MRI Knee Protocol and Management Guidelines
X-ray should always be the initial imaging modality for knee evaluation, followed by MRI without contrast when internal derangement is suspected after negative radiographs. 1, 2
Initial Imaging Approach
- Radiographs should be the first imaging study for knee evaluation, with a minimum of anteroposterior and lateral views 1, 2
- Order radiographs if any Ottawa knee rule criteria are present: age >55 years, focal tenderness at patella or fibular head, inability to bear weight for 4 steps immediately after injury, or inability to flex knee to 90 degrees 3, 2
- Additional radiographic views to consider based on clinical suspicion include patellofemoral view for suspected patellar fractures/subluxation 1
- Radiographs should be obtained regardless of Ottawa criteria if the patient has gross deformity, palpable mass, penetrating injury, prosthetic hardware, altered mental status, or neuropathy 2
MRI Protocol After Negative Radiographs
- MRI without IV contrast is the appropriate next imaging study when radiographs are negative but clinical suspicion remains high for internal derangement 2, 4
- The basic MRI protocol must include:
- MRI evaluation should include assessment of:
- Ligamentous structures (cruciate and collateral ligaments)
- Menisci
- Articular cartilage
- Bone marrow for contusions or occult fractures
- Soft tissues and bursae 4
Specific Clinical Scenarios and Management
Post-Traumatic Knee Pain
- For acute knee trauma with negative radiographs but persistent symptoms, MRI without contrast is recommended to evaluate for meniscal and ligamentous injuries 1, 2
- MRI has high sensitivity and specificity for detecting internal derangements: 85-91% sensitivity and 88-95% specificity for meniscal and cruciate ligament injuries 5
- Consider MRI if there is significant joint effusion, inability to fully bear weight after 5-7 days, mechanical symptoms, or joint instability 2
Knee Pain in Patients Over 50 Years
- Always obtain radiographs first in patients over 50 years with knee pain 3, 6
- MRI should be considered only if symptoms are not explained by osteoarthritis alone or if the appropriate treatment option requires MRI 6
- MRI can detect additional features not seen on radiographs but should be ordered selectively in older patients 6
Post-Total Knee Arthroplasty
- For asymptomatic patients with total knee arthroplasty, only radiographs are appropriate for routine follow-up 1
- For pain after total knee arthroplasty with suspected periprosthetic fracture, obtain radiographs first (rating 9/9), followed by CT without IV contrast (rating 8/9) if needed 1
- For suspected component loosening after total knee arthroplasty, CT without IV contrast (rating 7/9) is preferred over MRI (rating 3/9) 1
- For instability concerns after total knee arthroplasty, radiographs followed by fluoroscopy (rating 7/9) are recommended 1
Common Pitfalls to Avoid
- Failing to obtain radiographs before MRI, which occurs in over 60% of cases 6
- Ordering MRI for knee osteoarthritis in older patients without specific indications for advanced imaging 6
- Not documenting Ottawa or Pittsburgh criteria findings when deciding whether to order radiographs 3
- Omitting assessment of the ability to bear weight, which is a critical factor in determining the need for imaging 3, 2
- Using MRI with contrast for routine knee evaluation, which is rarely indicated and receives low appropriateness ratings (1/9) in most clinical scenarios 1
Follow-up Management Based on MRI Findings
- Meniscal tears: Refer to orthopedics if mechanical symptoms are present; otherwise, consider conservative management 2, 5
- Ligamentous injuries: Complete tears of the ACL or PCL generally warrant orthopedic referral, especially in active individuals 2, 5
- Bone contusions: Usually managed conservatively with protected weight-bearing and symptomatic treatment 7
- Osteochondral lesions: May require surgical intervention depending on size and location 7