Yash Chaudhry DO¹; Nicholas Abate DO¹; Jackson Harvi BS¹; Shrijal Desai MS¹; Mitesh Pyush Shah MD^2
1Philadelphia College of Osteopathic Medicine
²Mainline Health Orthopaedics & Spine

Keywords: Osteochondritis dissecans, OCD, throwing athlete, gymnast, elbow

Introduction
Posterior wall fractures account for up to 30% of all acetabular fractures and are the most common subtype [1, 2]. Often associated with a concomitant hip dislocation, they are frequently the result of high energy mechanisms such as motor vehicle accidents. An axial load applied through the femur, as often seen in dashboard injuries, can lead to impaction of the femoral head on the posterior surface of the acetabulum [1]. Indications for surgical management rely on the stability of the hip joint, which can be determined intraoperatively using a dynamic fluoroscopic examination under anesthesia. For those treated with open reduction and internal fixation, an accurate and congruent reduction is crucial to a successful outcome [3].

Anatomy
The acetabulum is a complex bony structure that houses the femoral head and allows force transmission from the lower extremity to the axial skeleton. It consists of six components: the anterior and posterior columns, the anterior and posterior walls, the medial wall, and the acetabular dome. The anterior column extends from the posterosuperior ilium to the pubic tubercle, while the posterior wall extends from the greater sciatic notch to the ischial tuberosity [4]. These two structures form an inverted Y that provides support to the anterior and posterior walls, respectively, and connects the acetabulum to the rest of the pelvis [5]. The posterior wall is larger than the anterior wall, projecting more laterally and further from the support of the columns. It is the most commonly fractured structure within the acetabulum [4].

The Judet and Letournel classification is the most widely accepted classification system for acetabular fractures. This system divides the fractures into five elementary and five associated patterns [5]. The elementary patterns include posterior wall, posterior column, anterior wall, anterior column, and transverse. The associated patterns include associated both column, transverse with posterior wall, T-type, anterior column or wall with posterior hemitransverse, and posterior column with posterior wall [5].

Presentation
Posterior wall fractures are frequently associated with high-energy mechanisms such as motor vehicle accidents or falls from significant heights [1]. Commonly, an axial load applied along the length of the femur leads to impaction of the femoral head on the posterior aspect of the acetabulum. This is particularly common in dashboard injuries, where the hip and knee are flexed [2]. Flexion, adduction, and internal rotation lead to dislocation of the femoral head, which can fracture off a piece of the posterior wall with it as it dislocates [2].

Patients will present frequently with the affected lower extremity shortened and internally rotated. A thorough neurovascular exam is crucial as the sciatic nerve can be in very close proximity to the zone of injury and may also be injured during surgical management as well [2]. If the hip is dislocated, it should be reduced emergently under sedation in the trauma bay or emergency room. Skeletal traction may be required to maintain the reduction of the hip or to reduce pressure on the articular surface from incarcerated fragments [3].

Radiology
Diagnosis of posterior wall acetabular fractures should be made clinically and with various imaging modalities. The plane of the ilium is approximately 90° to the plane of the obturator foramen, and both structures are oriented approximately 45° to the frontal plane [6]. On this basis, Judet et. al. proposed that the anterior-posterior (AP) view and two 45° oblique views of the pelvis can be used to study the radiographic anatomy of the acetabulum [7]. Therefore, standard preoperative radiographic examinations should include the AP and two 45° oblique Judet views of the injured hip. Routine preoperative computed tomography (CT) scans should be performed to facilitate detailed fracture pattern evaluation, detection of intra-articular fragments, assess for marginal impaction (in which the articular fragment and subchondral bone are impacted into the underlying cancellous bone, disrupting the smooth chondral surface), begin estimation of stability, and to help inform surgical planning [8].

On the AP view, the rim of the posterior wall approximates a straight line and is more vertical than the anterior wall [6]. The course of the posterior wall is most easily identified by following the lateral most aspect of the ischium cranially. Any break or deficit in this line indicates fracture or displacement of the posterior rim of the acetabulum [6]. The obturator oblique view is especially helpful in diagnosing a posterior wall fracture because it places the posterior wall almost perpendicular to the x-ray beam and minimizes overlay of the anterior wall. A CT scan provides additional information specific to posterior wall fractures that is not readily apparent on plain radiographs [1]. Besides accurately characterizing the size of the posterior wall fragment, the CT scan should be evaluated for marginal impaction and the size and number of any intraarticular fragments [1].

Moed et al. performed a retrospective study to evaluate the role of CT in predicting hip stability in posterior wall fractures of the acetabulum [9]. They analyzed three methods of calculating posterior wall fracture fragment size on CT and compared it to findings on dynamic fluoroscopic exam under anesthesia (EUA). They found that the method of measuring fragment size at the level of the largest posterior wall deficit was more accurate than the Calkins method (which measures the smallest amount of intact acetabular arc) and the Keith method (which measures fragment size at the level of the fovea) [9]. However, given the low risk of EUA and the inherent problems in measuring CT cuts, they concluded that it is safest to assume the fracture is unstable unless proven stable by dynamic fluoroscopic stress testing under general anesthesia [9]. New measurement techniques of CT imaging have been reported with high sensitivity and specificity rates for diagnosing fracture patterns associated with hip instability [10], but currently EUA remains the gold standard method for the determination of hip stability status after posterior wall fractures of the acetabulum [1, 9, 11].

The EUA is performed with the patient lying supine on a radiolucent operating room table under general anesthesia [12]. The hip is brought to neutral rotation in an extended position. A direct AP fluoroscopic image of the hip joint is obtained. The medial joint space at this point is documented. The hip is then flexed to 90 degrees and an axial load is applied through the femur. Fluoroscopic images are taken following the flexion and loading of the hip and the medial joint space is assessed and compared to its baseline. Any widening of this medial joint space would suggest instability of the hip [12]. The hip is brought through the same flexion and loading again at 20 degrees of internal rotation and 20 degrees of adduction, and fluoroscopic images are again obtained. This whole process is then repeated to obtain fluoroscopic obturator oblique images of the hip. If at any point during the exam, the presence of either subluxation or dislocation of the femoral head is appreciated, then the exam is positive for hip instability [12].

Treatment
Dislocated hips should be emergently reduced with or without skeletal traction as needed. Historically, fractures involving less than 20% of the posterior wall were considered small and treated nonoperatively, while those greater than 50% of the posterior wall were considered large and treated with open reduction and internal fixation [2]. However, recent evidence has suggested that even those consisting of less than 20% of the posterior wall may benefit from a dynamic fluoroscopic EUA [11]. 

Nonsurgical Management
Posterior wall fractures found to be stable using the above-described methods can be treated nonoperatively with a period of toe-touch or touch-down weight bearing for approximately 6 to 8 weeks [1]. It is critical during this period to obtain frequent radiographic follow up to ensure that the congruency of the joint is not lost. Following this initial period, weight bearing status is progressed over the next 6 to 8 weeks [12].

Surgical Management
Fracture patterns with hip instability as well as those with articular incongruity are indicated for surgical management [3]. This incongruity can be due to either impaction of the articular surface or loose fragments in the joint space. Unstable hips may require skeletal traction to maintain reduction, as well as reduce pressure on the articular surface from incarcerated fragments in the joint space. Historically, fixation was performed after a delayed period due to concerns over intraoperative bleeding [3, 13]. However, recent evidence has led to a shift in management towards earlier fixation [1, 2, 13]. Certain situations such as an irreducible or locked hip dislocation, concomitant hip dislocation and ipsilateral femoral neck fracture, open fracture, or dislocated hip that cannot be maintained in a reduced position even with the assistance of traction require emergent surgical intervention [3].

The most common surgical approach for open reduction and internal fixation of a posterior wall fracture is the Kocher-Langenbeck approach [1]. While the modified Gibson and Ganz trochanteric flip osteotomy offer alternatives for certain patterns, the Kocher-Langenbeck, which can be performed in either lateral or prone position, is the workhorse approach [14]. In the lateral position, skeletal traction can be used throughout the case to distract the femoral head, and soft tissue will fall with gravity away from the surgical field [15, 16]. The prone position offers increased access to the quadrilateral surface [15, 16]. Regardless of position, it is critical during the case to keep the hip extended and the knee flexed to reduce tension on the sciatic nerve [3].

The incision is placed over the greater trochanter, with one limb extending approximately 6 cm directed towards the posterior superior iliac spine (PSIS) and the other extending straight down the longitudinal axis of the femur approximately 10 to 15 cm [15]. After incising through the subcutaneous fat and the iliotibial band, the raphe of the gluteus maximus is identified and split up towards the proximal extent of the incision. If needed, part of the gluteus maximus insertion onto the femur can also be released. The piriformis and conjoined short external rotator tendons are tagged and released approximately 1.5 cm away from their insertion onto the greater trochanter as opposed to directly off of bone in order to protect the medial femoral circumflex artery running underneath, which is the vascular supply to the femoral head [17]. The piriformis will lead medially to the greater sciatic notch, the conjoined tendon to the lesser sciatic notch, and the quadratus to the ischial tuberosity. These landmarks can be useful during dissection where there has been significant soft tissue injury and hematoma. These tagged tendons can then be posteriorly retracted over the sciatic nerve to aid in protecting it during the remainder of the case [15]. In the typical anatomic relationship, the sciatic nerve is deep to the piriformis muscle and superficial to the conjoined tendon, however, this can be altered in approximately 10% of patient’s anatomy, and therefore, caution should be used during dissection until the sciatic nerve has been safely identified [18].

When approaching the posterior aspect of the hip joint, the trauma from the fracture can lead to deformation of normal anatomy. Any devitalized musculature requires debridement. The gluteus minimus, which often demonstrates the brunt of the trauma from the injury, is elevated off of the posterior wall and superior aspect of the acetabulum to visualize the fracture fragments [3]. The fracture should be debrided of hematoma so that reduction can be obtained. It is vital that this debridement does not devitalize or strip posterior capsular attachments off of any chondral fragments [3]. If traction is required to observe the joint surface or extract any incarcerated fracture fragments, this can be applied through traction from a fracture table or by manually distracting the hip joint by pulling on a Schanz pin placed in the proximal femur [2, 16]. If the articular surface demonstrates an impacted joint surface, the intact femoral head can be used as a template to recreate the acetabular surface [3]. The impacted fragments can then be reduced onto the head, and the bony defect left behind can be backfilled with bone graft. The posterior wall fragments can then be fixed in place using lag screws or, if the fragments are too small, spring plates. Finally, an overlying buttress plate is used to span the fracture from the ilium to the ischium [14, 19]. Comprehensive fluoroscopic evaluation must be used to ensure that any screws used are not excessively long. Weight bearing after surgery is typically limited to toe-touch weight bearing for a period of 6 to 8 weeks [1, 2], followed by a period of progressive weight bearing over several weeks. In a systematic review of 12 retrospective and prospective case series, Heare et. al. demonstrated no difference in complication rates or functional outcome scores between early (less than 12 weeks prior to full unrestricted weight bearing) and late weight bearing after surgically treated posterior wall fractures [20].

Outcomes and Complications
Nerve traction and injury is one of the most common early complications following surgical fixation of posterior wall injuries as approximately 20% of patients with posterior wall fractures sustain some form of neurologic injury [2]. The sciatic nerve can often be subjected to traction injury, thus maintaining the position of hip extension and knee flexion is vital during surgery [3]. Additionally, the formation of postoperative hematoma can lead to compression of the nerve – this should be recognized and surgically treated as soon as possible to avoid long-term damage [1]. Infection is less common, however it can be associated with devitalization or damage to the surrounding soft tissue, such as a Morel-Lavallee lesion [3]. Routine venous thromboembolic chemical and mechanical prophylaxis is recommended as deep venous thrombosis occurs in approximately 11-15% patients [3].

The most consequential late complication is avascular necrosis (AVN) of the femoral head, particularly in young patients. The blood supply of the femoral head can be disrupted with either the initial traumatic injury or iatrogenically from the surgical approach. Delay in initial reduction of the hip in fracture-dislocations is associated with a higher risk of osteonecrosis, presumably from the twisting and tension placed on the soft tissue around the hip in its dislocated state [21]. The treatment for AVN is total hip arthroplasty [3]. Other long term complications include post-traumatic osteoarthritis, which can occur at very high rates despite an anatomic reduction of the articular surface. In a retrospective review of 42 patients with posterior wall fractures with follow up at 2 years, Saterbak et. al. reported that 26% had complete obliteration of joint space at one year [22]. In another retrospective review of 121 cases of surgically treated posterior wall fracture with a mean of 53 months of follow up, Pascarella et. al. demonstrated that early reduction of hip dislocation and improved articular reduction were positive predictors of patient functional outcome, while other associated injuries and nerve palsy were negative predictors [23]. Patients with posterior wall fractures will likely not return to their pre-injury levels of function, however. Moed et. al. demonstrated a decreased Merle d’Aubigne score in patients with a history of posterior wall fracture compared to a control population and demonstrated residual functional deficits in the posterior wall population [24].

Conclusion
Posterior wall acetabular fractures are the most common acetabular fracture pattern and require prompt recognition, particularly if associated with a hip dislocation. Stability of the hip joint determines whether treatment involves surgical fixation; this is best determined with a dynamic fluoroscopic EUA. An anatomic reduction is associated with improvement in postoperative functional outcomes; however these patients will likely carry some functional deficit compared to their pre-injury status.

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