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

Surgical technique guide for Revision Total Knee Replacement - Patellar Component (Resurfacing/Revision) - FRCS exam preparation

Core Procedure
intermediate
By OrthoVellum Medical Education Team

Reviewed by OrthoVellum Editorial Team

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High-yield overview

Medial parapatellar arthrotomy via previous incision, with careful patellar eversion to prevent fracture or extensor mechanism injury | Core

Primary Indications:

  • Symptomatic patellar component loosening with adequate bone stock
  • Polyethylene wear with metallosis or synovitis
  • Patellar fracture with component loosening
  • Component malposition causing maltracking
  • Secondary resurfacing of unresurfaced painful patella
  • Failed metal-backed patellar component

Bone Stock Classification:

  • Adequate (≥10mm): Standard revision component
  • Compromised (5-10mm): Thin button, trabecular metal augment, or patelloplasty
  • Deficient (<5mm): Patelloplasty, allograft, or patellectomy (last resort)

Critical Danger Structures

Patellar Tendon

Location: Inferior pole of patella to tibial tubercle. Risk of avulsion during eversion especially in stiff knees or with osteopenic bone.

Quadriceps Tendon

Location: Superior pole of patella extending proximally. Risk of rupture during forced flexion or aggressive exposure techniques.

Patellar Bone Stock

Location: Within patella substance. Measure from anterior cortex to articular surface. Minimum 10mm needed for safe resurfacing.

Anterior Femoral Cortex

Location: Anterior aspect of distal femur. Risk of notching during femoral preparation causing stress riser and potential fracture.

Superior Lateral Genicular Artery

Location: Runs transversely deep to the lateral retinaculum and vastus lateralis, just proximal to the lateral femoral condyle, before entering the peripatellar anastomotic ring. It is a major contributor to patellar blood supply. Division during lateral release causes bleeding/haematoma and, combined with sacrifice of the fat pad (inferior contributions), risks patellar osteonecrosis.

Mnemonic

STOCK

Patellar Bone Stock Assessment Algorithm

Mnemonic

TRACK

Patellar Maltracking Causes and Assessment

Positioning and Preparation

Patient Position: Supine on radiolucent table with leg holder or bump under thigh. Tourniquet applied to upper thigh. Regional or general anesthesia with appropriate DVT prophylaxis initiated.

Surgical Approach: Medial parapatellar arthrotomy via previous incision, with careful patellar eversion to prevent fracture or extensor mechanism injury. Use most lateral previous incision if multiple scars present.

Pre-operative Planning Checklist:

  • Review skyline and lateral radiographs for patellar bone stock
  • CT scan if bone thickness uncertain
  • Note previous implant type (metal-backed vs all-poly)
  • Plan alternative strategies based on bone stock
  • Have cerclage wire, bone graft, and patellectomy options available

Operative Technique

Step 1: Exposure and Patellar Assessment

Exposure and Patellar Assessment: Use previous scar (most lateral if multiple). Develop skin flaps carefully to avoid ischemia. Perform medial parapatellar arthrotomy. Assess patella: measure bone thickness with calipers, check for fracture lines, osteolysis, component loosening, polyethylene wear, metal backing failure. Assess tracking with trial components or existing prosthesis.

Clinical Pearl

Technical Tip: EXAM KEY: Pre-operative imaging crucial - skyline view shows patellar bone stock, tilt, subluxation. CT can assess bone thickness accurately. Intraoperatively, patellar thickness measured from articular surface to anterior cortex should be documented. Normal patella 24-26mm thick, post-primary TKR 14-18mm. Minimum 10mm needed for safe revision. Mark fracture lines with methylene blue if present.

Dangers at this step

  • Skin flap necrosis from thin or multiple previous incisions
  • Completing fracture line during manipulation
  • Avulsing patellar tendon during exposure in stiff knee

Step 2: Patellar Eversion (if necessary)

Patellar Eversion (if necessary): For failed patellar component requiring removal, must evert patella for access. Flex knee progressively to 30 degrees, 60 degrees, then 90 degrees while applying gentle lateral pressure on patella. Release adhesions in lateral gutter if needed. If patella will not evert safely, perform lateral release (outside-in or inside-out) or proceed with knee flexed without eversion.

Clinical Pearl

Technical Tip: EXAM KEY: Patellar eversion is dangerous in stiff knees, thin patellae, or osteopenic bone. Alternative: flex knee 90-110 degrees and work on patella in situ without eversion. Quadriceps snip can help but increases extensor mechanism complication risk. Document pre-operative extensor lag (indicates tenuous mechanism). Consider leaving well-fixed, well-positioned components if patellar access too risky.

Dangers at this step

  • Patellar fracture during forced eversion (most common complication)
  • Patellar tendon avulsion from tibial tubercle or inferior pole
  • Completing pre-existing stress fracture
  • Quadriceps tendon rupture in stiff knee with forced flexion

Step 3: Patellar Component Removal

Patellar Component Removal: Use thin flexible osteotomes to disrupt cement-bone or bone-implant interface. Work circumferentially around component starting from most accessible edge. For metal-backed components, remove metal shell first, then polyethylene and cement. For all-poly cemented components, use osteotome and gentle mallet or slap hammer attached to component. Remove slowly to avoid fracture.

Clinical Pearl

Technical Tip: EXAM KEY: Metal-backed patellar components (largely abandoned) have higher failure rate - metallosis, osteolysis, dissociation. Modern components are all-polyethylene (dome-shaped or anatomic). For well-fixed ingrown cementless components, may need Gigli saw underneath. Ultrasonic cement removal helpful for well-fixed cemented components. Take your time - rushing causes fracture. Have patellar cerclage wire available for intraoperative fracture.

Dangers at this step

  • Patellar fracture (comminuted, transverse, or vertical)
  • Excessive bone loss from aggressive osteotome use
  • Perforation through thin remaining bone into joint
  • Avulsion of quadriceps or patellar tendon during component extraction

Step 4: Cement and Fibrous Membrane Removal

Cement and Fibrous Membrane Removal: Remove all cement, fibrous interface membrane, and necrotic bone down to viable bleeding bone. Use curettes, rongeurs, and small osteotomes carefully. Avoid excessive force or high-speed burr on thin bone. Pulsatile lavage to remove cement particles and debris. Measure remaining bone thickness with calipers from anterior cortex to prepared surface.

Clinical Pearl

Technical Tip: EXAM KEY: Complete cement removal essential to assess true remaining bone stock and achieve revision component fixation. Gentle technique critical - thin patellar bone fractures easily. Small curettes and hand instruments safer than power tools. After cement removal, bleeding bone should be visible (viability indicator). Measure thickness in multiple locations - often asymmetric bone loss. Send tissue samples for culture (occult infection).

Dangers at this step

  • Fracture through attenuated bone during cement removal
  • Perforation into articular surface
  • Excessive bone removal reducing remaining stock
  • Thermal injury from burr (avoid if possible)

Step 5: Bone Stock Assessment and Decision Making

Bone Stock Assessment and Decision Making: Measure patellar bone thickness (anterior cortex to prepared surface). Assess bone quality and defects. Categorize: Adequate (10mm or more) - standard revision component. Compromised (5-10mm) - thin revision component, bone graft augmentation, or patelloplasty. Deficient (less than 5mm) - consider alternatives: trabecular metal augmentation, patellar allograft, or patellectomy (last resort).

Clinical Pearl

Technical Tip: EXAM KEY: Decision algorithm based on bone stock. 10mm or more: proceed with revision component (all-poly dome or anatomic design, 8-12mm thick). 5-10mm: options include thin revision button (8mm), trabecular metal button, morsellized bone graft augmentation, or patelloplasty (denude remaining cartilage, smooth bone, no resurfacing). Less than 5mm: patellar allograft reconstruction with component, patelloplasty alone, or patellectomy. Patellectomy causes extensor lag, weakness, pain - avoid if possible.

Dangers at this step

  • Oversizing component on thin bone (perforation, fracture)
  • Undertreating with patelloplasty when resurfacing possible
  • Proceeding with resurfacing when bone stock inadequate

Step 6: Patellar Tracking Assessment

Patellar Tracking Assessment: With trial femoral and tibial components in place, assess patellar tracking through ROM. Normal tracking: patella centers in trochlear groove by 30 degrees flexion, tracks centrally through full flexion. Assess for lateral tilt, subluxation, or maltracking. Identify causes: femoral component malrotation (internal rotation), lateral retinacular tightness, patella alta/baja, trochlear dysplasia.

Clinical Pearl

Technical Tip: EXAM KEY: Patellar tracking crucial for success - maltracking causes pain, wear, loosening, fracture. No-thumb test: reduce patella without thumb pressure, flex knee - patella should stay centered. If lateral subluxation: check femoral rotation (internal rotation causes maltracking), check Q-angle, consider lateral release. If medial subluxation: check for over-released lateral retinaculum, femoral external malrotation. Intraoperative tracking with trial components predicts post-op outcome.

Dangers at this step

  • Missing femoral malrotation as cause of maltracking
  • Performing unnecessary lateral release (creates instability)
  • Over-releasing lateral structures causing medial instability

Step 7: Lateral Retinacular Release (if indicated)

Lateral Retinacular Release (if indicated): Indications: lateral patellar tilt greater than 10 degrees, lateral subluxation, tight lateral retinaculum preventing central tracking. Technique: inside-out approach preferred (safer for vessels). Release lateral retinaculum from lateral border of patella extending from superior to inferior pole. Use cautery for hemostasis. Check tracking after release - should improve to central tracking.

Clinical Pearl

Technical Tip: EXAM KEY: Lateral release performed in 10-20% of revisions, less common in primary. Inside-out technique: from medial arthrotomy, insert scissors or blade underneath lateral retinaculum, divide under direct vision, reduces risk to lateral superior genicular vessels. Outside-in technique: direct visualization laterally, but higher vascular injury risk. Modern trend: avoid lateral release if possible (use optimal femoral rotation, proper component sizing). If needed, partial release may suffice.

Dangers at this step

  • Lateral superior genicular artery injury (bleeding, hematoma)
  • Over-release causing medial subluxation and instability
  • Hematoma formation (use drain if extensive release)
  • Skin necrosis if combined with lateral incision

Step 8: Patellar Preparation for Component (if adequate bone stock)

Patellar Preparation for Component (if adequate bone stock): If bone stock 10mm or more, proceed with patellar preparation. Use patellar cutting guide or freehand technique to create flat surface parallel to anterior cortex. Resect minimum bone necessary (typically 2-3mm more than primary to achieve flat surface). Goal: composite thickness (remaining bone plus component) equals pre-operative patellar thickness (24-26mm, plus or minus 2mm acceptable).

Clinical Pearl

Technical Tip: EXAM KEY: Patellar resection principles - Preserve maximum bone stock while achieving flat surface. Resect parallel to anterior cortex (avoid oblique cuts). Composite thickness (bone plus component) equals native thickness plus or minus 2mm. Thickening more than 2mm causes overstuffing (limited flexion, pain, fracture). Thinning more than 2mm causes patella baja effect, potential instability. Measure with calipers before and after. Central peg holes minimize stress concentration vs peripheral pegs.

Dangers at this step

  • Excessive resection leaving inadequate bone for fixation
  • Oblique resection creating asymmetric component seating
  • Perforation into anterior cortex or joint surface
  • Lateral or medial perforation losing peg fixation

Step 9: Peg Hole Preparation

Peg Hole Preparation: Use drill bit to create peg holes matching revision component design. Most modern components have 3-4 pegs (1 central dome, 2-4 peripheral) or single central peg. Drill perpendicular to prepared surface. Depth: 8-12mm depending on remaining bone thickness. Avoid perforation. Trial component to ensure proper seating without rocking.

Clinical Pearl

Technical Tip: EXAM KEY: Peg configuration varies by manufacturer. Central peg designs reduce stress concentration vs all-peripheral pegs (early metal-backed designs). Drill perpendicular to surface - oblique drilling weakens bone. Depth gauge critical to avoid perforation. Remaining bone between peg holes and articular surface should be 5mm or more for strength. Trial component must seat fully without gaps or rocking - redo holes if needed.

Dangers at this step

  • Perforation through remaining bone into joint
  • Fracture during drilling (especially if thin bone or osteopenic)
  • Peg holes too close to periphery (fracture during impaction)
  • Asymmetric hole depth causing component tilt

Step 10: Cementation and Component Insertion

Cementation and Component Insertion: Prepare bone surface by pulsatile lavage and thorough drying (critical for cement interdigitation). Mix antibiotic-loaded bone cement. Apply cement to prepared patellar surface and undersurface of component. Insert component while cement doughy, ensuring proper orientation (matched to trochlear groove). Press firmly and hold with patellar clamp or manual pressure until polymerized. Remove excess cement.

Clinical Pearl

Technical Tip: EXAM KEY: Patellar cementation technique crucial - thin cement mantle (1-2mm) provides secure fixation without heat necrosis. Dry bone essential - use suction, swabs, thrombin-soaked gauze. Apply cement to both bone and component. Orient component to match femoral trochlea (usually slight lateral offset). Maintain pressure during polymerization - prevents gaps. Cement exotherm can cause thermal necrosis in thin bone - thin cement mantle and avoid excessive cement. Remove excess cement before polymerization.

Dangers at this step

  • Thermal necrosis from thick cement mantle or excessive cement
  • Incomplete seating leaving gaps (early loosening)
  • Cement extrusion into joint (third-body wear, impingement)
  • Malorientation causing edge loading and accelerated wear
  • Fracture during component impaction

Step 11: Alternative: Patelloplasty (if inadequate bone stock)

Alternative: Patelloplasty (if inadequate bone stock): If bone stock 5-10mm and component not feasible, perform patelloplasty. Denude remaining articular cartilage and fibrous tissue. Use rongeurs, curettes, and burr to create smooth patellar surface. Contour to match trochlear shape. Preserve anterior cortex. This leaves unresurfaced but smoothed patellar surface to articulate with femoral component.

Clinical Pearl

Technical Tip: EXAM KEY: Patelloplasty indications: insufficient bone stock for safe component (less than 10mm), elderly low-demand patient, significant comorbidities. Technique: remove all cartilage and necrotic bone, create smooth contoured surface, preserve anterior cortex. Outcomes: moderate improvement in pain (60-70% satisfaction), inferior to successful resurfacing but better than patellectomy. Counsel patients regarding residual anterior knee pain and crepitus. Still requires optimal patellar tracking.

Dangers at this step

  • Excessive bone removal compromising structural integrity
  • Incomplete cartilage removal leaving irregular surface
  • Fracture during contouring
  • Anterior cortex violation

Step 12: Management of Intraoperative Patellar Fracture

Management of Intraoperative Patellar Fracture: If fracture occurs: assess pattern (transverse, vertical, comminuted). Transverse: tension band fixation (two parallel 1.6mm K-wires plus 18-gauge cerclage wire figure-8). Vertical: if non-displaced, consider component fixation alone; if displaced, lag screw plus or minus cerclage. Comminuted: attempt reconstruction if possible, or consider partial patellectomy of fragments, or total patellectomy (last resort).

Clinical Pearl

Technical Tip: EXAM KEY: Intraoperative patellar fracture occurs in 1-3% of revisions (higher than primary). Transverse fracture most common - managed with tension band fixation plus component if bone stock adequate. Bury K-wire ends subcortically to prevent migration. Vertical fracture: often stable with component fixation alone if non-displaced. Comminuted: very difficult - may need patellectomy. Post-op: protected weight-bearing 6 weeks, limited ROM until healing, brace in extension between therapy sessions.

Dangers at this step

  • Missing fracture and proceeding without fixation
  • K-wire migration causing soft tissue irritation
  • Wire prominence causing skin breakdown
  • Inadequate fixation leading to fracture displacement
  • Avascular necrosis of patellar fragments

Step 13: Final Tracking Assessment and ROM Check

Final Tracking Assessment and ROM Check: After patellar component insertion (or patelloplasty), perform final tracking assessment with all components in place. Reduce patella and flex knee from full extension to maximum flexion. Patella should track centrally in trochlear groove without tilt, subluxation, or clunk. Assess ROM - should achieve 0 degrees extension and 110-130 degrees flexion without restriction. Check for patellofemoral crepitus or impingement.

Clinical Pearl

Technical Tip: EXAM KEY: Final checks before closure: 1) Patellar tracking central throughout arc, 2) No patellar clunk (impingement on femoral component), 3) ROM matches trial assessment, 4) Composite patellar thickness appropriate (not overstuffed), 5) No extensor lag when extending passively. Document ROM and tracking for medicolegal record. If maltracking persists, identify cause: femoral rotation error, inappropriate component sizing, inadequate lateral release, or excessive lateral release.

Dangers at this step

  • Accepting maltracking (causes pain, wear, failure)
  • Overstuffing causing limited flexion
  • Missing patellar clunk syndrome (needs femoral notchplasty)
  • Inadequate ROM requiring manipulation

Step 14: Closure and Hemostasis

Closure and Hemostasis: Perform thorough lavage (6-9L pulsatile) to remove all cement particles, bone fragments, and debris. Achieve meticulous hemostasis - use cautery for bleeding points. Consider drain if extensive lateral release performed or large dead space. Close medial parapatellar arthrotomy with interrupted absorbable sutures (No.2 or No.5) in flexion. Close subcutaneous layers and skin. Apply compression dressing.

Clinical Pearl

Technical Tip: EXAM KEY: Patellar region highly vascular - hemostasis crucial to prevent hematoma (infection risk, adhesions). If lateral release performed, inspect lateral gutter for bleeding from lateral superior genicular vessels. Tranexamic acid (1g IV induction, 1g closure) reduces blood loss 30-40%. Close arthrotomy in 30-40 degrees flexion to avoid tension. Test closure by extending knee - should hold without gapping. Compression dressing over patella reduces swelling and hematoma formation.

Dangers at this step

  • Inadequate hemostasis causing hematoma
  • Retained cement particles (third-body wear)
  • Closure under tension (dehiscence risk)
  • Drain malposition causing pain or vessel injury

Step 15: Post-Operative Rehabilitation Protocol

Post-Operative Rehabilitation Protocol: Elevate leg, ice, compression. TED stockings and chemical thromboprophylaxis (LMWH or DOAC) for 35 days. IV antibiotics 24h. Day 1: begin quadriceps sets and ankle pumps. Day 2: mobilize WBAT with frame or crutches. CPM machine 0-60 degrees advancing to 0-90 degrees by week 2 if tolerated. If patellar fracture: protect with brace locked in extension for 6 weeks, limited ROM protocol (0-60 degrees weeks 2-6, advance after radiographic healing).

Clinical Pearl

Technical Tip: EXAM KEY: Early mobilization crucial for ROM and preventing arthrofibrosis. Quadriceps strengthening essential for patellar function and stability. If intraoperative fracture or compromised bone stock: more protected rehabilitation - brace in extension, limited ROM initially, progressive weight-bearing. Remove drain 24-48h. Wound check day 3. Radiographs: AP, lateral, skyline views confirm component position, patellar tracking, no fracture. Discharge day 3-5. Outpatient review 2 weeks (wound), 6 weeks (ROM, radiographs), 3 months, 1 year. Monitor for anterior knee pain, crepitus, instability.

Dangers at this step

  • Aggressive early ROM causing component loosening or fracture displacement
  • Inadequate quadriceps strengthening (extensor lag, instability)
  • Wound complications (dehiscence, necrosis in thin skin flaps)
  • Deep infection (higher risk in revision)
  • Persistent anterior knee pain (multifactorial)
  • Re-fracture during rehabilitation if inadequate healing

Complications

Patellar Revision Complications

Evidence Base

Malrotation causing patellofemoral complications after total knee arthroplasty

II
Berger RA, Crossett LS, Jacobs JJ, Rubash HE • Clin Orthop Relat Res
Clinical Implication: Before blaming the patellar component for maltracking, image and correct femoral (and tibial) rotation - internal malrotation is the dominant correctable cause and may mandate femoral, not patellar, revision.
Verify on PubMed (PMID 9917679)

Isolated patellar component revision of total knee arthroplasty

IV
Berry DJ, Rand JA • Clin Orthop Relat Res
Clinical Implication: Isolated patellar revision is deceptively difficult with a high complication burden - counsel patients accordingly and have fracture-fixation and patelloplasty/patellectomy fallbacks ready.
Verify on PubMed (PMID 8425331)

Patellar resurfacing versus nonresurfacing in total knee arthroplasty: a meta-analysis of randomised controlled trials

I
Chen K, Li G, Fu D, Yuan C, Zhang Q, Cai Z • Int Orthop
Clinical Implication: The principal measurable benefit of resurfacing is fewer reoperations, not less anterior knee pain - so secondary resurfacing for pain alone in a well-tracking knee should be counselled cautiously.
Verify on PubMed (PMID 23529719)

Patellar resurfacing versus nonresurfacing in total knee arthroplasty: an updated meta-analysis of randomized controlled trials

I
Chen K, Dai X, Li L, Chen Z, Cui H, Lv S • J Orthop Surg Res
Clinical Implication: Contemporary high-volume evidence favours resurfacing for lower reoperation and crepitus, reinforcing that a symptomatic unresurfaced patella with good bone stock is a reasonable secondary-resurfacing indication.
Verify on PubMed (PMID 33494774)

National joint registry evidence on patellar resurfacing (NJR, AOANJRR, NZJR)

Guideline
National Joint Registry (UK); Australian Orthopaedic Association National Joint Replacement Registry; New Zealand Joint Registry • National arthroplasty registry annual reports
Clinical Implication: Registry data support all-polyethylene over metal-backed buttons and provide population-level reassurance that resurfacing lowers revision, but exact percentages differ by registry, year and case-mix - quote them as trends, not fixed numbers.

Clinical Decision Scenarios

Use these scenarios to practise clinical reasoning and management decisions

CLINICAL SCENARIOStandard

CLINICAL PROMPT

"A 68-year-old woman presents 8 years after primary TKA with progressive anterior knee pain worse with stairs. Her patella was not resurfaced at primary surgery. Skyline radiograph shows mild lateral tilt and 12mm patellar bone thickness. What is your approach?"

PRACTICAL APPROACH
This is a case of symptomatic unresurfaced patella following primary TKA, which is a recognized indication for secondary patellar resurfacing. My systematic approach would be: **Initial Assessment:** - Confirm pain is patellofemoral in origin (not referred from hip or spine) - Assess for infection: baseline CRP/ESR, aspiration if any suspicion - Evaluate implant stability: radiographs for loosening, assess femoral and tibial components - Review tracking: skyline view shows mild lateral tilt **Bone Stock Analysis:** - 12mm bone thickness is adequate for safe resurfacing (minimum 10mm required) - Can accommodate standard 8-10mm all-poly dome component - Target composite thickness: 24-26mm (original patellar thickness) **Operative Plan:** - If femoral and tibial components stable and well-positioned: isolated patellar resurfacing - Address lateral tilt: may need limited lateral release if tracking does not improve with resurfacing alone - Use standard medial parapatellar approach through previous incision - Verify femoral component rotation (internal rotation is commonest cause of maltracking) **Technical Considerations:** - Minimal bone resection (2-3mm) to achieve flat surface - Central peg dome design preferred - Verify no-thumb test tracking after component placement
CLINICAL SCENARIOStandard

CLINICAL PROMPT

"During patellar revision, you encounter a transverse fracture through the middle of the patella while trying to remove a loose cemented component. The two fragments are approximately equal size. How do you proceed?"

PRACTICAL APPROACH
This is an intraoperative patellar fracture, which occurs in 1-3% of patellar revisions. A transverse fracture with equal fragments is the most favorable pattern for fixation. My approach: **Immediate Assessment:** - Assess fragment size and bone quality in each fragment - Determine if adequate bone stock remains for component fixation - Check extensor mechanism integrity (quadriceps and patellar tendons) - Complete cement removal from both fragments carefully **Fracture Fixation - Tension Band Technique:** 1. Two parallel 1.6mm Kirschner wires passed from inferior to superior pole 2. 18-gauge cerclage wire in figure-of-8 configuration around K-wire ends 3. Tension wire and twist to compress fracture 4. Bury K-wire ends subcortically to prevent migration and skin irritation 5. Check fracture stability through ROM **Patellar Component Decision:** - If combined bone stock of both fragments 10mm or more from anterior cortex: proceed with revision component fixation - Component pegs should be positioned to avoid fracture line if possible - If bone stock inadequate: perform patelloplasty after fixation **Post-operative Protocol:** - Hinged knee brace locked in extension for 6 weeks - Protected weight-bearing with crutches/frame - Limited ROM: 0-60 degrees weeks 2-6, advance after radiographic healing confirmed - Quadriceps sets day 1, but avoid active extension exercises for 6 weeks - Radiographs at 2, 6, 12 weeks to monitor healing
CLINICAL SCENARIOStandard

CLINICAL PROMPT

"You are reviewing a 72-year-old diabetic man 4 years after revision TKA with patellar resurfacing. He has persistent anterior knee pain. Radiographs show the patellar component is well-fixed with no lucency. The skyline view shows central tracking. CRP and ESR are normal. What are the potential causes and your management approach?"

PRACTICAL APPROACH
Persistent anterior knee pain after TKA with normal radiographs and inflammatory markers is a challenging diagnostic and therapeutic problem. I would approach this systematically: **Differential Diagnosis:** 1. **Patellofemoral causes**: Component malposition, overstuffing, femoral malrotation (not visible on plain radiographs) 2. **Referred pain**: Hip osteoarthritis, lumbar radiculopathy, peripheral neuropathy (especially in diabetic) 3. **Soft tissue**: Patellar tendinitis, quadriceps tendinitis, fat pad impingement 4. **Regional pain syndromes**: CRPS (check for allodynia, color changes) 5. **Low-grade infection**: Normal inflammatory markers do not exclude 6. **Psychological factors**: Depression, catastrophizing, secondary gain **Systematic Evaluation:** - **Clinical examination**: Hip ROM, lumbar spine, peripheral sensation (diabetic neuropathy), CRPS features - **Imaging**: CT for component rotation (transepicondylar axis assessment), MRI for soft tissue pathology - **Aspiration**: Despite normal CRP/ESR, aspirate to exclude low-grade infection - **Diagnostic injections**: Hip injection if hip pathology suspected, selective nerve blocks **Component Position Assessment:** - Composite patellar thickness on lateral radiograph (overstuffing greater than 2mm above native) - Femoral component rotation on CT (target 3-5 degrees external to transepicondylar axis) - Patellar tilt and shift on skyline view **Management Algorithm:** 1. Conservative: Quadriceps strengthening, patellar taping, NSAIDs, physiotherapy 2. Injections: Corticosteroid if inflammatory, botulinum if muscle imbalance 3. Pain management referral if no correctable mechanical cause 4. Revision surgery ONLY if clear mechanical cause identified (malrotation, overstuffing)

References

  1. Berger RA, Crossett LS, Jacobs JJ, Rubash HE. Malrotation causing patellofemoral complications after total knee arthroplasty. Clin Orthop Relat Res. 1998;(356):144-153. PMID: 9917679.

  2. Berry DJ, Rand JA. Isolated patellar component revision of total knee arthroplasty. Clin Orthop Relat Res. 1993;(286):110-115. PMID: 8425331.

  3. Chen K, Li G, Fu D, Yuan C, Zhang Q, Cai Z. Patellar resurfacing versus nonresurfacing in total knee arthroplasty: a meta-analysis of randomised controlled trials. Int Orthop. 2013;37(6):1075-1083. PMID: 23529719.

  4. Chen K, Dai X, Li L, Chen Z, Cui H, Lv S. Patellar resurfacing versus nonresurfacing in total knee arthroplasty: an updated meta-analysis of randomized controlled trials. J Orthop Surg Res. 2021;16(1):83. PMID: 33494774.

  5. National Joint Registry (England, Wales, Northern Ireland, Isle of Man and Guernsey). Annual Report 2023. Available from: https://www.njrcentre.org.uk

  6. Australian Orthopaedic Association National Joint Replacement Registry (AOANJRR). Hip, Knee & Shoulder Arthroplasty Annual Report 2023. Adelaide: AOA; 2023. Available from: https://aoanjrr.sahmri.com

  7. Pagnano MW, Scuderi GR. Patellar component resurfacing. In: Insall JN, Scott WN, eds. Surgery of the Knee. 4th ed. Philadelphia: Churchill Livingstone; 2006:1665-1676.

  8. Tria AJ Jr, Harwin SF. Patellar complications in total knee arthroplasty. In: Callaghan JJ, Rosenberg AG, Rubash HE, eds. The Adult Knee. Philadelphia: Lippincott Williams & Wilkins; 2003:1457-1476.

  9. Keblish PA, Varma AK, Greenwald AS. Patellar resurfacing or retention in total knee arthroplasty. A prospective study of patients with bilateral replacements. J Bone Joint Surg Br. 1994;76(6):930-937.

  10. Brick GW, Scott RD. The patellofemoral component of total knee arthroplasty. Clin Orthop Relat Res. 1988;(231):163-178.

Revision TKA Patellar Component - Exam Summary

Clinical summary