Biomechanics

  • Kevin Kirby, DPM, describes translational equilibrium and rotational equilibrium and how these common physics concepts can be used by the podiatrist to better understand how joint motions and joint stability occur, and how more accurate predictions can be made regarding the internal forces and moments acting on the structural components of the foot and lower extremity. In addition, free body diagram analysis is introduced along with clinical examples of how the concepts of ankle joint and subtalar joint equilibrium will allow the podiatrist to better comprehend the internal forces and moments that are involved in certain foot and lower extremity mechanically-based pathologies.

  • Kevin Kirby, DPM, discusses the important physics concepts of forces and moments as they apply to the biomechanics of the foot and lower extremity for the treating podiatrist.

  • Kevin A. Kirby, DPM, demonstrates how the hip joint can store and release elastic strain energy. When a patient is lying completely relaxed in a supine position, manually rotating the hip into an internally rotated position and then releasing the lower extremity shows how the hip joint may store and release transverse plane elastic strain energy. When the capsular ligaments and muscles that cross the hip joint are stretched by internal hip rotation, these soft tissue structures will store elastic strain energy or potential energy. When the limb is suddenly released, the stored elastic strain energy is converted into kinetic energy that causes a rapid external rotation acceleration of the thigh, leg and foot due to rapid shortening of these ligaments and muscles. This storage and release of transverse plane elastic strain at the hip is an important contributor to the gait phenomenon known as abductory twist. With the abductory twist, rapid external rotation of the foot occurs at the time of heel off in individuals whose hip has been excessively internally rotated during the late midstance phase of gait by excessive pronation of the subtalar joint. Elastic strain energy is also an important energy conservation mechanism in many forms of animal locomotion.

    For a related video on the abductory twist, see http://www.podiatrylive.com/_biomechanical_abductory_twist .

  • David J. Levine, DPM, CPed, provides a how-to guide for adding a shoe lift to help patients with leg length discrepancy.

     

    Dr. Levine is a Fellow of the American Society of Podiatric Surgeons, and the American Academy of Podiatric Sports Medicine. He is in private practice, and is the director and owner of the Frederick, Md.-based Walkright and Physician's Footwear, a comprehensive pedorthic facility. For more information or to contact Dr. Levine, visit www.Levinefeet.com .

  • Kevin Kirby, DPM, demonstrates the use of the subtalar joint axis locator, which he designed with Simon Spooner, PhD, in 2005. Dr. Kirby notes the subtalar joint axis locator may be beneficial in accurately assessing the spatial location of the subtalar joint axis during both weightbearing and non-weightbearing function of the foot. Dr. Kirby says future experimental work may further illustrate the important biomechanical significance of the spatial location of the subtalar joint axis upon the kinetics of the foot and lower extremity during weightbearing activities, and how abnormalities in subtalar joint axis location can create abnormal biomechanics that lead to various pathologies within the foot and lower extremity.

     

    Dr. Kirby is an Adjunct Associate Professor in the Department of Biomechanics at the California School of Podiatric Medicine at Samuel Merritt University. He is the Director of Clinical Biomechanics at Precision Intricast, Inc., and is in private practice in Sacramento, Ca.

  • Kevin Kirby, DPM, discusses the biomechanical impact of the abductory twist, a sudden abduction motion of the foot which occurs at the time of heel-off during walking gait. The abductory twist is a relatively common gait abnormality, which occurs when the naturally occurring external motion of the pelvis above the foot during late midstance is not being matched by corresponding subtalar joint supination and tibial external rotation during late midstance.

     

    Dr. Kirby is an Adjunct Associate Professor in the Department of Biomechanics at the California School of Podiatric Medicine at Samuel Merritt University. He is the Director of Clinical Biomechanics at Precision Intricast, Inc., and is in private practice in Sacramento, Ca.