Lower limb involvement in spinal function and low back pain

To evaluate evidence for involvement of the lower limb in spinal function and low back pain (LBP).

A hypothesis based on a critical review of the relevant biomechanical and clinical literature.

The spine resembles an inverted pendulum that supports the weight of the upper body; its stability requires a moving base that is provided by the joints of the lower limb, especially the hip. However, the sacroiliac joints are unlikely to be important for spinal function. The changing pattern of gait and development of lumbar lordosis, in early childhood, provide evidence for the inter-dependence of spinal curvature and lower limb action. Clinical signs associated with LBP may be associated with an inability to rotate the trunk about the hips. These include disorientation of the pelvis and weakness or tightness of muscles around the hip. The "sway back" posture seen in LBP involves flexion of the hip, knee and ankle to compensate for abdominal and back muscle weakness.

In order to understand the varied clinical presentation of LBP patients, the function of the spine should be considered in the context of the whole body, especially the lower limb.