Mechanical factors and patellofemoral osteoarthrosis.

This paper investigates the possible role of mechanical stress in the development of the osteoarthrotic lesions frequently observed in the patellofemoral compartment of the knee joint. First the location of these destructive lesions was determined by studying the location and pattern of contact in the patellofemoral joint. The study was carried out on 39 cadaveric knees for the range of flexion 0 degrees -120 degrees. It was shown that the lesions were localised to the areas corresponding to the range of flexion 40 degrees -80 degrees. These areas have been shown to be subjected to a low stress for most of the time and to a much higher stress for only part of the time. This mode of stressing this area of the cartilage is a consequence of the style of life of the average Western man in which the most predominant activity is level walking, during which the load and in turn the stress are much lower than they are during other ambulatory activities such as ramp and stair ascent and descent. The same area of the cartilage seems to be subject to a similar mode of stress during sedentary occupations. It is suggested that this mode of stressing the cartilage conditions it chemically, and hence mechanically, to transmit low stresses, so that when the much less frequent but higher stresses are applied it cannot transmit them without sustaining some damage.