Page 607 - Adams and Stashak's Lameness in Horses, 7th Edition

Lameness of the Distal Limb 573

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A B
Figure 4.148. (A) Open comminuted mid‐diaphyseal fracture of plates on the dorsolateral and dorsomedial sides of the metatarsus.
the metatarsus in a 7‐month‐old weanling. (B) Postoperative view Additional screws were placed in lag fashion from outside the plates
demonstrating fracture repair with two broad dynamic compression to secure the butterfly fragments.

Etiology and older had two or more sites of fusion. The rate of
metacarpal fusion/horse/year appeared to be at least 10
The enlargement of the splint bones associated with
this disease results from proliferation of fibrous tissue times higher than the rate of painful exostoses causing
fusion, indicating that this process occurs subclinically
and osteoperiostitis. The causes are tearing of the inter- in most horses. 75
osseous ligament that binds a small metacarpal bone to Imbalanced nutrition or overnutrition in young
the large metacarpal/metatarsal bone, external trauma, horses has also been implicated in the development of
and healing of a transverse or longitudinal fracture. If splints. Imbalances and deficiencies in calcium and
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the inflammation associated with the periosteum is suf- phosphorus have been associated with an increased inci-
ficient, over time it will result in ossification (prolifera- dence of splints. However, no well‐documented studies
tive exostosis) of the splint bone. The size of the splint have proven this to be true. In many cases horses that
usually depends on the degree of inflammation and the are suspected of having a calcium and phosphorus
surface area involved. In any case, the splint usually imbalance also grow rapidly. It may be that their
assumes an elongated form, lying parallel to the small increased weight causes sufficient compressive forces so
metacarpal bone. that splints develop as a result of this, rather than the
The second metacarpal bone is more frequently imbalance. In general, young horses that are poorly con-
involved because of the difference in its articulation formed, overweight, and overexercised have a greater
with the carpus. The second metacarpal bone is entirely chance of tearing the interosseous ligament before meta-
articular, and its articulation is flatter than that of the carpal fusion is complete.
fourth metacarpal bone. Ex vivo biomechanical evalua-
tion of the second metacarpal bone has shown that it
plays a significant role in torsional stability of the car- Clinical Signs
pus. It is proposed that excessive loading can lead to
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tearing of the interosseous ligament in the region that is The condition is most common in young horses
most frequently affected. Metacarpal fusion progresses undergoing heavy training, but cases occasionally
normally with aging, and 78% of all horses 2 years old occur in older, mature horses. Heat, pain, and swelling