The aim of this prospective study was to determine the prevalence of bone marrow oedema (BME) in asymptomatic knees of athletes and to investigate the factors associated with appearance of BME in this group.

A total of 25 asymptomatic athletes who competed at an international, national or county level during their most recent sport season were recruited in this study and had MRI scan of both knees (n=50). MRI scans were reported independently by two experienced musculoskeletal radiologists. Statistical analysis included Cohen's kappa test to identify inter-observer agreement for MRI diagnosis of bone marrow oedema and multiple logistic regression model to identify the factors associated with BME on MRI scan.

There was very good agreement between radiologists for diagnosis of BME (Kappa = 0.896). Seven participants (28%) were found to have BME. Six of the participants had BME in unilateral knees and one participant had BME in bilateral knees. The commonest location of BME was medial femoral condyle (62.5%) The amount of time spent in preseason training (34-38 weeks) was significantly associated with appearance of BME (P=0.048)

BME seems to be common in asymptomatic athletes and one should realize that this finding might not be related to the clinical complaints of the patients. The results of the present study show that there is a training effect associated with BME. Knowing what is a ‘normal’ or ‘abnormal’ scan is important for a competitive athlete, as erroneously diagnosing BME as the underlying cause of athletes' symptoms could lead to decreased playing time or inappropriate therapy.