There are many factors involved in the aetiology of chondromalacia of the patella If possible, the appropriate operative procedure should be chosen for each patient, hence attempting to eliminate the cause of softening of the cartilage Increased pressure over the lateral facet, with or without reduced pressure over the medial facet of the patella, resulting from lateral positioning or tilting of the patella, the Wiberg/Baumgartl-types III and IV, and the 'Hunter's Hat' form are important causes.
With reduced pressure, the cartilage is inadequately stressed and consequently receives insufficient nourishment As the medial facet is particularly thick and has little contact with the femoral condyle, nutritional disturbance is almost a normal occurrence Longitudinal osteotomy of the patella has been found to improve the contact of the medial surface of the patella with the femoral condylar groove The analgesic effect of this surgical procedure may derive from the resultant reduction in subchondral interstitial pressure, presuming that the pain in chondromalacia patellae, like that of osteoarthritis, is a manifestation of raised intramedullary pressure To ensure an improvement in patellar tracking the osteotomy is combined with a lateral capsular release.