Gait and Joint Mechanics

Tom Andriacchi, PhD, Stanford University

The Next Steps Towards Understanding Musculoskeletal Pathology 

Restoration of ambulatory function is one of the primary goals of treating disability associated with musculoskeletal pathology. The present state of the art will be illustrated with examples that highlight the unique understanding that comes from applying the methods of gait and joint mechanics to clinical problems. In considering future developments this presentation will illustrate how the current methods evolved from several historical milestones going back to the work of Borelli (circa 1600). Borelli was among the first to apply mechanical principles to analyze how muscular levers act to move and stabilize skeletal segments. These concepts described by Borelli are still used today and provide a framework to illustrate the potential benefits of introducing new disciplines to understanding the complexity of the musculoskeletal system. Finally, the future of gait and joint mechanics will be discussed using examples to illustrate how integrating biological and structural elements with gait mechanics can enhance our understanding of musculoskeletal pathology.

Key points will include:

  • The selection gait variables to address specific clinical questions.
  • The efficiency of using basic time-distance measures (walking speed, cadence, and stride length) for addressing fundamental clinical questions.
  • The use of external measures (kinematics and kinetics) during gait as mechanical signals (“mechanokines”) that influence biological and structural response
  • The unique information that can be gained by integrating gait mechanics with biological and structural markers when assessing musculoskeletal health.

Cartilage Biomechanics and Mechanobiology

Alan J Grodzinsky, ScD, Massachusetts Institute of Technology

From a historical perspective, clinicians and engineers during the 1960s/70s were motivated by the intractable problem osteoarthritis to compare the mechanical and physicochemical properties of normal vs osteoarthritic cartilages from human and animal joints. At the same time, progress on understanding the biochemical composition of cartilage matrix motivated discoveries of the contribution of specific groups of ECM molecules to tissue-level mechanical properties. The highly charged nature of the large aggregating proteoglycans of cartilage (named ‘aggrecan’ in 1988/89) further motivated studies of the electromechanical contributions to biomechanical stiffness and fluid permeability, incorporated into detailed theoretical models of cartilage’s poroviscoelastic properties. Throughout the decades, advances in instrumentation, including the introduction of atomic force microscopy to cartilage biomechanics, enabled new investigations at the pericellular matrix and cellular scales, and even molecular-scale studies of aggrecan and collagen mechanics.

In parallel, discoveries in molecular cell biology over the past 30+ years enabled the evolution of cartilage mechanobiology. Investigators initially focused on the effects of mechanical forces on the anabolic and catabolic responses of chondrocytes in cartilage explants and hydrogel cultures in vitro to static, dynamic and injurious loading forces, and compared the responses to those in the cartilages of whole joints in animals subjected to loading modalities in vivo. Tremendous progress continues to be made by many labs worldwide, and now incorporates systems biology and big-data approaches to an expanded focus on transcriptomic, genomic, proteomic, glycomic, and metabolomic studies across the molecular, cellular and tissue-level length scales of cartilage. Thus, today’s state-of-the-art knowledge of cartilage biomechanics and mechanobiology is truly multiscale, and continues to be motivated by the biology, engineering, and clinical perspectives of joint disease.