How to Treat Dorsal Metacarpal Disease with Regional Tiludronate and Extracorporeal Shock Wave Therapies in Thoroughbred Racehorses

1. Introduction

Dorsal metacarpal disease (DMD) or bucked shins is a common condition seen in racehorses caused by inadequate bone modeling and remodeling resulting in fatigue failure of the third metacarpal bone (MCIII).^1–3  Initially, these horses demonstrate sensitivity to palpation of the dorsal cortex of MCIII in the absence of lameness. The pain and inflammation arises from the formation of new periosteal bone in response to the decreased bone stiffness as a result of high strain cyclic failure.^1–3  However, lameness is often observed as continual high-strain cyclic loading and inadequate bone remodeling occurs resulting in failure of the bone.^1–3  The most common fracture configuration is an incomplete stress fracture involving the mid-distal dorsal lateral cortex of MCIII.³

Several techniques have been described to manage dorsal cortical stress fractures, including conservative or surgical management. Surgical management includes osteostixis, an intracortically placed screw, or combination of the two techniques.^4–8  Conservative management is acceptable for horses without a stress fracture; however, it is typically not advocated for horses with a fracture due to inadequate healing and the persistence of a radiographic fracture line several months after diagnosis along with a high rate of recurrence.⁶  Therefore, surgical intervention is the treatment of choice for horses with a fracture. However, the success rates have been variable, and the time for these horses to reach the first race is often 8 or more months, resulting in significant loss to the owner and trainer.^3–8 

Tiludronate is a bisphosphonate that reportedly is efficacious to treat horses with bone spavin, navicular disease with osteolytic lesions, or osteoarthritic lesions of the thoracolumbar vertebral column.^9–11 Bisphosphonates were first synthesized in the 1960s and are thought to be the most potent inhibitors of bone resorption clinically available to human patients.¹² Inhibition of osteoclasts is the main pharmacological action, which in turn inhibits bone resorption. Therefore, slowing down bone remodeling will help restore a normal bone balance between bone resorption and formation.¹² In the horse, evidence of the inhibitory action of tiludronate on bone resorption and the resulting effect of bone mineral density has been reported in a model of disuse osteoporosis induced by a cast.¹³ Additionally, tiludronate has been shown to have anti-inflammatory properties by decreasing the amount of nitric oxide and cytokines released from activated macrophages, which promote early inflammatory responses.¹⁴

Extracorporeal shock wave therapy (ESWT) is used to treat various musculoskeletal disorders in horses including DMD in Thoroughbred racehorses.¹⁵ The specific mechanism that ESWT mediates its effects is largely unknown. Although multiple studies have documented the analgesic effects of ESWT, the precise mechanism is unknown,^16–18 and no research has investigated its effect on bone healing in the horse. In the rabbit, ESWT has been shown to promote bone healing by increasing neovascularization and upregulation of angiogenic and osteogenic growth factors.¹⁹ Because DMD results from both a mechanical and biological imbalance, addressing both of these aspects should improve the outcome of this disease. Therefore, the primary objective of this report is to describe a new technique that should be considered for the conservative treatment of DMD in Thoroughbred racehorses.

2. Materials and Methods

Horses were included in the study if they were sensitive to palpation over the dorsal aspect of MCIII and had radiographic evidence of a stress fracture or significant periosteal remodeling with bone loss along the dorsal aspect of MCIII. The treatment protocol involved 3 parts: (1) regional limb perfusion with tiludronate, (2) ESWT along the affected aspect of MCIII, and (3) a modified exercise program. After conclusion of the 6-week protocol, if radiographs confirmed complete healing of the site, the horse was returned to training. The trainers were encouraged to begin galloping the horse before a gradual return to regular training. However, if radiographs did not confirm complete healing of the site, the horse continued to jog and radiographs were repeated at 2-week intervals until complete healing was confirmed.

Technique

Tiludronate Treatment

Each horse was sedated with a combination of detomidine HCLa (0.005–0.01 mg/kg, IV) and butorphanol tartrate^b (0.005–0.002 mg/kg, IV), depending on the temperament of the horse. The cephalic vein was isolated through an Esmarch-type tourniquet application at the level of the mid radius. Distal to the tourniquet, the cephalic vein was aseptically prepared and a 22-gauge butterfly catheter was placed in the cephalic vein; 50 mg of tiludronate^c q.s. to 60 mL in saline was placed IV for a total of 30 minutes. The site of venipuncture was wrapped with a gauze bandage to prevent extravasation of the perfusate while the tourniquet was in place. After the perfusion was complete, the tourniquet was removed and the treatment was repeated every other week for a total of 3 treatments, beginning on the second week.

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