chapter 10: Patellar Dislocation
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.
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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