Fracture of the third Phalanx in Horses

Fracture of the third Phalanx (P₃, Coffin Bone) in Horses or Fractures of the distal phalanx are an uncommon cause of lameness compared to the numerous other conditions that affect the horse’s foot. Although all breeds and classes of horses can be affected, there appears to be a higher incidence observed in racing breeds.

Although fractures of P3 can assume a variety of configurations, these fractures can be classified into 7 types–

1. Type I fractures are nonarticular oblique palmar/plantar process (wing) fractures.
2. Type II fractures are articular oblique palmar or plantar process (wing) fractures and are by far the most common type.
3. Type III fractures are sagittal articular fractures that roughly divide the distal phalanx into 2 separate halves. These fractures are uncommon and represent 3% to 4% of fractures of the distal phalanx and occur more commonly in the hindlimb than the forelimb.
4. Type IV fractures are articular fractures involving the extensor process. They occur most frequently in the forelimbs and can be bilateral.
5. Type V fractures are comminuted articular or nonarticular fractures and can be a variety of configurations.
6. Type VI fractures are nonarticular solar margin fractures of the distal phalanx.
7. Type VII fractures are nonarticular fractures of the palmar or plantar process of the distal phalanx in foals.

Etiology

• Single event trauma
• Repetitive trauma leads to stress related fracture of P3

Clinical Signs

• Acute onset of moderate to severe lameness
• Lameness worsen within 24 hours due to acute inflammation and swelling
• In case of chronic fractures of P3, the signs of lameness are usually diminished
• Increased digital pulse
• Swelling and edema noticed above the pastern joint
• Hoof tester examination induces severe pain
• Horses with large chronic extensor process fractures may have enlargement of the dorsal aspect of the coronary band and abnormal growth of the dorsal hoof wall. As the hoof grows, it develops a “V” or triangular shape called a buttress foot.

Diagnosis

• Radiographic examination used to diagnose and classify the type of P3 fracture
• MRI
• CT
• Scintigraphy

Treatment

Options for treating horses with P3 fractures include confinement alone, confinement with corrective shoeing or foot casts, lag screw fixation (types II, III, and IV), and surgical removal of the fracture/fragment (type IV only). The decision often depends on the age and intended use of the horse, specific characteristics of the fracture, and financial constraints of the owner.

Types of shoes that may be used include a bar shoe with clips , a continuous rim-type shoe, or the Klimesh contiguous clip shoe. All of these approaches appear to effectively prevent expansion of the hoof wall during weight-bearing, thus stabilizing the fracture. Regional anaesthesia of the foot often aids application of the shoe and many horses walk more comfortably shortly after the foot is immobilized.

In most cases the foot should remain in one of these shoes for 6 to 8 months, with the shoe reset every 4 to 6 weeks. Once clinical improvement has occurred, a less restrictive type of shoe (bar shoe only or bar shoe with quarter clips) may be used.

Horse should not be worked for approximately 8 to 10 months, and in some cases, 1 year of rest may be necessary for clinical improvement.

Prognosis

In general the prognosis for non-articular P3 fractures (types I, V, VI, and VII) is usually very good for all ages of horses if sufficient rest is given. A 50% return to soundness has been reported for horses with type II wing fractures treated conservatively. The type of P3 fracture with the most variable prognosis is type III fracture. Regardless of the treatment used, horses with type III fractures have a worse prognosis to return to performance than the other types of P3 fractures, and re-fracture of the bone may occur.