Does the Patella Always Have to be Resurfaced

1. High-Yield Summary

• The Core Controversy: Management of the patella during primary total knee arthroplasty (TKA) remains one of the most enduring debates in adult reconstruction, divided between routine resurfacing, selective resurfacing, and routine retention.
• Clinical Practice Variance: Geographic and regional philosophy varies markedly; North American surgeons resurface the patella in > 85% to 90% of primary TKAs, whereas European, Nordic, and Asian registries historically report resurfacing rates below 10% to 20%.
• Primary Trade-Off: Routine resurfacing significantly reduces the risk of postoperative anterior knee pain and secondary reoperation for secondary resurfacing, but introduces component-specific complications including patellar fracture, aseptic loosening, polyethylene wear, and osteonecrosis.
• The Secondary Resurfacing Paradox: Performing secondary patellar resurfacing for persistent anterior knee pain after an unresurfaced primary TKA yields unpredictable satisfaction, with symptom resolution achieved in only approximately 50% to 60% of cases.
• Critical Technical Rule: When resurfacing, preserve a minimum of 12 to 15 mm of residual native bone stock, medialize the patellar button to enhance tracking, restore composite thickness without overstuffing, and maintain the lateral superior genicular blood supply.

2. Patellofemoral Anatomy & Biomechanics

The patellofemoral joint operates as a dynamic, modified plane synovial articulation that amplifies quadriceps moment arm efficiency by 30% to 50% during terminal knee extension. Joint reaction forces (PJRF) across the patellofemoral articulation escalate dramatically with flexion angle, reaching 0.5 to 1.0 times body weight during level walking, 3.0 to 4.0 times body weight during stair ascent, and up to 7.0 to 8.0 times body weight during deep squatting.

Vascular Danger Zones & Retinacular Corridors

The patella derives its blood supply from an anastomotic peripatellar arterial ring formed by the superior and inferior medial genicular arteries, the superior and inferior lateral genicular arteries, and the anterior tibial recurrent artery. Key surgical boundaries include:

• Medial Parapatellar Arthrotomy: Transects the medial genicular branches, rendering the anterior and lateral vascular contributions critical for patellar viability.
• Lateral Superior Genicular Artery (Danger Zone): Courses across the superior border of the lateral retinaculum approximately 1.5 cm proximal to the joint line. Vigorous or unmonitored lateral retinacular release endangers this vessel; combined transection of both medial and lateral supplies induces patellar devascularization and increases the risk of osteonecrosis and stress fracture.
• Infrapatellar Fat Pad (Hoffa’s Fat Pad): Houses the inferior anastomotic vessels entering the inferior pole of the patella. Complete excision of Hoffa’s pad further reduces patellar perfusion by 20% to 30%. When performing extensive soft-tissue mobilization, preserving the lateral peri-patellar tissue bridge is paramount.

3. Pathogenesis & Biomechanical Mechanics

Patellofemoral kinematics following TKA are dictated by trochlear design conformity, component rotational alignment, joint line preservation, and composite extensor mechanism balance.

Trochlear Groove Conformity & Tracking Forces

Modern femoral components feature a deepened, anatomical trochlear groove with a lateralized sulcus and an extended proximal flange that accommodates native patellar geometry through deep flexion. In an unresurfaced patella, mismatch between the biconcave native articular cartilage and a non-conforming femoral groove creates localized contact stress concentrations exceeding 20 to 30 MPa, leading to accelerated chondral wear, subchondral sclerosis, and secondary anterior pain.

Overstuffing & Joint Line Elevation

Increasing the composite anteroposterior dimension of the patella (the remaining bone plus the polyethylene button) beyond native thickness tightens the extensor mechanism in flexion, elevates patellofemoral contact pressure, and causes early flexion contracture. Similarly, proximal elevation of the tibiofemoral joint line (patella baja relative to the joint) causes the patella to engage the femoral trochlea later in flexion, shifting contact stresses to the inferior pole and predisposing to patellar clunk syndrome in posterior-stabilized designs.

4. Natural History & Clinical Epidemiology

In patients undergoing primary TKA with patellar retention, progressive articular cartilage loss occurs predictably over time. Prospective randomized studies demonstrate that 20% to 40% of unresurfaced patellae develop progressive radiographic degenerative changes within 5 to 10 years. However, radiographic progression correlates imperfectly with clinical pain; a substantial proportion of patients with severe radiographic patellofemoral changes remain clinically asymptomatic.

Conversely, anterior knee pain occurs in approximately 8% to 15% of resurfaced knees compared to 15% to 25% of unresurfaced knees. Secondary surgical intervention to resurface an initially retained patella is required in 2% to 10% of unresurfaced cohorts over a 10-year period, representing the single most frequent reason for reoperation in retained-patella series.

5. Clinical Presentation & Physical Examination

History

Patients with symptomatic patellofemoral pathology following TKA present with retropatellar or peripatellar aching provoked by loading the flexed knee. Key historical features include pain during stair ascent and descent, difficulty rising from low chairs (the “theater sign”), and painful catching or crepitation during transitional movement.

Physical Examination Maneuvers

• Active Extension & Dynamic Tracking: Observe the “J-sign”, where the patella abruptly shifts laterally as the knee reaches terminal extension (0° to 10°), signaling lateral retinacular tightness or internal rotation of the femoral/tibial component.
• Patellar Compression & Grind Test: Direct manual compression of the patella into the trochlea with active quadriceps contraction reproduces localized anterior pain and identifies friction crepitus.
• Patellar Tilt & Glide Assessment: At 20° to 30° of flexion, normal patellar mobility allows 2 quadrants of medial and lateral translation. Restriction of medial glide (< 1 quadrant) indicates pathologically tight lateral retinacular tethering.
• Palpation for Patellar Clunk: Palpate the suprapatellar pouch while moving the knee from 90° flexion to full extension; a distinct palpable or audible pop between 30° and 45° indicates entrapment of a suprapatellar fibrous nodule within the intercondylar box of a posterior-stabilized prosthesis.

6. Imaging and Radiographic Sizing

Standard Radiographic Series

• Weight-Bearing AP and True Lateral: Evaluates tibiofemoral alignment, component seating, joint line position, and patellar height (Insall-Salvati ratio [normal 0.8–1.2] or Caton-Deschamps index).
• Axial Merchant / Sunrise View (30° to 45° Flexion): The definitive projection for patellar evaluation. Quantifies the patellar congruence angle, patellar tilt angle (normal > 8° opening laterally), and central trochlear seating.
• CT Rotational Scan (Berger Protocol): Mandatory when evaluating postoperative patellar maltracking or recalcitrant pain. Measures femoral component rotation relative to the transepicondylar axis and tibial component rotation relative to the tibial tubercle. Internal rotation of either component exponentially increases lateral patellofemoral shear forces.

Intraoperative Sizing Benchmarks

Caliper measurement of native patellar thickness prior to resection establishes the baseline reference (typically 20 to 26 mm in males, 18 to 22 mm in females). The goal is exact restoration of baseline composite thickness with zero net addition.

7. Classification & Decision-Making Framework

Surgeons navigate three distinct clinical strategies based on patient etiology, anatomic criteria, and intraoperative cartilage status:

8. Surgical Technique & Decision Strategies

When the decision to resurface is made, precise technical execution is critical to avoid component failure, extensor mechanism rupture, or maltracking.

Step 1: Caliper Measurement and Exposure

Measure the native patellar thickness across its thickest central ridge with a digital caliper. Expose the entire periphery of the patella, debriding hypertrophic synovial plicae and excising peripheral osteophytes to restore the native elliptical geometry before placing resection guides.

Step 2: Symmetric Planar Resection

Perform an osteotomy strictly parallel to the anterior cortical plane. An asymmetric resection (cutting too thin medially or laterally) creates uneven load distribution, patellar tilt, and component shear:

• The 12 to 15 mm Safety Threshold: Never resect bone to leave less than 12 to 15 mm of residual native patellar bone. Resecting below 12 mm exponentially increases the risk of catastrophic intraoperative or postoperative transverse patellar fracture.
• Resection Depth Rule: The depth of resected bone must exactly equal the thickness of the chosen polyethylene implant (typically 8 to 10 mm).

Step 3: Component Medialization & Sizing

Select a component size that maximizes coverage of the resected bony surface without overhang beyond the cortices. Position the patellar button as medial as possible on the cut surface. Medialization shifts the patellar ridge medially, decreases the effective quadriceps angle (Q-angle), improves central trochlear engagement, and reduces lateral retinacular strain.

Step 4: Circumpatellar Electrocautery Denervation

Whether resurfacing or retaining the patella, perform circumferential electrocautery denervation of the patellar rim at a depth of 1 to 2 mm. This ablation interrupts substance P-containing nociceptive afferent nerve endings within the peripatellar soft tissues, significantly reducing postoperative anterior knee pain without jeopardizing primary arterial inflow.

Critical Move: The “No-Thumbs” Tracking Rule

Following cementation and trialing through a full arc of motion (0° to 120°), assess patellofemoral tracking without applying manual pressure to the patella (the “no-thumbs” rule). The patella must remain centrally seated within the femoral sulcus without tilting, subluxation, or liftoff from 0° to 100° of flexion. If lateral liftoff occurs, verify rotational alignment of the femoral and tibial components before considering an “inside-out” lateral retinacular release with preservation of the superior lateral genicular artery.

9. Clinical Outcomes & Functional Recovery

Modern systematic reviews, meta-analyses, and multicenter randomized trials demonstrate that overall functional scores (Knee Society Score, Oxford Knee Score, WOMAC) do not show dramatic differences between resurfaced and non-resurfaced cohorts. However, key outcome metrics demonstrate consistent patterns:

• Anterior Knee Pain: Meta-analyses confirm a statistically significant reduction in anterior knee pain favoring patellar resurfacing (relative risk approximately 0.77; 95% CI 0.60–0.98).
• Reoperation & Revision Risk: The overall reoperation rate is significantly lower in the resurfaced group (relative risk 0.67; 95% CI 0.50–0.89), driven predominantly by secondary resurfacing operations performed for persistent pain in retained cohorts.
• Patient Satisfaction & Preference: In bilateral simultaneous randomized studies where each patient receives one resurfaced and one unresurfaced knee, overall satisfaction remains high across both groups, with no distinct patient preference for the resurfaced or retained side.

10. Complications & Revision Scenarios

Complications specific to patellar management range from minor soft-tissue irritation to devastating structural extensor failures:

11. Pearls and Pitfalls

12. Controversy & Registry Evidence

National joint registries provide vast longitudinal real-world data that illuminate distinct regional philosophies and outcomes:

• The Registry Divide: In the American Joint Replacement Registry (AJRR), the patella is resurfaced in over 85% of primary procedures. Conversely, the Swedish Knee Arthroplasty Register (SKAR) and the Australian Orthopaedic Association National Joint Replacement Registry (AOANJRR) have historically recorded resurfacing rates below 5% and 30%, respectively, although rates in Australia have steadily climbed toward 60% over the past two decades.
• Secondary Resurfacing Success Rate: When an unresurfaced patella is revised secondarily for isolated anterior knee pain, registry data reveal that patient satisfaction rates hover around only 50% to 60%. The unpredictable outcome of secondary resurfacing represents a primary rationale cited by North American surgeons for routine primary resurfacing.
• Implant Design Evolution: Modern “patella-friendly” femoral designs with an anatomic trochlear sulcus, smooth lead-in radii, and lateralized trochlear geometry have substantially narrowed the clinical performance gap between resurfaced and retained patellae in primary osteoarthritis.

13. Evidence-Based Synthesis

Modern clinical decision-making is grounded in high-quality randomized controlled trials and prospective registry analyses, corroborated by seminal biomechanical and anatomical descriptions.

14. References

• Breeman S, Campbell M, Dakin H et al. Patellar resurfacing in total knee replacement: five-year clinical and economic results of a large randomized controlled trial. J Bone Joint Surg Am. 2011. doi:10.2106/JBJS.J.00725 [Level I (Therapeutic): Therapeutic Randomized Controlled Trial]
• Wood DJ, Smith AJ, Collopy D et al. Patellar resurfacing in total knee arthroplasty: a prospective, randomized trial. J Bone Joint Surg Am. 2002. doi:10.2106/00004623-200202000-00004 [Level I (Therapeutic): Therapeutic Randomized Controlled Trial]
• Burnett RS, Boone JL, McCarthy KP et al. A prospective randomized clinical trial of patellar resurfacing and nonresurfacing in bilateral TKA. Clin Orthop Relat Res. 2007. doi:10.1097/BLO.0b013e31812f783b [Level I (Therapeutic): Therapeutic Randomized Controlled Trial]
• Longo UG, Ciuffreda M, Mannering N et al. Patellar Resurfacing in Total Knee Arthroplasty: Systematic Review and Meta-Analysis. J Arthroplasty. 2018. doi:10.1016/j.arth.2017.08.041 [Level I (Therapeutic / Meta-Analysis): Systematic Review / Meta-Analysis]
• Thiengwittayaporn S, Srungboonmee K, Chiamtrakool B. Resurfacing in a Posterior-Stabilized Total Knee Arthroplasty Reduces Patellar Crepitus Complication: A Randomized, Controlled Trial. J Arthroplasty. 2019. doi:10.1016/j.arth.2019.04.050 [Level I (Therapeutic): Therapeutic Randomized Controlled Trial]

15. Master Class Pro-Tip

“The secret to foolproof patellar management in total knee arthroplasty lies not in dogma, but in caliper discipline and component medialization. Never trust visual estimation alone; measure your bone before the cut and verify all four quadrants afterward. Preserve a minimum of 12 to 15 mm of solid native cancellous bone. Medialize your patellar button against the medial cortical cortex to recreate the anatomical ridge and decrease the functional Q-angle. Finally, perform circumferential electrocautery denervation of the patellar periphery to neutralize substance P sensory afferents while carefully protecting the superior lateral genicular arterial corridor. If tracking fails the ‘no-thumbs’ test at 90° of flexion, always verify femoral and tibial component rotational alignment before dividing the lateral retinaculum.”

Master Class Surgical Pearl: Patellofemoral Decision-Making & Resurfacing in Total Knee Arthroplasty