Holding Power of Orthopedic Screws Comparison of Self‐tapped and Pre‐tapped Screws in Foal Bone

Comparison was made of the holding power of orthopedic screws inserted self‐tapped or after pre‐tapping in foal bone. Third metacarpal and metatarsal bones were used. Comparative trials were made between screws inserted at the same site in the corresponding bones from the contralateral limbs of the same foal. A MTS servohydraulic tensile testing machine was used to perform screw pullouts at a displacement rate of 19 mm/sec. The 5.5 mm cortical screws had significantly greater holding power than 6.5 mm cancellous screws when both were inserted self‐tapped (p = 0.0056). Pre‐tapped insertion of 5.5 mm screws produced a significantly greater holding power than self‐tapped insertion of 5.5 mm screws (p = 0.018). Pre‐tapped insertion of 6.5 mm screws produced a significantly greater holding power than self‐tapped insertion of 6.5 mm screws (p = 0.0000). In internal fixation of fractures in foals, insertion of 5.5 mm and 6.5 mm screws pre‐tapped in metaphyseal bone is recommended because it produces greater holding power than self‐tapped insertion.