Joint replacement surgery, arthroplasty, can have a long build-up. Insurance may require the patient to lose weight prior to the surgery. They may need to speak with a physical therapist to discuss rehabilitation. On the physician's side, there is one extremely important step that must be completed: planning. For many surgeries, the surgeon has a plan prior to the day of the procedure. Some tools that can aid this planning are imaging methods, such as CT and magnetic resonance imaging (MRI).1
Surgeons are beginning to turn toward imaging methods that can help physician visualize the 3D structures inside the patients bodies. One of these methods uses magnetic resonance to create images of the tissue structures within the body. The magnet inside the scanner manipulates the magnetic field around the patient and uses spatial encoding to create images with accurate spatial information. This method can aid surgical planning by mapping the area of the surgery and helping the surgeon prepare for unexpected complication.1
In the case of arthroplasty, the goal is to remove and replace an injured joint. This means that the physician has to remove the damaged tissue and portions of the joint to implant a prosthesis. The prosthesis may be personalized for the patient's joint. As the surgery occurs, the physician must align the implant with the joint to help reduce future complications from the surgery.
Total knee replacement surgery often includes patient specific instrumentation (PSI), which takes a 3D model created based on computed tomography (CT) or MRI images to help physicians plan for their operations. The model is created using computer software to aid in converting the data. This surgical plan may be vital to avoid complications during the surgery. PSI may help visualize deformities and abnormalities in the patient. This can help with determining the best prosthetic to implant and the best course of action to implant it. The surgeon must still be prepared for any unexpected complications. The PSI may not always be accurate in alignment due to the changes in alignment and sizing that the physician must make throughout the course of the operation.2 As a result, PSI may prove useful in the case of deformities, which can be seen in cases involving trauma.
MRI as an underused PSI tool
In the cases of deformities, CT is most often used as the PSI guidance tool. However, one study suggests that MRI can result in equivalent or better accuracy when compared to CT.3 CT images are obtained using a large number of X-rays to create images from more angles than simple X-ray can provide. This creates detailed images of the bone and tissues inside a patient's body. MRI, on the other hand, creates images using a superconducting magnet within the MRI scanner. The magnet manipulates the magnetic field and utilizes coils, which intercept the signals created in the patient, to create images from a variety of angles. This can also produce three-dimensional images with the help of a computer and radiologist.
In the aforementioned study, MRI resulted in a lower proportion of coronal outliers relative to limb mechanical axis.3 Some other aspects of placement, the femoral and tibial components, showed no significant difference. Basically, MRI may improve the placement of the implant in the coronal plane without sacrificing any accuracy from CT.
CT and MRI can be used to guide the placement of implants in cases involving arthroplasty. MRI has a slight edge over CT in terms of coronal plane placement without losing any accuracy from CT. This aids surgeons in their placement of implants and could potentially improve long-term outcomes in patients who require arthroplasty. This may ultimately improve the patient's ability to move and stay active after the surgery.
1. Robert J. Ogg. "Surgical Planning MRI." StJude.org. Web. 13 March 2019.
2. Lorenzo Mattei, et al. "Patient specific instrumentation in total knee arthroplasty: a state of the art." Ann Transl Med. April 2016; 4(7): 126. Web. 13 March 2019. doi: 10.21037/atm.2016.03.33.
3. VV An, et al. "Accuracy of MRI-based vs. CT-based patient-specific instrumentation in total knee arthroplasty: A meta-analysis." J Orthop Sci. January 2017; 22(1): 116-120. Web. 13 March 2019. doi: 10.1016/j.jos.2016.10.007.