What Is Patellar Luxation?
The patella, or kneecap, is a small bone embedded within the quadriceps tendon that slides up and down within a groove called the trochlear sulcus as the knee bends and straightens. In a healthy dog, it stays firmly within this groove during movement. Patellar luxation describes the condition in which the patella slips out of that groove — either temporarily or permanently — causing pain, instability, and the characteristic intermittent lameness that owners often describe as a skipping or bunny-hopping gait.
It is one of the most frequently diagnosed orthopaedic conditions in dogs and is particularly common in small and toy breeds, though larger breeds are not immune. The condition can affect one or both hind limbs and ranges considerably in severity, from occasional mild skipping to permanent dislocation with significant functional impairment.
Medial Versus Lateral Luxation
Patellar luxation is classified by the direction in which the patella displaces. Medial luxation, where the kneecap slips inward toward the body's midline, is by far the most common form and is the type predominantly seen in small and toy breeds. Lateral luxation, where the kneecap displaces outward, is less common and more typically associated with larger breeds and giant breeds, where it may occur alongside other developmental abnormalities of the hindlimb.
The underlying cause in both cases usually involves a combination of anatomical factors including a shallow trochlear groove, abnormal positioning of the quadriceps muscle group, deviation of the tibial crest where the patellar tendon attaches, or bowing of the bones of the hind limb. These structural abnormalities mean the patella is constantly pulled in a direction that encourages it to slip out of its normal position.
Breeds Most Commonly Affected
Among small and toy breeds, Chihuahuas, Pomeranians, Yorkshire Terriers, Toy Poodles, Cavalier King Charles Spaniels, and French Bulldogs are among those most frequently presented with medial patellar luxation. Bichon Frises, Miniature Pinschers, and Boston Terriers also appear commonly in clinical practice.
In larger breeds, lateral patellar luxation is more likely to be seen in dogs such as Labrador Retrievers, Great Danes, and Saint Bernards, often in conjunction with hip dysplasia or other conformational issues of the hindquarters. The management and surgical approach may differ depending on the size of the dog and the direction of luxation.
Grading the Severity
Vets use a grading system from one to four to describe the severity of patellar luxation, and this grading strongly influences treatment decisions.
- Grade 1: The patella can be manually luxated during examination but returns to the groove spontaneously and does not luxate during normal activity.
- Grade 2: The patella luxates spontaneously during movement and may remain displaced temporarily, causing intermittent skipping. It returns to the groove on its own or with gentle manipulation.
- Grade 3: The patella is permanently luxated but can be manually replaced. The dog typically walks with the stifle in a semi-flexed posture.
- Grade 4: The patella is permanently luxated and cannot be manually repositioned. Significant skeletal deformity of the limb is usually present.
Recognising the Signs
The classic presentation of patellar luxation is the skipping gait — the dog takes a few normal steps and then suddenly holds the back leg up for a stride or two before continuing normally. This occurs when the patella slips out, the dog extends the leg to pop it back into place, and then carries on. Many owners initially dismiss this as the dog stepping on something, as it can appear quite brief and intermittent.
In more severe cases, the dog may carry the leg for extended periods, be reluctant to jump or use stairs, show reduced activity levels, or develop a crouching, wide-based stance at the back end. Muscle atrophy of the affected limb may develop over time. Pain levels vary — some dogs appear unbothered by lower grades while others show significant discomfort.
Treatment Options
Grade 1 luxations without clinical symptoms are often managed conservatively with weight control, physiotherapy, and joint support. Regular monitoring is important as some dogs progress to higher grades over time.
Surgery is recommended for Grade 2 cases that are causing frequent clinical signs, and is strongly advised for Grades 3 and 4 regardless of apparent pain levels, as the joint damage caused by a permanently displaced patella is progressive and the skeletal deformity will worsen without correction.
Trochlear Modification
Deepening the trochlear sulcus is a central component of most surgical repairs. This can be achieved through trochleoplasty techniques including sulcoplasty, in which a wedge of bone and cartilage is removed and replaced at a deeper level, or block recession, which creates a deeper channel for the patella to track within. The goal is to create a groove deep enough that the patella cannot escape during normal movement.
Tibial Crest Transposition
If the point at which the patellar tendon attaches to the tibia is positioned too far medially or laterally, it creates a directional pull that encourages luxation. Tibial crest transposition involves carefully cutting this bony prominence and repositioning it so that the quadriceps mechanism pulls the patella in a straight line, keeping it within the groove.
Soft Tissue Procedures
Tightening the joint capsule on the side away from the direction of luxation, and releasing tension on the side toward which the patella displaces, helps correct the soft tissue imbalance contributing to the problem. These procedures are typically performed alongside bony corrections rather than in isolation.
Recovery and Long-Term Outlook
Recovery from patellar luxation surgery generally involves four to eight weeks of restricted exercise, progressing through gentle lead walks before returning to normal activity. Physiotherapy exercises to rebuild quadriceps strength are an important part of the recovery process.
The prognosis following surgery is generally very good for Grades 1 to 3, with the majority of dogs returning to comfortable, normal function. Grade 4 cases require more complex surgery and carry a more guarded prognosis. As with all joint conditions, some degree of osteoarthritis will develop over time, and long-term management including appropriate nutrition, weight control, and joint supplementation remains relevant throughout the dog's life.