With the growing popularity of equestrian sports, the incidence of athletic injuries in horses has also risen. Among these injuries, proximal sesamoid bone fracture (PSBF) and flexor tendinitis are particularly common in the forelimbs of sport horses and represent major causes of musculoskeletal impairment. A 5-year-old horse presented with obvious symptoms such as swelling at the left fetlock joint and metacarpal region after exercise. Through lameness assessment, diagnostic imaging, and hematological testing, the horse was diagnosed with PSBF complicated by flexor tendinitis. The affected horse was treated with non-steroidal anti-inflammatory drugs combined with low-intensity pulsed ultrasound (LIPUS) therapy. After treatment, local microcirculation at the fracture and flexor tendon sites was improved, tissue healing was accelerated, and clinical indicators were stabilized. This case report demonstrates the potential of LIPUS-assisted therapy in promoting the recovery of horses with PSBF and concurrent flexor tendinitis, providing a valuable clinical reference for the management of complex musculoskeletal injuries in veterinary practice.