• Theerachai Apivatthakakul, Jason L Koerner, Sutiwat Luangsod, Thanawat Buranaphatthana, Joshua Parry, Michael Hadeed, August Funk, Stephen Stacey, and Cyril Mauffrey.
• Department of Orthopaedics, Faculty of Medicine, Chiang Mai University, Thailand; Excellence Center in Osteology Research and Training Center, Chiang Mai University.
• Injury. 2021 Aug 1; 52 (8): 2104-2110.

PurposePrevious research has been unable to elucidate the exact factors that contribute to hip instability in the setting of posterior wall acetabular fractures. The purpose of this study was to determine the influence of posterior wall fracture fragment size and fracture angle on the stability of the hip joint in a cadaveric model.MethodsSix fresh human cadavers (12 hips) were used. Specimens underwent pre-procedure CT evaluation and were then randomized to one of three groups: posterior wall fragment size (FS) of 15%, 20% and 25%. Osteotomies were performed starting at a fracture angle (FA) of 40°. The specimens underwent an exam under anesthesia (EUA). If the hip remained stable, the fracture angle was increased in 20° increments and re-tested until it became unstable.ResultsIn the group with a FS of 15%, all hips were stable with a FA of 40°. Increasing the FA to 60° caused all hips to be unstable (subluxation or dislocation). In the group with a FS of 20% and 25%, all hips were unstable with a FA of 40°.ConclusionIn all specimens, a FS of 15% and FA of 40° were stable on EUA. Varying combinations of increasing FS size and increasing FA were all unstable. This study provides data for a CT-based measurement to predict hip instability in the setting of posterior wall acetabular fractures based on FS and FA. More research is required to validate this data in a clinical setting.Copyright © 2021. Published by Elsevier Ltd.

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