Paper 08: Reflection index may be a better predictor of revision hip arthroscopy as compared to alpha angle

Objectives: Femoroacetabular impingement (FAI) is a common cause of hip pain in young adults. Hip arthroscopy has been recognized as a low risk and minimally invasive procedure to reduce the risk of progression to osteoarthritis. While hip arthroscopy has a high success rate with a return to sport rate of 72 to 100%, there still exists a failure rate of 13.2 to 15.1% and a revision rate of 3.8 to 4.5%. One of the most common causes of failure or revision is under or over resection of the CAM lesion. The reflection index is a novel radiographic parameter to assess the adequacy of CAM resection. The purpose of this study was to evaluate a cohort of patients who underwent revision hip arthroscopy to assess whether the reflection index can be utilized to predict postoperative outcomes and the risk of revision surgery. We hypothesized that patients who did not undergo revision arthroscopy would have reflection indexes closer to one as compared to those who did undergo revision arthroscopy.
Methods: Patients undergoing revision hip arthroscopy by a single surgeon at an urban, academic, tertiary referral center between 2016 and 2021 were retrospectively identified using current procedural terminology (CPT) codes. An age matched control cohort of patient undergoing primary hip arthroscopy without a subsequent revision was also identified using CPT codes. Inclusion criteria consisted of failed primary hip arthroscopy for FAI characterized by pain, mechanical symptoms or instability unresponsive to conservative treatment (e.g., physical therapy, nonsteroidal anti-inflammatory medications, or intra-articular corticosteroid injections), skeletal maturity, presence of pre-operative 45° Dunn lateral and AP pelvis radiographs (i.e. prior to revision hip arthroscopy in study group and prior to primary hip arthroscopy in control group). Exclusion included advanced osteoarthritis with Tönnis grade 2 changes or greater. Patient characteristics and medical comorbidities were collected for all patients and matched between revision and control groups. Patients were assessed radiographically with standing anteroposterior (AP) pelvis, AP hip, 45° Dunn lateral, and false profile radiographs were obtained for each patient. LCEA was measured on the AP pelvis radiograph while the alpha angle, and HNOR were measured on the 45° Dunn lateral. The reflection index was calculated using the 45° Dunn lateral radiograph as previously described by Paliobeis et al. Surgical technique for both revision and index cases were standardized. All radiographic measurements, as well as patient demographics and comorbidities were summarized and compared between revision and control groups using the student T test. For comparisons between all radiographic measurements and likelihood of revision arthroscopy, we used multinomial logistic regression models controlling for potential confounding variables.
Results: Thirty-seven patients who underwent revision hip arthroscopy were compared with sixty-one patients who did not undergo revision hip arthroscopy. Demographic data was not significantly different between cohorts. Elevated Tonnis angle, LCEA, and alpha angle were all significantly associated with an increased risk of revision arthroscopy. A lower offset ratio was significantly associated with an increased risk of revision arthroscopy. A reflection index farther from one was significantly associated with an increased risk of revision arthroscopy. Both normal reflection index as well as normal alpha angle were significantly associated with a lower risk of revision hip arthroscopy. However, the reflection index was a stronger predictor of revision in the group with a normal alpha angle.
Conclusions: Over or under resection of the CAM lesion can be a risk factor for persistent pain after hip arthroscopy and the need for revision arthroscopy. Alpha angle has been the standard for assessment of CAM resection. The reflection index is a novel radiographic parameter to assess the adequacy of CAM resection. Both normal reflection index as well as normal alpha angle were significantly associated with a lower risk of revision hip arthroscopy. However, the reflection index predicted revision in the group with a normal alpha angle. As such, the reflection index may be a better overall predictor of revision hip arthroscopy and could be utilized intraoperatively to improve patient outcomes."