The bones of the foot need to be extremely flexible allowing the foot to point, twist and flex; and in other positions also need to be absolutely rigid, such as pushing off or jumping to protect the ankle from being sprained, or worse, broken. The key to this ability is the subtalar joint, below the ankle, which until now, doctors couldn’t see rotating while standing.

Ankle sprains are one of the commonest reasons for people to attend Accident and Emergency departments. In most cases, the subtalar joint is also injured but, it is hidden, causing challenges for physicians to diagnose sprains, which often leads to long-term ankle instability. If left untreated, an injury to the subtalar joint can lead to flat feet and even arthritis.

The study used standing CT scans and sophisticated image analysis to better understand how the subtalar joint works in eight men and women in three different positions.

“This is the first time this technique has been used in humans,” said study lead author Dr. Gianluca Tozzi. “It is non-invasive and gives clinicians a perfect view of a patient’s subtalar joint motion under full weight-bearing, making it possible for the first time to determine the joint’s center of rotation which, in turn, opens the possibility of much-improved design of joint replacements.

“Being able to see the subtalar joint in action is made possible by a combination of 3D imaging (computed tomography) and digital volume correlation,” he added. “The technology has a huge potential to be expanded, allowing doctors to see any strain in the bone, greatly improving clinical diagnosis.”

Study co-author, orthopedic surgeon Andrew Goldberg explained that currently, surgery for arthritis usually involves joining the bones together making them stiff in a procedure known as joint fusion. While this is a successful procedure to treat pain, it does remove a mobile joint which can lead to stiffness and long-term wear of other joints that have to pick up the slack.

“No one has ever been able to replace this complex joint. This new research helps us to better understand the complex biomechanics of the foot and could pave the way for new treatments that just aren’t currently available,” he commented.

Reference:

Fernandez, MP, et al. “Centre of Rotation of the Human Subtalar Joint Using Weight-Bearing Clinical Computed Tomography.” Scientific Reports, 2020; 10 (1) DOI: 10.1038/s41598-020-57912-z