Article
Old battle with new implant systems – biomechanical comparison of intramedullary versus extramedullary fixation concepts of stable pertrochanteric fractures
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Authors
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Jana Felicitas Schader
- AO Research Institute, Davos Platz, Switzerland
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Ivan Zderic
- AO Research Institute, Davos Platz, Switzerland
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Jan Dauwe
- AO Research Institute, Davos Platz, Switzerland
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Christoph Sommer
- Kantonspital Graubünden, Chur, Switzerland
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Boyko Gueorguiev
- AO Research Institute, Davos Platz, Switzerland
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Karl Stoffel
- Universität Basel, Universitätsspital Basel, Basel, Switzerland
| Published: | October 26, 2021 |
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Outline
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Objectives: Since the elderly population proportion is growing, securing sufficient fixation stability of pertrochanteric fractures within this cohort is crucial. The two current principally different concepts to address these fractures implement either intra- or extramedullary fixation. The purpose of this study was to evaluate the biomechanical competence of the intramedullary TFN-ADVANCED Proximal Femoral Nailing System (TFNA) with a blade head element as compared with the extramedullary Femoral Neck System (FNS) for fixation of stable pertrochanteric fractures in a human cadaveric model.
Methods: Ten pairs of fresh-frozen human cadaveric femora from 7 male and 3 female donors, aged 80±8 years (range 70-92 years) were implanted pairwise with either TFNA or FNS. A stable pertrochanteric fracture AO/OTA 31-A1 was created and all specimens were biomechanically tested under progressively increasing cyclic loading until failure in 20° femoral shaft adduction. The peak axial force of each cycle increased by 0.1 N/cycle, starting from 500 N. Interfragmentary and relative bone-implant movements were monitored by motion tracking (Figure 1 [Fig. 1]).
Results and Conclusion: Bone mineral density did not differ significantly between the femora implanted with TFNA or FNS, P=0.31. Initial axial construct stiffness was not significantly different between TFNA and FNS, P=0.34. Similarly, implant migration, rotation of the femoral head fragment around the neck axis, varus tilting and leg shortening remained with no significant difference between TFNA and FNS after 3,000 test cycles, P≥0.10. However, cycles to 15° varus tilting and 15 mm leg shortening were significantly higher for TFNA compared to FNS, P<0.01.
From a biomechanical perspective, despite the comparable initial stability between the two implant systems, with its current design FNS is not a valid alternative to TFNA for treatment of stable pertrochanteric fractures, because of the relatively short lateral support plate resulting in its lift-off under dynamic axial loading.
