Compressive forces achieved in simulated equine third metacarpal bone lateral condylar fractures of varying fragment thickness with Acutrak Plus screw and 4.5 mm AO cortical screws.

This study compares the compression pressure of two types of screws, Acutrak Plus (AP) and AO cortical screws (AO), when used to repair a specific type of bone fracture (lateral condylar fractures) in horse’s metacarpal bones. Results show that AO screws provide greater compression pressure, and thus may be more suitable, particularly for thicker bone fragments.

Study Objective and Methodology

• The main objective of this research was to compare the compressive pressures generated by two types of screws, 6.5 mm Acutrak Plus (AP) and 4.5 mm AO cortical screws (AO), in the fixing of simulated lateral condylar fractures in equine third metacarpal bones (MC3).
• In the in vitro experimental setup, the researchers used horse cadaver MC3 bones to simulate complete lateral condylar fractures. These fractures were created at 20, 12 and 8 mm axial distances from the epicondylar fossa.
• A pressure sensor was used to measure the interfragmentary compression before the screws were placed in the bone for fracture fixation.
• The mean compression pressure (CP) values for each type of screw were compared using a statistical t-test. The researchers also compared the CP between the different fracture thickness groups, with statistical significance set at P<.05.

Study Findings

• The AO screw configurations generated significantly greater compression pressure as compared to AP configurations. The average CP for AP screws was only 21.6%, 26.2%, and 34.2% that of AO screws for 20, 12, and 8 mm fragment thicknesses, respectively.
• While the 12 and 8 mm fracture groups showed better compression characteristics than the 20 mm group, they were still significantly weaker than AO fixations.
• Given that primary bone healing, good articular alignment, and rigid fixation are vital goals of surgical fracture repair, the researchers recommend caution when using AP screws, especially for complete fractures.

Study Conclusions and Recommendations

• Maintaining the overall stability of a repair is crucial, and interfragmentary compression plays a significant role in this stability. Hence, AP screws should ideally only be used when dealing with thin lateral condyle fracture fragments, as the compression tends to decrease with an increase in fragment thickness.
• These findings have important clinical implications for the repair of fractures in horses, particularly those affecting the third metacarpal bone. The selection of screw type could significantly impact the efficacy and durability of fracture repair and ultimately the animal’s recovery and health.