Effects of Off-Axis Elliptical Training on Reducing Pain and Improving Knee Function in Individuals With Patellofemoral Pain

Abstract

Objective: To examine whether an off-axis elliptical training program reduces pain and improves knee function in individuals with patellofemoral pain (PFP).

Design: Controlled laboratory study, pretest-posttest.

Setting: University rehabilitation center.

Participants: Twelve adult subjects with PFP.

Interventions: Subjects with PFP completed an exercise program consisting of 18 sessions of lower extremity off-axis training using a custom-made elliptical trainer that allows frontal plane sliding and transverse plane pivoting of the footplates.

Main outcome measures: Changes in knee pain and function posttraining and 6 weeks after training were evaluated using the Knee Injury and Osteoarthritis Outcome Score (KOOS) and International Knee Documentation Committee (IKDC) scores. Lower extremity off-axis control was assessed by pivoting and sliding instability, calculated as the root mean square (RMS) of the footplate pivoting angle and sliding distance during elliptical exercise. Subjects' single-leg hop distance and proprioception in detecting lower extremity pivoting motion were also evaluated.

Results: Subjects reported significantly greater KOOS and IKDC scores (increased by 12-18 points) and hop distance (increased by 0.2 m) after training. A significant decrease in the pivoting and sliding RMS was also observed after training. Additionally, subjects with PFP demonstrated improved pivoting proprioception when tested under a minimum weight-bearing position.

Conclusions: An off-axis elliptical training program was effective in enhancing lower extremity neuromuscular control on the frontal and transverse planes, reducing pain, and improving knee function in persons with PFP.

Clinical relevance: This study provides a novel intervention approach to enhance the control of the frontal and transverse plane motions of the lower extremities during functional weight-bearing activities. This novel off-axis elliptical training may be incorporated with other common treatment options currently available for PFP to augment the effects of musculoskeletal rehabilitation for the PFP population.

Figure 1

Design of the robotic off-axis elliptical trainer with motorized footplates that allow transverse-plane pivoting and frontal plane sliding motions of the lower extremities during elliptical exercise (A). Real-time audiovisual feedback regarding the instantaneous footplate pivoting-sliding positions and frontal-plane lower limb alignment was displayed on the computer monitor in front of the subject (B).

Figure 2

An example of the limb positions for the pivoting proprioception testing. In this example, the left leg (foot in the lowest position) was at the weight-bearing condition in which the subject shifted the weight to the left leg, and the right leg (knee flexed) was at the minimum-weight-bearing condition.

Figure 3

Angular (A) and sliding (B) RMS values during elliptical exercise (mean ± SD) before and after the completion of the training program. *Significantly less than the pre-training value.

Figure 4

Angular proprioceptive threshold to detect lower extremity transverse-plane rotation under weight-bearing and non-weight-bearing conditions (mean ± SD) before and after the completion of the training program. *Significantly less than the pre-training value.