Chapter 1 Biomechanics PDF

McGlamry's Foot and Ankle Surgery ISBN: 978-1-9751-3606-2 | 5th_Edition Fishco, William | Marcoux, John | Vickers, Daniel | Butterworth, Michelle | Carpenter, Brian (Print pagebreak 1)(Print pagebreak 2)(Print pagebreak 3) CHAPTER 1 Biomechanics Douglas H. Richie Jr. INTRODUCTION The human foo...

McGlamry's Foot and Ankle Surgery ISBN: 978-1-9751-3606-2 | 5th_Edition Fishco, William | Marcoux, John | Vickers, Daniel | Butterworth, Michelle | Carpenter, Brian (Print pagebreak 1)(Print pagebreak 2)(Print pagebreak 3) CHAPTER 1 Biomechanics Douglas H. Richie Jr. INTRODUCTION The human foot contains unique features enabling the primary functions of upright standing and bipedal ambulation. The goal of reconstructive foot and ankle surgery is restoration of function to the appendage that will lead to improvement of mobility for the patient. To achieve this goal, the planning of any surgical procedures requires a detailed knowledge of how the foot functions during standing and walking. More importantly, the surgeon must fully understand all of the factors that affect mobility of the foot and how they are ultimately controlled by the central nervous system. Biomechanics is a broad discipline encompassing many areas of study. This chapter will focus on certain topics that are most relevant to the foot and ankle surgeon, enabling the integration of knowledge of foot function into the planning and execution of surgical procedures. A study of gait, focusing on the interaction of the foot with the ground as well as its interaction with proximal skeletal segments will give an introduction to moments, forces, and muscle actions. Next, a review of recent kinematic studies will give new insight into the contributions of multiple joints to overall motion of the foot, dispelling previous notions about modeling of skeletal segments of the foot during gait. Muscles and tendons, which span multiple essential joints of the foot, will be evaluated from the standpoint of power and moment arm. The physiology of sensorimotor mechanisms that control posture and lower extremity movement will be reviewed. Finally, the unique anatomic features of the human foot will be explored to elucidate how this appendage can provide compliance, stiffness, and energy storage necessary for bipedal ambulation. Much of the insight into the function and mechanical behavior of the human foot has been gained from research contributed by several different scientific disciplines including biomechanics, movement science, neuroscience, physical medicine, and physical therapy. Terminology from these disciplines differs somewhat from common terminology used in the podiatric community. Therefore, a review of terminology is required before exploring the topics. TERMINOLOGY Biomechanics is a study of the mechanics of a living body, especially of the forces exerted by muscles and gravity on the skeletal structure. 1 Studies of human movement use methods of mechanical engineering studying time, mass, force, center of gravity, moments of force, and motion. The foot and ankle surgeon should be familiar with these terms and definitions as they are commonly used in publications relevant to foot and ankle surgery. Gait studies and force plate studies utilize the millisecond as the primary unit for time. Repeated events over short periods of time are measured in frequency or hertz, abbreviated Hz. 1 Hz is one cycle per second. For example, a force plate may sample ground reaction force (GRF) at 500 Hz, which is 2-ms interval between samples. The mass of an object is normally measured in kilograms (kg). The force acting on an object is measured in Newton. The force applied by earth's gravity on a mass of 1 kg is 9.81 N. One Newton is the force exerted by gravity on a mass of 102 g or 3 oz. Cadaver studies often apply axial load to a limb to simulate body weight. A 70-kg adult will produce a downward force from gravity of 686.7 N. Therefore, to simulate quiet standing, a cadaver model of one leg will apply axial load of ˜350 N. The center of mass is often referred to as the center of gravity in studies of human walking and standing. The center of gravity is thought to be located immediately in front of the lum-bosacral junction in an upright standing human. The center of gravity can actually move away from the body depending on the movement. The moment of force is defined as a force acting at a distance from a rotational axis. The distance is known as the lever arm or moment arm. A moment of force will cause a skeletal segment to rotate at a single joint or multiple joints. Moment of force can also be termed moment or torque. Moment of force is calculated by: M = F × D, where M is the moment of force in Newton-meters (N-m), F is the force in Newton (N), and D is the distance in meters (m). The angle of the force vector can have significant effects on the magnitude of moment of force. The above equation assumes that the ocp999 | 96.77.2.195 | 01 April 2022 3:34:16 Utc  McGlamry's Foot and Ankle Surgery ISBN: 978-1-9751-3606-2 | 5th_Edition Fishco, William | Marcoux, John | Vickers, Daniel | Butterworth, Michelle | Carpenter, Brian force vector is aligned perpendicular to the joint axis, which applies maximal moment. If the force vector is oriented