Objective This 3 year retrospective observational study aims to determine the diagnoses causing medical downgrading in a high readiness Royal Marine Commando unit, and to direct future investment to reduce numbers downgraded.

Methods Medical and administrative records were used to ascertain diagnoses, aetiology, time downgraded, and whether men returned to full duties.

Results 4.4% of unit strength was lost through medical downgrading. 43% was due to soft tissue lower limb injuries, of which 41% was due to anterior knee pain syndrome. Low back pain accounts for 24% of the total. Median length of downgrading episodes was 3 months (range 1-40 months). Low back pain and lower limb soft tissue related episodes were longer (median 9 months p= 0.001, and 10 months p=0.003 respectively). Fractures (median 2 months p < 0.001) and general surgical problems (median 2 months p=0.013) were shorter than the overall mean. Orthopaedic conditions related to overuse had longer periods of downgrading (median 6 months) compared to trauma (median 3 months p = 0.01). 9.3% of completed episodes of downgrading resulted in a medical discharge and 1.9% in a permanently reduced medical category.

Conclusions Conditions that respond rapidly to secondary care interventions have shorter episodes of downgrading compared to overuse conditions. Therefore, prevention and improved rehabilitation facilities are likely to be more effective than further secondary care investment in reducing medical downgrading. More timely use of permanent medical downgrading and medical discharge could reduce temporary downgrading by 20%.