Description
Plain radiographs are typically used as the first-line modality for assessment of lower extremity conditions. Computed tomography (CT) is used for evaluation of tumors, metastatic lesions, infection, fractures, and other problems. Magnetic resonance imaging (MRI) is the first-line choice for imaging of many conditions, but CT may be used in these cases if MRI is contraindicated or unable to be performed

OVERVIEW
*Conservative therapy — (Musculoskeletal) should include a multimodality approach consisting of a combination of active and inactive components. Inactive components such as rest, ice, heat, modified activities, medical devices (such as crutches, immobilizer, metal braces, orthotics, rigid stabilizer, or splints, etc. and not to include neoprene sleeves), medications, injections (bursal, and/or joint, not including trigger point), and diathermy, can be utilized.

Active modalities may consist of physical therapy, a physician-supervised home exercise program**, and/or chiropractic care.

**Home exercise program (HEP) — The following two elements are required to meet guidelines for completion of conservative therapy:

• Information provided on exercise prescription/plan AND
• Follow up with member with information provided regarding completion of HEP (after suitable 4-week period), or inability to complete HEP due to physical reason, i.e., increased pain, inability to physically perform exercises. (Patient inconvenience or noncompliance without explanation does not constitute “inability to complete” HEP).

Joint implants and hardware — Dual-energy CT may be useful for metal artifact reduction if available but is also imperfect as the correction is based on a projected approximation of X-ray absorption, and it does not correct for scatter.⁷⁴ Dual-energy CT can be used to characterize crystal deposition disease, such as gout versus CPPD (calcium pyrophosphate deposition).⁶¹

CT and osteolysis — Since computed tomography scans show both the extent and the location of lytic lesions, they are useful to guide treatment decisions, as well as to assist in planning for surgical intervention when needed, in patients with suspected osteolysis after total hip arthroplasty (THA).

American Academy of Pediatrics “Choosing Wisely” Guidelines advise against ordering advanced imaging studies (MRI or CT) for most musculoskeletal conditions in a child until all appropriate clinical, laboratory and plain radiographic examinations have been completed. “History, physical examination, and appropriate radiographs remain the primary diagnostic modalities in pediatric orthopedics, as they are both diagnostic and prognostic for the great majority of pediatric musculoskeletal conditions. Examples of such conditions would include, but not be limited to, the work up of injury or pain (spine, knees and ankles), possible infection, and deformity. MRI examinations and other advanced imaging studies frequently require sedation in the young child (5 years old or less) and may not result in appropriate interpretation if clinical correlations cannot be made. Many conditions require specific MRI sequences or protocols best ordered by the specialist who will be treating the patient … if you believe findings warrant additional advanced imaging, discuss with the consulting orthopedic surgeon to make sure the optimal studies are ordered.”⁷⁵

GENERAL INFORMATION

It is an expectation that all patients receive care/services from a licensed clinician. All appropriate supporting documentation, including recent pertinent office visit notes, laboratory data, and results of any special testing must be provided. If applicable: All prior relevant imaging results and the reason that alternative imaging cannot be performed must be included in the documentation submitted.

Where a specific clinical indication is not directly addressed in this guideline, medical necessity determination will be made based on widely accepted standard of care criteria. These criteria are supported by evidence-based or peer-reviewed sources such as medical literature, societal guidelines and state/national recommendations.
 

Policy
INDICATIONS FOR LOWER EXTREMITY CT (FOOT, ANKLE, KNEE, LEG or HIP)
(Plain radiographs must precede CT evaluation.)

Some indications are for MRI, CT, or MR or CT arthrogram. More than one should not be approved at the same time.

If a CT arthrogram fits approvable criteria below, approve as CT.

Joint or muscle pain without positive findings on an orthopedic exam as listed below and after X-ray completed^1,2,3 (does not apply to young children). If MRI contraindicated or cannot be performed or requested as a CT arthrogram:

• Persistent joint or musculotendinous pain unresponsive to conservative treatment*, within the last 6 months which includes active medical therapy (physical therapy, chiropractic treatments, and/or physician supervised exercise**) of at least four (4) weeks, OR
• With progression or worsening of symptoms during the course of conservative treatment

 
Joint specific approvable provocative orthopedic examination tests and suspected injuries⁴ (If MRI contraindicated or cannot be performed or requested as a CT arthrogram).
Note: With a positive orthopedic sign, an initial x-ray is always preferred, however, it is not required to approve advanced imaging UNLESS otherwise specified in bold below. Any test that suggests joint instability requires further imaging (list is not all inconclusive)

ANKLE^5,6,7

• Syndesmotic injury (high ankle injury) with tenderness to palpation over the syndesmosis (AITFL — anterior inferior tibiofibular ligament) and any of the following:
  • Positive stress X-rays
  • Squeeze test
  • Cotton test
  • Dorsiflexion external rotation test.
• Unstable lateral injury to ATFL (anterior talofibular ligament) with suspicion of a possible associated fracture around the ankle or a possible osteochondral injury of the talus AFTER non-diagnostic or inconclusive X-rays and any ONE of the following:
  • Positive stress X-rays
  • Positive anterior drawer test
  • Positive posterior drawer test
• Achilles tendon tear
  • Thompson test

KNEE^{1,8,9,10,11,12}

• Anterior cruciate ligament (ACL) Injury
• Positive testing:
  • Anterior drawer
  • Lachman’s
  • Pivot shift test

OR

• Suspected ACL Rupture — Acute knee injury with physical exam limited by pain and swelling AFTER initial X-ray completed^13,14
  • Based on mechanism of injury, i.e., twisting, blunt force
    • Normal X-ray:
      • Extreme pain, inability to stand, audible pop at time of injury, very swollen joint
    • Abnormal X-ray:
      • Large joint effusion on X-ray knee effusion
• Acute mechanical locking of the knee not due to guarding¹⁵
• Meniscal injury/tear (A positive test is denoted by pain or audible/palpable clunk)
  • McMurray’s Compression
  • Apley’s
  • Thessaly test
• Patellar dislocation (acute or recurrent)
  • Positive patellofemoral apprehension test
  • Radiographic findings compatible with a history of patellar dislocation (i.e., lipohemarthrosis or osteochondral fracture)
• Posterior cruciate ligament (PCL) injury
  • Posterior drawer
  • Posterior tibial sag (Godfrey or step-off test)
• Medial collateral ligament tear
  • Positive valgus stress testing/laxity
• Lateral Collateral ligament tear
  • Positive Varus stress testing/laxity 

HIP

• Femoroacetabular impingement (FAI)/ Labral tear
  • Anterior Impingement sign (aka FADIR test)^16,17,18
  • Posterior Impingement sign (Pain with hip extension and external rotation on exam)¹⁹
  • Persistent hip mechanical symptoms (after initial radiographs completed) including clicking, locking, catching, giving way or hip instability with a clinical suspicion of labral tear and/or radiographic findings suggestive of FAI (i.e., cross over sign/pistol grip deformity) and suspected labral tear
  • To determine candidacy for hip preservation surgery for known FAI²⁰

NOTE: For evaluation of both hips when the patient meets hip MRI guidelines (X-ray + persistent pain unresponsive to conservative treatment) for both the right and left hip, Pelvis MRI (NIA_CG_037) is the preferred study:

• If labral tear is suspected and fulfills above criteria, then bilateral hip MRIs are the preferred studies (not pelvis MRI)
• If bilateral hip arthrograms are requested and otherwise meet guidelines, bilateral hip MRIs are the preferred studies (not pelvis MRI)
   

Tendon rupture after X-ray^21,22,23,24 (not listed in above) — If MRI contraindicated or cannot be performed:

• High clinical suspicion of specific tendon rupture based on mechanism of injury and physical findings (i.e., palpable defect in quadriceps or patellar tendon rupture)

Trauma
Bone Fracture (If MRI contraindicated or cannot be performed)

• Hip and femur
  • Suspected occult, stress or insufficiency fracture with a negative or non- diagnostic initial X-ray:²⁵
    • Approve an immediate CT if contraindication to MRI or MRI cannot be performed (no follow up radiographs required)
• Non-hip extremities: suspected occult, stress, or insufficiency fracture
  • If X-rays, taken 10 – 14 days after the injury or clinical assessment, are negative or nondiagnostic²⁶
  • If at high risk for a complete fracture with conservative therapy (e.g., navicular bone), then immediate CT is warranted²⁷
• Pathologic or concern for impending fracture on X-ray²⁸ — approve immediate CT
• Suspected ligamentous/tendon injury with known fractures on x-ray that may require surgery

Fracture Nonunion

• Nonunion or delayed union as demonstrated by no healing between two sets of X-rays. If a fracture has not healed by 4 – 6 months, there is delayed union. Incomplete healing by 6 – 8 months is nonunion.

Osteochondral Lesions (defects, fractures, osteochondritis dissecans) and X-ray done:^{8,29,30,31,32}

• Clinical suspicion based on mechanism of injury and physical findings

Joint Prosthesis/Replacement

• Suspected joint prosthesis loosening or dysfunction, (i.e. pseudotumor formation) after initial X-rays^33,34
• Suspected metallosis with painful metal on metal hip replacement after initial X-rays
  • After initial X-rays and Cobalt - chromium levels > 7ppb³⁵
  • Abnormal joint aspiration

Extremity Mass

• Mass or lesion after non-diagnostic X-ray or ultrasound.³⁶ MRI preferred. CT is better than MRI to evaluate mass calcification or bone involvement and may complement or replace MRI:³⁷
  • Baker’s cyst should be initially evaluated with ultrasound
  • If superficial, then ultrasound is the initial study
  • If deep, then X-ray is the initial study
• Vascular malformations
  • After initial evaluation with ultrasound and results will change management or for preoperative planning³⁸
    • CTA is also approvable for initial evaluation
  • Follow up after treatment/embolization

Known Primary Cancer of the Extremity^{39,40,41,42,43}

• Initial staging primary extremity tumor
• Follow-up of known primary cancer of patient undergoing active treatment within the past year or as per surveillance imaging guidance for that cancer
• Signs or symptoms or imaging findings suspicious for recurrence
• Suspected metastatic disease with signs/symptoms and after initial imaging with radiographs

Further evaluation of indeterminate or questionable findings on prior imaging and MRI cannot be performed or CT is preferred (i.e., tumor matrix):

• For initial evaluation of an inconclusive finding on a prior imaging report (i.e., X-ray, ultrasound, MRI) that requires further clarification.
• One follow-up exam of a prior indeterminate MR/CT finding to ensure no suspicious interval change has occurred. (No further surveillance unless specified as highly suspicious or change was found on last follow-up exam

Osteonecrosis (avascular necrosis [AVN], Legg-Calve-Perthes Disease) when MRI is contraindicated or cannot be performed:^44,45,46

• To further characterize a prior abnormal X-ray
• Normal or indeterminate X-rays but symptomatic and high risk (e.g., glucocorticosteroid use, renal transplant recipient, glycogen storage disease, alcohol abuse,⁴⁷ sickle cell anemia⁴⁸)
• Known osteonecrosis to evaluate a contralateral joint after initial X-rays

Loose bodies or synovial chondromatosis and after X-ray or ultrasound completed (If MRI contraindicated or cannot be completed)

• In the setting of joint pain or mechanical symptoms⁴⁹

Infection of Bone, Joint, or Soft Tissue Abscess^50,51
Note: MRI and nuclear medicine studies are recommended for acute infection as they are more sensitive in detecting early changes of osteomyelitis.^52,53 CT is better at demonstrating findings of chronic osteomyelitis (sequestra, involucrum, cloaca, sinus tracts) as well as detecting soft tissue gas and foreign bodies.⁵⁴

• Abnormal X-ray or ultrasound
• Negative X-ray but with a clinical suspicion of infection
  • Signs and symptoms of joint or bone infection include:
    • Pain and swelling
    • Decrease range of motion
    • Fevers
  • Laboratory findings of infection include any of the following:
    • Elevated ESR or CRP
    • Elevated white blood cell count
    • Positive joint aspiration
• Ulcer (diabetic, pressure, ischemic, traumatic) with signs of infection (redness, warm, swelling, pain, discharge which may range from white to serosanguineous) that is not improving despite treatment and bone or deep infection is suspected⁵⁵
  • Increased suspicion if size or temperature increases, bone is exposed/positive probe-to-bone test, new areas of breakdown, new smell⁵⁶
• Neuropathic foot with friable or discolored granulation tissue, foul odor, non-purulent discharge, and delayed wound healing⁵⁷

Pre-operative/procedural evaluation

• Pre-operative evaluation for a planned surgery or procedure

Post-operative/procedural evaluation

• When imaging, physical, or laboratory findings indicate joint infection, delayed or non- healing, or other surgical/procedural complications
• Trendelenburg sign or other indication of muscle or nerve damage after recent hip surgery

For evaluation of known or suspected autoimmune disease (e.g., rheumatoid arthritis) and MRI is contraindicated or cannot be performed⁵⁸

• Further evaluation of an abnormality or non-diagnostic findings on prior imaging
• Initial imaging of a single joint for diagnosis or response to therapy after plain films and appropriate lab tests (e.g., RF, ANA, CRP, ESR)
• To determine change in treatment or when diagnosis is uncertain prior to start of treatment
• Follow-up to determine treatment efficacy of the following:
  • Early rheumatoid arthritis
  • Advanced rheumatoid arthritis if X-ray and ultrasound are equivocal or non- contributory

Known or suspected inflammatory myopathies (If MRI contraindicated or cannot be performed): (Includes polymyositis, dermatomyositis, immune-mediated necrotizing myopathy, inclusion body myositis)^59,60

• For diagnosis
• For biopsy planning

Crystalline Arthropathy 

• Dual-energy CT can be used to characterize crystal deposition disease (i.e., gout) after
  • Appropriate rheumatological work up and initial X-rays AND
  • After inconclusive joint aspiration or when joint aspiration cannot be performed OR⁶¹
  • In the setting of extra-articular crystal deposits (i.e., tendons or bursa)

Peripheral Nerve Entrapment (e.g., tarsal tunnel, Morton’s neuroma) and MRI is contraindicated or cannot be performed, including any of the following^62,63,64,65

• Abnormal electromyogram or nerve conduction study
• Abnormal X-ray or ultrasound
• Clinical suspicion and failed 4 weeks conservative treatment including at least 2 of the following (active treatment with physical therapy is not required):
  • Activity modification
  • Rest, ice, or heat
  • Splinting or orthotics
  • Medication

Leg length discrepancy

• CT scanogram^66,67

Foreign Body⁶⁸

• Indeterminate X-ray and ultrasound

Painful acquired or congenital flatfoot deformity in an adult, after X-ray completed and MRI is contraindicated or cannot be performed.

• After failure of active conservative therapy listed above^69,70

Pediatrics

• Osteoid Osteoma after an X-ray is done⁷¹
• Painful flatfoot (pes planus) deformity with suspected tarsal coalition, not responsive to active conservative care⁷²
  • When MRI cannot be performed
  • Extra-articular coalition is suspected (bony bridges around the joints)
  • When needed for surgical planning⁷³
     

References 

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Coding Section

Codes	Number	Description
CPT	73700	Computed tomography, lower extremity; without contrast material
	73701	with contrast material(s)
	73702	without contrast material, followed by contrast material(s) and further sections

Procedure and diagnosis codes on Medical Policy documents are included only as a general reference tool for each policy. They may not be all-inclusive.

This medical policy was developed through consideration of peer-reviewed medical literature generally recognized by the relevant medical community, U.S. FDA approval status, nationally accepted standards of medical practice and accepted standards of medical practice in this community, Blue Cross Blue Shield Association technology assessment program (TEC) and other nonaffiliated technology evaluation centers, reference to federal regulations, other plan medical policies, and accredited national guidelines.

"Current Procedural Terminology © American Medical Association. All Rights Reserved" 

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