Visible mechanical stabilization

A study is being conducted in Freiburg, Germany, on ankle stability diagnostics. A new MRI procedure shows changed joint congruency in the neutral position and when controlled strain is applied, with and without wearing an orthosis. This is the key to quantifiable mechanical instability. And it makes room for additional evidence relating to the stabilizing effect of the semi-rigid MalleoLoc orthosis.

Diagnosing an unstable ankle is challenging and has its limitations and flaws in practice, in particular when it comes to mechanical instability. That is a reason for the generally high level of research interest – in medicine as well as in kinesiology. A potentially powerful parameter is the size of the contact area between the ankle’s cartilage surfaces. The higher their dynamic congruency, the more stable the joint. The measurable congruency changes during lateral opening, but has not been investigated much in connection with instabilities and injury mechanisms. The same applies to the question to what extent ankle orthoses can influence joint congruency.Against this background, Freiburg University Hospital’s Clinic for Orthopedics & Trauma Surgery and Freiburg University’s Institute for Sports and Sports Science started a new scientific study in November 2019. They focused on two key issues: “We are investigating to what extent our newly developed MRI procedure can provide reliable, quantifiable information about the ankle, and its mechanical instability in particular,” Dr. med. Markus Wenning from Freiburg University Hospital explains. His research partner PD Dr. Dominic Gehring from Freiburg University adds: “In addition, we’re checking to what extent quantifiable evidence can be provided for the stabilizing effect of the MalleoLoc orthosis.”

New dynamic measurement procedure

The foundation and measurement background for the current study is an innovative MRI procedure that has been developed by the researchers and tested in a pilot study for mechanical diagnostics of ankle instability. Using high-resolution 3D imaging, the joint congruency is measured across the cartilage contact area (CCA), horizontally, laterally and medially in the area of the talus, fibula and tibia. The innovative approach: all measurements are taken in the neutral position using an arthrometer system in a functional position in plantar flexion and supination, i.e. with the foot being lowered and rotated and subjected to strain. “The equinus foot position with inversion engages the injury mechanism and, under controlled conditions, triggers the opening of the lateral ankle,” Dr. Dominic Gehring explains. “Using 3D imaging provided by the dynamic MRI, we are able to depict the pathology of joint instabilities much more precisely than with two-dimensional X-rays or stress ultrasound images,” Dr. Markus Wenning adds. “This method also enables us to quantify the instability because we can collect standard values.” This could be used to complement the clinical examination, allowing us to objectify and, most importantly, reproduce the diagnosis of mechanical instabilities. In particular, the differentiation between mechanical and functional instability is vital for subsequent treatment. The results can then supply important criteria to inform the decision whether surgery, an orthosis or sensorimotor training should be chosen.

Test subjects with stable ankles versus unstable ankles

50 subjects are taking part in the controlled, randomized joint study conducted by Freiburg University Hospital and Freiburg University. Their selection included comprehensive screening related to functional and mechanical instability. “The goal was to identify two groups. One healthy group, i.e. people without any problems at all , that can serve as a control group with stable ankles and as reference for standard values. And one group with restricted functionality and indications of mechanical instability,” Dr. Dominic Gehring reports.
The test subjects underwent various functional stability tests, such as the Y balance test , and documented their subjective feelings of stability during everyday activities and exercise using a questionnaire. Screening equally included manual tests on the ankle where talus shift and talus tilt were clinically assessed in terms of stability or instability, as well as stress sonography that was used to check the degree of the joint opening with the help of imaging.

Arthrometric measurements using MRI with and without an orthosis

During the 3D MRI scan, the test subjects’ joint congruency is measured, using a pneumatically operated arthrometer, with the foot being in the neutral position and in a functional position under controlled strain. In this device, pneumatic cylinders ensure that a simulated weight load of up to 50 kilograms, depending on the joint position, is applied axially to the foot. Afterwards, the test subject slowly enters the MRI together with the arthrometer slide. The measurement takes about six minutes. The screen then displays the three-dimensional image of the joint , which is visibly opened in a functional position and shows reduced contact areas. “In test subjects with stable ankles, this is usually about 30 per cent , according to our initial assessment ,” Dr. Markus Wenning notes. “Patients with unstable ankles, on the other hand, can lose up to 90 per cent of their contact area in a functional position.” The laxity that can be recognized during this process makes the forced position in the arthrometer easier for those with unstable ankles than those with stable ankles, who sometimes get irritated. The simulated injury mechanism, however, never reaches the actual strain threshold but always remains at a pain-free, physically and ethically justifiable level.
The study design’s additional measurement conditions include the comparison with and without the MalleoLoc orthosis in the MRI to enable an enhanced assessment of the effects of external stabilization for therapeutic intervention.

Evidence from imaging to treatment decisions

There are good reasons why the MalleoLoc is being examined as a treatment measure using these innovative MRI-based stability diagnostics: “A previous study already showed the evident effectiveness of the semi-rigid MalleoLoc in secondary injury prevention. With our current procedure, we are able to visualize the mechanical component of its effect and measure it using the parameter of joint congruency,” Dr. Dominic Gehring explains. He was in charge of the study on the ankle orthosis in dynamic stability tests using a tilting plate that was controlled at random and over which the test subjects had to walk. It proved that the MalleoLoc reduces inversion angles and inversion speed. In the critical moment of twisting an ankle, this can contribute to preventing recurring structural damage during the supination trauma. The tilting plate spontaneously and quickly triggered the opening of the ankle during walking. In the current study, the strain is applied in a fixed (static) position during a much longer period, based on the MRI sequence of about six minutes.

First results and outlook

The measurement series of the Freiburg study are almost complete. “Thanks to the images, we’re optimistic that our MRI procedure works for diagnostics,” the two study directors report. “It is able to depict the clinical manifestation of mechanical instability very well , and it’s a quantifiable tool that delivers reproducible results,” Dr. Markus Wenning summarizes. The pilot study showed that healthy test subjects with stable ankles lose around 30 per cent of joint surface contact when subjected to strain. Those with unstable ankles, however, lose between 60 and 90 per cent of contact area. “If our follow-up study confirms these findings, it may be possible to categorize patients with a congruency loss of more than 50 per cent as mechanically unstable,” the orthopedist explains. “Even if we need to bear in mind that this ankle instability is, in addition to purely mechanical factors, a dynamic process that doesn’t allow a dichotomous categorization within the meaning of 100 per cent stability or instability. The clinical relevance of this potential cutoff value must , of course, be investigated in other studies.” In line with the objective of the study, the data they just collected could be used as initial standard values that allow a valid quantification of the relationship between mechanical instability and the loss of contact area.
“We can also measure the stabilizing effect of the MalleoLoc and verify it using imaging. Previous images show an influence on the joint congruency, and we’re expecting noticeable differences with and without the orthosis in our analysis,” Dr. Dominic Gehring believes.
The results will be made available during the year. The validation of the MRI-based diagnostics also offers additional potential for the research on the root causes of individual symptoms. Syndesmotic and other periarticular insufficiencies that don’t just focus on the upper ankle can’t yet be depicted with current procedures. Further studies and complementing measurements in other joint positions can enlighten this topic, just like a combination of a classic gait analysis and imaging techniques to display joint congruency could provide new insight in kinesiology. 

Images: Udo Schönewald, Patrick Seeger, Universitätsklinikum Freiburg, Bauerfeind