Fractures of the First and Second Phalanx in Horses
P1 Fractures
Fractures of the first/proximal phalanx (P1) can occur in any type of horse used for performance. There are several types:
Small osteochondral “chip” fractures along the dorsal margin of the proximal joint surface
Sagittal (complete or incomplete)
Comminuted
Fragments of the palmar or plantar proximal aspect of P1, which may be associated with osteochondrosis (see osteochondral fragments image)
Courtesy of Dr. Matthew T. Brokken.
Chip fractures of the dorsoproximal aspect of P1 typically involve the medial aspect of the joint and occur in horses that exercise at speed. These fractures are typically traumatic in origin and result from hyperextension of the fetlock joint. Acute lameness and increased effusion in the fetlock joint, along with sensitivity to firm flexion of the fetlock, are clinical signs that a fracture may be present and radiographic examination indicated.
In nonracing breeds, a chip fracture can be evident on radiographs. Its clinical importance, however, should be determined with diagnostic analgesia before it is implicated as a source of lameness. (See Regional Anesthesia in Horses for discussion of specific anesthetic techniques used to localize lameness.)
The cause of proximopalmar and proximoplantar osteochondral fractures in horses is unknown. One hypothesis is that they are due to osteochondrosis; another is that they are fractures. Axial fractures are classified as type I fractures and are generally articular. Type II fractures are located abaxially and typically have minimal articular cartilage present. Type I fractures are generally associated with lameness at speed, accompanied by clinical signs similar to those of dorsoproximal P1 fractures. These fractures are more common in the hindlimb, and intra-articular diagnostic analgesia is often needed to confirm that they are a cause of lameness.
Diagnosis of P1 fractures in horses is confirmed by radiographic examination (see P1 fracture images). Multiple oblique radiographic views may be necessary to ensure visibility of the fractures.
For palmar or plantar osteochondral fractures, oblique radiographic views with the beam raised approximately 20° from horizontal can be helpful for identification.
The diagnosis of sagittal or comminuted fractures of P1 is typically straightforward, based on marked lameness and swelling.
Incomplete, short sagittal P1 fractures can be more difficult to diagnose. Their detection sometimes requires special radiographic views deviated a few degrees from true dorsopalmar or dorsoplantar, or nuclear scintigraphy.
Courtesy of Dr. Matthew T. Brokken.
If occult fracture lines are suspected with a P1 fracture, CT imaging is essential for accurate diagnosis and reconstruction.
Osteochondral chip fractures can be removed arthroscopically with an excellent prognosis if no other abnormalities within the joint exist.
Routine, nondisplaced sagittal P1 fractures can be repaired by internal fixation using screws placed in lag fashion via stab incisions.
More complex P1 fractures typically require open reduction and repair via lag screws to enable accurate realignment of the articular surface of the fetlock to limit postoperative arthritis.
Careful attention should be paid to the fracture configuration to ensure that all components are incorporated in the repair.
Conservative treatment of severely comminuted P1 fractures consists of cast immobilization for up to 12 weeks, with or without transfixation pins through the third metacarpal/tarsal bone.
Complications of P1 fracture repair in horses include implant failure, poor alignment at the fracture site leading to secondary arthritis, and contralateral limb laminitis.
P2 Fractures
Fractures of the second/middle phalanx (P2) can occur in any breed. They occur most commonly, however, in horses working in tight circles, such as Quarter Horses and warmblood breeds.
The most common fractures of P2 are either palmar/plantar eminence fractures of proximal P2 or comminuted fractures (see P2 fracture images).
Courtesy of Dr. Matthew T. Brokken.
Most P2 fractures in horses are treated with internal fixation or a transfixation pin cast. Residual lameness typically is present and depends on the extent of osteoarthritis that develops in the distal interphalangeal joint and, to a lesser extent, in the proximal interphalangeal joint (if not arthrodesed in the fracture repair).
The prognosis with P2 fractures depends on how comfortable the horse is after fracture stabilization, which largely determines the risk of contralateral limb laminitis.
Fractures of the Proximal Sesamoid Bones in Horses
Fractures of the proximal sesamoid bones in horses are classified according to their location in the bone. They are almost exclusively an injury of racehorses.
The most common sesamoid fractures in Standardbreds and Thoroughbreds are apical (see sesamoid bone apical fracture images). They are due to overextension and often are associated with suspensory ligament damage. Other fracture configurations include midbody, basilar, abaxial, axial, and comminuted, and they can involve one or both sesamoids.
Courtesy of Dr. Matthew T. Brokken.
Most sesamoid fractures, apart from some abaxial and basilar fractures, are articular.
Clinical signs include heat, pain, and acute lameness, which is exacerbated by flexion of the fetlock. Sesamoid fractures are often accompanied by hemarthrosis and synovial effusion of the metacarpophalangeal/tarsophalangeal joint.
Diagnosis is confirmed by radiographic examination.
Apical sesamoid fractures are removed arthroscopically and carry a good prognosis for return to athletic function.
In studies of Thoroughbred racehorses, horses with apical fractures of the forelimb medial proximal sesamoid have been found to be less likely to return to racing after fragment removal, compared with horses with fractures of the hindlimb.
The presence of suspensory desmitis in the affected limb worsens the prognosis after surgery.
The size and shape of apical sesamoid fractures do not appear to affect racing performance.
Midbody sesamoid fractures typically require reduction using lag screw fixation, and there is a fair to good prognosis of returning to racing. The prognosis for basilar fractures involving a portion of the sesamoid is fair compared with that for fracture of most of the base or fracture accompanied by articular disease, each of which has a poor prognosis.
Complete disruption of the suspensory apparatus due to simultaneous fracture of both sesamoid bones is a catastrophic injury commonly referred to as a "breakdown." The resultant severe fetlock hyperextension also causes vascular compromise on the palmar aspect of the limb; however, some horses can be salvaged for breeding by surgical arthrodesis of the fetlock joint.
Osteoarthritis of the Proximal Interphalangeal Joint in Horses
Osteoarthritis of the proximal interphalangeal joint (also called "high ringbone") is a common cause of lameness in horses used for a variety of disciplines; it is most common in Western performance horses. The osteoarthritic process can start with a single traumatic episode, or it can be the result of wear and tear, or overuse. Rarely, it may be the result of developmental orthopedic disease or infection.
Courtesy of Dr. Matthew T. Brokken.
The proximal interphalangeal joint is a low-motion joint that is unforgiving to high loads placed on it. Osteoarthritis in the pastern, as elsewhere, is characterized by cartilage loss and periarticular new bone formation.
In chronic cases of pastern osteoarthritis, lameness is typically subtle at first and becomes more noticeable as the disease progresses.
Radiographic findings in cases of proximal interphalangeal joint osteoarthritis may include periarticular new bone formation, subchondral lysis or sclerosis, and loss of joint space (typically the medial aspect of the joint; see proximal interphalangeal joint and metacarpophalangeal joint osteoarthritis images).
Courtesy of Dr. Matthew T. Brokken.
In the early stages of proximal interphalangeal joint osteoarthritis, diagnostic analgesia is typically required to localize the lameness. (See Regional Anesthesia in Horses for discussion of specific anesthetic techniques used to localize lameness.) In addition, a positive response may be evident on lower limb flexion.
Oral or intra-articular anti-inflammatory medication can temporarily relieve the clinical signs of lameness due to osteoarthritis. Intra-articular injection of ethanol into the proximal interphalangeal joint can induce chemical arthrodesis. Surgical arthrodesis of the pastern joint is frequently required to manage lameness and possibly restore performance (see pastern arthrodesis image).
Courtesy of Dr. Matthew T. Brokken.
The prognosis for return to performance is better for horses with affected hindlimbs than for horses with affected forelimbs.
Palmar Osteochondral Disease of the Fetlock in Horses
Palmar osteochondral disease of the fetlock affects the subchondral bone of the palmar/plantar aspects of the distal metacarpal/metatarsal condyles and is a common cause of performance-limiting lameness in Standardbred and Thoroughbred racehorses. It is thought to be a stress remodeling response to intense activity in young racehorses and is associated with lameness referable to the fetlock region.
Typically, the lameness improves with a block of the palmar/plantar metacarpal/metatarsal nerves proximal to the fetlock. Intra-articular analgesia of the fetlock joint can have varying results and is less reliable to improve lameness.
Radiographic signs of palmar osteochondral disease of the fetlock may be minimal. The changes are identified earliest by the use of nuclear scintigraphy, PET, CT, or MRI. Treatment consists of controlled exercise.
See Regional Anesthesia in Horses for discussion of specific anesthetic techniques used to localize lameness.
Sesamoiditis in Horses
The sesamoid bones in horses are maintained in position by the branches of the suspensory ligament proximally and by a number of sesamoid ligaments distally.
Because of the great stress placed on the fetlock during fast exercise, the abaxial portion of the proximal sesamoid bones is susceptible to stress-related injury. Sesamoiditis is a clinically distinctive condition characterized by inflammation of the sesamoid bones.
The clinical signs of sesamoiditis are similar to but less severe than those resulting from sesamoid fracture. The amount of damage determines the extent of lameness and swelling. Pain and heat are evident on palpation and flexion of the fetlock joint.
Radiographic evidence of sesamoiditis includes focal osteolysis and enlarged vascular channels (or linear defects in the abaxial margin of the proximal sesamoid bones). The insertion of the suspensory ligaments should be carefully evaluated by ultrasonographic examination for concurrent lesions.
The recommended treatment is enforced rest and supportive care to combat inflammation and soreness.
Chronic Proliferative Synovitis in Horses
Proliferative synovitis is enlargement of the fibrocartilaginous pad on the dorsoproximal aspect of the joint capsule attachment of the fetlock joint. This inflammation is thought to be due to repetitive trauma from exercise.
Proliferative synovitis is found most frequently in racing Thoroughbreds; it can also develop in Standardbreds and nonracing breeds. Clinical signs include fetlock joint effusion, firm swelling over the dorsoproximal aspect of the fetlock joint, lameness, decreased range of motion, and a positive response to firm flexion of the fetlock.
Palpation can yield a tentative diagnosis of proliferative synovitis. Radiography can reveal associated osteolysis at the proximal aspect of the dorsal midsagittal ridge of the distal third metacarpal bone on the lateromedial projection. The radiolucency is a result of the damage to the cortical bone from the overlying fibrous mass.
Ultrasonography can also be useful in diagnosing proliferative synovitis. The synovial pad is considered abnormal if it is > 4 mm thick and has rounded distal margins, or if hyperechoic regions are found within the pad.
Proliferative synovitis is treated by surgical excision via arthroscopy.
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