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Fractures of the Posterior Wall of the Acetabulum

Baumgaertner, Michael R. MD

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Journal of the American Academy of Orthopaedic Surgeons: January 1999 - Volume 7 - Issue 1 - p 54-65
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Abstract

Of all types of acetabular fractures, the posterior-wall fracture is the most common and the seemingly easiest to treat. In Letournel's series of 940 acetabular fractures, 24% were isolated posterior-wall fractures, and another 26% involved a fracture of the posterior wall as part of a more complex fracture pattern.1 The familiarity of the posterior approach to the hip and the simplicity of the fracture pattern lead many surgeons to treat posterior-wall fractures when they might otherwise refer more complicated acetabular fractures.

Despite the routine nature of posterior-wall fractures, poor outcomes occur frequently. In Epstein's longterm follow-up of 150 posterior-wall fractures, 88% of patients treated in a closed manner had an unsatisfactory result, but so did 37% of patients who underwent early open reduction and internal fixation.2 A recent study reported a 30% failure rate within the first year after fixation.3 Letournel1 and Matta4 achieved perfectly anatomic reductions of posterior-wall acetabular fractures in 94% to 100% of their cases, and they have independently demonstrated that residual displacements greater than only 1 mm after fixation of most types of acetabular fractures are associated with clinically significant joint deterioration when patients are assessed at long-term follow-up.

The purpose of this article is to review the assessment and management of the isolated posterior-wall acetabular fracture, emphasizing the factors influencing outcome that the treating physician can control. Associated fracture patterns that involve the posterior wall will not be discussed.

Etiology

Most fractures are the result of the sudden deceleration of an unrestrained occupant during a motor vehicle crash. Force is transmitted from the floorboard to the foot or from the dashboard to the flexed knee through the femur to the femoral head. With the hip flexed and in varying degrees of adduction and internal rotation, as the femoral head dislocates, it fractures the posterior wall. The specific location of the fracture can be predicted from the position of the extremity at impact.1 Generally, the shape of the acetabular fracture made by the femoral head is an arc of varying size with a radius of curvature that approximates that of the head.

Because of the indirect nature of the fracturing force, it is unusual to see significant direct soft-tissue injury in the area of the hip, but associated injuries to the extremity are common. Major knee ligament (e.g., posterior cruciate) injuries, osteochondral lesions, and foot injuries can be missed unless the remainder of the extremity is carefully assessed. The physician should critically evaluate the status of the sciatic nerve before and after attempts at closed reduction. A neurologic injury occurs in 18% to 22% of patients who sustain posterior-wall fracture-dislocations.1,5 Awareness and documentation of a motor or sensory deficit (even a minor one) avoids postoperative confusion and allows appropriate preoperative counseling.

Classification

The posterior-wall fracture is one of the elementary fracture patterns of the acetabular fracture classification system proposed by Letournel and co-workers in 1964.6 Although slightly modified subsequently, this system has been validated by 30 years of observation and has gained virtually universal acceptance by acetabular-fracture surgeons. In an attempt to create a unified classification system for all fractures, the Orthopaedic Trauma Association recently codified Letournel's classification into a format that is consistent with the AO Comprehensive Classification of Fractures, allowing computerized categorizing of posterior-wall fractures.7,8

In this system, there are three basic patterns of posterior-wall fractures (Fig. 1). The simplest pattern is a fracture line that creates a single posterior fragment. Single-fragment posterior-wall fractures occurred in 30% of fractures in Letournel's series.1 They can occur in the posterosuperior aspect of the joint and involve the roof, or weight-bearing “dome,” of the joint. When these fractures occur posteroinferiorly, they take in a varying amount of ischium.

Fig. 1
Fig. 1:
The three subgroups of posterior-wall fractures. In the first type, a fracture line creates a single posterior fragment. The second type is a multifragment fracture. The third type (also called a marginal impaction or acetabular depression fracture) is a single-fragment or multifragment wall fracture in which some of the articular surface medial to the primary fracture line has been impacted into the cancellous bone of the posterior column by the dislocating femoral head, rotating the osteochondral fragment out of its anatomic plane.

The second variant is the multi-fragment posterior-wall fracture. This pattern is seen in about a third of cases and can be further classified on the basis of the number and location of fragments.

The third type of wall fracture is the one considered to be the most complex and difficult to treat. In addition to a single-fragment or multifragment wall fracture, some of the articular surface remaining medial to the primary fracture line is impacted into the cancellous bone of the posterior column by the dislocating femoral head, rotating an osteochondral fragment out of its anatomic plane. The mechanism and resulting joint incongru-ency are similar to those seen when the lateral femoral condyle creates a split-depression fracture of the tibial plateau. Termed “marginal impaction” by Letournel1 and “acetabular depression fracture” by Brumback et al,9 this type is reported to occur in approximately one fourth of all posterior-wall fractures.

Posterior hip fracture-dislocations cause a spectrum of osseous injuries. The large, isolated single-fragment posterior-wall fracture is relatively uncommon; the surgeon must expect and be prepared to anatomically reduce and stabilize the marked comminution and impaction of the posterior wall that is frequently found if the patient is to benefit from open treatment.

Radiologic Diagnosis

The anteroposterior (AP) radiograph of the pelvis is an essential diagnostic test in most blunt-trauma evaluation protocols. Provided the film is of good quality, most acetabular fractures can be recognized on this view. If the hip has not been reduced, the wall fragment is usually seen to be displaced with the femoral head, and the defect in the posterior wall is readily apparent (Fig. 2, A). It is impossible to completely assess a posterior-wall fracture on an AP radiograph, but this view is very helpful in excluding other fracture patterns.

Fig. 2
Fig. 2:
Images of a 37-year-old woman with a left-hip fracture-dislocation. A, The hip is dislocated with the femur adducted and internally rotated. Note the defect in the posterior acetabular border and the wall fragment above the displaced femoral head. B, After closed reduction, a wall defect remains, and there is evidence of marginal impaction (arrow) but the amount of posterior-wall fracture-displacement is not obvious. C, The obturator oblique radiograph shows the wall fragment clearly. D, Axial CT image demonstrates significant marginal impaction and an inadequately reduced wall fracture.

Of the six fundamental radiographic landmarks of the acetabulum described by Letournel,1,6 five will be seen to be intact and unaffected by an isolated posterior-wall fracture. Only the posterior rim will be disrupted, although once the dislocation is reduced, the over- lying femoral head may make this finding subtle. To exclude an associated acetabular fracture that includes a fracture of the posterior wall, the other landmarks (anterior rim, iliopectineal line, ilioischial line, tear drop, and acetabular roof) should be confirmed to be intact. Marginal impaction, if present, can often be recognized on the AP radiograph as a curved, dense subchondral line that is out of anatomic position (Fig. 2, B). All radiographic views, but particularly the AP view (which has the opposite hip for comparison), should be scrutinized to confirm that a concentric reduction with a normal clear space exists between the femoral head and the remaining acetabulum and that no incarcerated fragment is preventing complete anatomic reduction.

The obturator oblique view, obtained by rotating the patient 45 degrees onto the unaffected side, displays the obturator ring as nearly circular and uncovers the posterior aspect of the acetabulum from the anterior wall and the femoral head. It usually shows the full extent of the fracture fragment, the amount of displacement, and the defect in the acetabulum (Fig. 2, C). Incarcerated fragments in the anterior aspect of the joint are best seen on this view. The opposite oblique view (the iliac oblique) is obtained by rotating the patient 45 degrees onto the side of the fracture. The unbreached borders of the greater and lesser sciatic notches confirm that the posterior column is intact, but the wall fracture is usually obscured.

Computed tomography (CT) is probably the single most valuable tool in assessing posterior-wall acetabular fractures, provided individual images through the joint are contiguous and not more than 3 to 5 mm thick (Fig. 2, D). It is always helpful to include the contralateral acetabulum for comparison. If closed management is being considered, CT scanning utilizing 3-mm overlapping sections is mandatory to definitively exclude incarcerated fragments and subtle joint incongruity that can be missed on plain radiographs (Fig. 3, A and B).

Fig. 3
Fig. 3:
Images of a 65-year-old man with a right posterior-wall fracture. A, After closed reduction, it is difficult to appreciate the extent of the fracture on the AP radiograph. B, CT image shows an incarcerated osteochondral fragment in the joint (arrow), a comminuted rim fragment, and a completely deficient posterior wall. C, Another, more distal CT scan shows marginal impaction.

During dislocation, the ligamentum teres frequently avulses a small bone fragment, which appears as a free fragment on the CT scan. As long as it is small, low in the joint, and restricted to the confines of the cotyloid fossa, such a fragment is not in itself an indication for open management.

Computed tomography greatly facilitates the assessment of fracture comminution and residual displacement. It is the ideal study for identifying posteromedial marginal impaction in a fragment that is rotated externally. However, superior impaction of the lateral aspect of the roof, which can occur in the plane of the axial CT section, may be more clearly appreciated on an AP radiograph or with CT reconstructions. With thin sections, increased bone density can be seen where impaction into the cancellous bed has occurred (Figs. 2, D; 3, C). In addition, CT is frequently used to quantify the amount of posterior wall that remains after fracture by allowing comparison of the fractured side with the intact contralateral wall.10–12

Management Options

Although Epstein2 recommended primary open reduction for all posterior-fracture dislocations, most protocols employ urgent closed reduction with the use of adequate sedation and muscle relaxation. Reduction is immediately followed by clinical assessment of hip stability performed by cautiously flexing and slightly adducting the hip while feeling for subluxation. Sciatic nerve function should be re- assessed and documented. Subsequently, the adequacy of the reduction and the size and displacement of the fragments are assessed radiographically.9 Absolute operative indications include deteriorating sciatic nerve function after attempted closed reduction and the presence of an incarcerated fragment that prevents congruent reduction of the head to the intact acetabulum. Inability to achieve a closed reduction and the presence of a femoral neck fracture are also absolute indications for open management.

With the widespread use of CT scanning, the amount of the posterior wall that is fractured or impacted (and therefore cannot support the femoral head) can be accurately determined before surgery. Several authors have attempted to define how much of the posterior wall is needed to maintain hip stability.10–12 There is general agreement that fractures involving 50% or more of the posterior wall are unstable and demand surgical repair, whereas fractures involving 20% or less are generally stable and can be managed by activity restriction with careful observation. Vailas et al10 demonstrated no hip subluxation at 90 degrees of flexion, 20 degrees of internal rotation, and 20 degrees of adduction in cadaver hemipelves with fractures involving 25% of the posterior wall if the posterior capsule was intact. Of the 9 hips with a complete capsulectomy, only 1 (11%) was unstable.

There is no consensus on treatment of fractures that are clinically stable but involve 20% to 50% of the posterior wall. For these fractures, treatment decisions should be based on the patient's clinical situation (age, activity level, expectations, other injuries) as well as the likelihood that the surgeon can achieve the desired surgical result without complications. Although the long-term effect on joint biomechanics of reducing the contact area of the posterior wall has not been adequately studied, Olson et al13 demonstrated near doubling of the contact force on the superior aspect of the acetabulum after simulated posterior-wall fracture in cadavers. Subsequently, they showed that even small rim fractures that would not cause clinical instability greatly altered joint-contact characteristics.14

If the hip is stable and closed management is elected, bed rest is instituted until the acute pain of the fracture-dislocation subsides. Most authors believe that skeletal traction is not indicated. Historically, a prolonged period of bed rest with or without traction has been recommended, but the need for this has never been documented.12,15 Restrictions against provocative ranges of motion (“total hip precautions” against adduction, internal rotation, and excessive flexion) until capsular healing occurs certainly appear appropriate, but bed rest longer than that necessary for comfort is not justified by any available data.16 Weight bearing should be limited until there is evidence of fracture healing.13,17 It is imperative to monitor very closely any patient who is managed nonoperatively with the use of only activity restrictions. Radiographs (and repeat CT scanning if evidence of instability exists) should be obtained 1, 3, 6, and 12 weeks after fracture, at the minimum.

Surgical Treatment

For isolated injuries, if the hip is reduced and nerve function is stable, emergency operation is not warranted. Surgery should proceed as soon as the patient, the operating suite, and the surgical team are prepared, usually within 72 hours of injury. Maintaining the hip in mild abduction and external rotation should obviate the need for preoperative skeletal traction. If there is gross instability or if there are bone fragments within the joint, skeletal traction to neutralize the joint reaction force is indicated to prevent secondary mechanical damage to the articular cartilage.

Most of the instruments and implants necessary to manage a posterior-wall fracture are available in general orthopaedic operating rooms. Small-fragment (3.5-mm) cortical screws of standard lengths are used with reconstruction plates that allow contouring in all three planes. A spiked-ball pusher to manipulate and reduce wall fragments and a T-handled universal chuck mounted with a Schanz screw, which can be inserted into the greater trochanter to distract the femoral head, are helpful accessories (Fig. 4). As blood loss is rarely less than 700 to 1,000 mL, intraoperative red blood cell salvage systems are usually an effective adjunct to minimize transfusion requirements.

Fig. 4
Fig. 4:
Instruments and implants for treatment of posterior-wall fractures: from left to right, spiked-ball pusher, T-handled universal chuck with Schanz screw, implant template, 3.5-mm reconstruction plates, reconstruction plate bending irons, and pliers.

Use of somatosensory evoked potentials to monitor sciatic nerve function intraoperatively remains controversial. The technique is recommended by some authors to help minimize the risk of iatrogenic nerve insult,5,18 but others consider it unnecessary and have reported very low rates of neurologic complications without the added expense and surgical time associated with monitoring.19

An operating table that allows unrestricted multiplanar and oblique fluoroscopic visualization of the pelvis is preferred over a standard operating table or a fracture table because it greatly facilitates intraoperative assessment of the reduction and fixation. The C arm is positioned to be brought perpendicular to the table on the side opposite the surgeon. With combinations of table tilt and C-arm cant and rotation, AP and Judet views can be obtained, as well as individual oblique views that show screws end-on or in perfect profile to confirm exact length and position relative to the joint and pelvic cortices.

The Kocher-Langenbeck posterior approach is always used for isolated posterior-wall acetabular fractures. The patient can be in the lateral or prone position with the involved extremity draped freely. Although lateral positioning is more familiar to most surgeons, the prone position is preferred if there is an extensive posterior-wall fracture with gross instability or if the fracture involves the roof of the acetabulum, because prone positioning tends to slightly extend and abduct the hip, thus helping to keep the femoral head reduced. In addition, the hip extension afforded by prone positioning (along with knee flexion) decreases the risk of stretch injury to the sciatic nerve.

It is important to appreciate that the approach for repair of a posterior-wall acetabular fracture is not the same as a posterior approach for total hip arthroplasty. Anatomic planes are blurred due to muscular hematoma from the recent trauma, and landmarks that are normally easily identified may be absent or markedly distorted. The sciatic nerve is directly at risk as it passes through the zone of injury and should be visually identified in every case, as it is immediately superficial to where implants must be placed. Perhaps the most important difference between fracture surgery and replacement arthroplasty is that the viability of the wall fragments and the femoral head itself must be maintained; dissection must proceed with this caveat in mind.

The skin and fascial incisions are centered at the posterosuperior aspect of the greater trochanter and extend distally along the shaft and proximally toward, but not entirely to, the posterior superior iliac spine. The gluteus maximus muscle is split proximally until the first crossing branches of the inferior gluteal nerve are reached (further dissection will denervate the part of the muscle anterosuperior to the incision). The osseous insertion of the gluteus maximus onto the femur is routinely released about 1 cm from its attachment to facilitate atraumatic posterior retraction.

Careful posteromedial dissection on the superficial surface of the quadratus femoris will identify the sciatic nerve, which is frequently in two physically separate trunks at this level. The lateral edge of the nerve is then followed proximally through the fracture zone to where it exits the pelvis through the greater sciatic notch, deep to the piriformis muscle. With the nerve identified and freed from impinging bone fragments, any blood-filled bursal tissue or avulsed musculature can be safely debrided.

The interval between the inferior gemellus and the quadratus femoris is identified to avoid any inadvertent dissection into the quadratus, which would risk injury to the medial femoral circumflex artery supplying the femoral head. The tendons of the piriformis and obturator internus are identified and carefully elevated off the joint capsule before sectioning. This allows the fractured wall fragments to maintain their capsular attachments, which are frequently their only remaining blood supply. The tendons are cut in midsubstance, and the muscle ends are tagged. Retraction on these muscles allows exposure of the retroacetabular surface posteriorly to the border of the greater sciatic notch and the bursa around which the obturator internus tendon exits the inner pelvis through the lesser notch. This tendon can be sutured to the gluteus fascia to create a soft-tissue sling that retracts and protects the sciatic nerve from the edge of a blunt-tipped nerve retractor maintained in the lesser notch. Nerve retractors in the greater notch, where the nerve is unprotected, should be used cautiously or not at all.

If further inferior exposure is necessary, the origin of the quadratus femoris as well as the hamstrings can be taken down off the ischium. The pudendal nerve is medial to the field and is not at risk. Hip extension and knee flexion are maintained throughout the procedure, and the sciatic nerve is intermittently inspected for inadvertent compromise.

The gluteus minimus is elevated off the capsule and ilium as necessary. It is important to cautiously elevate near the superior border of the sciatic notch to avoid laceration of the superior gluteal nerve, artery, or vein, which may lie directly on bone at this level. Anterior and superior exposure is facilitated by hip abduction, which relaxes the muscle and protects the superior gluteal nerve from traction palsy. The field can be maintained by placing Steinmann pins into the superolateral ilium.

The first step in the reduction and fixation stage is always to inspect the joint. The wall fragments are rotated back on their capsular attachments, and the fracture surfaces are debrided of clot and callus. A Schanz screw placed into the trochanter is usually adequate to distract the femoral head, allowing examination of both articular surfaces, removal of incarcerated fragments, and flushing of debris from the joint. The size and shape of any free cartilaginous fragments should be noted before they are discarded. Free osteochondral fragments of significant size are marked for orientation and set aside for later reconstruction. If sustained distal retraction is desired, the femoral distractor can be used effectively with one pin in the ilium and the other in the trochanter.

After joint cleansing, the femoral head is reduced to the intact acetabulum, and the quality of the joint reduction is evaluated. An anatomic reduction is implied if only the edge of intact acetabular articular surface is seen through the fracture plane, and it is concentric and perfectly satisfied by the femoral head. Marginal impaction exists if there is any acetabular cartilage that does not anatomically cup the reduced femoral head but instead is rotated to face toward the plane of the fracture. If not corrected, not only will this aspect of the joint be incongru-ent, but the displaced articular osteochondral segment will prevent anatomic reduction of the overlying wall fragment. Therefore, fragments that are marginally impacted must be recognized, elevated, and supported with bone graft before addressing other wall fragments.

The concentrically reduced femoral head acts as a template to guide the reduction. A narrow Cobb elevator can be used to create a plane along the cortex of the quadrilateral surface, deep to the depressed articular surface and underlying cancellous bone, and then to rotate the fragments en bloc to elevate the depression (Fig. 5). Any free osteochondral fragments are reoriented and reduced to the head as well. To support the reduced joint surface, a bone graft from the greater trochanter is packed into the defect that is created behind the elevator. The femoral head prevents overelevation but allows aggressive impaction of the graft into the defect such that after the procedure, the grafted area appears more dense than the surrounding cancellous bone (Fig. 6).

Fig. 5
Fig. 5:
Technique for dealing with marginal impaction and a free osteochondral fragment. A, With the femoral head concentrically reduced to the intact acetabulum, the wall fragment with attached capsule (W) is reflected with a dental pick to reveal the marginal impaction (I) and the free osteochondral fragment (F), which is temporarily removed. B, After harvesting of cancellous autograft (G) from the greater trochanter, an elevator is used to undermine and derotate the impacted fragment. The femoral head guides the reduction and prevents overelevation. The autograft is impacted into the defect created by elevation. C, After repositioning and support of the osteochondral free fragment with additional graft, the wall fragment is finally repositioned. As the joint is no longer visible, the reduction must be judged from the retroacetabular fracture line. D, The reconstructed posterior wall is supported by a buttress plate and an appropriately directed lag screw.
Fig. 6
Fig. 6:
Postoperative CT images corresponding to Figure 3, B and C. Some devitalized articular cartilage had to be discarded. Note densely impacted graft supporting the joint surface but preventing complete reduction of the retroacetabular cortex. The safe corridor of the screw and the trochanteric bone-graft donor site can also be seen.

Reduction and fixation of posterior-wall rim fragments that are at- tached to the capsule is attempted only after the correction of any marginal impaction, as this step prevents further unobstructed inspection of the articular surface. Slight abduction and external rotation relaxes the capsule and allows the fragments to be manipulated. A spiked-ball pusher is helpful in completing and maintaining the reduction. Alternatively, temporary fixation can be achieved with small Kirschner wires directed away from the joint. The quality of the joint reduction must frequently be inferred from the reduction of the retroacetabular cortical fracture lines and the continuity of the posterior rim.

Definitive fixation of the wall fracture generally requires buttress plating. Very rarely, a large single fragment can be adequately stabilized with three to five lag screws. Goulet et al17 demonstrated that the combination of a buttress plate and lag screws provided a fourfold increase in local effective stiffness (P<0.05) and doubling of the load to failure (3,306 vs 1,666 N [P=0.05]) in a posterior-wall fracture model compared with the use of two lag screws alone. A 3.5-mm straight reconstruction plate with seven to nine holes was used. It can be helpful to contour the plate on a pelvic model preoperatively and subsequently fine-tune the shape of the plate in the operating room. Leaving the plate very slightly underbent aids in the reduction. If the plate is fixed to the ischium with distally directed screws and to the lateral aspect of the ilium with superiorly directed screws, it will be slightly tensioned as it is seated, compressing the wall fragments.

Screws must be directed away from the joint to avoid penetration, but because of the small fragments frequently involved, the depth of the acetabulum, and the fact that the joint cannot be easily visualized after fracture reduction, violation of the joint can occur. Suggestions for avoiding this complication have come from various authors, including Bosse,20 who noted that screws placed in any position on the acetabular rim would not violate the joint as long as they were placed in the coronal plane perpendicular to the long axis of the body. However, as these planes of reference can be difficult to assess intraoperatively, other methods of assessment should be employed as well.

Placing Kirschner wires tangential to the articular surface under direct vision at the proximal and distal extent of the intact acetabular rim allows a fixed plane of reference.1 Screws placed parallel to or directed away from these wires should avoid the joint (Fig. 7). Letournel1 described, and Ebraheim et al21 attempted to quantitate, the relationship between the distance from the acetabular rim and the angle of the screw needed to safely avoid the joint. In general, maintaining the buttress plate at least 6 to 9 mm from the acetabular rim and directing the screws parallel or posterior to the coronal plane helps to decrease the incidence of penetration.

Fig. 7
Fig. 7:
Placement of a Kirschner wire tangential to the joint surface provides a reference for safe screw location and direction.

The use of specially modified spring plates has been suggested for the control of rim fragments deemed critical for stability but too small for lag-screw fixation and too peripheral to be adequately buttressed.17,22 This technique involves cutting and acutely bending the end of a one-third tubular plate to fashion two hooks that can catch the rim fragment. The plate is contoured so that its central section is raised off the bone. When the plate is anchored to the bone, with either a screw or an overlying reconstruction plate, the spring plate bends and fully engages the spikes in the rim fragment (Fig. 8). The surgeon who elects to use this technique must be cognizant of the fact that failure to position the hooks properly or postoperative displacement or even resorption of the rim fragment may expose the femoral head to the plate itself.

Fig. 8
Fig. 8:
Images of a 20-year-old man with a multifragment posterior-wall fracture. A, CT scan demonstrates marginal impaction, wall comminution, and a peripheral rim fragment attached to the posterior capsule. B, Follow-up radiograph obtained 1 year after surgery shows the rim fragment captured by a spring plate. The plate lies under the buttress plate and is fixed additionally by a screw.

Before wound closure, the hip is taken through a range of motion to confirm the stability of fixation. Additionally, the surgeon should palpate and listen for any grating of the joint with motion, suggesting misplaced hardware. It is very helpful to manipulate the position of the table and the C arm so that screws near the joint are viewed end-on and appear as a circle on the monitor. If the projection shows the implant outside the joint clear space, the screw is unquestionably safe (Fig. 9). Any muscle of questionable viability should be resected before the torn capsule and the tendons of the short rotators and gluteus maximus insertion are repaired anatomically. The fascia and dermis are then closed in routine fashion. Hard-copy film of the key fluoroscopic images as well as an AP view of the pelvis should be obtained before the patient leaves the operating room.

Fig. 9
Fig. 9:
Intraoperative oblique fluoroscopic images obtained before buttress-plate application suggest (left) and confirm (right) safe screw placement by showing the two lag screws end-on and outside the joint clear space.

Postoperatively, patients complete their perioperative antibiotic regimen and continue thromboem- bolism prophylaxis.23 Before discharge, a complete set of pelvic radiographs should be obtained in the radiology suite unless the intraoperative films are of excellent quality. If any question remains regarding the quality of the reduc- tion or the position of the hardware, a postoperative CT scan can be obtained. Fracture healing and the status of the joint should be monitored radiographically with an AP view of the pelvis 6 weeks, 12 weeks, and 6, 12, and 24 months after surgery (Fig. 10).

Fig. 10 A,
Fig. 10 A,:
Postoperative obturator oblique view of same patient shown in Figures 3 and 6 demonstrates the reconstructed posterior wall, the plate contour, and the diverging screw pattern. B, Intermediate follow-up AP radiograph obtained at 30 months shows well-preserved joint space.

Motion restrictions against adduction, internal rotation, and excessive flexion are maintained for 4 to 6 weeks. Even though the fixation rarely involves the area of the joint that resists the resultant forces of weight bearing, touchdown weight bearing should be maintained for a period of at least 6 to 8 weeks. Olson et al13 have shown that even perfect anatomic reduction and rigid internal fixation of a simple posterior-wall fracture does not restore normal load transfers across the joint. In another study, Goulet et al17 noted a small margin of safety between construct strength and expected physiologic loads.17

Strengthening exercises should start at 6 weeks and continue for at least 6 months. Dickinson et al24 examined patients an average of 21 months after posterior-wall acetabular surgery (minimum, 6 months) and reported a 43% reduction in abductor strength in patients who had satisfactory reductions and who had completed a postoperative physical therapy program. They postulated that the weakness was permanent and was related to the amount of exposure and the force of retraction on the superior gluteal neurovascular bundle during surgery.

Complications

Hematoma and infection are rare but serious complications that are best managed prophylactically. Their occurrence necessitates prompt surgical drainage. Like thromboembolism, they are not unique to acetabular fractures; therefore, their diagnosis and treatment will not be discussed further.

Iatrogenic injury to the sciatic nerve is related not only to fracture pattern and approach but also to the preoperative status of the nerve and the experience of the surgical team.5 Letournel and Judet1 reduced the rate of sciatic palsy from 18% in their first 126 cases in which the Kocher-Langenbeck approach was used to 3.3% in the subsequent 211 cases. Almost invariably, the peroneal division is injured with or without some tibial compromise, and although the prognosis for improvement is good, it is uncommon to regain completely normal muscle and sensory function. Although the primary means used to avoid nerve injury are visualization of the nerve and positioning of the extremity to minimize tension during retraction, somatosensory evoked potential monitoring has been used to identify nerve compromise so that corrective actions can be taken before irreversible changes occur.5,18

Osteonecrosis following operative management of acetabular fractures is generally overdiagnosed. When Kocher-Langenbeck approaches have been used, rates as high as 42% within the first year after surgery have been reported.25 Rapid mechanical destruction of the femoral head can occur from the injury itself, due to osteochondral impaction or cartilage crushing, or can be the result of inadequate reduction, loss of reduction with recurrent instability, or violation of the joint by inadvertently retained bone fragments or screws. These diagnoses should be excluded before considering a diagnosis of posttraumatic osteonecrosis of the femoral head, which does not present until at least several months after injury. Epstein2 identified osteonecrosis in 5.3% of surgically treated posterior-wall fractures. Letournel and Judet1 reported a 7.5% incidence of osteonecrosis in 227 fractures that included a posterior dislocation and that were treated surgically within 21 days of injury.

Heterotopic bone formation occurs less frequently after a Kocher-Langenbeck approach for a posterior-wall acetabular fracture than after an extensile approach for associated fractures. Nevertheless, it still occurs in 20% of patients who have not received prophylactic therapy and is clinically significant (Brooker grade III or IV) in more than 7%.1 Male sex and head injury are factors that tend to increase the risk. Treatment with indomethacin (25 mg three times a day, starting on the day of surgery and continuing for 4 to 6 weeks) has been recommended as effective, safe, and inexpensive prophylaxis against heterotopic ossification26,27; however, a recent randomized prospective study by Matta and Siebenrock28 questions the efficacy of this method. Low-dose perioperative irradiation (700 to 1,000 cGy within 48 hours of surgery) is effective in reducing the incidence and severity of heterotopic ossification after acetabular fracture,29,30 but the unknown potential for late complications from radiation discourage treatment with this modality for the isolated posterior-wall fracture in the typically young patient.

Outcome

Patients with posterior hip dislocations that are associated with minimal acetabular rim fractures do well provided reduction is prompt and atraumatic.16 There is no question that unstable fracture-dislocations that receive delayed treatment have dismal clinical outcomes, with failure rates approaching 90%.1,2,16 It is in the light of these extremes that the results of acute stabilization should be viewed. In the study of Pantazopoulos et al,31 more than 90% of patients who had undergone anatomic reduction of a posterior-wall fracture had a very good clinical result 2 to 15 years (average, 7 years) postoperatively, compared with only 50% of patients whose reductions had 1 to 3 mm of residual displacement.

In Letournel's series,1 19 (16%) of 119 perfectly reduced posterior-wall fractures were found to have developed significant osteoarthrosis at follow-up, which was as long as 25 years. The rate of posttraumatic arthrosis after a perfectly reduced posterior-wall fracture was higher than the 10% rate for all types of acetabular fractures that had an anatomic reduction, but was much lower than the 38% rate of arthrosis for posterior-wall fractures that were not reduced anatomically. Overall, Letournel reported an 18% rate of unsatisfactory outcome for posterior-wall fractures.

Femoral head impaction, cartilage necrosis, and posterior-wall resorption can lead to arthrosis even after anatomic reconstruction of the acetabulum. Despite achieving perfect reductions in all 22 posterior-wall fractures treated, Matta had a 32% clinical failure rate in this group, higher than that for any other fracture pattern in his series of 262 fractures.4

Summary

Patients who sustain an unstable posterior-wall acetabular fracture have a guarded prognosis. An anatomic reduction is achievable in the great majority of cases and is a prerequisite to long-term hip survival. Although not even a perfect surgical reconstruction of a joint will guarantee long-term function, that goal must be the mind-set of surgeons who choose to treat this injury, because the results of imperfect or unstable reductions are clearly inferior and usually unsatisfactory.

References

1. Letournel E, Judet R; Elson RA (transed): Fractures of the Acetabulum, 2nd ed. Berlin: Springer-Verlag, 1992.
2. Epstein HC: Posterior fracture-dislocations of the hip: Long-term follow-up. J Bone Joint Surg Am 1974;56:1103-1127.
3. Saterbak AM, Marsh JL, Brandser E, Nepola JV, Turbett T: Outcome of surgically treated posterior wall acetabular fractures. Orthop Trans 1997;21:627.
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