While high ankle sprains are often clinically ascribed to excessive external foot rotation, no experimental study documents isolated anterior tibiofibular ligament (ATiFL) injury under this loading. We hypothesized that external rotation of a highly everted foot would generate ATiFL injury, in contrast to deltoid ligament injury from external rotation of a neutral foot. Twelve (six pairs) male cadaveric lower extremity limbs underwent external foot rotation until gross failure. All limbs were positioned in 208 of dorsiflexion and restrained with elastic athletic tape. Right limbs were in neutral while left limbs were everted 208. Talus motion relative to the tibia was measured using motion capture. Rotation at failure for everted limbs (46.8 AE 6.18) was significantly greater than for neutral limbs (37.7 AE 5.48). Everted limbs showed ATiFL injury only, while neutral limbs mostly demonstrated deltoid ligament failure. This is the first biomechanical study to produce isolated ATiFL injury under external foot rotation. Eversion of the axially loaded foot predisposes the ATiFL to injury, forming a basis for high ankle sprain. The study helps clarify a mechanism of high ankle sprain and may heighten clinical awareness of isolated ATiFL injury in cases of foot eversion prior to external rotation. It may also provide guidance to investigate the effect of prophylactic measures for this injury. ß

No 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.

While previous studies have investigated the effect of shoe-surface interaction on injury risk, few studies have examined the effect of rotational stiffness of the shoe. The hypothesis of the current study was that ankles externally rotated to failure in shoes with low rotational stiffness would allow more talus eversion than those in shoes with a higher rotational stiffness, resulting in less severe injury. Twelve (six pairs) cadaver lower extremities were externally rotated to gross failure while positioned in 20 deg of pre-eversion and 20 deg of predorsiflexion by fixing the distal end of the foot, axially loading the proximal tibia, and internally rotating the tibia. One ankle in each pair was constrained by an American football shoe with a stiff upper, while the other was constrained by an American football shoe with a flexible upper. Experimental bone motions were input into specimen-specific computational models to examine levels of ligament elongation to help understand mechanisms of ankle joint failure. Ankles in flexible shoes allowed 6.7±2.4 deg of talus eversion during rotation, significantly greater than the 1.7±1.0 deg for ankles in stiff shoes (p = 0.01). The significantly greater eversion in flexible shoes was potentially due to a more natural response of the ankle during rotation, possibly affecting the injuries that were produced. All ankles failed by either medial ankle injury or syndesmotic injury, or a combination of both. Complex (more than one ligament or bone) injuries were noted in 4 of 6 ankles in stiff shoes and 1 of 6 ankles in flexible shoes. Ligament elongations from the computational model validated the experimental injury data. The current study suggested flexibility (or rotational stiffness) of the shoe may play an important role in both the severity of ankle injuries for athletes.

A direct method to express the center of pressure (CoP) measured by an insole pressure sensor system (IPSS) into a known coordinate system measured by motion tracking equipment is presented. A custom probe was constructed with reflective markers to allow its tip to be precisely tracked with motion tracking equipment. This probe was utilized to activate individual sensors on an IPSS that was placed in a shoe fitted with reflective markers used to establish a local shoe coordinate system. When pressed onto the IPSS the location of the probe's tip was coincident with the CoP measured by the IPSS (IPSS-CoP). Two separate pushes (i.e., data points) were used to develop vectors in each respective coordinate system. Simple vector mathematics determined the rotational and translational components of the transformation matrix needed to express the IPSS-CoP into the local shoe coordinate system. Validation was performed by comparing IPSS-CoP with an embedded force plate measured CoP (FP-CoP) from data gathered during kinematic trials. Six male subjects stood on an embedded FP and performed anterior/posterior (AP) sway, internal rotation, and external rotation of the body relative to a firmly planted foot. The IPSS-CoP was highly correlated with the FP-CoP for all motions, root mean square errors (RMSRRs) were comparable to other research, and there were no statistical differences between the displacement of the IPSS-CoP and FP-CoP for both the AP and medial/lateral (ML) axes, respectively. The results demonstrated that this methodology could be utilized to determine the transformation variables need to express IPSS-CoP into a known coordinate system measured by motion tracking equipment and that these variables can be determined outside the laboratory anywhere motion tracking equipment is available.