Biomechanical Evaluation of Patellar Fixation

The femur was identified as a rigid body. The other models and implants were identified as linear elastic isotropic materials. The elastic moduli of the patella, patellar tendon, cannulated screw, suture anchor and anchor line were set as 15 GPa, 660 MPa, 110 GPa, 110 GPa, and 200 MPa, respectively, according to material properties and practices [12 (link)–14 (link)]. The Poisson's ratio of the patella, cannulated screw, and suture anchor was 0.3. The Poisson's ratios of the patellar tendon and anchor line were 0.4 and 0.36, respectively (Table 1). The friction coefficient at the anchor-bone interface was 0.6. Starting with a preload of 30 N, the anchoring system was strained.Table 1

The Properties of the materials in the biomechanical test

	Patella	Cartilage	Patellar tendon	Cannulated screw	Cable	Suture Anchor	Anchor line	Femur
Specification	–	Thickness:3 mm	–	diameter:3.0 mm	Diameter: 2 mm	diameter: 1 mm	diameter:0.5 mm	–
Elastic modulus	15GPa	5 MPa	660 Mpa	110GPa	110GPa	110GPa	200 MPa	Rigid
Poisson's radio	0.3	0.46	0.4	0.3	0.3	0.3	0.36

The change in the fracture gap and stress distribution on the components of the models were employed to evaluate the stability of different fixation types. Three paired points were defined on the proximal fragment and distal fragment of the patella to evaluate the displacement of fragments after loading. All of the finite element analyses were completed in ANSYS 17.0.