Mastering Open Reduction & Internal Fixation of the Posterior Acetabulum

Comprehensive Introduction and Patho-Epidemiology

Defining the Posterior Wall Fracture

A posterior wall fracture represents one of the five elementary fracture types initially described in the landmark classification system by Émile Letournel and Robert Judet. It is fundamentally defined as a disruption of the posterior rim of the socket portion of the hip's constrained ball-and-socket joint. This disruption separates a segment of the articular surface that involves varying amounts of the bony posterior wall of the acetabulum. The fracture can manifest as a single, large osteochondral fragment or present as a highly comminuted array of pieces, often complicated by marginal articular impaction.

Crucially, by strict Letournel definition, the posterior column—and therefore the radiographic ilioischial line—remains anatomically intact, despite the varying degrees of retroacetabular surface disruption. This distinguishes the isolated posterior wall fracture from the more complex associated fracture patterns, such as the posterior column with posterior wall fracture. The wall fracture can exist in isolation or as a component of an associated acetabular fracture (e.g., transverse plus posterior wall). Understanding this distinction is paramount for both accurate radiographic diagnosis and the formulation of an appropriate surgical strategy.

The natural history of these injuries, when left untreated or managed nonoperatively in the presence of instability, is uniformly poor. The primary goal of treating acetabular fractures is to achieve a stable, congruent hip joint with an anatomically reduced articular surface, thereby mitigating the incidence of post-traumatic osteoarthritis. Historically, Epstein documented that up to 88% of patients treated with closed reduction alone for unstable posterior fracture-dislocations experienced unsatisfactory long-term outcomes. Consequently, anatomic reduction and rigid internal fixation have become the gold standard for displaced or unstable posterior wall fractures.

Mechanism of Injury and Pathogenesis

Acetabular fractures occur when a high-energy force is transmitted from the femur, through the femoral head, directly into the acetabulum. The specific pattern of the resulting fracture is dictated by the precise position of the hip (degree of flexion, adduction, and rotation) at the exact moment of impact, combined with the magnitude and vector of the traumatic force. Because these are typically high-energy injuries, they are frequently seen in the context of polytrauma.

A classic and highly common mechanism of injury for posterior wall fractures and associated fracture-dislocations is a motor vehicle collision. In this scenario, an unrestrained occupant is seated with a flexed knee; upon collision, the knee strikes the dashboard. This creates a massive axial load directed along the anatomical axis of the femur, violently driving the femoral head into the posterior aspect of the acetabulum. When the hip is flexed to approximately 90 degrees and is in a neutral coronal and axial plane orientation, the posterior articular surface of the joint bears the brunt of this stress, resulting in the classic posterior wall fracture.

Variations in hip positioning alter the fracture morphology. With less hip flexion (hip closer to extension) and a force applied along the femoral shaft, a superior posterior wall variant typically results, which may include a portion of the adjacent acetabular roof. Conversely, a posterior inferior fracture pattern involves the inferior horn of the articular surface, the subcotyloid groove, and frequently extends into the superior ischium. The amount of comminution, displacement, and articular impaction is directly proportional to the quality of the host bone and the magnitude of the applied force.

Fracture-Dislocations and Marginal Impaction

A critical variation of the posterior wall fracture is the fracture-dislocation, wherein single or multifragmented pieces of the posterior wall are sheared off and separated by the forcibly dislocating femoral head. This specific pattern is highly associated with osteochondral impaction of the articular surface of either the femoral head or, more commonly, the remaining intact margin of the acetabular wall. This "marginal impaction" represents a zone of articular cartilage and subchondral bone that has been crushed and rotated into the underlying cancellous bone bed.

In the setting of a posterior wall fracture or fracture-dislocation, the joint capsule faces one of two fates. It may rupture entirely, allowing the femoral head to dislocate through the defect, often resulting in varying sizes of free wall fragments and severe labral tearing. Alternatively, the capsule may remain intact, tethered to the wall fragment and the femur, with all displacement occurring directly through the fracture site. When the capsule ruptures and the head dislocates, the fracture edges frequently fragment, creating loose osteochondral bodies that can lead to devastating incarceration or abrasion upon reduction of the femoral head if not meticulously cleared.

Detailed Surgical Anatomy and Biomechanics

Osteology of the Acetabulum

The acetabulum is a complex, hemispherical cavity situated on the lateral aspect of the pelvis, formed by the confluence of the ilium, ischium, and pubis. Architecturally, it is conceptualized as being composed of two columns, two walls, and a roof. The anterior and posterior columns form an inverted "Y" structure and are robustly attached to the sacrum via the thick trabecular bone of the sacral buttress. The articular surface of the joint, which is lunate in shape, sits upon the anterior and posterior walls and the superior roof, located within the arms of this inverted Y.

The anatomic roof is precisely located between the anterior inferior iliac spine and the ilioischial notch of the acetabular margin. From a functional standpoint, the weight-bearing dome is the most critical articular portion of the acetabulum. This is determined clinically by 45-degree roof arc measurements on anteroposterior (AP) and Judet radiographs. This functional dome must accommodate the excursions of all resultant force vectors during normal daily activities to prevent rapid joint degeneration.

Two additional anatomic segments of the posterior acetabulum warrant specific consideration during surgical reconstruction. The posterosuperior segment acts as the structural bridge between the weight-bearing roof and the posterior wall. The posteroinferior segment comprises the lower part of the posterior wall and the posterior horn of the articular cartilage. Disruption in either of these zones significantly alters the biomechanical stability of the hip joint and necessitates specific plate contouring techniques to achieve rigid neutralization.

Capsuloligamentous Structures and the Labrum

The hip is a highly constrained ball-and-socket joint, heavily reliant on its robust soft tissue envelope for dynamic and static stability. The capsule surrounding the joint extends from the bony acetabular rim to the intertrochanteric line anteriorly and to the femoral neck posteriorly. This capsule is not uniform; it is dramatically thickened in specific areas to create distinct, powerful ligaments that resist dislocation.

Anteriorly, the iliofemoral ligament (the Y ligament of Bigelow) exists as two stout bands and is the strongest ligament in the human body, resisting hyperextension. The inferior capsule is supported by the pubofemoral ligament, which limits abduction. Posteriorly, the capsule is strengthened by the ischiofemoral ligament, which spirals from the ischial rim to the superior neck, tightening during internal rotation and extension. Preservation or meticulous repair of the posterior capsule during surgical approaches is vital for restoring postoperative stability.

The acetabular labrum is a circumferential fibrocartilaginous structure attached to the bony rim. It serves to deepen the socket, creating a suction seal that enhances synovial fluid lubrication and makes the joint inherently more stable. Biomechanically, the labrum adds an additional 10% of coverage to the femoral head. In posterior wall fractures, the labrum is frequently torn or remains attached to the displaced bony fragment. Repairing the labrum or retaining its attachment to the fracture fragment is critical for restoring the fluid mechanics and stability of the hip.

Vascular Anatomy and Perfusion

Due to the massive area of muscular attachments, the blood supply to the acetabulum and surrounding pelvis is vast and complex. Small arteries generally start peripherally and flow centrally, parallel to each other. Understanding this vascularity is essential to avoid catastrophic intraoperative hemorrhage and to preserve the perfusion of fracture fragments to ensure union.

A complete vascular circle supplies multiple nutrient vessels around the periphery of the acetabulum. The artery of the roof of the acetabulum (a branch from the superior gluteal artery), the obturator artery, and the inferior gluteal artery are the main contributors. The superior gluteal artery is particularly vulnerable as it exits the greater sciatic notch; laceration here can result in exsanguinating hemorrhage that retracts into the pelvis, requiring emergent angiographic embolization or a separate ilioinguinal approach for control.

Specific nutrient foramina dictate the internal osseous perfusion. The largest nutrient foramen on the internal aspect of the ilium is reliably located 1 cm lateral to the sacroiliac joint and 1 cm above the iliopectineal line, fed by a branch of the iliolumbar artery. Externally, a branch of the superior gluteal artery feeds the largest nutrient foramen in the center of the iliac wing. The obturator artery supplies foramina in front of the sciatic notch, just below the iliopectineal line, and provides the crucial acetabular branch that feeds the cotyloid fossa via small perforators.

Exhaustive Indications and Contraindications

Determining Hip Stability

The primary indication for operative intervention in posterior wall fractures is hip instability. While roof arc and subchondral arc measurements are highly useful for transverse or column fractures, they do not accurately apply to typical isolated posterior wall fractures. Instead, the size of the posterior wall fragment plays a dominant role in predicting whether the femoral head will remain concentrically reduced under physiologic loads.

Multiple authors have attempted to define the critical size of the fragment that reliably predicts instability. In classic cadaveric biomechanical studies, fragments that included greater than 50% of the posterior wall were universally unstable, while those comprising less than 20% were consistently stable. However, clinical studies have refined these parameters, revealing that acetabuli with less than 34% of the posterior wall intact are generally unstable, whereas those with greater than 55% intact are stable.

Despite attempts to strictly quantitate fragment size using 3D CT to define operative indications, dynamic stress examination under anesthesia remains the most definitive method to predict instability. Fluoroscopy-assisted dynamic stress testing, typically performed after closed reduction, allows the surgeon to detect subtle subluxation and define a stable or unstable joint without relying solely on static fragment size measurements.

Surgical Indications and Contraindications Table

Patient Evaluation and Associated Injuries

Acetabular fractures are typically the result of high-energy trauma; therefore, a rigorous trauma evaluation (ATLS protocol) is mandatory to identify associated life-threatening injuries. While severe hemorrhage and hemodynamic instability are rarely associated with isolated fractures of the posterior wall, the superior gluteal artery and vein may be lacerated when fractures extend superiorly into the greater sciatic notch.

Patients frequently present with severe hip or groin pain and a classic shortened, internally rotated, and adducted lower extremity due to the posterior, superior dislocation of the femoral head. Soft tissue injuries around the pelvis must be carefully evaluated. The skin overlying the hip and pelvis should be inspected for subcutaneous fluctuance, ecchymosis, or cutaneous anesthesia, which are hallmarks of a Morel-Lavallée lesion. Initial debridement of these closed degloving lesions, along with a delay in internal fixation, is strongly recommended to prevent deep infection.

A meticulous neurologic examination at the time of injury is absolutely critical, as deficits are seen in up to 30% of cases. The peroneal division of the sciatic nerve is the most commonly injured neural structure, particularly when the femoral head is dislocated posteriorly, stretching the nerve over the displaced bony fragments. Documenting this deficit prior to any reduction maneuver or surgical intervention is medicolegally and clinically essential.

Pre-Operative Planning, Templating, and Patient Positioning

Advanced Imaging Protocols

The diagnosis and precise classification of an acetabular fracture begin with the initial trauma AP radiograph of the pelvis. However, two 45-degree oblique radiographs—the Judet views (iliac oblique and obturator oblique)—must be obtained to fully delineate the fracture pattern and aid in treatment planning. Completing the five-view pelvis series with pelvic inlet and outlet views allows for the evaluation of any occult injuries to the pelvic ring.

A high-resolution CT scan of the pelvis is the cornerstone of modern preoperative planning. It is invaluable for defining the exact degree of displacement, identifying intra-articular fragments, and characterizing marginal articular impaction. The CT scan is optimally obtained after the initial closed reduction of the hip dislocation to accurately assess joint congruity and the true size of the posterior wall defect.

Furthermore, 3D CT reconstructions allow the surgeon to precisely determine the size and number of incarcerated fragments that must be removed from the joint. Preoperative templating software can be utilized to map the location of impaction that must be elevated and to select the appropriate length and contour of reconstruction plates. Anticipating the need for structural bone graft (often harvested from the greater trochanter or iliac crest) to support elevated marginal impaction is a critical step in the planning phase.

Patient Positioning and Operating Room Setup

The choice of patient positioning is dictated by the surgical approach, which for isolated posterior wall fractures is almost exclusively the Kocher-Langenbeck approach. Patients can be positioned either in the prone position or the lateral decubitus position, depending on surgeon preference and the presence of associated injuries.

The prone position is heavily favored by many experienced pelvic surgeons as it allows the weight of the leg to naturally distract the hip joint when the knee is flexed to 90 degrees, relaxing the sciatic nerve and providing excellent visualization of the posterior column. A specialized traction table or a radiolucent flat Jackson table with a supracondylar femoral traction pin can be utilized to facilitate intraoperative joint distraction.

Alternatively, the lateral decubitus position is preferred by surgeons who are more accustomed to this setup from primary total hip arthroplasty. It allows for easier airway management by anesthesia and facilitates conversion to a surgical hip dislocation (Ganz approach) if extensive intra-articular work or femoral head fixation is required. Regardless of the position, the entire hemipelvis and lower extremity must be prepped and draped free to allow for dynamic manipulation of the hip during reduction and fluoroscopic imaging.

Fluoroscopic Integration

Intraoperative fluoroscopy is indispensable. The C-arm must be positioned to easily obtain AP, iliac oblique, and obturator oblique views without compromising the sterile field. The surgeon must verify that the C-arm can swing freely under the table to achieve these views before the incision is made. Preoperative verification of the fluoroscopic angles ensures that the surgeon can accurately assess the reduction of the posterior wall, the elevation of the marginal impaction, and the trajectory of the hardware to prevent intra-articular screw penetration.

Step-by-Step Surgical Approach and Fixation Technique

The Kocher-L

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