Timing of Physical Therapy and Lumbar Muscle Atrophy in Adolescent Athletes With Spondylolysis

OBJECTIVE: To compare the change in the functional cross-sectional area (FCSA) of lumbar paraspinals (multifidus-primary; erector spinae-secondary) between participants prescribed rest before physical therapy (PT) and those starting PT immediately in adolescent athletes with active lumbar spondylolysis. DESIGN: Multicenter randomized controlled trial. SETTING: Two pediatric hospitals in the United States. PATIENTS: Fifty-three adolescent athletes (mean age 14.1 ± 1.5 years; 40% female) were randomized to immediate PT (n = 25) or rest before PT (n = 28). INTERVENTIONS: Immediate PT participants began within 1 week of diagnosis. Rest before PT participants delayed PT until their pain resolved with daily activities for 2 consecutive days. MAIN OUTCOME MEASURES: Change in FCSA of the lumbar multifidus (primary outcome) and erector spinae at the L4-L5 level, measured by magnetic resonance imaging at baseline and 3 months. RESULTS: The immediate PT group demonstrated significantly greater improvements in multifidus FCSA compared with the rest before PT group [7% increase vs 1.4% decrease; mean difference 8.4% (95% CI, 1.5-18.0); P = 0.03; partial η2 = 0.09]. Multifidus atrophy occurred in 50% of rest before PT group and only 20% of the immediate PT group. Time to PT initiation was associated with multifidus size at 3 months ( r = 0.41, P < 0.001). No significant change or between-group differences were observed in erector spinae FCSA ( P = 0.69). CONCLUSIONS: Immediate PT preserved and increased multifidus FCSA, while rest before PT was associated with higher rates of atrophy. Early rehabilitation may protect lumbar stabilizing musculature in adolescent athletes with spondylolysis, potentially reducing risk of recurrent or chronic low back pain.