Patellar Resurfacing in TKA — Controversies

Whether to resurface the patella during total knee arthroplasty (TKA) remains one of the most contentious controversies in arthroplasty surgery. Anterior knee pain originating from the patellofemoral joint is one of the most common complaints after TKA, occurring in approximately 5–10% of patients. Proponents of routine patellar resurfacing argue that replacing the arthritic patellar articular surface eliminates a source of ongoing pain and reduces the need for secondary patellar resurfacing. Opponents argue that patellar resurfacing adds surgical complexity, carries specific complications, and that well-designed femoral component trochlear geometry provides sufficient patellofemoral kinematics without resurfacing. National practice varies enormously — the UK (guided by NICE TA304, 2011) recommends against routine patellar resurfacing; Australia and many parts of the USA resurface routinely.

• Anatomy of the patellofemoral joint in TKA: the patella is a sesamoid bone within the quadriceps-patellar tendon mechanism; it articulates with the trochlear groove of the femur; TKA femoral components are designed with a trochlear groove that the native patella (if not resurfaced) articulates against; the design of the femoral component trochlear groove (depth, width, lateral wall height) is critical for patellofemoral tracking regardless of whether the patella is resurfaced
• Patellar resurfacing — what it involves: the articular surface of the patella is resected to a flat surface using a dedicated patellar cutting guide; a polyethylene button (dome-shaped or anatomical — cruciform or oval) is cemented onto the resected patellar surface; the patellar bone must be at least 12–15 mm thick after resurfacing to avoid patellar fracture (a feared complication); patellar tracking must be assessed after implantation by the `no thumb test` — the knee is taken through a range of motion without manually guiding the patella; if the patella tracks centrally without lateral subluxation, patellar tracking is adequate
• Patelloplasty: when the patella is not formally resurfaced, some surgeons perform patelloplasty — removal of osteophytes, denervation of the patella (peripheral electrocautery of the fat pad and peripatellar soft tissues — destroys the peripatellar nerve fibres that mediate patellofemoral pain), and smoothing of the articular surface; this is intended to improve patellofemoral outcomes without formal resurfacing

• Meta-analyses and RCTs: the evidence from RCTs and meta-analyses is conflicting; a 2014 Cochrane review (Pavlou et al.) analysed 34 RCTs and concluded there was no clinically important benefit from routine patellar resurfacing in terms of overall functional outcomes (KSS, WOMAC, Oxford Knee Score) or reoperation rates; anterior knee pain rates were similar between resurfaced and non-resurfaced groups in most studies; a 2005 Cochrane review reached similar conclusions; NICE Technology Appraisal 304 (2011) reviewed the evidence and concluded that routine patellar resurfacing was not cost-effective based on current evidence, and recommended against it as routine practice
• Studies favouring resurfacing: some RCTs and registry studies show a significantly higher secondary patellar resurfacing (reoperation) rate in patients whose patella was NOT resurfaced at primary TKA — rates of secondary patellar resurfacing of 3–8% have been reported; proponents argue this persistent reoperation risk justifies routine primary resurfacing; the TOPKAT trial (UK multicentre RCT, 2019 — the largest UK RCT of patellar resurfacing in TKA) showed no significant difference in OKS at 5 years between resurfaced and non-resurfaced groups, supporting the non-resurfacing approach
• The `patellar friendly` femoral component argument: modern TKA femoral components are designed with improved trochlear geometry (`patellar-friendly` designs) — deeper trochlear grooves, laterally elevated trochlear walls, and continuous trochlear-to-condylar curvature that guides the native patella throughout the range of motion without requiring a polyethylene button; these design improvements have narrowed the functional difference between resurfaced and non-resurfaced TKA, supporting the non-resurfacing approach

• Selective resurfacing — when to resurface: most surgeons who do not routinely resurface will selectively resurface in specific circumstances — (1) severe patellofemoral OA (bone-on-bone patellofemoral involvement; marked patellar articular surface damage at the time of surgery); (2) pre-operative patellofemoral pain as the dominant symptom; (3) inflammatory arthritis (rheumatoid arthritis — patients with RA have a higher rate of secondary patellar resurfacing if not resurfaced at primary TKA; RA also affects patellar bone, making late secondary resurfacing more difficult); (4) obese patients (BMI >35 — higher patellofemoral loads); (5) surgeon preference / high-volume centre practice
• Contraindications to patellar resurfacing: patellar bone stock <12 mm (post-resection patellar thickness must be ≥12–15 mm to avoid avascular necrosis or patellar fracture); bipartite patella; previous patellar surgery; patellar bone deficiency (post-trauma, osteonecrosis)

• Secondary patellar resurfacing — the salvage procedure: when a non-resurfaced patella causes persistent anterior knee pain after primary TKA, secondary patellar resurfacing (adding a patellar button to the previously unresurfaced patella) can be performed; the results of secondary patellar resurfacing are inferior to primary resurfacing — approximately 50–70% of patients gain meaningful pain relief; the outcome is better when performed for `true` patellofemoral pain (identifiable articular source) vs unexplained anterior knee pain; the decision to perform secondary resurfacing should be made carefully after excluding component malalignment (particularly femoral/tibial internal rotation), infection, and loosening
• Femoral component rotation and the patellofemoral joint: internal rotation of the femoral component (placing the component internally rotated relative to the transepicondylar axis) is the most common technical error causing patellofemoral problems after TKA (regardless of patellar resurfacing); internal rotation shifts the trochlear groove medially and the tibial tubercle-to-trochlear groove distance (TT-TG) increases, causing lateral patellar maltracking; the femoral component must be externally rotated relative to the posterior condylar axis — typically 3° of external rotation for a posterior referencing system, or aligned to the transepicondylar axis for an anterior referencing system
• The `clunk syndrome`: a distinct complication of posterior-stabilised (PS) TKA — a thick fibrous nodule forms on the anterior aspect of the femoral component`s posterior cruciate-substituting cam and post mechanism; during active knee extension, this nodule catches on the intercondylar box of the femoral component, producing an audible and palpable clunk; the clunk is typically felt at approximately 30–45° of flexion during extension; treatment — arthroscopic excision of the fibrous nodule; clunk syndrome is less common with modern PS designs that have improved cam-and-post geometry

• Patellar resurfacing in TKA: major controversy; UK — NICE TA304 (2011) recommends AGAINST routine resurfacing; Australia and USA often resurface routinely; TOPKAT trial (UK 2019) — no difference in OKS at 5 years
• Cochrane evidence: no clinically significant benefit from routine resurfacing for overall function or reoperation rate; anterior knee pain similar between groups in most RCTs
• Selective resurfacing indications: severe patellofemoral OA; pre-op PF pain dominant; rheumatoid arthritis; obesity (BMI >35); surgeon preference
• Patellar bone stock: NEVER resect to <12 mm residual thickness; minimum 12–15 mm to avoid patellar fracture; measure before and after resection
• No-thumb test: knee through ROM without manually guiding patella after implantation; patella should track centrally; lateral subluxation = maltracking = correct with lateral release or check component rotation
• Patellar fracture: most feared complication of resurfacing; <12 mm bone stock + AVN + devascularisation from aggressive lateral release; stable fractures — conservative; displaced — ORIF; comminuted — patellectomy
• Femoral component internal rotation: MOST COMMON technical error causing patellofemoral problems; shifts trochlear groove medially → lateral patellar tracking; must externally rotate femoral component 3° from posterior condylar axis (or align to TEA)
• Secondary patellar resurfacing: salvage for persistent anterior knee pain after non-resurfaced TKA; 50–70% pain relief; inferior to primary resurfacing; exclude component malrotation and infection first
• Clunk syndrome: PS TKA; fibrous nodule on cam-post catches on intercondylar box at ~30–45° during extension; audible clunk; arthroscopic nodule excision
• Patellar AVN: aggressive lateral retinacular release + resurfacing devascularises patella; preserve medial blood supply; if established → observation or patellectomy