Correlation of Pelvic Incidence With Cam and Pincer Lesions

Background: The sacropelvic parameter of pelvic incidence (PI) is a position-independent anatomic parameter that regulates lumbar lordosis and pelvic orientation. While it has been extensively studied in relation to spine pathology, only a single study has correlated PI with femoroacetabular impingement (FAI). Hypothesis: Decreased PI would be associated with an increased prevalence of cam and pincer lesions. Study Design: Controlled laboratory study. Methods: Measurements of the acetabulum, proximal femur, and sacropelvis were made bilaterally on 40 cadaveric specimens, for a total of 80 hips. Twenty specimens had the presence of bilateral cam deformities (alpha angle >55 degrees), and 20 age- and sex-matched specimens had bilateral normal hips. Pincer lesions were defined as an anteversion <15 degrees. Pelvic incidence and acetabular version were measured using standardized lateral photographs and a goniometer, respectively. Independent-samples t tests were performed to evaluate for differences in measured parameters between groups. Results: The mean PI was 43.1 degrees 8.6 degrees for hips with a cam lesion and 47.7 degrees 9.3 degrees for normal hips, demonstrating a significant association between decreased PI and the presence of a cam lesion (P = .02). The mean version of acetabula with pincer lesions (n = 28) was 11.4 degrees +/- 2.5 degrees, and the mean version of normal acetabula (n = 52) was 20.1 degrees +/- 3.8 degrees. The mean PI of hips with pincer lesions was 42.5 degrees +/- 8.5 degrees, significantly less than that of normal hips, 47.0 degrees +/- 9.2 degrees (P = .04). Conclusion: This study supports a recent study that suggested patients with pincer impingement have a smaller PI than the healthy population, and it is the first to demonstrate a significant association between decreased PI and cam-type femoral deformity. Based on results of this study, further clinical study of the effects of pelvic geometry on FAI is warranted. Clinical Relevance: While the study results do not prove a causal relationship, it is theorized that the restriction of range of motion and biomechanical adaptations of the pelvis around the hip joints resulting from a smaller PI may affect hip development and FAI. The influence of mechanical factors beyond the hip joint in the development of FAI should be considered by clinicians.