TKA PATELLAR COMPLICATIONS
Fracture | Instability | Clunk Syndrome | Aseptic Loosening
GOLDBERG CLASSIFICATION (FRACTURES)
Critical Must-Knows
- Patellar complications are the most common cause of TKA reoperation (historically up to 50%)
- Extensor mechanism integrity is the key determinant of management for fractures
- Patellar clunk syndrome presents as a painful 'clunk' at 30-45 degrees of flexion (extension from flexion)
- Malrotation of femoral/tibial components is a major cause of patellar instability
- Avascular necrosis risk is increased by lateral retinacular release (sacrifices superior lateral genicular artery)
Examiner's Pearls
- "Look for component malrotation on axial CT (Berger Protocol)
- "Patellar clunk is treated with arthroscopic debridement of the fibrous nodule
- "Goldberg classification drives treatment: Is the extensor mechanism working? Is the implant loose?
- "Avoid ORIF for patellar fractures in TKA if possible - high non-union rate (poor bone stock)
Clinical Imaging
Imaging Gallery
Critical TKA Patellar Exam Points
Extensor Integrity
Must assess active straight leg raise. Inability implies Type III/IV fracture or tendon rupture requiring surgery.
Component Malposition
Internal rotation of femoral or tibial component is a classic cause of instability and anterior knee pain.
Blood Supply
Superior Lateral Genicular Artery. At risk during lateral release. Damage leads to patellar AVN and fracture.
Patellar Clunk
Fibrous nodule at superior pole. Clunks at 30-45° flexion. Differentiate from crepitus or instability.
Quick Decision Guide: Patellar Complications
| Scenario | Diagnosis | Treatment | Key Pearl |
|---|---|---|---|
| Painful clunk at 30-45° flexion | Patellar Clunk Syndrome | Arthroscopic Debridement | Resect fibrous nodule |
| Fracture, SLR possible, Implant stable | Goldberg Type I | Non-operative (Brace) | Watch for displacement |
| Fracture, SLR possible, Implant LOOSE | Goldberg Type II | Revision Arthroplasty | Remove loose button/cement |
| Fracture, NO SLR, Implant stable | Goldberg Type III | Surgical Repair/ORIF | High failure rate |
| Patellar dislocation, component malrotation | Patellar Instability | Revision of Malrotated Component | Soft tissue release fails if malrotated |
MALROTATIONCauses of Patellar Instability
Memory Hook:MALROTATION involves Malposition, Alignment, Lateralization - Remember internal rotation is the enemy!
MILSGoldberg Classification (Fractures)
Memory Hook:MILS helps decide if surgery is needed - Mechanism and Implant stability are key.
SAVERisks of Lateral Release
Memory Hook:SAVE the Superior Lateral Genicular Artery to prevent AVN and fracture!
Overview and Epidemiology
Historical Context
Historically, patellar complications were responsible for up to 50% of TKA failures. Modern implant designs (smoother trochlea, better instrumentation) have significantly reduced this, but it remains a leading cause of reoperation.
Risk Factors: Fracture
- Vascular: Lateral release (AVN)
- Technical: Over-resection (less than 12mm), excessive thermal necrosis
- Patient: Osteoporosis, high activity, male gender
Risk Factors: Instability
- Component: Internal rotation (Femur/Tibia), Medialization of femoral component
- Soft Tissue: Tight lateral retinaculum, loose MCL (valgus)
Anatomy and Biomechanics
Blood Supply: The Critical Concept
The patella is supplied primarily by the genicular anastomosis. The Superior Lateral Genicular Artery and Inferior Lateral Genicular Artery are most critical. A wide lateral retinacular release sacrifices the Superior Lateral Genicular Artery, significantly increasing the risk of patellar AVN and subsequent fragmentation/fracture.
Biomechanical Forces
| Variable | Effect on Patella | Surgical Pearl |
|---|---|---|
| Internal Rotation (Femur) | Increases Q-angle | Avoid internal rotation! Use Whiteside's line/TEA |
| Internal Rotation (Tibia) | Lateralizes Tubercle | Align to medial 1/3 tibial tubercle |
| Medialized Femoral Comp | Increases Q-angle | Lateralize femoral component to improve tracking |
| Thick Patella (Overstuffing) | Increases shear force | Measure pre-op thickness and reproduce it |
Classification Systems
Goldberg Classification
The standard classification for periprosthetic patellar fractures.
| Type | Mechanism Intact? | Implant Stable? | Treatment |
|---|---|---|---|
| Type I | YES | YES | Non-operative (Imm. Range of Motion) |
| Type II | YES | NO | Revision (Excise loose button/cement) |
| Type III | NO (Disrupted) | YES | Surgery (Repair/ORIF + liner exchange) |
| Type IV | NO (Disrupted) | NO | Surgery (Resection/Patellectomy/Allograft) |
Type II Pearl
For Type II (Loose implant, Intact mechanism), if the bone stock is poor, it is often better to remove the loose button and leave the patella unresurfaced (patelloplasty) rather than attempting to recement a new button onto a shell of bone.
Clinical Assessment
History
- Instability: "Knee gives way", "Patella jumps out"
- Clunk: Painful catch/clunk at 30-45 degrees flexion
- Fracture: Acute pain, inability to straight leg raise
- Pain: Anterior knee pain, worse with stairs/rising
Examination
- Observation: Q-angle, Valgus alignment
- Palpation: Fibrous nodule (Clunk), Tenderness
- Dynamic: Patellar tracking (J-sign), Active SLR (Mechanism integrity)
- Implant: Assess for gross loosening/instability
Rule Out Infection
In any painful TKA, infection must be ruled out first. Aseptic loosening and patellar complications can mimic infection. Obtain ESR/CRP and aspirate if elevated.
Investigations
Imaging Protocol
- AP/Lateral: Fracture, implant position, bone stock
- Skyline (Merchant): Critical for assessment of patellar tilt, subluxation, and fracture profile
- Indication: Instability or Anterior Knee Pain
- Assess: Rotational alignment of femoral and tibial components
- Femur: PCA (Posterior Condylar Axis) vs TEA (Transepicondylar Axis)
- Tibia: Geometric center vs Tubercle
- Indication: Pain with normal X-rays/CT
- Finding: Increased uptake ('hot') patella may suggest stress fracture or loosening
Berger Protocol
The Berger Protocol typically combines femoral and tibial rotation.
- Internal Rotation of Femoral Comp + Internal Rotation of Tibial Comp = Severe Patellar Instability. Even minor internal rotation of both can summate to cause significant tracking issues.
Management Algorithm
Management of Patellar Fracture
Based on Goldberg Classification.
Principles:
- Preserve extensor mechanism (Priority #1)
- Preserve bone stock
- Avoid surgery if mechanism is intact (Type I)
Treatment Steps
- Cylinder cast/brace in extension for comfort
- Allow weight bearing as tolerated
- Start immediate ROM (if stable) to prevent stiffness
- Extensor mechanism is intact but button is loose.
- Surgery: Remove loose button.
- Decision: Recement (if good bone greater than 12mm) vs Resection Arthroplasty (Patelloplasty).
- Extensor disrupted, Button stable.
- Surgery: Repair extensor mechanism + ORIF (Tension band).
- Outcome: Poor. High failure rate. Consider allograft if repair poor.
- Disrupted + Loose.
- Surgery: Remove button + Reconstruct mechanism (Allograft/Mesh).
- Typically requires removal of loose bodies and major reconstruction.
Management decisions depend on patient factors and fracture stability.
Surgical Technique
Revision for Patellar Instability (Malrotation)
Surgical Steps
- Medial parapatellar approach (standard).
- Extensive synovectomy.
- Inspect patellar tracking before dislocating/everting.
- Use epicondylar axis (TEA) and Whiteside's line.
- Confirm internal rotation of femoral component.
- Remove femoral component carefully (preserve bone).
- Osteotomes/Gigli saw if cemented.
- External Rotation: Set femoral component in 3 degrees external rotation relative to posterior condyles (or parallel to TEA).
- Lateralization: Use an offset stem or shift component laterally to improve tracking.
- "No Thumbs" test: Patella should track centrally without thumb pressure throughout ROM.
Complications
| Complication | Risk | Management | Prevention |
|---|---|---|---|
| Extensor Mechanism Rupture | High in Type III/IV | Allograft/Mesh Reconstruction | Avoid aggressive ROM |
| Avascular Necrosis | Lateral Release | Observation > Patellectomy | Preserve Sup Lat Genicular Artery |
| Non-union of Fracture | Common (Poor bone) | Accept if painless/stable | Optimized fixation |
| Recurrent Instability | Malrotation not addressed | Revision TKA | Correct component rotation |
Postoperative Care
Rehabilitation Protocol
- Fracture/Repair: Hinged knee brace locked in extension.
- Weight Bearing: WBAT with brace locked in extension.
- Revision TKA: Often WBAT, start ROM immediately if stable.
- Fracture: Start passive ROM limited to 0-30 degrees (if repair strong).
- Clunk Resection: Immediate full ROM allowed.
- X-rays: Check at 2 weeks and 6 weeks for alignment/displacement.
- Unlock brace for walking (if SLR control good).
- Progressive flexion as tolerated.
- Strengthening (quadriceps) starts late (3 months) for fractures.
- Full functional activity.
- Monitor for late loosening or recurrence of instability.
Strict adherence to range of motion limits is required for extensor repairs.
Outcomes and Prognosis
Patellar Fracture
- High Complication Rate: Surgical repair fails in 20-30% of cases.
- Non-union: Common (30-50%) but often painless if Type I.
- Best Outcome: Type I treated non-operatively (96% success).
Patellar Clunk
- Excellent: Arthroscopic debridement has greater than 95% success rate.
- Recurrence: Rare if sufficient nodule resected.
Instability
- Revision: Success depends on identifying cause.
- Malrotation: Revising components has 80-90% success.
- Soft Tissue Only: Lateral release alone has high failure if malrotation missed.
Extensor Rupture
- Poor Prognosis: Primary repair has high failure rate.
- Reconstruction: Allograft/Mesh often required.
- Salvage: Arthrodesis may be end stage.
Evidence Base
Goldberg Classification
- Established 4 types of periprosthetic patellar fractures
- Key determinant: Status of extensor mechanism + Implant stability
- Type I (Intact/Stable) has best prognosis
- Type III/IV (Disrupted) have poor outcomes
Patellar Clunk Syndrome
- Original description of fibrovascular nodule
- Defined characteristic 'clunk' from flexion to extension
- Associated with posterior stabilized (PS) designs
- Treatment: Arthroscopic debridement is successful
Non-operative Mgmt of Type I
- 78 patellar fractures analysis
- Non-operative treatment for extensive mechanism intact (Type I) had 96% success
- Operative treatment for Type II had 50% failure/complication rate
- Supports conservative management whenever possible
Effect of Component Rotation
- Defined combined internal rotation limits
- Internal rotation of femur OR tibia correlates with patellar subluxation
- Combined internal rotation is predictive of severity
- CT scan is gold standard for assessment
Vascular Supply and Lateral Release
- Lateral retinacular release damages superior lateral genicular artery
- Increases risk of patellar AVN and fracture
- Recommended selective use, not routine
- Try to preserve vessel if release necessary
Exam Viva Scenarios
Practice these scenarios to excel in your viva examination
Scenario 1: Patellar Clunk
"A 68-year-old female, 1 year post-op PS-TKA. Doing well but complains of a painful 'catch' or 'clunk' when she stands up from a chair. No pain at rest. ROM 0-120."
Scenario 2: The Fracture
"A 75-year-old male, 5 years post-TK. Falls onto knee. Pain, swelling. X-ray shows a transverse fracture of the patella. The button appears well-fixed."
Scenario 3: Evaluation of Instability
"A patient presents with anterior knee pain and feelings of instability 2 years post-TKA. She feels the kneecap 'jumps'. On exam, she has a positive J-sign and lateral apprehension."
MCQ Practice Points
Vascular Risk in Lateral Release
Q: Which arterial structure is most at risk during a lateral retinacular release in TKA? A: Superior Lateral Genicular Artery (SLGA) - The SLGA runs in the lateral retinaculum. A wide lateral release can transect this vessel, compromising patellar blood supply and increasing the risk of avascular necrosis and fracture.
Management of Type I Fracture
Q: A patient with a well-fixed TKA sustains a patellar fracture after a fall. She is able to perform a straight leg raise. The implant appears stable on X-ray. What is the Goldberg classification and appropriate management? A: Type I - Non-operative - This is a Goldberg Type I fracture (Intact extensor mechanism + Stable implant). The active straight leg raise confirms mechanism integrity. Treatment is non-operative (immobilizer/brace) as surgical intervention has a high complication rate.
Cause of Late Instability
Q: What is the most likely cause of late-presenting patellar instability after TKA? A: Component Malrotation - While all can cause issues, component malrotation (especially internal rotation of the femoral or tibial component) is a leading cause of mechanical patellar instability. Polyethylene wear can cause late instability but malrotation is the primary mechanical driver.
Extensor Mechanism Rupture Management
Q: Why is primary repair of a chronic patellar tendon rupture in TKA contraindicated? A: High Failure Rate - Primary repair of chronic disruptions (especially in revision scenarios) has an excessively high failure rate. Management requires reconstruction using either an extensor mechanism allograft or synthetic mesh (e.g., Marlex), rather than simple suture repair.
Patella Baja and Joint Line
Q: How does excessive joint line elevation affect the patella? A: Pseudo-Patella Baja - elevating the joint line (e.g., with thick poly or distal femoral augments) causes "pseudo-patella baja". The patella tendon length is normal, but the patella impinges on the tibial post or poly during flexion, reducing ROM and causing anterior pain.
Australian Context
AOANJRR Data
- Patellar/Extensor causes account for ~7% of all revisions.
- Patellar resurfacing remains controversial but AOANJRR data shows lower revision rate with resurfacing (cumulative).
Guidelines
- Infection: Prior to Revision for "Instability" or "Pain", Australian guidelines mandate ruling out PJI (aspiration).
- Referral: Complex extensor mechanism reconstruction often requires tertiary referral (allograft availability).
TKA PATELLAR COMPLICATIONS
High-Yield Exam Summary
Key Classifications
- •Goldberg I: Intact mech, Stable implant → Non-op
- •Goldberg II: Intact mech, Loose implant → Revision/Patelloplasty
- •Goldberg III: Disrupted mech, Stable implant → Repair + Fixation
- •Goldberg IV: Disrupted mech, Loose implant → Salvage/Reconstruct
Patellar Clunk
- •Fibrous nodule at superior pole
- •Catches in intercondylar box (PS knees)
- •Clunk at 30-45° extension
- •Rx: Arthroscopic debridement
Instability Causes
- •Internal Rotation of Femoral Comp
- •Internal Rotation of Tibial Comp
- •Valgus alignment
- •Tight lateral retinaculum
- •Medialized femoral component
Management Pearls
- •Avoid surgery for Type I fractures (high complication rate)
- •CT scan critical for instability (assess rotation)
- •Lateral release endangers Superior Lateral Genicular Artery
- •Berger Protocol: Combined internal rotation predicts instability
Blood Supply
- •Genicular anastomosis
- •Superior Lateral Genicular Artery (Most important)
- •Inferior Lateral Genicular Artery
- •Avoid deep lateral dissection
Evidence
- •Ortiguera & Berry: 50% failure rate for Op Rx of Type I
- •Berger: Rotation is key to tracking (CT Scan)
- •Hozack: Defined Patellar Clunk Syndrome
- •AOANJRR: Resurfacing has lower cumulative revision rate
- •Scuderi: Lateral release compromises SLGA blood supply