Fig 1.
Participant recruitment flow diagram.
The flow diagram describes how the participants were recruited and selected to the drop jump test.
Table 1.
Demographic data of the participants; ACL-injured participant, treated with surgery and physical therapy (ACLR), ACL-injured participant, treated with physical therapy (ACLPT) and healthy-knee controls (CTRL). Group mean values are given as Mean (SD).
Fig 2.
Illustration of one asymptomatic control performing the vertical drop jump test. Each participant was instructed to jump from a 0.4 m high platform and was instructed to land on both legs simultaneously. A vertical jump followed immediately after the first landing. The first landing sequence (marked by a square) was analysed in this study, and was divided into a Preparation phase, which started after the take-off when the person had maximally extended knees, followed immediately by an Action phase, which ended when the person reached their maximum knee flexion angle.
Fig 3.
Description of helical axis variables.
The 3D angle between the finite helical axis (FHA) of the knee during a movement interval of ~15° and the AP axis of the knee illustrate the relationship between the magnitude of abduction-adduction relative to magnitude of movement in other planes (flexion-extension and inward-outward rotation). Hence if the ΔAP inclination is 90°, the FHA is normal to the AP axis and the knee motion occurs in the sagittal and/or transverse planes. An inclination of 0–90° means adduction occurs (the smaller number the more adduction in relation to other knee movement), while an inclination of 90–180° indicates that abduction occurs (the larger number the more abduction in relation to other knee movements).
Fig 4.
A-B. Knee joint motion during the vertical drop jump test. Fig 4A illustrates the knee joint motion for the Preparation and Action phases after a vertical drop jump, averaged for each group. Group mean curves given for non-dominant knees of CTRL (thick black line, plus standard deviation shaded in grey), ACLR injured knees (dashed line) and ACLPT injured knees (dotted line). In Fig 4B, the knee joint movement of an ACLPT participant’s injured knee during Preparation and Action is illustrated by angle-angle diagrams (upper row) and knee helical axes (bottom row). The vertical lines in the angle-angle diagrams mark the flexion intervals that were used when computing the FHA’s. The vertical line in the helical axis plots marks the thigh’s mid-sagittal plane. This participant had an almost constant ΔAP inclination during the Preparation phase (ΔAP inclination about 84°). During the Action phase however, the ΔAP inclination ranged from 80 to 124°.
Table 2.
Knee range of motion and duration when landing after a vertical drop jump.
Table 3.
Knee helical axis variables when landing after a vertical drop jump.
Table 4.
Principal component analyses for significant variables during the preparation and action phases of the drop jump test.