Medial knee loading is altered in subjects with early osteoarthritis during gait but not during step-up-and-over task

<div><p>This study evaluates knee joint loading during gait and step-up-and-over tasks in control subjects, subjects with early knee OA and those with established knee OA. Thirty-seven subjects with varying degrees of medial compartment knee OA severity (eighteen with early OA and sixteen with established OA), and nineteen healthy controls performed gait and step-up-and-over tasks. Knee joint moments, contact forces (KCF), the magnitude of contact pressures and center of pressure (CoP) location were analyzed for the three groups for both activities using a multi-body knee model with articular cartilage contact, 14 ligaments, and six degrees of freedom tibiofemoral and patellofemoral joints. During gait, the first peak of the medial KCF was significantly higher for patients with early knee OA (<i>p</i> = 0.048) and established knee OA (<i>p</i> = 0.001) compared to control subjects. Furthermore, the medial contact pressure magnitudes and CoP location were significantly different in both groups of patients compared to controls. Knee rotation moments (KRMs) and external rotation angles were significantly higher during early stance in both patient groups (<i>p</i> < 0.0001) compared to controls. During step-up-and-over, there was a high variability between the participants and no significant differences in KCF were observed between the groups. Knee joint loading and kinematics were found to be altered in patients with early knee OA only during gait. This is an indication that an excessive medial KCF and altered loading location, observed in these patients, is a contributor to early progression of knee OA.</p></div

Averaged total, medial and lateral KCF (above) and knee moments (below) during stance phase of gait.

<p>Knee moments in the sagittal, frontal and transversal planes are presented. The gray shaded area corresponds to the standard deviation of the control group. ^<b>*</b> indicates a significant difference between established OA and control group. ^<b>#</b> indicates a significant difference between early OA and control group. ^<b>+</b> indicates a significant difference between the early and established OA.</p

Group-averaged contact pressure distributions on the articular surfaces of medial tibial plateau at the time instant of the first peak medial KCF.

<p>To obtain these averaged contact pressure distribution maps, the average contact pressure was calculated for every triangle of the medial tibial surface mesh and presented on a representative surface model. Results are presented for the control group (C0, on the left), the early knee OA group (EA, in the middle), and the established knee OA group (ES, on the right).</p

Multibody 12 degree of freedom knee model [53] including ligaments and an elastic foundation contact model.

<p>Multibody 12 degree of freedom knee model [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0187583#pone.0187583.ref053" target="_blank">53</a>] including ligaments and an elastic foundation contact model.</p

Medial knee loading is altered in subjects with early osteoarthritis during gait but not during step-up-and-over task - Fig 1

<p><b>Flow charts of the limbs selection for gait (A) and step-up-and–over (B).</b> The final number of the analyzed limbs are indicated in bold. During gait, 11%, 50% and 7% of the total knees diagnosed with early OA presented K&L of 0, 1 and 2, respectively. During step-up and -over, 17%, 47% and 6% of the total knees diagnosed with early OA presented K&L of 0, 1 and 2, respectively. Numerical problems are indicated as <i>n</i>.<i>p</i>.</p

Simulation of surface strain in tibiofemoral cartilage during walking for the prediction of collagen fibre orientation

<p>The collagen fibres in the superficial layer of tibiofemoral articular cartilage exhibit distinct patterns in orientation revealed by split lines. In this study, we introduce a simulation framework to predict cartilage surface loading during walking to investigate if split line orientations correspond with principal strain directions in the cartilage surface. The two-step framework uses a multibody musculoskeletal model to predict tibiofemoral kinematics which are then imposed on a deformable model to predict surface strains. The deformable model uses absolute nodal coordinate formulation (ANCF) shell elements to represent the articular surface and a system of spring-dampers and internal pressure to represent the underlying cartilage. Simulations were performed to predict surface strains due to internal pressure, loading induced by walking, and the combination of both loading due to pressure and walking. Peak femoral and tibial cartilage deflections were slightly greater than 1 mm during simulated walking. First principal strain magnitudes within the cartilage surface ranged up to 3%. Time-averaged first principal strains agreed best with split line maps from the literature when surface loading due to internal cartilage pressure was included. This result suggests there may be a connection between pressure-induced surface strain patterns and the collagen fibre orientation patterns that emerge.</p