An Orthopaedist's Review of Diabetic Foot Wounds and Osteomyelitis

Matthew R. DeSanto, BS; Luke V. Weber, BS; Emmanuel Nageeb, BS; Kyle Petersen, MD; Jeffrey Junko, MD

Disclosures

Curr Orthop Pract. 2020;31(5):423-428. 

In This Article

Diagnostics

Initial Management of Diabetic Foot Ulcers

Regarding examination of diabetic foot ulcers, it is imperative that healthcare providers exclude necrotizing fasciitis, wet gangrene, and other surgical emergencies. After it has been determined the patient is stable, one may proceed with an appropriate workup. This typically begins with a thorough physical examination, laboratory work-up, and three-view radiographs of the affected extremity.

An important initial step of the physical examination is recognizing the size of the ulcer. Both the width and depth of the wound can be highly predictive of osteomyelitis. Ulcers greater than 3-mm deep are associated with osteomyelitis 82% of the time, whereas ulcers less than 3-mm deep are associated 33% of the time. Any ulceration with exposed bone, evidenced visually or through probe manipulation, had underlying osteomyelitis.[30] Further, those with a surface area of greater than 2 cm2 have a specificity and sensitivity of 92% and 56% accordingly.[30] Another simple yet highly valuable test is the probe-to-bone test. This test has been shown to be 85% to 91% specific with a 66% to 87% sensitivity.[31,32] This is one of the most readily available tests but requires a certain level of knowledge regarding bony relationship to surface anatomy.

Historically, radiographs have been the only imaging modality to help diagnose osteomyelitis, but in recent decades new imaging modalities have aided in the diagnosis of osteomyelitis by supplementing plain films. Osteomyelitis typically must be present for at least 2 wk to have significant enough cortical destruction to be seen on radiographs. This delayed presentation often causes missed diagnoses, given the sensitivity of 54% and specificity of 68% for the diagnosis of osteomyelitis using radiographic imaging (Table 1).[33] A form of imaging with higher diagnostic value is MRI, with and without contrast, which has a sensitivity of 90% and specificity of 79%.[33] Another imaging modality with high sensitivity, but much lower specificity, is leukocyte scintigraphy. This methodology provides sensitivity of 82.7% but a specificity of only 44.6%. Furthermore, one of the best imaging modalities for diagnosis of osteomyelitis is the fluorodeoxyglucose-positron emission tomography. This imaging technique has a sensitivity of 92.3% and specificity of 92%, but it is seldomly used because of expense and limited availability.[34]

Four laboratory tests are commonly considered diagnostically impactful and ordered in the workup of a diabetic foot ulcers: erythrocyte sedimentation rate (ESR), C-reactive protein (CRP), procalcitonin, and white blood cell count (WBC). Both ESR and CRP are markers of inflammation, while procalcitonin and WBC provide more insight on potential infectious etiologies. In the presence of diabetic foot ulcers, WBC >14×109/L (74% sensitivity, 82% specificity for osteomyelitis) and procalcitonin >0.3 (81% sensitivity, 71% specificity for osteomyelitis) help diagnose osteomyelitis. Associated sensitivity and specificity calculations regarding these diagnostic laboratory values are shown in Table 2. Additionally, these tests can help monitor responses to treatment. CRP is expected to normalize close to a week after beginning appropriate administration of antibiotics. ESR provides longer monitoring as it takes up to 3 months to completely normalize.[35–37] Although normalization of ESR and CRP can be helpful in monitoring the response to antibiotics and improving resolution of osteomyelitis, no accepted test is available to monitor long-term resolution of osteomyelitis.[4,38]

Many studies vary in their cutoff for ESR and CRP for the diagnosis of osteomyelitis; however, Michail et al.[36] found that an ESR greater than 67 mm/h had 84% and 75% accuracy for sensitivity and specificity, respectively, and a CRP >14 mg/dL had 85% sensitivity and 83% specificity in the setting of a diabetic foot infection.

If concerned for osteomyelitis, we do not recommend superficial cultures because they lack specificity and are only accurate 38% of the time.[39] This may negatively guide antibiotic therapy and lead to development of increased antibiotic resistance.[40,41] Historically, the gold standard for obtaining cultures has been bone biopsy,[4,42] but recent studies have suggested that deep tissue culture may be comparable in accuracy with greater accessibility.[43,44]

Osteomyelitis Versus Charcot Arthropathy

Osteomyelitis, otherwise known as infection or inflammation of bone and bone marrow, is considered to be a relatively severe progression of improperly healing diabetic ulcers. Radiographically, osteomyelitis typically is less diffuse than Charcot arthropathy (CA), which commonly affects a greater percentage of the foot. Additionally, if an ulcer is present, osteomyelitis is classically seen in close proximity to the ulcer/abscess or sinus track, helping to differentiate CA from osteomyelitis.[45–47] Despite these statements, diagnosis based on imaging alone can be very difficult, and a satisfactory physical examination holds great importance. The typical treatment and workup for osteomyelitis and diabetic foot ulcers are discussed below.

Commonly confused with osteomyelitis, CA was first described by Charcot.[48] Both have similar presentations as they commonly occur in diabetics, and at times both occur concurrently. This quandary may lead to difficulty in establishing the proper diagnosis.[49] Charcot arthropathy is a progressive condition of the musculoskeletal system that is characterized by joint dislocations, pathologic fractures, and debilitating deformities due to soft tissue destruction.[50] CA is linked to diabetic foot ulcers, as both are customarily caused by polyneuropathy and weakened perfusion. In CA, pronounced physical changes include fragmentation, dislocation, and rocker bottom foot.[16,51] Treatment for CA classically involves total contact casting which disperses the pressure uniformly throughout the entire pedal area.[52] Now, one of the best ways to distinguish CA from osteomyelitis is elevation of the affected extremity. If the patient has dependent rubor, meaning that the erythema of the foot improves with elevation, the likelihood of CA as opposed to osteomyelitis is greater.[53] Table 3 provides details of key characteristics of the two disease processes.

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