Osteosynthesis with Blocked Nail (“interlocking nail”) as a Treatment for Fracture of the Third Metatarsal after Metatarsophalangeal Arthrodesis with Modified Intramedullary Nail in Equine

Background: The metacarpal/metatarsophalangeal joints, as well as the suspensory apparatus, are usually affected by injuries, due to the intense physical demand during sports and great range of motion, predisposing to degenerative processes, trauma and rupture of the suspensory apparatus. In this case, arthrodesis is the main technique indicated. Such surgical techniques have a poor prognosis due to post-surgical complications, such as implant infection. Therefore, the study of procedures that promote better joint stabilization is important, with reduced surgical time and tissue exposure, decreasing significantly the chance of infection and other possible complications.Case: A 5-year-old male horse was referred to the hospital with a history of trauma and a lacerating wound in the metatarsal plantar region of the left hindlimb. The animal presented grade IV (I-V) claudication of the left hindlimb with hyperextension of the metatarsophalangeal joint and significant pain on palpation, evidencing the rupture of the superficial, deep digital flexor tendons and suspensory ligament of the fetlock. The initial surgical treatment was performed using the arthrodesis technique described by [16]. The intramedullary nail was used with fixation of the plate on the plantar face of the first phalanx together with a single plate fused to the pin, adjusted according to size of the first phalanx, 13 mm thick x 15 cm long, forming an angle between 120º and 140º. 24 hours after surgery, there was a simple spiral diaphyseal fracture (type A), in the middle third of the third metatarsal bone in the region of the proximal end, due to the lever held by the short nail against the diaphysis cortex. To treat the complication, an intramedullary 316 L surgical steel rod 13 mm thick x 21 cm long was used, filling the entire spinal canal. The nail had three holes at the proximal end and two holes at the distal end allowing the fixation of screws for cortical bone of 5.5 mm at the ends of the third metatarsal bone, stabilizing the fracture. Radiographic control of the limb was performed each 15 days, with immobilization for 90 days after surgery, thus verifying total consolidation. Concomitantly with the immobilization time, the patient showed improvement in the condition and adequate joint stabilization, presenting degree II (I-V) of lameness, due to the process of ankyloses elapsed from joint degeneration. After 10 months, the horse showed a reduction in claudication, classified as grade I (I-V). The owner was satisfied with the functional and aesthetic result of the treatment, where the animal started to be mounted and used for walks.Discussion: In this case, the treatment indicated was an arthrodesis of the metatarsophalangeal joint, due to the hyperextension of the metatarsophalangeal joint and rupture of the suspensory apparatus, since they play a fundamental supporting role. There are many arthrodesis techniques for the metacarpal/metatarsophalangeal joints; however, most of them present several complications, such as implant failure, infections and laminitis of the contralateral limb. For this reason, the development of new techniques that show satisfactory results and less disadvantages in the post-surgical period are fundamental. The nails are advantageous in relation to other fixation methods, presenting lower cost, practical application and allow the support of the fractured limb after return from anesthesia. In the case of simple spiral shaft fractures (type A), the blocked nail system promotes satisfactory stability in the fracture focus, especially for open fractures. When compared to the dynamic compression plate, it is less invasive and can be implanted as a semi-closed surgical procedure, beyond to supporting high loads in vivo.