Poster 214: The Effect of Femoral Retroversion on Hip Range of Motion – A 3D Computational Analysis

OBJECTIVES: A subset of patients undergoing hip arthroscopy suffers from persistent pain and dysfunction which can be secondary to a number of factors. Femoral rotational deformities are often overlooked and/or providers are unsure when to address femoral deformities. Currently, there is limited to no data guiding surgeons when to consider a femoral osteotomy at the time of hip arthroscopy for FAI. Through previously validated computer-assisted 3D modeling software, this study sought to answer two questions: 1) How much femoral retroversion is too much to render cam femoroplasty ineffective in improving range of motion (ROM)? 2) In the setting of an osteotomy, what degree of femoral version correction would be sufficient to improve impingement free ROM? METHODS: Ten patients were selected with symptomatic focal cam impingement lesions who underwent hip arthroscopy and had pre- and post-operative computed tomography (CT) scans. These patients were screened for normal acetabular morphology and demonstrated no radiographic signs of osteoarthritis. Pre- and post-operative 3D modeling of the involved hip was performed and subsequently dynamized with the femoral version set at (15, 5, -5 and -15 degrees) to define the impingement free ROM and location of impingement with maximum hip flexion and maximum hip internal rotation (IR) at 90 degrees of hip flexion. RESULTS: Mean alpha angle pre and post cam resection were 66°±7.6 ° and 44°±4.9° respectively and were significantly different (p=0.003). Location of impingement shifted during hip flexion from the medial to anterior femoral neck with decreasing femoral version while the IR impingement location remained on the anterior femoral neck and was unaffected by femoral version. Kruskal-Wallis testing demonstrated decreasing femoral version significantly decreased hip flexion and IR ROM in both the pre and post cam resection groups (p<0.0003). Impingement free ROM, as defined by hip flexion and IR greater than 90° and 10° respectively, was only identified in the 5 and 15 degree femoral anteversion models irrespective of whether cam femoroplasty had been performed. In the post cam resection group, hip IR ROM was significantly less with any level of decreasing femoral version (p<0.002) while hip flexion ROM was significantly less with any level of decreased femoral version when compared to 15 degrees of anteversion (p<0.04). When assessing the degree of change in ROM between the pre and post cam resection groups, femoral version had contrasting effects on hip ROM with decreasing femoral version showing less improvement with hip IR ROM while the femoral retroversion models had significantly greater improvements in hip flexion ROM when compared to the 15 degree anteversion model (p=0.02). CONCLUSIONS: Decreasing femoral version demonstrates significantly decreased hip flexion and IR both in the presence and absence of a CAM lesion. After cam femoroplasty, any level of decreased femoral version has a significant effect on hip ROM when compared to normal femoral anteversion. Femoral version seems to be the predominant factor in determining the amount of hip IR ROM in flexion and to a certain extent hip flexion ROM irrespective of the cam FAI. Impingement free ROM was only identified within the femoral anteversion models even after cam femoroplasty suggesting that recurrent mechanical collision and intra-articular damage seen with FAI may still be present with any level of true femoral retroversion. This study provides insight into the changes in hip flexion and IR that can be expected following both cam resection and simulated femoral osteotomy.