This document addresses the use of both computed tomography (CT) and magnetic resonance imaging (MRI) in the outpatient setting for the diagnosis, evaluation and management of conditions of the hip, pelvic bones, knee, ankle and foot. CT and MRI are used to evaluate joints and soft tissues of the extremity. However, neither are generally the initial imaging study used in the outpatient setting and are usually performed after standard radiographs.

Note: Please see the following related document for additional information:

• RAD.00049 Low Field and Conventional Magnetic Resonance Imaging (MRI) for Screening, Diagnosing and Monitoring

Medically Necessary:

I.  General Lower Extremity for any lower extremity site (see additional indications for specific anatomy):
Computed Tomography (CT) or Magnetic Resonance Imaging (MRI) is considered medically necessary for the evaluation of the lower extremities (hip, pelvic bones, knee and ankle) for any of the following (see Discussion section for relative preference for MRI vs. CT):

A. Trauma or Fracture

• Significant trauma when preliminary x-rays do not provide adequate diagnostic information for:
  • Demonstration of the anatomy of fractures and subluxations (CT preferred); or
  • Identification of non-displaced fractures and stress fractures (MRI preferred); or
• To evaluate fracture in any of the following situations:
  • Confirm an occult fracture, following initial x-rays; or
  • Define the extent of an acute fracture and position fracture fragments; or
  • To assess fracture healing, for callus formation and solid bony union (CT only).

B. Malignancy

• Suspected bone or soft tissue tumor by preliminary imaging (e.g., bone scan or x-ray) or significant abnormality on physical examination (i.e., palpable mass) (MRI preferred); or
• Follow up of primary bone tumor; or
• Follow up of single bone metastasis after treatment
  • Evaluation of lesion density and adjacent bone (CT preferred); or
  • Differentiation between a benign and malignant process (MRI preferred).

C. Infectious Process

• For diagnosis of osteomyelitis, abscess or septic arthritis, following initial evaluation with x-rays or bone scan, including evaluation of infectious complications of diabetic foot disease (MRI preferred); or
• Location of sequestra in osteomyelitis (MRI preferred).

D. Evaluation of Known Diseases or Conditions

• Hemarthrosis documented by arthrocentesis (MRI preferred); or
• Neuropathic osteodystrophy (e.g., Charcot Joint) when additional information is needed (beyond that provided by x-rays) to direct treatment decisions (e.g., evaluation of infection); or
• Ligament or tendon injuries unresponsive to 4 weeks of conservative treatment* or if physical examination suggests an injury requiring repair or reconstruction (MRI preferred); or
• For pre-operative planning or post-operative reassessment of complex or intra-articular fractures.

E. Evaluation of Signs or Symptoms

• Persistent lower extremity pain that is unresponsive to 4 weeks of conservative treatment* and not diagnosed after initial assessment on conventional radiographs; or
• Suspected osteochondral lesion.

F. Other

• Abnormalities on other imaging (e.g., x-rays or bone scans) requiring additional information to direct treatment decisions; or
• CT or MRI accompanying an arthrogram.

II. Hips/Pelvic Bones
Magnetic Resonance Imaging (MRI) is considered medically necessary for the evaluation of the hips or pelvic bones for any of the following:

• Suspected osteonecrosis of the femoral head; or
• Suspected intra- or extra-articular abnormality (e.g., loose body, synovial osteochondromatosis); or
• Slipped femoral capital epiphysis after initial radiographic evaluation; or
• Tears of the acetabular labrum; or
• To evaluate sacroiliitis following inconclusive sacroiliac joint x-rays; or
• Legg-Calve Perthes Disease; or
• When criteria for CT are met, but CT is contraindicated.

Computed Tomography (CT) is considered medically necessary for the evaluation of the hips or pelvic bones for any of the following:

• Suspected fracture; or
• Osteonecrosis, when the individual is unable to undergo an MRI or bone scan and when x-rays are normal or inconclusive; or
• To assist in surgical planning or post-operative reassessment, in individuals with known hip osteonecrosis and femoral head collapse; or
• To evaluate chronic hip pain and suspected osteoid osteoma, following negative or inconclusive hip x-rays; or
• To evaluate sacroiliitis, following inconclusive sacroiliac joint x-rays; or
• When criteria for MRI are met, but MRI is contraindicated.

III. Knee

Magnetic Resonance Imaging (MRI) is considered medically necessary for the evaluation of the knee for any of the following:

• Meniscal tear, cruciate, collateral or multiligament injury with pain and instability evidenced by Pivot shift test, positive McMurray's sign (meniscus injury) positive Lachman's test (ACL injury), locking; or
• Suspected meniscal tear or ligament injury without instability non-responsive to 4 weeks of conservative treatment*; or
• Avascular necrosis, after standard x-rays; or
• Intra-articular loose body; or
• Locking or significant instability; or
• Chondromalacia Patella; or
• Osteochondritis Dissecans; or
• Posteromedial cyst (Baker's cyst) when ultrasound is non-diagnostic; or
• Persistent knee pain with persistent or recurrent swelling or joint tenderness refractory to 4 weeks of conservative treatment*; or
• Post-operative evaluation following repair of a ligamentous or tendinous tear, with new symptoms; or
• When criteria for CT are met, but CT is contraindicated.

Computed Tomography (CT) is considered medically necessary for the evaluation of the knee for any of the following:

• Suspected tibial plateau fractures when no other ligament or meniscal injury is suspected; or
• To define the anatomy of a fracture and to aid in the planning of a surgical procedure; or
• When criteria for MRI are met, but MRI is contraindicated.

IV. Ankle/Foot
Magnetic Resonance Imaging (MRI) is considered medically necessary for the evaluation of the ankle or foot for any of the following:

• When any of the following conditions are suspected:
  • Avascular necrosis of talus after standard x-rays; or
  • Tendon rupture; or
  • Intra-articular loose body; or
  • Ligament and tendon injuries, if no response to 4 weeks of conservative treatment*; or
  • Tarsal coalition, following foot x-rays; or
  • Tarsal tunnel with neuropathy secondary to entrapment that has not responded to 4 weeks of conservative treatment*; or
  • Morton's neuroma, if there is diagnostic uncertainty or if MRI results will affect the treatment plan; or
  • Persistent ankle pain with persistent or recurrent swelling or joint tenderness refractory to 4 weeks of conservative treatment*; or
  • When criteria for CT are met, but CT is contraindicated.

Computed Tomography (CT) is considered medically necessary for the evaluation of ankle or foot for any of the following:

• Suspected fracture not diagnosed by previous imaging; or
• Tarsal coalition, following foot x-rays; or
• When criteria for MRI are met, but MRI is contraindicated.

* For the purposes of this document, conservative treatment is defined as appropriate pharmacologic interventions, physical therapy or exercises.

Not Medically Necessary
CT or MRI of the lower extremity is considered not medically necessary for any of the following:

• When the above criteria are not met; or
• As a screening tool (i.e., in asymptomatic individuals without a previous diagnosis or specific clinical indications); or
• As a routine follow-up for a knee or hip arthroplasty procedure.

Repeat imaging of the same body part by the same or similar imaging technology, when there is no change in clinical status (e.g., deterioration), persistent diagnostic problem, or medical intervention which warrants interval re-assessment is considered not medically necessary for CT or MRI lower extremity except where specified above as medically necessary.

The following codes for treatments and procedures applicable to this document are included below for informational purposes.  Inclusion or exclusion of a procedure, diagnosis or device code(s) does not constitute or imply member coverage or provider reimbursement policy.  Please refer to the member's contract benefits in effect at the time of service to determine coverage or non-coverage of these services as it applies to an individual member.

Computed tomography (CT), sometimes called CAT scan, is a diagnostic tool that uses special x-ray equipment to obtain image data from different angles around the body, then uses computer processing of the information to show a cross-section of body tissues and organs. The CT requires less time than MRI and can be performed in acute settings where advanced monitoring and life support are needed for an unstable individual.

Magnetic resonance imaging (MRI) is a diagnostic technique that uses a cylindrical magnet and radio waves to produce high quality multiplanar images of organs and structures within the body without x-rays or radiation. The body's hydrogen atoms react to the magnetic field and pulses of radio waves. This reaction is changed to an image by a computer. CT and MRI are valuable imaging techniques most often used when preliminary diagnostics or symptoms suggest an abnormal condition requiring further analysis.

The ability of either MRI or CT scans to image the extremities is well documented and the indications listed above summarize the most prevalent signs, symptoms and conditions. As noted in the Clinical Indications, there are many overlapping indications for CT and MRI. Imaging modality will depend on the specific indication and individual circumstances. The following situations describe indications where there is a relative preference for one imaging technique over another.

Imaging Preference Based on Indication:

• CT scanning is preferred for suspected fracture or fracture non-union when x-ray or bone scan is non-diagnostic
• MRI is generally preferred for:
  • Evaluation of soft tissue, including muscles, tendons, ligaments, fat, blood vessels, nerves, and synovial tissues
  • Diagnosis or characterization of non-displaced, incomplete, or stress fractures
  • Evaluation of chronic pain when preliminary imaging is non-diagnostic and symptoms are non-responsive to 4 weeks of conservative treatment

Imaging Preferences Based on Individual Circumstances 

The following are examples of specific individual characteristics that may dictate the preference of one imaging modality over another.

• The use of CT in children requires careful assessment of the risks, benefits and uses of the studies. Generally, children are more sensitive to radiation than adults and with their longer life expectancy there is a larger window of opportunity for incurring radiation damage
• Absolute and relative contraindications for scans requiring administration of intravascular contrast material may include:
  • Documented allergy from prior contrast administration or a history of atopy
  • Impaired renal function, when considering an enhanced CT with intravascular iodinated contrast agents
  • Multiple myeloma
• Contraindications for MRI may include situations where individuals:
  • Had placement of metal devices within the body. However, for those who have small amounts of implanted metal not located in the imaging area, an open MRI may be appropriate
  • Have intracranial surgical clips placed for an aneurysm that are not compatible with the use of MRI
  • Have conditions requiring external devices for care (e.g., portable oxygen tank)
  • Are claustrophobic; an open MRI may be appropriate

Peer Reviewed Publications:

1. Attarian DE, Guilak F. Observations on the growth of loose bodies in joints. Arthroscopy. 2002; 18(8):930-934.
2. Bencardino JT, Palmer WE. Imaging of hip disorders in athletes. Radiol Clin North Am. 2002; 40(2):267-287.
3. Brenner DJ, Hall EJ. Computed tomography--an increasing source of radiation exposure. N Engl J Med. 2007; 357(22):2277-2284.
4. Chin KR, Barr SJ, Winalski C, et al. Treatment of advanced primary and recurrent diffuse pigmented villonodular synovitis of the knee. J Bone Joint Surg Am. 2002; 84-A(12):2192-2202.
5. El-Dieb A, Yu JS, Huang GS, Farooki S. Pathologic conditions of the ligaments and tendons of the knee. Radiol Clin North Am. 2002; 40(5):1061-1079.
6. Emery KH, Bisset GS 3rd, Johnson ND, Nunan PJ. Tarsal coalition: a blinded comparison of MRI and CT. Pediatr Radiol. 1998; 28(8):612-616.
7. Maldjian C, Rosenberg ZS. MR imaging features of tumors of the ankle and foot. Magn Reson Imaging Clin N Am. 2001; 9(3):639-657.
8. Moore SL. Imaging the anterior cruciate ligament. Orthop Clin North Am. 2002; 33(4):663-674.
9. Nguyen B, Brandser E, Rubin DA. Pains, strains, and fasciculations: lower extremity muscle disorders. Magn Res Imaging Clin North Am. 2000; 8(2):391-408.
10. Shepard MF, Hunter DM, Davies MR, et al. The clinical significance of anterior horn meniscal tears diagnosed on magnetic resonance images. Am J Sports Med. 2002; 30(2):189-192.

Government Agency, Medical Society, and Other Authoritative Publications:

1. American College of Radiology. ACR Appropriateness Criteria^®. Available at: http://www.acr.org/SecondaryMainMenuCategories/quality_safety/app_criteria.aspx. Accessed on January 7, 2010.
   • Acute Trauma to the Knee (2008)
   • Avascular Necrosis of the Hip (2009)
   • Chronic Ankle Pain (2009)
   • Chronic Hip Pain (2008)
   • Follow-up of Malignant or Aggressive Musculoskeletal Tumors (2008)
   • Imaging After Total Hip Arthroplasty (2005)
   • Imaging After Total Knee Arthroplasty (2006)
   • Metastatic Bone Disease (2009)
   • Non-Traumatic Knee Pain (2008)
   • Soft Tissue Masses (2009)
   • Suspected Ankle Fractures (2008)
2. American College of Radiology. Practice guideline: Available at: http://www.acr.org/SecondaryMainMenuCategories/quality_safety/guidelines.aspx Accessed on January 7, 2010.
   • Practice guideline for the performance and interpretation of magnetic resonance imaging (MRI) of the ankle and hindfoot (2006)
   • Practice guideline for the performance and interpretation of magnetic resonance imaging (MRI) of the knee (2006)
   • Practice guideline for the performance of computed tomography (CT) of the abdomen and computed tomography (CT) of the pelvis (2006)
   • Practice guideline for the performance of magnetic resonance imaging (MRI) of the soft tissue components of the pelvis (2006)
3. Centers for Medicare and Medicaid Services. Available at: http://www.cms.hhs.gov/mcd/index_list.asp?list_type=ncd. Accessed on January 04, 2010.
   • National Coverage Determination: Computerized Tomography. NCD# 220.1. Effective March 12, 2008.
   • National Coverage Determination: Magnetic Resonance Imaging (MRI). NCD #220.2. Effective September 28, 2009.

Ankle
Computed tomography (CT)
Foot
Hip
Knee
Lower extremity
Magnetic resonance imaging (MRI)
Pelvis