C. Methods

Selection of the Participant

The subject was selected from the Wake Forest University football team based on the following set of criteria: 1) Must have undergone ACL reconstructive surgery within the past year and 2) Must not have experienced any other significant lower extremity injuries.

Filming Set-Up

Filming occurred in the Biomechanics Laboratory at Wake Forest University using a Panasonic HC-V700 High Definition video camera. A seven-meter straight walking path was measured on the elevated track with a tape measure in order to give the participant three meters to settle into a gait pattern and speed before crossing in front of the camera. The camera was placed 2.89 meters perpendicularly from the four-meter mark on the path in order to maximize the size of the participant on the video screen and capture all markers in each frame. The camera was leveled to the floor on the tripod, and a reference stick was placed in the foreground of the frame.

Filming of the Participant

The subject was asked to arrive wearing compression shorts and no shoes in order to improve the accuracy of measurements taken during filming. Joint markers were created and placed on the acromion process, greater trochanter, between the lateral condyle of the femur and head of the fibula at the center of the knee joint, on the lateral malleolus of the fibula, and at the base of the fifth metatarsal on both the affected and unaffected legs in order to assess the angles at the hip, knee, and ankle during gait (Figure 2). The subject was first asked to walk from right to left along the pathway to gather data on the unaffected leg at natural gait speed. This was repeated five times with 30 second breaks between each trial. The participant was then instructed to walk at a faster pace along the same pathway, and again, repeated this five times with 3o second breaks between each trial. In order to quantify this increased gait speed, researchers timed how long it took for the subject to walk the seven-meter path and used this data to calculate the average velocity for each trial. Researchers also recorded the number of steps that the participant took to walk the seven-meter path. After resting for one minute, the subject repeated the aforementioned procedure, walking in the opposite direction, in order to obtain data on the affected leg. At the completion of filming, there were five film segments per condition: 1) Unaffected leg at natural gait speed 2) Unaffected leg at increased gait speed 3) Affected leg at natural gait speed and 4) Affected leg at increased gait speed.

Digitizing

Video files were transferred from the camera to a computer and were opened in Windows Movie Maker. Each trial was trimmed so that the footage captured one complete stride, beginning and ending with a heel strike of the leg in the foreground. The film clips were converted from Windows Media File to Microsoft AVI format, and the audio from each trial was removed. In order to obtain data regarding joint angles, the three highest quality film clips for each condition were analyzed using MaxTRAQ. Each joint marker was labeled, their positions were indicated for every frame of the participant's stride, and the angles for the hip, knee, and ankle joints were calculated by the software. Figure 2 shows the angles measured, where complete hip and knee extension and complete plantarflexion were defined as 180°. The frames and times corresponding to heel strike of the leg in the foreground were recorded in Microsoft Excel for data normalization and analysis.

Figure 2. Joint angle and marker reference. Joint markers were placed on the acromion process, greater trochanter, center of the knee joint, lateral malleolus of the fibula, and base of the fifth metatarsal. Complete extension of the hip and knee and complete plantarflexion were defined as 180°.

Data Analysis

The Microsoft AVI file was opened using Microsoft Excel, and gait speed, stride length, and percent of gait cycle spent in midstance were calculated using the hip, knee, and ankle angles and the corresponding horizontal coordinates. The data was normalized for each trial using the equation:

The normalized gait cycle data for the hip, knee, and ankle joints were then graphed for a selected trial from each condition. Stride length was determined by calculating the change in horizontal distance of the ankle coordinates between heel strikes for each trial. Gait speed for one complete gait cycle was determined by dividing the change in the ankle's horizontal distance by the change in time from heel strike to heel strike. The percent of the gait cycle spent in midstance was determined by dividing time spent in midstance by total gait cycle time and multiplying by 100. Average stride length, gait speed, and percent of gait cycle spent in midstance were then calculated for each condition by averaging the data across each condition's three trials.