Session VII Pelvis and Acetabulum

Outcome of Surgically Treated Posterior Wall Acetabular Fractures

Andrea M. Saterbak, MD, J. L. Marsh, MD, E. Brandser, MD, J. V. Nepola, MD, T Turbett, BS

University of Iowa Hospitals and Clinics, Iowa City, IA

Purpose: To define the radiographic parameters of posterior wall acetabular fractures that may predict early failure.

Materials and Methods: Among 116 acetabular fractures in 115 patients who underwent open reduction and internal fixation, there were 56 fractures with posterior wall components which were classified by the method of Judet-Letournel as posterior wall or transverse type with associated posterior wall. Two groups were established based on the development of early degenerative failure. Early failure was defined as complete joint space loss on at least one radiographic view at minimum 1 year followup. Fifty-one cases were available with a minimum 1 year follow-up. The analysis therefore consisted of two groups. Group 1 (n=15, early failure) and Group 2 (n=36, no failure). The patients were evaluated at an average 42 month follow-up with a clinical exam, radiographs and functional outcome assessment. To determine radiographic factors predictive of failure, an extensive analysis of preoperative radiographs and CT scans was done assessing the height, depth, displacement, and comminution of the posterior wall fracture. Similar measurements were also applied to a transverse (primary fx.) fracture when present. Postoperative x-rays were reviewed to assess reduction, hardware placement degenerative joint disease, heterotopic ossification, and avascular necrosis of the femoral head. Three cases with obvious reasons for rapid failure other than the fracture pattern (infection - 1, poor reduction of a transverse fracture - 3) were excluded from Group 1 prior to statistical analysis. Radiographic predictors of outcome were determined using Fisher's Exact Test for statistical analysis.

Results: Eleven (21%) of 51 cases developed early radiographic failure at less than 1 year without other obvious reasons for failure. Radiographic features that were associated with early failure included severe initial displacement of the posterior wall fragment (p<.001), comminution of the posterior wall fragment (p<.001), and the presence of a posterior wall fracture with extension up into the dome, including the subchondral arc and extending inferiorly into the ischial facet (p<.001). Nine of the fifteen early failure cases required a salvage procedure (THR or fusion) by 18 months post injury. Of the thirty-six cases in the non-failure group, no cases of advanced degenerative change on radiographs were noted. However, four cases had radiographic evidence of AVN without subchondral collapse. Clinical follow-up was achieved at an average of 42 months, and included Merle d'Aubigne and Iowa hip scores and MFA outcome scores.

Conclusion: Complex posterior wall acetabular fractures are challenging, even for the most experienced traumatologist. Rapid, early failure despite anatomic fixation has been attributed to post-traumatic chondrolysis, infection, or aberrant screw placement. This study suggests that posterior wall fracture displacement comminution, or an extended posterior wall fracture pattern may contribute to the rapid failure process.