Abstract
Bending, in addition to compression, is recognized to be a common loading pattern in long bones in animals. However, due to the technical difficulty of measuring bone deformation in humans, our current understanding of bone loading patterns in humans is very limited. In the present study, we hypothesized that bending and torsion are important loading regimes in the human tibia. In vivo tibia segment deformation in humans was assessed during walking and running utilizing a novel optical approach. Results suggest that the proximal tibia primarily bends to the posterior (bending angle: 0.15°–1.30°) and medial aspect (bending angle: 0.38°–0.90°) and that it twists externally (torsion angle: 0.67°–1.66°) in relation to the distal tibia during the stance phase of overground walking at a speed between 2.5 and 6.1 km/h. Peak posterior bending and peak torsion occurred during the first and second half of stance phase, respectively. The peak-to-peak antero-posterior (AP) bending angles increased linearly with vertical ground reaction force and speed. Similarly, peak-to-peak torsion angles increased with the vertical free moment in four of the five test subjects and with the speed in three of the test subjects. There was no correlation between peak-to-peak medio-lateral (ML) bending angles and ground reaction force or speed. On the treadmill, peak-to-peak AP bending angles increased with walking and running speed, but peak-to-peak torsion angles and peak-to-peak ML bending angles remained constant during walking. Peak-to-peak AP bending angle during treadmill running was speed-dependent and larger than that observed during walking. In contrast, peak-to-peak tibia torsion angle was smaller during treadmill running than during walking. To conclude, bending and torsion of substantial magnitude were observed in the human tibia during walking and running. A systematic distribution of peak amplitude was found during the first and second parts of the stance phase.
Highlights
Evidence suggests that both the geometry and the mechanical properties of long bones adapt to the mechanical load they are exposed to [1,2,3]
In the absence of an easy way to assess in vivo mechanical loads acting on bones, bone geometry, which is deemed to be causally related to its loading history, has been taken to predict the in vivo bone loading history [4,5]
By analyzing a stack of peripheral quantitative computed tomography images taken across the human tibia, it was concluded that the almost circular distal tibia seems to be adapted to compressive loading patterns, while the non-circular geometry of the proximal tibia is the result of increased torsion and bending [5]
Summary
Evidence suggests that both the geometry and the mechanical properties of long bones adapt to the mechanical load they are exposed to [1,2,3]. By analyzing a stack of peripheral quantitative computed tomography (pQCT) images taken across the human tibia, it was concluded that the almost circular distal tibia seems to be adapted to compressive loading patterns, while the non-circular geometry of the proximal tibia is the result of increased torsion and bending [5]. There are several problems with this approach [6] These include a lack of absolute values of cross-sectional geometric properties and a potential misalignment between the loading history and bone cross-sectional geometry [6]. It is obvious, and that accurate measurements of real-world in vivo bone loading patterns are needed
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