Roundtable Insights On Imaging For Foot And Ankle Wounds

Author(s): 
Clinical Editor: Lawrence Karlock, DPM

   Nuclear medicine imaging (NMI) does play “a very distinct role” in managing diabetic wounds, according to Dr. Judge. When considering any unusual wounds or chronic wounds that seem to be getting worse despite meticulous local wound care, Dr. Judge pursues ancillary imaging to detect the underlying culprit.

   Through extensive use of NMLI in her clinical practice, Dr. Judge has found NMLI to be “extremely helpful in identifying the entire spectrum of disease from malignancy to infection.”

   Using Neutrospec, one of the newer agents on the market, Dr. Judge says one can perform the imaging within a few hours after injection. She says the monoclonal antibody imaging agent is easy to obtain and given its ability to create an in vivo leukocyte label, it is “the technique of choice for many cases in wound care management.”

   Q: What role does MRI play in the treatment of lower-extremity wounds?

   A: Drs. Ford and Zgonis agree that MRI is valuable in determining the presence of soft tissue versus bone infection as well as the extent of the involvement. Dr. Zgonis adds that MRI is a “great tool” when there is ulcer or osteomyelitis involvement in the forefoot and the patient has no Charcot destructive changes. With advances in technique and interpretation, Dr. Ford says specialized MRI is “probably the most accurate and useful test other than biopsy.”

   However, Drs. Zgonis and Ford also sound a few cautionary notes. Postsurgical changes, Charcot neuroarthropathy, trauma, fractures and avascular necrosis may generate false positives, according to Dr. Zgonis. He also notes that MRI results can be difficult to interpret when there is a coexisting Charcot deformity with an underlying bone or soft tissue infection.6

   Given issues of cost and potential “overkill” with MRI, Dr. Ford notes that he reserves the imaging modality for difficult and inconclusive cases.

   While Dr. Judge uses MRI very frequently when it comes to managing musculoskeletal pathology, she says MRI can be problematic with chronic wounds.

   When assessing patients with chronic wounds, Dr. Judge cautions that there is often a biomechanical shift as the patient is offloading the wound. This results in the patient modifying his or her gait and ambulation, and shifting weight onto other uninvolved regions of the foot and ankle. As a result of this weight shift, Dr. Judge says it is very common for a MRI to reveal an increased intramedullary edema in bone, which in and of itself can confound the interpretation of the exam. In this case, she says one may “overzealously” interpret the extent of the infection.

   Additionally, if there is infection within the medullary component of bone, Dr. Judge notes the MRI can show a very extensive degree of this inflammatory change that is often far out of proportion to what one sees clinically. Dr. Judge explains that when any infection propagates into normal regions of bone, it causes an inflammatory front that shows the body has promoted a road block to the degenerative process.

    “The problem here is that the MRI cannot distinguish between benign and infectious inflammatory change, and ultimately shows one large region of increased signal change that can overestimate the actual extent of pathology,” points out Dr. Judge.

   Dr. Judge also notes that MRI is precluded in cases of retained foreign bodies such as stents, staples and internal fixation devices.

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