Patella luxation (PL) is a common orthopaedic disease in dogs and it also occurs in cats.

The patella can move in both directions – medial patella luxation (MPL) where the “knee cap” slips inwardly and lateral patella luxation (LPL) – where the patella slips outward.

Patella luxation is mostly a congenital or developmental disease. Rarely is it caused by a trauma. It may occur at birth, during the growth stage or later in life. The condition is typically observed in small breed dogs younger than 3 years. Breeds which are commonly affected are Miniature and Toy Poodles, Cavalier King Charles Spaniels, Yorkshire Terriers, Chihuahuas, and Griffons. Small mixed breed dogs are also affected.

The condition can be unilateral or bilateral (one or both legs). The severity of the luxation can vary from the dog being asymptomatic or showing only mild lameness intermittently. However, when luxation is present at birth, the dog typically has a grade III and IV condition which is associated with skeletal deformities. In these cases, the dog may be unable to walk. In young puppies, surgical corrections are recommended and performed at 1 – 3 months of age.

As the dog ages, patella luxation degenerates the articular cartilage of the knee joint. Maintaining an adequate supply of articular cartilage requires normal joint junction between the femoral trochlea and patella. Articular cartilage damage leads to osteoarthritis.

Dogs with PL are also prone to rupturing the cranial cruciate ligament due to joint instability.

Anatomy of dog’s patella

The patella is an oval shaped sesamoid bone on the quadriceps tendon. It is connected to the fabella by the medial and lateral patellofemoral ligament.

The patella is the lever arm favouring the extension of the quadriceps. The patellofemoral joint increases the mechanical efficiency of the quadriceps mechanism which flexes and extends the hip and stifle joint to propel the dog forward.

When the quadriceps femoris, patella, trochlea, patella ligament and tibial tuberosity are correctly aligned, then patella luxation or subluxation does not occur. However, when there is misalignment, the patella is able to slip or rotate.

4 grades of patella dislocation in dogs

• Grade I – The animal rarely shows lameness and carries the limb occasionally. The patella can be manually luxated when the stifle is extended but returns to the trochlea when released. No crepitation is apparent.

• Grade II – Luxation occurs more frequently. Lameness is intermittent and mild. Patella moves easily when the foot is rotated and the patella is pushed. The injuries from constant friction between the patella and femoral condyle result in crepitation and discomfort.

• Grade III – The patella is permanently luxated with the torsion of the tibia and deviation of the tibial crest between 30 – 60 degrees. Despite the permanent luxation, the animal can use the limb with the stifle held in a semi-flexed position.

• Grade IV – The patella is permanently luxated but not possible to reposition it. The limb may be carried if unilateral or the animal moves in a crouched position with the limbs partially flexed or carried.

Signs of patella luxation in dogs

In severe cases of patella luxation (III and IV) severe angular and rotational deformities of the femur and tibia are seen, with the limb taking on an S-shaped conformation. In these cases, surgery restores the normal alignment of the quadriceps.

Dogs with medial patella luxation results in a “bow legged” appearance while lateral patella luxation may have a knock-kneed appearance, particularly when the luxation is bilateral.

In less severe cases, owners may observe mild clinical symptoms. The dog may show intermittent lameness which is not associated with pain or discomfort. When the dog moves, they may flex the stifle abruptly and then bring it back to normal position after a flick of the limb.

In older animals with grade I or II luxation, lameness may worsen due to degeneration in the joint or a possible rupture of the crucial ligament.

Treatments for dogs with patella luxation

Surgery for canine patella luxation

Surgical treatment for dogs that are asymptomatic is not considered necessary. However, it is recommended for young puppies with skeletal deformities. The goal of surgery is to realign the extensor apparatus to restore normal stifle biomechanics and stabilise the femoropatella joint.

There are two types of surgical procedures – soft tissue reconstruction and bone reconstruction. They include the following:

• Deepening femoral trochlea (trochleoplasty)

• Tibial tuberosity transposition

• Medial soft tissue release on the luxation side

• Lateral soft tissue tightening on the other side than that of the luxation

• Transplant the origin of the rectus femoris muscle

• Corrective osteotomy including shorten the femur to reduce luxation

The success of surgery is supported by post-operative measures including physical therapy which aims to prevent post-operative complications and favour early recovery of muscle mass and function of the limb.

Conservative treatment for patella luxation

For dogs with asymptomatic or mild lameness, conservative treatment choices are recommended. The objective of conservative treatment is to strengthen and reinforce the quadriceps femoris muscles. Dogs treated conservatively have a good prognosis although there is the risk of developing degenerative lesions associated with osteoarthritis and cranial cruciate ligament rupture. Conservative treatment programmes should consider this risk and address is appropriately.

A study investigated the association of patella lesions with the animal’s age, body weight and degree of luxation. The study made observations about cartilage erosion, the extent of erosion, morphology of patella (concave or flat), exposure of subchondral bone, and presence of enthesophytes which are abnormal projections on the bone at the attachment of a tendon or ligament which is caused by stress.

The study found a high incidence of patella lesions particularly in grade II and III luxations. These animals exhibited intermittent and persistent lameness but they continued to use the limb. The use of the limb leads to joint wear. This finding contrasts with dogs with grade IV luxations who do not bear weight on the affected limb but drag it or shift their weight forward.

Joint wear injuries are observed in animals where the quadriceps is misaligned allowing the kneecap to dislocate and brush against the lateral or medial condyle during limb movement. These injuries are more severe in dogs weighing more than 15 kg.

The frequency and severity of articular lesions is higher among animals weighing 15 kg or more due to greater load on the joint which causes biomechanical instability. Biomechanical stability is essential for adequate supply of blood to the articular cartilage in the stifle. Inadequate nutrition results in joint degeneration

Massage therapy for dogs with patella luxation

Massage therapy and remedial exercise can benefit dogs with mild patella luxation. The goal of therapy is to strengthen the quadriceps muscles and to maintain normal function of the stifle to slow the progression of degenerative joint disease.

Therapy may include the following:

• Massage – Relieve muscle tension and spasms caused by the dog shifting their weight, albeit only slightly in many cases, from the affected limb. Massage also stimulates the circulatory system to draw nutrients to the stifle to nourish the articular cartilage and remove waste from the joint. Finally, massage is effective is managing pain and discomfort associated with mild patella luxation.

• Passive range of motion – A therapist moving the dog’s limbs through their normal range of motion helps to realign the dog’s perception of the position of the affected limb’s muscles, tendons and fascia. Resetting the dog’s proprioception of the limb allows the dog to use the limb as normally as possible which reduces compensatory muscle strain. It also helps supply the cartilage with nutrients to prevent degeneration. In short, passive range of motion exercises maintains the joint’s movement and keeps the cartilage healthy.

• Remedial exercises – A remedial exercise programme aims to maintain muscle mass and strength in the affected limb. Exercises including weight shifting, hill walking, and sit to stand exercises may be effective.

Full Stride provides remedial massage and exercise therapy in Brisbane’s north. Please leave me a comment on how you manage your dog’s patella luxation.

Until next time, enjoy your dogs.

Sources:

Cleuza M.F. Rezende, Renato César Sachetto Tôrres, Anelise, Carvalho Nepomuceno, Juliana Soares Lara and Jessica Alejandra, Castro Varón (2016). Patella Luxation in Small Animals, Canine Medicine – Recent Topics and Advanced Research, Prof. Hussein Kaoud (Ed.), InTech, DOI: 10.5772/65764.

Di Dona, F., Della Valle, G., Balestriere, C., Lamagna, B., Meomartino, L., Napoleone, G., … & Fatone, G. (2016). Lateral patella luxation in nine small breed dogs. Open veterinary journal, 6(3), 255-258.

Tsompanidou, P., Prassinos, Ν. N., Sideri, Κ. Ι., Kazakos, G. M., & Tsimopoulos, G. (2013). Retrospective study of 95 dogs with patella luxation. Hellenic Journal of Companion Animal Medicine Volume, 2(2), 15.