Anatomy and Biomechanics Relevant to Spondylolisthesis

Spondylolisthesis is characterized by the abnormal translation of one vertebral body on another. The exact cause of spondylolisthesis is not well understood but certainly involves specific anatomic and mechanical factors that predispose for a slip to occur. In this chapter we discuss the principle of spinal balance and the important role that sacropelvic morphology and spinopelvic alignment play in overall sagittal alignment. Patients with high pelvic incidence with associated increased pelvic tilt are at high risk for progression of spondylolisthesis due to the large shear forces present at the lumbosacral junction. Lastly, we describe the different types of dysplasia that can occur at the lumbosacral junction, including a domed S1 endplate, lumbosacral kyphosis, and dysplasia at the pedicles, lamina, or facets. These anatomic and biomechanical factors are critical to understanding the pathogenesis and risk for progression of spondylolisthesis and help guide both non-operative and operative treatment.