NAVLE Musculoskeletal

Feline Patellar Luxation Study Guide

📅 March 28, 2026 ⏱ 25 min read

Patellar luxation (PL) is the displacement of the patella (kneecap) from its normal position within the trochlear groove of the femur.

Overview and Clinical Importance

Patellar luxation (PL) is the displacement of the patella (kneecap) from its normal position within the trochlear groove of the femur. While less common in cats than dogs, patellar luxation represents an important cause of pelvic limb lameness in feline patients. Unlike dogs, many clinically normal cats have physiological laxity in the patellofemoral joint, making diagnosis more nuanced.

Approximately 80% of cats with patellar luxation have bilateral involvement. Medial patellar luxation (MPL) accounts for approximately 95% of cases in cats, with lateral patellar luxation (LPL) being rare.

High-YieldPatellar subluxation is considered a NORMAL finding in cats due to their wider, flatter patella relative to the trochlear groove. This is distinct from pathological patellar luxation. Do not confuse physiological laxity with clinical disease on the NAVLE.

Breed	Clinical Significance
Devon Rex	Highest predisposition; genetic component suspected
Abyssinian	38% prevalence reported in some studies; may have concurrent hip dysplasia
Siamese	Genetic predisposition reported
British Shorthair	Overrepresented in some studies
Domestic Shorthair	Most commonly affected breed overall (62% of cases due to population prevalence)
Bengal	Emerging breed predisposition in referral populations

Anatomy of the Feline Stifle

The stifle joint (knee) connects the femur to the tibia and fibula. The patella is a sesamoid bone embedded within the quadriceps tendon that articulates with the trochlear groove on the cranial distal femur.

Key Anatomical Structures

Patella: Largest sesamoid bone; wider and flatter in cats than dogs
Trochlear groove: V-shaped groove on cranial distal femur; shallower in affected cats
Trochlear ridges: Medial and lateral ridges that contain the patella
Patellar ligament: Connects patella to tibial tuberosity
Quadriceps mechanism: Quadriceps muscle, patella, patellar ligament, and tibial tuberosity

NAVLE TipThe feline patella is proportionately WIDER and FLATTER compared to dogs. This results in physiological patellar laxity that is considered normal in cats. Less than 50% of the patella sitting within the trochlear groove indicates a shallow groove requiring surgical intervention.

Grade	Description	Clinical Significance
Grade I	Patella can be manually luxated but returns spontaneously when pressure is released	Usually incidental finding; minimal clinical signs; conservative management often sufficient
Grade II	Patella luxates spontaneously with stifle flexion; remains luxated until leg is extended/rotated or manually repositioned	Intermittent lameness; may progress; surgery often recommended if symptomatic
Grade III	Patella is permanently luxated but can be manually reduced; reluxates immediately when released	Persistent lameness; surgical correction recommended
Grade IV	Patella is permanently luxated and cannot be manually reduced; severe skeletal deformities present	Severe limb dysfunction; complex surgery required; 50% recurrence rate post-surgery

Etiology and Pathophysiology

Developmental (Congenital) Causes

The majority of feline patellar luxation cases are developmental in origin. The trochlear groove forms in response to persistent motion of the patella during growth. If the pelvic limb or quadriceps mechanism is malaligned, the patella may not track properly, resulting in a shallow trochlear groove.

Contributing Anatomical Abnormalities

Shallow or hypoplastic trochlear groove
Hypoplasia of the medial femoral condyle
Medial displacement of the tibial tuberosity
Abnormal angulation of the femur or tibia (varus/valgus deformity)
Tibial rotational abnormalities (internal or external torsion)

Traumatic Causes

Only approximately 17% of feline patellar luxation cases are associated with a history of trauma. Traumatic luxation results from disruption of the soft tissue structures (joint capsule, retinaculum) with forceful displacement of the patella.

Breed Predisposition

High-YieldDevon Rex = D for Developmental PL. Remember that Devon Rex cats have the HIGHEST breed predisposition to developmental patellar luxation. Cats diagnosed with developmental PL should NOT be used for breeding.

View	Findings to Evaluate
Craniocaudal	Patella position (medial or lateral to trochlea), femoral varus/valgus, tibial tuberosity displacement, femoral condyle symmetry
Mediolateral	Joint effusion, degenerative changes, meniscal mineralization, tibial tuberosity size and shape
Skyline (patellofemoral)	Trochlear groove depth (greater than 50% of patella should sit below trochlear ridges), patella position relative to groove

Clinical Signs

Clinical signs vary widely depending on the grade of luxation and whether one or both limbs are affected. Unlike dogs, lameness severity does NOT always correlate with luxation grade in cats. Some cats with low-grade luxation may have significant lameness, while others with higher grades may show minimal clinical signs.

Common Clinical Presentations

Intermittent hindlimb lameness: Most common presenting sign
"Skipping" gait: Characteristic non-weight bearing for several strides that resolves spontaneously
Crouched or shuffling gait: Especially with bilateral involvement
Reluctance to jump: Difficulty reaching elevated surfaces
Intermittent stifle locking: May cause sudden distress and vocalization
Leg extension/kicking: Cats may kick the leg to snap the patella back into place
Bow-legged stance: With bilateral Grade III-IV medial luxation

Important Clinical Distinctions from Dogs

Many cats with PL may be asymptomatic or have subtle signs
Unlike dogs, NO clear association between PL and cranial cruciate ligament rupture in cats
Osteoarthritis is less commonly associated with PL in cats than dogs
Some cats spontaneously resolve their lameness without surgery

Treatment	Details
Weight management	Reduce stress on affected joint; critical for overweight cats
Activity modification	Controlled exercise, avoid high-impact activities, limit jumping
NSAIDs	Meloxicam (0.05 mg/kg PO q24h after initial loading dose) or robenacoxib for pain and inflammation
Joint supplements	Glucosamine, chondroitin, omega-3 fatty acids; polysulfated glycosaminoglycan (Adequan) for cartilage protection
Physical therapy	Range of motion exercises, hydrotherapy, muscle strengthening

Grading System (Modified Putnam Scale)

The Putnam grading scale, originally developed for dogs, is applied to cats with slight modifications. Grading is essential for treatment planning and prognostication.

Exam Focus: Remember the grading mnemonic: Grade 1 = Luxates manually, Returns spontaneously. Grade 2 = Luxates Spontaneously, Stays out. Grade 3 = Permanently out, Reducible manually. Grade 4 = Permanently out, Irreducible.

Technique	Description and Indications
Trochleoplasty (Sulcoplasty)	Deepens the trochlear groove. Types: wedge recession, block recession, or semi-cylindrical recession. Goal: greater than 50% of patella sits below trochlear ridges
Tibial Tuberosity Transposition (TTT)	Relocates tibial tuberosity to realign the quadriceps mechanism. Important: Higher complication rate in cats than dogs (22% implant-related complications)
Trochlear Ridge Augmentation (TRA)	Polyethylene prosthesis placed on trochlear ridge to prevent luxation. Good outcomes reported with low major complication rate (7%)
Corrective osteotomy	Femoral or tibial osteotomy for severe angular or rotational deformities. Reserved for Grade IV with marked skeletal abnormalities

Diagnosis

Physical Examination

Diagnosis is primarily made through orthopedic palpation of the stifle joint. The examination should be performed both awake and under sedation, as some cats mask signs when stressed.

Key Examination Findings

Gait observation: Watch for skipping, shuffling, or crouched gait
Patellar palpation: Assess location and ability to luxate/reduce the patella
Range of motion: Flex and extend stifle while palpating patellar tracking
Crepitus: Grating sensation with chronic luxation or cartilage damage
Muscle atrophy: Quadriceps atrophy in chronic cases
Cruciate ligament assessment: Evaluate cranial drawer and tibial thrust (though less commonly concurrent in cats)

Radiographic Findings

Standard orthogonal radiographs (mediolateral and craniocaudal views) of the stifle are recommended. A skyline view of the trochlear groove is helpful for assessing groove depth.

High-YieldOn the NAVLE, remember: The skyline view assesses trochlear groove depth. If less than 50% of the patella sits within the trochlear groove, the groove is considered SHALLOW and trochleoplasty is indicated.

Grade	Success Rate	Recurrence Risk
Grades I-III	74% success with no complications	Low (approximately 5% reluxation rate)
Grade IV	Variable; guarded prognosis	Approximately 50% recurrence

Treatment

Conservative Management

Conservative management may be appropriate for Grade I and some Grade II luxations with minimal clinical signs. Unlike dogs, some cats with patellar luxation can spontaneously resolve their lameness without surgery.

Surgical Management

Surgical correction is recommended for cats with persistent lameness, Grade III-IV luxation, or failure of conservative management. Surgery is typically a multimodal approach combining several techniques.

Bone Reconstruction Techniques

Soft Tissue Techniques

Medial retinacular release: Releases tight medial tissues for MPL
Lateral capsular imbrication: Tightens stretched lateral tissues for MPL
Partial parasagittal patellectomy: Reduces patella width; unique to cats due to their wide, flat patella

NAVLE TipTibial tuberosity transposition (TTT) has a HIGHER complication rate in cats than dogs (22% vs 4%). The most common major complication is implant-related. Consider this when counseling owners about feline patellar luxation surgery.

Feature	Cats	Dogs
Patellar anatomy	Wider, flatter patella relative to trochlea	Patella fits more snugly in trochlear groove
Normal laxity	Patellar subluxation is normal	Minimal physiological laxity
CCL association	NO clear association with CCL rupture	Concurrent CCL disease common
TTT complications	22% implant-related complications	4% implant-related complications
Conservative outcome	Some spontaneously resolve without surgery	Less likely to resolve without surgery

Prognosis and Complications

Surgical Outcomes

Reported Complications

Overall complication rate: 26% (20% major, 6% minor)
Implant-related complications: Most common major complication with TTT
Patellar reluxation: 5% overall; higher with previous stifle surgery
Seroma formation: Minor complication
Surgical site infection: Minor complication
Tibial fracture: Rare but reported with TTT

Risk Factors for Complications

Previous ipsilateral femoral fracture (significantly higher complication risk)
Grade IV luxation (higher minor complication rate)
Previous stifle surgery (8x higher reluxation risk)
Tibial tuberosity transposition (5.5x higher major complication risk)

High-YieldGrade IV Prognosis Memory Aid: 'Grade FOUR = FIFTY percent recurrence.' Remember this for NAVLE questions about prognosis.

Postoperative Care

Activity restriction: Strict cage rest for 8 weeks; no jumping or running
Pain management: NSAIDs, opioids as needed, gabapentin for neuropathic component
Physical therapy: Passive range of motion, warm and cold packing under veterinary guidance
Recheck schedule: Radiographs at 2, 6, and 12 weeks postoperatively
Long-term monitoring: Progression of degenerative joint disease reported in 75% of cases

Key Differences: Feline vs. Canine Patellar Luxation

Memory Aids for the NAVLE

"DEVON = D for Developmental PL" Devon Rex has the highest breed predisposition to DEVELOPMENTAL patellar luxation

"Cats are NOT small dogs" for Patellar Luxation: Normal = Subluxation is physiologic in cats Other = No CCL association (unlike dogs) TTT = Higher complication rate in cats Spontaneous = Some resolve without surgery

"Grade FOUR = FIFTY percent" Grade IV patellar luxation has approximately 50% recurrence rate after surgery

"Grading Made Simple": Grade I = Luxates manually, Returns spontaneously Grade II = Luxates Spontaneously, Stays out until extended Grade III = Permanently out, Reducible manually Grade IV = Permanently out, Irreducible

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