**1. Introduction**

Biomechanics is a sub-branch of mechanics that studies the concepts of mechanics applied to the musculoskeletal system and the biomaterials used for treating orthopedic diseases. The structure, function, and motion of musculoskeletal tissues and their changes in orthopedic diseases are the main research topics of this science. The basic knowledge of the physical, chemical, and mechanical properties of biomaterials used for producing implants and prostheses is key to the orthopedic surgeon's understanding of why certain materials are used instead of others. The functional (mechanical) performance of implants and prostheses is strictly related to

their material composition and design, being therefore the basic knowledge that the orthopedic surgeon should master and potentially influence his surgical planning or clinical decision.

Biomechanics encompasses the traditional branches of mechanics: kinematics, statics, and dynamics.

Kinematics is the study of motion without considering the forces that cause it and includes concepts such as trajectory, velocity, and acceleration. Motion can be a combination of translations and rotations, with translations involving the same displacement vector for all points in the body, while rotations involve different displacement vectors for different points.

Statics characterizes the forces acting on an object at rest or moving at constant velocity with zero acceleration. These forces can be direct forces or moments, which are equal and opposite forces acting on a body separated by a distance. The application of forces and moments to a body changes its state of rest. Equilibrium is a key principle in statics, and a body is in equilibrium when the sum of all applied loads is zero. In joints, applied forces include external loads such as body weight and internal loads such as muscle forces generated to maintain the joint in equilibrium. The equilibrium principle is used to analyze joint loading in a static context, where the joint of interest is studied in isolation from the rest of the body, and all forces and moments acting on it are identified. The resulting joint reaction force is then determined using the equilibrium condition.

Dynamics, a branch of mechanics, is concerned with the effects of forces on an object and the changes they produce in the object's motion. It encompasses the principles of both statics and kinematics by examining the actions of forces and the resulting motion and acceleration of the object. In orthopedic biomechanics, dynamic analysis is frequently utilized for activities such as gait studies. This involves determining the acceleration of body parts at any given time and the forces necessary to create these accelerations. The resulting forces are then determined using static analysis methods to obtain the resulting forces over the desired range of motion.

The interaction of biomaterials with tissues and cells is the ability of a biomaterial to perform its function without eliciting toxic or injurious effects on biological systems and is called biocompatibility, and it influences the mechanical performance of implants/prostheses in the short and long term. Nowadays, the biocompatibility concept includes bioinertia, biofunctionality, and biostability (acute and chronic toxicity of materials to tissues). Biointegration or colonization of implants by neighboring tissues is also framed in the concept of biocompatibility and is an important factor in the long-term biomechanical performance of implants/prostheses that should not be overlooked in clinical decisions.

Synthetic materials mainly metals and their alloys used for implants/prostheses are classified according to their biocompatibility as well as by their mechanical properties, such as tensile, compressive, and shear strength; hardness; stiffness; fatigue resistance to cyclic or acute loading; and creep behavior. The creep concept is a type of metal deformation that occurs at stresses below the yield strength (at elevated temperatures); it defines the stress at which metal begins to plastically deform. Factors such as ease of manufacture, cost, and production quality dictate the potential for the application of a biomaterial in orthopedics.

Load-deformation and stiffness, stress-strain, and elasticity are interconnected concepts to the understanding of the mechanical performance of implants and bone tissue that will be addressed in this chapter.

## *Biomechanical Basis of Bone Fracture and Fracture Osteosynthesis in Small Animals DOI: http://dx.doi.org/10.5772/intechopen.112777*

A thorough understanding of the unique biomechanical properties, characteristics, and behaviors of bone tissue, their alterations in disease, and the implants used in companion animal orthopedic surgery is essential for achieving successful results when attempting to manipulate bone healing. There is a consensus in the field of orthopedic surgery for companion animals that mastering these principles is associated with a low rate of postoperative complications.

A basic understanding of biomechanical principles and biomaterials knowledge is a fundamental skill for the companion animal orthopedic surgeon and forms an important component in the education of surgical trainees.

In this chapter, the information provided is divided into five main areas: biomechanical basic concepts, fracture biomechanics, biomechanics of bone tissue, applied fracture biomechanics to common clinical presentations in small animal osteosynthesis, and biomechanics of implant biomaterials, covering what the authors considered in-depth knowledge of biomechanical principles of bone fracture and applied biomechanics to fracture osteosynthesis in small animals.

The main objective of this chapter is to provide information about biomechanics applied to fracture management in small animals that will help the veterinary surgeon to take more evidence-based decisions with the ultimate goal of surgical success.
