Full Ball & Socket Joint Description. [Continued from above] . . . In the shoulder joint, the spherical head of the humerus (upper arm bone) fits into the glenoid cavity of the scapula (shoulder blade). The glenoid cavity is a small and shallow cavity that permits the shoulder joint the greatest range of motion in the human body.
Lumbar lordosis refers to the inward curvature of the spine just above the buttocks. The National Institutes of Health reports that lordosis is caused by spondylolisthesis. Spondylolisthesis is a condition in which a spinal bone slips out of its normal space and onto the bone below it.
Causes of lordosis and contributing factors: Certain medical conditions may cause the curvatures in the spine to change. In addition, changes in one part of the spine may cause other parts of the spine to become unstable, or to change to change to compensate for the instability in other parts of the spine. Spondylolisthesis occurs when one vertebra slips forward in relation to the ones above and below it.