Feline Hip Luxation Study Guide

Overview and Clinical Importance

Coxofemoral luxation (hip luxation) is the most common joint luxation in cats, accounting for up to 90% of all joint luxations in this species. The condition involves displacement of the femoral head from the acetabulum, resulting in significant pain, lameness, and functional impairment. Understanding the anatomy, diagnosis, and management of coxofemoral luxation is essential for the NAVLE examination and clinical practice.

Hip luxation in cats is most commonly caused by vehicular trauma (motor vehicle accidents), accounting for the majority of cases. Other causes include kicks, fights, falls from height, and unknown trauma. Concurrent injuries occur in approximately 55% of patients, making thorough patient evaluation critical before addressing the luxation.

Anatomy of the Coxofemoral Joint

The coxofemoral joint is a diarthrodial ball-and-socket joint formed by the articulation of the femoral head with the acetabulum. The spherical femoral head fits into the cup-shaped acetabulum, allowing multiaxial movement including flexion, extension, abduction, adduction, and rotation.

Primary Stabilizers

Secondary Stabilizers

• Acetabular labrum: Thin fibrocartilaginous band extending laterally from dorsal acetabular rim
• Transverse acetabular ligament: Extension of labrum across acetabular notch
• Synovial fluid: Creates hydrostatic pressure maintaining joint congruency
• Periarticular muscles: Gluteal muscles (superficial, middle, deep), hip adductors, and hip abductors

Etiology and Pathophysiology

The pathogenesis of coxofemoral luxation involves disruption of the stabilizing structures of the hip joint. During trauma, forces applied to the rear limb exert supraphysiologic stress on the femur. As the animal falls laterally, the distal femur is placed in adduction, distracting the femoral head from the acetabulum until the ligament of the femoral head and joint capsule stretch and tear. When the greater trochanter strikes the ground, the femoral head is forced over the dorsal rim of the acetabulum.

Direction of Luxation

Clinical Presentation and Physical Examination

History

Most cats present with acute onset of non-weight bearing lameness following known or suspected trauma. Road traffic accidents are the most common cause. Cats may have concurrent injuries including thoracic trauma, urinary tract injury, pelvic fractures, or soft tissue wounds.

Clinical Signs by Direction of Luxation

Physical Examination Tests

Thumb Displacement Test (Pinch Test)

Place your thumb in the ischiatic notch between the greater trochanter and ischiatic tuberosity. In a normal hip, when the femur is externally rotated, the greater trochanter will occupy this space and displace your thumb. In a luxated hip, external rotation of the femur will NOT displace your thumb from the notch because the femoral head is not seated in the acetabulum.

Anatomic Landmark Assessment

Palpate the relationship between three landmarks: greater trochanter, ischiatic tuberosity, and iliac wing. In a normal hip, these form a triangle with the greater trochanter being the most ventral point. With craniodorsal luxation, the greater trochanter is no longer ventral to the other landmarks.

Diagnostic Imaging

Radiography

Standard ventrodorsal and lateral radiographs of the pelvis are essential for confirming diagnosis and planning treatment. Radiographs should ALWAYS be obtained before attempting closed reduction.

Radiographic Evaluation Checklist

• Direction of luxation: Confirm whether craniodorsal or caudoventral
• Femoral head integrity: Check for fractures of femoral head or neck
• Acetabular integrity: Assess for acetabular fractures
• Capital physeal fracture: Rule out in immature cats (Salter-Harris Type I)
• Avulsion fractures: Look for avulsion of ligament of femoral head or greater trochanter
• Contralateral hip: Evaluate for bilateral luxation or hip dysplasia
• Pre-existing osteoarthritis: Affects treatment selection

Treatment Options

Treatment of coxofemoral luxation in cats can be broadly categorized into: closed reduction, open reduction with stabilization, and salvage procedures. The choice depends on duration of luxation, concurrent injuries, joint stability after reduction, cost considerations, and overall patient health.

Treatment Comparison

Closed Reduction Technique

Timing is critical: Closed reduction should be attempted within 24-48 hours of injury when possible. After 4-5 days, muscle contraction and fibrosis make closed reduction difficult or impossible.

Technique for Craniodorsal Luxation

• Place patient under general anesthesia in lateral recumbency with affected limb up
• Apply countertraction using a towel wrapped in the inguinal region
• Externally rotate the limb to move femoral head away from ilium
• Apply distocaudal traction to bring femoral head near acetabulum
• Apply pressure on greater trochanter while internally rotating limb
• A palpable 'pop' indicates successful reduction
• Move hip through range of motion for 15-20 minutes to displace blood clots and debris
• Apply Ehmer sling and confirm reduction with radiographs

Post-Reduction Bandaging

Femoral Head and Neck Excision (FHO/FHNE)

FHO is a salvage procedure that removes the femoral head and neck, allowing formation of a functional pseudarthrosis (false joint). This eliminates bone-on-bone contact and associated pain while providing functional weight-bearing through fibrous tissue formation.

Indications for FHO

• Femoral head or neck fractures not amenable to repair
• Acetabular fractures with significant articular damage
• Failed closed or open reduction
• Chronic luxation with severe joint damage
• Pre-existing severe osteoarthritis or hip dysplasia
• Financial constraints precluding THR

FHO Outcomes in Cats

Cats generally have excellent functional outcomes following FHO due to their lighter body weight and ability to compensate. Active cats with good muscle mass recover faster. Most cats recover fully within 6 weeks and regain essentially normal function with minimal decreased range of motion or limb shortening.

Prognosis and Complications

Prognosis by Treatment

• Closed reduction: Approximately 50% success rate; bandage placement may reduce reluxation risk
• Toggle rod stabilization: 86-89% success rate; 11-14% reluxation rate
• FHO: Excellent limb function in cats; eliminates reluxation possibility
• Conservative management: Cats may develop functional pseudarthrosis even without treatment

Complications

• Reluxation: Most common complication; occurs in ~50% of closed reductions
• Osteoarthritis: Progressive OA develops in 55-62% of patients post-luxation
• Sciatic neurapraxia: Usually temporary; may occur with FHO
• Bandage complications: Skin irritation, pressure sores, swelling with Ehmer sling
• Implant failure: Rare with toggle stabilization if proper technique used