“…Conversely, Bradley and Dandy [3] reported an incidence of 1.2% based on an analysis of OCD lesions seen on the femoral condyles during 5000 knee arthroscopies, and Marsden and Wiernik found an incidence of 4% in all knee radiographs reviewed from 18,405 radiographs of male patients in a military hospital. To our knowledge, no previous studies have formally assessed the incidence of OCD in relatives of patients who had previously been treated for OCD of the knee, although some reports have described case series of lesions among twins [5,9,15,17,19,21] and families with genetic syndromes [1,24]. In each of these reports, including ours, the incidence among family members was higher than expected based on the incidence of OCD in the general population, suggesting an underlying genetic component to disease development.…”