Biomechanical Comparison of Fixed- versus Variable-Angle Locking Screws for Distal Humerus Comminuted Fractures

Abstract

Background To compare the stability of fixed- versus variable-angle locking constructs for the comminuted distal humerus fracture (AO/OTA 13-A3). Methods Eight pairs of complete humeri harvested from eight fresh frozen cadavers were used for the study. We fixed the intact humeri using 2.7-mm/3.5-mm locking VA-LCP stainless steel distal humerus posterolateral (nine-hole) and medial (seven-hole) plates. An oscillating saw was used to cut a 1-cm gap above the olecranon fossa. The specimens were loaded in axial mode with the rate of 1 mm per 10 seconds to failure, and stress-strain curves were compared in each pair. The mode of failure was recorded as well as the load needed for 2- and 4-mm displacement at the lateral end of the gap. Results The stiffness of the constructs, based on the slope of the stress-strain curve, did not show any difference between the fixed- versus variable-angle constructs. Likewise, there was no difference between the force needed for 2- or 4-mm displacement at the lateral gap between the fixed- and variable-angle constructs. The mode of failure was bending of both plates in all specimens and screw pull-out in four specimen pairs in addition to the plate bending. Conclusions Our results did not show any difference in the biomechanical stability of the fixed- versus variable-angle constructs. There was not any screw breakage or failure of the plate-screw interface.

Biomechanical Design Optimization of Distal Humerus Fracture Plates: A Review

“…This conflicts with another study on double plating of IAFs, which demonstrated that fixed-angle transverse screws produced lower axial stiffness and strength when using parallel plates, but the trend was reversed for perpendicular plates [ 51 ]. Double plating of EAFs using only fixed-angle transverse screws provided higher axial stiffness and force at smaller, but not at larger, construct displacements versus double plating using only variable-angle screws [ 74 ].…”

Low Transcondylar Fractures of the Distal Humerus: A Multicenter Cohort Study

“…Distal humerus fractures in older adults present a challenge for orthopedic surgeons. [19][20][21] The classic treatment for undisplaced fractures is cast immobilization. 8,22,23 However, due to high nonunion rates, 23 rigid fixation and early return to function to avoid loss of elbow motion are the goals of the treatment.…”

Plate Osteosynthesis

“…[8] Similarly, no difference in stiffness of construct in stress-strain curve while using VA-LCP as compared to fixed counterparts was noted in biomechanical testing in distal humerus comminuted fracture models. [9] There was also no screw breakdown or failure at plate-screw interface thus making it an alternative implant in selected cases.…”