Hip Dislocation, Femoral Head, and Acetabular Fractures

Introduction

The hip is the deepest and most constrained ball-and-socket joint in the human body, with stability derived from the bony congruity of the femoral head within the acetabulum, the strong fibrous capsule, the labrum, and the surrounding musculature. The forces required to dislocate the hip are substantial — typically motor vehicle deceleration or high-energy fall — and hip dislocation is therefore a marker of significant trauma with associated injury patterns. The forces involved frequently fracture either the femoral head (the Pipkin patterns) or the acetabulum (the Letournel patterns), producing a spectrum of injuries ranging from simple posterior dislocation reducible at the bedside to complex acetabular fractures requiring extensile exposure and operative reconstruction. The functional consequences of these injuries are dominated by the risk of avascular necrosis of the femoral head (related to dislocation duration), post-traumatic arthritis (related to articular congruity), and sciatic nerve injury (a recognized complication of posterior dislocation). This chapter, drawing principally on Rockwood and Green’s Fractures in Adults, AO Principles of Fracture Management, Apley & Solomon’s, and Miller’s Review of Orthopaedics, addresses the management of hip dislocation and the associated femoral head and acetabular fractures.

Surgical Anatomy

The acetabulum is formed by the fusion of three bones — ilium, ischium, and pubis — that come together at the triradiate cartilage (which fuses by age 14 to 16 years). The articular surface forms a horseshoe-shaped lunate surface with an inferior gap (the acetabular notch) covered by the transverse acetabular ligament. The acetabulum is supported by two columns of bone as described by Robert Judet and Émile Letournel in the 1960s — the anterior column (pubic and iliac components, extending from the iliac crest through the pelvic brim to the symphysis) and the posterior column (ischial and iliac components, extending from the greater sciatic notch through the ischium to the lesser sciatic notch). These two columns converge at the acetabular roof (the superior dome that bears the weight-bearing load). The columns are connected by the transverse anatomic strut of bone formed by the quadrilateral surface (the medial wall of the acetabulum). The femoral head is approximately spherical, covered with articular cartilage except for the fovea capitis (the central pit for the ligamentum teres). The blood supply to the femoral head is principally through the medial femoral circumflex artery (its deep branch ascending posteriorly along the femoral neck — the “retinacular vessels”), with smaller contributions from the lateral femoral circumflex and the ligamentum teres vessels (the latter important particularly in children). The retinacular vessels are vulnerable to disruption with hip dislocation and femoral neck fracture, producing the high rates of avascular necrosis associated with these injuries.

The sciatic nerve descends behind the acetabulum and posterior femur, exiting the pelvis through the greater sciatic foramen and passing beneath the piriformis. The nerve lies in close proximity to the posterior column and posterior wall of the acetabulum, making it vulnerable to traction or compression injury in posterior hip dislocations and during operative exposure of the posterior column. The obturator nerve and vessels pass through the obturator foramen and are vulnerable in fractures involving the quadrilateral surface and the medial wall. The femoral nerve and vessels descend anterior to the pelvic brim and are vulnerable in anterior column fractures and during the ilioinguinal approach to the acetabulum.

Hip Dislocation — Classification and Mechanism

The Thompson and Epstein classification (1951) of posterior hip dislocations divides them by associated fracture: Type I: Simple dislocation without significant associated fracture. Type II: Dislocation with a single large posterior wall fragment. Type III: Dislocation with comminuted posterior wall fracture. Type IV: Dislocation with fracture of the acetabular floor. Type V: Dislocation with fracture of the femoral head. The mechanism of posterior hip dislocation is most commonly the dashboard injury — flexed, adducted hip struck by anteriorly directed force on the femur during a motor vehicle accident — producing posterior translation of the femoral head out of the acetabulum, typically with associated posterior wall fracture. The mechanism of anterior dislocation is forced external rotation and abduction, with the hip dislocated anteroinferiorly (obturator type) or anterosuperiorly (pubic type). The clinical presentation of posterior dislocation is the lower extremity held in flexion, internal rotation, and adduction with apparent shortening. Anterior dislocation presents with the limb in abduction and external rotation, also with apparent shortening. Inferior dislocation (luxatio erecta of the hip) is rare and presents with the limb in marked flexion with the foot pointing toward the head. The sciatic nerve is injured in approximately 10 to 20 percent of posterior hip dislocations, typically a peroneal-division injury producing foot drop with preserved tibial function. Documentation of neurological status before reduction is mandatory.

Treatment of Hip Dislocation

The hip dislocation is an orthopedic emergency because of the time-dependent risk of avascular necrosis. The classical teaching is that reduction within 6 hours substantially reduces AVN risk, while delays beyond 12 hours predict high rates of AVN (up to 50 percent or more).

Closed reduction is attempted urgently in the emergency department with appropriate analgesia and muscle relaxation. The Allis maneuver is most commonly used: with the patient supine and an assistant stabilizing the pelvis, the surgeon stands on a stool over the bed and applies upward traction on the flexed knee while gently rotating the hip — bringing the femoral head over the posterior acetabular rim and into the joint. The Stimson technique with the patient prone and traction on the hanging leg is an alternative. The Bigelow and East Baltimore maneuvers describe other reduction methods. Post-reduction, the joint is reassessed clinically (range of motion testing) and radiographically. CT scan is mandatory after reduction in all hip dislocations to assess for: associated femoral head fracture, intra-articular loose bodies (which require operative removal), posterior wall fracture (with or without displacement), and concentric reduction (with attention to widening of the joint space suggesting interposed soft tissue). Indications for operative intervention after closed reduction include: irreducible dislocation, intra-articular loose bodies, displaced posterior wall fracture greater than 20 percent of the wall, persistent instability after reduction, and associated femoral head fracture with displaced fragments. Closed reduction failure is uncommon but requires urgent open reduction through a posterior (Kocher-Langenbeck) approach for posterior dislocations or an anterior approach for anterior dislocations. Post-reduction management for simple stable dislocations consists of brief immobilization (a few days for comfort) followed by progressive weight bearing. There is no convincing evidence that prolonged non-weight-bearing or hip precautions affect AVN risk, although many protocols still impose these restrictions in some form.

Femoral Head Fractures — The Pipkin Classification

Femoral head fractures, classically associated with posterior hip dislocation, are organized by the Pipkin classification (Garrett Pipkin, 1957): Type I: Femoral head fracture caudad (inferior) to the fovea. Type II: Femoral head fracture cephalad (superior) to the fovea, involving the weight- bearing surface. Type III: Femoral head fracture (type I or II) with associated femoral neck fracture. Type IV: Femoral head fracture with associated acetabular fracture. The clinical significance of the Pipkin types is the relationship to the weight-bearing surface — type I fractures, below the fovea, are typically extra-articular relative to weight-bearing and can often be excised; type II fractures involve the weight-bearing surface and require anatomical fixation; type III fractures combine the femoral head fracture with the femoral neck fracture, with substantial AVN risk; type IV fractures combine femoral head and acetabular fractures and require a coordinated reduction of both components.

Treatment of Femoral Head Fractures The treatment of Pipkin fractures is individualized: Pipkin I with a small inferior fragment: closed reduction of the dislocation typically reduces the fragment as well. Small displaced fragments below the weight-bearing surface can be excised; larger fragments are reduced and fixed with screws (headless compression screws to bury below the articular surface). Pipkin II: Anatomical reduction and fixation are essential. Approach options include the Smith-Petersen anterior approach (better visualization of the antero-superior weight- bearing surface, although the anterior capsulotomy and surgical hip dislocation may compromise the femoral head blood supply) and the Kocher-Langenbeck posterior approach with or without trochanteric flip osteotomy (Ganz approach) to allow safe surgical hip dislocation. Fixation is with headless compression screws. Pipkin III: Treatment depends on patient age. In younger patients, attempts at fixation of both the femoral head fracture and the femoral neck fracture are made, despite high AVN risk. In older patients, primary arthroplasty (total hip arthroplasty rather than hemiarthroplasty because of the acetabular injury) is increasingly favored. Pipkin IV: The femoral head fracture and the acetabular fracture must be addressed in a coordinated manner. The acetabular fracture is reduced and stabilized first; the femoral head fracture is then addressed, often through the same approach. The prognosis of femoral head fractures is dominated by the AVN risk, which approaches 20 to 50 percent in Pipkin II fractures with delayed reduction or extensive dissection.

Acetabular Fractures — The Letournel Classification

The Letournel classification (Robert Judet and Émile Letournel, 1964) of acetabular fractures organizes injuries into five elementary patterns and five associated patterns (combinations of elementary patterns). The understanding of column anatomy makes the system intuitive: the acetabulum has anterior and posterior columns plus the roof, and fractures involve various combinations. Elementary Patterns Posterior wall fracture: The most common elementary pattern (over 25 percent of acetabular fractures). The mechanism is typically the dashboard injury with the hip flexed. The injury involves the posterior wall of the acetabulum, often with associated posterior dislocation. Stability assessment depends on the percentage of the posterior wall involved (less than 20 percent typically stable, more than 40 percent unstable, intermediate range requiring stress examination). Posterior column fracture: Fracture of the posterior column from the greater sciatic notch through the obturator foramen into the ischium. Less common than posterior wall. Anterior wall fracture: Fracture of the anterior wall of the acetabulum. Uncommon.

Anterior column fracture: Fracture extending from the iliac crest through the anterior column. Subdivided by the level at which the fracture exits the anterior column (high, intermediate, low). Transverse fracture: A horizontal fracture line separating the iliac roof and ischial body components, crossing both columns. Subdivided by location of the fracture line (infratectal below the roof, juxtatectal at the roof, transtectal through the roof). Associated Patterns T-shaped fracture: A transverse fracture with an additional inferior vertical extension through the ischium and pubis — a transverse plus inferior split. Posterior column with posterior wall: Posterior column fracture combined with posterior wall fracture. Transverse with posterior wall: The most common associated pattern, combining a transverse fracture with posterior wall involvement. Anterior column with posterior hemitransverse: Anterior column fracture with a partial transverse component crossing the posterior column. Both-column fracture: The most complex pattern, with the entire acetabular component (both columns) dissociated from the iliac wing. The articular surface is no longer continuous with the intact ilium. The classical radiographic finding is the spur sign on the obturator oblique view.

Imaging and Surgical Planning for Acetabular Fractures

Acetabular fractures require comprehensive imaging: AP pelvis radiograph: Identifies the principal radiographic lines of the acetabulum and detects the major fracture pattern. Judet views: The obturator oblique (the affected hemipelvis rotated 45 degrees away from the X-ray beam) demonstrates the anterior column, the posterior wall, and the obturator foramen. The iliac oblique (the affected hemipelvis rotated 45 degrees toward the X-ray beam) demonstrates the posterior column, the anterior wall, and the iliac wing. CT scan with 3D reconstruction is now the standard for definitive characterization, surgical planning, and the identification of marginal impaction (depressed articular surface fragments that may require elevation and grafting during reduction). Surgical Approaches The choice of approach depends on the fracture pattern: The Kocher-Langenbeck (posterior) approach is used for posterior wall and posterior column fractures, transverse fractures, and posterior-dominant associated patterns.

The ilioinguinal approach (Letournel) through three windows (lateral over the iliac crest, middle between the external iliac vessels and the iliopsoas, medial between the spermatic cord/round ligament and the external iliac vessels) is used for anterior column fractures, anterior wall fractures, anterior column with posterior hemitransverse, and both-column fractures. The anterior intrapelvic (modified Stoppa) approach has gained popularity as an alternative or addition to the ilioinguinal, providing improved visualization of the quadrilateral surface and posterior column from anterior. The combined approaches (Kocher-Langenbeck plus ilioinguinal in sequence) are reserved for fractures requiring access to both columns. The extended iliofemoral approach (Letournel) provides comprehensive access to the entire acetabulum but is associated with substantial morbidity (heterotopic ossification, abductor weakness, infection) and is now rarely used. Surgical Reduction and Fixation The principles of acetabular fracture surgery are anatomical reduction of the articular surface and rigid fixation to permit early motion. Reduction is achieved with reduction clamps, ball-spike pushers, and bone hooks, with intraoperative fluoroscopy confirming column reduction. Fixation is typically with reconstruction plates contoured to the column anatomy plus interfragmentary screws. Specific to the posterior wall, buttress plate fixation along the posterior column with screws into the posterior column body is the standard. The Matta criteria for reduction quality assess residual displacement: anatomical (≤1 mm), imperfect (2 to 3 mm), and poor (>3 mm). Anatomical reduction correlates with good long-term outcomes; imperfect or poor reductions have substantially worse outcomes.

Outcomes and Complications

The functional outcomes of acetabular fracture surgery correlate with several factors: Quality of reduction: Anatomical reduction is the strongest predictor of good outcome. Letournel’s classic data demonstrated 80 percent good or excellent outcomes with anatomical reduction versus 30 percent with imperfect reduction. Patient age: Older patients have worse outcomes, particularly with severe fracture patterns. The 60-year-old patient with comminuted acetabular fracture has substantially worse outcomes than the 25-year-old with the same pattern. Fracture pattern: Posterior wall fractures with marginal impaction, both-column fractures with significant comminution, and patterns with associated femoral head injury all have poorer prognoses. Associated injuries: AVN of the femoral head, post-traumatic arthritis, sciatic nerve injury — all reduce functional outcomes.

The principal complications include post-traumatic arthritis (the most common long- term consequence, with rates of 10 to 30 percent at 10 to 20 years), avascular necrosis (3 to 9 percent), heterotopic ossification (10 to 90 percent depending on approach and prophylaxis — much higher with extended iliofemoral than Kocher-Langenbeck; prophylaxis with single-dose radiation or indomethacin can reduce incidence), sciatic nerve injury (10 to 30 percent in posterior approaches, often transient peroneal-division injury), infection (1 to 5 percent, higher with combined approaches), and vascular injury (rare but potentially catastrophic, particularly to the corona mortis — an anastomotic vessel between the obturator and external iliac systems crossing the superior pubic ramus, encountered in the ilioinguinal approach).

Special Considerations

Elderly Acetabular Fractures Acetabular fractures in the elderly population have substantially different characteristics from those in younger patients — typically lower energy mechanism, more commonly anterior column or anterior column with posterior hemitransverse patterns, often with dome impaction (the “Gull sign” of medial impaction of the acetabular dome into the pelvis). The management is challenging because of osteoporotic bone quality, frequent comorbidities, and the high failure rate of ORIF in this population. Increasing attention has been given to primary total hip arthroplasty (with cage or revision components to bridge the acetabular defect) as an alternative to ORIF in selected elderly patients. The choice depends on patient age, functional demands, fracture pattern, and bone quality.

Pediatric Acetabular Fractures Pediatric acetabular fractures are uncommon and have a substantially different appearance because of the open triradiate cartilage. Injuries to the triradiate cartilage (Salter-Harris- like injuries of the acetabulum) may produce growth arrest and progressive acetabular dysplasia, with long-term consequences for hip development. Management is generally conservative, with operative intervention reserved for displaced patterns. The orthopedic surgeon must consider the growth implications when planning any operative intervention near the triradiate cartilage. Postoperative Management Postoperative management includes VTE prophylaxis (high risk in this population — see Topic Trauma-7), early hip range of motion to prevent stiffness (typically beginning the day after surgery), protected weight bearing for 8 to 12 weeks (typically toe-touch or partial weight bearing depending on fixation stability), and heterotopic ossification prophylaxis in patients with extended approaches or high risk profiles.

Summary and Take-Home Points

The hip dislocation is an orthopedic emergency requiring urgent closed reduction to minimize avascular necrosis risk, with the Thompson-Epstein classification organizing the typical posterior dislocation patterns by associated fracture. Post-reduction CT is

mandatory to assess for intra-articular loose bodies, posterior wall fractures, and concentric reduction. Surgical intervention after closed reduction is indicated for displaced posterior wall fractures, intra-articular loose bodies, persistent instability, and associated femoral head fractures. The Pipkin classification of femoral head fractures organizes them by relationship to the fovea and by associated injuries. Pipkin I and II fractures require evaluation of weight- bearing involvement and may be excised or fixed depending on size and location; Pipkin III combines femoral head with neck fracture (high AVN risk); Pipkin IV combines femoral head with acetabular fracture (requires coordinated reduction). The Letournel classification of acetabular fractures organizes them by column anatomy into five elementary and five associated patterns. The radiographic assessment uses the AP pelvis plus Judet (obturator oblique and iliac oblique) views and CT with 3D reconstruction. The surgical approach (Kocher-Langenbeck posterior, ilioinguinal anterior, modified Stoppa, or combined) is chosen to match the fracture pattern. Anatomical reduction is the principal predictor of good long-term outcome, with the Matta criteria assessing reduction quality. The complications include post-traumatic arthritis, AVN, heterotopic ossification, sciatic nerve injury, and infection. Elderly acetabular fractures have increasingly been managed by primary total hip arthroplasty as an alternative to ORIF. The chapters that follow continue through the proximal femur — the femoral neck and pertrochanteric fractures that represent the principal fragility fracture burden in the elderly — and on through the rest of the lower extremity.