Medial Patellar Luxation
Patella luxation occurs frequently in dogs and is present occasionally in the cat. The condition is either congenital or acquired, with most being congenital. The age at onset of clinical signs, progression of joint deterioration, and degree of lameness associated with patellar luxation are highly variable. Small breeds of dogs present almost exclusively with medial patellar luxation (MPL), with lateral patellar luxation (LPL) found primarily in the larger breed dogs; however, over 80% of the dogs which are medium, larger and giant breed dogs also have MPL. Therefore, MPL should be recognized as more common than LPL in all breed sizes. The reported frequency of bilateral luxation has a broad range from ~20%-65%, with bilateral disease recognized as the rule rather than the exception.
Limited well researched investigation of the cause of patellar luxation concluded there are skeletal changes or anatomic deformities in the pelvic (rear) limb causing a complex series of derangements that characterize medial patellar luxation in the small dog. Therefore it should be considered an inherited disease in these breeds and it is advisable to discourage breeding of these animals.
ARE THERE DIFFERENT DEGREES OR SEVERITIES SEEN IN PATIENTS WITH MEDIAL PATELLA LUXATION?
The degree and severity of luxation has been classified into four grades for purposes of discussing diagnosis, prognosis, and deciding on the method of surgical repair.
Grade I: Intermittent patellar luxation with manual dislocation of the patella on full extension of the knee and spontaneous reduction upon release. The patella clinically stays in the groove and usually only with manual force will it dislocate.
Grade II: Frequent patellar luxation with manual pressure or with flexion of the stifle. The patella is usually in the trochlear groove most of the time, but it can spontaneously dislocate upon flexion or weight bearing.
Grade III: Permanent luxation. Reduction is possible with manual pressure. The patella is dislocated most of the time but can be reduced with manual pressure.
Grade IV: Permanent luxation where manual reduction is not possible because the patella is fixed in a dislocated position due to anatomic deformity and scar tissue development.
In addition to the above mentioned classification, the severity of anatomic abnormalities of the pelvic limb is more pronounced as the luxation increases. Some of the anatomic abnormalities include changes in the femoral neck (anteversion, angle of inclination), bowed distal femur, shallow trochlear sulcus (groove), tilted joint from an underdeveloped medial condyle, torsion of the tibial crest and the entire tibia, medial bowing of the proximal tibia, and internal rotation of the foot.
WHAT CLINICAL SIGNS WILL I SEE?
Classically an owner either describes the dog carrying the leg, then tries to “shake it” and the dog suddenly returns to normal or a varying degree of persistent or intermittent lameness is seen. Palpation of the patella will allow for a diagnosis from your Veterinarian. Three groups of patients with patellar luxation have been defined: 1.) Neonates or older puppies that manifest severe musculoskeletal deformities and gait abnormalities, 2.) young, mature animals with intermittent progressive lameness, and 3.) older animals which present with acute onset of lameness associated with degenerative changes or progression of the degree of dislocation present. The grade of patellar luxation, severity of osteoarthritis present, duration of the problem and concurrent orthopedic problems such as a ruptured cranial cruciate ligament, all determine the severity of clinical signs seen. The outcome with surgery in all three groups of dogs is similar. It is important that a thorough orthopedic exam be performed to rule out other possible causes for the lameness present, even if the patella is luxating.
WHAT IS THE TREATMENT FOR THIS CONDITION?
There is disagreement about management of dogs that are asymptomatic. Some surgeons regard all MPL dogs are candidates because failure to restore normal stifle biomechanics may result in growth deformities when very young, osteoarthritis, and ruptured cruciate ligaments. Others suggest surgical repair be performed only when dogs are clinically lame because some dogs have lifelong patellar luxation without clinical signs. No good prospective studies with adequate controls for assessing nonsurgical versus surgical therapy are available. There is no dispute that surgery significantly improves the functional use of the limb in dogs with lameness from medial patellar luxation.
The literature states that 90% of the dogs undergoing surgery for correction of a patellar luxation will have no lameness but almost half will have some degree of recurrent luxation usually a Grade I in severity. Most surgeons feel that the degree of recurrence in their experience is not this high, rather much less (10%?), and they concur with 90% of the patients doing well. In a majority of the stifles, osteoarthritis will occur in the non repaired as well as the repaired stifle. Concurrent rupture of the cranial cruciate ligament is seen in 15-20% and it is not possible determine if patellar luxation increases the risk of cranial cruciate rupture, but most surgeons feel this is an added risk in patients with a MPL. We routinely will perform surgery on both knees at the same time if it is indicated. They recover well and this avoids two separate surgeries.
WHAT IS DR. WILLER’S RECOMMENDATION?
Over the years I have been asked by referring veterinarians on numerous occasions when to perform surgery. With the knowledge of what has been published in the literature, my interactions with other surgeons around the country, along with my personal experiences with patella luxation in all ages, breeds, severities, both acquired and congenital, I have developed conclusions and recommendations which have resulted in positive experiences.
I recommend surgery on any dog with clinical signs of lameness caused by luxation of the patella regardless of the grade of luxation. I recommend with few exceptions, repair of patella luxation in all dogs without clinical signs if the grade of luxation is Grade II, III, or IV. I do not recommend surgery on nonclinical Grade I patellar luxation as I feel these are the cases with occult disease long term. However, should clinical signs develop, or if the degree of luxation becomes a Grade II or more, surgery would be recommended. In my experiences, most Grade II, III, and IV patella luxations progress with clinical signs over the years. Perhaps this is why we perform surgeries on many older dogs with MPL.
WHAT ARE THE SUCCESS RATES IN YOUR EXPERIENCE?
We should expect a 90% chance of a good to excellent result long term with surgery on Grade I-III MPL. I feel that the prognosis for Grade IV patellar luxation with severe bone deformities is guarded to poor, but we have had many successes with surgery also, therefore the attempt to improve upon the degree of lameness should be considered. Repeat surgery to correct a recurrence of patellar luxation is not common in my experiences, perhaps 1-2 modification surgeries per 50 cases.
WHAT IS INVOLVED WITH SURGERY?
The type of surgery performed depends on the severity of the anatomic abnormalities present. Textbooks give guidelines for what may be required; however, experience and decision making at the time of surgery will give reproducible and repeatable results. A combination of imbrication techniques on the soft tissues, deepening the groove (wedge trochleoplasty), tibial crest transposition, antirotational sutures, release incisions, extent of the release incisions, patellar stabilization sutures, and concurrent repairs of the ruptured cranial cruciate ligament may be necessary depending on the severity of the problem. I feel like there is an art to this surgery to achieve consistent and successful outcomes. In my experience, all of the patients require some improvement in the bone alignment so a tibial crest transposition is commonly part of my repair. I currently do not perform any rectus femoris muscle transpositions at the level of the hip joint. If it is a Grade IV, corrective osteotomies (cutting the bone) may be necessary. If the patient has bilateral patellar problems whereby surgery is indicated, we commonly perform surgery on both knees at the same time. In fact, I recommend this in most all cases with the exception of the very severe Grade IV where we may stage them apart.
In more recent years we have performed corrective femoral osteotomies and placement of a bone plate in larger dogs with patella luxations when the curvature of the femur is greater than approximately 13-16 degrees. When dogs have severe bowleggedness and curvature of the femur, just transposing the tibial crest may not be adequate, therefore an osteotomy is indicated to improve the alignment. Lastly, there are innovative techniques on the horizon that may become more popular. One such technique is the use of prosthetic trochlear grooves which are anchored on the femur replacing the severely arthritic and worn off trochlear ridges thus providing a prosthetic groove with the ability to correct alignment as well.
WHAT ARE THE AFTERCARE REQUIREMENTS WHEN I TAKE MY PET HOME?
The patients should be allowed early active use of the limb. Bandage or splinting is usually not recommended. Prevention of jumping, running, multiple stairs, and off leash activity is required for the first 6-8 weeks. House activity is fine, but on a leash when outside to eliminate. Some patients may need more involved physical therapy and consultation with a physical therapist should be considered. Pets that have undergone bilateral surgery may actually try to support weight on their front legs in the early postoperative period. Very shortly they become more comfortable and start using their legs. With surgery and adequate post operative care we can expect good results and return to full activity at approximately 3 months. Please read an example take home instruction sheet below.
EXAMPLE OF POST OPERATIVE TAKE HOME INSTRUCTION SHEET:
Limit activity to no running, jumping, rough play, or multiple stairs for 6-8 weeks to allow for the crest to heal, and the tissues to strengthen. After this time frame gradual return to normal activity with longer walks over a 3-4 week transition is allowed. Consequently, at approximately 12 weeks, return to full activity is acceptable. 5-10 minute leash walks to eliminate and stroll around 2-3 times a day during the first 6-8 weeks is allowed. Walking in the house is okay too. Placing the leg to the ground at the slow walk by stitch removal should be noted, sometimes sooner and then we should see continued gradual improvement with the use of the leg. 85-90% of these patients will have an acceptable good functional weight bearing result. Risks include recurrence of luxation of the patella and infection, but this is less than 5% in my experience.
Send home with Antibiotics for about 7 days, (cephalexin), and pain management (rimadyl, tramadol, other).
Recheck at staple/stitch removal in 10-14 days, then recheck one month or so later as a final recheck.