A 15-year-old female gymnast presents to the clinic with a 4-month history of localized low back pain. She notes that the pain is exacerbated by back extension during her routines and improves with rest. She denies any radiation of pain down her legs or changes in bowel or bladder function. Past medical history is negative. On physical examination, there is an exaggerated lumbar lordosis and a palpable step-off at the lumbosacral junction. Hamstring tension is noted bilaterally. Neurological examination is unremarkable. Lateral radiographs of the lumbar spine demonstrate that the L5 vertebral body has shifted anteriorly relative to the S1segment by approximately 30%.
Which of the following is the most likely underlying cause of this patient’s condition?
The correct answer is:
C) Fracture of the pars interarticularis
This patient has spondylolisthesis, specifically the isthmic type, which is common in adolescent athletes who perform repetitive back extension (e.g., gymnasts, football linemen). Spondylolisthesis refers to the anterior displacement of one vertebra over another (in this case, L5 over S1). It is most commonly caused by spondylolysis, which is a stress fracture or defect in the pars interarticularis. When this defect is bilateral, the vertebral body can slip forward. The palpable "step-off" and hamstring tightness are classic physical exam findings.
Answer choice A: Congenital malformation of the sacral facets, is incorrect. While dysplastic spondylolisthesis exists due to congenital abnormalities, it is much less common than the isthmic type seen in athletic adolescents.
Answer choice B: Degenerative changes of the facet joints, is incorrect. Degenerative spondylolisthesis typically occurs in older adults (usually >50 years old) due to long-standing osteoarthritis and remodeling of the facet joints, most commonly at the L4−L5 level.
Answer choice D: Herniation of the nucleus pulposus, is incorrect. A herniated disc typically presents with radiculopathy and positive straight-leg raise tests. It does not cause the bony step-off or anterior vertebral displacement seen on imaging in spondylolisthesis.
Answer choice E: Metastatic infiltration of the vertebral body, is incorrect. Pathologic spondylolisthesis can occur due to malignancy weakening the bone, but this would be highly unusual in a 15-year-old gymnast and would typically be accompanied by systemic symptoms like weight loss or night pain.
Key Learning Point
Spondylolisthesis is the forward slippage of a vertebral body, most commonly occurring at L5−S1. In adolescents, it is usually a progression of spondylolysis, which is a defect in the pars interarticularis. Clinical clues include localized back pain with extension, hamstring tightness, and a palpable step-off on examination.
