Summary of Ordering Guidelines (Musculoskeletal System Condition)
The following summaries are based on the Canadian Association of Radiologists Diagnostic Imaging Referral Guidelines (http://www.car.ca/en/standards-guidelines/guidelines.aspx). Physicians are encouraged to consult the full guidelines for more detailed information on recommended imaging for the wide range of patient conditions.
Musculoskeletal System Conditions
Initial assessment of most problems in the musculoskeletal system ordinarily includes plain film radiographs.
CT is the next most appropriate investigation for the following indications:
- Assessment of trauma where there is a high clinical suspicion and the plain film examination is negative
- Assessment of suspected fracture or dislocation in regions of complex anatomy (eg. pelvis, sterno-clavicular joint, wrist)
- Characterization of fracture complexity, displacement and angulation
- Characterization of suspected focal osseous lesions
- Assessment of suspected inflammatory or degenerative disease in joints (eg. hip joints, sacro-iliac joints)
- Evaluation of bones or joints where there has been placement of orthopedic hardware
- Patients with contraindications to MRI
MRI is the most appropriate modality for the following indications:
- Suspected osteomyelitis
- Suspected avascular necrosis
- Evaluation of soft tissue mass lesions
- Local staging of primary bone tumors
- Acute disruption of tendonous structures
- Suspected rotator cuff tears
- Suspected ligamentous tear or meniscal tear in the knee
Depending on the condition in question, it may still be most appropriate to refer a patient for a consultant’s opinion prior to requesting an imaging procedure. Please consider the following common musculoskeletal imaging requests from this perspective:
For patients with acute trauma plain film radiography is the appropriate first line imaging test. CT may be utilized with equivocal plain film findings or to characterize injuries in anatomically complex regions. MRI may be utilized in select body regions (hip, scaphoid) to identify fractures when plain film studies are negative. Depending on resource availability bone scanning may be utilized as an alternative investigative technique to identify radiologically occult fractures.
In suspected osteomyelitis conventional radiologic evaluation is indicated as the initial imaging step. Bone scanning is a very sensitive technique in evaluating osseous infection but may be non-specific. MRI is indicated and is the preferred imaging modality in suspected osseous infection allowing assessment of marrow based and soft tissue abnormalities. It may be particularly useful in identifying spread of adjacent soft tissue infection to bone as well as assessing for infection with neuropathic joint disease or infection complicating trauma.
Suspected Avascular Necrosis
In patients at risk for avascular necrosis plain film radiographs are indicated as the initial imaging modality. As plain films may be negative for months MRI is the most appropriate follow-up investigation. In addition to being very sensitive in the detection of avascular necrosis it allows precise documentation of the extent of disease and aids in planning surgical therapy. Bone scanning may be considered as an alternate sensitive but less specific examination.
Soft Tissue Masses
Ultrasound is an appropriate initial modality in characterizing soft tissue mass lesions. It allows distinction of cystic from solid lesions and may allow definitive assessment of lipomatous tumors. MRI provides the best overall assessment of soft tissue mass lesions. While in some cases there may be features that allow a specific diagnosis in the majority of circumstances the role of MRI is in characterizing the extent of the lesion prior to surgical excision. With this in mind the MRI imaging work-up should not delay a timely surgical referral.
Suspected Metastatic Disease
In a patient with a known primary neoplastic lesion plain film radiography of the symptomatic region is the most appropriate initial investigation. Bone scanning is a widely available and sensitive examination of use in assessing for the presence and extent of metastatic disease. MRI is not routinely utilized in the evaluation of metastatic disease. In select circumstances MRI may be utilized in staging metastatic disease for resection or in the pre-surgical planning of pathologic fractures.
Primary Bone Tumours
In patients with symptoms concerning for a neoplastic bone lesion plain film evaluation is suggested as an initial investigation. If an aggressive appearing lesion is identified characterization and staging with MRI is indicated. Referral to an orthopedic oncologist is advised.
Suspected Rotator Cuff Tear
MR is the preferred imaging modality for patients with shoulder pain with suspected rotator cuff disruption. MRI allows confirmation of the presence and size of tears of the rotator cuff tendons. It may identify alternate explanations of shoulder pain including bursitis, bicipetal tenosynovitis, impingement syndrome, as well as degenerative changes in the acromio-clavicular and gleno-humeral joints. The evaluation of the joints capsule and labrum requires the intra-articular administration of contrast and is generally performed as a pre-surgical evaluation. Both ultrasound and CT Arthrography are alternate diagnostic tests that may be performed in the assessment of suspected rotator cuff tears.
Suspected Meniscal or Ligamentous Tears in the Knee
In patients with suspected internal derangements of the knee MRI is the most appropriate investigation. The superior soft tissue resolution of this technique allows accurate identification and characterization of meniscal and ligamentous injuries. Alternate explanations for the patient’s symptoms may be identified including osteochondral injuries, osseous contusion, patello-femoral dysfunction and degenerative change. MRI has limited sensitivity in identifying recurrent injuries in patients with prior meniscal resection but may be utilized in suspected meniscal injuries in patients who have had prior cruciate ligament reconstruction.
Dilute gadolinium may be injected into joints to evaluate disruption of internal joint structures. This is typically done in radiology departments under fluoroscopic guidance. This technique is primarily used in evaluating labral-capsular abnormalities in shoulder joints, labral tears and femero-acetabular impingement in hips and inter-carpal ligamentous injuries and triangular fibrocartilage tears in the wrist. CT arthrography is an alternate more widely available technique that may provide satisfactory diagnostic information for these clinical problems.
Multi-site Bone and Joint Problems
As with other regions of the body MR can provide high resolution focused images of smaller regions utilizing dedicated receiving coils. Multiple body regions cannot be imaged simultaneously. Each region requiring positioning of the patient in a dedicated coil for the body region and the acquisition of a series of images in different planes. Typical imaging time in the musculoskeletal system is about 30 minutes per region assessed. While multiple contiguous body regions and separate regions may be performed the prolonged imaging time may make the examination difficult for the patient to tolerate. Wherever possible focused examinations of the region of primary concern are preferable.