Revision Total Knee Replacement - Patellar Component (Resurfacing/Revision)

Indications. Revision of the patellar component is considered for:

• Symptomatic patellar component loosening with adequate remaining bone stock
• Polyethylene wear with metallosis or synovitis
• Patellar fracture associated with component loosening or displacement
• Component malposition causing maltracking
• Secondary resurfacing of a painful patella left unresurfaced at primary TKR
• A failed metal-backed patellar component The one decision that matters — bone stock drives everything. Before committing, confirm the pain is genuinely patellofemoral (not referred from the hip or spine), exclude infection with baseline CRP and ESR (and aspiration if there is any doubt), and verify the femoral and tibial components are stable and well-positioned. Isolated patellar work is appropriate only when the rest of the construct is sound. The operative strategy then follows the measured bone stock:

Exposure options. The standard route is a medial parapatellar arthrotomy through the previous incision (use the most lateral of several scars to protect the lateral skin blood supply). When exposure is difficult in a stiff knee, extend with a quadriceps snip (a 45-degree cut into the quadriceps tendon — improves access for a modest extensor penalty); reserve V-Y quadricepsplasty for severe stiffness (greater exposure but it weakens the extensor mechanism); and use a tibial tubercle osteotomy when the widest exposure is needed or a concurrent tibial revision is planned, as it preserves the extensor mechanism. Consent specifically for patellar fracture, extensor mechanism injury (quadriceps or patellar tendon), the small risk of needing patelloplasty or patellectomy if bone stock is worse than expected, persistent anterior knee pain, and the higher infection risk of revision surgery. Setup. Supine on a radiolucent table with a leg holder or thigh bump, upper-thigh tourniquet, regional or general anaesthesia. Review the skyline and lateral radiographs (and a CT if patellar thickness is uncertain), note the previous implant type (metal-backed versus all-polyethylene), and have cerclage wire, bone graft and patellectomy options available before starting.

The goal: expose the patella through the previous medial parapatellar incision, remove the failed component without fracturing the bone, clear all cement and membrane, measure the residual stock, and then resurface, augment, patelloplasty or patellectomy as the stock dictates — finishing with central, stable patellar tracking. The exposure is laid out as the first steps below.

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Rehabilitation | Phase | Timing | Weight-bearing and motion | Key points | |-------|--------|---------------------------|------------| | 1 | 0 to 2 weeks | WBAT with frame or crutches; CPM 0 to 60 degrees, advancing to 0 to 90 | Quadriceps sets and ankle pumps from day 1; wound check day 3 | | 2 | 2 to 6 weeks | Full weight-bearing; ROM toward 110 degrees | Scar care and quadriceps strengthening; drain out by 24 to 48h | | 3 | 6 to 12 weeks | Full activity, building strength | Outpatient radiographs (AP, lateral, skyline) at 6 weeks | | 4 | 3 to 12 months | Unrestricted | Radiographs at 1 year; monitor anterior knee pain and crepitus | If an intra-operative fracture was fixed or the bone stock was poor, protect with a brace locked in extension for 6 weeks and limit ROM (0 to 60 degrees for weeks 2 to 6), advancing only after radiographic healing. Tranexamic acid (1g at induction, 1g at closure) reduces blood loss by about 30 to 40 percent; chemical thromboprophylaxis (LMWH or DOAC) continues for 35 days. Complications

The resurfacing debate. Whether to resurface the patella at primary TKR remains contested. The pooled randomised evidence — Chen and colleagues' 2013 meta-analysis (14 trials, 1725 knees) and the updated 2021 meta-analysis (32 trials, 6887 knees) — shows resurfacing lowers the reoperation rate and patellofemoral crepitus and modestly improves Knee Society and function scores, with no significant difference in anterior knee pain, range of motion or patient satisfaction. The 2013 data quantified an absolute reoperation reduction of about 4 percent (a number needed to treat of 25). The practical implication for revision is that a painful unresurfaced patella with good bone stock and sound tracking is a reasonable indication for secondary resurfacing, but resurfacing for pain alone should be counselled cautiously. Registry evidence. The large arthroplasty registries (NJR, AOANJRR, NZJR) consistently report modestly lower cumulative revision for resurfaced or routinely-resurfacing practice than for leaving the patella unresurfaced, and markedly higher revision for metal-backed patellar components — which have been largely abandoned in favour of all-polyethylene designs. Practice varies by region between routine, selective and never-resurface strategies, reflecting surgeon training and implant design more than a single global standard; exact percentages differ by registry, year and case-mix, so quote them as trends rather than fixed numbers. Pathoanatomy of patellar maltracking. When tracking is abnormal the patellar component is rarely the primary culprit. Berger and colleagues showed on CT that patellofemoral complications correlate with excessive combined (femoral plus tibial) internal component rotation: small internal rotation (1 to 4 degrees) causes tilt and lateral tracking, moderate (3 to 8 degrees) causes subluxation, and large (7 to 17 degrees) causes dislocation or late failure. The lesson — before blaming or revising the patella, image and correct femoral (and tibial) rotation, which may mandate femoral rather than patellar revision.