The Axial Injury Tolerance of the Human Foot/Ankle Complex and the Effect of Achilles Tension

Abstract

Axial loading of the foot/ankle complex is an important injury mechanism in vehicular trauma that is responsible for severe injuries such as calcaneal and tibial pilon fractures. Axial loading may be applied to the leg externally, by the toepan and/or pedals, as well as internally, by active muscle tension applied through the Achilles tendon during pre-impact bracing. The objectives of this study were to investigate the effect of Achilles tension on fracture mode and to empirically model the axial loading tolerance of the foot/ankle complex. Blunt axial impact tests were performed on forty-three (43) isolated lower extremities with and without experimentally simulated Achilles tension. The primary fracture mode was calcaneal fracture in both groups. However, fracture initiated at the distal tibia more frequently with the addition of Achilles tension (p < 0.05). Acoustic sensors mounted to the bone demonstrated that fracture initiated at the time of peak local axial force. A survival analysis was performed on the injury data set using a Weibull regression model with specimen age, gender, body mass, and peak Achilles tension as predictor variables (R2 = 0.90). A closed-form survivor function was developed to predict the risk of fracture to the foot/ankle complex in terms of axial tibial force. The axial tibial force associated with a 50% risk of injury ranged from 3.7 kN for a 65 year-old 5th percentile female to 8.3 kN for a 45 year-old 50th percentile male, assuming no Achilles tension. The survivor function presented here may be used to estimate the risk of foot/ankle fracture that a blunt axial impact would pose to a human based on the peak tibial axial force measured by an anthropomorphic test device.

Non-collision injuries in urban buses—Strategies for prevention

“…Following the literature review, this study focused on the head and lower extremities. The injury criteria and threshold values (Eppinger et al, 1999;Funk et al, 2002;Ivarsson et al, 2004; are summarized in Table 1 and Table 2, where injuries have been categorised Deterioration of bone strength after the age of fifty has been well documented in tests on femoral cortical bone (Takahashi et al, 2000;Yamada, 1970). Similarly, theoretical age dependent HIC scaling factors have been proposed based on brain material properties (Eppinger et al, 1999).…”

“…The validity of the injury response model is based on the extensive validation of the Madymo 50 th percentile male occupant model in frontal and rear impact eg (Don et al, 2003;Happee et al, 1998;Kroonenberg et al, 1998) and of the detailed Madymo leg model (Funk, 2001;Funk, 2002;Manning, 1998). The hand model developed in this paper accurately reproduces the grip strength measured on volunteers (Mathiowetz, 1985).…”

In-vehicle extremity injuries from improvised explosive devices: current and future foci

“…However, there was no clear description of the lower limb injury pattern, nor were there any results on the outcomes of these injuries. As a result, researchers in the field have resorted to extrapolating injury profiles from studies based on automotive impact loading conditions [24,25]. Based on these cadaveric studies, current NATO guidelines stipulate that the critical injury threshold for AV-mine tests is 5.4 kN, measured in the tibia component of a Hybrid III anthropometric test device [26].…”

Foot and ankle forces during an automobile collision: the influence of muscles

“…Muscle forces reduced the external force (F RF ) because the foot was held in plantarflexion on the pedal, thus slowing the motion of the heel towards the toepan and mitigating external impact force. This mechanism can be observed in cadaver experiments and may result in fewer calcaneal fractures, but more pylon fractures of the tibia (Funk et al, 2002). The quadrupling of peak Achilles tendon force from MN to MX is due not only to increased activation, but also to the force-velocity and force-length relationship in muscle, specifically during an eccentric contraction when high force production is possible.…”

“…Obviously, muscle activation level could exacerbate axial loading injuries, such as tibial fractures, as has been shown by others using cadaver surrogates and numerical simulations (Cappon et al, 1999;Crandall et al, 1996;Funk et al, 2002;Kitagawa et al, 1998a, b;McMaster et al, 2000;Parenteau et al, 1996;Rudd et al, 1998). The relationship between muscle activation and the subsequent external and internal forces during a collision was complex.…”