Medial patellar luxation (MPL) in adult dogs is frequently seen in the toy breeds although MPL has recently been increased in large or giant breeds as well. The age, which luxation manifests, varies with each dog. For instance, MPL is obvious at the time of birth in some cases while MPL becomes apparent during growth period in other cases. Moreover, in a mild MPL case without surgical correction, minor traumatic injury may trigger concurrent anterior cruciate ligament rupture. Consequently, the motor function of the stifle joint will be significantly reduced.

The main objective of the treatment for MPL is to correct the alignment of the extensor unit that consists of quadriceps femoris-patella-patellar ligament in order to normalize the function of the unit. To achieve this, the following procedures should be carried out.

Soft tissue: The quadriceps femoris should be realigned in order to correct the imbalance of muscular tension between the vastus lateralis and the vastus medialis. Contracture and laxity of the articular capsule will be normalized through the procedure that gives appropriate tension and flexibility to the capsule.

Bone structure: Skeletal hypoplasia includes shallow and flat femoral trochlea with small patella, underdeveloped femoral condyle, and other deformed bone structure. Such abnormal conditions should be corrected dynamically. In addition to this, tibial crest transposition may be carried out for the purpose of realignment of the quadriceps femoris and tension modification of the patella ligament.

However, the pathology of MPL is varied and ranges from mild cases that rarely show luxation to severe cases with permanent luxation. A number of MPL cases initially develop in acute form and later become chronic. Orthopedic surgeons should not overlook the complication such as Legg-Calve-Perthes disease (avascular necrosis of femoral head), anterior cruciate ligament rupture, or other articular disorders, especially immune mediated arthritis.

Surgical treatment of MPL has been done combining various techniques based on the surgeons' preference and experience. Due to the absence of standard MPL surgical technique, a number of surgical failures have been observed. There were even some mild MPL cases that had been classified in Grade 2 before surgery, however, patients showed recurrent MPL following surgery. Most major surgical failures are caused through the surgeries when the veterinarians are less familiar with techniques, or they do not have enough knowledge about the disease regarding the pathological background and/or therapeutic method. The most common complication after MPL surgery is recurrent luxation and the second is inconformity of the trochlear structure such as the patella following excessive trochleoplasty, dislocation or inadequate fixation of the implanted trochlear bone grafts, and failed transposition of the tibial crest. Moreover, concurrent immune mediated arthritis, that causes uncontrollable synovitis and abnormal secretion of synovial fluid, is an important complication in postoperative therapy.

In line with the problems along with MPL surgical correction described above, our research group reviewed the failure cases treated with conventional methods and set guidelines for surgical indication. The conditions considered to be excluded from MPL surgery are neurological diseases in the hind limbs, the decreased flexion range of stifle joint (at most 30-degree) when extended manually, and immune mediated arthritis.

MPL surgical method is improved with the following revisions of the conventional techniques and the procedures. However, there is no difference in the basic concept between these techniques. The specific descriptions of improvement are as follows.

1.  Monofilament non-absorbable surgical suture has been recommended for closing the joint capsule. However, our groups have experienced the complications resulted from monofilament nonabsorbable surgical suture, which stimulated the joint or forming fistula. Therefore, our groups prefer using synthetic monofilament absorbable surgical suture, which can be expected to keep tensions longer.

2.  In severe cases, the development of muscles and increasing the range of joint motion could be attempted through passive extension and flexion exercise of the stifle joint before the surgeries. Accordingly, we conduct surgery after confirming the expansion of joint extension and improvement of gait. The exercise should be repeated 200 times both in the morning and in the evening, daily for two weeks.

3.  Amongst the composed muscles of quadriceps femoris, tension in the medial vastus should be relaxed and laxity of the lateral vastus should be normalized through the correction of the differences in muscular tension at the ends of both side muscles of parapatellar fibrocartilage.

4.  Thicken joint capsule to regain flexibility and elasticity of joint capsules.

5.   Accurate tibial crest fixation for correcting alignment of the quadriceps femoris and re-strain the relaxed patella ligament.

6.  Safe and accurate procedure of block recession trochleoplasty.

7.   Placement of a screw in the medial distal femur for preventing medial redisplacement of the quadriceps femoris, that causes medial patella luxation.

8.   Reconstruction of the trochlea by implanting bone/cartilage allografts in the cases with iatrogenic trochlear nonregeneration or necrosis.

Our groups have treated various MPL cases using the combination of advanced techniques. As a result, it is demonstrated that incidence of recurrent luxation and other complication was significantly reduced, and complicated multiple surgery cases were successfully performed. The improvement will be described during my presentation using slides and video.

References

1.  Slocum B, Devine T, and Boone E (1982) Wedge recession for treatment of recurrent luxation of the patella. Clin Orthop 164:48-51

2.  Singleton WB (1957) The diagnosis surgical treatment of some abnormal stifle condition in the dog. Vet Rec 69-70:1387

3.  Willhauer C, Vasseur P (1987) Clinical result of surgical correction of medial luxation of patella in dogs. Vet Surg 16:31

4.  Nagaoka K, Orima H (1995) A new surgical method of canine congenital patellar luxation. J Vet Med Sci 57:105-109