The Journal of Bone and Joint Surgery FURTHER STUDIES ON THE ETIOLOGY OF

Chondromalacia of the patellae has been described as “ a degenerative process of the articular cartilage of the patella of traumatic origin, characterised by fibrillation. fissuring and erosion “ (Smillie 1962). Budinger (1906) is credited with the first description of this lesion. De Palma, in 1954, typified the current widespread opinion of the etiology of this condition: “ It is generally conceded that repeated minor trauma or acute severe trauma are the etiological factors responsible for chondromalacia of the patella in the majority of cases.” I do not accept this theory, and in a previous paper (Outerbridge 1961) I presented a new concept to explain the etiology of chondromalacia patellae. The common occurrence of the condition and its tendency to begin on the medial patellar facet were pointed out. I had observed that in most human knees there is a ridge of varying height which crosses the medial femoral condyle at its osteochondral junction, and I suggested that patellar chondromalacia is caused, at least in part, by friction against the cartilage of the medial patellar facet as the patella rides over this ridge in the normal movement of the knee. It was conceded, however, that other factors such as age, sex, weight, height, occupation and power of the quadriceps mechanism might contribute to variations in the pathological picture. The length of th