1 . Current theories of the etiology of chondromalacia patellae do not explain satisfactorily either its great frequency or its common site of origin on the medial patellar facet.

2. The etiology can be more logically explained by the presence of a ridge on the upper anterior border of the cartilage of the medial femoral condyle, in most knees. This ridge, consisting of cartilage, or cartilage and bone, varies considerably in height and, in normal knee joint movement, causes considerable friction on the medial patellar facet.

3. The degenerative changes were found to be greater in the presence of the larger ridges, and–because of longer wear and tear–in the older patients.

4. This study indicates that chondromalacia was more severe in women than in men, and in patients overweight. Although the activity of the individual and the power of the quadriceps mechanism must play an extremely important part in this condition, it was not possible to assess this.

5. Two factors previously considered to be important in the etiology of this condition, namely, the length of the patellar tendon and Wiberg's Type III patellar shape, have not been confirmed in this study.

6. Resulting from the present investigation certain precautions are suggested in rehabilitation after operations on the knee, and a surgical method for discouraging the progress of this common, and sometimes disabling, condition has been devised.

1. Chondromalacia of the patella starts most frequently on the medial facet.

2. The anatomy of the medial femoral condyle is described, including the rim at its superior border, and the different arrangement at the upper border of the lateral femoral condyle.

3. Rubbing of the medial patellar facet on the rim at the upper border of the medial femoral condyle can explain in part the etiology of chondromalacia.