Equine Joint Luxations Study Guide

Overview and Clinical Importance

Joint luxation (dislocation) in horses refers to the complete displacement of articular surfaces, while subluxation represents partial separation. These injuries are relatively uncommon in horses compared to other species due to the robust ligamentous support of equine joints. However, when they occur, they represent significant orthopedic emergencies requiring prompt diagnosis and treatment.

Joint luxations in horses most commonly affect the coxofemoral (hip) joint, fetlock (metacarpophalangeal/metatarsophalangeal) joint, proximal interphalangeal (pastern) joint, stifle (femoropatellar/femorotibial) joint, and carpus. Additionally, tendon luxations, particularly of the superficial digital flexor tendon from the calcaneus, are clinically important conditions.

Coxofemoral (Hip) Joint Luxation

Anatomy and Pathophysiology

The coxofemoral joint is a ball-and-socket joint formed by the femoral head and the acetabulum. This joint is stabilized by the ligament of the femoral head (round ligament), the accessory femoral ligament (unique to horses), and the fibrocartilaginous acetabular rim. These structures provide robust support, making complete luxation relatively rare in adult horses.

Types of Coxofemoral Luxation

Etiology

• Trauma (falls, kicks, collisions)
• Secondary to upward fixation of the patella (in ponies)
• Forced abduction or rotation of the hindlimb
• Slipping on icy or wet surfaces

Clinical Signs

• Non-weight-bearing (toe-touching) lameness
• Higher point of the hock compared to contralateral limb
• External rotation of limb with outward rotation of stifle and toe
• Inward rotation of point of the hock
• Asymmetrical pelvis; prominent greater trochanter
• May be complicated by concurrent upward fixation of patella

Diagnosis

Physical examination: Palpation of greater trochanter, assessment of limb position/rotation, rectal palpation for cranioventral luxation.

Radiography: Standing lateral and ventrodorsal views confirm displacement. CT imaging excellent in foals and small ponies.

Ultrasonography: Evaluates joint position and soft tissue damage.

Treatment

Prognosis

Prognosis for return to athletic function is very guarded. Closed reduction possible in small ponies for pasture soundness. Larger horses have poorer prognosis due to difficulty maintaining reduction.

Upward Fixation of the Patella (Locked Stifle)

Anatomy and Pathophysiology

Unlike most species with a single patellar ligament, horses have three patellar ligaments (medial, middle, lateral) connecting patella to tibial tuberosity. The medial trochlear ridge is prominent, allowing the patella to "lock" as part of the stay apparatus for standing sleep.

Upward fixation occurs when the medial patellar ligament hooks over the medial trochlear ridge and fails to release, locking the reciprocal apparatus with the limb in extension.

Types of Patellar Fixation

Predisposing Factors

• Lack of fitness or poor quadriceps/biceps femoris muscle tone
• Straight or upright hindlimb conformation
• Downhill topline conformation
• Negative plantar hoof angle (low heels)
• Young horses that are unfit or growing rapidly

Clinical Signs

• Hindlimb held locked in extension with stifle and hock extended
• Fetlock flexed while rest of limb extended
• Jerky or hitching gait; sudden snapping release
• Horse may drag toe; difficulty on hills or soft footing

Diagnosis

Based on recognition of typical clinical signs. Patella can often be manually locked by pushing horse backward or pushing patella proximally. Radiographs if joint effusion present.

Release technique: Push horse backward while pushing patella medially and distally. Or pull limb forward with rope around pastern.

Treatment

Patellar Luxation

True patellar luxation (displacement from trochlear groove) is uncommon due to the prominent medial trochlear ridge. It occurs in lateral (most common, especially miniature horses), medial (rare, traumatic), and distal (very rare) directions.

Lateral Patellar Luxation

Congenital/Developmental: Most common in miniature horses and foals. Often bilateral. May be hereditary. Presents with stifle effusion and crouched stance.

Traumatic: Severe disruption of parapatellar support. Diffuse swelling. Little remaining healthy tissue for repair.

Treatment: Surgical - release of medial femoropatellar ligament, prosthetic lateral ligament replacement, mesh implant reinforcement. Recession wedge sulcoplasty for developmental cases.

Prognosis: Poor in larger horses and with OA. Foals have potential for athletic function with surgery.

Fetlock (MCP/MTP) Joint Luxation

Anatomy and Pathophysiology

The fetlock joints are high-motion joints stabilized by medial and lateral collateral ligaments, collateral sesamoidean ligaments, oblique distal sesamoidean ligaments, and joint capsule. Luxation occurs when forces exceed these structures.

Types and Mechanisms

Clinical Signs

• Acute onset non-weight-bearing lameness
• Visible angulation of limb; joint distension, heat, pain
• May be open (skin laceration) or closed
• Excessive movement in joint

Treatment

Closed luxations: Closed reduction under general anesthesia followed by cast immobilization for 8-12 weeks.

Open luxations: Surgical debridement, joint lavage, antibiotics (intra-articular amikacin 500 mg), reduction and casting.

Special technique: PVC splint with upper/lower thirds casted, middle open for wound management.

Prognosis

Good for breeding/pasture soundness. Persistent laxity leads to chronic OA. Guarded to poor for athletic performance.

Proximal Interphalangeal (Pastern) Joint Luxation

Anatomy and Types

The PIP (pastern) joint is a low-motion joint formed by P1 and P2, stabilized by collateral ligaments and palmar/plantar structures. Luxation/subluxation occurs in dorsal, palmar/plantar, medial, or lateral directions.

Clinical Signs

• Acute non-weight-bearing lameness (traumatic cases)
• Malalignment of pastern region; swelling; pain on manipulation
• Audible clicking when weight placed on limb (dorsal)
• Hyperextension of pastern (palmar subluxation)

Treatment

Conservative: For bilateral dorsal subluxation in young horses - anti-inflammatories and controlled exercise. May resolve with conditioning.

Pastern arthrodesis: Recommended for recalcitrant cases. Current gold standard: 3-hole LCP with two 5.5mm transarticular screws. Cast for 14 days post-surgery.

Prognosis

Prognosis after arthrodesis: Excellent for hindlimb (95%) and good for forelimb (81%) return to intended use. Overall 87% success. PIP is low-motion joint - fusion has minimal impact on gait.

Superficial Digital Flexor Tendon Luxation from Calcaneus

Anatomy and Pathophysiology

In the hindlimb, the SDFT forms a fibrocartilaginous cap over the point of the calcaneus, attached by thick retinacula (calcaneal insertions). Luxation occurs when retinaculum tears or cap is damaged. Lateral luxation (medial retinacular tear) is most common.

Clinical Signs

• Acute onset severe lameness; marked swelling at point of hock
• Visible displacement of SDFT; audible clicking during movement
• Tendon can be manually moved and may return to position
• Distension of calcaneal bursa; horse may be very anxious when moving

Diagnosis

Physical exam: Palpation reveals displaced tendon. May confuse with capped hock when swelling severe.

Ultrasonography: Essential - evaluates calcaneal insertions, partial tears, fibrocartilage cap damage.

Radiography: Rules out calcaneal fractures; usually shows soft tissue swelling only.

Treatment

Other Joint Luxations

Elbow (Cubital) Joint Luxation

Rare - most common in foals/young horses following trauma. Presents with grade 4-5/5 forelimb lameness, lateral ulna deviation, "dropped elbow." Treatment: closed/open reduction with surgical stabilization (knotless bone anchors, FiberTape).

Carpal Joint Luxation

Carpometacarpal joint most commonly affected. Associated with trauma/athletic activity. Often has avulsion fractures. Treatment: partial carpal arthrodesis with LCP provides stable fixation.

Summary: Equine Joint Luxations at a Glance