1 Introduction

Total knee arthroplasty (TKA) continues to be safe and efficacious in treating advanced osteoarthritis with good outcomes and symptom relief.¹ However, patellar management during TKA has remained a controversial topic. Patellar resurfacing grew prominence in the early 1990s, with studies demonstrating significant reductions in revision, anterior knee pain (AKP), and improved postoperative knee function for patients with resurfaced patellae when compared to patients without.^2–7 By 2012, the Orthopedic Research Network reported that 96 % of TKAs involved patellar resurfacing.⁸ Other studies advocating for patellar resurfacing suggested improved range of motion, as well as reduced rates of reoperation and revision.^9,10

Contrarily, some questioned the clinical impact and necessity of routine resurfacing. There are studies that have noted no significant postoperative differences between resurfaced and non-resurfaced patients regarding AKP, revision, complication, and functional outcomes.^11–16 Patellar resurfacing is also associated with increased risk of patellar fracture, avascular necrosis (AVN), risk of asymmetric resection, loss of bone, and increased surgical time.¹⁷ A systematic review performed by Simpson et al. noted that modern TKA components were associated with increased articular surface for patellar tracking. Thus, resurfacing with these “patellar friendly implants” was not associated with lower rates of anterior knee pain, complications, reoperations, or clinically significant improvement in knee function, possibly explaining the improved outcomes of resurfaced patellae in older studies.¹¹ Furthermore, Alamino et al. conducted a prospective study of patients undergoing bilateral TKA wherein one patella was preserved and the contralateral was resurfaced. Results demonstrated no significant differences in clinical or functional outcomes, and revision rates after minimum 7 years follow-up.¹³

Current literature continues to yield conflicting results. The current standard from the American Academy of Orthopedic Surgeons reports there is no difference between patellar surfacing or non-patellar resurfacing in TKA.¹⁸ Similarly, the National Institute for Health and Care Excellence (NICE) concluded that current clinical evidence was not sufficient to recommend either routine, selective, or no resurfacing in primary TKA, but did note a net cost savings for patients with their patella resurfaced, despite a more expensive initial cost.¹⁹ The purpose of this study was to add to the literature and compare the results of a matched cohort of resurfaced versus non-resurfaced patellae after total knee arthroplasty.

2 Methods

This study was an IRB approved retrospective review 1941 patients who underwent primary TKA with and without patellar resurfacing between 2016 and 2020. Patients included were those with a diagnosis of primary knee osteoarthritis. Patients excluded were those with a history of previous knee surgery and alternative indications for surgery. Demographics including age, sex, body mass index (BMI), medical comorbidities, ethnicity, and race were collected for all patients. The decision for resurfacing was at the discretion of 7 different surgeons.

After exclusions, 41 TKAs without patellar resurfacing and with 2-years of minimum follow-up were identified. Of these, 38 were matched based on age (exact), sex (exact), and BMI (±10) to 38 TKAs that had patellar resurfacing. Complications such as patellar fracture, instability, AKP, and revision surgery following TKA were documented. Instability was defined as symptomatic knee giving way or subluxation. Patient characteristics between cases and controls were compared using paired t‐test for continuous variables and Chi‐square test for categorical variables.

3 Results

Age (mean 65.3 years) and gender distributions were identical between the two cohorts, with females representing the majority of resurfaced and non-resurfaced groups (78.9 %). There was no statistical significance in either race, ethnicity, or BMI between groups. The most common comorbidity in the resurfaced group was diabetes mellitus (39.5 %) versus diabetes and COPD in the non-resurfaced group (21.1 %). There was no significant difference in comorbidities between the two groups (Table 1).

Length of stay after surgery was equal between the two groups with an average of 2.9 days in the resurfaced group (range 1–10) and in the non-resurfaced group (range 1–13). There were 3 patients who underwent manipulation under anesthesia (MUA) for stiffness in the non-resurfaced group versus none in the resurfaced group (p = 0.44). There was 1 major patellofemoral complication in both the resurfaced group (patellar fracture) and the non-resurfaced group (patellar tendon tear), requiring nonoperative management and revision surgery, respectively. Anterior knee pain was noted in 4 patients in the non-resurfaced group, as opposed to none in the resurfaced group (p = 0.37), and instability in 2 patients in the non-resurfaced group versus 1 in the resurfaced group (p = 0.44) (Table 2).

4 Discussion

Overall, the results of this study demonstrated no significant differences in the postoperative outcomes between patients with resurfaced and non-resurfaced patella in TKA regarding complications, revision surgery, AKP, and instability. The patients in each cohort were well matched, as demonstrated by the lack of significant difference between their demographics and comorbid conditions.

The two major complications noted in this study was 1 patellar fracture (resurfaced cohort) and 1 patellar tendon tear (non-resurfaced cohort) indicating conservative management and revision surgery, respectively. It has been noted that patellar fractures are a known complication of patellar resurfacing, demonstrating an increased risk of 0.2–21 %, versus a 0.05 % incidence in non-resurfaced patellae.^20–22 Canton et al. also noted that resurfaced patella make up 99 % of post-TKA patellar fractures.²³ Oftentimes, such as in the patient in this study, patellar fractures are stable, and minimally displaced; thus, nonoperative management is sufficient. However, there are instances wherein open reduction internal fixation (ORIF), patellectomy, patelloplasty, and/or complete revision arthroplasty are needed.^21,24 The patient who suffered a patellar tendon tear underwent an autograft hamstring repair, but ultimately was diagnosed with a periprosthetic infection – which likely was the culprit of the initial tear. After implant and explant of antibiotic spacer, synthetic mesh was used to repair the extensor mechanism defect.²⁵ Extensor mechanism injury usually is associated with resurfacing of the patella; however, this injury occurred in a patient without a resurfaced patella, contrary to previous studies.^26,27 Additionally, the lack of resurfacing in many cases allows for increased bone stock for fixation of a patella fracture or suture anchorage of a tendon tear.

Although the findings of this study were most consistent with publications that reported no differences in outcomes after patellar resurfacing,^11–16 it is important to note that the results here demonstrated a non-significant increased incidence of AKP, knee instability, and stiffness necessitating MUA. AKP continues to be a factor in TKA in general, with a reported prevalence of 4–49 %.²⁸ Some theories describe AKP as related to quadricep strength, patellar position, as well as patellar thickness and resurfacing.^29,30 It is theorized that maintaining native patellar anatomy may lead to AKP because of patellar mal-tracking, significant cartilage wear, and patellar surface irregularities.³¹ Therefore, some surgeons elect to resurface the patella in order to curb against AKP,^31–33 although there continues to be conflicting evidence on whether resurfacing truly mitigates AKP.^{3–7,11–16} Results from this study demonstrate that there are no significant differences in AKP between resurfaced and non-resurfaced patella, but it should be cautioned that there seemed to be a trend towards greater incidence of AKP in the non-resurfaced cohort. Besides patellar resurfacing, patellar denervation has also presented itself as another possible option to AKP; however, several studies have noted that the reduction of AKP only improves early clinical outcomes and disappears after 12 months follow-up.^34–36 Unlike this study, instability and stiffness have been reported in resurfaced patellae, likely from poor patellar tracking or under resection leads to overstuffing of the patellofemoral joint, respectively.^17,37

This study has several limitations. Sample size of this study was significantly reduced when matching the cohorts. Thus, deviations from previously reported results are likely due to variability within the small cohort included in this study. Additionally, due to its retrospective approach, the clinical assessment and judgement for management of the patella was not clearly defined. Outcomes of this study were obtained from in a single, tertiary referral center, so these results might not be generalizable to other institutions. Lastly, the discretion of when to resurface was at the choosing of 7 different surgeons, possibly instilling a selection bias as to which patient receives a resurfaced patella.

5 Conclusion

Patellar management in primary TKA remains a topic for debate, with many studies advocating for and against patellar resurfacing. The justification of patellar resurfacing with a polyethylene dome is to allow the native patella to articulate with the prosthesis in a more physiologic manner, thereby reducing wear and stress on the knee. Although this study demonstrated no significant outcome differences in either patellar management, there was a non-significant trend towards increased pain, stiffness, and instability in patients without resurfaced patellae; thus, surgeons should continue to be cautious of possible indications for patients necessitating selective patellar resurfacing.

Ethical approval and patient consent

IRB approved.

Funding

None.

Ethical and patient's consent

This retrospective study was IRB approved.

Funding

This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.

CRediT authorship contribution statement

Hassan Farooq: Methodology, Formal analysis, Data curation, Investigation, Writing – original draft, Writing – review & editing, Visualization. William Oetojo: Methodology, Formal analysis, Data curation, Investigation, Writing – original draft, Writing – review & editing, Visualization. Safi Bajwa: Methodology, Data curation, Writing – original draft. Nicholas M. Brown: Conceptualization, Methodology, Validation, Investigation, Writing – original draft, Writing – review & editing, Visualization, Supervision, Project administration.