Session I - Pelvis

Open Reduction and Internal Fixation of Posterior Wall Fractures of the Acetabulum

Berton R. Moed, MD; Seann E. Willson Carr, MS; J. Tracy Watson, MD; Wayne State University, Detroit, MI

Purpose: To evaluate the outcome of surgical treatment of unstable posterior wall fractures of the acetabulum.

Material & Methods: Between 1986 and 1998, open reduction and internal fixation were performed on 109 acute posterior wall acetabular fractures associated with hip joint instability in skeletally mature patients. The fractures all presented as unilateral injuries. One patient died from unrelated causes during the follow-up period. Fourteen patients had inadequate follow-up and could not be contacted for additional evaluation. Inclusion in the study group required a minimum of 1 year follow-up (92 patients) or the presence of a clearly poor clinical result before 1 year (2 patients). Therefore, there were 94 patients included for study with follow-up averaging 3.5 years (range, 1- 13 years).

Eighty-four patients initially presented with a dislocation of the hip joint requiring reduction, 3 of these being irreducible with closed manipulation. Ten patients had occult hip instability. Of the 84 hips requiring reduction, 73 were reduced within 12 hours of injury, 6 were reduced between 12 and 24 hours following injury, and 5 were reduced more than 24 hours after injury. Fifty-five patients sustained associated extremity, spine or multiple-system trauma. Nine patients presented with the clinical findings consistent with an incomplete traumatic injury to the ipsilateral sciatic nerve and 1 presented with femoral nerve palsy.

All patients were evaluated preoperatively using 3 standard plain radiographs (an anteroposterior and 2 Judet 45-degree oblique pelvic radiographs) and a 2-dimensional computed tomography (CT) scan. Patients with a history of dislocation were maintained preoperatively in distal femoral skeletal traction; those with suspected occult instability were placed at bed rest; and those with irreducible dislocations were taken for emergent operative intervention. Surgical treatment was performed as soon as the patient's general medical condition would allow. The delay to surgery was also related to transfer of the patient from a referring institution. The overall time from injury to surgery averaged 7 days (range, 0 - 20 days).

Ninety-two fractures were fixed using lag screws supplemented by buttress plates and 2 with screws alone. Operative findings included intra-articular free fragments in 25 (27%), injury to the femoral head in 12 (13%), acetabular articular impaction (marginal impaction) injury in 44 (47%), and extensive fracture comminution (defined as greater than 3 separate fragments) in 35 (37%). An attempt was made to replace all free fragments and elevate all impacted areas. However, due to lack of adequate attached cancellous bone and the multitude or size of the free or impacted fragments, some residual deficit (defined as >3 mm of gap) was known to be left in at least 39 cases (41%).

Prior to discharge from the hospital, the 3 standard pelvic radiographs were obtained in order to assess fracture reduction. Beginning in 1991, these plain radiographs were supplemented with a postoperative 2-dimensional CT, which was obtained in 59 patients. After discharge from the hospital, patients were scheduled for evaluation (including the 3 standard pelvic radiographs) at 2 weeks, 6 weeks, 3 months, 6 months, 1 year, and annually thereafter. Most patients did not return for all of these scheduled visits. Data, including all complications, were recorded at each patient visit, the last of which served as the information used for this study. In addition, an attempt was made to contact all patients who did not return for follow-up that was sufficient for this study.

At the final follow-up examination, the patient's functional outcome was evaluated using the clinical grading system developed by d'Aubigne and Postel and subsequently modified by Matta. The radiographs were also graded according to the criteria described by Matta. Additional patient, fracture and radiographic variables were also collated in an attempt to identify possible associations with functional outcome. These included patient age, gender, time to reduction of the dislocation (categorized as <12 hours, 12 - 24 hours, and > 24 hours), impaction injury to the femoral head, involvement of the weight-bearing acetabular dome, intra-articular fracture comminution (defined as >3 fragments), presence of marginal impaction, residual fracture gap as measured on the postoperative CT, radiographic evidence of osteonecrosis of the femoral head, and radiographic evidence of severe heterotopic ossification.

Results: Fracture reductions were graded as anatomical (0-1 mm displacement) in 92 and imperfect (2-3 mm displacement) in 2, as determined by plain radiography. However, postoperative CT obtained in 59 cases revealed incongruency of more than 2 mm in 6 and fracture gaps of 2 mm or more in 44. Complications included 1 deep wound infection, 7 patients with deep vein thrombosis, and one revision surgery to redirect an errant screw. Clinical outcome was graded as excellent in 34 patients (36%), good in 49 (52%), fair in 2 (2%), and poor in 9 (10%). Radiographic results were excellent in 79 hips (84%), good in 4 (4%), fair in 2 (2%), and poor in 9 (10%). There was a strong association between clinical outcome and radiographic grade. Variables identified as risk factors for an unsatisfactory result included age greater than 55 years, a delay of > 24 hours from the time of injury to reduction of a hip dislocation, a residual fracture gap greater than 1 cm, and severe intra-articular comminution.

Discussion And Conclusion: The apparent reported disparity between the accuracy of surgical fracture reduction, as determined by plain radiographs obtained postoperatively, and clinical outcome is only partially explained by the limitations of plain radiography. Other variables are involved; many are under the surgeon's control but some are not. Rather than involving one simple fracture fragment, the majority of posterior wall fractures are comminuted or are associated with impaction injury of the articular surface into the underlying cancellous bone along the margin of the posterior wall fracture line (marginal impaction). Accurate repositioning of all of these small fragments is difficult and sometimes not attainable. However, anatomic reconstruction of the acetabular articular surface remains the ultimate surgical goal. It is our belief that the additional effort expended on our patients was rewarded by improved clinical results. Despite some recent reports to the contrary, good overall results should be expected. Especially in view of our findings, every effort should be made to avoid unnecessary delays and ensure a timely reduction of a dislocated hip. As is the case with other acetabular fracture types, the best results are predicated on anatomic fracture reduction.