Evaluation of compression generated by self compressing Orthofix bone pins and lag screws in simulated lateral humeral condylar fractures

Abstract

SummaryA simulated lateral humeral condylar fracture was created in each of the 52 humeri collected from 26 dogs. One humerus from each pair was stabilized with a 2.0 mm cortical bone screw which was inserted in lag fashion. The other humerus from each pair was stabilized with a 2.2 mm threaded diameter Orthofix pin inserted across the condyle. Prior to each repair, an antirotational K-wire was placed and then the Pressurex Sensitive film was inserted in the osteotomy site in order to determine the compressive pressure (MPa), compressive force (KN), and area of compression (cm2) achieved during fixation. The maximum insertional torque achieved before stripping was measured for each implant. The mean compression generated by insertion of a 2.0 mm lag screw was 20.36 ± 1.51 MPa compared to 18.88 ± 1.76 MPa generated by a 2.2 mm Orthofix pin (p<0.003). The mean area of compression generated by insertion of a 2.0 mm lag screw was 2.39 ± 1.29 cm2, compared to 1.16 ± 0.84 cm2 generated by insertion of a 2.2 mm Orthofix pin (p<0.0001). The mean compressive force (compression x area compressed) generated by insertion of a 2.0 mm lag screw was 4.96 ± 2.90 Kn, compared to 2.20 ± 1.65 Kn generated by insertion of a 2.2 mm Orthofix pin (p<0.0001). The mean insertion torque to failure for the lag screws was 0.49 ± 0.07 NM, compared to 0.91 NM ± 0.18 NM generated by the Orthofix pins (P<0.0001). Both repair methods are likely to be acceptable for the repair of similar fractures in small breed dogs.