Evaluation of a tapered-sleeve transcortical pin to reduce stress at the bone-pin interface in metacarpal bones obtained from horses.

The researchers investigated the effectiveness of a new type of pin, the tapered-sleeve transcortical pin (TSP), for fixing broken metacarpal bones in horses, and found it to be stiffer than conventional pins, distributing stress more evenly across the bone-pin interface, hopefully reducing complications like bone necrosis and infections.

Research Methodology

• This study tested the tapered-sleeve transcortical pin (TSP) on 14 third metacarpal bones from adult horses of various breeds. The metacarpal bones were cut in half providing 2 test specimens from each sample.
• Both conventional pins and TSPs of three different diameters (6.35, 7.94, and 9.50 mm) were inserted into the bone samples, with three specimens tested for each diameter and type of pin.
• The experimental setup was designed to mimic the typical conditions under which such pins are used in horses, replicating a sidebar-span skeletal fixation device.
• From there, single-cycle load-deflection tests were performed to measure the stiffness of each pin and the stress at the bone-pin interface.
• The researchers carried out additional cyclic fatigue tests for the TSPs to assess their fatigue characteristics and the stress conditions at the bone-pin interface under repetitive load.

Findings

• The TSP displayed significantly higher stiffness and load tolerance at the yield point. The TSP sustained a stiffness of 19,988 N/mm compared to the stiffness of a conventional 9.50mm pin which was found at 4,500 N/mm.
• The results from the cyclic tests aligned closely with existing data on the fatigue characteristics of bone.
• The researchers concluded that the TSP manages to distribute the stress at the bone-pin interface more evenly than conventional pins which may help reduce complications associated with the external fixation of the pin like pin-track infection, pin loosening and bone failure.

Implications

• The use of TSP may help reduce some major issues encountered with the use of conventional transcortical pins including bone necrosis, pin-track infection, pin loosening, and bone failure.
• The research indicates that the TSP could be a better alternative to conventional pins in the treatment of broken horse metacarpal bones and likely other fractures as well, particularly in cases where the bone must bear significant loads.