Page 582 - Adams and Stashak's Lameness in Horses, 7th Edition

548 Chapter 4

fractures that are not treated surgically. Most of these (2‐ and 3‐year‐old) racehorses and discovered that many
joints develop significant OA and restricted range of horses have increased size and number of vascular chan-
VetBooks.ir nosis is poor due to the loss of suspensory support and more than two irregular vascular channels had a
nels without lameness.
Yearling Thoroughbreds with
joint motion. If both sesamoids are fractured, the prog-
37,38
decrease in number of race starts and earnings at 2 and
only should be considered for salvage of valuable breed-
ing stock or in horses of great sentimental value. 3 years of age. This supports the idea that remodeling
85
is a normal response to training and that only if the
SESAMOIDITIS stresses exceed, the bones’ capability to strengthen
would microfracture and bone damage occur. Although
Sesamoiditis is observed frequently in racing horses radiographic vascular changes of bone remodeling were
and hunters and jumpers between 2 and 5 years of not associated with sesamoid fracture, the vascular
age. 60–62,89 The condition is characterized by pain associ- structures course along known lines of fracture in adult
ated with the proximal sesamoid bones and insertions of racehorses. The sesamoid bones have an extensive sen-
the SL that result in lameness. The pain is thought to sory nerve supply that may explain bone pain associated
result from inflammation at the interface of the SL with with trabecular bone injury. 26,27 Concurrent suspensory
the proximal sesamoid bones. 62,89 Concurrent SL branch branch injury may also contribute to the palpable pain
disease should be suspected in these horses. A significant and lameness in affected horses. 34,58,71
relationship between the presence of sesamoiditis and
the subsequent development of SL injuries has been doc- Clinical Signs
71
umented. Evidence of sesamoiditis suggests a 5 times
greater risk for developing injuries to the SL branch Symptoms of this condition are similar to those
with the onset of training. Pain, heat, and inflamma- caused by fracture of the sesamoid bone. In the early
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tion can usually be clinically detected at the insertion of stage, minimal swelling is observed, but increased heat
the SL during the active stages of the disease process, but may be felt over the abaxial surface of the sesamoid
marked lameness and limitations on performance can bone(s). As the disease progresses, visible enlargement of
also occur without any clinically detectable signs. 22,37 the soft tissues overlying the palmar/plantar surface of
Radiographs can reveal a range of changes from the fetlock can be seen as fibrosis of/around the injured
accelerated early remodeling response in the bones SL becomes apparent. On palpation, pain withdrawal
(increased size and number of vascular canals) to marked can usually be elicited by placing pressure over the
proliferation of bone along the abaxial margin of the abaxial surface of the sesamoid bones. In more advanced
sesamoid and increased bone density of the sesamoid. cases, pain may be elicited by applying pressure over the
The SL and the DSLs may also be affected and show branches of the SL. The horse will also likely be positive
calcified areas. The increased bone production is thought to distal limb flexion.
to result from inflammation from tearing of the attach- At exercise, the lameness varies considerably and
ments of either the SL or the DSLs. Young Thoroughbreds depends on the acuteness of the injury and its degree. In
with more severe radiographic signs of sesamoiditis are general, the lameness is most evident during the first
thought to be at increased risk to develop future suspen- part of exercise and is more exaggerated when the horse
sory branch injuries. However, it is also possible to see is exercised on hard surfaces. Perineural and/or intra-
58
radiographic changes indicating chronic sesamoiditis in synovial anesthesia is used infrequently to diagnose this
sound performing horses, suggesting that some horses condition. Horses respond to a low four‐point nerve
heal the injury and regain suspensory strength. 37 block, but not to an intra‐articular fetlock block, locat-
ing the lameness to the periarticular structures.
Etiology
Diagnosis
Any unusual strain to the fetlock region may produce
sesamoiditis. Most commonly in racehorses, hunters, The radiologic changes of true sesamoiditis have
and jumpers, it can affect any type of horse. It is caused been described as bony changes on the abaxial surface
by increased stress to the attachment of the SL to the or basilar region, increased number and irregularity of
sesamoid bones. Injury to the DSLs may also occur at the vascular channels, and increased coarseness and
their attachment to the basilar portion of the sesamoid mottling of the bone trabeculation (Figure 4.130). In
bones. acute cases, radiographs may have to be taken approxi-
The sesamoid bones have a substantial intraosseous mately 3 weeks after onset of the condition to deter-
blood supply that enters the midportion of the bone mine whether bony changes will occur on the sesamoid
through multiple abaxial channels that correspond to bones. The condition may also occur with tenosynovi-
the channels that enlarge in sesamoiditis, indicating tis, fracture of the sesamoid bones, and injury to the SL
bone remodeling. This may represent the initiation of from which it must be differentiated. Careful radio-
the remodeling response to bone stress of training, or it graphic interpretations of the mottled trabecular pat-
may reflect an increase in blood flow due to inflamma- tern seen in the proximal sesamoid bone are necessary
tion and injury to the SL, or both. The sesamoid bones to differentiate a fracture. Incomplete fracture can be
94
undergo intense remodeling in response to training, differentiated from these coarse vascular canals because
107
and the progression of radiographic changes correlates the fracture usually extends to the abaxial surface and
to bone response to remodeling and injury. the vascular canals do not. In addition, fracture lines
Interestingly, several studies have categorized the frequently run at different angles than the vascular
radiographic changes in sesamoid bones of young channels.