Pars Defect at L5: Diagnosis and Management

Introduction to Pars Defects

A pars defect at L5 is a stress fracture or break in the pars interarticularis, most commonly caused by repetitive hyperextension and rotational forces, particularly in young athletes 1, 2, 3

Initial imaging should include anteroposterior and lateral radiographs of the lumbar spine, with oblique views added to better visualize pars interarticularis defects 1, 2, 3
Standard radiography has low sensitivity for detecting spondylolysis in the absence of spondylolisthesis, particularly for non-displaced fractures 1
Oblique radiographic views are particularly useful for visualizing pars defects, showing the classic "Scotty dog" appearance with a collar or break in the dog's neck representing the defect 1, 2, 3

MRI without contrast is the preferred next step if radiographs are negative but clinical suspicion remains high, as it detects stress injuries involving the pars interarticularis without complete lysis and identifies vertebral marrow edema 1, 2, 3
CT has increased sensitivity for detecting non-displaced fractures and established spondylolysis compared to conventional radiography, and is complementary to MRI for higher specificity 1, 2
CT is particularly useful for follow-up imaging to assess healing of known pars defects after treatment 1, 2
SPECT bone scanning can detect early stress injuries before fracture completion 4

Chronic low back pain is the hallmark symptom, particularly in young athletes and weightlifters who engage in repetitive hyperextension activities 2, 3
The pain is typically mechanical in nature, worsening with activity and improving with rest 1, 2
Do not assume all back pain in young athletes is muscular—maintain high suspicion for pars defects in adolescents with mechanical low back pain, especially those involved in gymnastics, football, weightlifting, or other hyperextension sports 2, 3
Standard AP and lateral radiographs alone may miss pars defects—oblique views significantly improve detection rates 1, 2, 3