Characteristics of sagittal spine–pelvis–leg alignment in patients with severe hip osteoarthritis

The interaction between the sagittal alignment of the spine and pelvis and the compensatory mechanism in patients suffering from spinal disorders has been well documented. However, in patients with hip osteoarthritis (HOA), few studies have explored how the hip joint pathology could affect the sagittal alignment of the hip, pelvis and spine, and no reports have investigated whether these changes are involved in the pathogenesis of low back pain in these patients. The aims of this case–control study were to investigate the sagittal spine–pelvis–leg alignment in patients suffering from severe HOA and to understand whether the alignment was related to the occurrence of low back pain and the health-related quality of life in these patients.

Fifty-eight patients with severe HOA and 64 asymptomatic controls were studied. Digital lateral X-rays of the spine, pelvis and proximal femur were obtained with the patients placed in upright positions. The following radiographic parameters were measured to examine the sagittal alignment of the pelvis, hip and spine: pelvic incidence (PI), pelvic tilting (PT), sacral slope (SS), pelvic femoral angle (PFA), femoral inclination (FI), lumbar lordosis (LL), spino-sacral angle (SSA), C7 tilt (C7T) and T1 spinal-pelvic inclination (T1-SPI). The global balance patterns of spinal-pelvic alignment were classified as normal balance, slight unbalance and severe unbalance according to the relative position of the C7 plumb line to the sacrum and femoral heads. Short Form-36 questionnaire was carried out in the patients. Comparisons were carried out between the patients with HOA and the controls and between the HOA patients with or without low back pain. Correlation analysis was used to measure relationships between the HOA patients’ parameters.

There were no significant differences in the age and gender distribution between the HOA patients and control. Compared with the controls, the patients with HOA showed significantly higher SS and lower PT, similar PI in the pelvis, significantly smaller C7T, larger T1-SPI but comparable LL and SSA in the spine, and significantly smaller PFA but larger FI in the hip joint. In addition, the patients with HOA had a significantly greater incidence of severe unbalanced spinal-pelvic alignment than did the controls (22.4 vs 3.1 %, respectively). In patients with HOA, the PFA was significantly correlated with SS, SSA and FI but not with PI, LL or C7T; while the physical component score of short form-36 was significantly correlated with T1-SPI, C7T and FI. A comparison between the HOA patients with or without low back pain, however, showed no significant differences in the radiographic parameters, global sagittal balance patterns and Short Form-36.

The sagittal morphology of the pelvis in patients with severe HOA was normal and might not be involved in the development and progression of this disorder. Although the whole spine was involved in compensating for the flexed hip joint, the poor ability resulted in severely unbalanced spinal-pelvic alignment in these patients. The forward inclined spine and retroverted femur would contribute to the poor physical activities in these patients. However, the abnormal sagittal spine–pelvis–leg alignment in patients with severe HOA might not be involved in the pathogenesis of low back pain.