Metacarpal Injuries

The metacarpals are the three bones between the knee and the fetlock, collectively known as the metacarpus. The third metacarpal (shin) is the largest metacarpal and one of the strongest bones in the horse skeleton. The second and fourth metacarpals (splint bones) are the small bones on either side of the shin.

Dorsal Metacarpal Disease: Bucked Shins

Graphic example of a Bucked Shin.Inflammation and swelling on the front of the shin (bucked shins) results from a combination of factors including the concussion of the hoof hitting the ground, hemorrhage and stress fractures. This is particularly common among young horses that are trained too fast and too hard. The body responds to hard training by thickening the front of the shinbone (third metacarpal), but if training progresses too quickly, the body cannot keep up with the bone remodeling process and microfractures and hemorrhage develop. If training is continued, a callus will form.

Initially the horse will be reluctant to finish a training exercise. Swelling begins over the metacarpus and palpation is painful. Lameness, usually in both legs, follows.

Treatment for Bucked Shins

Following diagnosis, there is a short period of rest along with systemic and topical anti-inflammatories and physical therapy. Stall rest is not recommended; active training should be replaced by walking twice daily. Walking should be preceded by an application of warm moist heat and followed by ice/cold hydrotherapy. Alternating heat with cold therapy should be done twice daily, even if walking is not.

When pain is no longer present, walking and physical therapy can be intensified. Walking progresses to jogging, but if pain returns, the horse should return to walking. The goal of treatment is to slowly increase exercise levels to give the metacarpals a chance to adjust to the increased concussion of activity. Forms of therapy that may be used in addition to the standard treatment regime include LASER treatments and magnets. Surgical internal fixation is recommended in some cases.

Prior to resuming training re-shoe with corrective shoes with padding, which will lower the heels and eliminate toe grabs. A soft training surface is better than a hard track when training resumes.

Graphic representation of splints.Fractures of the Second and Fourth Metacarpals: Splints

Most of the common fractures to the second and fourth metacarpals (“splint bones”) are due to poor conformation, improper training and/or extensive training on a hard surface. There are two types of injuries: the “true splint” and the “blind splint.” In a true splint the ligament joining the splint bone to the third metacarpal is torn. In a blind splint this ligament is inflamed rather than torn; this type is more difficult to diagnose.

With both types of splints the horse exhibits lameness that may be mild or marked. Swelling of the surrounding tissues is visible, and pain is experienced upon palpation. If initial diagnosis occurs several weeks after the injury, swelling and pain may not be as noticeable.

Treatment for Splints

Surgical repair is recommended for fractures occurring in the lower third of the splint bones. Although most will heal with stall rest and physical therapy, a callus may develop in the area affecting the suspensory ligament, resulting in lameness. The leg is bandaged post-surgery. The horse should be rested until the sutures are removed and then walked for an additional two weeks. The leg should remain bandaged for three weeks after the sutures are removed.

Physical therapies aim at reducing inflammation with the use of systemic and/or topical anti-inflammatories, warm moist heat alternated with ice/cold therapy, and injections of corticosteroids if necessary.

Graphic example of internal fixation of a condylar fracture of the third metacarpal.Fractures of the Third Metacarpal

Transverse fractures usually occur in the middle of the third metacarpal and result from trauma, such as a fall or kick. With this type of fracture immediate lameness occurs and the horse is unable to bear any weight on the leg. Care must be taken to prevent further damage to the area. Typically a Robert Jones dressing is used to immobilize the leg and minimize further trauma prior to surgery.

Condylar fractures are vertical, originating in the base of the third metacarpal (see figure). Horses with these fractures are able to bear weight on the leg, but with obvious pain and marked lameness. Swelling is noted at the base of the metacarpus.

Treatment for Fractures of the Third Metacarpal

Transverse fractures require internal fixation with bone plating and lag screws. Older horses may require double plating. The leg is then put in a cast. Multiple cast changes are typically required post-surgery any time the horse expresses discomfort. When the final cast is removed the horse will require immobilization for some time afterwards; this is typically achieved with a Robert Jones dressing. In some cases the fracture is inoperable and euthanasia may be recommended.

Condylar fractures can be treated conservatively or surgically. If the fracture is incomplete, a conservative approach including casting, stall rest, and bandaging may be recommended. A complete fracture requires surgical internal fixation with lag screws. A cast is applied and changed as necessary for six weeks post-operatively. If treated within 48 hours of injury, the prognosis for most horses in returning to full athletic ability is good.