Increased peak contact stress after incongruent reduction of transverse acetabular fractures: A cadaveric model

Background. The objective of this study was to determine the peak contact p ressure with varying degrees of articular cartilage step-off in a transtect al acetabular fracture model. Methods: Five fresh frozen cadaveric hip joints were potted in a custom loa ding fixture. The five specimens were then tested at loads of 445 N (newton ) (100 lb) and 1,335 N (300 lb) intact and after a transverse osteotomy at step-off levels from 0 to 5 mm in 1-mm. increments. Results: Articular cartilage step-off of greater than 1 mm led to significa ntly increased contact stress at the loaded acetabular articular surface. M ean peak pressure measured at 1,335 N of loading in all intact specimens be fore the osteotomy was approximately 10 MPa. Peak pressure after a transver se acetabular fracture did not change when the fracture was perfectly reduc ed. At 1 mm of step-off, the peak pressure increased by approximately 20% b ut was not statistically significant. With step-off of > 2 min or greater, the peak pressure increase was approximately 50% and was statistically sign ificant. Conclusion. On the basis of our study, transverse acetabular fractures with greater than 1 mm of displacement can lead to significant increase in peak pressure at the articular surface.