The Prognostic Value of Antero-Lateral Femoral Head Preservation Extension in Post-collapse Femoral Head Necrosis.

BACKGROUND

The extent of antero-lateral wall preservation is crucial for early osteonecrosis of the femoral head (ONFH) prognosis. This study aimed to assess the predictive value of the anterior preserved angle (APA) and lateral preserved angle (LPA) of the femoral head in postcollapse ONFH prognosis.

METHODS

There were 77 patients (102 hips) who had Association Research Circulation Osseous stage III A ONFH enrolled in this study, with an average follow up of 7.3 years. Hips were categorized into the favorable and poor function groups based on the Harris Hip Score and whether a conversion to total hip arthroplasty occurred during follow up. The lateral preserved angle and anterior preserved angle were measured to quantify unaffected antero-lateral femoral head regions. Univariate and multivariate analyses were conducted to identify independent factors associated with hip function status. Cutoff values of LPA and APA were determined from receiver operating characteristic curves for predicting favorable hip function, while the survival rates were assessed using Kaplan-Meier survival analysis.

RESULTS

Ultimately, there were 49 hips in the poor function group and 52 hips in the favorable function group. Multivariate Cox regression analysis identified both LPA and APA as independent protective factors for hip function. Cutoff values were 44.6° for LPA and 41.1° for APA, respectively. The 10-year survival rates with poor joint function as the endpoint were 87.5% for LPA ≥ 44.6° and 17.6% for LPA <44.6° as well as 88.1% for APA ≥ 41.1° and 23.4% for APA < 41.1°. Similar results were obtained when considering collapse progression and secondary osteoarthritis changes as endpoints, respectively. Additionally, a satisfactory prognosis was observed when LPA ≥ 44.6° was combined with APA ≥ 41.1°.

CONCLUSIONS

In ONFH, femoral head collapse does not necessarily indicate a poor prognosis. Specifically, cases with LPA ≥ 44.6° and APA ≥ 41.1° are expected to have a favorable prognosis, enabling long-term "survival with collapse."