Ankle instability Giving biomechanics a helping hand
Walking, running, jumping – all of the body’s vertical movement forces have to be transmitted horizontally onto a small area.
While the thigh muscles are generally broad, the contours of the leg gradually taper downward all the way to the ankle, a narrow load-bearing structure which transforms forces – and which is a hotspot for trauma. Instability of the ankle – a structure where ligaments play a key role – is a major risk factor and can even lead to osteoarthritis further down the line. New orthoses which provide lateral stability meet the needs of this functionally challenging part of the anatomy. We paid a visit to the Sports Science Institute of the University of Freiburg in Germany to see how MalleoLoc L and MalleoLoc L3 are giving biomechanics a helping hand.Visitors to Freiburg who suffer from ankle instability may well find getting around the city quite challenging. Narrow water channels known as “Bächle” run along the streets of the old town and can often trip up tourists who aren’t paying attention to where they are going, causing them to stumble or even fall. Close to the city, the 1,284-meter-high Schauinsland mountain is a popular destination with visitors for its great views, but it also poses a challenge in terms of ankle stability. Many visitors, even if keen walkers, opt to take the cable car from the foot of the mountain instead. Help of this kind is very welcome. A very different kind of help for the ankles can be seen in action on this winter’s morning, just a few hundred meters away in the Sports Science Institute of the University of Freiburg.
Do the orthoses stabilize the ankle at the crucial moment?
A measurement laboratory, all in white. There are cameras everywhere, both on tripods and mounted on the walls. They are all pointing at a black catwalk, which has a special panel in the middle of it. Off to the side are computers and monitors. The test subject steps onto the catwalk. He has markers attached to his foot , calf, and knee that will enable the special cameras to capture every millimeter of movement around the ankle, the most exposed joint of the human body and therefore the one which is most vulnerable to injury. Johannes Lienhard, the test subject , is wearing Bauerfeind’s new MalleoLoc L3 ankle orthosis under the markers. The set-up is designed to test the performance of both the MalleoLoc L3 and its sister orthosis, the MalleoLoc L. Are the two orthoses capable of stabilizing the ankle at that critical moment of twisting when the foot steps onto unstable ground, to the extent that no supination trauma occurs? How is the inversion speed of the talus altered? How large are the relevant angles to the axes of motion? Is there a correlation between the data recorded about the biomechanical effect of the orthoses and the test subject’s own assessment of the stability collected later? These are the questions being investigated by the Freiburg study. The results may help specialists to devise therapies which reduce both the high re-injury rate and the long-term risk of osteoarthritis.
Simulated injury scenario
Johannes Lienhard takes five or six steps. Due to previous sprain injuries, the footballer suffers from ankle instability in his right leg and he is therefore a good test subject. There’s a sudden crack. The panel in the middle of the catwalk has given way underneath his foot. The noise echoes in the bare room. Johannes Lienhard staggers briefly and then stoically continues on his way. Later too, when performing rapid jumps from a standing position, he keeps his cool on the tilting platform, supported by one of the team’s outstretched hands. Dr. Dominic Gehring smiles. Everything is going according to plan. The key rule is: safety first. The study director and his team are in the midst of the measurement phase. Ten of the twenty test subjects have already been put through the simulated injury scenario, which is based on a tried and tested study design previously used to provide evidence of the stabilizing effect of the MalleoLoc ankle orthosis.1 “Our test subjects first have an introductory session to get them used to the set-up. The giving way of the panel is triggered by a control unit at random,” Dr. Gehring explains. “This makes sure that the muscles which stabilize the joint aren’t preactivated in expectation of the twisting movement.”
“The biomechanical function must be fulfilled”
The sports scientists in Freiburg are using this dynamic stability test to investigate the protection afforded by the MalleoLoc L and MalleoLoc L3 in everyday load-bearing situations. The Institute’s Director, Professor Dr. Albert Gollhofer, is quite clear in his views: “The biomechanical function must be fulfilled. And, solely on the basis of the series of measurements that we have performed with the prototypes, our expectation is that this function will indeed be fulfilled.” So far, modifications made to the standard product also fulfill this function. “The initial data suggests that the degree of stabilization is slightly lower than that of the well-known MalleoLoc,” reveals Study Director Dr. Gehring. “But in view of the unilateral design, this stands to reason and is desirable.”
Where exactly is the functional instability?
While the MalleoLoc has a U-shaped shell round both the lateral and medial sides of the ankle, MalleoLoc L and MalleoLoc L3 have an L-shaped shell that covers the lateral side of the ankle. This one-sided design allows for early post-traumatic therapy and means that the orthosis is flatter and fits more easily into any type of footwear. One of the benefits of this is that it boosts patient compliance – and, as the two scientists are keen to emphasize, compliance is one of the factors that determines the efficacy of a product. The MalleoLoc L3 also has a modular design, so the stabilizing protection that it provides can be adapted as required (turn to page 20 for more details about the MalleoLoc L3). Dr. Gehring and Prof. Gollhofer also believe that the support for proprioception provided by the MalleoLoc L3’s compression support and the MalleoLoc L’s optional plantar pad is a key factor: “This could be the key to therapy for functional instability. Unlike in the case of mechanical instability, with functional instability we often don’t know exactly where the core of the instability lies or what the cause is in each case.”
Johannes Lienhard can’t imagine the new orthoses being used when playing football. He explains that , unlike in everyday activities, football requires a direct feel for the ball with all parts of the foot. “But I’d certainly use it for going out walking!” Maybe on the Schauinsland mountain – for a stable footing.
1 Gehring D., Wissler S., Lohrer H., Nauck T., Gollhofer A.: Expecting ankle tilts and wearing an ankle brace influence joint control in an imitated ankle sprain mechanism during walking. Gait and Posture, 2014b; 39: 894–898.
Images: Patrick Seeger