The Implant-Cement Interface in Total Hip Arthroplasty
Despite being in clinical use for more than 40 years, the detailed function of cemented femoral stems is still not completely understood. After insertion into the femur, the behavior of the bone/cement/stem construct can be expected to depend on a number
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The Implant-Cement Interface in Total Hip Arthroplasty Georgios Digas and Johan Kärrholm
Introduction Despite being in clinical use for more than 40 years, the detailed function of cemented femoral stems is still not completely understood. After insertion into the femur, the behavior of the bone/ cement/stem construct can be expected to depend on a number of factors. A fundamental function performed by the bone cement is the transfer and distribution of the stress between the prosthesis and the bone. The success of cemented systems, in the long term, depends on many factors. The prosthesis itself can, depending on its material composition, shape, size, and surface finish, have a complex influence on its surroundings. Bone cement and its structural and mechanical characteristics in particular have a similar influence when combined with different stem designs. Thus, the quality and shape of the materials and interaction at the stem-cement interfaces are of great importance for long-term performance. The development of clinical loosening has been attributed to micromovements, abrasive wear, leakage, and even the pumping of joint fluid
G. Digas, MD, DSc, PhD (*) Department of Orthopaedics, General Hospital Xanthi, Xanthi 67100, Greece e-mail: [email protected] J. Kärrholm, MD Department of Orthopaedics, Sahlgrenska University Hospital, Mölndal SE-431 80, Sweden
out into the cement-bone interface. The initiation of this process may vary. There is, however, substantial evidence that debonding occurs between the cement and the stem, which may initiate loosening [1, 2]. Consequently, many stem designs are made to obtain firm fixation to the cement by the use of a collar, macrotexture, rough surface, or pre-coating with polymethylmethacrylate. A diametrically different opinion is that debonding of the stem is unavoidable and that the stem should therefore be designed to adapt to such an event. The polished double-tapered uncollared stem is an example of this [3].
Effect of Prosthetic Design and Choice of Material on Stem-Cement Interface Stem Material There are three types of materials that are commonly used for cemented femoral stems. These are cobalt–chromium alloys, stainless steel, and titanium alloys. The use of a titanium alloy (usually Ti-6AI-4V or Ti-5AI-2.5Fe, Ti-6AI-7Nb) was attractive because its stiffness is closer to that of bone and bone cement than the other two alloys. The clinical performance of stems made of titanium alloy seems to be closely related to stem design and especially to the choice of surface designs. Those with rougher surface have shown high failure rates [4, 5]. Some smooth and polished stems [6, 7] seem to perform well,
T. Karachalios (ed.), Bone-Implant Interface in Orthopedic Surgery, DOI 10.1007/978-1-4471-5409-9_4, © Springer-Verlag London 2014
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G. Digas and J. Kärrholm
36 Fig. 4.1 This photograph shows an Exeter stem extracted 10 years postoperative. Note the severe crevice corrosion at the medial surface of the stem
but these are also sensitive to changes of design,
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