The Science Behind Sternal Wire Materials
Following open-heart surgery, sternotomy wires are used to re-approximate the breastbone, or sternum, allowing it to heal securely. A common misconception is that these wires will be strongly attracted to magnets, such as those in a magnetic resonance imaging (MRI) scanner. The truth lies in the specific materials used, which are chosen for their biocompatibility and favorable physical properties. The vast majority of sternal wires are made from either 316L stainless steel or titanium.
- Titanium: This is a non-ferromagnetic metal, meaning it is not attracted to or affected by magnetic fields. It is also known for its strength, corrosion resistance, and excellent biocompatibility, making it a safe choice for medical implants.
- 316L Surgical Stainless Steel: This material is also largely non-ferromagnetic due to its low carbon content. While some intense manufacturing processes can induce slight, localized magnetism, the resulting effect is extremely minimal and does not pose a risk of movement inside an MRI scanner. Both materials are considered safe from magnetic displacement.
Magnetic Resonance Imaging (MRI) and Sternal Wires
For patients with sternal wires, MRI is a safe and common practice, but it is considered an "MR Conditional" procedure. This status means the scan can be performed safely under specific, controlled conditions. The most important consideration is not magnetic attraction, but radiofrequency (RF) heating. An MRI machine uses radio waves in addition to its strong magnetic field, and the conductivity of the metallic wires can cause a small amount of heat to be generated.
To manage this risk, a trained radiologist and technician follow specific protocols, such as limiting the scan sequences that might cause heating and monitoring the patient for any signs of discomfort. Minor, temporary sensations like muscle twitching have been reported in rare cases but serious injuries have not been noted in the available literature. In addition to monitoring for heating, patients are routinely screened to identify any other implants that might pose a greater risk, such as certain types of pacemakers.
Sternal Wires vs. Other Implants
While standard sternal wires are designed to be minimally magnetic and safe for MRIs, it is important to distinguish them from other medical implants with different characteristics. The following table provides a comparison.
A Comparison of Medical Implants and MRI Compatibility
| Implant Type | Primary Material | Magnetic Property | MRI Compatibility |
|---|---|---|---|
| Sternal Wires | 316L Stainless Steel, Titanium | Non-ferromagnetic or weakly magnetic | MR Conditional (Safe under specific conditions) |
| Dental Implants | Titanium | Non-ferromagnetic | MR Conditional (Safe; potential for minor image artifacts) |
| Pacemakers | Mixed materials | Ferromagnetic components | MR Unsafe or MR Conditional (Requires specific MRI-compatible model and precautions) |
| Magnetic Pectus Bars | Titanium-encased rare earth magnet | Ferromagnetic | MR Unsafe (Cannot be in MRI) |
Airport Security and Metal Detectors
Another common concern is whether sternal wires will trigger airport metal detectors. In most cases, the answer is no. The small mass of metal and its position deep within the body mean that walk-through metal detectors are typically not sensitive enough to be set off. Hand-held detectors, however, are more sensitive and could potentially detect the wires. It is not necessary to carry a medical ID card specifically for sternal wires, but informing the Transportation Security Administration (TSA) officer of your implant can ease the screening process if a handheld wand is used. This differs from larger metal implants, such as those for a hip or knee replacement, which are more likely to trigger alarms.
Beyond Magnetism: Other Sternal Wire Considerations
While the magnetic properties of sternal wires are not a primary concern, other potential issues are worth noting, though most are rare:
- Wire Fracture: In some cases, wires can break over time, leading to pain, instability, or clicking noises.
- Allergic Reaction: Allergic reactions, particularly to nickel in stainless steel wires, can occur but are very uncommon. Titanium wires offer a nickel-free alternative.
- Infection: In rare instances, infections around the sternotomy site can occur.
These potential complications are related to the physical properties and biomechanics of the implant, not its magnetic behavior. Symptomatic patients may have the wires removed, a procedure that is relatively quick and generally has a positive outcome.
The Concluding Verdict on Sternal Wires
The myth that sternum wires are strongly magnetic is based on a misunderstanding of the specialized, medical-grade metals used for implantation. By choosing materials like titanium and 316L stainless steel, manufacturers have created safe, stable implants that will not be pulled or dislodged by an MRI's powerful magnetic field. For patients undergoing an MRI, the primary consideration is the low-risk potential for radiofrequency heating, which is managed effectively by clinical staff. As with any medical implant, it is crucial to inform your healthcare provider and MRI technician about your sternal wires to ensure all necessary safety precautions are taken.
To learn more about implant safety guidelines, the website MRISafety.com provides a comprehensive database of device compatibility information.
