Biomechanical properties of human cadaveric ankle-subtalar joints in quasi-static loading.

The biomechanical properties of human ankle-subtalar joints have been determined in a quasi-static loading condition. The moving center of rotation was determined and approximated by a fixed point. The moment-angle characteristics of the ankle-subtalar joints about the fixed center of rotation have been measured under four basic movements: dorsiflexion, plantarflexion, inversion, and eversion. The method linearly increases rotation of the calcaneus until failure, and measures the moments, forces, and linear and rotational displacements. Failure was identified as the initial drop of moment on plot showing the moment representing gross injury or microfilament damage. In this study, 32 human ankle-subtalar joints have been tested to failure. The center of rotation of the ankle-subtalar joints was determined for a pure dorsiflexion (9 specimens), plantarflexion (7 specimens), inversion (8 specimens), and eversion (8 specimens). Failure in the joints occurred at an average moment of -33.1 +/- 16.5 Nm in dorsiflexion, 40.1 +/- 9.2 Nm in plantarflexion, -34.1 +/- 14.5 Nm in inversion, and 48.1 +/- 12.2 Nm in eversion. The failure angle was also determined in all four motions. Failure was best predicted by an angle of -44.0 +/- 10.9 deg in dorsiflexion, 71.6 +/- 5.7 deg in plantarflexion, -34.3 +/- 7.5 deg in inversion, and 32.4 +/- 7.3 deg in eversion. Injury was identified in every preparation tested in inversion and eversion, while it resulted in five of the nine preparations in dorsiflexion, and in three of the seven in plantarflexion. Injury occurred at -47.0 +/- 5.3 deg and -36.2 +/- 14.8 Nm in dorsiflexion, and at 68.7 +/- 5.9 deg and 36.7 +/- 2.5 Nm in plantarflexion. The results obtained in this study provide basic information of the ankle-subtalar joint kinematics, biomechanics, and injury. The data will be used to form a basis for corridors of the ankle-subtalar joint responses.

Foot-ankle injuries: influence of crash location, seating position and age.

Foot-ankle injuries have increased in relative importance in recent years. As a basis for future countermeasures, an epidemiology study has been undertaken using Swedish accident data from Folksam Insurance. The database consists of 805 foot-ankle injuries out of 57,949 car occupant injuries reported from 1985 to 1991. The influence of crash location, seating position and occupant age is determined for the frequency, incidence and rate of foot-ankle injury in car crashes. Frontal car crashes produce 76% of the AIS 2-3 foot-ankle injuries with 13% in side impacts and 8% in roll-overs. The rate of AIS 2-3 foot-ankle injury is 24.7 per 1000 occupants injured in all crash locations and is similar irrespective of seating positions. Ankle fractures and sprains both occur at an incidence of 3.7 per 1000 injuries, followed by malleolus fractures at 2.7 and midtarsal fractures at 2.4. The foot-ankle injury incidence and rate are significantly greater (p < 0.01) in near oblique-frontal crashes than for 12 o'clock frontals. For drivers in 11 o'clock and front passengers in 12 o'clock, the incidence is 27.8 per 1000 injuries as compared to 17.5 for drivers and front passengers in 12 o'clock crashes. Occupant age is not as significant as seating position and crash location; however, there are higher incidences for rear occupants > or = 60 years old in oblique frontal crashes. Using the new AAAM Impairment Injury Scale (IIS), 48% of the foot-ankle injuries are rated with residual impairment IIS 1-2. The incidence in near-seated occupants is 1.5 times greater in oblique frontal crashes than in frontals. The incidence for IIS 1-2 impairment in near oblique-frontal crashes is 12.8 per 1000 occupant injuries as compared to 8.3 in frontal crashes.

Validation of tagging with MR imaging to estimate material deformation.

Myocardial tagging with magnetic resonance imaging is useful for non-invasive estimation of in vivo heart wall deformation. To validate the method of strain estimation and quantify the error of deformation estimates, a deformable silicone gel phantom in the shape of a cylindrical anulus was built and imaged. Four observers digitized the displacement of magnetic tags in two deformation modes: axial shear, caused by a 45 degrees rotation of the inner cylinder, and azimuthal shear, caused by a 13.5-mm longitudinal translation of the inner cylinder. In axial shear, good agreement was found between the angular displacement of stripes painted on the gel and an analytic solution. Displacement of magnetic tags also agreed with that solution. Interobserver and observer-model errors in deformation estimates were quantified for homogeneous and nonhomogeneous strain analysis. In homogeneous strain analysis, errors in point localization produced relatively large errors, which were reduced in nonhomogeneous strain analysis. Both estimates were unbiased across the range of deformations.