Examination of the extension amounts of a medial collateral ligament pie-crusting model by a finite element method

Abstract Background: Medial collateral ligament (MCL) pie-crusting is implemented to balance the soft tissue when performing total knee arthroplasty. Although studies have been conducted on pie-crusting, a virtual MCL pie-crusting model has not been created so far, and pie-crusting has not been examined using the finite element method (FEM). This study investigates and validates MCL pie-crusting models using FEM. Methods: We developed three MCL pie-crusting models (model A to C) for finite element analysis. In model A, the MCL was single elastic body (Young’s modulus of 350 MPa ) with both ends attached to the bone (Young’s modulus of 17.7 GPa). In model B, the MCL bundled 19 elastic body and attached to both ends of the bone. In model C, the MCL bundled 19 elastic bodies, and an adhesive part (Young's modulus of 175 kPa) was set in the gap and attached to both ends of the bone. Model A-1 was not cut, and the left end of the bone was fixed and rightward forces of 80 N and 120 N were applied. An additional model A-2 was created with nine 1 mm × 0.1 mm cuts in the center of the elastic body. Model A-3 was developed considering nine and ten staggered cuts (19 total cuts) at two different locations, with a gap of 20 mm. Models A-4 to 8 had 28, 38, 47, 76, and 95 cuts performed similarly. Model B-2 was created with nine cuts in the center of the elastic body. Models C-2 to C-8, with the same cuts as model A, were also created and force applied in the same manner. The amount of extension for each model was measured. Results: Model A was extended by 0.0068and 0.010 mm, for approximately 10 punctures. Model B-2 was extended 1.34 mm and 2.01 mm, approximately twice as much as model B-1. Model C was extended by 0.34 and 0.50 mm for every 10 punctures added. Conclusions: Our results suggest model C is better suited for the mechanical analysis of pie-crusting.