Rotational Stiffness of Football Shoes Influences Talus Motion during External Rotation of the Foot

Abstract

Shoe-surface interface characteristics have been implicated in the high incidence of ankle injuries suffered by athletes. Yet, the differences in rotational stiffness among shoes may also influence injury risk. It was hypothesized that shoes with different rotational stiffness will generate different patterns of ankle ligament strain. Four football shoe designs were tested and compared in terms of rotational stiffness. Twelve (six pairs) male cadaveric lower extremity limbs were externally rotated 30 deg using two selected football shoe designs, i.e., a flexible shoe and a rigid shoe. Motion capture was performed to track the movement of the talus with a reflective marker array screwed into the bone. A computational ankle model was utilized to input talus motions for the estimation of ankle ligament strains. At 30 deg of rotation, the rigid shoe generated higher ankle joint torque at 46.2 ± 9.3 Nm than the flexible shoe at 35.4 ± 5.7 Nm. While talus rotation was greater in the rigid shoe (15.9 ± 1.6 deg versus 12.1 ± 1.0 deg), the flexible shoe generated more talus eversion (5.6 ± 1.5 deg versus 1.2± 0.8 deg). While these talus motions resulted in the same level of anterior deltoid ligament strain (approxiamtely 5%) between shoes, there was a significant increase of anterior tibiofibular ligament strain (4.5± 0.4% versus 2.3 ± 0.3%) for the flexible versus more rigid shoe design. The flexible shoe may provide less restraint to the subtalar and transverse tarsal joints, resulting in more eversion but less axial rotation of the talus during foot∕shoe rotation. The increase of strain in the anterior tibiofibular ligament may have been largely due to the increased level of talus eversion documented for the flexible shoe. There may be a direct correlation of ankle joint torque with axial talus rotation, and an inverse relationship between torque and talus eversion. The study may provide some insight into relationships between shoe design and ankle ligament strain patterns. In future studies, these data may be useful in characterizing shoe design parameters and balancing potential ankle injury risks with player performance.

Syndesmotic Ankle Sprains in Large Males

“…A kinematic predictor of syndesmotic injury was assumed, thus muscle forces were not considered during experimentation. Therefore, a nominal compressive load was applied to every specimen to simulate weight bearing during dynamic, injurious scenarios (Wei et al, 2012a(Wei et al, , 2010. This was assumed sufficient to induce joint congruency and subsequent ligament recruitment during applied foot rotation.…”

“…Through its linear actuator, the Instron imparted the desired preload along the global Z-axis (defined initially coincident with the long-axis of the tibia) and effective gross external foot rotation by rotating the tibia internally about the global Z-axis. For testing, all specimens were subjected to a compressive preload (FZ) targeting 2 kN (Table 6) along the global Z-axis, chosen to simulate weight-bearing during typical play situations (Wei et al, 2012a(Wei et al, , 2010. Through its rotary actuator, the Instron applied the external rotation in a half-sine waveform.…”

“…From the deficiencies in the imposed external boundaries found in the injurious pilot study (above), and to improve realistic syndesmotic injury re-creation, boundary conditions were changed (Figure 18, bottom) for the remainder of tests in the initially neutral ankle flexion posture (Runs 4-9). This change in boundary conditions was intended to mimic feet constrained in a cleat on the football field, where the cleat is planted in the turf and the tibia rotates internally over the constrained foot (Wei et al, 2012a). The test apparatus was designed to allow the foot and calcaneus to undergo natural inversion and eversion during applied external foot rotation.…”

“…To conceptualize the evolution of the external boundary conditions imposed on the legs in all the experiments discussed thus far in this chapter and Chapter 2, (Wei et al, 2012a). The evolution of boundary conditions from BC:A to BC:E (Table 8) encompass the efforts made to improve applied foot rotation experiments from the overlyconstrained legs in previous studies to a realistic re-creation of syndesmotic injury in cadaveric legs, from which reliable bone kinematics can be measured.…”

“…To focus on this kinematic predictor, muscle forces were not considered. Instead, as detailed in Chapter 3, a compressive load was applied to all specimens through the tibia, intending to simulate weight-bearing during typical dynamic play situations (Wei et al, 2012b(Wei et al, , 2012a(Wei et al, , 2010.…”