CONDITION

Luxating Patella in Dogs

Why this matters now

Luxating patella — a condition where the kneecap (patella) slides out of its normal position in the groove at the front of the knee joint — is one of the most common orthopaedic conditions in dogs, particularly in small and toy breeds. Yorkshire Terriers, Pomeranians, Chihuahuas, Cavalier King Charles Spaniels, French Bulldogs, and other small breeds are disproportionately affected, though the condition also occurs in medium and large breeds. In many dogs, the structural predisposition is present from birth as a developmental conformational abnormality, though the clinical signs may not become apparent until later in life. The condition is bilateral in a significant proportion of cases, meaning both knees are affected. It is frequently identified during routine veterinary examinations even before the owner has noticed any gait abnormality, particularly in lower grades where the patella can be manually displaced but returns to its normal position.

Luxating patella is traditionally graded from I to IV based on the degree of instability. Grade I patellae can be manually displaced but return spontaneously to the groove. Grade II patellae luxate spontaneously during movement and may remain displaced until manually repositioned or until the dog straightens the leg. Grade III patellae remain luxated most of the time but can be manually replaced, only to luxate again. Grade IV patellae are permanently luxated and cannot be repositioned. Progression through grades is not inevitable — many dogs remain stable at a given grade for their entire lives — but worsening can occur, particularly if the abnormal tracking produces erosion of the groove or secondary cartilage damage. A significant long-term consequence of patellar luxation is the increased risk of cranial cruciate ligament disease in the affected knee, as the abnormal biomechanics place additional stress on the cruciate ligament. The relationship between patellar luxation and subsequent cruciate rupture represents an important consideration in the overall management of the condition.

Signals & patterns

Early signals

Intermittent skipping gait

The hallmark early sign of patellar luxation is a distinctive skipping or hopping movement in a hind leg during walking or trotting. The dog may suddenly carry the affected leg for a few strides, then place it down again and continue normally. This occurs when the patella slips out of its groove and momentarily locks the knee in a flexed position; once the quadriceps muscle shifts the patella back into place, the dog walks normally again. These episodes may be brief, intermittent, and initially infrequent.

Brief hind leg extension

Owners may notice their dog occasionally kick the hind leg outward or backward while walking, as if trying to 'click' something back into place. This movement is the dog instinctively extending and rotating the leg to encourage the displaced patella to slide back into its groove. It may be so quick and subtle that it is easily missed or dismissed as a quirk.

Incidental finding on examination

In many dogs, patellar luxation is first identified by a veterinarian during a routine physical examination rather than from owner-reported clinical signs. The patella may be palpably loose or can be manually displaced from its groove during the orthopaedic assessment. Dogs with grade I luxation may show no outward signs at all, with the condition only detectable through physical examination.

Later signals

Persistent lameness

As the condition progresses, the episodes of lameness may become more frequent, longer-lasting, or continuous. The patella may spend more time out of its groove than in it, producing a consistently abnormal gait. The dog may preferentially non-weight-bear on the affected limb or adopt a crouched, bowlegged stance. In bilateral cases, both hind legs may be affected, producing a characteristic crouched or waddling gait.

Muscle wasting in the affected leg

Chronic luxation and the associated reduction in normal weight-bearing can lead to progressive atrophy of the quadriceps and other thigh muscles in the affected limb. The affected leg may appear noticeably thinner than the opposite leg, particularly when viewed from behind. This muscle loss further compromises the dynamic stability of the knee and can perpetuate the luxation.

Secondary joint changes and stiffness

Ongoing abnormal tracking of the patella gradually erodes the cartilage of both the patellar surface and the trochlear groove, promoting the development of osteoarthritis. The dog may show increasing stiffness after rest, reluctance to jump onto furniture or into cars, and progressive reluctance to engage in activities that load the hind legs. Crepitus — a grating sensation or sound within the joint — may develop as cartilage loss exposes the underlying bone surfaces.

Click to read about the biological mechanisms

How this is usually investigated

The investigation of patellar luxation centres on physical examination and orthopaedic assessment, supplemented by imaging studies to evaluate the degree of skeletal deformity, secondary joint changes, and concurrent conditions that may influence management decisions.

Orthopaedic examination and grading

Purpose: A thorough orthopaedic examination is the primary diagnostic tool for patellar luxation. The veterinarian assesses the patella's stability, whether it can be displaced and how readily it returns to the groove, and the overall alignment and function of the hind limbs. The condition is graded from I to IV based on the findings, which directly informs decisions about monitoring versus surgical intervention.
Considerations: Grading should ideally be performed with the dog relaxed, as muscle tension can affect how easily the patella can be displaced. Assessment of both hind legs is important given the high incidence of bilateral involvement. The examination also evaluates the integrity of the cranial cruciate ligament, as concurrent ligament disease significantly affects the management approach.

Radiography

Purpose: Radiographs of the stifle (knee) joints and, in some cases, full-length views of the femur and tibia provide information about the trochlear groove depth, the position of the tibial tuberosity, the degree of any angular or torsional limb deformities, and the presence and extent of osteoarthritic changes. Pre-surgical radiographic planning is essential for determining the specific surgical techniques required for each individual.
Considerations: Standard radiographic views may not fully characterise rotational deformities of the femur or tibia, which can influence surgical planning. In some cases, computed tomography (CT) scanning provides more detailed three-dimensional assessment of the skeletal anatomy, particularly in higher-grade luxations with significant angular or torsional deformity.

Gait analysis

Purpose: Observing the dog's gait on a level surface, including walking and trotting, helps characterise the functional impact of the luxation. The frequency and duration of luxation episodes, the degree of lameness, and the dog's ability to use the affected limb provide practical information about how the condition is affecting the animal's mobility and comfort.
Considerations: Gait assessment may vary between visits depending on whether the patella is luxated at the time of evaluation. Video recordings from the home environment can supplement in-clinic gait assessment by capturing episodes that may not occur during the relatively short examination period.

CT scanning (advanced cases)

Purpose: Cross-sectional imaging with CT provides detailed three-dimensional assessment of the skeletal anatomy that is not available from standard radiographs. It is particularly valuable for characterising femoral and tibial torsional deformities, precisely measuring trochlear groove depth and conformation, and planning complex corrective procedures in higher-grade luxations.
Considerations: CT scanning requires general anaesthesia and involves additional cost compared with standard radiography. It is most commonly utilised in cases where surgical correction is being planned and the surgeon needs detailed anatomical information to determine the specific combination of procedures required, particularly when corrective osteotomies (bone cutting and realignment) may be indicated.

Options & trade-offs

Management of luxating patella ranges from conservative monitoring in mild, asymptomatic cases to complex surgical reconstruction in higher grades or clinically significant cases. The decision-making process considers the grade of luxation, the degree of clinical signs, the dog's age and size, concurrent conditions, and the potential for progression.

Conservative management and monitoring

Dogs with grade I or low-grade II patellar luxation that show minimal or no clinical signs may be managed conservatively with regular monitoring. This approach involves periodic veterinary reassessment to check for progression, weight management to reduce stress on the joints, appropriate exercise to maintain muscle strength and joint stability, and targeted physiotherapy or rehabilitation exercises to strengthen the quadriceps and surrounding musculature.

Trade-offs: Conservative management avoids the risks and costs of surgery but does not address the underlying structural abnormality. There is an ongoing risk of progression, and the chronic abnormal patellar tracking may contribute to the development of osteoarthritis over time. Regular reassessment is important to identify any worsening that might change the management recommendation. The risk of cruciate ligament disease remains elevated in the affected knee.

Surgical correction

Surgical intervention is generally considered for higher-grade luxations (grades III-IV), lower-grade luxations that produce significant clinical signs, or cases that are progressing despite conservative management. The surgical approach is tailored to the individual dog's anatomy and typically involves a combination of procedures: trochleoplasty (deepening the groove), tibial tuberosity transposition (realigning the insertion point of the patellar tendon), soft tissue reconstruction (tightening the loose side of the joint capsule and releasing the contracted side), and in more severe cases, corrective osteotomies to address angular or torsional deformities of the femur or tibia.

Trade-offs: Surgical correction addresses the underlying structural abnormality and, when successful, can significantly improve limb function and comfort. However, it carries the inherent risks of any surgical procedure including infection, implant complications, and the possibility of re-luxation. The recurrence rate varies with the grade and the specific anatomy but is reported in a proportion of surgically treated cases. Post-operative rehabilitation is important for optimal outcomes and requires owner commitment to exercise restriction followed by a graduated return to activity. The cost of surgery can be substantial, particularly for higher grades requiring more complex procedures.

Multimodal pain management

For dogs with patellar luxation and associated osteoarthritis, multimodal pain management may be incorporated alongside either conservative or surgical management. This can include anti-inflammatory medications, joint supplements, weight management, physiotherapy, and environmental modifications to reduce joint stress. The approach aims to maintain comfort and mobility while addressing the secondary joint changes that accompany chronic patellar instability.

Trade-offs: Pain management addresses the symptoms of associated osteoarthritis but does not correct the underlying patellar instability. It may be most appropriate as an adjunct to other management strategies or in cases where surgical correction is not feasible due to patient factors, owner preferences, or financial considerations. Ongoing monitoring of response and adjustment of the management plan is typically required.

Common misconceptions

Misconception:

"Luxating patella always requires surgery"

Reality:

Many dogs with low-grade patellar luxation live comfortably without surgical intervention, particularly those with grade I or asymptomatic grade II luxation. The decision about whether surgery is beneficial depends on the grade, the presence and severity of clinical signs, the rate of progression, the dog's age and activity level, and the owner's goals and preferences. Surgery is generally reserved for cases where the luxation is causing significant functional impairment, pain, or progressive joint damage.

Misconception:

"Small dogs with luxating patellas are just being dramatic about the pain"

Reality:

The skipping or hopping gait characteristic of patellar luxation occurs because the displaced kneecap mechanically locks the knee in a flexed position, preventing normal extension. This is a structural limitation rather than a pain-driven behavioural response. However, the condition can cause discomfort, particularly as secondary osteoarthritis develops, and the fact that a dog may appear to resume normal walking quickly does not mean the luxation is insignificant. Chronic abnormal tracking and cartilage wear produce cumulative damage that may not be apparent in the early stages.

Misconception:

"Luxating patella only affects small breeds"

Reality:

While the condition is considerably more common in small and toy breeds, it also occurs in medium and large breed dogs. In larger breeds, lateral luxation (where the patella displaces to the outside of the knee) is relatively more common compared with the medial luxation that predominates in small breeds. The condition in larger breeds may involve different conformational abnormalities and can carry different clinical implications, including a potentially greater impact on weight-bearing function due to the higher body mass involved.

Observing and recording the frequency and duration of skipping episodes can help track whether the condition is stable or progressing over time. Noting whether episodes are becoming more frequent, lasting longer, or being triggered by lower levels of activity provides useful information about the trajectory. Maintaining lean body weight reduces the forces acting across the knee joint and may help slow secondary joint changes. Keeping the muscles of the hind legs strong through regular, moderate exercise — avoiding activities that involve sudden stops, tight turns, or repetitive jumping that may exacerbate the luxation — supports dynamic joint stability. Understanding the grading system and the relationship between patellar luxation and cruciate ligament health provides useful context for ongoing monitoring and for discussions about whether the condition warrants intervention at any given point.

Last reviewed: 24 April 2026 · Dr Alastair Greenway MRCVS