[Sagittal balance of the spine]

Abstract

Purpose of the study: The authors examined the modifications of sagittal shape and muscular functions in different vertebral diseases in order to investigate their correlations and to specify the role of hip extension in standing posture.

Materials and methods: We included 57 patients presenting various diseases, among which lumbar kyphosis, spondylosis and spondylolisthesis, backache and lumbar stenosis. We measured joint mobility (hip extension, lumbar flexion), muscular retractions (ilio-psoas, hamstrings, rectus femoris), and muscular strength (spine flexors and extensors, hamstrings, quadriceps femoris). On standing lateral x-rays, measurements were made of various spinal and pelvic parameters, among which the "pelvi-femoral angle", proposed by the authors for hip extension evaluation.

Results: There was a significant correlation between pelvi-femoral angle and pelvic backward tilting (r = 0.8037 p < 0.01). This angle can therefore be considered as fundamental for evaluation of sagittal posture. Characteristic abnormalities were found for each pathogenic group, notably for lumbar kyphosis and spondylolisthesis.

Discussion: Upright posture is secondary to hip extension and lumbar lordosis, and an optimal and economic standing posture is obtained when balance between these two phenomena is correct. In lumbar kyphosis pelvic modifications such as hip extension, and pelvic backward tilt-up arise compensating the anterior displacement of the center of gravity, while in spondylolisthesis, anterior displacement is secondary to sacral obliquity.

Conclusion: It is very important to evaluate the pelvis position in sagittal spinal diseases, in order to understand postural deterioration mechanisms. Lumbar kyphosis and spondylolisthesis are two examples of failure of upright posture.