Magnetic Resonance Imaging (MRI) of the knee joint is a non-invasive medical imaging technique primarily used to assess structural abnormalities and lesions within the knee. Utilizing a strong magnetic field and harmless radio waves, MRI produces high-resolution three-dimensional images of internal knee tissues, including bones, ligaments, tendons, cartilage, and surrounding soft tissues.
The key advantage of this technology is its lack of radiation exposure, making it especially suitable for patients requiring repeated monitoring or long-term observation. Clinically, it is commonly used to diagnose sports injuries, degenerative arthritis, or other complex symptoms, providing physicians with precise diagnostic information to formulate treatment plans.
MRI examinations are mainly divided into general and high-field types, with field strengths typically ranging from 1.5T to 3T. The principle involves aligning hydrogen nuclei in the body using a magnetic field, then exciting and receiving signals with radio pulses, which are reconstructed by a computer into cross-sectional images. This process can clearly display soft tissue issues such as ligament tears and meniscal injuries.
Compared to X-ray or ultrasound, MRI can better visualize minute internal joint structures, such as anterior cruciate ligament (ACL) or medial collateral ligament injuries. The examination takes approximately 20-40 minutes, requiring the patient to remain still to ensure image quality.
Patients should remove all metal objects beforehand and may be given earplugs to reduce noise. During the scan, they lie flat inside the scanner and must keep the knee fixed as instructed by the physician. The field strength setting and scan parameters are adjusted based on the lesion, such as using T1-weighted or T2-weighted sequences to highlight different tissue characteristics.
Basic scans can be performed without contrast agents, but gadolinium contrast may be added if vascular abnormalities are suspected to enhance imaging. There is no fixed "dose" concept for the scan, but the scanning time and sequence selection are decided by radiologists according to clinical needs.
MRI provides extremely high-resolution images of soft tissues, accurately showing the extent of ligament tears, meniscal injuries, and cartilage degeneration. This technology involves no ionizing radiation, making it particularly suitable for children or patients requiring repeated examinations, thereby reducing long-term cancer risk.
Most patients undergo the procedure safely, but there are extremely low risks involved. Patients with claustrophobia may experience anxiety or panic, which may require sedation. Metal objects (such as pacemakers or neurostimulators) can cause serious complications, so strict screening for contraindications is necessary before the scan.
Important Warning: Allergic reactions to gadolinium-based contrast agents containing potassium may cause nephrotoxicity, especially in patients with chronic kidney disease. The strong magnetic field during the scan may displace metallic implants, so contraindications must be carefully screened.
Contraindications include metallic implants (such as clips from open-heart surgery), electronic medical devices (like pacemakers), or women in early pregnancy. Pregnant women in later stages should have the procedure only after a thorough assessment by a physician. All metal objects, including braces, dental restorations, and electronic devices, must be removed before the scan.
Patients with claustrophobia or overweight (exceeding the scanner’s load capacity) may require open MRI scanners or staged procedures. During the scan, complete stillness is required; joint movement can cause blurred images and affect diagnosis accuracy.
MRI itself does not involve drugs or biological therapies, so there are no drug interactions. When combined with other examinations (such as X-ray or CT), MRI is usually a second-line test to confirm suspected diagnoses. Patients on anticoagulant therapy should be aware that contrast agents may affect kidney function.
If patients have metal implants, compatibility with MRI must be evaluated by the medical team, as some devices may shift or malfunction due to magnetic fields.
Multiple studies show that MRI has an accuracy rate exceeding 95% in diagnosing ligament tears, far higher than ultrasound’s 75-80%. The diagnosis of meniscal injuries has a consistency rate of over 90%, and can distinguish between complete tears and partial damage, aiding surgeons in planning surgical or conservative treatments.
Clinical guidelines list MRI as the gold standard for suspected internal joint structure injuries, especially in assessing pre- and post-arthroscopy changes. Its repeatability and precision are widely recognized. Large-scale follow-up studies indicate that MRI-guided treatment plans can reduce misdiagnosis rates and improve success rates.
Ultrasound can serve as an initial screening tool but is highly operator-dependent in resolution. X-ray can show bony issues but cannot evaluate soft tissues. Computed Tomography (CT) can display bone structures but involves ionizing radiation and has limited soft tissue resolution.
When MRI is not feasible, nuclear medicine scans (such as bone scans) can detect metabolic changes but have insufficient spatial resolution. The final choice depends on the patient’s specific condition (such as contraindications and symptom severity) and available medical resources.
What preparations are needed before undergoing knee MRI?
All metal objects, including jewelry, hairpins, and electronic devices, should be removed before the scan. Patients with claustrophobia should inform medical staff in advance to arrange open MRI or sedation. During the procedure, remaining still is essential, and loose clothing is recommended for ease of operation.
Are there any side effects after MRI? How can they be alleviated?
MRI does not cause tissue damage or radiation exposure, but prolonged confinement in a closed space may induce anxiety. If tinnitus occurs after the scan, earplugs can help reduce noise. Rarely, patients may experience worsening claustrophobia, and should notify medical staff immediately for management.
When can I receive the report after the scan? How does the result influence treatment planning?
Typically, the report is interpreted by a radiologist within 2-3 working days; urgent cases can be shortened to within 6 hours. The report precisely shows the extent of cartilage damage and ligament tears, guiding orthopedic surgeons in planning surgery or physical therapy, such as determining the need for arthroscopy based on meniscal injury severity.
What should diabetic patients pay attention to when undergoing MRI?
Diabetic patients should continue their blood sugar medications and monitor levels, as the scan may take 40-60 minutes. It is advisable to carry quick-acting glucose in case of hypoglycemia. When using gadolinium contrast, kidney function must be carefully evaluated, and the dose adjusted based on eGFR values.
Is it normal to experience increased joint pain after the scan? How should it be managed?
The procedure itself does not cause tissue damage, but maintaining certain positions for a long time may cause temporary discomfort. If joint swelling or pain worsens within 48 hours after the scan, immediate evaluation is recommended, as pre-existing conditions may have worsened under pressure. Ultrasound or blood tests may be needed to check for infection or acute sprain.
%201.svg)
Copyright © 2025 MedFrontiers. All Rights Reserved.
