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.