Heather McDonald Nope and Drs. Ty Hopkins, Matt Gage, Exercise Science
Nearly everyone involved in sports has witnessed or experienced an ankle injury. Often these primary injuries lead to secondary knee or hip pain. The purpose of this study was to learn more about how the body reacts to ankle injuries, in regard to absorbing energy in joints. The hypothesis states that subjects with chronic ankle instability will absorb more energy in the knee and hip. Conversely, subjects without chronic ankle instability will absorb more energy in the ankle.
The first step in testing our hypothesis was creating a safe and reliable technique to test subjects with ankle instability. No functional studies have been done on this population because of complications and the threat of further injury. The most applicable test, which does not pose a significant threat of injury we felt, was a single-leg drop test. This is a well-known and accredited technique mirroring real life actions. It involves the subject stepping off a step-platform onto a force plate, landing on one leg. The 44.5cm high platform was set at 3cm from a force plate. This height created enough force to collect reliable data without causing any pain to the subjects.
Data was recorded using the force plate and a Vicon Motion Analysis system. The force plate recorded ground reaction forces for every subject. Currently, the Vicon system is the most accurate way to capture biomechanical movement. Six cameras were placed at different angles around the force plate. Eight reflective markers were placed on important anatomical landmarks on each side of the body such as: the heel, second metatarsal, knee joint and anterior superior iliac spine. This system generated a 3-D representation of the subject’s motions using the markers and anatomical measurements as seen in Figure 1. These representations are then used to calculate moments of force values.
To ensure accurate data the cameras had to be positioned around the room so that at all times each reflective marker could be seen by at least two cameras. This pilot-testing portion was tedious and sometimes frustrating. Hours of tests were run to ensure that any subject would be visible to the cameras. I spent much of the time being the subject performing single-leg drops until I was an expert. Finally the correct camera placement was achieved and we proceeded to test trials with real subjects. These tests were run to check every portion of the procedure, especially to normalize the placement of the markers and consistency of measurements.
Once five test subjects completed the trials successfully the hardest part of the study began. Eighteen healthy and eighteen ankle instability subjects were needed. In a school of 32,000 it seems 32 people would not be hard to find. However, it was difficult to find people willing to help and even more difficult to qualify the subjects. To qualify as healthy, subjects were required to have no lower extremity pain and no ankle sprains in the last year. As aforementioned, the prevalence of ankle injuries made healthy subjects more difficult to find than assumed. Chronic ankle instability was assessed using Docherty’s Ankle Instability Instrument, a medically accepted questionnaire. At the beginning of the study, we wanted subjects with unilateral ankle instability. We felt this would generate the best data. Finding a person who only injures one ankle is nearly impossible to find. After great difficulty locating subjects we conducted further research and determined bilateral ankle instability would be fine as long as the subjects used their most unstable ankle in testing. We also attempted to pair an injured and healthy subject in sex, age and approximate weight. With all this criteria, finding participants was by far the most difficult portion of this study. I learned the value of correctly identifying the desired population for a study and aggressively soliciting their involvement. Most people forget or have many higher priorities than participating in a study. I also became an avid participant in nearly every study I saw and fit the qualifications.
Collecting the data occurred very successfully. On entering the lab, the weight and height of each subject was gathered and they warmed-up on a stationary bike for five minutes. During this time the cameras and computer were calibrated. Calibrating close to the drop time yielded better data than calibrating too early. Once the subject warmed-up, the reflective markers were placed and anatomical measurements, such as leg lengths were recorded. Subjects were asked to perform five drops with a minute rest between each drop. This break protected against fatigue and produced better form on the drops than fast repetition. Each subject was also required to wear noise-blocking headphones during the procedure.
Once all data was collected the initial data analysis consisted of insuring our data was reliable. Each trial was run through on the Vicon playback to check for continued motion sensing. If the cameras did not sense a marker, the 3-D representation of a subject’s movement became distorted. Most times this could simply be fixed by drawing in where the marker should have been. For each subject only the best three trials were kept, therefore any extreme data could be removed. After cleaning-up all the data, information could be imported to excel. There formulas were set up to convert the ground reaction forces and Vicon data into moment of force values. ANOVA probability tests will be run to see if the values are significantly different between healthy and chronic instability trials. A p-value of .5 will confirm our hypothesis
Unfortunately we ran out of time before all the data could be processed. However, we ran through one trial for a healthy and chronic instability subject and found encouraging results. Our hypothesis was supported by these few results. The healthy subject absorbed more energy in the ankle and less in the knee and hip, demonstrating by lower values. Comparatively, the chronic instability subject absorbed more in the knee and hip than in the ankle. Though these numbers are not nearly enough data to confirm our hypothesis it is encouragement to continue with the analysis. If the hypothesis is confirmed, which I believe will occur; this study prompts continued research to improve ankle injury treatment with other joint therapy.