The sesamoid bones are maintained in position by the branches of the suspensory ligament proximally and by a number of sesamoidean ligaments distally. Because of the great stress placed on the fetlock during fast exercise, the abaxial portion of the proximal sesamoid bones is susceptible to stress-related injury. Sesamoiditis is a clinically distinctive condition; however, it is poorly characterized pathologically.
The clinical signs are similar to, but less severe than, those resulting from sesamoid fracture. Depending on the extent of the damage, there are varying degrees of lameness and swelling. Pain and heat are evident on palpation and flexion of the fetlock joint. Radiographic evidence of sesamoiditis involves periarticular osteophytes, entheseophytes, focal osteolysis, and enlarged vascular channels (or linear defects in the abaxial margin of the proximal sesamoid bones). Grading scales for sesamoiditis exist and particularly note the vascular channels on radiographs. Severity of sesamoiditis on radiographs has been linked to a decrease in racing performance in one study. In another study, when radiographic signs of significant sesamoiditis were present, horses had a 5 times greater risk of developing clinical signs of suspensory ligament branch injury with onset of training.
The recommended treatment is enforced rest and symptomatic treatment to combat inflammation and soreness. The insertion of the suspensory ligaments should also be carefully evaluated by ultrasonography for concurrent lesions.