Patella Luxation
Patellar luxation is when the patella, or knee cap, moves out of it’s normal track on the femur (the thigh bone). Patella luxation may be traumatic in origin, but most commonly is due to deformities or malalignment of the femur and tibia (shin bone). Patella luxation can occur medially or laterally. Medial refers to the patella moving in toward the midline of the body and lateral refers to the patella moving out toward the outside of the body. Medial luxation is more common than lateral luxation because the trochlea (the groove in the femur that the patella tracks in) is lower on the medial aspect. Small dogs are more prone to luxation than larger dogs and 50% of cases are bilateral (in both knees).
Patellar luxation is graded I-IV as follows:
Grade I: The patella is in the track, but can be moved out with some force, usually it’s an incidental finding.
Grade II: The patella is in the track, but moves out with activity. Usually it is noticed because the dog “skips” when the patella luxates.
Grade III: The patella is usually off the track, but can be put back in place manually. Often associated with bony abnormalities/bow legged gait. Lameness may be present or even severe.
Grade IV: The patella is off the track and stays out, cannot be reduced manually. There is usually significant bony abnormalities and the dog may become non weight bearing on the limb.
How is patellar luxation diagnosed?
Gait: intermittent hopping/skipping on the limb, and they may be noted to kick that limb out. If they are non weight bearing or have a sudden exacerbation of lameness they may also have a cranial cruciate ligament rupture (see previous blog post) as medial patella luxation predisposes dogs to cruciate rupture.
Reluctance to jump
Posture: with medial patellar luxation, dogs often become bow legged, with lateral patellar luxation, dogs often become “cow hocked” or “knock kneed”. They have excessive hip and stifle (knee) flexion (bending), and lumbar kyphosis (rounded lower back).
Strength: weak thigh musculature with atrophy of the muscles
Range of motion: limited hip extension
Flexibility: tight muscles in the hip/leg (sartorius, medial hamstrings, quadriceps, adductors, and iliopsoas)
Palpation: your veterinarian can perform certain tests to feel for the luxation of the patella
X-rays or CT scan may be recommended to assess for degeneration of the joint and evaluate for surgical planning
TREATMENT:
Grades I-II patellar luxation can be treated non surgically, Grade III luxation could be treated conservatively if there are not bony abnormalities present, but most benefit from surgical intervention and then PT. Grade IV luxation requires surgical intervention.
SURGERY:
Surgery usually involves reconstruction of both the soft tissues and bone. The tibial crest (an outcropping of bone on the front of the tibia) is often transposed and pinned to realign the quadriceps so it is line with the bones and can work properly. Trochleoplasty to deepen the trochlear groove is performed if the trochlear groove is too shallow so the patella remains within the track. A femoral osteotomy may be performed if there is severe deformity of the femur to attempt to straighten the femur.
There is a great video demonstrating medial patellar luxation and surgical correction here
The physical therapy treatment focus for medial patellar luxation is on stretching the medial soft tissues and strengthening the lateral musculature to re-direct the pull on the patella. The goals are to decrease pain, increase flexibility of the medial soft tissues, increase the strength of the lateral thigh musculature, and normalize the gait and posture. This can be a lengthy process if the muscles are severely atrophied because it takes several months to build the muscle strength back up, so being diligent about the home exercise program is essential to success.
See today’s Facebook post for a case study on Sophie.
References:
Millis, Darryl L. & Levine, David. (2014). Canine Rehabilitation and Physical Therapy (2nd edition), Elsevier
Zink, Chris & Van Dyke, Janet B. (2018). Canine Sports Medicine and Rehabilitation (2nd edition), WILEY Blackwell
Animal Orthopedics Explained (2020 September 12), Medial Patella Luxation, https://www.youtube.com/watch?v=6C1UYv5IGt8
Up next week: IVDD (intervertebral disc disease)