Friis - Mechanical testing of orthopaedic implants

First edition

Elizabeth Friis

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ISBN: 978-0-08-100286-5 (print)

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D. Abel FDA Center for Devices & Radiological Health, Silver Spring, MD, United States

D.E. Anderson Harvard Medical School, Boston, MA, United States

P.M. Arnold University of Kansas School of Medicine, Kansas City, KS, United States

D.J. Bokor Macquarie University, Sydney, NSW, Australia

C. Clary University of Denver, Denver, CO, United States

J.J. Crisco Warren Alpert Medical School and Brown University, Providence, RI, United States

D. Dabirrahmani Macquarie University, Sydney, NSW, Australia

T.A. DeCoster University of New Mexico, Albuquerque, NM, United States

E.A. Friis University of Kansas, Lawrence, KS, United States

V.K. Goel University of Toledo, Toledo, OH, United States

L.C. Jones The Johns Hopkins University School of Medicine, Baltimore, MD, United States

T.J. Joyce School of Mechanical & Systems Engineering, Newcastle University, United Kingdom

J.S. Kawalec Kent State University College of Podiatric Medicine, Independence, OH, United States

L. Maletsky University of Kansas, Lawrence, KS, United States

E.M. Mannen University of Arkansas for Medical Sciences, Little Rock, AR, United States

S.L. Smith School of Mechanical & Systems Engineering, Newcastle University, United Kingdom

J.C. Thomas Oread Medical, Lenexa, KS, United States

L.D. Timmie Topoleski University of Maryland, Baltimore, MD, United States

A.K. Tsao Mid-Atlantic Permanente Medical Group, Largo, MD, United States

S.W. Wolfe The Hand and Upper Extremity Center, Hospital for Special Surgery, Weill Medical College of Cornell University, New York, NY, United States

T. Woods FDA Center for Devices & Radiological Health, Silver Spring, MD, United States

The musculoskeletal system consists principally of bone, muscle, tendon, ligament, and articular cartilage tissue. These are arranged throughout the body to provide internal support and allow motion to occur. Their specific configuration, however, varies with the anatomic site by virtue of the types of loads these tissues experience and the movements that they are required to perform. As such, while the musculoskeletal system is governed by a set of underlying principles, there is a great deal of local variance throughout. This is why treatments for musculoskeletal injury and disease are divided into regions such as craniomaxillofacial, oral, shoulder and elbow, hand and wrist, hip and knee, foot and ankle, spine, and others.

We have an aging population and one of the consequences of aging is the deterioration of the musculoskeletal system resulting in pain and loss of function. One of the most common age-related musculoskeletal diseases is osteoarthritis in which the articular cartilage of joints, especially of the hip and knee, becomes structurally compromised. This often results in the need for total joint replacement if more conservative measures fail. Other musculoskeletal conditions include congenital deformities, bone tumors, and trauma. These conditions may require mechanical means to augment and stabilize the musculoskeletal system, such as plates, screws, pins, nails, cages, soft tissue anchoring devices, and others. Recently, tissue engineering has emerged as a discipline that takes a biological approach to the repair and restoration of the musculoskeletal system.

It is important that orthopedic implants be designed to have mechanical properties suitable for their anticipated clinical requirements. This requires a thorough understanding of material properties and biomechanics. It also requires mechanical testing of the implants to ensure that they meet their performance specifications. Such testing can take many forms. For instance, components of total joint replacement devices may be tested under cyclic-loading conditions to establish fatigue performance and in joint motion simulators to measure surface wear. Plates and screws can undergo bend and shear testing to determine their inherent mechanical properties. Screw pullout strength can be tested in cadaver bone or a synthetic bone substrate to determine the holding power of the screw. The ability of these types of devices to restore and stabilize anatomy, however, often requires cadaver testing whereby the anatomical site is compromised to simulate the clinical condition and then repaired with the implants with the construct biomechanically tested. Consequently, there are many factors that must be considered when designing and conducting mechanical tests on orthopedic implants, including (1) the clinical use, (2) the nature of the device, (3) the substrate used, (4) static versus dynamic testing, (5) load magnitude and application rate, (6) fixturing requirements, (7) environmental conditions, (8) the types of data to be collected, and (9) ideally a way to compare the mechanical test results with the loading patterns and displacements likely to occur clinically. Nevertheless, despite the best efforts made to mechanically test orthopedic implants, the ultimate test is actual clinical use. The clinical use of medical devices in general, and orthopedic implants in particular, are governed by the various country-specific or region-specific regulatory bodies and their requirements should also be considered with respect to the types of mechanical tests performed.