Page 567 - Adams and Stashak's Lameness in Horses, 7th Edition

Lameness of the Distal Limb 533

Desmitis of the oblique, straight, and cruciate DSLs must be localized with perineural anesthesia. Sometimes
occurs in all types of performance horses with injury to there will be pain on deep palpation of the ligament. The
VetBooks.ir jump (e.g. event horses, show jumpers, field and show to fetlock or phalangeal flexion, and worsened when the
the oblique DSL being most common. Horses that
lameness is usually mild to moderate in severity, positive
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hunters, steeplechasers, and timber racehorses) and race
affected limb is in the inside of the circle. Palpation of
and Quarter horses used for western performance such the DSLs is best performed with the foot held off the
as reining, cutting, and barrel racing appear to be par- ground and the MCP/MTP joint flexed so the flexor ten-
ticularly prone to these injuries. However, injuries to dons are relaxed.
these ligaments may not be the sole cause of lameness in Swelling of a DSL must be differentiated from swell-
many horses. 30,65 ing of the medial or lateral branch of the SDFT, which is
The medial branch of the oblique DSL is more com- also located in the midpastern region. Passive fetlock
monly injured than the lateral branch in some studies and phalangeal flexion are commonly painful, and direct
although others report equal medial and lateral fre- digital pressure over the swollen region of the DSL for
quency, and the hindlimbs are more often affected than 30 seconds may increase the signs of lameness.
the forelimbs. 30,58,65 When the straight DSL is injured, it Although the clinical findings may indicate a problem
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is most often in the distal one‐third of the ligament. in the palmar/plantar pastern region, perineural anes-
Injuries to the DSLs can be the primary injury or can be thesia should be performed to rule out concurrent
part of a complex of lesions, all of which contribute to involvement of the foot. Perineural anesthesia of the PD
some part of the current lameness. Horses with a valgus nerve at the base of the sesamoid bone (basisesamoid
or varus limb conformation or long, sloping pasterns block) should improve the lameness in most cases as will
may be at increased risk for DSL injury. intrathecal block of the DFTS. However, an abaxial
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sesamoid or low four‐point block may be necessary if
the ligament injury is located proximally in the pastern.
4
Etiology
In addition, other concurrent problems should be closely
The DSLs are a functional continuation of the more evaluated because a recent report suggested that lesions
proximally located suspensory ligament and are an of the DSLs found on MRI were the sole cause of lame-
important part of the suspensory apparatus that pro- ness in only 2 of 58 horses. It should be kept in mind
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vides resistance to extension of the MCP/MTP joint dur- that most horses with obvious DSL injury on ultrasound
ing the stance phase. Hyperextension of the MCP/MCT exam would not have received an MRI by the authors.
joint can result in supraphysiologic strains in the sus- See Chapter 2 for more information on perineural
pensory apparatus, which may lead to injury to the anesthesia.
DSLs. Although the DSLs in total provide this functional
counter‐resistance to extension, each ligament has a sep-
arate function that may account for the specific injuries Diagnosis
that occur to these structures. Diagnostics that may help document an abnormality
The straight DSL is the only unpaired ligament and is to one of the DSLs include radiography, ultrasound, and
thought to contribute to sagittal stabilization of the MRI. Radiographic abnormalities that may suggest a
MCP/MTP and PIP joints. The straight DSL would most previous or concurrent injury of a DSL include entheso-
likely be injured during hyperextension, but surpris- phyte formation, avulsion fractures/fragments, and
ingly, injury to this ligament is less common than to the dystrophic mineralization within one of the DSLs.
oblique DSL. 58,61 The paired oblique DSLs are thought Enthesophyte formation at the attachment of the oblique
to play a prominent role in the limitation of rotation DSL at the palmar/plantar aspect of P1 is a relatively
and abaxial movements of the MCP/MTP joint. Injuries common finding and may be incidental (Figure 4.113).
to the oblique DSLs usually occur unilaterally, probably Enthesophyte formation at the proximal aspect of P1
as a result of asymmetric loading caused by abnormal and at the base of the proximal sesamoid bone is also
conformation, lateral/medial foot imbalances, a misstep, believed to be evidence of injury to the cruciate or short DSL.
or poor footing. Injuries to the oblique DSL are more Fractures/fragments of the base of the proximal
common than those to the straight or cruciate DSLs, sesamoid bone can involve the DSLs. Fragments from
4
although concurrent injuries to the straight and oblique either the dorsal aspect of the base of the proximal sesa-
DSLs have been reported. 58 moid bone or proximal palmar/plantar articular margin
of P1 typically involve the short DSL. Bone fragments
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Clinical Signs have also been observed on the nonarticular proximal
extremity of P1 and at the base of the sesamoid bones.
4
Horses with acute desmitis often present with a sud- These fracture fragments may involve the oblique,
den onset of lameness. Mild swelling of the palmar/plan- cruciate, or short DSLs. 4,55 Dystrophic mineralization
tar surface of the pastern region may be present as a associated with the DSLs may also be present radio-
result of digital sheath effusion. The effusion is most graphically, usually at the base of the sesamoid bones. It
commonly seen in acute cases (less than 3 weeks’ dura- is important to differentiate dystrophic mineralization
tion), but soft tissue swelling is usually not apparent in from avulsion fractures at the base of the sesamoid
most cases. Heat and pain with digital pressure may also bones because fracture fragments can and should be
be palpable in acute injuries. removed, whereas there is usually no treatment for
Horses with chronic injuries may have a more insidi- mineralization. 4
ous onset of lameness. Obvious heat, pain, and swelling Sonographic evidence of acute desmitis of the DSLs is
are rarely present, and the location of the lameness often manifested by a diffuse increase in ligament size, fiber