Intramedullary Osteosynthesis of Metadiaphyseal Proximal Tibial Fractures: An Optimized Implant Geometry Can Help to Solve the Problem

Biomechanical comparison of intramedullar versus extramedullar stabilization of intra-articular tibial plateau fractures

BACKGROUND

Fractures of the proximal tibia occur very often and are a great challenge for trauma surgeons to stabilize. Although locked nails were developed to stabilize these fractures, this technique has not been sufficiently investigated. The purpose of this study was to biomechanically assess the stability of locked intramedullary nailing compared to locked plating.

METHODS

16 fresh frozen human cadaveric tibiae were osteotomized in the meta-diaphyseal intersection with an osteotomy gap of 10 mm and a single osteotomy through the medial epicondyle to simulate a 41-C.2 fracture. Stabilization was performed with an angle stable locked Targon-TX nail (n = 8) and two additional canulated screws. The other testing group (n = 8) was treated with two canulated screws and a five-hole LCP-PLT. The bones were tested in a cyclic testing protocol with increasing loads under compression and a load sharing of 60 % through the medial tibial plateau and 40 % to the lateral side. Stiffness and fracture gap movement were measured and failure mode was assessed.

RESULTS

No significant differences were found between the two implants regarding load until failure. The stiffness of the intramedullary nailing group (927 N/mm) was statistically significantly higher than the stiffness of the plating group (564 N/mm). No differences were found for fracture gap movement in the z-axis. However, differences were found for dislocation of the proximal-lateral and proximal-medial fragments, with absolute values of 0.099 mm in the plate group and 0.66 mm in the nailing group at 800 N. Prior to failure, fracture gap movement was 0.22 mm for the plating group and 1.66 mm for the nailing group, a difference that was also statistically significantly different. The nailing group failed by screw cut-out while the plating group failed by screw breakage.

CONCLUSION

Nailing of proximal tibia fractures leads to a stiffer implant-bone construct than plating. Since no adverse effects were found after nailing it seems to be a good alternative to plating for intra-articular proximal tibia fractures, especially in patients with soft tissue problems.

Double or triple interlocking when nailing proximal tibial fractures? A biomechanical investigation

OBJECTIVES

To determine whether there are differences in stability between double and triple interlocked intramedullary nails used for the fixation of extraarticular proximal tibial fractures.

DESIGN

Randomized in vitro biomechanical-experimental laboratory investigation.

SETTING

Biomechanics laboratory of the Clinic for Trauma Surgery at the Johannes Gutenberg-University Mainz.

INTERVENTION

A 10-mm defect osteotomy was performed on six paired human tibiae, and the proximal and distal ends were potted in polymethylmethacrylate cement (PMMA). Each pair of bones was randomly stabilized with an intramedullary nail (IM-nail) with two interlocking options (PTN 2s) in one tibia, and with an IM-nail with three interlocking options (PTN 3s) in the corresponding contralateral bone. A biomechanical test of the bone implant construct was then performed with an axial force of 900 N. Displacement of bone fragments was measured and depicted as a force-displacement diagram.

MAIN OUTCOME MEASUREMENTS

Biomechanical construction stiffness.

RESULTS

The stiffness values for PTN 3s were significantly higher than for PTN 2s. In the group of PTN 2s, two out of six implants failed biomechanically with breakage of one proximal interlocking screw.

CONCLUSIONS

Given the parameters of this investigation, triple proximal interlocking provides more stability in nailed proximal tibia fractures than double proximal interlocking. Larger series with clinical follow-up after triple proximal interlocking in tibial nailing should be undertaken to further clarify these questions.

Intramedullary stabilization of extraarticular proximal tibial fractures: a biomechanical comparison of intramedullary and extramedullary implants including a new proximal tibia nail (PTN)

OBJECTIVES

To determine in the laboratory whether there are or are not differences between individual geometrical designs of intramedullary and extramedullary devices used for the fixation of extraarticular proximal tibial fractures.

METHODS

Five devices were tested: a newly developed Proximal Tibia Nail (PTN), conventional double-plate osteosynthesis (DPO), the Less Invasive Stabilization System (LISS), an augmented Unreamed Tibial Nail with a T-stabilization-plate (UTN + TSP), and an external fixator (ExFix). A 10-mm defect osteotomy was performed on paired human tibiae, and the proximal and distal ends were potted in polymethylmethacrylate cement (PMMA). Each pair of bones was randomly stabilized with the new PTN in 1 tibia (Groups PTN1 through PTN4) and in 1 of the 4 comparative implants in the corresponding contralateral bone. A biomechanical test of the bone implant construct was then performed with a vertical axial force of 350, 600, and 900 N, a bending moment of 6 Nm and a bidirectional rotational strain of 8 Nm. Displacement of bone fragments was measured and depicted as a force-displacement diagram.

RESULTS

For axial loading, significant differences were seen between the PTN 2 group compared to the LISS group (P = 0.016) and the PTN 4 group compared to the ExFix group (P = 0.016). No statistically significant differences were seen for the PTN 1 group compared to the DPO group (P = 0.125) and the PTN 3 group compared to the UTN + TSP group (P = 0.453). The bending stiffness of the PTN 1-4 groups was not significantly different from any of the 4 alternative implants. There was comparable torsional stiffness in all implant groups except for the UTN + TSP group, which was less stable and significantly different from the PTN 3 group (P = 0.016).

CONCLUSIONS

Given the parameters of this investigation, the new PTN would theoretically provide the same mechanical stability as the DPO in axial loading. Higher stability in axial loading may be present when compared to the LISS or the ExFix. Further clinical investigation of this implant will determine its usefulness among proximal tibial fixation devices.