Tibiofemoral cartilage strain and recovery following a 3-mile run measured using deep learning segmentation of bone and cartilage

Abstract

Objective: We sought to measure the deformation of tibiofemoral cartilage immediately following a 3-mile treadmill run, as well as the recovery of cartilage thickness the following day. To enable these measurements, we developed and validated deep learning models to automate tibiofemoral cartilage and bone segmentation from double-echo steady-state magnetic resonance imaging (MRI) scans.

Design: Eight asymptomatic male participants arrived at 7 a.m., rested supine for 45 ​min, underwent pre-exercise MRI, ran 3 miles on a treadmill, and finally underwent post-exercise MRI. To assess whether cartilage recovered to its baseline thickness, participants returned the following morning at 7 a.m., rested supine for 45 ​min, and underwent a final MRI session. These images were used to generate 3D models of the tibia, femur, and cartilage surfaces at each time point. Site-specific tibial and femoral cartilage thicknesses were measured from each 3D model. To aid in these measurements, deep learning segmentation models were developed.

Results: All trained deep learning models demonstrated repeatability within 0.03 ​mm or approximately 1 ​% of cartilage thickness. The 3-mile run induced mean compressive strains of 5.4 ​% (95 ​% CI ​= ​4.1 to 6.7) and 2.3 ​% (95 ​% CI ​= ​0.6 to 4.0) for the tibial and femoral cartilage, respectively. Furthermore, both tibial and femoral cartilage thicknesses returned to within 1 ​% of baseline thickness the following day.

Conclusions: The 3-mile treadmill run induced a significant decrease in both tibial and femoral cartilage thickness; however, this was largely ameliorated the following morning.

Keywords: Auto-segmentation; Cartilage deformation; Cartilage thickness; Magnetic resonance imaging; UNet.

Fig. 1

Bone Surface DistanceRepeatability Analysis Pipeline. (A) To assess bone surface repeatability, two DESS MRI scans from a single participant are inputted into the trained tibia and femur segmentation models. (B) The trained models predict the tibia and femur masks. (C) The outer contours from the predicted masks are extracted and reconstructed into 3D models using Geomagic Studio 11 (3D Systems; Research Triangle Park, North Carolina). (D) The tibia and femur models from Scan 1 and Scan 2 are aligned using an iterative closest point technique [6]. (E) Bone surface distances in the x-, y-, and z-directions are calculated between the two scans across all regions of interest [28]. M ​= ​medial and L ​= ​lateral.

Fig. 2

Bone and Cartilage 3D Model Reconstruction Pipeline. (A) Each DESS MRI scan is inputted into the 4 trained segmentation models, and binary masks are outputted for each of the 4 tissues. (B) Visualization of the predicted bone and cartilage masks overlaid on the original DESS MRI scan. (C) Mask contours are extracted, converted into point clouds, and reconstructed into 3D surface mesh models using Geomagic Studio 11 (3D Systems; Research Triangle Park, North Carolina). Tan color indicates the tibia and femur, while green indicates the tibial and femoral cartilage.

Fig. 3

Cartilage thickness maps for one participant pre-exercise, post-exercise, and after 24-h of recovery. Red represents thicker regions of cartilage, while blue represents thinner regions. Post-exercise cartilage thickness decreased compared to the pre-exercise and recovery time points, which were relatively similar. M ​= ​medial and L ​= ​lateral.

Fig. 4

Running-induced changes to cartilage thickness and strain. (A) Cartilage thickness decreased significantly pre-to post-exercise for both the tibial (p ​< ​0.0001) and femoral (p ​< ​0.01) cartilage. Subsequently, cartilage thickness increased back towards baseline thickness at the recovery time point for both the tibial (p ​< ​0.0001) and femoral (p ​< ​0.01) cartilage. Significant differences between baseline and recovery were not detected for either the tibial (p ​= ​0.37) or femoral (p ​= ​0.60) cartilage. (B) Running induced post-exercise compressive strains of 5.4 ​% (95 ​% CI ​= ​4.1 to 6.7) and 2.3 ​% (95 ​% CI ​= ​0.6 to 4.0) for the tibial and femoral cartilage, respectively.