The traumatic factor plays a prominent rôle in this condition. Two types of cases are noted: (1) the previously asymptomatic knee upon which has been imposed direct or indirect trauma, moderate or severe, and in which anatomical anomalies play little part; (2) the knee in which congenital or anatomical defects are prominent, with preexisting mid symptoms becoming aggravated by injury.

Associated injury to the intra-articular, capsular, and periarticular structures of the knee must be anticipated and adequately cared for at the same time as the plastic repair of the displaced patella, if complete relief is to be obtained and irremediable secondary changes are to be avoided.

Excellent results have been obtained in the main, irrespective of the type of operative manoeuver employed. The less satisfactory results do not reflect adversely, with consistency, on any one method.

The trend seems to favor the simpler extra-articular procedures which have proved so mechanically efficient, especially the medial and downward transplantation of the tibial tubercle, in whole, or in part as in the Goldthwait operation, and its attached patellar tendon, combining this, as may seem necessary, with medial capsulorrhaphy or a fasciaplasty of the Ober type.

However, the indications for the type of procedure or variation to be employed, depend entirely upon the nature of the individual case—whether it be of the congenital or of the pure traumatic type—and the associated pathological conditions present.

The Albee procedure is expressly indicated in those cases in which there is congenital deficiency of the lateral femoral condyle and the intercondylar sulcus.

An associated severe genu valgum must be corrected initially—for example, by supracondylar osteotomy—prior to any corrective measures on the patella itself. As in Case C. V., the osteotomy is combined with medial rotation of the lower fragment to bring the lateral femoral condyle e forward, a procedure devised by Graser.

A marked hiatus in the lateral capsule, following the patellar reduction, may require such a plastic repair as was performed by Dr. Mayer in his case.

Finally, severe associated tears of the medial patellar retinaculum and patellofemoral ligament, as in some traumatic cases, require coincident plastic repair. This underlying pathological process must be borne in mind in every acute traumatic case, even after successful closed reduction, and the danger of recurrent luxation must be anticipated. In the case where reduction is impossible, open correction is essential, and the tears should be repaired by several layers of interrupted mattress and continuous chromic catgut sutures. This was done in the case of one patient, F. C., aged twenty-five, not included in this series, who dislocated the right patella five days prior to reduction.