Vertebral Rotation in Functional Scoliosis Caused by Limb-Length Inequality: Correlation between Rotation, Limb Length Inequality, and Obliquity of the Sacral Shelf

Abstract

Background: Scoliosis is a structured rotatory deformity of the spine defined as >10° Cobb. Functional scoliosis (FS) is a curve < 10° Cobb, which is non-rotational and correctable. FS is often secondary to leg length inequality (LLI). To observe vertebral rotation (VR) in functional scoliosis due to LLI, one must demonstrate a correlation between LLI, sacral shelf inclination (SSI), and VR and discover a predictive value of LLI capable of inducing rotation. Methods: We studied 89 patients with dorso-lumbar or lumbar curves < 15° Cobb and radiographs of the spine and pelvis. We measured LLI, SSI, and VR. The patients were divided into VR and without rotation (WVR) groups. Statistical analysis was performed. Results: The mean LLI value was 6.5 ± 4.59 mm, and the mean SSI was 2.8 ± 2.53 mm. The mean value of LLI was 5.2 ± 4.87 mm in the WVR group and 7.4 ± 4.18 mm in the VR group. The mean SSI value for WVR was 1.4 ± 2.00 and that for VR was 3.9 ± 2.39. For each mm of LLI, it was possible to predict 0.12° of rotation. LLI ±5 mm increased the probability of rotation (R2.08 p < 0.0016), while this was ±2 mm for SSI (R2 0.22 p < 0.01). Each mm of LLI corresponded to 0.3 mm of SSI (R2 0.29, p < 0.01). Conclusions: FS secondary to LLI can cause VR, and 5 mm of LLI can cause SSI and rotation.