It has been observed that when treating bowlegged dogs (genu varum) with medial patellar luxation by the conventional methods, the result maybe an unacceptable degree of outward rotation of the stifle. In 1996 Barclay Slocum first described a technique for the supplementary treatment of individuals with marked genu varum, which involved transplantation of the origin of the rectus femoris muscle (RFMT). Details of the technique have now been published in the latest edition of Bojrab's textbook on Current Surgical Techniques 4th edition (1997).
The rectus femoris muscle, which is part of the quadriceps mechanism, originates on the shaft of the ilium, immediately cranial to the hip joint and makes up the craniomedial portion of the quadriceps muscle group. The remainder of the quadriceps muscle originates from the proximal femur. The insertion of the rectus muscle is on the medial aspect of the peri-patellar fascia. Dogs with a marked genu varum have a relative change in length of the rectus muscle, which leads to an increased medially directed force. This may contribute to luxation or subluxation of the patella.
Transplantation of the origin of the rectus to a position close to the insertion of the deep gluteal has been used in these individuals to redirect the forces within the quadriceps, thus preventing patellar luxation. It should be emphasized that this is a supplementary procedure and is combined with other procedures, such as tightening the lateral joint capsule, to insure a satisfactory outcome.
Surgical technique: The craniolateral approach to the hip is used. The gluteal muscles need to be retracted dorsally with a deep retractor (Langenbeck style). The origin of the rectus femoris muscle, which is from the ventral aspect of the ilium immediately cranial to the hip joint, can then be identified. There are two components to the origin, a tendinous part caudally and a muscular portion cranially. Careful blunt dissection is used to define the muscle's origin. A small (about 4mm) sharp osteotome is used to cut 3 sides of a rectangular block of bone dorsal, cranial and caudal to the origin of the rectus. The fourth medial cut is fractured. Once it is established that the muscle has been completely freed from the surrounding tissues, the block of bone with the muscle attached is then passed under the origin of the lateral vastus muscle. Care is needed to avoid trauma to the lateral circumflex artery and vein.
An area of bone close to the insertion of the deep gluteal muscle (cervical tubercle) is then prepared using a curette. The bone block is then secured using a loop of wire and a small K-wire. The distance that rectus femoris is transplanted laterally is determined by the severity of the genu varum. The wound is then closed routinely before the stifle is approached laterally and any additional procedures deemed necessary are performed.
Results: In the first series of cases RMFT was performed in eight dogs with 2 individuals having bilateral surgery, making a total of 10 procedures. The breeds affected were Queensland cattle dogs (2) and one each of the following breeds: Staffordshire Terrier, bull terrier cross, Labrador, German Shepherd, Rottweiler and a Rottweiler cross. Three dogs had previously had an unsuccessful operation on the stifle and 2 individuals had had successful conventional treatment of the opposite stifle. Additional procedures were performed in all stifles and included lateral femoral fascial imbrication (10), tibial crest transplantation (4), trochlear chondroplasty (3), and tibial plateau leveling (1). When followed-up by phone of the eight owners, 5 were completely satisfied with the results, one was satisfied and 2 were eventually pleased with the outcome although it took longer than they had anticipated.
Since then a number of other cases have had surgery and in most the medial patellar luxation has been successfully corrected by the addition of lateral fascial imbrication and trochlear chondroplasty, but without the need to perform tibial crest transplantation.
Complications: The most serious complication was a failure to correct the basic problem in one case. A reexamination of this case revealed the presence of significant tibial crest deviation that required correction. Intermittent subluxation persisted in one case, which resulted in a more prolonged recovery than anticipated. Pin migration occurred in one case, which caused trauma to the sciatic nerve and temporary neuropraxia. Follow-up radiographs in one case also revealed avulsion of the bone block from the wire suture.
Conclusions: RFMT is a useful additional surgical technique when treating medial patellar luxation in individuals with genu varum. Attention to detail is important if minor complications are to be avoided. It is important to recognise that, in order to achieve good results, all the causes of quadriceps displacement and patellar luxation should be addressed surgically. It should be emphasized that RFMT is a supplementary procedure, but in selected cases it continues to be used successfully when combined with a tightening the lateral joint capsule. By avoiding tibial crest transplantation in cases with marked genu varum the complication of excessive postoperative outward rotation of the stifle can be avoided.
References
1. Slocum B and Slocum TD. Rectus femoris transposition for medial patellar luxation. In: Bojrab MJ, ed. Current Techniques in Small Animal Surgery, 4th Edition. Baltimore: Williams and Wilkins, 1997: 1234-1237