Arthrodesis of the equine proximal interphalangeal joint: a biomechanical comparison of two parallel headless, tapered, variable-pitched, titanium compression screws and two parallel 5.5 mm stainless-steel cortical screws.

The study compares the biomechanical features and performance of two types of screws used for arthrodesis, a procedure where a joint is surgically fused to prevent movement, in horse limbs. The performance of parallel headless, tapered, titanium compression screws, and parallel stainless steel cortical screws show comparable performance in this setting.

Research Methodology

• The experimental research was conducted in vitro, i.e., outside a living organism, using twenty limbs from six cadaver horses. These included four complete sets of limbs and two partial sets, resulting in a total of four pairs of forelimbs and six pairs of hindlimbs.
• The researchers installed two parallel 5.5 mm cortical screws (referred to in the study as AO screws) on one limb in a pair and two parallel headless, tapered, titanium compression screws (referred to as Acutrak-Plus screws) on the contralateral, or opposite, limb. The screws were installed in ‘lag fashion’, a specific method of screw insertion often used in orthopaedic procedures.
• Each construct was tested by applying force in a three-point bending, dorsopalmar (or plantar) direction, at a loading rate of 5.83mm/s.
• The maximum bending moment at failure and overall stiffness were calculated using data from load-displacement curves.
• The data were then analyzed using statistical methods to understand the variability and comparative performance of the two screw types.

Findings

• There was no significant difference detected in bending moment or stiffness values between the two types of screws (the Acutrak-Plus and the AO screws).
• Errors due to limb side (left or right) and limb ends (forelimb or hind limb) were factored into the study, however, the results showed significant stiffness differences between the forelimb and hindlimb constructs.
• It was concluded that the performance of the Acutrak-Plus screws essentially matched that of the AO screws in this setting.
• This suggests that the Acutrak-Plus screws could provide an alternative method of fixation for proximal interphalangeal joint arthrodesis in horses.