J Am Acad Orthop Surg, Vol 16, No suppl_1, July 2008, S14-S19.
© 2008 the American Academy of Orthopaedic Surgeons
How are wear-related problems diagnosed and what forms of surveillance are necessary?
Henrik Malchau, MD, PhD and
Hollis G. Potter, MD
Dr. Malchau is Professor, Harvard Medical School, Co-Director, The Harris Orthopaedic Biomechanics and Biomaterials Laboratory, and Attending Physician, Adult Reconstructive Unit, Department of Orthopedics, Massachusetts General Hospital, Boston, MA. Dr. Potter is Chief, MRI Department, Director of Research, Department of Radiology and Imaging, Hospital for Special Surgery, and Professor of Radiology, Weill Medical School of Cornell University, New York, NY.
*The Implant Wear Symposium 2007 Clinical Work Group included John J. Callaghan, MD, John M. Cuckler, MD, Jorge O. Galante, MD, DMSc, Alejandro González Della Valle, MD, Stuart B. Goodman, MD, PhD, James I. Huddleston, MD, Lynne C. Jones, PhD, David G. Lewallen, MD, Henrik Malchau, MD, PhD, William Maloney, MD, Amanda Marshall, MD, Wayne Paprosky, MD, Hollis G. Potter, MD, Michael D. Ries, MD, Aaron Rosenberg, MD, Thomas P. Sculco, MD, Bernard N. Stulberg, MD, Audrey K. Tsao, MD, and Timothy Wright, PhD.
Dr. Malchau or a member of his immediate family has received research or institutional support from Zimmer, Biomet, and Smith & Nephew and is a consultant to or an employee of Smith & Nephew. Dr. Potter or a member of her immediate family has received research or institutional support from General Electric Health Care and is a consultant for Histogenics Corporation.
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Abstract
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Prospective, randomized clinical wear studies have shown significant wear reduction when highly cross-linked, e-beamed, melted polyethylene was compared with conventional polyethylene sterilized by gamma irradiation in air. More complete assessment of wear-induced osteolysis in the general total hip arthroplasty patient population must rely on registries with follow-up of large populations of patients through radiographic evaluation of wear-related factors, such as suboptimal placement of the implant components, osteolytic defects, and aseptic loosening. Follow-up radiographs should be obtained in the early postoperative period and at 1, 5, and 10 years postoperatively, and then every 1 to 5 years, thereafter depending on radiographic findings of osteolysis and its progression. When pathologic findings are present, further examinations, such as oblique Judet views and magnetic resonance imaging (MRI) with artifact minimization should be considered to provide a better determination of the extent of the osteolysis. Because conventional radiographs underestimate the prevalence and extent of osteolysis in many instances, diagnosis and surveillance should be performed with radiographic edge detection, spiral computed tomography (CT), MRI, radiostereometric analysis, and quantitation of wear and osteolysis, including bone and soft-tissue lesions. Helical CT has demonstrated excellent specificity in identifying and quantifying the extent of osteolysis. MRI can more accurately localize both osseous and soft-tissue particulate disease, and detect granuloma and compression on adjacent nerves and vessels.
Diagnosis and surveillance of wear-induced osteolysis includes measurement of wear to assess the extent of the generation of particulate debris, and imaging methods to assess the extent, location, and progression of the periprosthetic osteolysis process. Currently, the standard method for assessing clinical wear involves evaluation of serial radiographs to determine the amount of penetration of the femoral head over time into the polyethylene acetabular component of hip prostheses. Earlier manual techniques1-3 relied on visual determination of the femoral head and the edge of the acetabular cup. Unfortunately, these techniques can lead to highly variable outcomes. Thus, they lack the precision necessary to yield useful information, especially for short-term follow-up and in the hip with small amounts of wear.
Radiostereometric analysis (RSA)4 is the most accurate current method for determining the magnitude of penetration of the femoral head. This technique requires that small tantalum beads be placed in each region of interest. Using image analysis, relative displacements are calculated from sequential pairs of radiographs exposed over a reference grid. However, the requirement to use tantalum beads limits the use of this method to a small group of patients.
In the past decade, other computer-assisted methods have been developed, such as the Polywear5 (Draftware, Vevay, IN) and the Hip Analysis6 software programs (Orthopedic Biomedical Imaging Institute, Chicago, IL). These programs rely on edge detection and are less accurate than RSA because they use conventional plane anteroposterior and lateral radiographs of the hip. Their advantage, however, is that they can be applied to larger groups of patients. The accuracy of all of these techniques is affected by the quality of the radiographs.
Conventional modalities used to assess the magnitude of bone loss associated with osteolysis include longitudinal assessment using radiographs; however, conventional radiographs either fail to detect or grossly underestimate the extent of bone loss that will be encountered at revision surgery.7-9 Southwell et al10 showed that 45° oblique radiographs impart greater sensitivity for detection of periacetabular bone loss, particularly at the level of the posterior column and wall. Despite these improvements, Engh et al11 noted poor interobserver reproducibility (
= 0.28 to 0.44) in a study assessing osteolysis with radiographs. Proposing a new classification system, Saleh et al12 demonstrated improved interobserver reliability and improved correlation with intraoperative findings. Robertson et al13 demonstrated that radiographs underestimated bone loss by at least 20% in a cohort of 19 patients with failed arthroplasties, resulting in the selection of the correct type of prosthesis in only half of the patients who underwent revision. Limitations of radiographs are largely due to the fact that the three-dimensional, complex joint geometry, is assessed by a two-dimensional imaging process.
Computed tomography (CT) is also of limited use in assessing osteolysis due to beam-hardening artifact generated by the severe attenuation of the radiographic beam, caused by the juxtaposition of the high attenuation coefficient of metal with the lower attenuation coefficient of the surrounding soft tissue. This attenuation results in missing data or hollow projections during filtered back projection and reconstruction artifacts. Helical CT is more sensitive in the identification and quantification of periacetabular bone loss following hip arthroplasty compared with plain radiographs.14
Strategies to minimize the beam-hardening artifact include the use of multidetector helical CT at a higher kilovolt peak (140 kVp) and milliampere second (mAs), which improves penetration of the radiographic beam and results in superior image quality but also increases the effective dose of ionizing radiation. The use of an edge-enhancement bone algorithm is also efficacious, as is a soft-tissue algorithm in the presence of very dense metals. Further improvement can be achieved with the use of postprocessing software. Claus et al15 used a cadaveric model that was studied with CT; subsequent images were postprocessed using an algorithm to suppress metal-induced beam-hardening artifact. In their study, mean percent error was compared with a direct measured standard and was unrelated to lesion location but dependent on lesion size. They concluded that CT could be used more accurately than conventional radiographs to assess pelvic osteolysis.
Limitations of both radiographs and CT, however, lie in the fact that particle disease starts as a synovial process in the soft tissues; both modalities have limited soft-tissue contrast. Because of its direct multiplanar capabilities, superior soft-tissue contrast, and lack of ionizing radiation, magnetic resonance imaging (MRI) is a suitable standard by which to assess the magnitude of both periprosthetic bone loss and intracapsular burden of disease. Traditional MRI techniques have been limited by the presence of susceptibility artifact, resulting in image distortion and frequency shift due to the juxtaposition of very easily magnetized ferromagnetic metallic components and poorly magnetized, diamagnetic soft tissue. The magnitude of susceptibility artifact is proportional to the strength of the magnetic field and a component-specific susceptibility constant.
Optimal results in the literature have been achieved at 1.5 T.16 Diminished artifact is encountered with components made from oxidized zirconium alloy compared with those made from conventional cobalt-chromium alloy due to the diminished magnetic moment of zirconium.17 Modifications in pulse sequence parameters and optimized protocols have resulted in reduction of artifact with superior delineation of the surrounding soft-tissue envelope. In a study of 28 total hip arthroplasties (THAs) in 27 patients, MRI was proved to be more effective than plain radiographs in detecting the location and magnitude of periacetabular bone loss. MRI also delineated the intracapsular burden of particle disease that was not seen on either radiographs or CT.18 In a cadaveric simulated model of periacetabular osteolysis comparing optimized radiographs (using bilateral oblique views), optimized CT (with a high kVp, high mAs algorithm, and suitable postprocessing algorithm), and MRI, the latter had a sensitivity for lesion detection of 95.4%, compared with 74.7% for CT and 51.7% for plain radiographs.19 For radiographs and CT, lesion detection was dependent on lesion location, whereas MRI had consistently good sensitivity in all lesion locations. In another cadaveric study comparing MRI to radiographs, MRI was 95% sensitive in the detection of lesions, with a specificity of 98% and an accuracy of 96%, yielding a mean absolute error in determining lesion size of 0.8 ± 2.2 cm3.20
MRI strategies used to reduce the susceptibility artifact generated by the components include the use of a wide receiver sampling bandwidth, which diminishes the frequency shift generated by the components, as well as strategies aimed at increasing signal-to-noise ratio, such as increasing the number of acquisitions. Fast spin-echo techniques limit signal loss secondary to diffusion and thereby also increase overall signal-to-noise ratio.16 Suitable protocols using commercially available software are provided in Tables 1 and 2.
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Table 1 Hospital for Special Surgery Recommended Protocol for Magnetic Resonance Imaging of Total Hip Arthroplasty*
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Table 2 Hospital for Special Surgery Recommended Protocol for Magnetic Resonance Imaging of Total Knee Arthroplasty*
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The classic appearance of osteolysis on MRI is denoted by intermediate signal intensity replacement of the high-signal-intensity fat of the marrow. This sharp contrast resolution allows for manual segmentation of areas of bone loss, providing a volumetric assessment of osteolysis "load" suitable for longitudinal study. Distinct patterns of bone loss are observed; these can be characterized as expansion of the synovial envelope, allowing for an indolent erosion of the surrounding osseous structures (Figure 1) versus the particulate debris that is characteristically of intermediate to low intensity and often extends in a more eccentric fashion into the bone and thereby beyond the cortex into the surrounding soft tissues (Figure 2). The superior soft-tissue contrast of MRI also allows for detection of intracapsular burden of particle disease before osteoclastic resorption of bone, as well as compression of regional neurovascular structures by polyethylene granulomata or expansion of the pseudocapsule (Figure 2). The presence of component loosening is typically manifest as circumferential intermediate signal intensity between the metal component and surrounding bone or cement (Figure 3).
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Figure 1 Bilateral total hip arthroplasties in a 52-year-old woman were performed 9 years prior on the right hip and 7 years prior on the left. A, Coronal body coil fast inversion recovery image demonstrating fluid signal material replacing the ischia bilaterally, compatible with severe osteolysis. B, Sagittal fast spin-echo image of the right hip demonstrating fluid signal material with a well-defined low signal rim involving the ischium and posterior column (arrows).
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Figure 2 Sagittal fast spin-echo image in an 87-year-old man with a THA performed 21 years prior on the left hip demonstrating extensive periacetabular osteolysis (short arrows), with particulate material replacing the ischium and posterior column. The osteolysis abuts the sciatic nerve (long arrow).
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Figure 3 Axial fast spin-echo image in a 64-year-old man with a total knee arthroplasty of the right knee performed 7 years prior demonstrating loosening of the patellar component and prominent fibrous membrane formation at the anterior portion of the femoral component (short arrows). The joint effusion with particulate debris in the dependent portion of the lateral gutter (long arrow) is indicative of intracapsular burden of particle disease.
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These techniques enable the serial evaluation of painful and asymptomatic arthroplasties, allowing for the detection of particle disease at the origin of the adverse biologic reaction. This permits both quantitative assessment of intracapsular synovial load and osteolysis as well as qualitative assessment of patterns of bone loss.
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Prospective Studies
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Prospective, randomized clinical wear studies performed at Sahlgrenska University Hospital, Göteborg, Sweden,21,22 and Massachusetts General Hospital, Boston,23,24 showed significant wear reduction when highly cross-linked, e-beamed, melted polyethylene was compared with conventional polyethylene sterilized by gamma irradiation in air. Similar studies confirmed significant wear reduction in THAs performed both with highly cross-linked and melted polyethylene and with highly cross-linked and annealed polyethylene.
More complete assessment of wear-induced osteolysis in the general THA patient population must rely on registries with follow-up of large populations through radiographic evaluation of wear-related factors, such as suboptimal placement of the implant components, osteolytic defects, and aseptic loosening. Follow-up radiographs (anteroposterior and cross-table through lateral views of the hip joint) should be obtained in the early postoperative period and at 1, 5, and 10 years, and then every 1 to 5 years thereafter depending on radiographic findings of osteolysis and its progression. When pathologic findings are present, further examinations, such as oblique Judet views and MRI with artifact minimization, should be considered to provide a better diagnosis of the extent of the osteolysis. MRI can also be helpful in disclosing the etiology of pain in a patient presenting with normal radiographs.
CT and MRI can also help in diagnosing and determining the extent of wear-related problems in total knee arthroplasty (TKA). Serial knee radiographs can be used to determine the need for intervention in cases of extensive polyethylene wear. Unfortunately, no radiographic techniques are available to detect small amounts of wear following TKA.
In studies with small series of patients, RSA or Hip Analysis/Polywear measurements can be used to detect THA wear reliably. Unfortunately, these techniques are not widely accessible to the community surgeon. For surveillance of larger populations, a registry approach combined with development of screening tools aimed at accurately and inexpensively interpreting large numbers of radiographs seems necessary.
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Future Directions for Research
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Many patients with joint arthroplasties do not obtain regular follow-up examinations. Patients should be educated about the importance of regular follow-up and seeking routine, timely follow-up after THA and TKA. The development of patient education tools should be undertaken by organizations such as the American Academy of Orthopaedic Surgeons and the American Association of Hip and Knee Surgeons. These tools should focus on the lack of early symptoms of osteolysis and the risk of delaying treatment until failure occurs. Emphasis should be placed on educating patients of the need for continuous long-term follow-up even in the absence of symptoms. Linking such a program with the development of state and federal total joint registries would enable research to be done using stratified follow-up algorithms related to specific risks among different patient populations and implant types.
Image recognition software for automatic radiographic analysis of wear should be developed. The use of CT and MRI in diagnosing the extent of osteolysis should be extended to large numbers of cases to examine their efficacy and to establish guidelines for their clinical use in the evaluation of new hip and knee replacement designs. The need remains for better techniques to measure wear in TKAs.
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Figures
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Tables
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References
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Abstract
Prospective Studies
