Preserved Angle Thresholds and Prognosis in Post-Collapse ONFH

Investigators evaluated the anterior preserved angle (APA) and lateral preserved angle (LPA) as prognostic measures in stage III A osteonecrosis of the femoral head after collapse. This retrospective cohort included 77 patients and 102 hips, with a mean follow-up of 7.3 years. The analysis assessed whether APA and LPA were linked to long-term hip outcomes after collapse, with these angles serving as the primary measurements.

Hips were categorized by Harris Hip Score and by conversion to total hip arthroplasty during follow-up, defining favorable versus poor function for the main analysis. LPA and APA quantified preserved anterolateral femoral head regions. The report does not specify which covariates were included in the multivariable analysis. These outcome groupings and angle measures framed the prognostic comparisons.

In multivariable analysis, the investigators reported that both LPA and APA were independent protective factors for hip function status. In receiver operating characteristic analysis, the reported cutoffs were 44.6 degrees for LPA and 41.1 degrees for APA. The authors presented these values as thresholds separating more favorable from less favorable prognosis within the adjusted model.

The study also reported 10-year survival rates using poor joint function as the endpoint. Hips with LPA at least 44.6 degrees versus below 44.6 degrees were reported at 87.5% and 17.6%, respectively; for APA at least 41.1 degrees versus below 41.1 degrees, the corresponding rates were 88.1% and 23.4%. Similar patterns were reported when collapse progression and secondary osteoarthritis changes were used as endpoints. The authors reported a satisfactory prognosis in hips with both LPA ≥ 44.6° and APA ≥ 41.1°.

Key Takeaways

• In this retrospective cohort, preserved anterolateral femoral head anatomy was evaluated as a prognostic marker after collapse in stage III A osteonecrosis.
• Investigators reported both preserved-angle measures as independent protective factors for hip function status, and threshold values were identified for each measure.
• Higher angle groups had higher 10-year survival rates with poor joint function as the endpoint, and similar patterns were reported for collapse progression and secondary osteoarthritis outcomes.