Marcelo Mercadante

Biomechanical study: resistance comparison of posterior antiglide plate and lateral plate on synthetic bone models simulating Danis-Weber B malleolar fractures

Objective The purpose of this study was to compare different positions of plates in lateral malleolar Danis-Weber B fractures on synthetic bone: a lateral plate and a posterior antiglide plate. Methods Short oblique fractures of distal fibula at the level of the syndesmosys were simulated with a fibular osteotomy in sixteen synthetic fibula bones (Synbone®). Eight fractures were fixed with lateral plating associated with an independent lag screw, and the other eight were fixed with posterior antiglide plating with a lag screw through the plate. A strain gage was installed at the center of each plate at the osteotomy site. Supination and external rotation forces were applied to each of the two groups at the bend. Results The lateral position plate group suffered more deformity in response to supination forces compared to the group with the posterior antiglide plate, but this result was not statistically significant. In the tests with external rotation forces, the posterior antiglide plating group had significantly higher resistance (p < 0.05). Conclusion When subjected to external rotation forces, osteosynthesis with posterior antiglide plate models simulating type B fractures of the lateral malleolus of the ankle is more resistant than that of the neutralization plate.

Late postoperative analysis of the tip-apex distance (TAD) in pertrochanteric fractures: is there an accommodation of the implant within the bone?

INTRODUCTION This study measured the tip-apex distance (TAD) values in the immediate postoperative period and following weight-bearing and fracture impaction in patients undergoing osteosynthesis with dynamic hip screw and cephalomedullary nail. OBJECTIVE To correlate the Baumgaertner index in the immediate postoperative period with values obtained after impaction of the fracture with the accommodation of the cephalic implant in the femoral head. PATIENTS AND METHODS Radiographic TAD measurements were taken with AGFA-VIEW® of 82 patients with a mean age of 72 years with pertrochanteric fractures who were operated on and the fracture fixed with DHS- Synthes®, TFN-Synthes®, or Gamma Nail III-Stryker® in the immediate postoperative period, and following weight-bearing and fracture impaction (mean 3-8 weeks after surgery). RESULTS The overall average TAD decreased from 20.3mm to 18.2mm. Regardless of the instability of the fracture, the age of the patient or the implant used, TAD decreased between the immediate postoperative period and following fracture impaction. CONCLUSION The osteosynthesis of pertrochanteric fractures was associated with important accommodation of the cephalic implant in the femoral head with decreased TAD values after weight-bearing.

Avaliação da resistência mecânica de três diferentes pinos de Schanz às forças de torção em montagens do fixador externo monolateral

OBJECTIVE: The objective of this study was to evaluate the mechanical force of three different assemblies of a linear external fixator using 4.5 mm and 5.5 mm Schanz screws with a 3.2 mm-diameter root, and another screw with 5.5 mm diameter with a 4,5mm root. MATERIAL AND METHODS: The linear external fixator was assembled in a 500 mm-long polypropylene tube, with a 45-degree oblique angle cut in the center of the cylinder, with two Schanz screws in each segment. Eighteen assemblies were studied, divided into three groups of six pieces each. In the group 1, 4.5mm-diameter Schanz screws were used, in the group 2, 5.5mm-diameter Schanz screws, both with 3,2mm root were used. In the group 3, 5.5mm-diameter Schanz screws with a diameter root of 4.5mm were used. The mechanical tests were performed in a MT-100 torsion machine, and the resistance measurements were performed at 4.5o, 9.0o, 13.5o, and 18o of torsion. RESULTS: The 4.5mm Schanz screws with 3,2 mm root showed an average torsion resistance at 4.5o, 9.0 o, 13.5 o and 18.0 o, respectively of: 12.0 N/mm, 21.0 N/mm, 33.0 N/mm, and 46.0 N/mm. The 5.5mm Schanz screw with 3.2 mm root, showed as average resistance: 13.2 N/mm, 25.3 N/mm, 40.0 N/mm, and 51.2 N/mm, respectively. The tests with 5.5 mm Schanz screws with 4.5 mm root showed an average resistance of: 15.2 N/mm, 33.5 N/mm, 53.0 N/mm, and 70.0 N/mm. Statistical analysis with the Variance Analysis test and the Bonferronis test showed the absence of statistically significant differences among groups with root diameter of 3.2mm (4.5 mm and 5.5 mm). There was a statistically significant difference between the group with the 5.5mm Schanz screws with 4.5 mm root and the other two groups. CONCLUSIONS: 1- There was no statistically significant difference among assemblies of linear external fixator using 4.5mm and 5.5mm Schanz screws with 3.2mm root. 2- The linear external fixator with 5.5mm Schanz screws with 4.5mm root, showed a stronger mechanical resistance to the torsion, statistically significant, regarding the other two groups.