Roundtable Insights On Imaging For Foot And Ankle Wounds

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Other Key Points On Nuclear Medicine Leukocyte Imaging

When using nuclear medicine leukocyte imaging (NMLI), Molly Judge, DPM, says it is critical to use this imaging prior to any surgical manipulation of soft tissue, muscle, bone or joint.

Surgical manipulation distorts normal anatomic compartments, changes local anatomy and, most importantly, causes direct tissue damage that can mimic infection when using some NMLI techniques, according to Dr. Judge.

NMLI techniques such as 99mTc-HMPAO, combination imaging with 99mTc-MDP and Indium-labeled leukocytes and Neutrospec imaging are “all viable methods for pre-surgical assessment of chronic wounds.”

When treating noncompliant patients, Dr. Judge says NMLI can be particularly useful in ruling out indolent infection. Using NMLI can help document if there is no infection at the time of treatment, according to Dr. Judge. She adds that this can help counter any potential argument of misdiagnosis or delayed diagnosis in the event of limb loss despite the best of efforts.

She adds that the radiologist’s reading of NMLI is an important aspect of medical/legal documentation.

“If there is any unusual area of positivity in the extremity, there will be a caution in the radiologist’s report suggesting that this may represent an infectious process,” notes Dr. Judge.

When it comes to osteomyelitis (as shown above), there are a variety of imaging techniques one can use to help confirm the diagnosis, according to Thomas Zgonis, DPM. (Photo courtesy of Robert Snyder, DPM)
Here is a radiograph that reveals osteomyelitis. In regard to an initial radiolucency, Dr. Zgonis says underlying osteomyelitis requires five to seven days to manifest radiographically. (Photo courtesy of Lawrence Karlock, DPM)
This MRI STIR technique identifies the region of a loculated abscess formation that rests immediately beneath the remnant of cuboid bone. Note the intermedullary edema indicated by the increased signal intensity within the adjacent osseous structures of t
As one can see, the 99mTc-MDP study reveals the extent of degenerative bone in a “burned out” Charcot foot while the indium 24-hour image fails to reveal a focus of infection in that same patient with Charcot neuroarthropathy. (Photos courtesy of Molly Ju
Roundtable Insights On Imaging For Foot And Ankle Wounds
Roundtable Insights On Imaging For Foot And Ankle Wounds
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Author(s): 
Clinical Editor: Lawrence Karlock, DPM

   When is advanced imaging necessary for guiding one’s decision-making on the treatment of a lower-extremity wound? How reliable are radiographs when clinicians suspect osteomyelitis? Should you employ magnetic resonance imaging? Does nuclear medicine imaging have particular value in managing wounds? Our expert panelists tackle these questions and more in the following discussion.

   Q: What role do you see advanced imaging playing in the management of foot and ankle wounds?

   A: Molly Judge, DPM, says advanced imaging is unnecessary when it comes to clean, uncomplicated wounds that have a clear chance of resolving with local wound care. Lawrence Ford, DPM, concurs, noting it is limited to difficult cases in which clinical findings and standard X-rays are inconclusive.

   However, when patients have longstanding wounds (with or without a history of infection), Dr. Judge says it is “prudent to pursue some form of imaging” in order to confirm the absence of an underlying pathology that can confound the existing clinical condition.

   When local ulcerations fester long enough, Dr. Judge says these patients are at risk for a secondary bacterial infection, which can result in deep sinus formation, abscess and possibly osteomyelitis.

    “These are the complicating conditions that mandate advanced imaging to delineate the location and extent of infection,” emphasizes Dr. Judge. “This imaging will ultimately lend credence to the proposed wound care plan or prompt a change in the treatment plan altogether.”

   According to Thomas Zgonis, DPM, there are a variety of imaging techniques one can use to help confirm osteomyelitis. These imaging techniques include plain radiographs, nuclear imaging, magnetic resonance imaging (MRI), computerized tomography (CT) and diagnostic ultrasound. However, Dr. Zgonis cautions that each test has its limitations and one must carefully assess the patient’s comorbidities before ordering expensive and possibly unnecessary tests.

   When it comes to diagnosing osteomyelitis, in addition to the clinical assessment, Dr. Zgonis says one may need an imaging study to confirm and further assess the extent of deep soft tissue and bone involvement. However, he says the bone biopsy remains the gold standard for a definitive diagnosis of osteomyelitis. If the results from imaging are inconclusive, Dr. Zgonis says one should obtain sterile bone cultures if one has a high index of suspicion for underlying osteomyelitis. He adds that histopathologic analysis is necessary to confirm the diagnosis of osteomyelitis.

   Q: If a chronic wound “probes to bone” but has normal X-ray findings, how do you treat this?

   A: Citing a study by Grayson, et. al., Dr. Zgonis says the ability to probe to bone in the base of an infected pedal ulcer with a sterile blunt steel probe had a positive predictive value of 89 percent and a negative predictive value of 56 percent for osteomyelitis.1 He notes the researchers also concluded that if one palpates bone upon probing, specialized roentgenographic and radionuclide tests are unnecessary in diagnosing osteomyelitis.1

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