Abstract

Introduction: Distal femur fractures treated with lateral locking plates usually has poor callus formation with suboptimal healing. This has caused serious concerns regarding exact nature of healing and time of consolidation. Mechanical variables in plate fixation which affect rigidity of construct are controversial topics with regards to union. For most of the studies, primary endpoint of analysis was nonunion. No study has specific end point of union time. The main objective of this study is to test hypothesis that union time depends on rigidity related mechanical construct factors and to identify independent factors for union. Patients and methods: It’s a retrospective case control study. 32 distal femur fractures treated with locking plates between 2015 to 2017 were included. Patients with open fractures /steroid intake/ dialysis/DM/Smoking were excluded. Factors affecting construct like plate length/ empty holes/ total screw density (TSD)/ proximal screw density (PSD)/rigidity score/ presence or absence of screw crossing main fracture fragment were recorded and assessed for union time. Results: out of 32 patients, 23 patients who met all inclusion criteria’s with full follow up were analyzed. All the fractures united with index surgery. Two sample T test with CI and Regression analysis showed that union time was significantly affected by PSD and Rigidity score. 18 patients had rigidity score of 1 with mean union time of 19.78weeks(SD 7.06) while 4 patients with rigidity score of 2 had mean union Time of 35 weeks(SD 8.67);[ T value= -3.64, P value = 0.001,DF=20]. Eighteen patients with PSD <0.6 had mean union time of 19.78 weeks (SD 7.06) while 5 patients with PSD >0.6 had mean union time of 35.20 weeks (SD 8.67); [T value = -4.13, P value = 0.0013, DF = 21]. Type of fracture A/C was not associated with time of union [T value = -1.48, P value = 0.077, DF21]. Age, plate length, plate holes, empty holes, TSD are not significantly related with union time. Conclusion: In treatment of distal femur fractures with locking plates, union time depends on rigidity of construct and PSD. Rigidity score > 2 & PSD >0.6 leads to delayed union. We could evaluate predictors of union relative to construct stiffness. This has relevance while analyzing the literature and attempting to compare results of different studies. To prevent delayed union, less rigid construct can be achieved with PSD <0.6.

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