Spondylolysis / Pars Interarticularis Stress Fracture

Spondylolysis is a stress injury or fracture of the pars interarticularis, most often at L5, and a common identifiable cause of low back pain in adolescent athletes.

It is typical of sports that load the spine in extension and rotation. The injury runs from bone marrow oedema (a stress reaction) through an incomplete fracture to a complete defect, which may be unilateral or bilateral.

Most athletes do well with conservative care. Early and unilateral lesions heal most often; bilateral defects can lead to spondylolisthesis.

The pars interarticularis is the narrow bridge of bone between the superior and inferior articular processes. At L5 it is thin and takes high load during repeated lumbar extension and rotation. Around 85 to 95% of defects are at L5, with L4 a distant second.

The mechanism is usually repetitive loading rather than a single injury. Repeated hyperextension produces shear and compression at the pars: first a stress reaction, then an incomplete fracture, then a complete defect. Adolescents are particularly vulnerable while the pars is still maturing.

Bone health risk factors include:

• •Low energy availability and relative energy deficiency in sport (REDs), including menstrual dysfunction
• •Low vitamin D
• •A rapid rise in training load, poor sleep and recovery
• •A previous bone stress injury