The relationship between subacromial bursa thickness on ultrasound and shoulder pain in open water endurance swimmers over time

ObjectivesTo help clinicians understand the clinical relevance of subacromial bursa (SAB) thickness on ultrasound investigations in marathon swimmers.DesignA prospective, observational cohort study.MethodsTwenty two open-water marathon swimmers entered in a 19.7 km open-water event received comprehensive, bilateral, shoulder ultrasounds on three occasions: 4 months prior to the race, 2 weeks prior to the race and within 1 week after the race. The SAB thickness was measured in the longitudinal plane of supraspinatus, with other abnormailities also recorded. The swimmers completed questionnaires detailing presence and severity of shoulder pain, volume of swimming completed that week and their breathing pattern.ResultsSAB thickness increased with season progression: mean of 1.55 (± 0.68) 4 months prior to the race, 1.63 (± 0.68) 2 weeks prior to the race and 1.86 (± 0.69) 1 week after the race. SAB thickness is significantly (p = 0.05) correlated (β = 0.11) with kilometres swum in the pool in the preceding week. SAB thickness was not significantly correlated with pain when measured prior to the race. However, at 1 week post race, SAB thickness of shoulders with pain were significantly greater than those without pain, p-value = 0.032.ConclusionsSAB thickness increases with increasing swimming training. Commonly, this increase is not correlated to pain, suggestive of a painless adaptive process. The significant correlation between pain and SAB thickness soon after an exacerbating event suggests that painful acute SAB thickening is a different entity to chronic, painless adaptive SAB thickening. These two entities can only be differentiated by clinical history and examination.