A three-dimensional stress MRI technique to quantify the mechanical properties of the ankle and subtalar joint: Application to the diagnosis of ligament injuries

Chronic instability of the ankle and subtalar joint resulting from ligament damage are difficult to detect. Methods used to detect instability clinically are often unreliable and do not provide a complete picture of the joint motion. Studies were previously conducted in vitro and in vivo to improve the detection of instability and the understanding of joint motion. In vitro studies were conducted to measure the motion at the ankle and subtalar joint, however these tests cannot detect physiological conditions such as partial ligament rupture and the long-term effect of surgery. Some in vivo studies assess the motion of the hindfoot externally. These techniques are unable to detect motion at the ankle and subtalar joint and the measurements are affected by soft tissue interference. Other in vivo studies assess the internal joint motion with imaging modalities. One of these techniques uses the image processing and visualization software system 3DVIEWNIX to describe the joint motion. The 3D stress MRI (sMRI) technique was developed by combining the 3DVIWNIX software system with a MR compatible ankle-loading device to eliminate the limitations of the current in vivo methods. This method calculates morphological, architectural and kinematic properties of the joints. Data were collected from seven healthy volunteers and eight cadaver limbs. The in vitro data were obtained with the ligaments intact, after serially sectioning the anterior talofibular and the calcaneofibular ligaments and after simulated surgery. The data from the healthy volunteers were used to describe the contribution of the ankle and subtalar joint to the motion of the hindfoot and the effect of soft tissue interference on the joint motion. Significant changes were found in vitro between the condition with intact ligaments and both ligaments sectioned in the architectural and kinematic parameters at the ankle and subtalar joint. Surgical reconstruction restored these properties. 3D sMRI provides reliable measures of the morphology and architecture of the hindfoot in vivo and in vitro , describes the changes in the kinematics induced by loads in vivo and in vitro and it is capable of detecting ligament damage and the effects of surgical reconstruction in vitro .