Canine Hip Luxation Study Guide

Overview and Clinical Importance

Coxofemoral luxation (hip luxation) is the most commonly luxated joint in dogs, accounting for approximately 90% of all joint luxations. The condition occurs when the femoral head is displaced from the acetabulum, disrupting the ball-and-socket articulation of the hip joint. This represents a high-yield topic for the NAVLE examination due to its frequency in clinical practice and the importance of timely, appropriate intervention.

Vehicular trauma is the cause of up to 85% of coxofemoral luxations. Other causes include falls, jumping from moving vehicles, severe hip dysplasia, and spontaneous luxation in dysplastic joints. Craniodorsal luxation accounts for approximately 78-80% of cases, making it the most common direction of luxation.

Anatomy of the Coxofemoral Joint

The coxofemoral joint is a diarthrodial ball-and-socket articulation between the femoral head (the ball) and the acetabulum (the socket) of the pelvis. Understanding the stabilizing structures is critical for both diagnosis and treatment planning.

Primary (Major) Stabilizers

For luxation to occur, at least two of the major stabilizers must be disrupted. The primary stabilizers include:

• Ligament of the head of the femur (round ligament/teres ligament): Attaches the fovea capitis of the femoral head to the acetabular fossa and transverse acetabular ligament
• Joint capsule: Fibrous capsule that surrounds the joint and attaches to the acetabular rim and femoral neck
• Dorsal acetabular rim: Provides physical barrier preventing dorsal displacement of the femoral head

Secondary (Minor) Stabilizers

• Periarticular muscles: Deep, middle, and superficial gluteal muscles; iliopsoas; quadratus femoris; gemelli; internal and external obturator muscles
• Hydrostatic pressure: Created by synovial fluid within the joint space
• Ventral acetabular ligament: Provides additional ventral support

Pathophysiology and Mechanism of Injury

Craniodorsal Luxation (78-80% of cases)

This is the most common direction of luxation. The mechanism typically involves trauma to the rear limb that exerts supraphysiologic forces on the femur. The sequence includes: the animal falls laterally, placing the distal femur in adduction and distracting the femoral head from the acetabulum. The ligament of the femoral head and joint capsule are stretched until the greater trochanter strikes the ground, forcing the femoral head over the dorsal rim of the acetabulum. This causes tearing of the joint capsule (midsubstance tear or avulsion) and rupture of the round ligament.

Caudoventral (Ventral) Luxation (20-22% of cases)

Ventral luxations typically result from slipping or falling, classically on ice or slippery surfaces. The femoral head may become entrapped in the obturator foramen, which constrains hip adduction and internal rotation.

Clinical Presentation and Diagnosis

History

Owners typically witness trauma such as being hit by car (60-85% of cases), a fall, or jumping from a moving vehicle. Acute onset of severe lameness is the primary presenting complaint. Concurrent injuries are present in approximately 55% of animals and must be assessed before pursuing treatment for the hip luxation.

Clinical Signs by Luxation Type

Physical Examination Tests

The Triangle Test

With the patient in lateral recumbency and affected hip uppermost, palpate three anatomical landmarks: (1) the craniodorsal aspect of the iliac wing, (2) the tuber ischii, and (3) the greater trochanter. These should form a triangle with the tip pointing distally. In a normal hip, the greater trochanter lies below a line connecting the iliac wing and ischiatic tuberosity, positioned at approximately the caudal 2/3 point. In craniodorsal luxation, the greater trochanter is ON or above this line and at approximately the 1/2 position (equidistant from both points).

The Thumb Test

Place the thumb in the ischiatic notch while externally rotating the femur. In a normal hip, the thumb is displaced by the greater trochanter moving posteriorly during external rotation. If the thumb is NOT displaced, the joint is likely luxated.

Diagnostic Imaging

NEVER attempt closed reduction without first taking radiographs! Orthogonal radiographs (ventrodorsal and lateral) are essential to:

• Confirm the diagnosis and direction of luxation
• Evaluate for fractures of the acetabulum, femoral head, femoral neck, or greater trochanter
• Identify avulsion fractures of the capital femoral epiphysis
• Assess for pre-existing hip dysplasia or osteoarthritis
• Rule out Legg-Calve-Perthes disease
• Evaluate for concurrent pelvic fractures

Contraindications to Closed Reduction

Treatment Options

Treatment selection depends on the chronicity of the luxation, direction, severity of injuries, patient factors (age, weight, activity level), and financial considerations. Reduction and stabilization should be performed as soon as possible to minimize destruction of articular cartilage and before muscle spasticity and fibrosis prevent easy relocation.

Treatment Decision Summary

Closed Reduction Technique

Timing: Closed reduction should be attempted as soon as possible, ideally within the first 24-48 hours and no later than 4-5 days post-injury. After this time, muscle contracture and fibrosis make reduction difficult and often unsuccessful.

Anesthesia: General anesthesia is required (or heavy sedation with epidural block) as the procedure is painful and muscle relaxation is essential.

Technique for Craniodorsal Luxation

• Place patient in lateral recumbency with affected limb uppermost
• Apply countertraction with towel placed around inguinal region (assistant pulls dorsally)
• Apply distal traction and EXTERNAL rotation to position femoral head over acetabulum
• Maintain traction and INTERNALLY rotate limb while applying pressure to greater trochanter to seat femoral head
• Move hip through ROM for 20 minutes while pressing on greater trochanter to clear debris from acetabulum
• Confirm reduction with orthogonal radiographs
• Apply Ehmer sling for 10-14 days

Technique for Caudoventral Luxation

• Apply distal traction to free femoral head from obturator foramen
• Once freed, rotate femoral head laterally and cranially to seat in acetabulum
• Apply hobbles at stifle level (NOT hock level) for 6 weeks to prevent abduction

Ehmer Sling Application and Management

The Ehmer sling maintains the hip in internal rotation, flexion, and abduction while keeping the limb in a non-weight bearing position. It should be applied immediately after confirmed reduction.

Sling Duration and Monitoring

• Minimum duration: 7-10 days; typical duration: 10-14 days
• Daily examination: Check for loss of internal rotation, hip flexion, or abduction
• Palpate triangle daily to confirm continued reduction
• Monitor for bandage sores, inflammation, and distal limb edema
• Check for urine contamination in male dogs

Open Reduction Surgical Techniques

Indications for open reduction: Failed closed reduction, immediate reluxation after closed reduction, avulsion fracture of femoral head, concurrent injuries requiring immediate weight bearing, chronic luxation, hip dysplasia.

Salvage Procedures

Femoral Head and Neck Ostectomy (FHO)

Indications: Recurrent hip luxation, concurrent severe acetabular or femoral head fractures, coxofemoral osteoarthritis, failed closed and open reduction attempts, severe femoral head damage when THR not an option, client financial constraints.

Patient selection: Best results in dogs less than 40-45 lbs. Large and giant breeds have less favorable outcomes. The procedure removes the femoral head and neck, allowing formation of a fibrous pseudoarthrosis ("false joint") supported by the surrounding musculature.

Prognosis: Good to excellent for return to normal or near-normal function in small dogs. Functional deficits can occur in both small and large breed dogs. Early physical rehabilitation is CRITICAL for optimal outcomes. Complications include limb shortening, muscle atrophy, decreased ROM, and persistent lameness.

Total Hip Replacement (THR)

Indications: Chronic reluxation, severe osteoarthritis, femoral head damage in large breed dogs, failed FHO with poor functional outcome.

Outcomes: Greater than 95% of dogs can resume pain-free, active life with THR. Reluxation rate approximately 6%. This is the primary recommendation over FHO for large breed dogs when financially feasible.

Prognosis and Long-Term Outcomes

The prognosis after coxofemoral luxation is fair to good if reduction and stability are achieved soon after injury.

Common Complications

• Reluxation: Most common complication across all treatment methods
• Bandage/sling complications: Pressure sores, skin excoriation, swelling (50% of Ehmer sling cases)
• Implant complications: Migration, breakage, failure
• Progressive osteoarthritis: Develops in majority of cases over time
• Sciatic nerve injury: Especially with DeVita pinning
• Articular cartilage damage: From manipulation or implants