Measures

The following outcome measures were recorded before and after the 4 weeks of intervention for each participant.

Pain intensity was measured with a visual analogue scale consisting of a 100 mm line labeled with word descriptors by “no pain”/“worst imaginable pain” at each end of the scale. This scale is widely used, and is considered reliable and valid for pain recording.¹⁹ Participants were asked to report their pain perception before and after 4 weeks of intervention.

The functional scale used in this study for knee assessment was the Kujala scale,²⁰ a 13 item self-reported form. This tool assesses pain and difficulty during six activities (walking, squatting, jumping, stairs climbing, running, and sitting for lengthy periods). This tool also documents other symptoms including limping, failure to assume a unilateral stance on the involved limb, swelling, abnormal patellar tracking, atrophy, and knee flexion limitation. The Kujala scale (Arabic form) has been found to be valid and reliable in functional knee pain assessment^21,36. Similarly, Kujala scores were recorded before and after 4 weeks.

DKV was determined through Kinovea Computer programmer V.0.8.15 video analysis. This system has been found to be valid and reliable for calculating the range of motion in joints.²² In contrast, a tape measure was used to assess the 2D frontal plane projection angle (FPPA). The axes of each hip, knee, and ankle joint were delineated, and markers were located midway between the malleoli of the ankle joint, at the midpoint of the femoral condyles for the axis of the knee joint, and at the central line from the anterior superior iliac spine to the knee joint axis. This technique has been reported to decrease intra- and inter-rater error, and to increase reliability, in comparison with manual calculations via video.²³

With a video camera (ON EOS Rebel T3i/600D, fixed on a tripod at knee level, 3 m from the center of the landing floor, with video at 1080 p resolution at 30 fps), snapshots at the maximum knee valgus were taken. Participants were asked to flex the non-tested leg's knee from the floor and then to perform a squat with the tested leg.

Normative 2D FPPA or DKV values have been reported to usually be between 5° and 12° in women.²⁴ A knee valgus displacement greater than 10.6° suggests a PFP with sensitivity and specificity of .75 and .85, respectively. The associated positive probability ratio is 5.²⁵ For DKV, the reading used as a predictor was that of the pre-intervention measurement.