18 Sep What is Osteomyelitis of the Foot and how is it Managed?
Osteomyelitis (OM) refers to the inflammation or infection of the bone and bone marrow. It is a common complication of poorly controlled diabetes mellitus and is associated with high morbidity as it may lead to leg amputation if poorly managed. The risk for amputation in acute diabetic infections is four times higher with OM than with soft tissue infection alone. OM is a serious infectious disease and requires aggressive therapy and likely hospital stay. Treatment for OM in the diabetic foot includes antibiotic therapy and surgical procedures as needed, including surgical debridement with excision of the osteomyelitis bone and/or amputations. Limb salvage is the main goal of OM treatment. Early diagnosis and appropriate treatment are necessary to reduce the need for leg amputation.
In diabetics with poorly controlled blood glucose levels, there is the development of microvascular disease (diabetic vasculopathy) which compromises the blood supply to the peripheral structures retarding the healing process. Furthermore, poorly controlled diabetes also leads to immune dysfunction, increasing the likelihood of opportunistic and/or extensive infections. In these patients, the infection tends to spread contiguously, typically from a skin ulcer quite commonly seen in this patient population. The risk of developing OM increases if the ulcer is larger than 2×2 cm.
The most common sites of OM are in the forefoot (90%) followed by the midfoot (5%) and hindfoot (5%). The most common bones involved in the foot, including the first metatarsal head, fifth metatarsal head, and the calcaneus.
Evaluation of the diabetic foot ulcer includes the measurement of site, size, periphery, depth, content, and adjacent skin environment. In addition, the foot and lower extremity must also be assessed for the presence of any vasculopathy, neuropathy, and the extent of infection. This includes palpating the lower limb pulses and assessing for skin color, temperature, and capillary refill time. Also, ankle-brachial and toe-brachial pressure indices should be measured. Duplex ultrasound is used for the assessment of major arterial stenoses that may warrant vascular intervention. Furthermore, the presence of diabetic neuropathy is also a concern in these patients and should be screened for.
Lab testing in these patients includes white blood cell (WBC) count, C-reactive protein (CRP), erythrocyte sedimentation rate (ESR), Hemoglobin A1C, blood urea nitrogen/creatinine, albumin, and hemoglobin). ESR, WBC, CRP, ESR, and Pro-Calcitonin all tend to be higher in OM compared to soft tissue infection.
Medical imaging plays a major role in the diagnosis and management of OM. The first step is plain radiography, although it has been found to have variable sensitivity, and even the specificity of radiographs is limited when it comes to distinguishing OM from Charcot neuroarthropathy joint disease. Magnetic resonance imaging (MRI) is considered the modality of choice for diagnosing diabetic foot OM, with a sensitivity of about 90% and a specificity of about 80%. Bone scintigraphy (three-phase bone scan using Technetium-99m-Medronic Acid Bisphosphonate) detects areas of high bone turnover, which allows for high sensitivity (80-90%) in detecting OM but has very poor specificity (50%).
Single-photon emission computerized tomography Single-photon emission computerized tomography (SPECT) bone scan provides both anatomical and functional information with improved specificity. A WBC scan (+/- SPECT) is useful as it shows soft tissue infection and can complement the bone scan to improve the overall sensitivity and specificity (up to 80-90%). Positron emission tomography using 18-fluorine 2-fluoro-2deoxy-D-glucose (FDG-PET) has a sensitivity of 80-100% and a specificity of 93%. A bone biopsy is considered to be the gold standard for the diagnosis of OM.