ANGULATED SCREW PLACEMENT IN THE LATERAL CONDYLAR BUTTRESS PLATE FOR SUPRACONDYLAR FEMORAL FRACTURES

Certain supracondylar femoral fractures are not amenable to internal f ixation with fixed angle devices. In these instances, the condylar but tress plate is the recommended alternative; however, this is a less ri gid device. Because of the decreased rigidity and strength of this dev ice, there is a tendency toward varus angulation and malunion. In six fresh-frozen human knee specimens, segmental osteotomies were created to mimic supracondylar femoral fractures. The medial cortex was comple tely removed to make the fracture unstable to varus deformity. The fra cture was fixed with a lateral condylar buttress plate using 4.5 mm sc rews. Each specimen was tested once with all the screws installed perp endicular to the plate, and again with the middle screw just proximal to the fracture, angled 45 degrees diagonally across the fracture into the subchondral bone of the medial femoral condyte. For the construct with all screws placed perpendicular to the buttress plate, the initi al stiffness was 410 N/mm, and after 1000 cycles it was 230 N/mm. With a screw placed diagonally across the fracture site, stiffness increas ed to 833 N/mm on the first cycle, and 796 N/mm after 1000 cycles. In all specimens with the screws placed perpendicular to the plate, the d istal fragment had a permanent varus deformity after 1000 cycles, unde r no load, of 0.91 mm. For the diagonal screw condition, the average m agnitude far all six specimens was 0.42 mm. This simple means of screw angulation in the plate strengthened the overall construct to resist the tendency toward varus deformity. The attractive features include t he ease of application, and the use of an existing construct. (C) 1998 Elsevier Science Ltd. All rights reserved.