar instability? Rotational malalignment should be sought. In the event of femoral and/or tibial rotational malalignment, revision surgery should be considered. If not performed, options consist of medial patello-femoral ligament reconstruction and/or medialization tibial tuberosity osteotomy. (4) What is the best management of patellar clunk syndrome? When physiotherapy fails, arthroscopic resection can be considered. Recurrence can be treated by open resection, despite the higher risk of complications with this method. (5) What is the best management of anterior knee pain? The patient should be evaluated for causes amenable to treatment (fracture, instability, clunk, osteonecrosis, bony impingement on the prosthetic trochlea). If patellar resurfacing was performed, loosening should be considered. Otherwise, secondary resurfacing is appropriate only after convincingly ruling out other causes of pain. A painstaking evaluation is mandatory before repeat surgery for anterior knee pain: surgery is not in order in the 10% to 15% of cases that have no identifiable explanation. (6) What can be done to treat patellar defects? Available options include re-implantation (with bone grafting, cement, a biconvex implant, or a metallic frame), bone grafting without re-implantation, patellar reconstruction, patellectomy (best avoided due to the resulting loss of strength), osteotomy, and extensor apparatus allograft reconstruction.

Level Of Evidence: V, expert opinion.

Patellar complications following total knee arthroplasty (TKA) have begun to emerge as a major cause of failure. In an effort to understand some of the mechanical factors that might contribute to patellar component failure, a biomechanical study was performed. Quadriceps force and anterior patellar strain were measured during dynamic flexion in 10 fresh, paired human cadaver knee joints. First, tests were performed in the intact knee, followed by either posterior cruciate ligament (PCL) retention or sacrifice of TKA without patellar resurfacing. Tests were then performed following patellar resurfacing with an overly thick, optimum and thin, bony patella. Patellar strain increased in each specimen (with flexion angles of up to 80 degrees), was most pronounced as the bony patella became thinner, was closest to the intact knee when the patella was not resurfaced, and was unaffected by PCL retention or sacrifice. Patellar osteotomy, resulting in a bony patellar thickness of less than 15 mm, resulted in significantly increased strain. TKA systems should include instrumentation that allows precise restoration of overall patellar thickness while maintaining a bony patellar thickness of at least 15 mm.

Background: Whether to resurface the patella during total knee arthroplasty (TKA) remains debated. One often cited reason for not resurfacing is inadequate patellar thickness. The aim of this study was to describe the implant survivorships, reoperations, complications and clinical outcomes in patients who underwent patellar resurfacing of a thin native patella.

Methods: From 2000 to 2010, 7,477 patients underwent primary TKA with patellar resurfacing and had an intraoperatively, caliper-measured patella thickness at our institution. Of these, 200 (2.7%) had a preresection patellar thickness of ≤19 millimeters (mm). Mean preresection thickness was 18 mm (range, 12-19). Mean age was 69 years, mean body mass index was 31 kg/m, and 93% of the patients were women. Median follow-up was 10 years (range, 2-20).

Results: At 10 years, survivorships free of any patella revision, patella-related reoperation, and periprosthetic patella fracture were 98%, 98%, and 99%, respectively. There were 3 patella revisions (1 aseptic loosening, 2 periprosthetic joint infections). There were 2 additional patella-related reoperations for patellar clunk. There were 3 nonoperatively managed periprosthetic patella fractures. Radiographically, all nonrevised knees had well-fixed patellae. Knee society scores improved from mean 36 points (interquartile range [IQR] 24-49) preoperatively to mean 81 points (IQR 77-81) at 10-year follow-up.

Conclusion: Resurfacing the thin native patella was associated with high survivorship free of patellar revision at 10-year follow-up. Nevertheless, there was 1 case of patellar loosening and 3 periprosthetic patella fractures. These risks must be weighed against the known higher incidence of revision when the thin native patella is left unresurfaced.

With patellar thickness averaging 24.0 mm and 21.9 mm in Singapore men and women undergoing total knee arthroplasty, achievement of precut thickness is difficult if the recommended residual bony thickness of 15 mm is maintained. We retrospectively compared the clinical outcome of 56 patellae resurfaced 12 mm (mean residual thickness, 13.7 mm). Both groups were comparable in terms of demographic characteristics, presentation, precut patellar thickness, and operative details (P> .05). Knee scores (P= .627), extensor mechanism function (P= .625), and postoperative range of motion (P= .344) were comparable. Differences in the overall (P= .167) and patellar (P= .061) complication rates as determined by chi-square test on the SPSS 10.0 program were not significant, although there were 4 patella-related complications in group 2. Increased patella-related complications may be associated with an excessive patellar composite of the patellofemoral articulation. A residual patellar thickness of <12 mm did not appear to affect the clinical outcome in this series.

Background: Little data exist on the influence of patellar thickness on postoperative motion or complications after total knee arthroplasty (TKA). This study addresses the following questions: Is postoperative motion influenced by change in composite patellar thickness? Is change in patellar thickness associated with more complications? And do more complications occur in the knees with a patellar bone remnant (<12 mm) and a native patellar thickness <18 mm?

Methods: In total, 3655 TKAs were performed by 3 surgeons over a 28-year interval. All knees had caliper measurement of patellar thickness before the patellar cut, after implantation of the component and postoperative motion recorded in the database 1 or 2 years after TKA.

Results: Patellar composite thickness was the same (1034 knees), thicker (1617 knees), and thinner (1004 knees). A significant but weak relationship was identified between the change in patellar thickness and motion (P < .01, ρ = -0.046); an increase in "composite patellar thickness" of 10 mm would result in a 3° loss of knee motion. Significant differences were identified between change in thickness and manipulations (P < .05), ruptures (P = .01), and patellar clunk/crepitus (P < .01). Examining knees with bone remnant thicknesses (<12 mm/≥12 mm), there was no difference in fractures (P = .26). No extensor ruptures occurred in knees with remnant thickness <12 mm. Comparing knees with native bone thickness (≤18 mm/>18 mm), significant differences were found in fractures (P < .01) and patellar radiolucencies (P = .01).

Conclusion: As this data does not demonstrate a strong tendency toward losing motion when the patellar thickness is increased, the authors recommend avoiding compromise of the patellar bone stock and tendon insertion. When native patellar bone is thin (<18 mm), we recommend maintaining 12 mm of patellar bone stock and accept the increase in composite thickness.

Unlabelled: Anthropometric patellar dimensions can influence implant design and surgical techniques in patellar resurfacing for TKA. We measured anthropometric patellar dimensions in 752 osteoarthritic knees (713 in females and 39 in males) treated with TKA in 466 Korean patients and compared them with reported dimensions for Western patients. We investigated the effects of postoperative overall thickness deviations, residual bony thickness after bone resection, and postoperative deviations of component center positions from median ridge positions versus clinical and radiographic outcomes evaluated 1 year after surgery. Korean patients undergoing TKA had thinner and smaller patellae than Western patients. We found no associations between preoperative to postoperative overall thickness differences and clinical and radiographic outcomes and no differences between knees with a residual bony thickness 12 mm or greater and knees with a residual thickness less than 12 mm, with the exception of WOMAC pain scores. We found no associations between postoperative deviations of component center position and clinical or radiographic outcomes. Our findings indicate bone resection for patellar resurfacing can be flexible without jeopardizing clinical outcome.

Level Of Evidence: Level IV, prognostic study. See the Guidelines for Authors for a complete description of levels of evidence.

Purpose: Patellar thickness is a concern in total knee replacement with patellar resurfacing because of the risk of patellar fracture or implant loosening. The aim of this study was to evaluate if patellar thickness is related to clinical outcome in the absence of patellar fracture or implant loosening.

Methods: Early results of 169 patients who underwent total knee replacement with patellar resurfacing were reviewed to assess the effect of patellar thickness on clinical outcome. The mean follow-up was 13 months. The range of motion, Knee Society Score, Function Score and WOMAC Score were assessed preoperatively, at day 0, 6 months and 1 year. Radiographs were assessed for patellar fracture or implant loosening.

Results: Thirty-one percent of all patients had preoperative thickness <21 mm. Seven percent had <12 mm residual thickness after patellar cut, all were female. Twenty-three percent had ≥1 mm increase of thickness after surgery. Radiographs did not show any patellar fracture or implant loosening. However, preoperative patellar thickness <21 mm had poorer gain in range of motion at 1 year. Preoperative range of motion had greater influence on postoperative range of motion than preoperative patellar thickness. Residual thickness <12 mm had lower gain in WOMAC score at 1 year and an increase in thickness ≥1 mm postoperatively was associated with lower gain in WOMAC score at 6 months.

Conclusions: Early results of patellar resurfacing with preoperative thickness <21 mm or residual thickness <12 mm were found to be inferior even in the absence of patellar fracture or implant loosening. Conservative cutting resulting in 1 mm increase in thickness was also found to have inferior clinical results.

Level Of Evidence: II.

Patellar resection thickness during total knee replacement (TKR) has been cited as a contributor to patellar fracture, anterior knee pain and quadriceps efficiency; however, optimal thickness required to minimize clinical complications remains unclear. The objectives of the current study were to determine how patellar resection thickness and bone quality impacts patellar bone strain, kinematics, and quadriceps efficiency. A series of specimen-specific finite element models of the knee joint with distributed patellar bone material properties were developed. Each specimen was virtually implanted with a TKR system. Each specimen was analyzed with patellar bone resected to thicknesses which varied from 9 to 14 mm. Simulations with reduced modulus bone were also performed. Each model perturbation was evaluated during a dynamic squat cycle, and bone strain, quadriceps force and six-degree-of-freedom kinematics were predicted. Highest peak bone strain was predicted in the thinnest patellae, indicating greatest risk of patellar fracture; highest median bone strain was predicted in the thickest patellae. Consistent differences in quadriceps efficiency were predicted; in early flexion the thickest patellae required the least quadriceps force. Greater sagittal plane tilt was observed for the thinnest patellae. Reduced modulus models (50% lower modulus) demonstrated an increase in peak bone strain of up to seven times the original modulus models. Understanding the complex interactions between patellar resection thickness, muscle requirements, kinematics, bone quality, and bone property distribution may aid in developing an understanding of which patients are most at risk from patellar fracture and anterior knee pain and how best to treat individuals to reduce potential complications.

Similarly, one low quality study supported equivalent pain metrics among patients with resurfaced versus nonresurfaced patellae after TKA (Chun 2017). KOOS-Pain with resurfaced versus non-resurfaced patellae was analyzed in two high quality studies with contradictory findings (Raaij 2021, Aunan 2016). One highquality study suggested better anterior pain at rest and while walking in the non-resurfaced cohort (Roberts 2015). Finally, two high quality studies (Raaij 2021, Ali 2016) reported similar KOOS-QoL and KOOS-Sports scores regardless of patellar management while one study (Aunan 2016) reported superior KOOS-QoL and -Sport scores among patellar resurfacing patients.

Composite knee scores demonstrated a similar pattern of conflicting findings, with the majority of studies describing equivalent outcomes according to WOMAC (Kaseb 2018, Chun 2017), HSS (Kaseb 2018, Chun 2017), KOOS total (Kaseb 2018, Kaseb 2019), and the Feller patellofemoral scores (Dong 2018, Koh 2019). In contrast, the KSS total score was found to be higher among patients who underwent patellar resurfacing according to three (Dong 2018, Aunan 2016, Ha 2019) of seven high quality studies, while the remaining studies reported no difference based on patellar management (Raaij 2021, Kaseb 2018, Roberts 2015, Thiengwittayaporn 2019).

Four high-quality studies highlighted that adverse event rates were similar regardless of patellar management, including total revisions (Dong 2018), infection (Aunan 2016), crepitus (Dong 2018, Thiengwittayaporn 2019, Koh 2019), patellar fracture, and quadricep tendon rupture (Aunan 2016).

Patellar complications are a source of poor total knee arthroplasty (TKA) outcomes that can require re-operation or prosthetic revision. Complications can occur with or without patellar resurfacing. The objective of this work is to answer six questions. (1) Have risk factors been identified, and can they help to prevent patellar complications? Patellar complications are associated with valgus, obesity, lateral retinacular release, and a thin patella. Selecting a prosthetic trochlea that will ensure proper patellar tracking is important. Resurfacing is an option if patellar thickness is greater than 12mm. (2) What is the best management of patellar fracture? The answer depends on two factors: (a) is the extensor apparatus disrupted? and (b) is the patellar implant loose? When either factor is present, revision surgery is needed (extensor apparatus reconstruction, prosthetic implant removal). When neither factor is present, non-operative treatment is the rule. (3) What is the best management of patellar instability? Rotational malalignment should be sought. In the event of femoral and/or tibial rotational malalignment, revision surgery should be considered. If not performed, options consist of medial patello-femoral ligament reconstruction and/or medialization tibial tuberosity osteotomy. (4) What is the best management of patellar clunk syndrome? When physiotherapy fails, arthroscopic resection can be considered. Recurrence can be treated by open resection, despite the higher risk of complications with this method. (5) What is the best management of anterior knee pain? The patient should be evaluated for causes amenable to treatment (fracture, instability, clunk, osteonecrosis, bony impingement on the prosthetic trochlea). If patellar resurfacing was performed, loosening should be considered. Otherwise, secondary resurfacing is appropriate only after convincingly ruling out other causes of pain. A painstaking evaluation is mandatory before repeat surgery for anterior knee pain: surgery is not in order in the 10% to 15% of cases that have no identifiable explanation. (6) What can be done to treat patellar defects? Available options include re-implantation (with bone grafting, cement, a biconvex implant, or a metallic frame), bone grafting without re-implantation, patellar reconstruction, patellectomy (best avoided due to the resulting loss of strength), osteotomy, and extensor apparatus allograft reconstruction.

Level Of Evidence: V, expert opinion.

Purpose: Patellar thickness is a concern in total knee replacement with patellar resurfacing because of the risk of patellar fracture or implant loosening. The aim of this study was to evaluate if patellar thickness is related to clinical outcome in the absence of patellar fracture or implant loosening.

Methods: Early results of 169 patients who underwent total knee replacement with patellar resurfacing were reviewed to assess the effect of patellar thickness on clinical outcome. The mean follow-up was 13 months. The range of motion, Knee Society Score, Function Score and WOMAC Score were assessed preoperatively, at day 0, 6 months and 1 year. Radiographs were assessed for patellar fracture or implant loosening.

Results: Thirty-one percent of all patients had preoperative thickness <21 mm. Seven percent had <12 mm residual thickness after patellar cut, all were female. Twenty-three percent had ≥1 mm increase of thickness after surgery. Radiographs did not show any patellar fracture or implant loosening. However, preoperative patellar thickness <21 mm had poorer gain in range of motion at 1 year. Preoperative range of motion had greater influence on postoperative range of motion than preoperative patellar thickness. Residual thickness <12 mm had lower gain in WOMAC score at 1 year and an increase in thickness ≥1 mm postoperatively was associated with lower gain in WOMAC score at 6 months.

Conclusions: Early results of patellar resurfacing with preoperative thickness <21 mm or residual thickness <12 mm were found to be inferior even in the absence of patellar fracture or implant loosening. Conservative cutting resulting in 1 mm increase in thickness was also found to have inferior clinical results.

Level Of Evidence: II.

Background: Whether to resurface the patella during total knee arthroplasty (TKA) remains debated. One often cited reason for not resurfacing is inadequate patellar thickness. The aim of this study was to describe the implant survivorships, reoperations, complications and clinical outcomes in patients who underwent patellar resurfacing of a thin native patella.

Methods: From 2000 to 2010, 7,477 patients underwent primary TKA with patellar resurfacing and had an intraoperatively, caliper-measured patella thickness at our institution. Of these, 200 (2.7%) had a preresection patellar thickness of ≤19 millimeters (mm). Mean preresection thickness was 18 mm (range, 12-19). Mean age was 69 years, mean body mass index was 31 kg/m, and 93% of the patients were women. Median follow-up was 10 years (range, 2-20).

Results: At 10 years, survivorships free of any patella revision, patella-related reoperation, and periprosthetic patella fracture were 98%, 98%, and 99%, respectively. There were 3 patella revisions (1 aseptic loosening, 2 periprosthetic joint infections). There were 2 additional patella-related reoperations for patellar clunk. There were 3 nonoperatively managed periprosthetic patella fractures. Radiographically, all nonrevised knees had well-fixed patellae. Knee society scores improved from mean 36 points (interquartile range [IQR] 24-49) preoperatively to mean 81 points (IQR 77-81) at 10-year follow-up.

Conclusion: Resurfacing the thin native patella was associated with high survivorship free of patellar revision at 10-year follow-up. Nevertheless, there was 1 case of patellar loosening and 3 periprosthetic patella fractures. These risks must be weighed against the known higher incidence of revision when the thin native patella is left unresurfaced.

With patellar thickness averaging 24.0 mm and 21.9 mm in Singapore men and women undergoing total knee arthroplasty, achievement of precut thickness is difficult if the recommended residual bony thickness of 15 mm is maintained. We retrospectively compared the clinical outcome of 56 patellae resurfaced 12 mm (mean residual thickness, 13.7 mm). Both groups were comparable in terms of demographic characteristics, presentation, precut patellar thickness, and operative details (P> .05). Knee scores (P= .627), extensor mechanism function (P= .625), and postoperative range of motion (P= .344) were comparable. Differences in the overall (P= .167) and patellar (P= .061) complication rates as determined by chi-square test on the SPSS 10.0 program were not significant, although there were 4 patella-related complications in group 2. Increased patella-related complications may be associated with an excessive patellar composite of the patellofemoral articulation. A residual patellar thickness of <12 mm did not appear to affect the clinical outcome in this series.

Background: Little data exist on the influence of patellar thickness on postoperative motion or complications after total knee arthroplasty (TKA). This study addresses the following questions: Is postoperative motion influenced by change in composite patellar thickness? Is change in patellar thickness associated with more complications? And do more complications occur in the knees with a patellar bone remnant (<12 mm) and a native patellar thickness <18 mm?

Methods: In total, 3655 TKAs were performed by 3 surgeons over a 28-year interval. All knees had caliper measurement of patellar thickness before the patellar cut, after implantation of the component and postoperative motion recorded in the database 1 or 2 years after TKA.

Results: Patellar composite thickness was the same (1034 knees), thicker (1617 knees), and thinner (1004 knees). A significant but weak relationship was identified between the change in patellar thickness and motion (P < .01, ρ = -0.046); an increase in "composite patellar thickness" of 10 mm would result in a 3° loss of knee motion. Significant differences were identified between change in thickness and manipulations (P < .05), ruptures (P = .01), and patellar clunk/crepitus (P < .01). Examining knees with bone remnant thicknesses (<12 mm/≥12 mm), there was no difference in fractures (P = .26). No extensor ruptures occurred in knees with remnant thickness <12 mm. Comparing knees with native bone thickness (≤18 mm/>18 mm), significant differences were found in fractures (P < .01) and patellar radiolucencies (P = .01).

Conclusion: As this data does not demonstrate a strong tendency toward losing motion when the patellar thickness is increased, the authors recommend avoiding compromise of the patellar bone stock and tendon insertion. When native patellar bone is thin (<18 mm), we recommend maintaining 12 mm of patellar bone stock and accept the increase in composite thickness.

Patellar resection thickness during total knee replacement (TKR) has been cited as a contributor to patellar fracture, anterior knee pain and quadriceps efficiency; however, optimal thickness required to minimize clinical complications remains unclear. The objectives of the current study were to determine how patellar resection thickness and bone quality impacts patellar bone strain, kinematics, and quadriceps efficiency. A series of specimen-specific finite element models of the knee joint with distributed patellar bone material properties were developed. Each specimen was virtually implanted with a TKR system. Each specimen was analyzed with patellar bone resected to thicknesses which varied from 9 to 14 mm. Simulations with reduced modulus bone were also performed. Each model perturbation was evaluated during a dynamic squat cycle, and bone strain, quadriceps force and six-degree-of-freedom kinematics were predicted. Highest peak bone strain was predicted in the thinnest patellae, indicating greatest risk of patellar fracture; highest median bone strain was predicted in the thickest patellae. Consistent differences in quadriceps efficiency were predicted; in early flexion the thickest patellae required the least quadriceps force. Greater sagittal plane tilt was observed for the thinnest patellae. Reduced modulus models (50% lower modulus) demonstrated an increase in peak bone strain of up to seven times the original modulus models. Understanding the complex interactions between patellar resection thickness, muscle requirements, kinematics, bone quality, and bone property distribution may aid in developing an understanding of which patients are most at risk from patellar fracture and anterior knee pain and how best to treat individuals to reduce potential complications.

Background: Patellar complications are a consequential cause of failure of primary total knee arthroplasty (TKA). The purpose of this study was to evaluate the association of demographic and patient factors with the long-term risk of patellar complications as a function of time in a very large cohort of primary TKAs performed with patellar resurfacing.

Methods: We identified 27,192 primary TKAs utilizing cemented all-polyethylene patellar components that were performed at a single institution from 1977 through 2015. We evaluated the risk of any aseptic patellar complication and any aseptic patellar reoperation or revision, subanalyzed risks of reoperation or revision for loosening, maltracking/instability, and wear, and evaluated the risk of clinical diagnosis of patellar fracture and clunk/crepitus. The mean age at TKA was 68 years (range, 18 to 99 years); 57% of the patients were female. The mean body mass index (BMI) was 32 kg/m2. The primary diagnosis was osteoarthritis in 83%, and 70% of the TKAs were posterior-stabilized. Median follow-up was 7 years (range, 2 to 40 years). Risk factors for each outcome were evaluated with Cox regression models.

Results: Nine hundred and seventy-seven knees with all-polyethylene patellae developed patellar complications. Survivorship free from any aseptic patellar complication was 93.3% at 20 years. Twenty-year survivorship free from any aseptic patellar reoperation was 97.3% and free from any aseptic patellar revision was 97.4%. Fifteen-year survivorship for the same end points for procedures performed from 2000 to 2015 was 95.7%, 99.2% and 99.3% respectively, representing substantial improvements compared with implants placed before 2000. Univariate analysis demonstrated that male sex (hazard ratio [HR], 1.4), an age of <65 years (HR, 1.3), and a BMI of ≥30 kg/m2 (HR, 1.2) were associated with increased risk of patellar complications (all p ≤0.01). Posterior-stabilized designs were associated with fewer patellar reoperations and revisions overall (HR, 0.4 and 0.4; p < 0.001) but higher risk of patellar clunk/crepitus (HR, 14.1; p < 0.001).

Conclusions: The 20-year survivorship free from any aseptic patellar complication in this series of cemented all-polyethylene patellae was 93%. Important risk factors for any aseptic patellar complication were male sex, an age of <65 years, a BMI of ≥30 kg/m2, and a patella implanted before 2000.

Level Of Evidence: Prognostic Level IV. See Instructions for Authors for a complete description of levels of evidence.

Unlabelled: Anthropometric patellar dimensions can influence implant design and surgical techniques in patellar resurfacing for TKA. We measured anthropometric patellar dimensions in 752 osteoarthritic knees (713 in females and 39 in males) treated with TKA in 466 Korean patients and compared them with reported dimensions for Western patients. We investigated the effects of postoperative overall thickness deviations, residual bony thickness after bone resection, and postoperative deviations of component center positions from median ridge positions versus clinical and radiographic outcomes evaluated 1 year after surgery. Korean patients undergoing TKA had thinner and smaller patellae than Western patients. We found no associations between preoperative to postoperative overall thickness differences and clinical and radiographic outcomes and no differences between knees with a residual bony thickness 12 mm or greater and knees with a residual thickness less than 12 mm, with the exception of WOMAC pain scores. We found no associations between postoperative deviations of component center position and clinical or radiographic outcomes. Our findings indicate bone resection for patellar resurfacing can be flexible without jeopardizing clinical outcome.

Level Of Evidence: Level IV, prognostic study. See the Guidelines for Authors for a complete description of levels of evidence.

Background: Whether to resurface the patella during total knee arthroplasty (TKA) remains debated. One often cited reason for not resurfacing is inadequate patellar thickness. The aim of this study was to describe the implant survivorships, reoperations, complications and clinical outcomes in patients who underwent patellar resurfacing of a thin native patella.

Methods: From 2000 to 2010, 7,477 patients underwent primary TKA with patellar resurfacing and had an intraoperatively, caliper-measured patella thickness at our institution. Of these, 200 (2.7%) had a preresection patellar thickness of ≤19 millimeters (mm). Mean preresection thickness was 18 mm (range, 12-19). Mean age was 69 years, mean body mass index was 31 kg/m, and 93% of the patients were women. Median follow-up was 10 years (range, 2-20).

Results: At 10 years, survivorships free of any patella revision, patella-related reoperation, and periprosthetic patella fracture were 98%, 98%, and 99%, respectively. There were 3 patella revisions (1 aseptic loosening, 2 periprosthetic joint infections). There were 2 additional patella-related reoperations for patellar clunk. There were 3 nonoperatively managed periprosthetic patella fractures. Radiographically, all nonrevised knees had well-fixed patellae. Knee society scores improved from mean 36 points (interquartile range [IQR] 24-49) preoperatively to mean 81 points (IQR 77-81) at 10-year follow-up.

Conclusion: Resurfacing the thin native patella was associated with high survivorship free of patellar revision at 10-year follow-up. Nevertheless, there was 1 case of patellar loosening and 3 periprosthetic patella fractures. These risks must be weighed against the known higher incidence of revision when the thin native patella is left unresurfaced.

The patellar resurfacing is still a controversial and unresolved problem. The choice to use the patellar resurfacing in the total knee prosthesis (TKP) is decided by the surgeon's experience; he analyzes the thickness, the shape, consumption of the surface and he chooses the use of patellar resurfacing or to limit itself to cheiloplasty, denervation, or often to the release of the lateral wing ligament. He also assesses the metabolic state of the bone linked to Osteoporosis and the potential fragility of the joint and kneecap in particular. Bone loss after total knee arthroplasty (TKP) may lead to periprosthetic fractures that are associated with significant costs (morbidity, economic, etc.) and pose a challenge to operative fixation. The literature doesn't express a definitive judgment on the two options, since the results can be overlapped on average. Each option has advantages and disadvantages to be considered in the overall balance of the patellar operation. In reality, however, this technical choice requires more consolidated decision-making criteria so as to minimize the incidence of post-surgical femoral-patellar pain syndrome, the second cause of failure, which frequently leads to revision of the implant. The balance between experience and evidence can be a compromise in the choice of surgery. The experience documented in the literature must identify the parameters capable of constructing an algorithm aimed not only at the secondary resurfacing rate, but at the overall clinical evaluation. This has implications also for the rehabilitation of these patients after surgery.

Background: Leaving the patella unresurfaced in total knee arthroplasty (TKA) is increasing due to modern patella-friendly implants, awareness that complications are not uncommon with resurfacing, and knowledge that historical studies were scientifically confounded. This study examined the effect of selective patellar resurfacing on patient-reported outcome measures (PROMs) using modern implants and techniques in cohorts rigorously matched for demographics and osteoarthritis severity.

Methods: A total of 166 TKAs performed without patellar resurfacing were case-control matched to 166 TKAs with patella resurfacing. Case-control matching was based on demographics, American Society of Anesthesiology Physical Status, comorbidities, and osteoarthritis severity. No significant differences were observed between cohorts for demographics (P ≥ .347), comorbidities (P ≥ .443), or radiographic osteoarthritis severity (P ≥ .078). Radiographic alignment and prospectively collected PROMs were evaluated preoperatively and at latest clinical follow-up.

Results: Preoperatively, patellar tilt was less for the unresurfaced patella group (3 versus 4°, P = .003); however, postoperative patellar tilt was not different (3 versus 3°, P = .225). At a mean of 2.1 years follow-up (range, 1 to 7), University of California Los Angeles Activity Level was significantly higher for the unresurfaced patella group (6.3 versus 5.5, P = .002), but the mean group difference did not reach a minimal clinically important difference. There were no other significant differences in PROMs or reoperation rates between cohorts (P ≥ .135).

Conclusion: In contemporary cruciate retaining and substituting TKA designs, not resurfacing the patella in select patients may achieve comparable PROMs and re-operation rates; and potentially greater activity level compared to patella resurfacing at early follow-up.

Level Of Evidence: III.

Background: Patellar resurfacing is optional during total knee replacement (TKR). Some surgeons always resurface the patella, some never resurface, and others selectively resurface. Which resurfacing strategy provides optimal outcomes is unclear. We assessed the effectiveness of patellar resurfacing, no resurfacing, and selective resurfacing in primary TKR.

Methods: A systematic review and meta-analysis was performed. MEDLINE, Embase, Web of Science, The Cochrane Library, and bibliographies were searched to November 2021 for randomised-control trials (RCTs) comparing outcomes for two or more resurfacing strategies (resurfacing, no resurfacing, or selective resurfacing) in primary TKR. Observational studies were included if limited or no RCTs existed for resurfacing comparisons. Outcomes assessed were patient reported outcome measures (PROMs), complications, and further surgery. Study-specific relative risks [RR] were aggregated using random-effects models. Quality of the evidence was assessed using GRADE.

Results: We identified 33 RCTs involving 5,540 TKRs (2,727 = resurfacing, 2,772 = no resurfacing, 41 = selective resurfacing). One trial reported on selective resurfacing. Patellar resurfacing reduced anterior knee pain compared with no resurfacing (RR = 0.65 (95% CI = 0.44-0.96)); there were no significant differences in PROMs. Resurfacing reduced the risk of revision surgery (RR = 0.63, CI = 0.42-0.94) and other complications (RR = 0.54, CI = 0.39-0.74) compared with no resurfacing. Quality of evidence ranged from high to very low. Limited observational evidence (5 studies, TKRs = 215,419) suggested selective resurfacing increased the revision risk (RR = 1.14, CI = 1.05-1.22) compared with resurfacing. Compared with no resurfacing, selective resurfacing had a higher risk of pain (RR = 1.25, CI = 1.04-1.50) and lower risk of revision (RR = 0.92, CI = 0.85-0.99).

Conclusions: Level 1 evidence supports TKR with patellar resurfacing over no resurfacing. Resurfacing has a reduced risk of anterior knee pain, revision surgery, and complications, despite PROMs being comparable. High-quality RCTs involving selective resurfacing, the most common strategy in the UK and other countries, are needed given the limited observational data suggests selective resurfacing may not be effective over other strategies.

Background: Surgeons may "usually" resurface the patella during total knee arthroplasty (TKA), "rarely" resurface, or "selectively" resurface on the basis of certain criteria. It is unknown which of these 3 strategies yields superior outcomes. Utilizing New Zealand Joint Registry data, we investigated (1) what proportion of surgeons employs each of the 3 patellar resurfacing strategies, (2) which strategy is associated with the lowest overall revision rate, and (3) which strategy is associated with the highest 6-month and 5-year Oxford Knee Score (OKS).

Methods: Two hundred and three surgeons who performed a total of 57,766 primary TKAs from 1999 to 2015 were categorized into the 3 surgeon strategies on the basis of how often they resurfaced the patella during primary total knee arthroplasty; with "rarely" defined as <10% of the time, "selectively" as ≥10% to ≤90%, and "usually" as >90%. For each strategy, the cumulative incidence of all-cause revision was calculated and utilized to construct Kaplan-Meier survival curves. The mean 6-month and 5-year postoperative OKS for each group were utilized for comparison.

Results: Overall, 57% of surgeons selectively resurfaced, 37% rarely resurfaced, and 7% usually resurfaced. The usually resurfacing group was associated with the highest mean OKS at both 6 months (38.57; p < 0.001) and 5 years postoperatively (41.34; p = 0.029), followed by the selectively resurfacing group (6-month OKS, 37.79; 5-year OKS, 40.87) and the rarely resurfacing group (6-month OKS, 36.92; 5-year OKS, 40.02). Overall, there was no difference in the revision rate per 100 component years among the rarely (0.46), selectively (0.52), or usually (0.46) resurfacing groups (p = 0.587). Posterior-stabilized TKAs that were performed by surgeons who selectively resurfaced had a lower revision rate (0.54) than those by surgeons who usually resurfaced (0.64) or rarely resurfaced (0.74; p < 0.001).

Conclusions: Usually resurfacing the patella was associated with improved patient-reported outcomes, but there was no difference in overall revision rates among the 3 strategies.

Level Of Evidence: Therapeutic Level III. See Instructions for Authors for a complete description of levels of evidence.

Early arthroplasty designs were associated with a high level of anterior knee pain as they failed to cater for the patello-femoral joint. Patellar resurfacing was heralded as the saviour safeguarding patient satisfaction and success but opinion on its necessity has since deeply divided the scientific community and has become synonymous to topics of religion or politics. Opponents of resurfacing contend that the native patella provides better patellar tracking, improved clinical function, and avoids implant-related complications, whilst proponents argue that patients have less pain, are overall more satisfied, and avert the need for secondary resurfacing. The question remains whether complications associated with patellar resurfacing including those arising from future component revision outweigh the somewhat increased incidence of anterior knee pain recorded in unresurfaced patients. The current scientific literature, which is often affected by methodological limitations and observer bias, remains confusing as it provides evidence in support of both sides of the argument, whilst blinded satisfaction studies comparing resurfaced and non-resurfaced knees generally reveal equivalent results. Even national arthroplasty register data show wide variations in the proportion of patellar resurfacing between countries that cannot be explained by cultural differences alone. Advocates who always resurface or never resurface indiscriminately expose the patella to a random choice. Selective resurfacing offers a compromise by providing a decision algorithm based on a propensity for improved clinical success, whilst avoiding potential complications associated with unnecessary resurfacing. Evidence regarding the validity of selection criteria, however, is missing, and the decision when to resurface is often based on intuitive reasoning. Our lack of understanding why, irrespective of pre-operative symptoms and patellar resurfacing, some patients may suffer pain following TKA and others may not have so far stifled our efforts to make the strategy of selective resurfacing succeed. We should hence devote our efforts in defining predictive criteria and indicators that will enable us to reliably identify those individuals who might benefit from a resurfacing procedure. Level of evidence V.

Background: Modern total knee arthroplasty (TKA) femoral components are designed to provide a more optimal articular surface for the patella whether or not it has been resurfaced. Previous systematic reviews comparing outcomes of patellar resurfacing and no resurfacing combine both historic and modern designs.

Aims: The aim of this study was to investigate the effect of patellar resurfacing in modern "patellar friendly" implants on (1) incidence of anterior knee pain, (2) patient reported outcomes (3) complication rates, and (4) reoperation rates compared with unresurfaced patellae in primary TKA.

Methods: MEDline, PubMed and google scholar studies were evaluated using SIGN assessment tool and data analysis was conducted using Review Manager 5.2 on only randomised controlled trials. The search terms were: arthroplasty, replacement, knee (Mesh), TKA, prosthesis, patella, patellar resurfacing, patellar retaining.

Results: Thirty-two randomised controlled studies were identified that reported the type of TKA implant used: 11 used modern "patellar friendly" implants; and 21 older "patellar non-friendly" implants. Among "patellar friendly" TKAs there were no significant differences in anterior knee pain rates between resurfaced and unresurfaced groups. Patellar resurfacing with "patellar friendly" implants had significantly higher clinical (mean difference (MD) -0.77, p = 0.007) and functional (MD -1.87, p < 0.0001) knee society scores (KSS) than unresurfaced counterparts but these did not exceed the minimal clinically important difference (MCID). Resurfacing with "patellar friendly" implants was not associated with a significant (p = 0.59) difference in the Oxford knee score (OKS), in contrast when a "patellar non-friendly" implant was used there was a significant difference (MD 3.3, p = 0.005) in favour of resurfacing. There was an increased risk of reoperation for unresurfaced TKAs with "non-patellar friendly" implants (Odds ratio (OR) 1.68, 95% CI 1.03-2.74, p = 0.04), but not for unresurfaced patellae with "patellar friendly" implants (OR 1.17, CI 0.59-2.30).

Conclusions: Patellar resurfacing in combination with a modern patellar friendly implant was not associated with a lower rate of anterior knee pain, complications, or reoperations compared to not resurfacing, nor did it give a clinically significant improvement in knee specific function. In contrast patellar resurfacing in combination with a "non-friendly" TKA implant was associated with a significantly better OKS and lower reoperation rate. Implant design should be acknowledged when patellar resurfacing is being considered.

Several high quality studies with contradictory results conclude that patellar resurfacing and non-patellar resurfacings are both viable options. Nine high quality studies reported equivalent functional outcomes with resurfaced versus non-resurfaced patellae using the KSS function (Raaij 2021 Aunan 2016, Dong 2018, Kaseb 2018, Roberts 2015), range of motion (Kaseb, 2018, Roberts 2015, Thiengwittayaporn 2019), stiffness (Aunan 2016), KOOS-ADL (Raaij 2021, Dong 2018, Aunan 2016, Ali 2016), KOOS Symptoms (Aunan 2016, Ali 2016, Kang 2019), KSS stairs (Roberts 2015), and Feller patellofemoral scores (Koh 2019). Such equivalence was furthered by one additional moderate quality study (Kaseb 2019) and three low quality studies (Albrecht 2016, Hsu 2006, Chun 2017). Only three high quality studies suggested improvement in certain function metrics among patients with patellar resurfacing, including the KSS function score (Ha 2019), active range of motion (Roberts 2015), and total patellar score (Thiengwittayaporn 2019).

Five high quality analyses reported no difference in pain metrics including VAS pain (Kaseb 2018, Ali 2016, Koh 2019), Kujala anterior knee pain scale (Kaseb 2018), anterior knee pain as a symptom (Dong 2018, Thiengwittayaporn 2019), continued pain (Koh 2019), and the feller patellofemoral score for anterior knee pain (Koh 2019) among patients with and without patellar resurfacing after TKA. Similarly, one low quality study supported equivalent pain metrics among patients with resurfaced versus nonresurfaced patellae after TKA (Chun 2017).

There is continued debate about the efficacy and indications for patellar resurfacing in total knee arthroplasty (TKA), especially with the emergence of patella-friendly designs. This study aimed to compare the postoperative outcomes in patients undergoing TKA with or without patellar resurfacing using the same implant design. This is a retrospective cohort study of patients who underwent TKA including those with patellar resurfacing (PR group) and those without (NPR group). Demographic data included age, gender, side of surgery, operative time, and body mass index (BMI). Outcomes included preoperative, 2-week, 6-week, and 1-year postoperative Knee Injury and Osteoarthritis Outcome Score and Joint Replacement (KOOS, JR) values along with knee range of motion (ROM). Postoperative complications were recorded. The power analysis with a large effect size indicated that a minimum sample size of 54 was required for Student's t-test and 34 for the paired t-test. A total of 90 medial pivot (MP) TKA were included in this study. There were 30 knees in the PR group and 60 in the NPR group. There was no significant difference between the groups for all demographic data, preoperative and postoperative ROM, and KOOS, JR values at all time points (p > 0.05 for all variables). The KOOS, JR significantly improved in the NPR groups at 2 weeks, 6 weeks, and 1 year postoperatively when compared with the preoperative score and at 6 weeks and 1 year postoperatively in the PR group (p < 0.01). No revisions related to the patellofemoral joint were observed in patients initially undergoing patellar resurfacing. One patient in the NPR group required secondary patellar resurfacing. The patella-friendly MP TKA yielded favorable postoperative outcomes, with or without patellar resurfacing. Improvements in KOOS, JR were observed earlier in the NPR group when compared with the PR group, suggesting that patellar resurfacing may not always be necessary for modern TKA designs.

Level Of Evidence:  Retrospective cohort study, Level III.

Background: The decision to resurface the patella in total knee arthroplasty (TKA) is controversial. While there is some consensus that leaving the patella unresurfaced increases risk of reoperation, there is conflicting evidence about patient reported outcomes or indications for resurfacing. This study sought to determine recent rates of patellar resurfacing, examine factors affecting rates of resurfacing, and analyze the associations between patellar resurfacing and both revision rates and patient-reported outcome measures (PROMs).

Methods: The American Joint Replacement Registry was used to identify primary TKAs performed for osteoarthritis between 2012 and 2021. Cases were classified as resurfaced patella and unresurfaced patella (URP). Outcomes analyzed included trends in patellar resurfacing, factors influencing rate of resurfacing, revision rates, operative time, and 2 PROMs.

Results: Rates of patellar resurfacing decreased and rates of URP increased significantly faster in ambulatory surgery centers and among high volume surgeons. Operative time was significantly lower in URP versus resurfaced patella (88.15 versus 89.90 minutes). The URP were significantly more likely to require revision surgery (odds ratio = 1.206 (1.078, 1.35), P = .0011). There was no significant difference in the likelihood of achieving the minimal clinically important difference in PROMs between resurfaced and nonresurfaced TKAs at 1 year (odds ratio = 1.060 (0.710, 1.581), P = .7755).

Conclusion: There was no difference in minimal clinically important difference between resurfaced and URPs and no clinically relevant difference in operative time. However, URPs were more likely to require revision surgery. Therefore, the decision not to resurface should be made carefully considering the known risk of revision and the uncertain benefit.

Background: There is currently a lack of evidence to identify the optimal patellar implant design in total knee arthroplasty (TKA). The aim of this study was to assess clinical, intraoperative, radiographic, and scintigraphic differences between inlay (IN), onlay round (OR), and onlay oval (OO) patellar implants.

Methods: A parallel-group, double-blinded, randomized trial compared IN, OR, and OO patellar implants using the same posterior-stabilized TKA prosthesis for each. Patient outcomes were prospectively followed for a minimum of 2 years, with survivorship outcomes followed for a mean of 5 years. The primary outcome was the between-group differences in the mean Kujala score change from preoperatively to 2 years postoperatively. The secondary outcomes included differences in other knee-specific and general health outcomes, intraoperative characteristics, radiographic parameters, patellar vascularity, and implant survivorship.

Results: A total of 121 participants (40 in the IN group, 41 in OR group, 40 in the OO group) were allocated to 1 of 3 implant designs. At 2 years postoperatively, there were no significant differences in Kujala score changes between groups (p = 0.7; Kruskal-Wallis test). Compared with the IN group, the OR group showed greater improvements in Knee injury and Osteoarthritis Outcome Score (KOOS) Activities of Daily Living and in KOOS Quality of Life compared with the OO group. However, the OO design exhibited better bone coverage and lower lateral facetectomy rates compared with the IN and OR designs. The IN group had more lateral contact compared with the OO group (p = 0.02; Fisher exact test), but the overall value for lateral contact was not significant (p = 0.09; chi-square test). There were no differences in postoperative scintigraphic vascularity (p = 0.8; chi-square test). There was 1 revision for infection at 3 years postoperatively in the OO group, and no revision in the other groups.

Conclusions: Patellar design did not influence patellofemoral outcomes or survivorship. However, OR implants showed improvements in some secondary patient-reported outcome measures, and OO implants exhibited superior bone coverage and improvements in several intraoperative, radiographic, and scintigraphic outcomes. These findings, combined with superior long-term implant survivorship from previous studies, add support for the use of onlay designs in TKA.

Level Of Evidence: Therapeutic Level I. See Instructions for Authors for a complete description of levels of evidence.

Unlabelled: There are a number of options available to manage the patella when revising a failed total knee arthroplasty. If the previous patellar component is well-fixed, undamaged, not worn, and compatible with the femoral revision component, then it can be retained. When a patellar component necessitates revision and is removed with adequate remaining patellar bone stock, an onlay-type all-polyethylene cemented implant can be used. Management of the patella with severe bony deficiency remains controversial. Treatment options for the severely deficient patella include the use of a cemented all-polyethylene biconvex patellar prosthesis, patellar bone grafting and augmentation, patellar resection arthroplasty (patelloplasty), performing a gull-wing osteotomy, patellectomy, or the use of newer technology such as a tantalum (trabecular metal) patellar prosthesis. Severe patellar bone deficiency is a challenging situation because restoration of the extensor mechanism, proper patellar tracking, and satisfactory anatomic relationships with the femoral and tibial components are critical for an optimal clinical outcome.

Level Of Evidence: Level IV, therapeutic study. See the Guidelines for Authors for a complete description of levels of evidence.