Many Americans face the need for joint replacement surgery at some point in their lives. There are a wide variety of reasons that one may need joint replacement, including previous injury and osteoarthritis. Osteoarthritis, a degenerative form of arthritis, is the most common reason a patient may need joint replacement. When they have this surgery, called an arthroplasty, the physician and patient must decide whether the replacement joint will be ceramic or metal.
What is arthroplasty?
Arthroplasty (joint replacement surgery) is frequently done in the hip and knee, though other joints like the ankle or elbow may be replaced as well. During this surgery, surgeons remove an damaged joint with an artificial one. This artificial joint is a prosthesis.1 Most physicians do not consider arthroplasty until other treatment options have failed, though it often relieves joint pain and may help the patient have a better quality of life.1,2
Some of the types of artificial joints that can be implanted during the surgery are metal, ceramic and plastic. Each option can replace certain spots in different joints. The most common prostheses are often metal, which can have implications for future health care and imaging. The prosthesis may provide relief to the patient, but if there is recurring pain after the surgery, additional imaging and tests of the joint may need to be done.
- Metal: Many knee implants include metal and plastic. Implants that include metal often include other materials so that metal surfaces never come into contact with one another.3 Cobalt chrome is the most common type of knee implant, though titanium is available for people with a nickel allergy. For hip replacement, metal can be used in a metal on plastic prosthesis. Metal on plastic is considered one of the best options, the other being ceramic on plastic.
- Ceramic: Ceramic implants are used more often for hip replacement than for the knee.3 Hip implants that contain ceramic may be ceramic on ceramic or ceramic on plastic prosthesis. The first type has good durability but a risk of breaking and squeaking. The second is one of the most common implants, alongside metal on plastic, and may be wear-resistant.
- Plastic: Plastic is often used in both hip and knee implants.3 This is frequently the second material in implants that contain metal. It is common for plastic to be included in prosthesis. In hip implants, newer plastic called polyethylene has become one of the major materials. This plastic suffers less degradation than the plastic used in earlier implants.
Imaging with implants
Arthroplasty has a direct affect on imaging tests. During computed tomography (CT), implants can cause beam hardening which interferes with the image quality necessary for the radiologist and doctor.4 The implant being imaged must be MR-safe or MR-conditional to be safely scanned, though MR-conditional implants may require certain limitations or alterations to the sequences. In magnetic resonance (MR), the implant, especially those containing metal, can cause a distortion in the image.4 This distortion is called a susceptibility artifact caused by the interference in the magnetic field due to the implant.
From the start, the preferred method for investigation of joint implanted regions of interest has been regular X-ray. As the field of magnetic imaging has progressed, the radiology teams have begun to employ artifact correction techniques to minimize the effects of the patient's implant.5,6 A couple of different techniques have been used to reduce artifacts during MRI imaging. Some MR manufacturers have begun offering solutions through their software as well.6
There is also evidence that the material used in the prosthetic affects the size of the artifact created on MRI.7 Metal creates the largest distortion, while ceramic creates the smallest. Metal creates the largest distortion because it is highly susceptible to the pull of the magnetic field. As the strength of the scanner increased, the gap between the distortion rates also increased. Ceramic implants generated less artifacts at both 1 and 1.5 T.7 This allows for easier imaging than that of the metal ones.
Arthroplasty, or joint replacement surgery, can be completed using prosthetics of metal, plastic, and ceramic make-up. Each of these materials impacts MR images obtained after surgery, with ceramic being least affected and metal being the most affected. This can cause problems with follow up or imaging of new injuries to the replacement location. In some cases, the imaging can be completed using susceptibility correction techniques. However, with so many Americans needing joint replacement surgery at some point in their lives, it may benefit patients to consider the amount of distortion caused by these different materials.
1. Stanford Health Care. Arthroplasty (Total Joint Replacement Surgery).” stanfordhealthcare.org. Web. 12 March 2019. <https://stanfordhealthcare.org/medical-treatments/a/arthroplasty.html>.
2. John Hopkins Medicine. “Arthroplasty.” Hopkinsmedicine.org. Web. 12 March 2019. <https://www.hopkinsmedicine.org/healthlibrary/test_procedures/orthopaedic/arthroplasty_92,p07677>.
3. Douglas E. Padgett and Russell E. Windsor. "Understanding Implants in Knee and Hip Replacement." HSS.edu. 13 August 2013. Web. 12 March 2019. <https://www.hss.edu/conditions_understanding-implants-in-knee-and-hip-replacement.asp>.
4. JG Cahir, et al. "CT and MRI of hip arthroplasty." Clin Radiol. 2007 Deceber; 62(12): 1163-1171. Web. 12 March 2019. <https://www.ncbi.nlm.nih.gov/pubmed/17981163>.
5. Catherine L. Hayter, et al. "MRI After Arthroplasty: Comparison of MAVRIC and Conventional Fast Spin-Echo Techniques." American Journal of Roentgenology. September 2011; 197(3). Web. 12 March 2019. <https://www.ajronline.org/doi/full/10.2214/AJR.11.6659>.
6. Soo-Jung Choi, et al. "Metal Artifact Reduction With MAVRIC SL at 3-T MRI in Patients With Hip Arthroplasty." AJR AM J Roentgenol. January 2015; 204(1): 140-147. Web. 12 March 2019. doi: 10.2214/AJR.13.11785.
7. Elisabetta Panfili, et al. "Magnetic resonance imaging (MRI) artefacts in hip prostheses: a comparison of different prosthetic compositions: Abstract." La radiologia medica. February 2014; 119(2): 113-120. Web. 12 March 2019. <https://link.springer.com/article/10.1007/s11547-013-0315-6>.