The SL of the forelimb is commonly injured in horses that participate in a variety of disciplines, including racehorses and sport horses.1–5 Suspensory ligament desmitis is often associated with decreased performance and can be a career-ending injury.1–5 Lesions of the SL can develop at its proximal, midbody, or distal region,6 and the prognosis and rate of recurrence following an SL injury vary and are dependent on the anatomic region involved.2,6,7 Injuries to the midbody region and distal branches of the SL tend to heal poorly and have a higher rate of recurrence than do injuries to the proximal region of the SL.2,6,7 Unlike horses with lesions of the midbody region or distal branches of the SL, up to 90% of horses with acute lesions of the proximal region of the SL return to their previous level of activity following stall rest.8 Event horses with desmitis of the midbody region of the SL have a high rate of desmitis recurrence despite extended rest, which might be caused by failure of the ligament to heal completely.2 Additionally, although sport horses with lesions of the distal branches of the SL generally have a fair prognosis, the lesion recurrence rate can be high.2,7,8
The reason for regional variations in the healing and reinjury rates of the SL is unclear and may be caused by zones of hypovascularity within the midbody region and distal branches of the SL in a manner analogous to zones of hypovascularity identified within the SDFTs9 and deep digital flexor tendons10 that have been associated with a predisposition to injury and incomplete healing. In human patients, results of multiple studies11–18 suggest that regions of hypovascularity are associated with ruptured tendons and a poor healing response in those regions following injury to the tendons of the rotator cuff,15–17 calcaneus,12,13 biceps brachii,14 and quadriceps femoris18 and in the common extensor origin of the elbow joint.11
The principal and microvascular anatomy of the SDFTs9 and deep digital flexor10 tendons of horses have been described. To our knowledge, a detailed study to describe the microvascular anatomy of the forelimb SL of horses has not been performed. Therefore, the purpose of the study reported here was to use results of contrast-enhanced CT, microvascular injection (ie, Spalteholz tissue-clearing technique19), and routine histologic evaluation to describe the blood supply of the SL of the forelimb of horses. It was hypothesized that zones of hypovascularity would exist in the midbody and distal regions of the SL. The presence of hypovascular zones in these areas could provide a possible mechanistic explanation for the poor healing and high rate of recurrence for injuries to the midbody region and distal branches of the SL.
Superficial digital flexor tendon SL Suspensory ligament
75% Iopamidol, Bracco Diagnostics, Princeton, NJ.
GE Brightspeed, GE Healthcare, Waukesha, Wis.
Mimics, Materialise, Leuven, Belgium.
Black Magic, Higgins, Bellwood, Ill.
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