Direct in vivo quantification of the 3D talocrural and subtalar finite helical axes
© Sheehan; licensee BioMed Central Ltd. 2008
Published: 26 September 2008
In an attempt to understand the etiology of ankle joint injury and degeneration, numerous models have been created as a means to estimate ankle joint forces. Due to a lack of non-invasive in vivo measurement techniques, the kinematics required to drive these models have typically been acquired in cadavers or using external markers to infer internal bone motion. This has left some uncertainty as to the validity of these models. Thus, the purpose of this study was to non-invasively quantify the 3D in vivo finite helical axes (FHA) of the subtalar and talocrural joints.
Twenty healthy subjects (25.9 ± 4.1 years, 70.3 ± 12.8 kg, 174.1 ± 7.7 cm) participated in this IRB approved study. Subjects were placed supine in a 1.5 T MR imager (LX; GE Medical Systems, Milwaukee, WI, USA) after obtaining informed consent. An MRI-compatible device was used to apply a plantarflexion (PF) load. This device allowed natural 3D motion at both joints of the hindfoot. While subjects cyclically plantar-flexed and dorsiflexed their ankle at 35 cycles/min, aided by an auditory metronome, fast-PC MR images (anatomic and x, y, and z velocity images, temporal resolution = 72 ms, imaging time = 2:48) were collected . The sagittal-oblique imaging plane contained the tibia, calcaneus, and talus. The 3D time dependent tibial, talar and calcaneal attitudes were quantified through integration of the velocity data . From these data the FHAs were determined.
The data from this study clearly confirmed that neither joint is a simple hinge joint and that ankle rotation arose primarily from the talocrural joint. The tendency of the subtalar and talocrural FHAs to rotate and translate will impact the calculation of tendon and ligament moment arms and, thus, alter the moment producing capabilities of the force generating structures at the ankle joint. Future modelling studies should investigate the sensitivity of the model outputs to variations in the FHA direction and location.