Abstract
Objective The aim of this study was to compare the interfragmentary compressive force and area
of compression generated by cortical screws inserted as either a lag screw or position
screw in simulated lateral humeral condylar fractures.
Study Design Ex vivo biomechanical study.
Materials and Methods Thirteen pairs of cadaveric humeri from skeletally mature Merinos with simulated
lateral humeral condylar fractures were used. Pressure sensitive film was inserted
into the interfragmentary interface prior to fracture reduction with fragment forceps.
A cortical screw was inserted as a lag screw or a position screw and tightened to
1.8Nm. Interfragmentary compression and area of compression were quantified and compared
between the two treatments groups at three time points.
Results After fracture reduction using fragment forceps (Time point 1: T1), there was no
significant difference in interfragmentary compression and area of compression between
the two treatments. A combination of fragment forceps and a cortical screw inserted
as a lag screw (Time point 2: T2) produced significantly greater interfragmentary
compression and area of compression compared with the same screw inserted as a positional
screw. After removal of the fragment forceps, leaving only the cortical screw (Time
point 3: T3), both the interfragmentary compression and area of compression remain
significantly greater in the lag screw group.
Conclusion Lag screws generate a greater force of compression and area of compression compared
with position screws in this mature ovine humeral condylar fracture model.
Keywords position screw - lag screw - interfragmentary compression - lateral humeral condylar
fractures - area of compression
