Pipkin Classification | Associated Hip Dislocation | AVN Risk
- Pipkin I = BELOW fovea (non-weight-bearing) - may excise if small fragment
- Pipkin II = ABOVE fovea (weight-bearing) - MUST fix or excise
- Pipkin III = associated femoral neck fracture - high AVN risk, often arthroplasty
- Reduce dislocation URGENTLY - every hour increases AVN risk
- “Fovea is the KEY landmark - above vs below determines treatment
- “Posterior dislocation = anterior approach for ORIF (avoid posterior blood supply)
- “CT scan ESSENTIAL after reduction - assess fragment size and location
- “Time to reduction is the most important prognostic factor
Femoral Head Fractures
Reduce hip dislocation within 6 HOURS. AVN risk increases exponentially with time. Reduce in ED if possible, OR if not. Do NOT delay for elaborate imaging.
After concentric reduction confirmed on XR. CT defines fragment size and location. Assess for loose bodies in joint. Plan surgical approach and fixation.
Overview
Overview
Femoral head fractures are uncommon injuries that almost exclusively occur in association with traumatic hip dislocation, most commonly posterior. First classified by Pipkin in 1957, these fractures result from high-energy trauma where the femoral head impacts against the acetabular rim during dislocation.
The critical determinant of outcome is the time from injury to reduction. Prolonged dislocation leads to stretching and occlusion of the medial femoral circumflex artery (MFCA), the primary blood supply to the femoral head. Avascular necrosis (AVN) rates increase dramatically after 6 hours of dislocation.
The Pipkin classification guides management by distinguishing between fragments involving the weight-bearing (superior to fovea - Type II) and non-weight-bearing (inferior to fovea - Type I) portions of the femoral head. Types III and IV represent more complex injuries with associated femoral neck and acetabular fractures respectively.
For the orthopaedic examination, you must know the Pipkin classification, understand the urgency of reduction, and be able to discuss surgical approaches and indications.
Anatomy
Anatomy and Blood Supply
Femoral Head Anatomy
- Superior aspect of femoral head
- Covered by articular cartilage
- Critical for hip biomechanics
- Pipkin II involves this area
- Small depression on femoral head
- Attachment of ligamentum teres
- Landmark for Pipkin classification
- Below fovea = non-weight-bearing
Blood Supply (CRITICAL KNOWLEDGE)
- Primary blood supply to femoral head (80%)
- Arises from profunda femoris
- Courses posterior to femoral neck
- Gives off retinacular arteries
- AT RISK with posterior dislocation
- Minor contribution to head
- Supplies greater trochanter primarily
- Branch of obturator artery
- Supplies small area around fovea
- Contribution variable (significant in 10-20%)
- NOT adequate to prevent AVN alone
Why Posterior Dislocation Threatens Blood Supply
- MFCA courses posteriorly
- Dislocation stretches/kinks artery
- Prolonged dislocation = ischemia
- Reduction relieves stretch
- But damage may be done if delayed
Key Point: Anterior approach for ORIF after posterior dislocation avoids further damage to already compromised posterior blood supply.
Classification Systems
Pipkin Classification (1957)
- Fragment Location
- Below fovea
- Key Feature
- Non-weight-bearing zone
- Management
- Excise small, ORIF if large
- Fragment Location
- Above fovea
- Key Feature
- Weight-bearing zone
- Management
- ORIF required
- Fragment Location
- I or II + neck fracture
- Key Feature
- Very high AVN risk
- Management
- Arthroplasty (elderly) or fix
- Fragment Location
- I or II + acetabular fracture
- Key Feature
- Complex polytrauma
- Management
- Combined approaches
The fovea is the critical landmark. Above fovea = weight-bearing = must fix. Below fovea = non-weight-bearing = may excise if small.
Clinical Presentation
Clinical Presentation
Mechanism
- Motor vehicle accidents (dashboard injury)
- Fall from height
- Sporting injuries (rare)
- Industrial accidents
- Hip flexed and adducted (sitting position)
- Knee impacts dashboard
- Force transmitted along femur
- Posterior dislocation with head fracture
History
- Severe hip/groin pain
- Cannot move leg
- Leg appears shortened and internally rotated
- History of high-energy trauma
- Knee injuries (PCL, patella fracture)
- Femoral shaft fracture (floating hip)
- Other pelvic/acetabular fractures
- Sciatic nerve injury (10-20%)
Physical Examination
Classic Posterior Dislocation Position:
- Hip flexed, adducted, internally rotated
- Shortened leg
- Obvious deformity
- Unable to move hip
Neurovascular Assessment (MANDATORY):
- Assessment
- Foot dorsiflexion/plantarflexion, sensation
- Injury Rate
- 10-20%
- Assessment
- Toe extension, dorsum sensation
- Injury Rate
- Higher risk
- Assessment
- Toe flexion, plantar sensation
- Injury Rate
- Lower risk
- Assessment
- Femoral, popliteal, DP, PT
- Injury Rate
- Rare injury
Document Nerve Status BEFORE Reduction:
- Crucial for medicolegal purposes
- Differentiate injury from iatrogenic damage
- Most recover with reduction
Differential Diagnosis
- Key Distinguishing Features
- Flexed, adducted, internally rotated shortened limb; smooth concentric head on post-reduction film
- Discriminating Investigation
- Post-reduction CT shows congruent joint, no intra-articular fragment
- Key Distinguishing Features
- As above plus intra-articular bone fragment relative to fovea
- Discriminating Investigation
- CT defines fragment size and supra- vs infra-foveal location
- Key Distinguishing Features
- Shortened, externally rotated limb; pain on axial loading
- Discriminating Investigation
- AP pelvis/CT shows neck lucency; if combined with head fragment it is Pipkin III
- Key Distinguishing Features
- May co-exist; joint instability or incongruity after reduction
- Discriminating Investigation
- CT shows posterior wall defect; combined head injury is Pipkin IV
- Key Distinguishing Features
- Flexed, abducted, externally rotated limb
- Discriminating Investigation
- AP pelvis shows head inferomedial; obturator type lies near foramen
- Key Distinguishing Features
- Atraumatic or low-energy, insidious groin pain, no acute deformity
- Discriminating Investigation
- MRI shows subchondral oedema; not an acute fracture pattern
Investigations
Investigations
Initial Imaging
- First-line investigation
- Confirm dislocation
- Assess for associated fractures
- Do NOT delay reduction for imaging
- Assess posterior dislocation
- May be difficult to obtain
Post-Reduction Imaging
AP and Lateral Hip:
- Confirm concentric reduction
- Look for joint space widening (interposed fragment)
- Assess for associated fractures
CT Scan (ESSENTIAL After Reduction)
- All hip dislocations after reduction
- Assess femoral head fracture pattern
- Identify loose bodies
- Plan surgical approach
- Fragment size (% of head)
- Fragment location (above/below fovea)
- Articular step-off
- Loose bodies in joint
- Associated acetabular fracture
- Femoral neck integrity
3D Reconstruction
- Helpful for surgical planning
- Visualize fragment orientation
- Assess head sphericity
- Plan screw trajectory
MRI (Usually Not Acute)
- Assess for early AVN (weeks later)
- Cartilage damage assessment
- Not routine in acute setting
Management Algorithm
Management Principles
Priority Order:
- URGENT REDUCTION - Under 6 hours target
- Assess fragment size and location (CT)
- Remove incarcerated fragments/loose bodies
- Fix weight-bearing fragments
- Monitor for AVN
Hip dislocation is a TIME EMERGENCY. AVN risk increases dramatically after 6 hours. Reduce in ED if possible. Do NOT delay for elaborate imaging.
Surgical Technique
Smith-Petersen (Anterior) Approach
Preferred for posterior dislocations - protects MFCA
- Supine on radiolucent table
- Affected hip slightly externally rotated
- C-arm available
- Interval between sartorius and tensor fascia lata
- Develop interval to expose hip capsule
- Identify ascending branch of lateral femoral circumflex
- T-capsulotomy for exposure
- Excellent visualization of femoral head
- Direct access to anterior/superior head
- Can see fragment and reduce anatomically
This approach protects the posterior blood supply.
Complications
Complications
Avascular Necrosis (AVN)
Risk Factors:
- Dislocation time (most important)
- Multiple reduction attempts
- Pipkin type (III highest)
- Severity of initial injury
- Age (higher in older patients)
Incidence by Type:
- AVN Rate
- 10-15%
- AVN Rate
- 15-25%
- AVN Rate
- 40-60%
- AVN Rate
- 20-30%
- Under 6 hours: 10-15%
- 6-12 hours: 20-40%
- Over 12 hours: 50%+
- Conservative initially if asymptomatic
- Core decompression for early stages
- Total hip arthroplasty for advanced disease
- Young patients: consider joint preservation
Post-Traumatic Arthritis
20-50% at 10 years
- Residual articular incongruity
- Cartilage damage at injury
- AVN progression
- Retained loose bodies
- Activity modification
- NSAIDs
- Intra-articular injections
- Total hip arthroplasty for end-stage
Heterotopic Ossification
- Delayed surgery
- Extensive soft tissue trauma
- Male gender
- Head injury
- Indomethacin 75mg daily x 6 weeks
- Single-dose radiation (700 cGy)
- Low-dose radiation for high risk
Sciatic Nerve Injury
10-20% with posterior dislocation
- Most recover after reduction
- Peroneal division worse than tibial
- EMG at 3-4 weeks if no recovery
Recurrent Dislocation
- Rare
- Usually due to malreduced posterior wall
- May need revision fixation
Postoperative Care
Immediate Postoperative (0-2 weeks)
- Abduction pillow or wedge
- DVT prophylaxis (enoxaparin)
- Pain management
- Hip precautions if needed
- Wound checks
- Protected weight-bearing (toe-touch)
- Gentle ROM exercises
- DVT prophylaxis continued
Early mobilization reduces DVT risk.
Outcomes and Prognosis
Overall Outcomes
- Good/Excellent Result
- 80-90%
- AVN Rate
- 10-15%
- Prognosis
- Best
- Good/Excellent Result
- 70-80%
- AVN Rate
- 15-25%
- Prognosis
- Moderate
- Good/Excellent Result
- 40-50%
- AVN Rate
- 40-60%
- Prognosis
- Poor
- Good/Excellent Result
- 50-60%
- AVN Rate
- 20-30%
- Prognosis
- Variable
Prognostic Factors
Reduction under 6 hours. Pipkin I with small fragment. Anatomic reduction achieved. Young patient. No associated fractures.
Delayed reduction over 12 hours. Pipkin III pattern. Non-anatomic reduction. Multiple reduction attempts. Associated neck fracture.
Long-Term Results
- Develops in 20-50% at 10 years
- Related to articular incongruity
- Cartilage damage at time of injury
- May progress despite good initial result
- Most patients return to daily activities
- High-impact activities often limited
- Athletes may have difficulty returning to sport
- Occupational modifications may be needed
Guidelines, Registries & Global Practice
Global Epidemiology
Femoral head fractures are rare injuries that occur almost exclusively after high-energy posterior hip dislocation, most often from motor vehicle dashboard injuries or falls from height. According to PubMed, the contemporary EFORT narrative review (Menger et al., 2021) confirms they remain uncommon and are still classified worldwide using the 1957 Pipkin system, with osteonecrosis, post-traumatic arthritis and heterotopic ossification as the principal drivers of poorer long-term outcome.
Side-by-Side Guidance and Evidence
- Core Position
- Emergent closed reduction of the dislocation, then CT, then ORIF of weight-bearing fragments; anterior approach favoured after posterior dislocation
- Evidence Basis
- Expert consensus on level III-IV cohorts
- Core Position
- Reduce dislocation as an emergency, document neurovascular status, post-reduction CT mandatory, definitive fixation in a unit with pelvic-acetabular expertise
- Evidence Basis
- Standards for trauma (consensus)
- Core Position
- Classification-led: excise small non-weight-bearing fragments, fix supra-foveal fragments with countersunk headless screws
- Evidence Basis
- Technique consensus
- Core Position
- Approach individualised to fragment location, displacement and loose bodies; no single approach proven superior for osteonecrosis
- Evidence Basis
- Narrative review (Menger 2021)
Registry and Pooled Evidence
Because femoral head fractures are rare, no national joint registry isolates them as a discrete cohort; registry data (AOANJRR in Australia, NJR in England and Wales, AJRR in the United States) inform only the salvage arthroplasty pathway for Pipkin III injuries and post-traumatic arthritis. The highest-level synthesis comes from pooled studies: a meta-analysis of Pipkin I-II fractures found the posterior approach reduced heterotopic ossification without affecting osteonecrosis (Wang et al., 2016), while a systematic review of surgical hip dislocation reported osteonecrosis in 12%, heterotopic ossification in 25% and osteoarthritis in 16% (Khalifa et al., 2021).
Practice Variation
- Approach: North American and many European units favour the anterior (Smith-Petersen) approach after posterior dislocation to protect the medial femoral circumflex artery; others prefer the Ganz surgical hip dislocation for full articular visualisation, accepting trochanteric osteotomy-related risk.
- Heterotopic ossification prophylaxis: more routinely used after anterior and extensile approaches; indometacin or single-dose radiotherapy regimens vary by region.
- Salvage in the elderly: primary total hip arthroplasty for Pipkin III in older patients is widely accepted internationally, reflecting the very high osteonecrosis risk of combined head-and-neck injuries.
- Standard trauma pathway: in major trauma centres internationally, femoral head fractures are managed with emergent reduction within 6 hours under general anaesthesia, universal post-reduction CT, and protocolised rehabilitation according to fracture pattern and fixation.
Viva Scenarios
Viva Scenarios
Clinical Decision Scenarios
Practise clinical reasoning and management decisions out loud
“A 32-year-old male involved in a high-speed MVA presents with his right leg shortened, flexed, and internally rotated. AP pelvis shows posterior hip dislocation. What is your management?”
“After reduction of a posterior hip dislocation, CT shows a femoral head fracture with a fragment involving 35% of the head.”
“A CT after reduction of a posterior hip dislocation shows a Pipkin II fracture - the fragment involves 30% of the femoral head above the fovea. No associated neck or acetabular fracture.”
MCQ Practice Points
Q: What is the key anatomical landmark in the Pipkin classification?
A: The fovea capitis. Type I = below fovea (non-weight-bearing), Type II = above fovea (weight-bearing). The fovea determines whether fixation is mandatory.
Q: What is the target time for reduction of a traumatic hip dislocation?
A: Under 6 hours. AVN risk is 10-15% if reduced within 6 hours, rising to over 50% if delayed beyond 12 hours.
Q: Which surgical approach is preferred for ORIF of a femoral head fracture after posterior hip dislocation?
A: Anterior (Smith-Petersen) approach. This protects the already-compromised posterior blood supply (MFCA) from further damage.
Q: What is the primary blood supply to the femoral head?
A: Medial femoral circumflex artery (MFCA) provides 80% of blood supply via retinacular vessels. It courses posteriorly and is at risk with posterior dislocation.
Q: How should a Pipkin III fracture be managed in an elderly patient?
A: Total hip arthroplasty. The combination of femoral head and neck fracture has very high AVN rates (40-60%). In elderly patients, arthroplasty provides better functional outcomes.
At a Glance
Femoral head fractures (Pipkin classification) occur with posterior hip dislocations and are orthopedic emergencies. URGENT reduction within 6 hours is critical - AVN risk increases exponentially with delay. Pipkin I (fragment inferior to fovea) can often be excised. Pipkin II (fragment involves weightbearing dome) requires ORIF. Pipkin III (with femoral neck fracture) often needs arthroplasty due to high AVN risk. Pipkin IV (with acetabular fracture) requires addressing both injuries. Post-reduction CT scan is ESSENTIAL to assess fragment size and location. Time to reduction is the most important prognostic factor.
- Fragment Location
- Below fovea (non-weight-bearing)
- Management
- Excise fragment, remove loose bodies
- Fragment Location
- Below fovea but over 20% surface
- Management
- Consider ORIF with countersunk screws
- Fragment Location
- Above fovea (weight-bearing)
- Management
- ORIF REQUIRED - countersunk screws
- Fragment Location
- Any + femoral neck fracture
- Management
- Fix neck urgently + address head
- Fragment Location
- Any + femoral neck fracture
- Management
- Total hip arthroplasty
- Fragment Location
- Any + acetabular fracture
- Management
- Fix acetabulum through posterior + anterior approach for head
- Fragment Location
- Interposed fragment
- Management
- Emergent open reduction
- Fragment Location
- Any type
- Management
- Still reduce urgently, accept higher AVN risk
PIPKINPIPKIN for Classification
Hook:PIPKIN: I below, II above - just remember 'I is Inferior, II is Superior to fovea'!
FOVEAFOVEA for Management
Hook:The FOVEA is your landmark - above it means weight-bearing!
TIMEAVN Risk Factors
Hook:TIME is the enemy of the femoral head blood supply!
SIXSIX for Reduction Time
Hook:SIX hours - reduce by six or pay the price!
Exam Cheat Sheet
Exam Day Cheat Sheet
Critical Timing
- Reduce dislocation within 6 HOURS
- AVN rate 10-15% if under 6 hours
- AVN rate over 50% if over 12 hours
- Do NOT delay for elaborate imaging
Pipkin Classification
- Type I: Below fovea (non-weight-bearing)
- Type II: Above fovea (weight-bearing)
- Type III: I or II + femoral neck fracture
- Type IV: I or II + acetabular fracture
Management by Type
- Type I small: excise fragment
- Type I large (over 20%): consider ORIF
- Type II: ORIF with countersunk screws
- Type III elderly: THA
Surgical Approach
- Posterior dislocation: use ANTERIOR approach
- Protects remaining MFCA blood supply
- Smith-Petersen interval
- Pipkin IV: combined approaches
Post-Reduction CT
- MANDATORY for all hip dislocations
- Assess fragment size and location
- Identify loose bodies
- Plan surgical approach
Complications
- AVN: 10-60% depending on type
- Post-traumatic arthritis: 20-50%
- Sciatic nerve injury: 10-20%
- Heterotopic ossification: prophylaxis indicated
Quick Reference: Key Numbers
- Value
- Under 6 hours
- Value
- 10-15%
- Value
- Over 50%
- Value
- 10-20%
- Value
- 40-60%
- Value
- Over 20%
- Value
- 6-8 weeks
- Value
- 1-2 years
Pipkin Summary Table
- Fragment
- Below fovea
- Associated Fracture
- None
- Treatment
- Excise (small) or ORIF (large)
- Fragment
- Above fovea
- Associated Fracture
- None
- Treatment
- ORIF
- Fragment
- Any
- Associated Fracture
- Femoral neck
- Treatment
- Arthroplasty (elderly) or fix
- Fragment
- Any
- Associated Fracture
- Acetabulum
- Treatment
- Combined approach
Evidence Base
Time to Reduction and Osteonecrosis (Landmark)
- In 100 adult posterior hip dislocations, avascular necrosis occurred in 4.8% of hips reduced within 6 hours versus 52.9% of hips reduced after 6 hours
- Higher-grade (Stewart-Milford grade III-IV) dislocations had a significantly higher osteonecrosis rate; skeletal traction and non-weight-bearing showed no protective benefit
Long-Term Outcome of Posterior Hip Dislocation
- In 33 patients followed a mean of 49 months, the Pipkin scheme was a useful predictor of outcome: Pipkin 1-2 injuries did significantly better than Pipkin 3-4 (p less than 0.02)
- Overall 67% good, 18% fair and 15% poor results, with outcome dependent on anatomic reduction, restoration of stability and removal of all interposed fragments
Surgical Approach and Osteonecrosis Risk
- The Kocher-Langenbeck posterior approach was associated with a 3.2-fold higher incidence of avascular necrosis compared with the Smith-Petersen anterior approach
- 3 mm cannulated screws with threaded washers gave poor functional outcomes and are contraindicated for femoral head fixation
Anterior vs Posterior Approach (Meta-Analysis)
- Pooled analysis of five case-control studies of Pipkin I-II fractures found the posterior approach significantly reduced heterotopic ossification compared with the anterior approach
- No significant differences were found between approaches for functional outcome, osteonecrosis or post-traumatic arthritis
Surgical Hip Dislocation (Ganz) Outcomes
- Across nine studies (129 fractures), surgical hip dislocation achieved satisfactory clinical outcome in 85% and anatomical reduction in 74% at a mean 38.4 months
- Avascular necrosis occurred in 12%, heterotopic ossification in 25% and osteoarthritis in 16%; trochanteric osteotomy nonunion (3.4%) is a unique risk of this approach
Contemporary Narrative Review
- Femoral head fractures are rare, typically follow posterior hip dislocation and are classified with the 1957 Pipkin system, which remains the most widely used scheme
- Emergency closed reduction followed by approach selection guided by fracture location, displacement, joint congruity and loose fragments is the current standard; osteonecrosis, post-traumatic arthritis and heterotopic ossification drive poorer outcomes