TKA PERIPROSTHETIC FRACTURES
Supracondylar Femur | Tibial Plateau | Patella | Lewis and Rorabeck Classification
LEWIS & RORABECK CLASSIFICATION (Supracondylar)
Critical Must-Knows
- Lewis & Rorabeck classification determines treatment based on displacement and prosthetic stability
- Anterior femoral notching increases fracture risk 4-fold - assess on lateral radiographs
- Type III fractures require revision arthroplasty with long cemented stems, NOT simple ORIF
- Retrograde IM nailing requires open intercondylar box in femoral component for nail passage
- Bone quality and fixation are paramount - osteoporotic bone requires locked plating or cemented stems
Examiner's Pearls
- "In viva, examiners test ability to classify fracture AND assess prosthetic stability independently
- "Type II vs Type III distinction: Examine AP and lateral radiographs for lucency, subsidence, alignment
- "Surgical approach selection depends on implant compatibility (open box vs closed box femoral component)
- "Australian context: AOANJRR reports increasing revision burden from periprosthetic fractures with aging population
Clinical Imaging
Imaging Gallery
Critical TKA Periprosthetic Fracture Exam Points
Classification Pitfall
Type II vs Type III error. A displaced fracture with a loose prosthesis is Type III, NOT Type II. Check for lucency, subsidence, and alignment on radiographs before committing to ORIF.
Anterior Notching
Iatrogenic stress riser. Notching greater than 3mm of the anterior femoral cortex during TKA increases periprosthetic fracture risk 4-fold. Always check lateral radiographs for this feature.
Implant Compatibility
Retrograde nail requires open box. Closed-box femoral components do not allow passage of a retrograde IM nail. Must use lateral locked plating or revision arthroplasty instead.
Bone Quality Assessment
Osteoporosis changes everything. Severe osteoporosis (T-score below -2.5) often necessitates revision arthroplasty with cemented stems rather than ORIF, especially in Type II fractures.
Quick Decision Guide
| Fracture Type | Prosthesis Status | Bone Quality | Treatment | Key Pearl |
|---|---|---|---|---|
| Type I (Non-displaced) | Stable, no lucency | Good | ORIF with locked lateral plate | Can trial non-operative if minimal comorbidities |
| Type II (Displaced) | Stable, well-fixed | Good, open box | Retrograde IM nail | Check femoral component - must have open box |
| Type II (Displaced) | Stable, well-fixed | Good, closed box | Lateral locked plate (LISS/NCB) | Biological plating with indirect reduction |
| Type II (Displaced) | Stable | Osteoporotic | Consider revision with stems | ORIF has high failure rate in poor bone |
| Type III | Loose or failing | Any | Revision TKA with long stems | ORIF will fail - must address prosthetic loosening |
SDFLewis and Rorabeck Classification
Memory Hook:SDF = Stability Determines Fixation - assess prosthetic stability FIRST to guide treatment!
FORNOWFracture Risk Factors Post-TKA
Memory Hook:FORNOW these patients are at risk - optimize bone health and fall prevention before TKA!
NUMBComplications of ORIF for Periprosthetic Fractures
Memory Hook:NUMB outcomes from ORIF in poor bone - consider revision arthroplasty upfront if severe osteoporosis!
Overview and Epidemiology
Clinical Significance
Periprosthetic fractures around TKA are increasing with the aging population and higher activity levels in arthroplasty patients. These fractures represent a major source of morbidity, healthcare cost, and revision burden. The Australian Orthopaedic Association National Joint Replacement Registry (AOANJRR) reports that periprosthetic fractures account for 10-15% of all TKA revisions in Australia.
Demographics
- Incidence: 2.5% of primary TKA, 5-10% after revision TKA
- Age: Mean 70-75 years, predominantly elderly females
- Timing: Bimodal - early (intraoperative, first 2 years) or late (greater than 5 years post-op)
- Mechanism: Low-energy falls in 80%, high-energy trauma 10%, spontaneous 10%
Impact
- Mortality: 30% at 1 year, comparable to hip fractures
- Functional loss: Only 50% return to pre-fracture mobility
- Healthcare burden: Average cost greater than $50,000 AUD per case
- Revision rate: 20% require further surgery within 2 years
Anatomy and Biomechanics
Distal Femur After TKA
Anterior Femoral Notching - Stress Riser
Anterior cortical notching greater than 3mm during femoral component preparation increases periprosthetic fracture risk 4-fold. The notch creates a stress concentration point in the supracondylar region, where bending moments are highest during gait. Always assess lateral radiographs for notching when evaluating periprosthetic fractures.
Biomechanical Changes Post-TKA
- Stress shielding: Stiff femoral component alters load distribution
- Stress concentration: At tip of femoral component and anterior notch
- Reduced bone density: Stress shielding causes proximal femur bone loss
- Alignment changes: Valgus alignment shifts medial-lateral forces
Fracture Location Distribution
- Supracondylar femur: 80% of all periprosthetic fractures
- Tibial plateau: 10-15% (often metaphyseal collapse)
- Patellar: 5% (typically in cementless patella or over-resection)
- Polyethylene post: Rare, posterior-stabilized designs
| Location | Mechanism | Risk Factors | Treatment Complexity |
|---|---|---|---|
| Supracondylar femur | Bending moment, stress concentration | Anterior notching, osteoporosis | High - requires plate or revision |
| Tibial plateau | Subsidence, metaphyseal collapse | Cementless stems, poor bone quality | Moderate - often requires stems |
| Patella | Trauma, over-resection | Cementless fixation, thin patella | Low to moderate - excision vs ORIF |
Classification Systems
Lewis & Rorabeck Classification (Distal Femur)
| Type | Fracture Displacement | Prosthesis Stability | Treatment | Outcomes |
|---|---|---|---|---|
| Type I | Non-displaced (under 5mm shift, under 5° angulation) | Stable, well-fixed | ORIF with locked plate OR conservative (elderly, low demand) | Union rate over 85%, good function |
| Type II | Displaced (over 5mm shift OR over 5° angulation) | Stable, no lucency, no subsidence | ORIF (plate or IM nail) based on implant design and bone quality | Union rate 75-85%, 15-20% require revision |
| Type III | Any displacement | Loose (lucency, subsidence, malalignment) | Revision TKA with long cemented stems (greater than 100mm beyond fracture) | Union rate 60-75%, high complication rate 30-40% |
Critical Distinction: Type II vs Type III
The KEY decision is assessing prosthetic stability on radiographs:
- Stable (Type I/II): No lucency at bone-cement or cement-implant interface, no subsidence, maintained alignment
- Loose (Type III): Progressive radiolucent lines (over 2mm), subsidence (over 2mm component migration), malalignment (over 3° from neutral)
If in doubt, obtain contralateral TKA radiographs for comparison OR stress fluoroscopy in operating room before committing to ORIF.
Clinical Assessment
History
- Mechanism: Fall from standing height (most common), trauma, spontaneous
- Pain: Acute onset, inability to weight-bear, above or below knee
- Function: Loss of ambulation, inability to perform straight leg raise (if patellar)
- Red flags: Neurovascular compromise, open fracture, compartment syndrome
- Index surgery: Date of TKA, indication, implant type, any complications
- Medical history: Osteoporosis, steroid use, rheumatoid arthritis, neurological disorders
Examination
- Look: Deformity, swelling, ecchymosis, skin integrity, alignment
- Feel: Point tenderness, crepitus, warmth (infection vs acute fracture)
- Move: Range of motion at knee (compare to contralateral), extensor lag
- Special tests: Straight leg raise (patellar fracture), neurovascular examination
- Implant assessment: Palpate for warmth, effusion suggesting loosening or infection
- Gait: Inability to weight-bear, antalgic gait, Trendelenburg if tibial fracture
Infection Masquerading as Fracture
Periprosthetic joint infection (PJI) can present with acute pain, swelling, and inability to weight-bear, mimicking fracture presentation. If clinical suspicion for infection exists (wound drainage, fevers, elevated inflammatory markers), aspirate the joint before surgical fixation to rule out PJI. CRP over 100 mg/L or ESR over 60 mm/hr in the absence of other inflammatory conditions should raise suspicion.
Investigations
Imaging Protocol
Views: AP and lateral knee, AP and lateral femur (full length), contralateral knee for comparison
Assess for:
- Fracture displacement (under or over 5mm, under or over 5° angulation)
- Prosthetic stability: Lucency at bone-cement interface (over 2mm progressive), subsidence (component migration), alignment
- Anterior femoral notching on lateral view (stress riser)
- Bone quality: Osteopenia, cortical thickness, canal diameter
Indications: Complex fracture patterns, assess prosthetic fixation, pre-operative planning for revision
Benefits:
- Better delineation of fracture pattern (comminution, extension into joint)
- Assessment of bone stock for revision (metaphyseal defects, cortical thickness)
- Templating for stem length and diameter
Blood tests: ESR, CRP, WCC (baseline and compare to 6-week post-TKA values)
Joint aspiration: If CRP over 100 or clinical suspicion of infection
- Synovial fluid WCC (over 3000 cells/microL suspicious)
- Polymorphonuclear percentage (over 80% concerning)
- Culture and sensitivities (hold antibiotics if possible)
Alpha-defensin: Point-of-care test (90% sensitivity, 95% specificity for PJI)
DEXA scan: If not done recently, assess T-score (below -2.5 indicates severe osteoporosis)
Implications:
- Severe osteoporosis favors revision arthroplasty over ORIF
- Consider medical optimization (vitamin D, calcium, bisphosphonates, teriparatide)
Management Algorithm
Type I Management: Non-Displaced Fracture, Stable Prosthesis
Treatment Options:
Decision Pathway
Indications:
- Elderly, low-demand patient (limited community ambulator)
- Significant medical comorbidities (high anaesthetic risk)
- Minimal displacement (under 2mm shift, under 3° angulation)
- Good bone quality
Protocol:
- Hinged knee brace locked in extension for 6 weeks
- Touch weight-bearing with crutches for 8-12 weeks
- Serial radiographs at 2, 6, 12 weeks to assess for displacement
- Progress to full weight-bearing at 12 weeks if union evident
Risks: 15-20% loss of reduction requiring delayed ORIF, knee stiffness, nonunion (5-10% in elderly)
Indications:
- Younger, higher-demand patient
- Any concern about compliance with non-weight-bearing
- Minimal comorbidities
Technique:
- Lateral locking plate (LISS, NCB, or similar periarticular plate)
- 3-4 screws proximal to fracture, 3-4 distal screws (locking)
- Bridge plating technique (no stripping of periosteum)
- Early range of motion, progressive weight-bearing
Outcomes: Union rate over 85%, return to function 75-80%
Type I Treatment Decision
In exam scenarios, examiners often present an 85-year-old with Type I fracture and ask for management. Safe answer is ORIF with locked plate in most cases UNLESS patient is bedbound or high anaesthetic risk. Conservative treatment should be reserved for very select cases with shared decision-making about risks of loss of reduction.
Surgical Technique
Lateral Locked Plate Fixation (LISS/NCB)
Pre-operative Planning
Consent Points
- Infection: 2-5% superficial, 1-2% deep
- Nonunion: 15-20% in osteoporotic bone
- Malunion: 5-10% varus/valgus deformity
- Hardware prominence: 10-15%, may require removal
- Neurovascular injury: Peroneal nerve 1-2%
- Need for revision: 15-20% within 2 years
Equipment Checklist
- Implants: LISS or NCB periarticular plate, appropriate length (9-13 holes typical)
- Screws: 4.8-5.0mm locking screws (at least 8-10 screws)
- Reduction aids: Pointed reduction clamps, K-wires, Schanz pins
- Imaging: C-arm with lateral and AP views, ensure can visualize full plate length
- Backup plan: Revision TKA set on standby if prosthesis found loose intraoperatively
Patient Positioning
Setup Checklist
Supine on radiolucent table (Jackson or standard OR table with radiolucent extension).
- Bump under ipsilateral hip for neutral rotation
- Contralateral leg in well-leg holder or leg holder
- Affected leg free-draped from hip to ankle
- C-arm from contralateral side for lateral views (beam parallel to floor)
- Confirm adequate AP and lateral imaging of entire femur before draping
- Have radiology technician practice obtaining femoral component views
- Prep entire leg from hip to ankle
- Include contralateral knee if templating required intraoperatively
- Impervious stockinette to foot, isolate foot at ankle level
Surgical Approach: Lateral Submuscular
Step-by-Step Approach
Landmarks: Lateral femoral epicondyle to proximal lateral femur Length: 8-12cm depending on fracture extent and plate length Orientation: Straight lateral, centered over lateral intermuscular septum
Incision Placement
Keep incision posterior enough to allow submuscular plate passage but anterior enough to avoid sciatic nerve (greater than 2cm from posterior femoral cortex on lateral view). Use fluoroscopy to mark ideal trajectory if uncertain.
Layer: Incise fascia lata along lateral intermuscular septum Identify: Vastus lateralis muscle (anterior) and lateral intermuscular septum Elevate: Lift vastus lateralis off lateral intermuscular septum, creating submuscular space Protect: Perforating vessels - ligate or cauterize
DO NOT open fracture site - this is bridge plating! Palpate: Confirm fracture location by feeling step-off or gap Reduction: Use traction, manipulation, and K-wires or Schanz pins for provisional alignment Imaging: Confirm reduction on AP and lateral fluoroscopy (acceptable: under 5° varus/valgus, under 5mm translation)
Submuscular tunnel: Use McDonald clamp or plate insertion guide to create epiperiosteal tunnel deep to vastus lateralis Plate passage: Slide plate proximally under muscle (keep plate on bone surface!) Positioning:
- Plate centered on lateral femoral cortex
- Distal end 1-2cm above femoral component (no impingement!)
- Confirm on fluoroscopy before fixation
Plate-Implant Clearance
The distal extent of the plate MUST NOT impinge on the femoral component. Leave at least 1cm gap. If fracture is very distal (within 5cm of component), consider revision arthroplasty instead of plating.
Sequence:
- Distal locking screws first (3-4 screws, bicortical locking)
- Check reduction with fluoroscopy - adjust if needed before proximal fixation
- Proximal locking screws (4-6 screws, bicortical)
- Fill all available holes in osteoporotic bone for maximal stability
Technique:
- Drill through locking guide sleeve
- Measure depth with depth gauge (both cortices + 5mm for safety)
- Insert locking screw, tighten until head seats in plate (do NOT overtighten!)
- Confirm screw threads engage far cortex on fluoroscopy
Screw working length: At least 4-6 screws proximal and 3-4 screws distal to fracture for adequate fixation.
Fluoroscopy: AP and lateral views confirming:
- Fracture reduction maintained
- All screws bicortical
- No screw penetration into knee joint
- No plate impingement on femoral component
Stability: Manually stress fracture under fluoroscopy - should be stable with minimal motion
Closure
Closure Steps
- Irrigate submuscular space with 3L normal saline
- Cauterize perforating vessels
- Consider drain if significant oozing (remove at 24-48 hours)
- Close fascia lata with 0 Vicryl interrupted sutures
- Ensure closure is watertight to prevent muscle herniation
- 2-0 Vicryl subcuticular for subcutaneous layer
- 3-0 Monocryl or staples for skin
- Sterile dressing, compressive wrap
- Hinged knee brace locked in extension for comfort and protection
- Touch weight-bearing with walker for 6 weeks
- Early range of motion exercises (0-90°) starting day 1
Complications
| Complication | Incidence | Risk Factors | Prevention | Management |
|---|---|---|---|---|
| Nonunion | 20-30% (ORIF in osteoporotic bone) | Osteoporosis, smoking, diabetes, infection | Optimize bone health pre-op, rigid fixation, avoid soft tissue stripping | Revision ORIF with bone graft OR conversion to revision TKA with stems |
| Malunion | 10-15% | Inadequate reduction, loss of fixation, patient non-compliance | Intraoperative fluoroscopy, locked fixation, early weight-bearing restriction | If symptomatic: Corrective osteotomy OR revision TKA if severe (over 10° deformity) |
| Hardware failure | 10-15% (plate), 5% (nail) | Screw pullout in osteoporotic bone, premature weight-bearing | Locked screws, fill all plate holes in poor bone, weight-bearing restrictions | Revision ORIF with longer plate or conversion to revision TKA |
| Infection (PJI) | 3-5% | Diabetes, immunosuppression, prior infection, hematoma | Antibiotic prophylaxis, meticulous sterility, drain if needed | Acute: Debridement and component retention OR single-stage revision. Chronic: Two-stage revision |
| Stiffness/arthrofibrosis | 15-20% | Prolonged immobilization, heterotopic ossification, infection | Early ROM, CPM machine, aggressive physical therapy | Manipulation under anesthesia at 6-12 weeks OR open arthrolysis if severe |
| Neurovascular injury | 1-2% | Peroneal nerve stretch, vascular injury during reduction or fixation | Gentle reduction, avoid forceful manipulation, check pulses intraoperatively | Nerve injury: Observation, AFO if foot drop. Vascular: Immediate repair by vascular surgery |
| Mortality | 30% at 1 year | Age over 80, multiple comorbidities, low baseline function, delay to surgery | Optimize medical comorbidities, early surgery (within 48 hours if possible), multidisciplinary care | Palliative care involvement if appropriate, maximize function even if fracture healing suboptimal |
Periprosthetic Fracture Mortality is Comparable to Hip Fractures
30% mortality at 1 year for elderly patients with periprosthetic supracondylar fractures, similar to neck of femur fractures. Medical optimization, early surgery, and multidisciplinary orthogeriatric care are essential to improve outcomes. In very frail patients, non-operative management with pain control and palliative care may be appropriate after shared decision-making.
Postoperative Care and Rehabilitation
Rehabilitation Timeline After ORIF
Immobilization: Hinged knee brace locked in extension for ambulation
Weight-bearing: Touch weight-bearing with walker (10-15kg max on affected limb)
DVT prophylaxis:
- Enoxaparin 40mg SC daily OR rivaroxaban 10mg daily for 6 weeks
- TED stockings and sequential compression devices
Pain management: Multimodal analgesia (paracetamol, NSAIDs if not contraindicated, opioids PRN)
Mobilization: Out of bed to chair day 1, transfer training with physiotherapy
Weight-bearing: Touch weight-bearing with walker, progress to 25% body weight at 4 weeks if radiographs stable
ROM exercises:
- Passive ROM 0-60° with physiotherapy (brace unlocked for exercises)
- Active-assisted ROM with physio
- Quadriceps sets, straight leg raises
Precautions: No active knee flexion against resistance, no squatting
Radiographs: At 2 weeks and 6 weeks to assess alignment, hardware position, early healing
Weight-bearing: Progress from 50% to full weight-bearing as tolerated based on:
- Radiographic evidence of callus formation
- Patient pain level
- Stability on examination
ROM: Goal 0-100° by 12 weeks, progress passive to active ROM
Strengthening: Progressive resistance exercises (quadriceps, hamstrings, hip abductors)
Radiographs: At 12 weeks - should see bridging callus on at least 3 of 4 cortices
Weight-bearing: Full weight-bearing without aids if radiographic union (bridging callus on 3/4 cortices)
Functional goals:
- Independent ambulation
- Stairs (step-over-step pattern)
- Return to activities of daily living
Radiographs: At 6 months final assessment of union, alignment, hardware integrity
Criteria for union: Bridging callus on 3/4 cortices, pain-free weight-bearing, no tenderness at fracture site
Surveillance: Annual radiographs to assess for hardware failure, loss of reduction, late prosthetic loosening
Return to activities: Low-impact activities (walking, swimming, cycling) encouraged. Avoid high-impact sports (running, jumping).
Hardware removal: Consider at 18-24 months if prominent and symptomatic AFTER confirmed radiographic union
Weight-Bearing Progression Rationale
Touch weight-bearing for first 6 weeks allows soft tissue healing and early callus formation while preventing catastrophic hardware failure. Progress to partial weight-bearing at 6 weeks stimulates further bone healing via controlled mechanical stress (Wolff's law). Full weight-bearing at 12 weeks assumes radiographic union is progressing - if not, delay full weight-bearing until 16-20 weeks.
Delayed Union is Common
Periprosthetic fractures have slower healing than native bone fractures due to osteoporosis, age, and altered biomechanics. Average time to union is 5-7 months for ORIF cases. If no radiographic progression of healing at 4-6 months, consider bone stimulation (ultrasound or pulsed electromagnetic fields) or revision surgery with bone grafting.
Outcomes and Prognosis
| Treatment | Union Rate | Functional Outcome | Revision Rate | Notes |
|---|---|---|---|---|
| ORIF - Lateral Plate | 75-85% (good bone), 60-70% (osteoporotic) | Good to excellent in 70%, return to pre-fracture function 50% | 15-20% require revision within 2 years | Best for Type II with good bone quality and closed-box implants |
| ORIF - Retrograde Nail | 80-90% | Good to excellent in 75-80%, faster mobilization than plate | 10-15% require revision | Requires open-box design, good for bilateral fractures |
| Revision TKA with Stems | 65-80% (fracture union) | Fair to good in 60%, limited by age and comorbidities | 20-25% require further revision | Necessary for Type III, higher complication rate but addresses prosthetic loosening |
| Non-operative (Type I) | 70-80% (selected cases) | Fair in 50%, high rate of stiffness and functional loss | 15-20% loss of reduction requiring delayed ORIF | Reserved for very elderly, high-risk patients with minimal displacement |
Predictors of Poor Outcome
Poor prognostic factors:
- Age over 80 years (mortality risk, poor healing)
- Severe osteoporosis (T-score below -2.5) - high nonunion rate with ORIF
- Type III fractures with prosthetic loosening (complex reconstruction, longer recovery)
- Medical comorbidities (diabetes, renal failure, immunosuppression)
- Smoking (2-3 times higher nonunion rate)
- Delay to surgery (over 7 days associated with worse outcomes)
Best outcomes: Type II fractures in patients under 75 with good bone quality, stable prosthesis, treated with ORIF within 48 hours.
Evidence Base and Key Trials
Periprosthetic Fracture Treatment Outcomes: Plate vs Nail
- Systematic review of 1223 periprosthetic supracondylar fractures
- Union rate: 84% for lateral locked plating, 87% for retrograde IM nailing
- Complication rate: 24% for plating (hardware prominence, screw pullout), 18% for nailing
- Revision surgery: 16% for plate, 12% for nail
- No significant difference in final functional outcomes between techniques
AOANJRR Periprosthetic Fracture Revision Data
- Periprosthetic fractures account for 12% of all TKA revisions in Australia
- Incidence increasing with aging population (2.1% to 2.8% over 10 years)
- Revision for periprosthetic fracture has 20% re-revision rate at 5 years
- Cemented stems associated with lower revision rate than uncemented in fracture setting (15% vs 25%)
- Mortality at 1 year post-revision for fracture: 28% (comparable to hip fracture mortality)
Osteoporosis and Periprosthetic Fracture Risk
- Cohort study of 15,321 primary TKA patients with DEXA scans
- T-score below -2.5: 4.2% periprosthetic fracture rate at 5 years
- T-score -1.0 to -2.5: 2.1% fracture rate
- T-score over -1.0: 1.3% fracture rate
- Treatment with bisphosphonates or teriparatide reduced fracture risk by 40%
Early vs Delayed Surgery for Periprosthetic Fractures
- Retrospective cohort of 412 periprosthetic supracondylar fractures
- Surgery within 48 hours: Union rate 88%, mortality 22% at 1 year
- Surgery delayed 7-14 days: Union rate 76%, mortality 35% at 1 year
- Each day of delay associated with 2% increased mortality risk
- Early surgery group had better functional outcomes (WOMAC scores) at 1 year
Anterior Femoral Notching and Fracture Risk
- Case-control study of 116 periprosthetic fractures vs 232 controls
- Anterior cortical notching over 3mm: 4.3 times increased fracture risk
- Notching location corresponded to fracture location in 92% of cases
- Average time from TKA to fracture: 2.8 years with notching vs 6.5 years without
- Biomechanical analysis showed 30% reduction in torsional strength with 3mm notch
Exam Viva Scenarios
Practice these scenarios to excel in your viva examination
Scenario 1: Classification and Initial Management (2-3 min)
"An 82-year-old woman presents to ED after a fall at home. She has a right TKA performed 5 years ago for osteoarthritis. Radiographs show a supracondylar femur fracture 8cm above the femoral component with 10mm of lateral translation. The femoral component appears well-fixed with no lucency. How would you assess and manage this patient?"
Scenario 2: Surgical Technique Decision (3-4 min)
"You are planning surgery for the patient in Scenario 1. On reviewing the lateral radiograph more carefully, you note the femoral component has a closed-box design. The patient's bone quality appears osteoporotic with thin cortices. Walk me through your surgical plan."
Scenario 3: Type III Fracture and Complication Management (2-3 min)
"A 74-year-old man with a TKA performed 8 years ago falls and sustains a supracondylar femur fracture. Radiographs show the fracture is displaced with 5° of valgus angulation. You also note progressive radiolucent lines around the femoral component and 3mm of component subsidence compared to prior radiographs. How would you manage this?"
MCQ Practice Points
Classification Question
Q: A 78-year-old woman sustains a periprosthetic supracondylar fracture 6 years after TKA. Radiographs show 8mm of fracture displacement with the femoral component appearing well-fixed with no lucency. What Lewis & Rorabeck type is this?
A: Type II - Displaced fracture (over 5mm) with stable, well-fixed prosthesis. Type I would be non-displaced (under 5mm, under 5° angulation). Type III would have evidence of prosthetic loosening (lucency, subsidence, or malalignment). The key is assessing prosthetic stability independently from fracture displacement.
Surgical Technique Question
Q: What is the critical pre-operative assessment required before planning retrograde intramedullary nailing for a Type II periprosthetic supracondylar fracture?
A: Assessment of femoral component intercondylar box design on lateral radiograph. An open-box design with adequate height (over 10mm) and width (over 12mm) is REQUIRED to allow passage of a retrograde nail (typically 9-10mm diameter). Closed-box designs do NOT allow nail passage and require lateral locked plate fixation instead. Attempting to nail through a closed box will cause catastrophic implant damage.
Risk Factor Question
Q: Anterior femoral cortical notching during TKA component preparation increases periprosthetic fracture risk by how much, and what is the critical threshold depth?
A: 4-fold increased fracture risk when anterior cortical notching exceeds 3mm depth on lateral radiographs. The notch creates a stress concentration point in the supracondylar region where bending moments are highest during gait. Surgeons should assess all postoperative TKA radiographs for notching and counsel high-risk patients about fall prevention.
Treatment Decision Question
Q: An 85-year-old patient with severe medical comorbidities sustains a Type II periprosthetic supracondylar fracture. CT shows severe osteoporosis with thin cortices. What factors would make you consider revision TKA with stems instead of ORIF?
A: Severe osteoporosis (T-score below -2.5), very thin cortices (under 4mm), and poor bone quality are relative indications for revision TKA over ORIF in Type II fractures. ORIF in severe osteoporosis has nonunion rates of 30-40% and high risk of screw pullout. Revision with long cemented stems provides immediate stability and load-sharing fixation. Other factors: very distal fracture location (within 5cm of component), closed-box implant precluding nail, or patient factors suggesting ORIF will fail.
Complication Question
Q: What is the 1-year mortality rate for elderly patients with periprosthetic supracondylar fractures after TKA, and how does it compare to hip fractures?
A: Approximately 30% mortality at 1 year, which is comparable to neck of femur fractures in the elderly. This high mortality reflects the patient population (elderly, multiple comorbidities, osteoporosis) and the physiological stress of fracture and surgery. These fractures should be treated with the same urgency as hip fractures, with early surgery (within 48 hours if possible), multidisciplinary orthogeriatric care, and medical optimization to reduce mortality.
Outcome Question
Q: What is the expected union rate for Type II periprosthetic fractures treated with ORIF in patients with good bone quality vs severe osteoporosis?
A: Good bone quality: 75-85% union rate. Severe osteoporosis: 60-70% union rate. The 15-25% difference reflects the impact of bone quality on fracture healing and fixation stability. In osteoporotic bone, locking screws can pull out, plates can fail, and biological healing is impaired. This is why severe osteoporosis is a relative indication for revision TKA with cemented stems rather than ORIF, especially in Type II fractures.
Australian Context and Medicolegal Considerations
AOANJRR Data
- Revision burden: Periprosthetic fractures account for 12% of all TKA revisions in Australia
- Incidence trend: Increasing from 2.1% to 2.8% over 10 years (2013-2023) with aging population
- Re-revision rate: 20% at 5 years after revision for periprosthetic fracture
- Cemented vs uncemented stems: Cemented stems have lower revision rate (15% vs 25%) in fracture setting
- Mortality: 28% at 1 year post-revision for fracture, comparable to hip fracture mortality
Australian Guidelines
- ACSQHC: Australian Commission on Safety and Quality in Health Care recommends multidisciplinary orthogeriatric care for periprosthetic fractures
- DVT prophylaxis: Extended prophylaxis for minimum 6 weeks post-surgery (NHMRC guidelines)
- Bone health: Pre-operative DEXA scanning and osteoporosis treatment recommended for high-risk patients (Osteoporosis Australia)
- Funding: Periprosthetic fracture surgery covered under public system; private patients may have out-of-pocket costs
Medicolegal Considerations
Key documentation requirements:
- Informed consent: Document discussion of treatment options (ORIF vs revision TKA), expected outcomes, complications (nonunion 20-30%, infection 3-5%, mortality 30% at 1 year in elderly), and alternative approaches
- Prosthetic stability assessment: Document radiographic criteria used to classify fracture (Type I vs II vs III), including assessment for lucency, subsidence, and alignment on AP and lateral views
- Implant compatibility: Document verification of femoral component design (open vs closed box) before planning retrograde nail - attempting to nail closed-box component is indefensible
- Medical optimization: Document pre-operative assessment of bone health (DEXA if available), medical comorbidities, and optimization of cardiopulmonary status
- Early surgery: Document rationale for timing of surgery - delay beyond 48 hours should have clear medical justification
- Postoperative complications: Document management of complications (nonunion, infection, hardware failure) and shared decision-making about revision surgery
Common litigation issues:
- Anterior femoral notching during index TKA leading to subsequent fracture (claims of substandard surgical technique)
- Wrong fixation method (attempting retrograde nail through closed-box component, or ORIF in Type III fracture)
- Delayed surgery (beyond 7 days) without medical justification, associated with worse outcomes
- Failure to diagnose prosthetic loosening pre-operatively (Type III misclassified as Type II, leading to ORIF failure)
TKA PERIPROSTHETIC FRACTURES
High-Yield Exam Summary
Key Classification
- •Lewis & Rorabeck Type I = Non-displaced (under 5mm, under 5°), stable prosthesis = ORIF or conservative
- •Type II = Displaced (over 5mm OR over 5°), stable prosthesis = ORIF (plate or nail based on implant design)
- •Type III = Any displacement + prosthesis loose (lucency, subsidence, malalignment) = Revision TKA with stems
- •Felix tibial: Type I (plateau) = revision, Type II (adjacent to stem) = plate ± stem extension, Type III/IV = standard fixation
- •Patellar: Intact extensor = conservative, disrupted extensor = surgical repair or patellectomy
Surgical Decision Algorithm
- •Type II + open-box component + good bone = Retrograde IM nail (85-90% union)
- •Type II + closed-box component OR osteoporotic bone = Lateral locked plate (75-85% union)
- •Type III (loose prosthesis) = Revision TKA with long stems (over 100mm beyond fracture) + cerclage cables
- •Severe osteoporosis in Type II = Consider revision TKA upfront (ORIF has 30-40% nonunion rate)
- •Open-box verification is MANDATORY before planning retrograde nail - catastrophic if attempted with closed box
Surgical Pearls
- •Lateral locked plate: Submuscular bridge plating, fill all holes in osteoporotic bone, leave 1cm gap from femoral component
- •Retrograde nail: Entry point center of intercondylar notch, bury nail 5mm below articular surface, confirm clearance from polyethylene
- •Revision TKA: Cemented stems preferred (immediate stability), cerclage cables for provisional fracture fixation, stem length = fracture + 100mm or 2 cortical diameters
- •Anterior femoral notching over 3mm = 4-fold fracture risk, assess on all lateral radiographs
- •Weight-bearing: Touch for 6 weeks, progress to full by 12 weeks if radiographic healing evident
Risk Factors
- •FORNOW = Female, Osteoporosis, Rheumatoid, Neurological, Old age, Warfarin/steroids
- •Anterior femoral notching over 3mm increases fracture risk 4-fold
- •Osteoporosis (T-score below -2.5) increases nonunion risk with ORIF to 30-40%
- •Revision TKA has 5-10% periprosthetic fracture rate (vs 2.5% for primary TKA)
Complications
- •Nonunion 20-30% with ORIF in osteoporotic bone, 10-15% in good bone, managed with revision ORIF or conversion to stemmed TKA
- •Hardware failure 10-15% (plate) or 5% (nail), due to screw pullout in poor bone or premature weight-bearing
- •Infection (PJI) 3-5%, requires debridement or two-stage revision based on chronicity
- •Mortality 30% at 1 year in elderly - comparable to hip fracture, treat with same urgency
- •Stiffness 15-20%, managed with early ROM, manipulation under anesthesia at 6-12 weeks if severe