Estabilización de fracturas Schatzker I de la meseta tibial. Estudio numérico comparativo mediante elementos finitos. Placas bloqueadas vs tornillos canulados

Objective

Surgical stabilization of split fractures of the lateral tibial plateau may involve percutaneous insertion of cannulated screws or more invasive implantation of locked plating systems. In any case, six to eight weeks of non-weight-bearing are recommended. By using the finite element (FE) method, this study aimed to assess whether immediate weight bearing can generate excessive interfragmentary motions (IM).

Methods

A validated femur-tibia FE model of a healthy patient was used. The tibia model was reconverted into geometry, and a Schatzker I fracture was re-created based on patient x-rays. Cannulated 6.5 mm cancellous bone screws, and a Polyax tibial locked plating system (Biomet Inc, USA) were modelled, and virtually implanted into the fractured tibia geometry. An axial force of 400 N pressed the femur model against the tibial plateau, simulating the weight of an 80 Kg patient in bipedal stance. IM were calculated as the displacements between two nodes initially superimposed in the fracture area

Results

Maximum IM calculated with the Polyax and with the cannulated screw fixations were around 0.1-0.15 mm, and 0.25-0.3 mm, respectively. Both systems led to similar IM up to 80-90% of applied body weight. However, applying over 20% of the simulated body weight might lead to a risk of compression bone fracture. With the Polyax system, bone stresses were better distributed, and remained below 100 MPa at 30% of body weight. Maximum stresses in the implants were about half the reported strength for the alloy simulated.

Conclusion

This study suggested that IM caused by weight bearing might not impede bone healing in a fracture stabilized with either a Polyax locked plating system or cannulated screws. However, cannulated screw systems could lead to harmful load concentrations in the bone with immediate weight bearing. Plate systems will allow around 50% of immediate weight bearing.