Effect of cam resection depth on clinical outcomes after primary hip arthroscopy

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Background: The amount of resection or the starting point of the resection on the femoral head for cam lesions in femoroacetabular impingement (FAI) is controversial. Aim: The purpose of this study was to study the effect of postoperative resection depth, and resection arc ratio of cam lesion on the frequency of achieving substantial clinical benefit (SCB), patient acceptable state (PASS) in modified Harris Hip Score (mHHS) and Hip Outcome Score Activity of Daily Living (HOS ADL ), 2 years postoperatively. Patients and methods: All patients who underwent first-time hip arthroscopy for FAI with a 2-year follow-up were included in this study. Patient-reported outcomes included the mHHS, HOS ADL , and visual analogue scale for pain (Pain VAS). Radiological parameters such as alpha angle traditional (α T ), alpha angle cartilage (α C ), resection arc ratio (% alpha angle cartilage -alpha angle traditional /360°), resection depth (‘’D’’mm) and resection depth ratio ‘D%’ (D/femoral head diameter %) were measured using the 45° Dunn view. Results: We identified 26 patients (27 hips) with 2-year follow-up. There were 10 female and 16 male patients. The mean age of the patients was 33 ± 12 years. Higher frequency of achieving SCB threshold for mHHS was related to labrum repair (73% vs. debridement ‘27%’ p = 0.03), lower preoperative α T (64° vs. 76°, p = 0.04), lower preoperative mHHS (54 vs. 81, p < 0.001) and higher preoperative VAS scores (8 vs. 7, p = 0.02). Higher frequency of reaching PASS threshold for mHHS was associated with lower α C (82°vs. 92° p:0.02), lower RA (8% vs. 11%, p = 0.03), lower D (2.8 mm vs. 4.5 mm p:0.03), lower D% (4.7% vs. 8.4% p = 0.04) and higher postoperative mHHS (97 vs. 82 p < 0.001). Conclusions: A higher frequency of achieving SCB for HOS ADL was related to lower D% (5% vs. 10.5%, p = 0.04). Cam resection depth affects the frequency of achieving clinically meaningful scores and resection depth less than 6% of the femoral head diameter seems to be appropriate for optimal results. The starting point of resection on head cartilage needs to be <90° when alpha angle is used for reference.