danish mEdical JOURnal 1 Dan Med J 65/6 June 2018 aBsTRacT INTRODUCTION: Short-term outcome after hip arthroscopy for femoroacetabular impingement (FAI) has been reported to improve hip function and decrease pain. Only few mid- term and long-term studies have been published. The ob- jective of this study was to report midterm results in a con- secutive cohort and to study the relation between cartilage lesions and the conversion rate to total hip arthroplasty (THA). METHODS: Eighty-four FAI patients were followed retro- spectively for 6-8 years. The conversion rate to THA, the peri-operative findings and the patient-reported outcome measures were reported. RESULTS: Fifteen of 84 (18%) patients were converted to THA. The five-year hip survival rate was 83.9% (confidence interval (CI): 75.1-91.5%). The THA group was significantly older, with a mean age of 46.9 years (CI: 42.8-50.8 years) compared with 39.0 years (CI: 36.6-41.6 years) in the non-THA group (p = 0.011). In the THA group, 13 of 15 patients were 40 years or older (p = 0.005). A high-grade acetabular or femoral cartilage lesion was associated with a higher risk of conversion to THA (p = 0.017 and p < 0.0001). Sixty-four of the 69 patients (93%) were willing to repeat their arthroscopy. CONCLUSIONS: The midterm results for arthroscopic hip- preserving surgery show a high level of patient satisfaction and a good functional outcome. The conversion rate to THA was 18%. High-grade cartilage lesions and age of 40 years and older are risk factors for conversion to THA. FUNDING: This work was supported by Aleris’ Research Foundation, Box 47134, 100 74 Stockholm, Sweden. Regis- tration number: 2014-24. TRIAL REGISTRATION: not relevant. Several studies have reported good or excellent short- term results for patients undergoing hip arthroscopy for femoroacetabular impingement (FAI) [1-3]. How- ever, there is a paucity of midterm and long-term fol- low-up studies, and they report moderate to good re- sults [4-7]. A midterm outcome study by Skendzel et al reported a high failure rate in FAI patients with joint space width (JSW) ≤ 2 mm undergoing hip arthroscopy [7]. A total of 86% of the patients underwent conversion to total hip arthroplasty (THA). The cohort with a JSW of > 2 mm had a conversion rate to THA of only 16%. Almost identical conversion rates were reported in a newly published ten-year follow-up study by Menge et al [3]. In Denmark arthroscopy of the hip is rarely per- formed if the JSW is less than 3 mm at the lateral sourcil. We hypothesise that patients with symptomatic FAI benefit from arthroscopic surgery and that the results are related to age and to the grade of cartilage degener- ation in the hip joint. The primary aim of the study was to report conver- sion rates to THA in a cohort of patients with FAI who had been operated arthroscopically by the senior au- thor, BL, from 2007 to 2009. The secondary aims were to report patient-re- ported outcome measures (PROMs) in the non-THA group, the peri-operative findings and a possible associ- ation between conversion rate and THA and the grade of acetabular cartilage lesion (Beck classification 0-4) [8, 9], and the grade of cartilage lesion on the femoral head (International Cartilage Research Society (ICRS) Classification 0-4) [10]. mEThOds This was a retrospective cohort study with 76-100- month follow-up. Using a hospital database, we iden- tified a total of 127 consecutive patients with FAI who underwent arthroscopic hip surgery performed by BL from 2007 to 2009 at a private clinic in Denmark. Inclusion criteria 1. A history of chronic hip pain refractory to conserva- tive treatment 2. Referred for possible arthroscopic surgery 3. X-ray examination of the hip using the antero-pos- terior view showing the morphology of the cam- type (alpha-angle > 55 degrees on the head-neck junction), pincer type (cross-over sign at the acetabular rim) or mixed type 4. JSW ≥ 3 mm at the lateral sourcil 5. Positive flexion, adduction and internal rotation (FADIR) test and/or positive flexion, abduction and external rotation (FABER) test 6. Full hip arthroscopy was performed. Good midterm results of hip arthroscopy for femoroacetabular impingement Niels Christian Kaldau 1, 3 , Stig Brorson 2 , Per Hölmich 3 & Bent Lund 1, 4 ORiGinal aRTiclE 1) Department of Orthopaedic Surgery, Aleris-Hamlet Hospital Aarhus 2) Department of Orthopaedic Surgery, Zealand University Hospital, Køge 3) Sports Orthopaedic Research Centre – Copenhagen, Department of Orthopaedic Surgery, Amager & Hvidovre Hospital 4) Department of Orthopaedic Surgery, Horsens Region Hospital, Denmark Dan Med J 2018;65(6):A5483