In vivo measurement of localized tibiofemoral cartilage strains in response to dynamic activity

Abstract

Background: Altered local mechanical loading may disrupt normal cartilage homeostasis and play a role in the progression of osteoarthritis. Currently, there are limited data quantifying local cartilage strains in response to dynamic activity in normal or injured knees.

Purpose/hypothesis: To directly measure local tibiofemoral cartilage strains in response to a dynamic hopping activity in normal healthy knees. We hypothesized that local regions of cartilage will exhibit significant compressive strains in response to hopping, while overall compartmental averages may not.

Study design: Controlled laboratory study.

Methods: Both knees of 8 healthy subjects underwent magnetic resonance imaging before and immediately after a dynamic hopping activity. Images were segmented and then used to create 3-dimensional surface models of bone and cartilage. These pre- and postactivity models were then registered using an iterative closest point technique to enable site-specific measurements of cartilage strain (defined as the normalized change in cartilage thickness before and after activity) on the femur and tibia.

Results: Significant strains were observed in both the medial and lateral tibial cartilage, with each compartment averaging a decrease of 5%. However, these strains varied with location within each compartment, reaching a maximum compressive strain of 8% on the medial plateau and 7% on the lateral plateau. No significant averaged compartmental strains were observed in the medial or lateral femoral cartilage. However, local regions of the medial and lateral femoral cartilage experienced significant compressive strains, reaching maximums of 6% and 3%, respectively.

Conclusion: Local regions of both the femur and tibia experienced significant cartilage strains as a result of dynamic activity. An understanding of changes in cartilage strain distributions may help to elucidate the biomechanical factors contributing to cartilage degeneration after joint injury.

Clinical relevance: Site-specific measurements of in vivo cartilage strains are important because altered loading is believed to be a factor contributing to the development and progression of osteoarthritis. Specifically, this methodology and data could be used to evaluate the effects of soft tissue injuries (such as ligament or meniscus tears) on cartilage strains in response to dynamic activities of daily living.

Keywords: biomechanics; cartilage; hopping; jumping; knee; magnetic resonance imaging; osteoarthritis; strain; stress test; tibiofemoral.

Figure 1

a) The surfaces of the tibia, femur, and articular cartilage were segmented for each sagittal 3T MR slice, b) stacked to form a wireframe model, and c) converted to 3D surface mesh models.

Figure 2

Representative cartilage thickness maps of pre-activity and post-activity femoral and tibial models. Thickness is represented in color, with thicker cartilage in red, and thinner cartilage in blue.

Figure 3

Femoral and tibial strain grids: 18 points on each femoral condyle and 9 points on each tibial plateau. L=lateral, C=center, M=medial, A=anterior, Mi=middle, P=posterior.

Figure 4

Local strain results for a) medial and b) lateral tibial plateaus. Please see Figure 3 for point location legend. Error bars represent standard error of the mean. * p<0.05 different from 0.

Figure 5

Local strain results for a) medial and b) lateral femoral condyles. Please see Figure 3 for point location legend. Error bars represent standard error of the mean. * p<0.05 different from 0.