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The purpose of this study was to report long-term outcome following arthroscopic debridement of articular cartilage lesions of the distal interphalangeal joint, diagnosed with high-field magnetic resonance imaging. Diagnosis was based on the results of diagnostic anesthesia, magnetic resonance imaging (MRI), and arthroscopy. Ten horses underwent arthroscopic evaluation for cartilage injury and received various intra-articular therapies after surgery. Three of ten horses had lesions that were surgically inaccessible. Four horses became sound and returned to their preoperative level of athleticism, and 1 horse returned to performance with continued intermittent lameness. None of the horses with an inaccessible lesion achieved soundness. Duration of lameness before surgery, preoperative evidence of degenerative joint disease, and surgical accessibility of cartilage injury did not exhibit clear influence on outcome. As a primary cause of lameness, articular cartilage injury of the distal interphalangeal joint carries a guarded prognosis for soundness with surgical therapy.

Objective – To evaluate the use of bone marrow derived mesenchymal stem cells (BMdMSC) to evaluate healing of the proximal suspensory ligament in horses with collagenase-induced desmitis and determine how evidence of healing on MRI and ultrasonographic examinations correlates to histologic and biochemical healing of the suspensory ligament. Animals – 6 horses Procedures – Clinical and MRI examinations were performed to confirm that the suspensory ligament was normal. Autologous bone marrow was collected from the tuber coxae, mesenchymal stem cells were cultured, expanded, and frozen at -80° C. Desmitis of the proximal suspensory ligament was induced with collagenase in both hindlimbs of each horse. One randomly assigned limb in each horse was treated with autogenous bone marrow derived mesenchymal stem cells (BMdMSC’s) at 2 weeks post collagenase injection, and the opposite limb was not treated. All horses were placed into a 6 months rest and rehabilitation program. Lameness examinations were performed throughout the study to determine clinical response to treatment. Healing was evaluated by MRI and ultrasound examinations 28, 90, and 200 days following induction of desmitis. Horses were euthanized at 228 days. Biochemical analysis of soluble collagen, DNA, proteoglycan and collagen type I and III were performed. Gross and histologic evaluation of ligament structure, fiber alignment, and collagen typing were used to define ligament architecture. Results – Immunohistochemical and histologic evaluation revealed improvements in ligament architectural organization, reduction in type III collagen, increases in type I collagen, and improvements in alignment of collagen fibers and fiber density in BMdMSC treated ligaments. There was no difference in biochemical indices between the two groups. MRI and ultrasound results revealed improvement in quality and rate of repair in BMdMSC treated and control ligaments over the course of the study. Ultrasonography underestimated ligament size and lesion size initially compared to MRI; however, at the conclusion of the study ultrasonographic examinations significantly overestimated lesion size. Low signal on Proton Density (PD) MRI at the previous site of desmitis correlated with histologic healing and collagen fiber reorganization at the conclusion of the study. Conclusions and Clinical Relevance – Intralesional injection of BMdMSC improves healing of the suspensory ligament. Rest alone has been a mainstay of treatment; however, ligaments treated with rest and intralesional injection of BMdMSC were more structurally normal than ligaments treated with rest alone. Ultrasound significantly underestimates the severity of ligament damage following an acute injury. MRI is recommended to determine an accurate estimate of the severity of damage to the proximal suspensory ligament in the rear limbs of horses.