Acetabular components

The next advance in total hip arthroplasty came with the development of various porous surface treatments which allow bone tissue to grow into the metal porous coating on the femoral stem of the hip implant and on the acetabular component of the total joint replacement. These developments arose because of patients who were not able to tolerate cemented implants because of allergies to the cement, methylmethacrylate. More youthflil patients are better served by a press-fit implant as well. Figure 12 shows the difference between textured and beaded surface-treated orthopedic prostheses. 

The acetabular component is as integral to successful total hip arthroplasty as is the femoral hip stem component. The life of the acetabular component depends on proper placement and bone preparation in the acetabular region of the hip girdle, proper use of bone cement, and superior component design. 

In 1971 a metal-backed polyethylene acetabular cup was introduced. This cup provided an eccentric socket which was replaceable, leaving the metal and replacing only the polyethylene. Because of the success of this component, metal-backed high density polyethylene (HDPE) liner is standard for prosthetic acetabular components. Research confirms that metal-backing reduces the peak stresses in the bone cement, and that HDPE forms a successfiil articulating surface for the prosthetic joint. 

Over time a large variety of materials have been used, including ivory, stainless steel, chromium—cobalt, and ceramics for the acetabular component. None proved sufficient. The implant material composition must provide a smooth surface for joint articulation, withstand hip joint stresses from normal loads, and the substance must disperse stress evenly to the cement and surrounding bone. 

Figure 15.1.1 A schematic diagram of the two components of an artificial hip the stem or femoral component and the socket or acetabular component.

Additional source of information for UHMWPE acetabular cups arises from the quantitative analysis of polarized Raman spectra. Figure 17.6 shows photographs and the outcome of such analysis for two acetabular cups, which were retrieved after substantially different in vivo lifetimes. The retrieved acetabular cups were both belonging to male patients and sterilized by y-rays, but produced by different processes. One acetabular component (manufactured in 2002 by Biomet Inc.) was prepared by isostatic compression molding and sterilized before implantation by a dose of 33 kGy of y-rays. It was retrieved due to infection after 2 years 5 months. This cup will be referred to as the short-term retrieval. The other retrieval (manufactured in 1995 by Zimmer Inc.) was prepared by Ram-extruded molding and sterilized in air by a dose of 25-37 kGy of y-rays. For this latter cup, the follow-up pe-... 

The foreign body response to carbon fibers is not chronic unless they fragment. One major problem has been the accumulation of wear debris near the acetabular components [129]. However, when used as ligament replacements, carbon fibers appear to induce a type of fibrosis in which collagen fibers align with the fibers. This suggests that carbon fibers can be used as a template for the formation of fibrous tissue [130] and indeed tendon fibroblast cells have been grown on a... 

L. S. Stem, M. T. Manley, and J. Parr, Particle size distribution of wear debris from polyethylene and carbon-reinforced acetabular components. Trans.-Second World Congress on Biomaterials, Washington, DC, 1984, v. 7, p. 66. 

Coathup, M.J., Blackburn, J., Goodship, A.E., Cunningham, J.L., Smith, T., and Blunn, G.W. (2005) Role of hydroxyapatite coating in resisting wear particle migration and osteolysis around acetabular components. Biomaterials, 26 (19), 4161-4169. 

Ohashi T., Inoue S., Kajikawa K., Ibaragi K., Tada T., Oguchi M., Aral T, and Kondo K. 1988. The cHnical wear rate of acetabular component accompanied with alumina ceramic head. In Bioceramics. Proceedings of 1st International Symposium on Ceramics in Medicine. H. Oonishi, H. Aoki, and K. Sawai (Eds.), pp. 278-283. Ishiyaku EirroAmerica, Inc. Tokyo. 

Recently, a cellular, structural biomaterial comprised of 15 to 25% tantalum (75 to 85% porous) has been developed. The average pore size is about 550 p,m, and the pores are fully interconnected. The porous tantalum is a bulk material (i.e., not a coating) and is fabricated via a proprietary chemical vapor infiltration process in which pure tantalum is uniformly precipitated onto a reticulated vitreous carbon skeleton. The porous tantalum possesses sufficient compressive strength for most physiological loads, and tantalum exhibits excellent biocompatibility [Black, 1994]. This porous tantalum can be mechanically attached or diffusion bonded to substrate materials such as Ti alloy. Current commercial applications included polyethylene-porous tantalum acetabular components for total hip joint replacement and repair of defects in the acetabulum. 

The prosthesis for total hip replacement consists of a femoral component and an acetabular component (Figure 45.8a). The femoral stem is divided into head, neck, and shaft. The femoral stem is made of Ti... 

The wear characteristic of the surface of tibial polyethylene is different from that of acetabular components. The point contact stress and sHding motion of the components result in delamination and fatigue wear of the UHMWPE [Walker, 1993]. Presumably because of the relatively larger particle size of polyethylene debris, osteolysis around a total knee joint is less frequent than in a total hip replacement. 

Typical processing steps in the manufacture of UHMWPE implants, starting with the resin powder (A). (B) Semifinished rods that have been consolidated from the resin powder. (C) Machining of the UHMWPE rods on a lathe. (D) UHMWPE acetabular components after machining. (Pictures provided courtesy of David Schroeder [Biomet, Warsaw, IN].)... 

Kurtz S.M., J. Turner, M. Herr, and A.A. Edidin. 2002. Deconvolution of surface topology for quantification of initial wear in highly crosslinked acetabular components for THA. JBMR (Applied Biomaterials) 63 492-500. 

These three interim implant designs, preserved in the collection at Wrightington Hospital, are shown in Figure 4.3. The PTFE components in Figure 4.3 were retrieved at revision surgery and are severely worn. The wear is most evident in the sectioned 25.3 mm diameter acetabular component. The femoral components, on the other hand, appear pristine. The femoral heads are polished to a mirror finish (note the reflection of my hands holding the camera). 

Example of an osteolytic lesion in the pelvis, located superior to the metal-backed acetabular component. (Courtesy of Av Edidin, Ph.D., Drexel University.)... 

Range of Clinical Wear Performance in Cemented Acetabular Components... 

Chamley and coworkers first developed radiographic techniques for evaluating the wear rate of UHMWPE acetabular components in patients. In 1973, Chamley and Cupic reported on the long-term wear performance in the first cohort of patients to receive a UHMWPE component between November 1962 and December 1963. During this time period, 170 patients received a cemented LFA with an UHMWPE component a total of 185 acetabular cups were implanted. Because of the elderly population originally implanted with the components, many had died or were too infirm to travel to the clinic for followup examination (more than two-thirds of the patients were older than 60 years of age at the time of implantation). Thus, only 106 out of the original 185 UHMWPE cups could still be evaluated after 9 or 10 years of implantation. The complications for this series included a 4-6% rate of infection, 1-2% rate of mechanical loosening, and a 2% incidence of late dislocation. 

Early in 1963, Chamley introduced the use of a semicircular wire marker on the back of the acetabular component to assist with the measurement of wear using radiographs. The photograph in Figure 5.4, taken of an unused Chamley cup from the collection at the Thackray Museum at Leeds, shows the wire marker inserted into the cement groove. Although the implant shown was produced between 1968 and 1975, the configuration of the wire marker was similar to that used in Chamley and Cupic s study. 

Linear Wear Rate (mm/year) Based on Radiographs for the Modular Harris-Gallante I Acetabular Component as a Function of Implantation Time... 

Qualitatively, the trends observed for cemented components also appear to be applicable to modular acetabular components, evaluated using current computer-assisted wear measurement techniques (Tables 5.2 and 5.3, and Figure 5.11). The box and whisker plots shown in Figure 5.11 compare the linear... 

Distribution of LWRs and VWRs estimated in a first-generation modular acetabular component design (Harris-Gallante Zimmer Warsaw, IN). These graphs show the tendency for the wear rates to decrease with implantation time. Results are compared based on analysis of A-P radiographs alone (two-dimensional), as well as based on the combined analysis of A-P and lateral radiographs (three-dimensional). (Based on data provided courtesy of J. Martell, M.D.)... 

Barrack R.L. 1996. Concerns with cementless modular acetabular components. Orthopedics 19 741-743. 

Hozack W.J., J.J. Mesa, C. Carey, and R.H. Rothman. 1996. Relationship between polyethylene wear, pelvic osteolysis, and clinical symptomatology in patients with cementless acetabular components. A framework for decision making. I Arthroplasty 11 769-772. 

Livermore ]., D. Ilstrup, and B. Morrey. 1990. Effect of femoral head size on wear of the polyethylene acetabular component. J Bone Joint Surg 72 518-528. 

Martell J., E. Berkson, and J.J. Jacobs. 2000. The performance of 2D vs. 3D computerized wear analysis in the Harris Galante acetabular component. Orthopaedic Transactions 25 564. 

In 1938, Wiles is reported to have performed the first hip arthroplasty, consisting of stainless steel femoral and acetabular components that were fixed to the bone without cement (1957). Although many clinical records of Wiles patients were lost in World War II, some radiographs of Wiles prosthesis can still be found at the Chamley Museum, as shown in Figure 6.2. 

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