Patellar Resurfacing in Primary Total Knee Arthroplasty

Decision to Resurface — Evidence Overview

Routine versus Selective versus Never Resurfacing

The patellar resurfacing debate centres on whether all primary TKAs should receive a patellar button, whether only selected patients should be resurfaced, or whether the patella should be left unresurfaced in all cases.

Routine resurfacing (resurface every primary TKA):

• Reduces anterior knee pain at 5-10 years in multiple meta-analyses
• Lowers reoperation rate for patellofemoral problems
• Supported by registry trends in Australia, UK and Scandinavia where resurfacing rates exceed 80 percent

Selective resurfacing (resurface when specific criteria met):

• Pre-operative anterior knee pain
• Inflammatory arthritis (rheumatoid, psoriatic)
• Patellar cartilage loss greater than grade 3 or eburnated bone
• Patellar maltracking or tilt on pre-operative imaging
• Patient age less than 60 years or high-demand activity

Never resurfacing (leave all patellae unresurfaced):

• Higher rates of anterior knee pain and secondary resurfacing procedures
• Registry data show reoperation rates for patellofemoral pain are 2-4 times higher when the patella is not resurfaced
• Still practised in some centres with careful patient selection and meticulous technique

Evidence Summary

Meta-analyses consistently show that resurfacing reduces anterior knee pain and reoperation compared with non-resurfacing, but the absolute difference is modest (approximately 5-10 percent absolute risk reduction). Inflammatory arthritis is the clearest indication for resurfacing. In osteoarthritis the decision remains surgeon preference with patient counselling.

Key Evidence

Patellar Anatomy Relevant to Resurfacing

Blood Supply

The patella receives blood from the prepatellar anastomosis formed by the superior and inferior geniculate arteries. The medial and lateral superior geniculate arteries run in the retinacula; the inferior geniculates enter distally. Aggressive peripheral stripping or thermal injury from the saw can devascularise the patella and increase avascular necrosis risk.

Patellar Morphology and Thickness

Native patellar thickness in adults averages 22-26 mm. The articular surface is convex; the medial facet is larger and steeper than the lateral. The patellar tendon inserts on the inferior pole; the quadriceps tendon on the superior pole. The goal of resurfacing is to restore the original anteroposterior dimension so that the extensor mechanism tension and patellofemoral joint line are preserved.

Patellofemoral Joint Kinematics

The patella engages the trochlear groove at approximately 20-30 degrees of flexion. In full extension the patella sits proximal to the trochlea. Component rotation (femoral internal rotation or tibial external rotation) shifts the trochlear groove laterally and increases lateral retinacular tension, producing tilt or subluxation.

Structures at Risk During Resurfacing

• Patellar bone stock — residual thickness less than 12 mm risks fracture
• Extensor mechanism — overstuffing greater than 2 mm increases forces
• Lateral retinaculum — may require release if tracking poor
• Superior geniculate vessels — preserve when possible to reduce AVN risk

Positioning and Preparation

Patient position: Supine on radiolucent table with a bump under the ipsilateral hip. Leg holder or sandbag used to maintain 90 degrees of knee flexion during exposure. Tourniquet applied to thigh at 250-300 mmHg.

Approach: Standard medial parapatellar arthrotomy extended proximally into quadriceps tendon and distally along medial border of patellar tendon. The patella is everted laterally for exposure.

Pre-resection measurements: Before any bone cuts, measure native patellar thickness with callipers at the midpoint of the medial-lateral axis. Record the value. Identify the point of maximum thickness (usually the median ridge).

Patellar Resurfacing — Step-by-Step

Step 1: Exposure and Osteophyte Removal

With the knee in extension, evert the patella. Remove all marginal osteophytes from the patellar perimeter, especially the lateral facet and superior pole. These osteophytes act as fulcrums and produce tilt even when component position is correct.

Step 2: Measuring Native Thickness and Planning Resection

Use callipers to measure the maximum anteroposterior thickness of the patella at the median ridge. Typical values are 22-26 mm in males and 20-24 mm in females. Plan the resection depth so that residual bone plus the chosen button thickness restores the original native thickness within 1 mm.

Most systems provide a resection guide that references the anterior patellar surface and removes a predetermined depth. The target residual bone thickness is usually 12-14 mm for a standard 8-10 mm button.

Step 3: Patellar Resection

Apply the patellar resection clamp or guide with the jaws parallel to the anterior surface. The cut must be perpendicular to the patellar long axis (superior-inferior) so that medial and lateral residual thickness are equal. Perform the cut with an oscillating saw under irrigation to reduce thermal necrosis.

After resection, measure the residual bone thickness at three points (medial, central, lateral). Any asymmetry greater than 1 mm requires recutting or use of an asymmetric button.

Step 4: Patellar Component Sizing and Fixation

Choose the largest button that fits the cut surface without overhang. The button should be medialised 2-3 mm relative to the median ridge to improve tracking. Cement the button with polymethylmethacrylate after pulsatile lavage and drying. Remove excess cement from the periphery.

Metal-backed or uncemented patellar components have higher failure rates in registry data and are not recommended for routine primary use.

Step 5: Patellar Tracking Assessment (No-Thumb Test)

After trialling all components, assess tracking with the no-thumb test. The patella must remain centred in the trochlear groove from full extension through 120 degrees of flexion without lateral subluxation or tilt greater than 5 degrees. The test is performed without any thumb pressure on the patella.

If the no-thumb test is positive, first verify component rotation (femoral not internally rotated, tibial not externally rotated), then remove any remaining lateral osteophytes, and finally consider a lateral retinacular release.

Step 6: Final Verification and Closure

Confirm composite thickness with callipers (bone plus button). Verify smooth patellar excursion without catching. Close the arthrotomy in layers with absorbable suture. No drain is required for isolated patellar resurfacing.

Post-operative Protocol

Immediate Phase (Day 0-14)

• Weight-bearing as tolerated with crutches or walker
• Quadriceps sets and ankle pumps from day of surgery
• Continuous passive motion if used for primary TKA protocol
• Wound review at 48 hours; sutures or staples removed at 10-14 days
• No specific patellar precautions beyond standard TKA protocol

Early Rehabilitation (Weeks 2-6)

• Active and active-assisted range of motion progressing to 0-120 degrees
• Quadriceps strengthening with straight-leg raises and short-arc quads
• Patellar mobilisation exercises to prevent adhesions
• Stationary cycling when 90 degrees flexion achieved

Late Rehabilitation (Weeks 6-12)

• Progressive resistance strengthening
• Proprioceptive and balance training
• Return to low-impact activities (walking, swimming, cycling)
• Stair climbing with reciprocal gait by 8-10 weeks

Long-term Expectations

• Full recovery of quadriceps strength by 6-12 months
• Anterior knee pain, if present, usually improves with quadriceps strengthening
• High-impact activities (running, jumping) discouraged after TKA regardless of resurfacing status