Artikel
Relative lateral wall thickness is a biomechanically valid measure of pertrochanteric femur fracture stability
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Autoren
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Kenneth Petrus van Knegsel
- Luzerner Kantonspital, Luzern, Switzerland
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Ivan Zderic
- AO Research Institute Davos, Davos, Switzerland
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Torsten Pastor
- AO Research Institute Davos, Cantonal Hospital Lucerne, Davos, Switzerland
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Emir Benca
- Universitätsklinik für Orthopädie und Unfallchirurgie, Medizinische Universität Wien, Wien, Austria
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Boyko Gueorguiev
- AO Research Institute Davos, Davos, Switzerland
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Peter Varga
- AO Research Institute Davos, Davos, Switzerland
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Matthias Knobe
- RWTH Aachen, Universität Zürich, Aachen, Germany
| Veröffentlicht: | 23. Oktober 2023 |
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Gliederung
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Objectives: The lateral wall thickness (LWT) is used to predict secondary lateral wall fractures (SLWF) and select appropriate treatment for pertrochanteric femur fractures (PFF). Recently, a new patient specific measurement method, relative LWT (rLWT) has been introduced and shown to predict SLWF with higher accuracy than LWT. This method uses threshold value of 50.5% LWT to differentiate between stable and unstable PFF. However, rLWT has not been validated biomechanically. We hypothesized that lower rLWT is associated with lower biomechanical stability compared to higher rLWT regarding SLWF.
Methods: Eight pairs of human cadaveric femora were randomly assigned in pairwise manner to receive simulated PFF by means of two osteotomies with an rLWT of either 40% or 60%. For fracture stabilization, an extramedullary rotationally stable screw-anchor system (RoSA) was used. Each specimen was tested cyclically to failure in 20° adduction via axial compression on the femoral head. Relative movements between femoral head, lateral wall fragment, shaft, and RoSA head element were continuously monitored throughout the test cycles via optical motion tracking.
Results: Initial construct stiffness, measured from the ascending slope of the initial quasi-static ramp, was 370.2 ± 212.5 N/mm for 40% and 405.7 ± 167.6 N/mm for 60% rLWT, with no statistically significant difference between the two groups, p = 0.766.
Similarly, outcomes measured over the first 10000 cycles intermittently at every 2,500 cycles in peak loading condition, namely head element telescoping, head element varus deformation, femoral head varus deformation, and LW fragment rotation in sagittal plane, remained without significant difference between the two groups, p > 0.193.
However, the numbers of cycles to fracturing of the lateral wall fragment, defined by its 5° rotation in sagittal plane, were significantly higher for 60% (41,819 ± 19,477) vs 40% (26,634 ± 12,947) rLWT, p = 0.008.
Discussion: From a biomechanical perspective, 40% rLWT was associated with significantly earlier fracturing compared to a 60% rLWT, allowing acceptance of the hypothesis. SLWF reduces stability, subsequently risking collapse and increasing postoperative morbidity, disability and the need for reoperation.
Conclusion: A 40% rLWT provided less stability in PFF compared to 60% rLWT, resulting in earlier SLWF.
