view on the proximal portion of the suspensory ligament. It has been
suggested that the presence of injury of the proximal part of the suspensory
ligament is most commonly recognized by the presence of ultrasonographic
enlargement with poor demarcation of the borders and diffuse reduction of the
echogenicity rather than by the presence of focal areas of hypoechogenicity,
but this is not in accordance with the focal nature of many lesions as observed
on high-field MR images. The cross-sectional area of the suspensory ligament
is difficult to measure at this level as the lateral and medial margins of the
ligament are usually invisible. Even so, the cross-sectional area of normal
suspensory ligaments was measured on MR images as 0.86 cm2 at the level
of the tarsometatarsal joint, 2.08 cm2 at 2 cm, 1.81 cm2 at 4 cm, 1.69 cm2 at
6 cm and 1.57 cm2 at 8 cm distal to the level of the tarsometatarsal joint.
Nuclear scintigraphy cannot be considered a sensitive tool for the detection of
PSD in the hindlimbs of lame horses. Both pool and bone phase images were
found to be abnormal in only 15 % of horses with ultrasonographic evidence
of PSD. Increased radiopharmaceutical uptake was associated with more
severe ultrasonographic lesions. Increased radiopharmaceutical uptake in the
proximoplantar aspect of the third metatarsal bone without detectable
ultrasonographic or radiographic abnormalities represents primary osseous
pathology such as stress injury or enthesopathy at the origin of the
suspensory ligament, rather than PSD per se.
Recent high-field MR imaging studies of horses with proximal plantar
metatarsal pain have indicated that proximal suspensory desmopathy and/or
enthesopathy (PSD) was identified as the cause of lameness in the majority of
them (55-80 %), while in 20-25% of horses a pathologic process unrelated to
the suspensory ligament was documented, and in 10-20% of cases no reason
for the lameness could be found in the proximal metatarsal or distal tarsal
regions. Lesions that were considered responsible for lameness but were
unrelated to the suspensory ligament included osteoarthritis of the distal tarsal
joints, osseous cyst-like lesions of the tarsal bones, tarsal bone edema,
enthesopathy of the intertarsal ligaments, osseous injury of the third or fourth
metatarsal bones, tendinopathy of the deep or superficial digital flexor tendon,
and desmopathy of the plantar ligament. Other injuries that should be
considered in the proximal plantar metatarsal region are stress fractures of the
plantar metatarsal cortex and avulsion fractures of the origin of the
suspensory ligament. Neuropathy of the deep branch of the lateral plantar
nerve may be the cause of pain in horses without imaging abnormalities.
High-field MR imaging findings in lame horses indicated that lesions of the
proximal part of the suspensory ligament consisted predominantly of focal
areas of signal increase, that extended on average from 14.2 mm to 50.4 mm
distal to the level of the tarsometatarsal joint, with lesion length varying from
4.3 mm to 107 mm. When comparing ultrasonographic with MR imaging
findings, ultrasonography was found to have a sensitivity of 66% and a
specificity of 31% for the diagnosis of confirmed PSD. Because of the high
incidence of false positive ultrasonographic diagnoses, ultrasonography was
considered of limited value for the detection of PSD. In comparison with highfield magnets, low-field MR imaging on standing horses only has a limited
ability to show anatomic detail of the proximal portion of the suspensory
15-‐18
February
2016
East
London
Convention
Centre,
East
London,
South
Africa
169