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Course 2008
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Rectus Femoris Transposition for Medial Patellar Luxation By Barclay Slocum, DVM and Theresa Devine Slocum, MS Treatment of medial patellar luxation has traditionally used the following techniques: Trochlear chondroplasty or trochlear recession has been successfully employed to control medial luxation if the patient has a shallow trochlear sulcus. If this technique is utilized when the sulcus is initially deep enough, patellar luxation will recur. Lateral transposition of the tibial tubercle is successful in restoring leg alignment and patellar relocation, if the tubercle is medially located. If patella-tubercle alignment is initially normal, then the lateral transposition of the tubercle will cause internal rotation of the tibia with respect to the stifle. Postsurgically, the dog will be bowlegged. If the dog is bowlegged prior to surgery, lateralizing the tibial tubercle will accentuate this conformation. The lateral fabella-to-patella suture has been used to prevent medial patellar luxation. The success of this technique is limited to Grade I medial patellar luxations, or more advanced luxations which have several adjunct procedures performed. The common thread in failures of these three techniques is a bowlegged conformation of the patient, whether pre-existing or created by surgical intervention. When this conformation is present with a medially luxated patella, a rectus femoris transfer, alone or in conjunction with other techniques, will alleviate most luxations without an osteotomy. The rectus femoris is the primary alignment muscle of the quadriceps muscle group since its origin on the pelvis causes it to span two joints, the hip and the stifle. If the patient favors carriage of the hindlimb with external rotation at the hip, the line of force of the rectus femoris is between the pelvis, cranial to the acetabulum and tibial tubercle. This creates a medially directed luxating pull on the patella and is one cause for medial patellar luxation. The transfer of the rectus femoris origin to the cervical tubercle eliminates the effects of the hip rotation on the medial patellar luxation, which reduces the luxation problem from a two joint to a one joint problem. If the patient has a varus bowing to the distal femur in addition to external rotation at the hip, the transposition of the rectus femoris may be as far lateral as the third trochanter. A pitbull, bull terrier, bullmastiff or rottweiler are the most frequent breeds to have this conformation. The tibial causes of patellar luxation such as medial placement of the tibial tubercle, varus proximal tibia, or internal torsion of the tibia must be addressed separately.
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