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chapter 10: Patellar Dislocation

Etiology

CONGENITAL FORM

The cause of this form of patellar dislocation may be an anomalous insertion of fibrous tissue into the lateral patella. In some patients, there is an abnormal band from the fas­cia lata to the patella (17, 63). In other patients, an abnormal fibrous band appears to arise from the vastus lateralis (64), which consists of a tendinous condensation insert­ing into the superolateral border of the patella. In either situation, the result is the same. The patella is drawn to the lateral side of the knee with the initiation of flexion.

ACQUIRED FORM

Hnevkovsky (65) awakened interest in progressive fibrosis of the quadriceps with his report of 12 cases in 1961. None of these were reported to involve patellar dislocation. However, since then, many more cases of progressive quadriceps fibrosis have been re­ported (58, 64‑67). Twenty‑eight of these cases involved permanent dislocation of the patella.

Some authors believe that quadriceps fibrosis is of congenital dysplastic origin sim­ilar to clubfoot, arthrogryposis, or congenital torticollis (8, 45, 67). However, in most cases one can obtain a history of multiple intramuscular injections (65, 66, 68, 69) into the thigh in infancy. This appears to have provoked a fibrous reaction that then be­comes progressively manifest as the femur increases in length out of proportion to the fibrotic muscle. Whatever the origin, only the vastus lateralis, intermedius, and rarely the rectus femoris have been reported to be involved. The tethering then inevitably pro­duces a lateral vector. Where the medial tissues hold, a progressive limitation of flex­ion occurs. When the medial soft‑tissue structures give way, permanent dislocation of the patella results.

 

 

 

 

 

        

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