Quantitative evaluation of residual bony impingement lesions after arthroscopic treatment for isolated pincer-type femoroacetabular impingement using three-dimensional CT

The objective of this study is to determine the clinical characteristics of residual bony impingement lesions after arthroscopic treatment for pincer-type femoroacetabular impingement (FAI); and to determine the effects of residual bony impingement lesions on the clinical outcomes after 2 years of follow-up.

From December 2010 to January 2012, 42 patients underwent arthroscopic surgery for symptomatic pincer-type FAI. Clinical outcomes were evaluated using the modified Harris Hip Score (mHHS) and satisfaction scores. To quantitatively evaluate the acetabular bony impingement lesions, the acetabular bony impingement angles were measured on three-dimensional CT scans. The incidence and residual rates of residual bony impingement were calculated. According to residual rates, the patients were divided into three groups: group 1, residual rate <10 %; group 2, residual rate 10–20 %; and group 3, residual rate >20 %.

Thirty patients met the inclusion criteria and were enrolled in this study. The mean age was 34.5 years. The mean follow-up was 26.3 months. Nineteen cases had residual bony impingement lesions after surgery. The incidence was 63.3 % (19/30). Sixteen cases (84.2 %) had residual bony impingement lesions posterior to the actual acetabular resection zones. The preoperative and postoperative bony impingement angles were 77.47° ± 21.31° and 12.94° ± 18.04°, respectively. The residual rate was 14.48 %. The overall mHHS significantly improved (P < 0.001) from 55.18 ± 7.96 preoperatively to 94.71 ± 4.39 postoperatively. The overall satisfaction rate was 76.66 %. The postoperative mHHSs of groups 1–3 were 95.86 ± 1.71, 95.23 ± 1.99, and 85.52 ± 6.41, respectively. Group 3 exhibited significantly lower postoperative mHHS compared to the other two groups (P = 0.001). The satisfaction rates in groups 1–3 were 92.86, 80, and 33.33 %, respectively. The satisfaction rate in group 3 was significantly worse than those of the other two groups (P = 0.017). There was a significant inverse linear relationship between the residual rate of bony impingement lesions and the postoperative mHHS (R ² = 0.516, P < 0.05).

The incidence of residual impingement lesions after arthroscopic pincer-type FAI correction was 63.3 %. The residual rate was 14.48 %. The residual impingement lesions were primarily in the posterior portion of the acetabulum. The clinical outcomes were associated with the residual rate of bony impingement lesions. The patients with residual rates >20 % exhibited significantly lower clinical scores and satisfaction rates.