Pars Interarticularis Defect

Excerpt

Pars interarticularis defect (otherwise referred to as spondylolysis) represents a common cause of axial back pain in adolescents, especially in the case of young athletes. The pars interarticularis (pars) lies between the superior and inferior articular process bilaterally at each vertebral level. Anatomically, one can describe the pars as the region between two, one superior and one inferior, zygapophyseal joints. The definition of pars interarticularis defect is a unilateral or bilateral overuse or fatigue stress fracture involving the pars interarticularis of the posterior vertebral arch. This injury occurs almost exclusively in the lower lumbar region, most often at L5 . Though history can be suggestive, especially in the case of young athletes involved in higher-risk sport (see below), diagnosis is made radiographically by the presence of fracture through the pars interarticularis. In cases of bilateral pars interarticularis defects, there is the potential for anterior or posterior spondylolisthesis (the slipping of one vertebral body relative to the adjacent segment). Spondylolisthesis can be graded based upon the percent degree of displacement of one vertebral body compared to the other. Grading of spondylolisthesis is included below in “staging.”

Two common clinical presentations of a pars defect include the imaging of an asymptomatic adolescent or adult in whom there is the incidental discovery of a pars defect. The second common presentation is an adolescent athlete involved in a sport requiring repetitive lumbar loading in extension and rotation, presenting with acute or insidious onset low back pain that is aggravated by continued lumbar loading. Although this history is typical, there is a broad differential diagnosis that might explain these symptoms. As such, the diagnosis of a pars interarticularis defect confirmation is only with radiographic support. Depending on the time of presentation and degree of injury, most cases of pars defects respond well to conservative treatment and relative rest from sport.