Pre-Reduction Position of Posterior Wall Fragment is Associated with Intra-Articular Displacement.

OBJECTIVES: To characterize the rate and risk factors for a posterior wall fragment becoming intra-articular following closed reduction in posterior acetabular fracture-dislocations when the fragment was positioned between the femoral head and acetabulum prior to reduction. METHODS: Design: Retrospective case series. SETTING: Regional Level 1 trauma center. PATIENT SELECTION CRITERIA: Patients with posterior wall, posterior column-posterior wall, or transverse-posterior wall acetabular fracture-dislocations and posterior hip dislocation between January 2019 and December 2023 were reviewed. Inclusion required pre- and post-reduction CT imaging demonstrating a posterior wall fragment between the femoral head and acetabulum. OUTCOME MEASURES AND COMPARISONS: Pre- and post-reduction CT scans were reviewed to define fragment position relative to the femoral head and determine whether fragments were intra- or extra-articular after reduction. RESULTS: Of 44 patients with a posterior wall fragment positioned between the femoral head and acetabulum prior to reduction, 21 (47.7%) had the fragment become intra-articular following closed reduction. All fragments that displaced into the joint were medial to the femoral head (100%) prior to closed reduction (mean age 37.4 years [18.0-77.0], 57.1% male) and 23 (52.3%) remained extra-articular (mean age 34.3 years [20.0-80.0], 65.2% male). Among intra-articular fragments, 21 of 21 (100.0%) were medial to the femoral head before reduction compared with 6 of 23 (26.1%) extra-articular fragments (p<0.001). Inferior fragment position was present in 20 of 21 (95.2%) intra-articular fragments and 8 of 23 (34.8%) extra-articular fragments (OR 37.5, 95% CI 4.2-333.1; p<0.001). Fragment length was 2.6 ± 1.1 cm versus 3.6 ± 1.0.98 cm (p=0.003). Medial fragment position was associated with non-concentric reduction (74.2% vs. 30.8%; OR 6.5, 95% CI 1.6-26.9; p=0.015), whereas inferior fragment position was not (p=0.172; OR 2.9, 95% CI 0.8-10.9; p=0.172). CONCLUSIONS: Medial and inferior posterior wall fragment position before reduction were each associated with post-reduction intra-articular translation, while medial position was also associated with non-concentric reduction. Recognition of this morphology may aid surgical planning and anticipation of fragment retrieval. LEVEL OF EVIDENCE: Prognostic Level IV.