Acetabular and spino‐pelvic morphologies are different in subjects with symptomatic cam femoro‐acetabular impingement

Abstract

Acetabular and spino-pelvic (SP) morphological parameters are important determinants of hip joint dynamics. This prospective study aimed to determine whether acetabular and SP morphological differences exist between hips with and without cam morphology and between symptomatic and asymptomatic hips with cam morphology. A cohort of 67 patients/hips was studied. Hips were either asymptomatic with no cam (Controls, n = 18), symptomatic with cam (n = 26) or asymptomatic with cam (n = 23). CT-based quantitative assessments of femoral, acetabular, pelvic, and spino-pelvic parameters were performed. Measurements were compared between controls and those with a cam deformity, as well as between the three groups. Morphological parameters that were independent predictors of a symptomatic cam were determined using a regression analysis. Hips with cam deformity had slightly smaller subtended angles superior-anteriorly (87° vs. 84°, p = 0.04) and greater pelvic incidence (53° vs. 48°, p = 0.003) compared to controls. Symptomatic cams had greater acetabular version (p < 0.01), greater subtended angles superiorly and superior-posteriorly (p = 0.01), higher pelvic incidence (p = 0.02), greater alpha angles and lower femoral neck-shaft angles compared to asymptomatic cams (p < 0.01) and controls (p < 0.01). The four predictors of symptomatic cam included antero-superior alpha angle, femoral neck-shaft angle, acetabular depth, and pelvic incidence. In conclusion, this study illustrates that symptomatic hips had a greater amount of supero-posterior coverage; which would be the contact area between a radial cam and the acetabulum, when the hip is flexed to 90°. Furthermore, individuals with symptomatic cam morphology had greater PI. Acetabular- and SP parameters should be part of the radiological assessment of femoro-acetabular impingement. © 2018 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:1840-1848, 2018.

Femoroacetabular Impingement: What the Surgeon Wants to Know

“…106 In addition to intra-articular anatomy, the "cone" of movement within which the hip functions is further dictated by extra-articular parameters including the proximal femoral anatomy, pelvic anatomy, and spinopelvic alignment and kinematics. 107 These native design features inherently allow a certain degree of "natural" impingement without causing irreversible cartilage damage. 108 On the femoral side are certain degrees of femoral head asphericity, as measured by the α 79 and omega 17 angles that will inevitably lead to impingement.…”

Bone density changes following surgical correction of femoroacetabular impingement deformities

“…The alpha angle is a static measure of the femoral head morphometry only and may not predict the risk of degeneration associated with FAI 25,30 . Recent work has shown that spinoepelvic parameters such as acetabular coverage and pelvic incidence differ between symptomatic and asymptomatic cam deformities 31 , and may play an important role through their effect on hip dynamics. More importantly, quantitative MRI techniques showed surgical correction of the cam deformity resulted in significant improvement in the macromolecular content of the cartilage layer at follow-up in the same patients 32 .…”

Imaging Methodology for Hip Preservation: Techniques, Parameters, and Thresholds

“…153 FAIS patients were recently shown to have higher PI and SS angles. 53,74 Recently, Mascarenhas et al 53 showed that increased SPPs are predictive of a hip symptomatic state, and Ng et al 137 corroborated this finding for PI. A significant contribution of these parameters for a symptomatic hip 53,137 and OA 135,136 was suggested.…”

“…Interestingly, in the presence of a cam morphology, a decreased NSA was acknowledged as a useful parameter to identify hips at risk of symptomatic FAI. 74…”