Functional status of the articularis genus muscle in individuals with knee osteoarthritis

Abstract

Objectives: To clarify the functional status of the articularis genus muscle (AGM) in individuals with knee osteoarthritis (OA) and to analyze the muscle's relationship with knee OA.

Methods: Fifty-two individuals with knee OA (mean age, 73.4 years), 50 elderly individuals without knee OA changes (mean age, 71.2 years) and 75 young individuals (mean age, 20.2 years) were observed the AGM using ultrasonography. The thickness of the AGM, the anteroposterior distance of the suprapatellar bursa, and moving distance of the muscle insertion were measured both at rest and during isometric contraction, and values during contraction were expressed as percentages of the values at rest (%Muscle-Increase, %Bursa-Increase).

Results: Muscle thickness at rest, %Muscle-Increase, %Bursa-Increase, and moving distance of the muscle insertion were significantly lower and anteroposterior distance of the suprapatellar bursa was significantly higher in the OA group than in the controls (p<0.001, all). In the OA group, these values for the AGM were significantly correlated with knee range of motion, knee pain, and Kellgren and Lawrence grade.

Conclusions: Individuals with knee OA exhibited atrophic changes and dysfunctions of the AGM, and these were associated with symptoms. Atrophic changes and dysfunctions of the AGM may be specific changes associated with knee OA.

Figure 1

Positioning of the participants during isometric knee extension.

Figure 2

Long-axis image of the AGM (arrowheads). The AGM was identified as the thin muscle located on the prefemoral fat pad inserting into the inferior aspect of the suprapatellar bursa (arrows). F: Femur, PFP: Prefemoral fat pad.

Figure 3

A, B. Analysis of the AGM. A. Long-axis image at rest. B. Long-axis image during isometric contraction. (a) or (a’) showed muscle thickness of the AGM. Increased muscle thickness during isometric contraction was expressed as a percentage of the thickness at rest (%Muscle-Increase = (a’ – a) / a). (b) or (b’) showed the anteroposterior distance of the suprapatellar bursa. The increased anteroposterior distance during contraction was expressed as a percentage of the distance at rest (%Bursa-Increase = (b’ – b) / b). The moving distance of the muscle insertion (c) was measured as the distance between points at rest (○) and during isometric contraction (☆).