Clinical implications regarding the thoracolumbar junction

At or near the thoracolumbar junction, the facet surfaces of the apophyseal joints change their orientation from near=frontal to near-sagittal planes. The exact point of this transition, is variable, often starting one or two junctions cranialward. This transition may create a sagittal plane hypermobility and instability at the region in specific cases.

This is evident when a young boy with cerebral palsy attempts to support himself up on his knees. The lack of control and weakness of his trunk muscles allows the thoracolumbar junction to collapse into the plane of least body resistance creating a hyperlordosis at the region.

As a second example, the aforementioned sharp transition in apopheseal joints may partially explain the relatively high incidence of traumatic paraplegia at the thoracolumbar junction. In certain high impact accidents involving trunk flexion, the thorax, held relatively rigid by the rib cage, is free to violently flex as a unit over the upper lumbar region. A large flexion torque delivered to the thorax may concentrate an excessive hyperflexion stress at the point of transition. If severe enough, the stress may fracture or dislocate the bony elements and possibly injure the caudal end of the spinal cord. Surgical fixation devices implanted to immobilize an unstable thoracolumbar junction are particularly susceptible to stress failure, compared with devices implanted in other regions of the vertebral column.

Reference: Neumann AD. Kinesiology of the Musculoskeletal System: Foundations for Rehabilitation. 2nd ed. Missouri: Mosby Elsevier. 2010; p. 348.