PURPOSE/HYPOTHESIS: To investigate if a pre-operative lateral/medial femoroacetabular joint space ratio (LM ratio) <1 predicts 15-year THA-free survivorship following primary hip arthroscopy for symptomatic acetabular labral tears. We hypothesized that patients with a LM <1 had a significantly increased long-term risk of converting to THA.

Methods

This study queried patients ≥18 years old who underwent hip arthroscopy for symptomatic acetabular labral tears secondary to FAI. Femoroacetabular joint space width (JSW) of the ipsilateral hip was collected using a computer-assisted, semi-automated method of assessing anteroposterior (AP) radiographs. Measurements were performed at 3 fixed locations per hip at 10° [lateral], 30° [central], and 50° [medial] with respect to a polar coordinate system. Patients with minimum 5-year follow-up, Tönnis grade 0 or 1, and JSW >2 mm were included. Lateral/medial joint space ratio was calculated by dividing lateral JSW by medial JSW. The study population was stratified into LMLow and LMHigh cohorts according to a LM ratio <1 or ≥1, respectively. 15-year THA-free survivorship was assessed using a Kaplan-Meier survival curve analyzed by log-rank test. A weighted Cox regression adjusting for baseline demographics and intraoperative findings was performed to identify independent adjusted-risk factors for converting to THA.

Results

Overall, 256 patients (LMLow: 95 [37.1%] vs LMHigh: 161 [62.9%]) met inclusion criteria. The were no differences between LM cohorts for age (LMLow: 39.0 ± 11.3 vs. LMHigh: 37.6 ± 11.6 years; P=.341) and BMI (LMLow: 25.6 ± 4.2 vs. LMHigh: 25.8 ± 4.3 kg/m2; P=.698). Within 15 years, a significantly greater proportion of LMLow patients underwent THA (24 [25.26%] vs 11 [6.83%]; P<.0001). By weighted cox regression controlling for age, sex, BMI, FAI type, Outerbridge grade, Beck classification of transition zone cartilage damage, and labral treatment (repair vs. debridement), having a LM <1 increased the 15-year risk of converting to THA by 139% (P=.024).

Conclusions

Patients with a LM <1 had a 139% higher adjusted-risk of converting to THA when assessing 15-year THA-free survivorship. These findings suggest that reduced JSW at the edge-loading area of the lateral acetabulum may be an important indicator for progressive osteoarthritis and long-term conversion to THA.