Unveiling the kinetic harmony between the hip and spine through Roussouly classification in healthy volunteers.

PURPOSE: This study investigated the influence of dynamic hip joint alignment on sagittal spinal alignment using the revised Roussouly classification. We hypothesized that variations in hip joint alignment during motion contribute to differences in spinal alignment.

METHODS

A cross-sectional study was conducted on 118 asymptomatic Japanese volunteers (36 males, 82 females; mean age: 36.3 years; mean BMI: 21.8). Radiographs were obtained in standing, standing extension, and flexed-seated positions. Parameters measured included lumbar lordosis (LL), pelvic incidence (PI), pelvic tilt (PT), sacral slope (SS), pelvic femoral angle (PFA), and hip angle (HipA = PFA − 7 + 0.37 × PI). Participants were categorized into Roussouly types 1, 2, 3AP, 3, and 4, and intergroup comparisons were analyzed statistically.

RESULTS

Participants were classified as type 1 (11.9%), type 2 (19.5%), type 3AP (23.7%), type 3 (26.3%), and type 4 (18.6%). Radiographic parameters PI, LL, and SS significantly increased with classification type (p < 0.01). Type 3AP showed the lowest PT and largest HipA in all positions, reflecting a flexed hip joint and increased LL. Type 2 showed the smallest lower lumbar lordosis (LLL) and limited LLL range of motion (ROM), indicating lumbar stiffness.

CONCLUSION

Dynamic hip joint alignment significantly influences sagittal spinal alignment. Roussouly type 3AP has an anteverted pelvis, increased LL, and flexed hip joint, requiring greater LL than expected for its PI. Type 2 is linked to reduced LLL and limited flexibility. These findings emphasize the importance of hip-spine dynamics in clinical assessments and spinal surgery planning.