Heterotopic ossification after arthroscopy for hip impingement syndrome

Background: Heterotopic ossification (HO) is a known complication of hip arthroscopy. We investigated incidence of HO after hip arthroscopy and determined whether revision for HO improved outcome. Methods: A retrospective study was conducted on 242 patients (140 men and 102 women, mean age: 36.2 +/- 9.5 years) who underwent hip arthroscopy for femoroacetabular impingement (FAI) between January 2016 and January 2018. The average followup period was 22.88 +/- 11.74 months (range: 11-34 months). Thirteen (5.37%) cases of HO (six men and seven women, five left hips and eight right hips; mean age: 37.5 +/- 4.7 years) were observed. Among them, four cases with HO with obvious pain symptoms and persistent non-remission underwent revision surgery to remove 110. Monthly follow-up was conducted. Visual analog scale (VAS), modified Harris Hip Score (mHHS), and non-Arthritis Hip Score (NAHS) were evaluated and compared between HO and non-HO patients. Independent sample t test, Mann-Whitney U test and the Chi-square test were used for inter-group comparisons. HO degree was evaluated using Brooker classification. Symptoms and function were evaluated before and after revision. Results: A total of 242 patients were involved in this study. Thirteen cases (5.4%) had imaging evidence of HO. Nine (9/13) were classified as Brooker stage I, three (3/13) Brooker stage II, and one (1/13) Brooker stage III. HO was detected by ultrasonography as early as 3 weeks after operation. After primary surgery, the mHHS of the HO group and non-HO group increased by 13.00 (8.50, 25.50) and 24.00 (14.00, 34.50) points (Z= 1.80, P = 0.08), NAHS increased by 18.00 (9.50, 31.50) and 26.00 (13.50, 36.00) points (Z= -1.34, P=0.18), and VAS decreased by 3.00 (2.00, 4.00) and 4.00 (3.00, 4.50) points (Z= -1.55, P=0.12). Average follow-up time after revision was 9.00 +/- 2.94 months; mHHS increased by 34.75 points (t= -55.23, P < 0.01) and NAHS by 28.75 points (t= 6.03, P < 0.01), and VAS decreased by 4 points (t=9.80, P < 0.01). HO and non-HO patients were similar for demographic and surgical data, and clinical and functional scores. Conclusion: HO incidence after arthroscopic treatment of FAI is similar to that found in previous studies. Most HO have no effect on clinical symptoms. Patients who undergo revision HO resection show improvement in pain and joint function.