In vitro comparison of transfixation and standard full-limb casts for prevention of displacement of a mid-diaphyseal third metacarpal osteotomy site in horses.

The study investigates the efficacy of two types of full-limb casts – transfixation and standard – in preventing displacement of a mid-diaphyseal third metacarpal osteotomy site in horses.

Research Methodology

• The research was carried out using six forelimbs from six horses that were euthanized for reasons not related to the musculoskeletal system.
• A unique approach was conducted in the mid-diaphysis of the third metacarpal bone, creating a 30 degree osteotomy.
• To maintain alignment during the casting, two 4.5-mm cortical bone screws were placed across the osteotomy site. Furthermore, two 6.35-mm Steinmann pins were placed from a directional manner on a lateral-to-medial direction in the distal aspect of the radius.
• A full-limb cast was applied which incorporates these pins.
• An extensometer was installed within the osteotomy site through a uniquely placed window in the dorsal aspect of the cast. After the screws were removed, displacement was recorded as the limb was axially loaded to a weight of 5,340 N (1,200 lb).
• In a similar manner, the pins were removed and a displacement test was done for a standard full-limb cast.

Research Results

• The test results showed that the transfixation cast significantly reduced displacement across the osteotomy site at 445 N (100 lb), 1,112 N (250 lb), 2,224 N (500 lb), and 4,448 N (1,000 lb) more effectively than the standard cast.

Conclusions

• The results suggest that a full-limb transfixation cast provides significantly higher resistance than a standard full-limb cast against axial collapse of a mid-diaphyseal third metacarpal osteotomy site when the bone is placed under axial compression.
• Based on the findings, the researchers propose the consideration of full-limb transfixation casts for the management of unstable fractures of the third metacarpal bone in horses.