Summary
Reasons for performing study: Tearing of the medial palmar intercarpal ligament (MPICL) has been recognised as a cause of lameness in the Thoroughbred, but diagnosis is difficult due to the nonspecific clinical signs, and can be achieved only by performing arthroscopy on the mid carpal joint (MCJ). It would be beneficial to be able to image the MPICL using ultrasonography to determine whether pathology is present in the ligament in order to aid diagnosis and prognosis.
Objectives: To determine whether the MPICL could be imaged using ultrasound from the dorsal aspect of the MCJ, and to describe the technique and normal ultrasonographic appearance of the ligament.
Methods: A pilot study was performed using 2 cadaver carpi. Each carpus in turn had the MPICL imaged simultaneously using arthroscopy and ultrasound, with a metallic probe positioned on the dorsal aspect of the ligament to highlight the position of the MPICL. Six further pairs of carpi had the MPICL imaged ultrasonographically followed by dissection of the carpus to evaluate the ligament and relate its anatomy to the ultrasound images. Finally, 15 Thoroughbreds with no history of lameness isolated to the carpus had their MPICLs assessed and measured ultrasonographically.
Results: The MPICL could be imaged via the dorsal aspect of the MCJ using standard ultrasound equipment. The body and division into medial and lateral branches could be seen as a distinct, moderately dense granular echogenic structure in the palmar aspect of the joint, with clearly defined margins.
Conclusions: The normal MPICL can be imaged reliably using ultrasound in the Thoroughbred from the dorsal aspect of the MCJ. There is a wide range in the normal width of the lateral aspect of the MPICL, but there is good symmetry between contralateral limbs.
Potential relevance: This report of the normal ultrasonographic appearance of the ligament will be beneficial in acting as a reference for the detection of pathology using ultrasound.
Summary
Proximal hindlimb lameness remains a diagnostic challenge despite modern imaging techniques. In the case described here, a fracture of the ischium produced false negative results on initial ultrasound and scintigraphy examinations, despite a 14 day delay from onset of clinical signs to the time of the nuclear bone scan. However, the history and clinical examination were strongly suggestive of a pelvic injury and this was only confirmed by the use of a novel radiographic technique.
False negative findings from diagnostic imaging can, and do, occur, even with high sensitivity techniques such as nuclear bone scans used after an appropriate delay period. Therefore, equal weighting should be given to all facets of a lameness investigation, including the history and clinical examination, while remembering the limitations of any imaging modalities used.
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