Objectives: It is recommended that the intra-articular component of a supracondylar distal femoral fracture be stabilized by a lag screw to create interfragmental compression. Generally, it is thought that lag screw fixation should precede any positional screw or locking screw application. This study compared 3 methods of maintaining interfragmentary compression after fracture reduction with a reduction clamp.
Methods: Intra-articular vertical split fractures were created in synthetic femora. A force transducer was interposed between the medial and lateral condyles and 20 lbs of compression was applied to the fracture with a reduction clamp. 3.5-mm cortical lag screws (group 1), 3.5-mm cortical position screws (group 2), and 5.4-mm distal locking screws through a distal femur locking plate (group 3) were placed across the fracture (n = 4/group). After screw placement, the clamp was removed and the amount of residual interfragmentary compression was recorded. After 2 minutes, a final steady-state force was measured and compared across groups.
Results: Locking screws placed through the plate (group 3) maintained 27% of the initial force applied by the clamp (P = 0.043), whereas positional screws (group 2) maintained 90% of the initial force applied by the clamp (P = 0.431). The steady-state compression force measured with lag screws (group 1) increased by 240% (P = 0.030) relative to the initial clamp force. The steady-state force in the lag screw group was significantly greater than groups 1 and 2 (P = 0.012).
Conclusions: When reducing intra-articular fractures and applying interfragmentary compression with reduction clamps, additional lag screws increase the amount of compression across the fracture interface. Compressing a fracture with reduction clamps and relying on locking screws to maintain the compression result in a loss of interfragmentary compression and should be avoided. This study lends biomechanical support that lag screws placed outside of the plate before locking screws for fracture fixation help maintain optimal interfragmentary compression.