Histological changes in the proximal suspensory ligament after neurectomy of the deep branch of the lateral palmar nerve of horses with induced proximal suspensory desmitis

Proximal suspensory desmitis (PSD) is a common cause of lameness in the pelvic limb, but could also affect the thoracic limb of competing and non-competing horses. Most horses diagnosed with PSD in a thoracic limb respond to rest followed by controlled exercise, but in a small percentage of affected horses, lameness persists. In one study, four horses chronically lame because of PSD in a thoracic limb became sound after neurectomy of the deep branch of the lateral palmar nerve (DBLPaN), which innervates the proximal aspect of the suspensory ligament (SL; Guasco et al., 2013). Whether neurectomy of the DBLPaN results in changes in the SL that might predispose the horse to re-injury is not known. The aim of this study was to describe the findings observed during quantitative lameness evaluation, gross and histological examination of the proximal portion of the suspensory ligament (SL) of the thoracic limbs of eight horses after neurectomy of the DBLPaN performed after inducing unilateral PSD by injecting collagenase into the proximal portion of the SL. The clinical response to neurectomy was resolution of lameness in all horses. Muscle fibers of the denervated ligaments presented atrophy and were infiltrated with fat and connective tissue, thereby reducing the strength and elasticity of the ligament.