Recurrent Dislocation of the Patella
The subject of slipping or dislocated patella is one regarding which much has been written and it has been discussed on so many occasions that one almost feels that an apology should be offered for an attempt to add anything to what has been said already regarding this condition. However, there are still several controversial points, and it is felt that our personal experience may prove of interest.
Slipping patella is the result of an abnormal laxity of the supporting structures about the knee which permits the occasional displacement of the patella to the outer side of the external condyle of the femur. The underlying predisposing causes may be (1) acquired or traumatic, (2) structural or congenital. The true congenital dislocations are those in which the patella develops away from its normal position and are not considered in this communication.
Trauma may be the original cause of a dislocation of the patella. In such cases, following a severe injury which is accompanied by a rupture of the quadriceps muscle, expansion on the inner aspect of the patella causes the knee to remain insecure, especially on extension against resistance, as for example, in descending stairs. But by far the greater number of dislocations of the patella occur without any such injury and are associated with predisposing structural conditions. The first and most important of these is a genu valgum deformity in which the pull of the quadriceps tends to displace the patella outward. Other such structural conditions may be an underdevelopment. . .