Individuals with spinal fusion surgery often question the compatibility of their implanted hardware, such as Harrington rods, with magnetic resonance imaging (MRI) scans. Harrington rods were widely used for scoliosis correction. This article discusses the considerations and safety measures for MRI scans in those with Harrington rods.
Understanding Harrington Rods
Harrington rods are surgical implants designed to correct and stabilize spinal curvatures, particularly those caused by scoliosis. Developed in 1953 by Paul Harrington, these devices were commonly used from the early 1960s until the early 2000s, with an estimated one million people receiving them. The instrumentation typically consisted of a stainless steel distraction rod fitted with hooks at both ends, secured onto vertebral laminae. This system aimed to reduce spinal curvature and provide stability during spinal fusion.
MRI Safety with Harrington Rods
The presence of Harrington rods introduces specific considerations for MRI safety due to their metallic components. A primary concern is the potential for heating of the metal implant during the scan, caused by the radiofrequency fields. Another consideration is magnetic attraction, especially with older rods made of stainless steel, which are ferromagnetic and susceptible to the MRI scanner’s strong magnetic field.
A more common issue with imaging spinal fixation hardware, including Harrington rods, is image artifact. These artifacts appear as streaks or distortions on MRI images, caused by the metal interfering with magnetic signals. This can obscure the area around the implant and limit diagnostic clarity. Modern MRI protocols and advancements in implant materials have mitigated some of these concerns. For instance, imaging at 1.5 Tesla (T) is often preferred over 3.0T to reduce potential heating and artifacts. Patients should report any unusual heat sensation.
Preparing for an MRI with Rods
Proper preparation is important for individuals with Harrington rods undergoing an MRI scan. Inform the MRI technologist and referring physician about the rods before the scan. Providing details about the rod material, if known, is helpful; older rods were typically stainless steel, while newer implants often use titanium or titanium alloys, which are less problematic. Bringing medical records, such as surgical reports or implant cards, can confirm the exact type of hardware and its MRI compatibility.
The pre-MRI screening process may involve additional steps, such as X-rays, to confirm the rod type, placement, and stability. MRI facilities may also inquire about the specific make and model number of the implanted device to determine its safety for the scan. During the procedure, patients should immediately communicate any discomfort, warmth, or unusual sensations to the technologist, who can then adjust parameters or pause the scan if needed.
Other Imaging Options
When an MRI is contraindicated or its diagnostic utility is limited by the presence of Harrington rods, alternative imaging modalities can provide valuable information. Plain film X-rays are a common choice, offering good visualization of bone structures and the position of the rods themselves. They are widely available and do not involve strong magnetic fields, making them safe for all metal implants. However, X-rays provide only two-dimensional views and limited detail of soft tissues or complex spinal anatomy.
Computed tomography (CT) scans are another frequently used alternative, providing detailed cross-sectional images of the spine and surrounding structures. CT scans are generally less affected by metallic implants than MRI, though they can still produce “beam-hardening” artifacts that might obscure some areas. While CT involves exposure to ionizing radiation, the detailed bone imaging it provides can be invaluable for assessing implant integrity or bony changes around the rods. Myelography, which involves injecting contrast dye into the spinal canal followed by X-rays or CT, can also be employed to visualize the spinal cord and nerve roots when MRI is not feasible.