The purpose of this presentation is to explain why studying whole joint biomechanics is important, outline the benefits and limitations of studying whole joint biomechanics using MRI, and highlight some new MR approaches that have potential for substantial improvements in studying joint biomechanics.
Learning Objectives
At the end of this session, attendees will be able to:
Joints play a central role in human movement. The mechanical demands on the hip, knee and spine are notable: they must simultaneously transmit loads of several times body weight and allow a large range of motion in all three anatomical planes. Disruption of a joint’s mechanical function by injury or disease can lead to severe disability. Restoration of joint mechanics to normal is a key objective of treatment.
Conventional biomechanics has relied on ex vivo studies, models and motion analysis. Ex vivo studies are of limited utility because of the difficulty of simulating in vivo load/movement combinations ex vivo. Models have been used to predict joint mechanics given certain inputs. Current model predictions are limited because a) models require simplifications of joint anatomy, mechanical properties and movement; b) model validation is difficult and often perfunctory and c) most model studies have been done on very small populations. Experimental measurements of activities using motion analysis provide substantial experimental data but do not provide direct measurements of some of the most clinically relevant parameters.
Imaging has substantial potential as a tool to study joint biomechanics, but its application to date has been quite limited. Biplanar radiography and rapid CT have been used to study joint motion with high accuracy. Models driven by radiographic measurements have been used to infer impingement. Limitations of these approaches include the use of ionizing radiation and poor imaging of soft tissue.
MRI has been used to measure joint kinematics, contact area, cartilage strain and muscle anatomy. Limitations of conventional MRI images include the inherent limits to postures that can be imaged, long imaging time and low resolution. Open MRI allows a much larger range of postures to be imaged than conventional MRI. Validating MRI measurements and linking them to relevant mechanical quantities are two essential steps that pose challenges to using MRI to study joint mechanics.
MRI methods have been used in a number of biomechanical studies that aimed to confirm hypotheses about the role of mechanical and structural changes at joints on osteoarthritis initiation and progression and to predict the effects of treatments that aim to correct these mechanical and structural changes.
Recent developments in MR have potential for more direct measurements of quantities of interest. Further exploration of MRI as a tool for joint biomechanics has potential to reduce the burden of joint disease and disorders.
d'Entremont AG, Wilson DR. Joint mechanics measurement using magnetic resonance imaging.Top Magn Reson Imaging. 2010 Oct;21(5):325-34.
Wilson, D. R., McWalter, E. J. & Johnston, J. D. The measurement of joint mechanics and their role in osteoarthritis genesis and progression. Rheum. Dis. Clin. North Am. 39, 21–44 (2013).