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CT and MRI of hip arthroplasty
Clinical Radiology (2007) 62, 1172e1173
COMMENTARY
CT and MRI of hip arthroplasty* D. Barron* Leeds Teaching Hospitals, Leeds, UK Received 26 April 2007; accepted 1 May 2007
The number of hip arthroplasties performed is steadily increasing due to many factors, not least because of improved life expectancy in the Western World. The complication rates for these are commendably low, but the sheer volume of implants means that there is now a significant cohort of patients with implant-related complications. Holistically assessing these patients is challenging and it is essential that the surgeon can make a fully informed decision before embarking upon any form of intervention. The article by Cahir et al.1 points out that the common complications encountered include infection, mechanical aseptic loosening, osteolysis, granulomatous disease, heterotopic new bone formation, fractures, and local nerve damage. Radiological assessment has inevitably become an integral part of the work-up. It is only recently that the range of imaging available for this group has expanded to include computed tomography (CT) and magnetic resonance imaging (MRI). Previously both of these were precluded by the excessive artefact associated with metal implants, indeed some radiologists may well miss those days as interpreting these challenging studies can be very time-consuming. It is important to appreciate that although both CT and MRI have dramatically improved, they should still be used in combination with other techniques rather than to supplant them. In addition, correlation with clinical and pathological findings remains mandatory. Plain radiographs remain a good initial assessment. These are readily accessible and provide an invaluable record of temporal change. This applies to prosthesis alignment, bony changes, and the boneecement interface. The latter is compared *
DOI of original article: 10.1016/j.crad.2007.04.018. * Tel.: þ44 113 3923768; fax: þ44 113 3928241. E-mail address: [email protected]
using the Gruen zones2 for the femoral component and the DeLee and Charnley zones3 for the acetabular component. Indeed, for the follow-up of many prostheses this remains the only radiological assessment carried out by the surgeon. When the surgeon is concerned about softtissue abnormalities, joint effusions or tendonbased pathologies, the advent of high-resolution probes, means that ultrasound is now the initial method of choice. This has the advantage of not being affected by in situ metalwork. In addition, it can be used for joint aspiration/soft-tissue biopsies. Where there is concern for low-grade infection in the joint replacement, fluoroscopically guided aspiration/local anaesthetic injection remains valuable in the diagnostic pathway. This provides information on any joint fluid, as well as providing incontrovertible evidence of the aspiration site. In addition, instillation of marcaine will give the surgeon information as to whether this is indeed the source of discomfort with a painful hip joint. Cahir et al. describe in detail how recent developments in both CT and MRI have been so successful that these are now important arms of the imaging pathway when used appropriately.1 The advent of multi-section technology has revolutionized CT and its potential applications. There is no doubt that this has applications, as discussed, with assessing the bone stock, prosthesis position, and for pre-surgical planning; however, many of the problems associated with metalwork are primarily of a soft-tissue nature. This is where the dramatic improvements in MRI technology have become invaluable, and where ultrasound is insufficient then MRI should be considered. Its role is well described by Cahir et al., and there is no doubt that where there is extensive soft-tissue abnormality then MRI provides valuable information on both its extent and its nature.1
0009-9260/$ - see front matter ª 2007 The Royal College of Radiologists. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.crad.2007.05.013
CT and MRI of hip arthroplasty
Recent technological advances mean that the imaging pathway for patients with hip arthroplasties may well involve multiple imaging techniques before a surgeon is willing to carry out a revision. Although this is certainly becoming best practice, the challenge we face will be ensuring that this does not become yet another unfunded service further stretching already paper-thin resources.
1173
References 1. Cahir JG, Toms AP, Marshall TJ, et al. CT and MRI of hip arthroplasty. Clin Radiol 2007;62:1163e71. 2. Gruen TA, McNeice GM, Amstutz HC. ‘‘Modes of failure’’ of cemented stem-type femoral components: a radiographic analysis of loosening. Clin Orthop 1979;141:17e27. 3. DeLee JG, Charnley J. Radiological demarcation of cemented sockets in total hip replacement. Clin Orthop Relat Res 1976;121:20e32.
COMMENTARY
CT and MRI of hip arthroplasty* D. Barron* Leeds Teaching Hospitals, Leeds, UK Received 26 April 2007; accepted 1 May 2007
The number of hip arthroplasties performed is steadily increasing due to many factors, not least because of improved life expectancy in the Western World. The complication rates for these are commendably low, but the sheer volume of implants means that there is now a significant cohort of patients with implant-related complications. Holistically assessing these patients is challenging and it is essential that the surgeon can make a fully informed decision before embarking upon any form of intervention. The article by Cahir et al.1 points out that the common complications encountered include infection, mechanical aseptic loosening, osteolysis, granulomatous disease, heterotopic new bone formation, fractures, and local nerve damage. Radiological assessment has inevitably become an integral part of the work-up. It is only recently that the range of imaging available for this group has expanded to include computed tomography (CT) and magnetic resonance imaging (MRI). Previously both of these were precluded by the excessive artefact associated with metal implants, indeed some radiologists may well miss those days as interpreting these challenging studies can be very time-consuming. It is important to appreciate that although both CT and MRI have dramatically improved, they should still be used in combination with other techniques rather than to supplant them. In addition, correlation with clinical and pathological findings remains mandatory. Plain radiographs remain a good initial assessment. These are readily accessible and provide an invaluable record of temporal change. This applies to prosthesis alignment, bony changes, and the boneecement interface. The latter is compared *
DOI of original article: 10.1016/j.crad.2007.04.018. * Tel.: þ44 113 3923768; fax: þ44 113 3928241. E-mail address: [email protected]
using the Gruen zones2 for the femoral component and the DeLee and Charnley zones3 for the acetabular component. Indeed, for the follow-up of many prostheses this remains the only radiological assessment carried out by the surgeon. When the surgeon is concerned about softtissue abnormalities, joint effusions or tendonbased pathologies, the advent of high-resolution probes, means that ultrasound is now the initial method of choice. This has the advantage of not being affected by in situ metalwork. In addition, it can be used for joint aspiration/soft-tissue biopsies. Where there is concern for low-grade infection in the joint replacement, fluoroscopically guided aspiration/local anaesthetic injection remains valuable in the diagnostic pathway. This provides information on any joint fluid, as well as providing incontrovertible evidence of the aspiration site. In addition, instillation of marcaine will give the surgeon information as to whether this is indeed the source of discomfort with a painful hip joint. Cahir et al. describe in detail how recent developments in both CT and MRI have been so successful that these are now important arms of the imaging pathway when used appropriately.1 The advent of multi-section technology has revolutionized CT and its potential applications. There is no doubt that this has applications, as discussed, with assessing the bone stock, prosthesis position, and for pre-surgical planning; however, many of the problems associated with metalwork are primarily of a soft-tissue nature. This is where the dramatic improvements in MRI technology have become invaluable, and where ultrasound is insufficient then MRI should be considered. Its role is well described by Cahir et al., and there is no doubt that where there is extensive soft-tissue abnormality then MRI provides valuable information on both its extent and its nature.1
0009-9260/$ - see front matter ª 2007 The Royal College of Radiologists. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.crad.2007.05.013
CT and MRI of hip arthroplasty
Recent technological advances mean that the imaging pathway for patients with hip arthroplasties may well involve multiple imaging techniques before a surgeon is willing to carry out a revision. Although this is certainly becoming best practice, the challenge we face will be ensuring that this does not become yet another unfunded service further stretching already paper-thin resources.
1173
References 1. Cahir JG, Toms AP, Marshall TJ, et al. CT and MRI of hip arthroplasty. Clin Radiol 2007;62:1163e71. 2. Gruen TA, McNeice GM, Amstutz HC. ‘‘Modes of failure’’ of cemented stem-type femoral components: a radiographic analysis of loosening. Clin Orthop 1979;141:17e27. 3. DeLee JG, Charnley J. Radiological demarcation of cemented sockets in total hip replacement. Clin Orthop Relat Res 1976;121:20e32.