Peak compressive strains as a function of normalised muscle force for static and dynamic loading.

<p>For static loading, articular cartilage surfaces do not touch below approximately 40% of maximal muscle force, then cartilage strain increased between about 40–70% of the maximal force, and remained almost constant from 70–80% of maximal force (n = 7). For dynamic loading, articular surfaces did not touch below ~40% of the maximal isometric muscle force. Beyond ~40% force porduction, cartilage strains increased almost lineary between 50–80% of the maximal force (n = 6). Vertical bars on the side show significant differences between groups.</p

Normalized (relative to maximum = 100%) knee extensor forces as a function of time.

<p>The medial tibio-femoral joint space narrowed during loading with (a) 35% of muscular loading (n = 7), the two cartilage surfaces never touch and no sign of cartilage deformation was noticed at this force. (b) 50% of muscular loading (n = 7), the cartilage-on-cartilage space reached zero and cartilage thickness decreased for these loading conditions. In both cases, medial tibio-femoral cartilage-on-cartilage space returned back to its original position in ~20s following the removal of force.</p

<i>In Vivo</i> Dynamic Deformation of Articular Cartilage in Intact Joints Loaded by Controlled Muscular Contractions

<p>(a) Exposed mouse knee preparation showing the medial tibial plateau (T), and the medial femoral condyle (F) with the meniscus removed. (b) Tibio-femorol cartilage-on-cartilage space decreased to zero during muscular loading. Arrows show cartilage deformation area.</p

Normalized (relative to maximum = 100%) knee extensor forces as a function of time.

<p>Muscles were stimulated for 8s at a voltage and frequency producing approximately (a) 50% of the maximal muscle force, cartilage compressive strain (mean ±1SD; n = 7) increased almost linearly 3s after the force application. Cartilage takes 20s for full recovery upon unloading. (b) 80% of the maximal isometric force. Cartilage compressive strain (mean ±1SD; n = 7) increased rapidly and reached near steady state conditions at 6s following force application. Cartilage tissue recovered to its original shape within approximately 45s following force removal.</p