“Supporting limb laminitis (laminitis developing in the hoof opposite a severely painful limb) can be one of the most challenging and often times unpredictable complications in horses with severe, unilateral lameness.” began Joanna Virgin, DVM, currently of Oakridge Equine Hospital, in Edmond, Okla., at the 2011 American Association of Equine Practitioners convention, held Nov. 18-22 in San Antonio, Texas. “This problem can be associated with fracture fixation (repair) and other painful orthopedic procedures, joint or tendon sheath infection, severe osteoarthritis, or neurological deficits, but it may occur secondary to any condition that results in prolonged, severe lameness in one limb. Many of these conditions, particularly fractures, are treated with half limb, full limb, or transfixation pin casts and support limb laminitis is a significant risk for these patients in the postoperative period.
“Previous (limited) research has found at least a 50% mortality rate associated with supporting limb laminitis,” she added. Various studies have found the incidence of the problem to range from 2.3-16% of all horses with unilateral (in one front or hind limb) lameness.
Very little research has been performed investigating risk factors for developing this complication, but Virgin reported previous research showed the duration and severity of the lameness significantly increase the risk. Some researchers believe that horses with poor foot conformation, such those with thin soles, low heels, and negative palmar angles (horses should normally have a slightly positive angle between the bottom of the coffin bone and the ground surface) could be predisposed, she added.
Thus far, there has been no association shown between these laminitis cases and the breed of the horse, gender, body weight, or limb affected (hind or fore), she added.
In the current study performed at Colorado State University with a team including Laurie Goodrich, DVM, PhD, Dipl. ACVS, and Gary Baxter, VMD, MS, Dipl. ACVS, among others, researchers evaluated case records of 113 horses that had been wearing a limb cast for at least two weeks and were at least one year old. They diagnosed supporting limb laminitis by observing characteristic clinical lameness signs and radiographic (X ray) evidence of sinking and/or rotation on lateromedial (from the side) radiographs.
Just over half the horses had hind-limb casts. Seventy-eight percent of the horses—regardless of limb affected—had half-limb casts. The rest (12%) had transfixation pin casts (casts which incorporate weight-supporting pins through the cannon bones) and full-limb casts (9%).
The most common reason for casting was pastern arthrodesis (fixation, 47%), followed by wound repair (29%), and fracture repair (5%), among others.
Of these 113 horses, she reported that 12% experienced supporting limb laminitis after wearing the cast an average of seven weeks. Nearly 20% of horses casted for more than four weeks got supporting limb laminitis.
Virgin et al. found several factors to be insignificant with regards to developing supporting limb laminitis in this group, including front vs. hind limbs, breed, presence of fractures, or weight-bearing capacity at presentation. Significant factors included full-limb vs. half-limb casts (horses that require treatment with a full-limb cast were at a fivefold greater risk), transfixation pin casts vs. other types (the former posing a 4.6-fold greater risk), and duration that horses required the cast. Additionally, she noted, there was a positive association between higher body weight and support limb laminitis (1% higher incidence for every 1 kg increase in body weight).
“In the population of horses treated with casts included in this study, the probability of support limb laminitis increased by 20% for every additional week that the horse required cast treatment," she relayed. "Unlike previous studies, however, it appears that heavier horses may be at an increased risk.
“The results of this study confirm the clinical opinion that support limb laminitis is a definite risk in horses that require treatment with half limb, full limb, or transfixing pin casts," she continued. "Pre- and post-operative pain management, timely treatment of the inciting lameness, and support limb prophylactic devices (preventive methods) are critical in these cases to prevent this complication."
She also recommended that further research is necessary to determine other risk factors which may help veterinarians better predict and prevent this complication in their patients.
Disclaimer: Seek the advice of a qualified veterinarian before proceeding with any diagnosis, treatment, or therapy.