Biomechanical investigation of the retrograde intramedullary nail fixation for distal femoral periprosthetic fracture after total knee arthroplasty

This study investigated the effect of fixation screw number of intramedullary nail on the postoperative stability of the femoral construct in treatment of periprosthetic fractures after total knee arthroplasty. With use of a material testing machine, both compressive and torsion tests were conducted to evaluate the biomechanical behavior of intact, and femora with periprosthetic fractures treated with retrograde intramedullary nail with 5-screw and 9-screw fixations. The results indicated the followings: 1) the average compressive stiffness for intact, 5-screw and 9-screw groups were 1,159±61.7, 950.6±18.6 and 958.2±26.1 N/mm, respectively. No statistical difference was found between 5-screw and 9-screw groups (p>0.05). However, significant difference was found between intact/5-screw and intact/9-screw groups (p<0.05). 2). the average torsion stiffness for intact, 5-screw group and 9-screw group were 5,527±71.2, 2,652±35.4 and 2,858±81.7 N*mm/Degree, respectively. Statistical difference was found between each other groups (p<0.05).