Distal limb cast sores in horses: risk factors and early detection using thermography

There is a lack of evidence-based data on the prevalence, outcome and risk factors of distal limb cast sores, and no objective tool has been described for the early detection of cast sores.

To investigate the prevalence, location, outcome and risk factors of cast sores after application of a distal limb cast and to determine whether static thermography of the cast is a valuable tool for the assessment of sores.

A prospective study was conducted on horses treated with a distal limb cast. At each cast removal, cast sores were graded as superficial sores (SS), deep dermal sores (DS) or full thickness skin ulcerations (FS). In several cases, a thermographic evaluation of the cast was performed immediately prior to removal and differences in temperature (AT) between the coolest point of the cast and 2 cast regions predisposed for sore development (dorsoproximal mc/mtIII and palmar/plantar fetlock) were calculated.

Mean +/- s.d. total casting time of 70 horses was 31 +/- 18 days. Overall, 57 legs (81%) developed at least SS. Twenty-four legs (34%) ultimately developed DS and one horse had an FS. Multivariable analysis showed that the severity of sores was positively associated with increasing age (OR: 1.111, P = 0.028), a normal (vs. swollen) limb (OR: 3387, P = 0.023) and an increase in total casting time (OR per week: 1.363, P = 0.002). The thermographic evaluation (35 casts) revealed that the severity of sores was positively associated with increasing deltaT (OR: 2.100, P = 0.0005). The optimal cut-off values for the presence of SS and DS were set at, respectively, deltaT = 23 and 43 degrees C.

Distal limb cast is a safe coaptation technique with increasing risk of developing sores with time. Thermography is a valuable and rapid clinical tool to monitor the development of cast sores.