Osteolysis and component loosening have been identified among the most common mechanisms for late total hip arthroplasty (THA) failure [1]. During normal activity, wear particles are released from metal-on-polyethylene (M-O-P) and ceramic-on-polyethylene (C-O-P) bearing surfaces. Adhesion and abrasion between the femoral head and polyethylene insert are the primary mechanisms for wear. Hydraulic pressure produced during normal hip movement forces joint fluid and polyethylene wear debris through the “effective joint space” [2].

Areas of the host bone-implant interface that are not sealed by circumferential bone contact, osseointegration, or polymethylmethacrylate (PMMA) cement bonding can allow access for polyethylene, metal, ceramic, or PMMA particles to the implant-bone interface. When exposed to particulate wear debris, macrophages initiate and osteoclasts mediate the process of bone resorption around initially stable implants [3, 4]. NFkappaB ligand (RANKL) , produced by osteoblastic stromal cells, fibroblasts, or activated T-cells, binds to receptors on the surface of osteoclast precursor cells and stimulates them to convert into active osteoclasts [5, 6]. Among biomaterials used in total hip arthroplasty, polyethylene has the highest potential to induce osteolysis, with sub-micrometer-sized particles more strongly associated with the osteolytic process than macroscopic debris [7]. Osteolysis also appears to be associated with more rapid release of polyethylene debris from the bearing surface, with higher volumetric wear and linear rates greater than 0.2 mm/year implicated with the development of radiographically evident osteolysis [8].

The radiographic presentation of osteolysis differs based on the patterns of particle access through the effective joint space around cemented and cementless total hip arthroplasty prostheses. For cemented components, the osteolytic process advances in a linear fashion along the cement-bone interface, beginning at the joint surface and extending to the most distant areas of bone-implant contact. The patterns of linear osteolysis around femoral and acetabular implants were first reported by Gruen and DeLee, respectively [9, 10]. When osteolysis develops in association with well-fixed, cementless components, the process results in a focal expansion within areas of the bone-host interface where the particles are able to gain access (Fig. 13.2) While implants may initially remain mechanically stable, progressive focal (balloon) osteolysis can undermine implant fixation and result in late loosening.

A variety of factors have been associated with either accelerated wear rates or catastrophic polyethylene liner failures. Kennedy et al. [11] reported an association of vertical acetabular component malposition with higher rates of osteolysis and linear polyethylene wear. Patil et al. [12] estimated that polyethylene liners placed in a position >45° of inclination were subject to a 40% increase in linear wear using a finite element analysis model. The utilization of larger head sizes and thinner polyethylene inserts has been associated with higher rates of wear and osteolysis with conventional polyethylene liners in total hip arthroplasty [13]. Berry et al. [14] reported catastrophic polyethylene liner failures only among inserts less than 5 mm thick. Polyethylene degradation can be accelerated under conditions intrinsic to the material. Sterilization processes used in the late twentieth century were occasionally performed in an oxygen-containing environment and this was associated with higher rates of wear and osteolysis [15, 16]. This process is notably magnified when the polyethylene remains in a non-implanted inventory for extended periods of time (shelf life). Puuolaka et al. [17] noted that polyethylene inserts with a shelf life greater than 3 years had a substantially higher rate of wear and osteolysis than those with a shorter time before implantation.

Irradiation introduced during the process of ultrahigh-molecular-weight polyethylene (UHMWPE) sterilization was noted to have an effect of reducing the linear and volumetric wear rate of polyethylene [18]. This cross-linking process increases the wear resistance of the polyethylene material in exchange for decreasing its fracture resistance. Several studies have now demonstrated a substantial reduction in the wear rate of highly cross-linked polyethylene used in contemporary total hip arthroplasty through the first 10 years after implantation, even when performed among younger patients [19–21]. The use of a ceramic femoral head has demonstrated reduced wear rates when used with a conventional polyethylene bearing, but the benefits have not yet been substantiated when coupled against a highly cross-linked polyethylene liner [22, 23]. Improvements in the durability of highly cross-linked polyethylene have contributed to the availability of larger femoral heads for primary total hip arthroplasty. Selection of femoral head size for an individual patient should take several factors into account: patient factors associated with hip dislocation (female gender, diagnosis other than osteoarthritis), acetabular component size, and minimum polyethylene liner thickness, and risk for wear of the replaced acetabular liner during the expected remaining years of a patient’s life. While the stability of hip replacement constructs is improved with the use of larger femoral head sizes, increased contact between the larger femoral head and polyethylene liner can contribute to higher rate of volumetric polyethylene wear [24].

The diagnosis of polyethylene wear can be made from a review of radiographic imaging studies, particularly when the femoral head migrates in a superolateral direction (Fig. 13.3). The amount of linear wear occurring in an acetabular component may be harder to define for components placed with less than a 40° inclination angle as wear will occur more medial or central within the acetabular liner. Osteolysis can be noted by the presence of osteopenia and loss of normal trabecular architecture around the implant. Iliac and obturator oblique Judet radiographs may be helpful in defining the presence of osteolysis, size of the defects, and integrity of the posterior and anterior columns. Cross-sectional imaging using computed tomography (CT) scan can provide greater detail of the characteristics and size of osteolytic defects and may be helpful [25] (Fig. 13.4).