Addition of a McLaughlin cerclage to locking plate fixation of distal patellar pole fractures reduces interfragmentary displacement – a biomechanical human cadaveric study

PURPOSE: To investigate whether the addition of a McLaughlin cerclage to locking plate fixation of distal patellar pole fractures provides improved biomechanical construct stability and reduced interfragmentary displacement. METHODS: A distal patellar pole fracture was simulated in sixteen fresh-frozen human cadaveric knees by a horizontal osteotomy in the distal third of the patella. Subsequently, locking plate fixation was performed. In a randomized half of the specimens, an additional McLaughlin wire cerclage was applied. The specimens were then subjected to 3000 cycles of extension starting at 90° of flexion under a maximum tensile load of 320 N. Using a Digital Image Correlation (DIC) system, the interfragmentary displacement between the proximal and distal fragments was measured at 1, 10, 20, 30, 50, 100, 500, 1000, 2000, and 3000 cycles. Statistical analysis was performed using repeated-measures ANOVA and Welch's unpaired t-t test at 3000 cycles. RESULTS: An additional McLaughlin cerclage significantly reduced interfragmentary displacement under cyclic loading in comparison to locking plate fixation alone. After 3000 cycles, displacement was 2.27 ± 1.84 mm with plate fixation alone and 0.36 ± 0.22 mm with additional McLaughlin cerclage (mean difference 1.91 mm; 95% CI 0.38-3.45 mm; p = 0.0215). CONCLUSION: An additional McLaughlin cerclage reduced interfragmentary displacement in distal patellar pole fractures. In cases of unstable distal pole patella fractures, the additional use of a McLaughlin cerclage may therefore be considered to enhance construct stability.