**1. Introduction**

Primary total hip and knee arthroplasty (THA, TKA) are among the top 5 most common procedures and among the top 5 fastest growing procedures performed across all surgical specialties in the United States [1]. Compared to the available 2014 National Inpatient Sampling figures, the estimated total annual United States use for primary TKA and THA is expected to increase in 2030 and 2040 by 182% and 401% for primary TKA and 129% and 285% for primary THA, respectively [2]. Similarly, projections for revision TKA (rTKA) and THA (rTHA) are estimated to increase from 2014 to 2030 by between 43% and 70% for rTHA and 78% and 182% for rTKAs [3]. Paramount to the success of total joint arthroplasty (TJA) is the correct choice of biomaterials which are used to reconstruct a particular joint.

Biomaterials are defined by the European Society for Biomaterials as "a material that interacts with the biological system to evaluate, treat, reinforce or replace a tissue, organ or function of the organism [4]." In THA and TKA these materials should exhibit a yield stress greater than physiological loading of the joint, while also preventing stress shielding of adjacent bone. These materials should also have an endurance limit which reduces the number of revisions required over a patient's lifetime, particularly as TJA procedures are increasingly being performed among younger patients [5]. Biomaterials can be considered as being either bioinert, biotolerant or

**Figure 1.** *Smith- Petersen acrylic Mould arthroplasty [9].*

bioactive. Bioinert materials such as ceramics and titanium, do not illicit a biological response from surrounding tissues. Biotolerant materials, such as stainless steel, result in the formation of a fibrous layer due to irritation of surrounding tissues. Bioactive materials, such as hydroxyapatite coatings, result in direct bone on-growth, bonding prosthesis to bone.

The development of orthopaedic biomaterials closely follows the evolution of arthroplasty. Glück used ivory secured with nickel plated screws to replace femoral heads destroyed by tuberculosis in 1891 [6]. Ivory heads were also adapted by Hey-Groves several years later [7]. Delbet developed rubber prosthetic femoral heads in 1919 [8]. Smith-Petersen, in 1932 developed the first mould arthroplasty (**Figure 1**), which consisted of a hollow glass hemisphere which was fitted over the femoral head to provide a new articular surface [9, 10]. This design was subsequently revised to a Vitallium cup, a cobalt-chromium-molybdenum alloy. Subsequently, during the 1940s and 1950s a plethora of stemmed prosthesis were popularised in an effort to achieve a more anatomic design. Attempts to enhance fixation of these stemmed prostheses resulted in the adoption of dental acrylic cement by both McKee and Haboush in 1953 [11, 12]. Another significant advancement in the field of THA came in the form of articulating prostheses. Wiles popularised the first metal-on-metal THA in 1938, which was among the earliest articulating designs, with both prosthetic femoral and acetabular components [13]. However, poor component stability led to high failure rates, which were later modified by McKee and Ring using varying metal-on-metal prostheses with more reliable fixation methods.

Ultimately, these early designs gave way to the Charnley era in the 1950's which laid the foundation for modern THA design. Charnley made three major contributions to THA including 1) low friction torque arthroplasty 2) use of polymethylmethacrylate to reliably fix components to bone and 3) the use of high-density polyethylene as a bearing material [6, 14].

A core understanding of the biomaterials used in joint arthroplasty is key to selecting the most appropriate materials for a specific task, patient and type of prosthesis. This chapter provides a practical general overview of modern arthroplasty materials (metal alloys, ceramics, polyethylene and polymethylmethacrylate) rather than an exhaustive description which can be found elsewhere.
