Advanced imaging of an incomplete fracture and exostosis of the third metacarpal bone in a young Warmblood horse

Abstract

Summary A 5‐year‐old Hanoverian gelding with acute moderate right forelimb lameness underwent nuclear scintigraphy, which identified marked increase in radiopharmaceutical uptake of the proximomedial aspect of the right metacarpus. Ultrasonography and radiography identified sclerosis and exostosis of the proximomedial aspect of the metacarpal bone III in‐between the suspensory ligament and the second metacarpal bone, and presence of a suspected fracture. The owner requested euthanasia of the gelding, and post‐mortem computed tomography and magnetic resonance imaging identified marked bone sclerosis and thickening of the palmar cortex of the metacarpal III (McIII), presence of an incomplete fracture in the palmar cortex of McIII and expansive exostosis from McIII extending in a palmar direction between the suspensory ligament and the second metacarpal bone. Histopathological examination confirmed the imaging findings of sclerosis and led to final diagnosis of a fracture of the palmar cortex of the McIII associated with an exostosis encroaching the medial aspect of the suspensory ligament. No abnormalities were present in the suspensory ligament or metacarpal bone II (McII).

Incomplete metacarpal fracture with exostosis or ‘blind splint’?

“…; Werpy and Redding ; Isgren et al . ), the bone proliferation seems to follow a curvilinear path around the suspensory ligament. This curvilinear projection is present at the same proximal to distal location in all these cases.…”

“…It has been surmised that the region of injury is difficult to detect on physical examination because the injury occurs on the axial (inner) side of the splint, between the small metacarpal bone and the suspensory ligament in the same region highlighted by Isgren et al . (). It has been reported that histologically, the affected interosseous ligament usually consists primarily of chondroid tissue, whereas the normal interosseous ligament is primarily composed of dense white fibrous connective tissue.…”

“…; Werpy and Redding ; Isgren et al . ). Calcification of this soft tissue plane may be what is visualised in these reports and may represent a traumatic enthesiophyte rather than an exostosis.…”

“…In the paper by Isgren et al (2020), the authors describe an injury to the proximal medial metacarpus in a young Warmblood that they characterised as an incomplete palmar metacarpal fracture with a resultant exostosis. While the clinical examination could not locate the source of pain, clinical imaging determined the location of the injury.…”

“…Historically, the term blind splint is a rather ambiguous concept most often described as inflammation of the interosseous ligament between the second and third metacarpal bones and is a lesion that is not readily detectable externally by observation or palpation (Goble 1982). It has been surmised that the region of injury is difficult to detect on physical examination because the injury occurs on the axial (inner) side of the splint, between the small metacarpal bone and the suspensory ligament in the same region highlighted by Isgren et al (2020). It has been reported that histologically, the affected interosseous ligament usually consists primarily of chondroid tissue, whereas the normal interosseous ligament is primarily composed of dense white fibrous connective tissue.…”