Introduction
The patella or knee cap, is a small bone buried in the tendon of the extensor muscles of the thigh. The patella rests just above and in front of the knee joint in the distal femoral trochlear groove of the femur.
The primary functional role of the patella is knee extension. It acts as a fulcrum during normal extension of the knee joint.
What is Patellar Luxation?
Patellar luxation is a common orthopedic problem in dogs, and occasionally seen in cats. It is a condition in which the patella or knee cap dislocates or moves out of the normal location. The knee cap glides outside the femoral groove when the knee is flexed. The consequence of this is the inability to properly extend the knee joint. Lameness, varying degrees of pain and osteoarthritis are all associated with this condition. Patella luxation affects both knees in half of all cases, potentially resulting in discomfort and loss of function.
Patellar luxation can be further characterized as medial (more common), lateral (less common) or bidirectional dislocation, depending on whether the knee cap glides on the inner or the outer aspect of the femoral groove.
How can I tell if my pet has Patella Luxation?
Patellar luxation is one of the most common causes of lameness in dogs. It is more common in smaller dogs, although dogs of all sizes can be affected. The vast majority of luxations are medial and diagnosed in small breed dogs.
A characteristic “skipping” lameness is often present with this condition. Typically dogs with Patellar luxations have an intermittent non-weight bearing lameness. They will appear normal most of the time, but become completely non-weight bearing when the knee cap is luxated intermittently. Those with patellar mechanical deficiencies in both knees will have a stiff, awkward gait with knees that do not extend properly. An occasional popping sound could be heard in the knee and, an instability of the knee can also be felt on palpation of the back leg.
Medial Patellar luxations are associated with a “bow-legged” confirmation, while lateral patellar luxations are associated with “knock-Kneed” posture”.
The age of onset of clinical signs are variable.
Most animals start to show signs as puppies or young adults, as the condition progresses, although it is also common that onset of signs are shown in more mature dogs.
What is the cause of patellar luxation?
Many toy or small breed dogs have a genetic predisposition for a luxating patella. The precise cause remains unclear in the majority of dogs, but is likely multifactorial. It seems to be primarily of genetic cause and is the consequence of selective breeding of dogs with a bow legged conformation. Early diagnosis of bilateral luxating patellas in the absence of trauma and breed disposition, supports the concept that patellar luxation results from a congenital or developmental malalignment of the entire quadriceps mechanism. Therefore, developmental luxating patellas are no longer considered an isolated disease of the knee, but rather a consequence of complex skeletal abnormalities that affect the entire alignment of the hind limb.
These include:
· Hip dysplasia, abnormal conformation of the hip joint
· Malformation of the femur or tibia
· Shallow Trochlear groove
· Deviation of the tibial crest, onto which the patella ligament attaches
· Atrophy or tightness of the quadriceps muscles, acting as a bowstring
· A long patellar ligament.
The longer the patella spends outside of the groove, the shallower the groove becomes.
As the patella moves in and out of the groove, it can wear holes in the cartilage of the patella itself and in the ridge that it rides over when it luxates. This causes pain and triggers a cascade of progressive osteoarthritis. Other structures within the knee such as the cranial cruciate ligament, may also be affected, when the abnormal pull of the quadriceps causes internal rotation of the tibia relative to the femur.
Patellar luxation occasionally results from a traumatic injury to the knee, thus causing sudden severe lameness of the affected hind limb.
Diagnosis
The diagnosis of a patellar luxation is essentially based on the palpation of an unstable knee cap on orthopedic examination.
During routine health checks, patellar luxations are usually picked up by your primary care vet, or upon highlighting clinical symptoms such as an abnormal gait or skipping, to your vet.
Upon finding a luxating patella, your primary care vet will advise a clinical assessment by our specialist orthopedic surgeon.
Furthermore, additional tests may be required to diagnose and confirm a patella luxation and also diagnose other conditions that may be associated with patella luxations, in order to advise the appropriate and correct treatment for your pet.
These may include:
· Sedation or general anesthetic in order to palpate and evaluate the knee and entire pet properly.
· Radiographs of the stifles, pelvis and spine
· Computed tomography (CT), to provide an image of the skeletal features of the entire hind quarter.
· Blood work and/or urine analysis as a precaution for anesthesia.
Treatment
Patellar luxations are categorized according to the Grade of luxation. Treatment is therefore decided accordingly.
These Grades are classified as follows:
· Grade 1
The Knee cap can be manipulated out of its groove, but returns to its normal position spontaneously and otherwise remains in the groove.
· Grade 2
The Knee cap glides out of its groove occasionally and can be replaced in its groove by manipulation. Is typically associated with skipping lameness when the knee cap moves.
· Grade 3
The Knee cap glides outside of its groove most of the time, but can be replaced in the groove via manipulation.
· Grade 4
The knee cap is permanently luxated and cannot be manually replaced inside the groove.
Patellar luxations that do not cause any symptoms should be closely monitored, but do not necessarily warrant surgical correction, especially in smaller dogs. If the episode of lameness is mild and infrequent, and the degree of osteoarthritis is mild, then non-surgical treatment is indicated.
Medical treatment commonly includes the use nonsteroidal anti-inflammatory drugs, with or without other analgesic drugs.
Physical rehabilitation therapy exercises are useful to strengthen the quadriceps mechanism.
Weight control is essential to limit any unnecessary stress on the limbs.
The same medical techniques are also important in the short-term management of dogs who are surgically treated, although the primary surgical goal is to minimize the requirement for long term exercise restrictions and medication.
Surgery is usually advised in cases with a Grade 2 and over. The primary aim of surgical treatment is to restore normal alignment of the quadriceps muscle relative to the entire limb, this may require reshaping of the bones and reconstruction of soft tissue.
One or several of the following Strategies may be required to correct patellar luxation.
· Tibial Tuberosity Transposition
The aim of this type of repair is to realign the insertion of the tendon spanning between the patella (knee cap) and the tibia (shin bone). The bone that this tendon is attached to is cut and attached in a more appropriate position.
· Femoral Varus Osteotomy
Correction of abnormally shaped femurs is sometimes necessary in animals with a severe bow in the femur. This surgery involves taking out a wedge of bone, correcting the deformity and repairing the femur using a plate and screws. Femoral varus is mostly performed on larger dogs and dogs with a higher grade of patellar luxation.
· Recession Sulcoplasty
When the groove that the patella normally glides within is to shallow, surgery can be performed to deepen the groove. Thus, enabling the knee cap to seat deeply in its natural position. This includes the removal of a block or wedge of cartilage and bone.
· Reconstruction Soft tissue
In most dogs with patellar luxation, the soft tissue on either side of the patella ligament is either too loose or too tight. Surgical reconstruction of the soft tissue is then performed accordingly.
Delaying any sort of treatment is never advised. In general if the condition is causing a clinical problem, the earlier it is addressed the better for the patient to eliminate any further damage to the affected structure or other structures.
What does post-operative care entail?
Each case is patient specific and post-operative care is dependent on the nature of the treatment and surgery option performed.
When a surgical procedure is performed to repair a luxating patellar, a soft padded support bandage is applied for a few days post operatively to assist in the reduction of swelling, decrease in pain and to prevent self-trauma.
Post-operative radiographs are taken to access adequate correction is performed.
Activity restriction is advised for 6-8 weeks. This usually involves cage rest at home.
Exercise should initially be limited to short, slow lead walks. A limited lead exercise programme will be supplied by the orthpaedic surgeon.
Physical rehabilitation exercises such as passive range of motion can accelerate recovery and limit muscle mass loss.
Professional physio therapy is also advised.
Radiographs should be obtained again at 6 weeks postoperatively to evaluate the progression of healing of the tibial crest transposition or corrective osteotomies.
Normal activity is then decided based on the findings.
Recurrence of knee cap instability is uncommon. Migration and breakage of surgical implants used and infections are an uncommon occurrence.
In Conclusion an early diagnosis is essential to prevent further development of the disease and severe secondary joint conditions.
At Craig View, we will supply you with a support team as well as further professional advice with regards to postoperative care and physiotherapy while always maintaining,
Compassion, Science and Perfection.
