Searching for the “sweet spot”: the foot rotation and parallel engagement of ankle ligaments in maximizing injury tolerance

Abstract

Ligament sprains, defined as tearing of bands of fibrous tissues within ligaments, account for a majority of injuries to the foot and ankle complex in field-based sports. External rotation of the foot is considered the primary injury mechanism of syndesmotic ankle sprains with concomitant flexion and inversion/eversion associated with particular patterns of ligament trauma. However, the influence of the magnitude and direction of loading vectors to the ankle on the in situ stress state of the ligaments has not been quantified in the literature. The objective of the present study was to search for the maximum injury tolerance of a human foot with an acceptable subfailure distribution of individual ligaments. We used a previously developed and comprehensively validated foot and ankle model to reproduce a range of combined foot rotation experienced during high-risk sports activities. Biomechanical computational investigation was performed on initial foot rotation from [Formula: see text] of plantar flexion to [Formula: see text] of dorsiflexion, and from [Formula: see text] of inversion to [Formula: see text] of eversion prior to external rotation. Change in initial foot rotation shifted injury initiation among different ligaments and resulted in a wide range of injury tolerances at the structural level (e.g., 36-125 Nm of rotational moment). The observed trend was in agreement with a parallel experimental study that initial plantar flexion decreased the incidence of syndesmotic injury compared to a neutral foot. A mechanism of distributing even loads across ligaments subjected to combined foot rotations was identified. This mechanism is potential to obtain the maximum load-bearing capability of a foot and ankle while minimizing the injury severity of ligaments. Such improved understanding of ligament injuries in athletes is necessary to facilitate injury management by clinicians and countermeasure development by biomechanists.

Higher Rates of Lower Extremity Injury on Synthetic Turf Compared With Natural Turf Among National Football League Athletes: Epidemiologic Confirmation of a Biomechanical Hypothesis

“…11,35 This mechanism requires significant loading, often associated with a blow to the injured limb, 14,25,28,36,41,42 and therefore may be less sensitive to surface type. In contrast, ankle sprains that involve less substantial ligamentous structures (eg, the talofibular or calcaneofibular ligaments) 11,35 may occur more frequently without a direct blow 4,21 and thus may be more sensitive to surface type. Second, within surface type (synthetic or natural), variability in the number, shape, and length of upright fibers differs among synthetic turf fields, while grass species, percentage ground cover, moisture content, and root zone components differ among natural turf fields.…”

Force-limiting and the mechanical response of natural turfgrass used in the National Football League: A step toward the elimination of differential lower limb injury risk on synthetic turf

“…(Kent et al, 2012) (Figure 1) Each of these loading modes was conducted at two power levels: a "full-power" level with the potential to generate injurious magnitudes of torque and force and a "reduced-power" level. (Ivarsson et al, 2005;Kajzer et al, 1999Kajzer et al, , 1997Kajzer et al, , 1993Kajzer et al, , 1990Kerrigan et al, 2003Kerrigan et al, , 2004Mait et al, 2018;Nie et al, 2017;Nyquist, 1986;Ramet et al, n.d.) The reduced-power translation tests generated forces similar to non-injurious ground reaction forces generated by elite athletes during play. (Kawamori et al, 2014;Riley et al, 2013;Smith et al, 2004;Valiant, 2013) The vertical preload was 2.0 kN in the reduced-power rotation tests and 2.8 kN in all other reduced-power and full-power tests.…”