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Background
The most common causes of back pain in adolescents and young adults are muscle strain or disc herniation. The purpose of this exhibit is to highlight important but less common causes of back pain in young adults: ring apophysis fractures, Scheuermann disease, overuse/stress injuries, and inflammatory spondyloarthropathies. Pregnant patients are a special case where back pain can be difficult to diagnose and is often be misattributed to physiologic changes.

Educational Goals / Teaching Points
Understand development of the vertebral body and role of ring apophysis. Distinguish between normal variants and findings of acute or chronic injuries to the spine and ring apophysis. Review causes of back pain in the adolescent and young adult beyond disc herniation. Understand mechanisms, types, and outcomes of vertebral stress injuries. Understand utility of magnetic resonance (MR) versus computed tomography (CT) in diagnosis of stress injuries, including MRI sequences beyond those typically used in standard lumbar MR protocols. Review pathophysiology and imaging appearance of changes and conditions associated with pregnancy/postpartum states and inflammatory arthropathies.

Key Anatomic/Physiologic Issues and Imaging Findings/Techniques
Prior to fusion of the ring apophysis with the vertebral body, a posterior ring apophysis fracture (PRAF) may cause narrowing of the spinal canal. This injury can be overlooked on MRI because the bone fragment mimics disc material. Unlike disc herniation, which is often treated conservatively, PRAF usually requires surgical removal of the displaced fragment. Limbus vertebra, in contrast, is an asymptomatic abnormality related to the ring apophysis. Scheuermann disease is a condition characterized by increased kyphosis of the thoracic spine. Although the deformity develops around the age of puberty, patients often do not develop symptoms until the 3rd or 4th decade. Pars and pedicular stress fractures are common in young athletes with low back pain. Radiographic recognition of these chronic injuries can be challenging, but is imperative to promote healing and reduce risk of re-injury. Newer MR sequences can help improve detection and assessment; CT can be more definitive to assess for discrete fracture lines in some cases. Inflammatory spondyloarthropathies include ankylosing spondylitis, psoriatic arthritis, and reactive arthritis. Spondyloarthropathy may occur in up to 53% of patients with IBD. Early diagnosis is possible with MRI. Hormonal and physical changes in pregnancy predispose patients to musculoskeletal problems. Low back pain and pelvic pain are the most reported issues. Misattribution of pain to pregnancy-related changes may lead to underdiagnosis of more severe causes of back pain, such as stress fractures and disc herniation/degeneration.

Conclusion
Awareness of less common causes of back pain and their imaging appearance in young patients, including pregnant patients, will decrease the risk of missed diagnosis.