Three-Zone threshold of acetabular cartilage damage predicts failure to achieve minimal clinically important difference after hip arthroscopy.

PURPOSE: To identify thresholds of acetabular chondral burden (number of Ilizaliturri zones involved) associated with failure to achieve minimal clinically important difference (MCID) following hip arthroscopy for femoroacetabular impingement, and to determine whether cartilage extent provides prognostic information independent of lesion severity (Outerbridge grade).

METHODS

We analyzed 168 consecutive patients who underwent hip arthroscopy with two year follow-up. Acetabular cartilage was assessed intraoperatively for extent (Ilizaliturri 6-zone classification) and severity (Outerbridge grading). Patients were categorized by chondral burden: 0 zones (N = 70), 1-2 zones (N = 62), or ≥ 3 zones (N = 36). Primary outcome was MCID achievement (≥ 9-point improvement) in Hip Outcome Score-Activities of Daily Living. Multivariable regression adjusted for age, sex, BMI, baseline function, and Outerbridge grade (Table 3).

RESULTS

MCID achievement differed significantly by chondral burden: 70% (0 zones), 79% (1-2 zones), and 50% (≥ 3 zones) (p = 0.011), representing a 29 percentage-point difference between groups. In multivariable analysis adjusting for Outerbridge grade and other confounders, the ≥ 3 zone group showed a trend toward reduced odds of achieving MCID (OR = 0.43, 95% CI: 0.18-1.02, p = 0.056). Extent and severity showed low correlation (ρ = 0.20), suggesting they represent distinct aspects of cartilage pathology.

CONCLUSION

Acetabular chondral involvement of ≥ 3 Ilizaliturri zones was associated with a lower probability of achieving clinically meaningful improvement after hip arthroscopy. Cartilage extent may provide prognostic information beyond lesion severity and should be considered during preoperative counseling and surgical decision-making.