Graduate Thesis Or Dissertation
 

A molecular and morphologic study of idiopathic fetlock hyperextension and suspensory apparatus breakdown in the llama

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  • Suspensory apparatus breakdown and hyperextension of the metacarpophalangeal and metatarsophalangeal (fetlock) joints is a common condition in the llama and has been observed in llamas of all ages. Llama breeders refer to the condition as "down in the pasterns" or "down in the fetlocks." The condition can result in debilitating lameness, most likely due to mineralization of soft tissues including the tendons and ligaments and/or osteoarthritis of the metacarpo/metatarsophalangeal, proximal interphalangeal and distal interphalangeal joints. Two forms exist, an induced form occurring from abnormal weight bearing such as a severe lameness in a contralateral limb, and an idiopathic form that affects multiple limbs. The idiopathic form is poorly characterized in the llama and has not been reported in the literature prior to the studies performed as part of this thesis. The specific aims of this thesis were to characterize the nature of suspensory apparatus breakdown in the llamas by use of ultrasonographic and radiographic evaluation, histologic evaluation, biochemical assessment of collagen, copper concentrations and lysyl oxidase activity, and molecular techniques to identify specific gene expression alterations and matrix connective tissue changes. The specific hypotheses were: 1) affected llamas would have ultrasonographic and histologic evidence of disruption of fibers in the suspensory ligament 2) affected llamas would have decreased copper concentrations and lysyl oxidase activity 3) affected llamas would have decreased gene expression of collagen type I and lysyl oxidase, and increased gene expression of collagen type III and matrix metalloproteinases as a result of ongoing repair of tendons and ligaments. High serum zinc concentration coupled with low liver copper concentration were found in llamas having metacarpo(tarso)phalangeal hyperextension. However, lysyl oxidase activity was no different between the affected and controls, even though the copper levels were lower in affected animals. In addition, other expected changes on radiographs and ultrasound were not as prevalent as hypothesized. No significant difference was appreciated between affected and control animals in expression levels of collagen types I or III, LOX or MMP-13, although there was a trend towards decreased expression of MMP-13 in affected animals. Mild proteoglycan accumulation was appreciated in the suspensory ligament of two of the six affected animals. No difference in distribution of collagen types I or III was appreciated on histologic section, and elastic fiber appearance was similar between the affected and control animals. This thesis suggests a different etiology to fetlock hyperextension than initially hypothesized.The lack of radiographic, ultrasonographic, histologic, and biochemical differences between affected and control animals supports a nondegenerative etiology for this condition.
  • Keywords: fetlock, Llama, Hyperextension, suspensory, collagen
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