Roundtable Insights On Imaging For Foot And Ankle Wounds

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    Dr. Zgonis says one should employ this test in the assessment of all acute and chronic foot ulcers that appear infected. He adds that this test may “obviate further advanced imaging to confirm the diagnosis of osteomyelitis.” Probing to bone and the presence of clinical and systemic signs of infection are “still the most reliable indicators of underlying osteomyelitis,” according to Dr. Zgonis.    Dr. Judge concurs that a chronic wound that probes to bone is particularly concerning as it may be a harbinger of impending osteomyelitis. When there is a negative X-ray in the presence of an open wound that probes to bone, Dr. Ford says either the bone is not infected or the bone is infected but just has not shown up on X-rays yet.    In regard to the initial radiolucency, Dr. Zgonis says underlying osteomyelitis requires five to seven days to manifest radiographically. He adds that it takes between 10 to 14 days for the first signs of sequestrum and involucrum to be noticeable.    Dr. Zgonis says one can use radiographs to determine the presence of soft tissue swelling, ulcer tracking, gas in the tissues, cortical irregularity and focal demineralization.2 When it comes to an early presentation of osteomyelitis, Dr. Zgonis notes that initial radiographs are usually abnormal in less than 5 percent of the patients. Yet by the third or fourth week, 90 percent of the patients will demonstrate clinical changes consistent with osteomyelitis.3    In the particular clinical scenario raised above, Dr. Judge says the lack of radiographic changes in bone would make her suspect an indolent soft tissue infection. When it comes to determining whether there is a microbial cause for treatment failure, Dr. Judge proceeds to use nuclear medicine leukocyte imaging (NMLI).    She says NMLI results will reveal one of three things. The results may indicate an infection and provide specifics on the location and extent of the infection. The results can identify when no infection exists and accordingly support the continued use of conservative care including second opinions. One can also use NMLI to diagnose a coincident inflammatory process similar to what one might see in the presence of hypertrophic bone or malignancy.    In addition to identifying and localizing an infectious process, Dr. Judge says using NMLI can help one delineate between bone and soft tissue infection.    Usually, if there is infected soft tissue and one can probe to bone, one is dealing with osteomyelitis, according to Dr. Ford. If the wound is not infected, Dr. Ford emphasizes obtaining a biopsy and culture of the exposed bone to determine whether the patient has osteomyelitis, and treating the patient accordingly based upon the results.    Q: What role do nuclear medicine studies play in the treatment of diabetic wounds?    A: Dr. Ford says the results can be “confusing due to the suspicion of false positives and false negatives.” He rarely finds nuclear medicine studies helpful in managing wounds. When there is exposed bone through a chronic wound on the plantar aspect of the foot, Dr. Ford points out that bony turnover is likely and a response of inflammatory cells will make it “extremely difficult” to distinguish between infection and inflammation.    He notes that he tends to rely more upon clinical findings, lab and microbiology studies, and standard X-rays. However, when there is no exposed bone in the wound, Dr. Ford says he will use nuclear medicine imaging more as the specificity for osteomyelitis would be greater.    Dr. Zgonis does order scintigraphy to confirm osteomyelitis as well as to determine its extent. Technetium-99 bone scans can be positive for numerous conditions including but not limited to osteomyelitis, Charcot neuropathy, fractures, systemic arthritides, bone tumors and postsurgical changes, according to Dr. Zgonis. While these scans are not “very specific,” he notes they are “quite sensitive” in diagnosing osteomyelitis. Dr. Zgonis adds that the literature supports the use of more specific tests including but not limited to Gallium-67, Indium-111, Tec-99 HMPAO and sulfur colloid scans in confirming osteomyelitis.4,5    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. Dr. Karlock (pictured) is a Fellow of the American College of Foot and Ankle Surgeons, and practices in Austintown, Ohio. He is a member of the Editorial Advisory Board for WOUNDS, a Compendium of Clinical Research and Practice. Dr. Ford is the Residency Director of the San Francisco Bay Area Foot and Ankle Residency Program at Kaiser Permanente in Richmond and Oakland, Ca. He is a Fellow of the American College of Foot and Ankle Surgeons. Dr. Judge is a certified nuclear medicine technologist and is a Fellow of the American College of Foot and Ankle Surgeons. She is board-certified in foot, ankle and reconstructive rearfoot and ankle surgery by the American Board of Podiatric Surgery. Dr. Judge has private practices in Toledo and Port Clinton, Ohio. She is the official foot and ankle physician for the Jamie Farr Owens Corning LPGA Classic sponsored by Kroger. Dr. Zgonis is an Assistant Professor within the Department of Orthopaedics/Podiatry Division at the University of Texas Health Science Center in San Antonio. He is an Adjunct Assistant Professor at the College of Podiatric Medicine and Surgery at Des Moines University in Des Moines, Iowa. Dr. Zgonis is also a Visiting Clinical Professor of Surgery within the Department of Orthopaedics and Traumatology at Thriasion General Hospital in Athens, Greece. He is an Associate of the American College of Foot and Ankle Surgeons.
 

 

References:

1. Grayson ML, Gibbons GW, Balogh K, Levin E, Karcmer AW. Probing to bone in infected pedal ulcers: A Clinical sign of underlying osteomyelitis in diabetic patients. JAMA 1995; 273:721-723.
2. Bonakdarpour A, Gaines VD. The radiology of osteomyelitis. Ortop Clin North Am 1983; 14:21.
3. Wheat J. Diagnostic strategies in osteomyelitis. Am J Med 1985;78:218-224.
4. Devillers A, Garin E, Polard JL, Poirier JY, Arvieux C, Girault S, et al. Comparison of Tc-99m-labelled antileukocyte fragment Fab' and Tc-99m-HMPAO leukocyte scintigraphy in the diagnosis of bone and joint infections: a prospective study. Nucl Med Commun 2000;2:747-53.
5. Larcos G, Bron ML, Sutton RT. Diagnosis of osteomyelitis of the foot in diabetic patients: value of 111 In-leukocyte scintigraphy. AJR 1991;157:527-531.
6. Zgonis T, Jolly GP, Buren BJ, Blume P. Diabetic foot infections and antibiotic therapy. Clin Podiatr Med Surg. 2003;20:655-69.

 

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