Hip-Spine Relationship in Femoroacetabular Impingement: Does Hip Arthroscopy Affect Pelvic Mobility?

Background: Femoroacetabular impingement (FAI) is a well-recognized cause of hip pain in adults. The hip-spine relationship between the femur, pelvis, and lumbosacral spine has garnered recent attention in hip arthroplasty. However, the hip-spine relationship has not been well described in patients with FAI.

Questions/purposes: The goal of this study was to determine whether lumbopelvic mobility is altered after hip arthroscopy. Does lumbopelvic motion, defined as the difference between standing and sitting measurements for sacral slope (SS), pelvic tilt (PT), and pelvic-femoral angle (PFA), change after hip arthroscopy for FAI?

Methods: Between June 2019 and March 2020, one surgeon performed 43 arthroscopic hip labral repair surgeries for FAI in active-duty military servicemembers. The diagnosis of FAI was made clinically and with standing AP pelvis, Dunn lateral, and false-profile radiographs. All patients underwent advanced imaging, including 3T MRI to identify labral tears and three-dimensional CT to characterize bony morphology. The musculoskeletal radiologist measured alpha angle, lateral center-edge angle, anterior center-edge angle, neck-shaft angle, femoral version, and acetabular version at 1200, 1300, 1400, and 1500 using CT. Patients also underwent a diagnostic fluoroscopic-guided injection with local anesthetic and corticosteroids; > 50% pain relief was considered a positive response to injection. During the study period, the operative surgeon did not perform any open procedures for FAI; all surgical treatment was performed arthroscopically. Preoperative sitting and standing radiographs were obtained from all patients. Ninety-five percent (41 of 43) of the cohort underwent adequate postoperative sitting and standing radiographs obtained 2 months after surgery, which were used for analysis in this retrospective study. The cohort was 71% male (29 of 41) and 29% female (12 of 41), with a mean age of 33 years. Within this military population undergoing primary hip arthroscopy, 30 were enlisted servicemembers and 11 were officers. SS, PT, and PFA were measured by four observers on sitting and standing lateral pelvic radiographs. Interclass correlation statistics indicated high reliability for SS, PT, and seated PFA (κ range 0.75 to 1.00) compared with lower reliability for standing PFA measurements (κ range 0.59 to 0.65). The delta between standing and sitting SS, PT, and PFA was compared perioperatively. Student t-test analysis was used for comparisons (p < 0.05).

Results: Lumbosacral motion in the sitting position changed after hip arthroscopy. Measurements of the standing lumbopelvic mobility did not change with hip arthroscopy: ΔSS = 1.8° (p = 0.13), ΔPT = -0.56° (p = 0.50), ΔPFA = 0.54° (p = 0.50). However, measurements of sitting lumbopelvic mobility did change with hip arthroscopy. SS diminished (Δ = -4.3°; p = 0.008), PT increased (Δ = +3.9°; p = 0.03), and PFA increased (Δ = +4.3°; p = 0.03) when patients were seated. These data may indicate that in the sitting position, less motion occurs at the spine and more motion occurs at the hip after hip arthroscopy.

Conclusion: This radiographic study suggested that lumbopelvic mobility in the seated position is affected by hip arthroscopy for FAI. The clinical significance of this observation remains unknown but warrants further investigation. Future studies should seek to determine whether changes in lumbopelvic mobility after hip arthroscopy have clinically relevant effects, either positive or negative.

Level Of Evidence: Level III, therapeutic study.