Patella luxation refers to the small bone (knee cap) which sits at the front of the knee joint and allows the muscles to extend the knee and lower part of the leg. In some dogs there are anatomical abnormalities which allow the knee cap to luxate or 'pop-out' of its normal groove. This causes pain and discomfort for the patient as the knee cap rubs on areas of the joint which are not covered with articulating cartilage, causing inflammation and the progression of osteoarthritis. As the disease progresses the cartilage becomes worn away and the knee cap rubs against the exposed bone causing additional pain.
Medial patella luxation generally presents in smaller breed dogs, at any age, although younger patients are most commonly presented. The condition is usually observed as an intermittent skip or even a persistant limp in one or both back legs.
The knee cap generally displaces medially (inwards) due to the abnormal alignment of the shin bone, patella tendon, knee cap and thigh bone. The groove which the knee cap sits in is often too shallow. The aim of surgery is to correct the alignment of the knee cap so that it is positioned within the groove and articulates on the normal cartilage where it should be.
Surgical correction should address the underlying factors for the condition. The main procedure for correction in the majority of cases is a tibial tuberosity transposition, which involves moving the bone and patella tendon which the knee cap attaches to. This involves cutting the bone, moving it laterally (outwards) and fixing it in position with wires. This small portion of bone then needs time to heal, usually 6-8 weeks, before returning to more normal activity. The other procedures used to correct the position of the knee cap are trochleoplasty (increasing the depth of the groove that the knee cap sits in), and soft tissue reconstruction (adjusting the tension of the soft tissues), to make it more difficult for the knee cap to pop out.
Outcomes following surgery are good, but are dependent upon the degree of damage to the joint at the time of surgery, with most patients expected to return to normal function and also delaying the inevitable progression of osteoarthritis.
Complications rates are low, with the most common complications being infection, usually less than 5%. Treatment usually only requires antibiotics in addition to the ones dispensed at the time of surgery. In a much smaller number of cases where the implants are infected or cause irritation to the soft tissues, removal of the implant via a short simple procedure performed under general anaesthesia, may be required once the bones have healed completely.
The other most common complication is related to the patient themselves, with over activity and excessive stress placed on the healing bone and implants, with either failure and breakage of the small bone the implants are anchored to. Generally, gentle lead controlled walks in incremenatlly increasing lengths are well tolerated in the weeks following patella surgery, however it is the short periods of high risk activity when these avoidable complications occur. Jumping, stairs, slippery floors, any off-lead activity will increase this risk and potentially cause catastrophic failure requiring repeat surgery. As the owner you will be the brains of the recovery and be responsible for enforcing the strict rest and confinement, rehabilitation program, and lead controlled walks, prior to a return to normal activity over a 12 week period.