Adult Reconstruction
Distal Femoral Osteotomy
Comprehensive guide to distal femoral osteotomy for lateral compartment osteoarthritis and valgus deformity - indications, surgical technique, outcomes, and complications
Reviewed by OrthoVellum Editorial Team
Orthopaedic clinicians and medical editors • Published by OrthoVellum Medical Education Team
High Yield Overview
DISTAL FEMORAL OSTEOTOMY
Valgus Correction | Lateral Compartment OA | Opening vs Closing Wedge
5-10%of all knee OA cases
10-15°typical correction angle
85%5-year survivorship
3-5°valgus overcorrection target
PUDDU CLASSIFICATION (DFO Types)
Medial Opening
PatternBiplanar osteotomy, easier fixation
TreatmentPreferred for larger corrections
Lateral Closing
PatternMore complex, removes bone
TreatmentLimited corrections, avoid peroneal nerve injury
Biplanar
PatternCombined technique for multiplanar deformity
TreatmentComplex deformities with rotation/translation
Critical Must-Knows
- Indications: Valgus malalignment greater than 5 degrees with lateral compartment OA in young active patients
- CORA principle: Center of Rotation and Angulation must be identified for accurate correction
- Target alignment: 3-5 degrees valgus overcorrection to shift load to medial compartment
- Peroneal nerve at risk: Lateral closing wedge risks stretch injury to common peroneal nerve
- Opening wedge advantages: Preserves bone stock, allows precise correction, safer for nerve
Examiner's Pearls
- "Medial opening wedge is preferred technique - safer and more versatile
- "Must address patellar height - opening wedge increases patella alta risk
- "Combine with ligament reconstruction if instability present (LCL, posterolateral corner)
- "Fujisawa point: target mechanical axis at 62% from medial tibial plateau edge
Critical DFO Exam Points
Indications
Valgus thrust gait with lateral compartment pain. Young patients (under 60), BMI less than 30, high activity demand. Failed conservative management. Isolated lateral compartment disease on imaging. Correctable deformity (not fixed flexion contracture greater than 15 degrees).
CORA Identification
Critical for surgical planning. Intersection of proximal and distal mechanical axes. Usually at metaphyseal-diaphyseal junction. Osteotomy must be at CORA level. Misplacement creates translation deformity.
Surgical Technique
Opening wedge preferred over closing. Use lateral distal femoral locking plate. Protect common peroneal nerve. Fill wedge gap greater than 10mm with bone graft or substitute. Check correction with intraoperative imaging.
Key Complications
Peroneal nerve palsy most feared. Delayed union or nonunion at osteotomy site. Loss of correction. Patella alta requiring later patella tendon shortening. Conversion to arthroplasty in 15-20% at 10 years.
Quick Decision Guide: Opening vs Closing Wedge DFO
| Scenario | Technique | Fixation | Key Pearl |
|---|---|---|---|
| Correction less than 10 degrees, good bone stock | Medial opening wedge | Lateral locking plate + allograft if gap over 10mm | Preserves bone, easier to adjust correction |
| Correction greater than 15 degrees, young patient | Medial opening wedge with structural graft | Dual plate fixation or medial support plate | Large gaps need structural allograft or autograft |
| Small correction, concern for patella alta | Lateral closing wedge | Lateral locked plate, careful nerve dissection | Lowers patella but risks peroneal nerve stretch |
| Combined deformity (valgus + procurvatum) | Biplanar osteotomy | Specialized locked plate with oblique cuts | Address all planes of deformity simultaneously |
Mnemonic
VALGUSDFO Indications Assessment
V
Valgus thrust
Dynamic valgus on gait - key clinical sign
A
Age under 60
Young active patients, not candidates for arthroplasty
L
Lateral compartment OA
Isolated lateral disease, medial compartment preserved
G
Good range of motion
Flexion over 100 degrees, FFD less than 15 degrees
U
Unloader brace failed
Conservative management exhausted
S
Stable ligaments
Or plan combined ligament reconstruction if unstable
Memory Hook:Think VALGUS deformity when considering DFO - the clinical presentation drives the indication!
Mnemonic
CORAPreoperative Planning Steps
C
Center of rotation
Intersection of mechanical axes on long-leg films
O
Osteotomy level
Must be at CORA to avoid translation
R
Required correction
Calculate degrees needed for 3-5 degree valgus overcorrection
A
Apex location
Apex of deformity determines wedge direction
Memory Hook:Find the CORA before you cut - accurate planning prevents translation deformities!
Mnemonic
NERVEComplications to Discuss
N
Nerve palsy
Common peroneal nerve - stretch or direct injury
E
Extension loss
Patella alta from opening wedge, loss of terminal extension
R
Recurrence
Loss of correction, valgus deformity returns
V
Vascular injury
Popliteal artery at risk with posterior hinge fracture
E
Evolution to arthroplasty
15-20% conversion rate at 10 years
Memory Hook:Mind the NERVE - peroneal nerve palsy is the nightmare complication to avoid!
Overview and Epidemiology
Clinical Context
Distal femoral osteotomy addresses valgus knee malalignment causing lateral compartment overload. While less common than varus deformity (treated with high tibial osteotomy), valgus deformity creates unique challenges: lateral soft tissue laxity, peroneal nerve proximity, and frequent associated LCL or posterolateral corner insufficiency. The surgery aims to realign the mechanical axis, reducing lateral compartment load and delaying or avoiding total knee arthroplasty in young, active patients.
Demographics
- Age: 40-60 years (too young for TKA)
- Activity level: High demand, athletic
- Gender: Females greater than males (constitutional valgus)
- BMI: Ideally less than 30 for optimal outcomes
- Failed conservative care: Bracing, injections, activity modification
Pathophysiology
- Mechanical overload: Valgus alignment shifts load laterally
- Cartilage degeneration: Lateral compartment wear, bone-on-bone
- Soft tissue laxity: Medial structures stretched, lateral contracted
- Thrust gait: Dynamic valgus increases with ambulation
- Progressive: Deformity worsens without intervention
Biomechanics and Mechanical Axis
Understanding CORA is Essential
The Center of Rotation and Angulation (CORA) is where the proximal mechanical axis and distal mechanical axis intersect. The osteotomy MUST be performed at the CORA level. If the osteotomy is placed away from CORA, the correction creates an undesirable translation deformity. For valgus knee, CORA is typically at the distal femoral metaphysis.
Mechanical Axis Alignment Goals
| Parameter | Normal | Valgus Deformity | Target Post-DFO |
|---|---|---|---|
| Mechanical axis deviation | 0mm (center of knee) | Lateral to knee center (over 10mm lateral) | 3-5mm medial (Fujisawa point at 62% from medial edge) |
| Anatomic femorotibial angle | 5-7 degrees valgus | Greater than 10 degrees valgus | 0-3 degrees valgus (slight overcorrection) |
| Lateral distal femoral angle (LDFA) | 88 degrees | Less than 85 degrees (valgus source) | 88-90 degrees (anatomic restoration) |
Fujisawa Point Target
- Definition: Mechanical axis at 62% from medial tibial edge
- Clinical significance: Optimal load distribution
- Measurement: On standing long-leg radiograph
- Overcorrection rationale: Shifts load to healthier medial compartment
- Evidence: Fujisawa 1979 study showed best outcomes at this point
CORA Determination
- Long-leg standing films: Essential for planning
- Draw mechanical axes: Hip center to ankle center
- Identify intersection: Where axes cross = CORA
- Measure correction needed: Angle to achieve target alignment
- Plan osteotomy level: At CORA to avoid translation
Classification of DFO Techniques
Medial Opening Wedge Technique
Advantages:
- Preserves bone stock (no bone removal)
- Easier to adjust correction intraoperatively
- Safer for common peroneal nerve (no stretch)
- Better fixation options with lateral locked plate
- Can correct larger deformities
| Wedge Size | Management | Healing Time |
|---|---|---|
| Less than 10mm gap | No graft needed, plate fixation alone | 8-12 weeks |
| 10-15mm gap | Bone graft substitute (calcium phosphate, DBM) | 12-16 weeks |
| Greater than 15mm gap | Structural allograft (tricortical iliac crest) | 16-24 weeks |
Disadvantages:
- Increases patellar height (patella alta risk)
- Delayed union if gap greater than 15mm without graft
- Requires bone graft or substitute for large gaps
- Potential for loss of correction during healing
This is the preferred technique for most DFO cases.
Clinical Assessment and Patient Selection
History
- Pain location: Lateral knee, worse with activity
- Valgus thrust: Dynamic valgus with walking
- Activity level: High demand, unable to continue sports
- Failed conservative: Bracing, NSAIDs, injections, physio
- Young age: Too young for arthroplasty (under 60)
- Functional goals: Return to impact activities
Examination
- Gait: Valgus thrust during stance phase
- Alignment: Standing - visible valgus deformity
- Range of motion: Flexion over 100°, FFD less than 15°
- Stability: Assess LCL, posterolateral corner
- Palpation: Lateral joint line tenderness
- Special tests: Varus stress (LCL competence)
Contraindications - Know When NOT to Operate
Absolute contraindications: Inflammatory arthritis (rheumatoid, psoriatic), active infection, severe osteoporosis, unrealistic patient expectations, medical unfitness.
Relative contraindications: Age over 65 years, BMI greater than 35, flexion contracture greater than 15 degrees, tricompartmental arthritis, patellofemoral arthritis, smoking (nonunion risk), noncompliance with rehab.
Patient Selection Criteria
| Factor | Ideal Candidate | Poor Candidate |
|---|---|---|
| Age | 40-55 years | Over 65 years |
| BMI | Less than 30 | Greater than 35 |
| Activity level | High demand, athletic | Sedentary, low demand |
| ROM | Flexion over 110°, FFD less than 10° | Flexion less than 90°, FFD over 20° |
| Compartment disease | Isolated lateral OA | Tricompartmental arthritis |
| Expectations | Realistic - delay TKA, reduce pain | Unrealistic - cure arthritis |
Investigations and Surgical Planning
Imaging Protocol
EssentialStanding Long-Leg Radiographs
Weight-bearing AP hip-to-ankle films are mandatory. Identify mechanical axis, measure MAD (mechanical axis deviation), calculate CORA, determine correction angle needed. Measure LDFA (lateral distal femoral angle) - normal 88 degrees. Assess joint line obliquity.
StandardKnee Radiographs
AP, lateral, skyline views of affected knee. Grade compartment arthritis (Kellgren-Lawrence or Ahlback). Assess patellofemoral joint. Measure posterior tibial slope if planning combined procedures.
If AvailableMRI Knee
Assess cartilage status in all compartments. Evaluate menisci (consider meniscal transplant if deficient). Check ligaments (LCL, PCL, posterolateral corner). Identify subchondral edema (predictor of pain).
AdvancedComputer-Assisted Planning
Software-based planning (TraumaCad, Materialise) for complex cases. Simulate correction, plan osteotomy cuts, create custom guides. Particularly useful for biplanar osteotomies.
Correction Angle Calculation
Target: Mechanical axis through Fujisawa point (62% from medial tibial edge), which corresponds to 3-5 degrees valgus overcorrection.
Calculation method:
- Measure current mechanical axis deviation (MAD) in mm
- Measure width of tibial plateau
- Calculate target MAD at 62% point
- Use trigonometry or planning software to determine correction angle
- Typically requires 10-15 degrees correction for symptomatic valgus
Example: If tibial plateau is 80mm wide, Fujisawa point is at 49.6mm from medial edge (62%). If current MAD is 20mm lateral, need to shift axis 69.6mm medially - this usually requires 12-14 degree correction.
Management Algorithm
📊 Management Algorithm
Click to expand
Conservative Treatment First-Line
All patients should trial nonoperative management for at least 6 months unless severe symptoms.
Conservative Treatment Pathway
0-6 weeksInitial Management
Activity modification, NSAIDs, ice, weight loss if BMI over 30. Physical therapy for quadriceps strengthening, hamstring stretching, gait training.
6-12 weeksAdvanced Conservative
Unloader bracing (medial unloader for valgus knee - pushes knee into varus). Intra-articular corticosteroid injection (diagnostic and therapeutic). Consider viscosupplementation (hyaluronic acid).
3-6 monthsDecision Point
If symptoms persist despite optimal conservative care, patient remains high demand and meets surgical criteria, proceed to surgical planning. If improved, continue conservative management with annual follow-up.
Indications for surgery: Persistent pain limiting activities, failed 6 months conservative care, suitable anatomy and patient factors.
Surgical Technique - Medial Opening Wedge DFO
Preoperative Planning
Consent Points
- Nonunion/delayed union: 5-10%, higher with large gaps
- Common peroneal nerve palsy: 2-5% (opening wedge lower risk)
- Loss of correction: 5-8% during healing
- Infection: 2% superficial, 1% deep
- Patella alta: Opening wedge increases height
- Conversion to TKA: 15-20% at 10 years
Equipment Checklist
- Implants: Lateral distal femoral locked plate (appropriate size)
- Power: Oscillating saw, drill
- Imaging: C-arm - confirm can visualize full correction
- Bone graft: Allograft or substitute if gap over 10mm
- Navigation: Optional - improves accuracy
- K-wires: For temporary fixation and guide pins
Patient Positioning
Setup Checklist
Step 1Position
Supine on radiolucent table. Bump under ipsilateral hip (30 degrees) for lateral exposure. Knee flexed over bolster at 20-30 degrees. Thigh tourniquet applied but not inflated (preserve blood supply to osteotomy).
Step 2Padding
- Bony prominences: Sacrum, contralateral heel
- Nerves: Ensure no pressure on peroneal nerve at fibular head
- Position bolster: Under distal femur/proximal tibia
Step 3Draping
- Landmarks exposed: ASIS to ankle
- Limb: Free drape to allow manipulation
- C-arm access: Confirm AP and lateral views obtainable
- Prepare both legs: For alignment comparison
Surgical Approach - Lateral Distal Femur
Exposure Steps
Step 1Skin Incision
Lateral longitudinal incision 10-12cm, centered over distal femoral metaphysis. Start 5cm proximal to joint line, extend proximally. Incise along lateral aspect of vastus lateralis.
Step 2Superficial Dissection
Incise iliotibial band longitudinally. Develop plane between vastus lateralis anteriorly and lateral intermuscular septum posteriorly. Retract vastus anteriorly to expose lateral femur.
Step 3Subperiosteal Exposure
Elevate periosteum from lateral distal femur. Expose anterior and posterior cortices for plate placement. Protect posteriorly - popliteal vessels behind bone. Place retractors carefully.
Step 4Confirm Level
Fluoroscopy AP and lateral to confirm adequate exposure of planned osteotomy site. Place K-wire as reference at CORA level (typically 3-4cm proximal to joint line).
Key surgical landmarks: lateral femoral condyle, adductor tubercle (posteromedially), vastus lateralis muscle.
Technical Pearls
Do's (Pearls)
- Biplanar osteotomy: More stable than uniplanar
- Preserve medial hinge: Critical for healing
- Use locked plate: Better hold in metaphyseal bone
- Intraoperative alignment: Cable test to confirm correction
- Bone graft gaps over 10mm: Prevents delayed union
Don'ts (Pitfalls)
- Don't break medial hinge: Open slowly, monitor fluoroscopy
- Don't under-correct: Aim for 3-5 degree valgus overcorrection
- Don't penetrate joint: Keep osteotomy 3cm proximal to joint line
- Don't forget graft: Large gaps without graft = nonunion
- Don't use tourniquet: Impairs bone healing at osteotomy
Intraoperative Troubleshooting
Common Problems and Solutions
| Problem | Cause | Solution |
|---|---|---|
| Medial hinge fractures during opening | Opening wedge too rapidly, osteoporotic bone | Add medial support plate, consider cancellous screws across hinge |
| Cannot achieve adequate correction | Soft tissue tension, incomplete osteotomy cut | Complete osteotomy cut, release contracted lateral structures |
| Plate does not contour to bone | Plate too straight for femoral anatomy | Contour plate before application, or choose anatomic plate design |
| Alignment check shows under-correction | Insufficient wedge opening | Open wider using calibrated spreaders, recheck with cable |
Complications
| Complication | Incidence | Risk Factors | Management |
|---|---|---|---|
| Common peroneal nerve palsy | 2-5% (opening), 10% (closing) | Lateral closing wedge, hematoma, poor positioning | Observation - most recover in 3-6 months. Nerve exploration if complete palsy. EMG at 6 weeks. |
| Nonunion / delayed union | 5-10% | Gap over 15mm, no graft, smoking, malnutrition | Bone stimulator, revision with bone grafting if persistent at 6 months |
| Loss of correction | 5-8% | Inadequate fixation, poor bone quality, early weight-bearing | Revision osteotomy if symptomatic, otherwise accept if minimal |
| Patella alta (opening wedge) | 10-15% | Large correction (over 15mm opening), pre-existing alta | Monitor patellar height (Caton-Deschamps index). Consider patella tendon shortening if CDI over 1.4 |
| Infection (superficial/deep) | 2% / 1% | Diabetes, smoking, prolonged surgery | Antibiotics, irrigation and debridement if deep. Retain hardware if stable. |
| Intra-articular fracture | Less than 5% | Osteotomy cut too distal, medial hinge fracture propagates | Convert to ORIF with additional screws if displaced, otherwise conservative |
| Conversion to TKA | 15-20% at 10 years | Age over 55, tricompartmental disease at index surgery | Planned endpoint - DFO buys time. Perform TKA when pain recurs. |
Peroneal Nerve Palsy Timeline
Peroneal nerve palsy typically manifests immediately post-op (stretch injury during surgery) or within 24-48 hours (hematoma compression). Foot drop is the key finding - loss of ankle dorsiflexion and toe extension. Most cases (80%) recover spontaneously over 3-6 months. Consider surgical exploration if complete palsy with no recovery at 3 months or progressive worsening.
Postoperative Care and Rehabilitation
Early Rehabilitation
Immediate Post-opDay 0-1
Hinged knee brace locked in extension. Neurovascular checks every 2 hours for 24 hours. Ice and elevation. DVT prophylaxis (LMWH or rivaroxaban). Pain management (multimodal - paracetamol, NSAIDs, opioids PRN).
Initial MobilizationDay 1-14
Non-weight-bearing (NWB) with crutches. Brace remains locked in extension for ambulation. Unlock brace for passive ROM exercises - 0-90 degrees. Quadriceps sets, straight leg raises. Drain removal at 24-48 hours if placed.
Progressive ROMWeek 2-6
Remain NWB on affected leg. Gradually increase ROM to 0-120 degrees. Quad strengthening, hamstring stretches. Brace locked in extension for ambulation, unlock for exercises. Wound check at 2 weeks, staples/sutures out at 14 days.
Why Non-Weight-Bearing Early?
Opening wedge osteotomy has no bone-to-bone contact - healing depends on graft incorporation and new bone formation bridging the gap. Early weight-bearing risks loss of correction or graft collapse. NWB for 6 weeks allows initial healing before load application.
Weight-Bearing Protocol Summary
| Time | Weight-Bearing Status | Brace | Activities |
|---|---|---|---|
| 0-6 weeks | Non-weight-bearing (NWB) | Locked in extension | Passive ROM, quad sets, SLR |
| 6-8 weeks | Touch-down WB (10-20kg) | Unlocked for exercise | TDWB with crutches, ROM 0-120° |
| 8-12 weeks | Progressive WB (25% every 2 weeks) | Wean off brace | Stationary bike, pool exercises |
| 12+ weeks | Full weight-bearing (FWB) | Discontinued | Progressive strengthening, ADLs |
| 6+ months | Full activities | None | Return to sport if healed |
Outcomes and Prognosis
| Outcome Measure | Expected Results | Predictors of Success |
|---|---|---|
| Pain relief | Significant improvement in 80-90% at 2 years | Younger age (under 55), isolated lateral OA, accurate correction achieved |
| Function and activity | Return to low-impact sports in 80%, high-impact limited | Pre-op activity level, BMI less than 30, good quad strength |
| Survivorship (avoiding TKA) | 85% at 5 years, 75% at 10 years, 60% at 15 years | Accurate correction (3-5° valgus), no PF arthritis, younger age |
| Alignment maintenance | Correction maintained in 90-95% long-term | Adequate fixation, bone healing at osteotomy, compliant with rehab |
Predictors of Poor Outcome
Age over 55 years: Lower survivorship, higher TKA conversion rate. BMI over 35: Increased load, higher failure rate. Tricompartmental arthritis: DFO does not address medial or PF disease. Flexion contracture over 15 degrees: Difficult to correct, poor function. Under-correction: Failure to achieve 3-5 degree valgus overcorrection leads to recurrent symptoms. Smoking: Nonunion risk, impaired healing.
Factors Favoring DFO Over TKA
- Age under 55 years (too young for TKA)
- High activity demand (impact sports)
- Isolated lateral compartment disease
- Desire to preserve native knee anatomy
- Good bone quality and soft tissue envelope
- Realistic expectations (DFO buys 10-15 years)
When TKA is Better Option
- Age over 65 years (TKA longevity expected)
- Low activity demand (sedentary lifestyle)
- Tricompartmental arthritis
- Severe flexion contracture (over 20 degrees)
- Poor bone quality (severe osteoporosis)
- Medical comorbidities limiting rehab compliance
Evidence Base and Key Trials
Puddu Classification and Opening Wedge DFO Technique
Puddu G, Cipolla M, Cerullo G, Franco V, Gianni E • Orthopedics (2007)
Key Findings:
- Described medial opening wedge technique with lateral plate fixation
- Reported 85% good-to-excellent results at mean 6 year follow-up
- Opening wedge preserves bone stock compared to closing wedge
- Recommended for corrections up to 15 degrees
Clinical Implication: Opening wedge is the preferred technique for most DFO cases - safer for peroneal nerve and allows larger corrections.
Limitation: Case series without control group, relatively short follow-up
Long-Term Survivorship After DFO
Backstein D, Morag G, Hanna S, Safir O, Gross A • Clin Orthop Relat Res (2007)
Key Findings:
- Retrospective review of 58 knees, mean follow-up 12.4 years
- Survivorship (avoiding TKA): 85% at 5 years, 79% at 10 years, 64% at 15 years
- Age under 50 had better survivorship than over 50 (89% vs 68% at 10 years)
- Accurate correction (mechanical axis through Fujisawa point) critical for success
Clinical Implication: DFO provides durable pain relief and function for 10-15 years in appropriately selected young patients.
Limitation: Retrospective study with variable techniques over time period
Complications After Distal Femoral Osteotomy
Nelissen EM, van Langelaan EJ, Nelissen RG • Int Orthop (2010)
Key Findings:
- Systematic review of 23 studies, 629 knees
- Overall complication rate 31% - nonunion 5%, loss of correction 8%, nerve palsy 4%
- Lateral closing wedge had higher nerve palsy rate (10%) vs opening wedge (2%)
- Opening wedge had higher delayed union (10%) but lower overall complication rate
Clinical Implication: Opening wedge DFO has lower nerve injury risk but requires careful attention to bone healing with grafting for large gaps.
Limitation: Heterogeneous studies with varying techniques and definitions of complications
Fujisawa Point - Optimal Mechanical Axis Target
Fujisawa Y, Masuhara K, Shiomi S • J Bone Joint Surg Am (1979)
Key Findings:
- Analysis of 54 knees after HTO, identified optimal mechanical axis position
- Best outcomes when mechanical axis passed through point 30-40% lateral to medial edge of plateau
- Corresponds to 62% from medial edge (Fujisawa point)
- Under-correction (varus) or over-correction (excessive valgus) had worse outcomes
Clinical Implication: Target mechanical axis at Fujisawa point (62% from medial tibial edge) for optimal load redistribution and outcomes.
Limitation: Originally described for HTO, extrapolated to DFO. Older study with limited follow-up.
Computer-Assisted DFO vs Conventional Technique
Ehlinger M, Spoor AB, Ollivier M, et al • Knee Surg Sports Traumatol Arthrosc (2020)
Key Findings:
- Comparative study: computer-assisted (n=42) vs conventional (n=38) DFO
- Computer-assisted had more accurate correction (within 2° of target in 93% vs 71%)
- Lower rate of under-correction with computer assistance
- No difference in complications or clinical outcomes at 2 years
Clinical Implication: Computer-assisted surgery improves accuracy of correction but does not necessarily improve clinical outcomes. Consider for complex or biplanar osteotomies.
Limitation: Single center study, relatively short follow-up, learning curve not accounted for
Exam Viva Scenarios
Practice these scenarios to excel in your viva examination
VIVA SCENARIOStandard
Scenario 1: Standard DFO Case (2-3 min)
EXAMINER
"A 48-year-old recreational tennis player presents with lateral knee pain for 2 years. Failed physiotherapy, bracing, and intra-articular injections. Examination shows valgus thrust on gait, lateral joint line tenderness, ROM 0-130 degrees, stable to varus stress. Long-leg radiographs show 12 degrees valgus alignment with isolated lateral compartment Ahlback Grade 2 osteoarthritis. Mechanical axis passes 25mm lateral to knee center. What is your assessment and management?"
EXCEPTIONAL ANSWER
This is a symptomatic valgus knee deformity with isolated lateral compartment osteoarthritis in a young, active patient. I would take a systematic approach: First, confirm this patient has exhausted conservative management including activity modification, NSAIDs, physiotherapy for quadriceps strengthening, and unloader bracing. Second, on examination I would document the valgus thrust, assess range of motion (excellent at 0-130 degrees), check ligamentous stability (LCL and posterolateral corner), and examine patellofemoral joint for crepitus. Third, on imaging I would confirm isolated lateral compartment disease, measure the mechanical axis deviation (25mm lateral indicates significant valgus), identify the CORA at the distal femoral metaphysis, and calculate required correction to achieve Fujisawa point target (62% from medial tibial edge, typically 3-5 degrees valgus overcorrection). My surgical plan would be medial opening wedge distal femoral osteotomy with lateral locked plate fixation. I would counsel about 85% survivorship at 5 years, realistic expectations of pain reduction and functional improvement, complications including nonunion (5-10%), nerve injury (2-5%), and eventual conversion to TKA in 15-20% by 10 years.
KEY POINTS TO SCORE
Systematic assessment: history, examination, imaging, surgical planning
Identify CORA and calculate correction to Fujisawa point
Opening wedge technique preferred - safer and more versatile
Realistic counseling about outcomes and conversion to TKA timeline
COMMON TRAPS
✗Forgetting to assess ligamentous stability - may need combined LCL reconstruction
✗Not identifying CORA - osteotomy away from CORA creates translation deformity
✗Choosing closing wedge without considering peroneal nerve risk
✗Unrealistic expectations - DFO is not curative, buys time before TKA
LIKELY FOLLOW-UPS
"How would you calculate the correction angle needed?"
"What if the patient also has Grade 2 LCL laxity?"
"Describe your fixation technique and weight-bearing protocol"
VIVA SCENARIOChallenging
Scenario 2: DFO Surgical Technique (3-4 min)
EXAMINER
"Walk me through your surgical technique for medial opening wedge distal femoral osteotomy. Include positioning, approach, osteotomy technique, fixation, and how you confirm adequate correction intraoperatively."
EXCEPTIONAL ANSWER
For medial opening wedge DFO, patient positioning is supine on radiolucent table with bump under ipsilateral hip for lateral exposure, knee flexed 20-30 degrees over bolster. No tourniquet to preserve blood supply to osteotomy. My approach is lateral longitudinal incision 10-12cm centered over distal femoral metaphysis, incise iliotibial band, develop plane between vastus lateralis and lateral intermuscular septum, subperiosteal exposure of lateral femur. For the osteotomy, I use a biplanar technique: place two parallel K-wire guides from lateral cortex aimed at medial cortex 1cm proximal to joint line under fluoroscopy, use oscillating saw to cut between wires leaving 5-10mm medial hinge intact, open wedge gradually with calibrated spreaders while monitoring alignment. Intraoperative correction is verified using alignment cable from hip center to ankle center on AP fluoroscopy - aim for mechanical axis through Fujisawa point (62% from medial tibial edge). For fixation, I use lateral distal femoral locked plate with 3-4 distal locked screws and 4-5 proximal locked screws, fill gaps greater than 10mm with structural allograft or bone graft substitute. Closure includes iliotibial band repair, subcutaneous layer, skin, and application of hinged knee brace locked in extension. Postoperative protocol is non-weight-bearing for 6 weeks, then progressive weight-bearing based on radiographic healing.
KEY POINTS TO SCORE
Lateral approach to distal femur preserving blood supply
Biplanar osteotomy with intact medial hinge for stability
Intraoperative alignment verification with cable test - critical step
Locked plate fixation with bone graft for gaps over 10mm
COMMON TRAPS
✗Breaking medial hinge - leads to instability and nonunion risk
✗Not verifying correction intraoperatively - under-correction is common pitfall
✗Inadequate fixation for large corrections - consider dual plates
✗Forgetting bone graft for large gaps - nonunion is predictable consequence
LIKELY FOLLOW-UPS
"What would you do if the medial hinge fractures during opening?"
"How do you decide between opening and closing wedge?"
"What is your target mechanical axis position and why Fujisawa point?"
VIVA SCENARIOCritical
Scenario 3: Complication Management (2-3 min)
EXAMINER
"A 52-year-old patient is 6 months post-DFO. Radiographs show no bridging callus across the osteotomy site. The patient has ongoing lateral knee pain and cannot weight-bear fully. How do you manage this delayed union or nonunion?"
EXCEPTIONAL ANSWER
This presentation is concerning for nonunion at the DFO osteotomy site. My immediate assessment would include detailed history about compliance with weight-bearing restrictions (early weight-bearing can cause nonunion), smoking status, nutritional status, and current symptoms. I would examine for tenderness at osteotomy site, assess alignment maintenance, and check for hardware failure. Investigations would include CT scan to definitively assess union (radiographs can underestimate healing), inflammatory markers to rule out infection, vitamin D and calcium levels. The differential diagnosis includes delayed union (still has healing potential), nonunion (no healing by 6 months), infection (low-grade), or hardware failure. Treatment depends on several factors: if alignment is maintained and patient has minimal symptoms, I would trial bone stimulator (ultrasound or electrical) with continued protected weight-bearing for 3 more months. If symptomatic nonunion with maintained alignment, I would perform revision surgery with bone grafting (iliac crest autograft or structural allograft), evaluate and augment fixation if needed, consider exchange to larger plate or add medial support plate. If alignment is lost or infection present, more extensive revision is needed - debridement, new fixation, staged grafting if infected. Prevention strategies for future cases include avoiding nonunion risk factors (optimize nutrition, smoking cessation mandatory), using bone graft for gaps over 10mm, ensuring adequate fixation, strict adherence to non-weight-bearing protocol early. I would counsel this patient that revision surgery has 80% success rate for achieving union, but timeline to full recovery is extended by 6-12 months.
KEY POINTS TO SCORE
Systematic workup: history, examination, CT scan to confirm nonunion
Differentiate delayed union (wait and stimulate) from true nonunion (needs surgery)
Revision surgery: bone grafting + fixation augmentation if symptomatic
Prevention: graft large gaps, optimize biology, strict NWB protocol
COMMON TRAPS
✗Assuming nonunion at 6 months without CT confirmation - may be delayed union
✗Missing occult infection as cause of failure to heal
✗Inadequate revision - must address both biology (graft) and mechanics (fixation)
✗Not counseling about extended recovery timeline - sets unrealistic expectations
LIKELY FOLLOW-UPS
"What are the risk factors for nonunion after DFO?"
"When would you consider conversion to TKA instead of revision DFO?"
"How do you rule out infection as a cause of nonunion?"
MCQ Practice Points
Biomechanics Question
Q: What is the Fujisawa point and why is it the target for mechanical axis correction in DFO? A: The Fujisawa point is located at 62% of the tibial plateau width measured from the medial edge. This corresponds to approximately 3-5 degrees valgus overcorrection from neutral. The mechanical axis passing through this point provides optimal load redistribution to the healthier medial compartment while avoiding excessive valgus and lateral soft tissue laxity. Original Fujisawa study (1979) showed best outcomes with mechanical axis at this location.
CORA Concept Question
Q: What is CORA and why must the osteotomy be performed at the CORA level? A: CORA stands for Center of Rotation and Angulation - the point where the proximal mechanical axis and distal mechanical axis intersect on long-leg radiographs. If the osteotomy is performed away from CORA, the correction creates an unwanted translation deformity in addition to the angular correction. For valgus knee, CORA is typically at the distal femoral metaphysis, 3-4cm proximal to the joint line.
Technique Comparison Question
Q: What are the advantages of medial opening wedge over lateral closing wedge DFO? A: Opening wedge advantages: (1) Preserves bone stock - no bone removal, (2) Safer for common peroneal nerve - no stretch injury risk, (3) More adjustable - easier to modify correction intraoperatively, (4) Allows larger corrections - closing wedge limited by nerve proximity. Main disadvantage is opening wedge increases patellar height (patella alta risk) and may require bone graft for large gaps.
Complication Question
Q: What is the most feared complication of DFO and how can it be prevented? A: Common peroneal nerve palsy is the most feared complication. Incidence is 2-5% with opening wedge, higher (10%) with closing wedge due to nerve stretch. Prevention strategies: (1) Choose opening wedge over closing when possible, (2) Meticulous nerve identification and protection during lateral approach, (3) Avoid excessive correction (over 15 degrees) with closing wedge, (4) Monitor for hematoma post-operatively which can compress nerve, (5) Consider prophylactic nerve decompression if high-risk case.
Indication Question
Q: What are the ideal patient characteristics for DFO? A: Ideal DFO candidate: Age 40-55 years (too young for TKA), high activity demand (wants to return to impact sports), isolated lateral compartment OA (medial and PF compartments healthy), BMI less than 30, good ROM (flexion over 100 degrees, FFD less than 15 degrees), stable ligaments or amenable to combined reconstruction, non-smoker, realistic expectations that DFO buys 10-15 years before eventual TKA.
Outcome Question
Q: What is the expected survivorship of DFO and what factors predict failure? A: DFO survivorship (avoiding conversion to TKA): 85% at 5 years, 75% at 10 years, 60% at 15 years. Predictors of failure: Age over 55, BMI over 35, under-correction (failure to achieve 3-5 degree valgus overcorrection), tricompartmental arthritis at index surgery, patellofemoral arthritis, flexion contracture over 15 degrees, smoking. Accurate correction to Fujisawa point is single most important technical factor.
Australian Context and Medicolegal Considerations
AOANJRR Data
- Osteotomy procedures rare: Less than 1% of knee procedures registered
- Conversion to TKA: Tracked as separate category - prior osteotomy
- Revision burden: Lower than primary TKA, but outcomes after conversion variable
- Australian practice: DFO less common than HTO due to valgus being less common
- Registry message: Young patient joint preservation important public health goal
Australian Guidelines
- ACSQHC VTE prophylaxis: LMWH or DOAC for major orthopedic surgery
- DVT risk: Moderate-high due to lower limb surgery and restricted mobility
- Duration: Until mobile (typically 10-14 days minimum)
- Antibiotic prophylaxis: Cefazolin 2g IV pre-incision (eTG guidelines)
- Blood conservation: Tranexamic acid 15mg/kg IV at incision and closure
Medicolegal Considerations
Key documentation requirements for DFO:
Informed consent must include:
- Realistic timeline - 6-12 months to return to activities, longer for bone healing
- Conversion to TKA expectation - 15-20% by 10 years, eventual endpoint for most
- Nerve injury risk - common peroneal nerve palsy 2-5%, may be permanent
- Nonunion risk - 5-10%, may require revision surgery
- Loss of correction - may need revision osteotomy
- Alternative of proceeding directly to TKA
Common litigation issues:
- Nerve palsy without documented nerve protection - ensure operative note details nerve identification
- Nonunion without bone graft for large gaps - standard of care to graft gaps over 10mm
- Under-correction - failure to achieve adequate realignment leads to early failure
- Patient selection errors - performing DFO in poor candidate (tricompartmental OA, elderly) leads to predictable failure
Public System Coverage:
- Distal femoral osteotomy with internal fixation covered under public hospital system
- Bone grafting procedures covered when required
- Document medical necessity and failed conservative care
Hospital Systems
- Public hospital access: Limited - typically reserved for younger patients, high demand
- Private coverage: Most private insurers cover with orthopedic policy
- Gaps: Implant costs can be significant (locked plates expensive)
- Rehabilitation: Requires intensive physiotherapy - ensure patient has access
- DVT prophylaxis: Mandatory in Australian hospitals (ACSQHC standard)
Consent Best Practice
- Timing: At least 48 hours before surgery (cooling-off period)
- Written material: Provide handout with diagrams, complication rates
- Document alternatives: TKA, ongoing conservative care, activity modification
- Realistic expectations: DFO buys time, not curative, most eventually need TKA
- Nerve palsy risk: Specifically mention peroneal nerve and foot drop possibility
- Revision risk: Nonunion may require further surgery
Distal Femoral Osteotomy
High-Yield Exam Summary
Key Anatomy & Biomechanics
- •CORA = Center of Rotation and Angulation - intersection of mechanical axes, osteotomy must be at CORA
- •Fujisawa point = 62% from medial tibial edge - target mechanical axis location
- •Common peroneal nerve at fibular head - at risk with lateral closing wedge
- •LDFA (lateral distal femoral angle) = 88° normal - valgus deformity less than 85°
- •Medial hinge (opening wedge) - must stay intact for stability and healing
Indications & Patient Selection
- •Age 40-60 years, high activity demand, isolated lateral compartment OA
- •Valgus thrust gait, ROM flexion over 100°, FFD less than 15°
- •Failed conservative care (bracing, injections, physio for 6 months)
- •BMI less than 30, non-smoker, realistic expectations
- •Correctable deformity - stable ligaments or amenable to reconstruction
Surgical Technique
- •Opening wedge preferred - preserves bone, safer for nerve, more adjustable
- •Lateral approach to distal femur, biplanar osteotomy, preserve medial hinge
- •Lateral locked plate fixation, bone graft if gap greater than 10mm
- •Intraop verification: alignment cable from hip to ankle, target Fujisawa point
- •Target correction: 3-5° valgus overcorrection to shift load medially
Postop Protocol
- •NWB 6 weeks in brace locked in extension for ambulation
- •Progressive WB weeks 6-12 based on radiographic healing (callus bridging)
- •FWB by 12 weeks if healed, return to low-impact sport at 6 months
- •High-impact activities permitted 9-12 months if asymptomatic
- •Radiographs at 6 weeks, 12 weeks, 6 months to monitor healing and alignment
Complications
- •Common peroneal nerve palsy 2-5% (opening), 10% (closing) - foot drop, most recover 3-6 months
- •Nonunion/delayed union 5-10% - higher if gap over 15mm without graft, smoking
- •Loss of correction 5-8% - inadequate fixation, early WB
- •Patella alta from opening wedge 10-15% - may need patella tendon shortening
- •Conversion to TKA 15-20% at 10 years - planned endpoint, buys time
Key Evidence & Outcomes
- •Fujisawa 1979: Mechanical axis at 62% point had best outcomes
- •Puddu 2007: Opening wedge technique, 85% good-excellent at 6 years
- •Backstein 2007: Survivorship 85% at 5y, 79% at 10y, 64% at 15y
- •Nelissen 2010: Overall complication 31%, opening lower nerve palsy than closing
- •Predictors of success: age under 55, accurate correction, isolated lateral OA, BMI under 30