Veterinary Surgery, 20, zyxwvu 4, 245-252, 1991 Desmotomy of the Accessory Ligament of the Superficial Digital Flexor Muscle in Equine Cadaver Limbs R. STUART SHOEMAKER, DvM, ALICIA L. BERTONE, DvM, PhD. Diplomate ACVS LOUAY N. MOHAMMAD, PhD and zyxwvut STEVEN W. ARMS, MSME Effects of longitudinal compression before and after transection of the accessory ligament of the superifical digital flexor (SDF) muscle were measured in eight equine cadaver forelimbs. When compression was increased from 890 N to 3115 N, the metacarpophalangeal (MCP) and carpal joints hyperextended 20" and 4", respectively, and strain in the SDF and deep digital flexor tendons was increased zyxwvut 3.5% and 1 zyxwv A%, respectively. The accessory ligament did not elongate. Immediately after transection of the accessory ligament at 3115 N load, a 2.8 mm gap formed between the transected ends of the accessory ligament, and the muscle belly of the SDF elongated and moved distad. The MCP joint hyperextended 15.8% further and strain of the SDF tendon increased 11.2% further. These results show that the accessory ligament transferred load in the SDF musculotendinous unit away from the muscle belly and that desmotomy altered this function. Decrease in the MCP joint angle indicated that the accessory ligament contributed to the support of the MCP joint under load. Increase in SDF strain after desmotomy was probably influenced by the change in the moment about the MCP joint and increased length of the SDF musculotendinous unit. ROXIMAL ACCESSORY DESMOTOMY (transection of the P accessory ligament of the superficial digital tlexor [SDF]) has been performed as a treatment for flexural de- formities of the metacarpophalangeal (MCP) joint in young horses and SDF tendinitis in race horses.'-' The accessory ligament attaches the musculotendinous junction of the SDF to the caudomedial surface of the radius (Fig. zyxwvut l).4.f' Studies to evaluate the biomechanical function of the SDF accessory ligament and its transection have not been per- formed. so explanations of the beneficial effects of the op- eration remain theoretical. The purpose of this study is to define the role of the accessory ligament in cadaver limbs when the limb is under static compression. Materials and Methods Eight cadaver forelimbs were obtained at necropsy from adult (aged 4-8 years) horses (body weight approximately 386 kg to 430 kg) without historic, visible. or palpable musculoskeletal abnormalities. Each limb was transected at the distal end of the humerus to preserve the origin of the SDF and deep digital flexor (DDF) musclc groups, and frozen at zyxwvu --70"('. Each limb was thawed to room temperature and se- cured in a servocontrolled testing machine,* with the hoof and humerus stabilized at 890 N (200 Ibs) to prevent slip- page (Fig. 2). The hoof was potted in a steel cylinder 3.8 cm deep. The humerus was cut at an angle and potted in a shallow oak cylinder 4 mm deep. A whole limb prep- aration was selected to maintain tissue fluids and mimic in vivo limb compression. Limb measurements were made at loads of 890 N and 3 1 IS N (700 Ibs) before surgery, and at zyxwvu 3 1 IS S after surgery. The antebrachium, meta- carpus. and pastern lengths were measured from the lateral tuberosity to the lateral styloid process of the radius, the dorsolateral surface of the carpometacarpal joint to the dorsolateral surface of the MCP joint. and the dorsolateral surface of the MCP joint to the coronarq band, respec- From the Department of Veterinary Clinical Sciences, School of Veterinary Medicine (Shoemaker, Bertone) and the Loutsiana Transportation ResearchCenter, Louisiana State University (Mohammad),Baton Rouge Louisiana and The Microstrain Company (Arms) Burlington Vermont Supported by the Equine Veterinary Research Program, Louisiana State University Presented at the 25th Annual Meeting of the American College of Veterinary Surgeons, 1990 Reprint requests Alicia L Bertone, DVM, PhD. Department of Veterinary Clinical Sciences, 1935 Coffey Road, The Ohio State University, Columbus, OH 43210 245