DIFFERENTIAL DIAGNOSIS
Differentiating between acute Charcot's arthropathy and osteomyelitis is challenging. The definitive diagnosis of Charcot's joint disease can be made with a synovial tissue 
biopsy, which will contain shards of bone and cartilage embedded deep into the synovium.6 A bone biopsy, on the other hand, is used to make the definitive diagnosis of osteomyelitis. These tests are highly invasive, however, and involve considerable risk to the patient.
Less invasive tests are available to aid in the differentiation of the two diseases. Plain radiographs are usually ordered first because of their widespread availability and low cost. The radiographs should consist of weight-bearing anteroposterior, lateral, and oblique views (see Figure 3). Unfortunately, plain radiographs are neither sensitive nor specific for differentiating between changes due to Charcot's arthropathy and those due to an infection; instead, radiographs provide anatomic information. These images should be evaluated for disorganization related to the stage of arthropathy. Specifically, attention should be directed to the talar-first metatarsal angle, the lateral calcaneal-fifth metatarsal angle, the talonavicular coverage angle, and the alignment of the weight-bearing axis of the lower extremity.7
MRI provides exquisite anatomic detail of both soft tissue and bone. This imaging technique is useful in differentiating between osteomyelitis (which produces a high-intensity signal on T2 images) and Charcot's arthropathy (which produces a low-intensity signal on T2 images), but these findings have a low specificity. Higher intensity signals on T2-weighted images can also be seen with osseous tumors, trauma, and osteonecrosis.6
Scintigraphic studies may also be helpful in evaluating patients with complex presentations. Three-phase bone scans reveal osteoclast and osteoblast activity but are nonspecific for true osteomyelitis. Therefore, using indium-labeled WBC imaging (which has a higher specificity for osteomyelitis) in addition to three-phase bone scanning has been shown to be more accurate for a diagnosis of osteomyelitis, even in the setting of Charcot's arthropathy (which may also demonstrate increased metabolic activity on bone scan). This combination of imaging techniques increases the sensitivity and specificity to 80% to 90%.8
STAGING CHARCOT'S ARTHROPATHY
Eichenholtz was the first to develop a system for staging Charcot's arthropathy.9 The system, originally 
consisting of three stages, is based on the changes seen on radiographs. The purpose of this classification system is to determine the patient's prognosis and to gauge the optimal timing for arthrodesis. Surgical intervention is most effective when performed during early stage 1 or late stage 3 disease.9
Stage 0 is the at-risk stage. This stage was added to the original Eichenholtz classification system to describe a patient with peripheral neuropathy who has sustained an acute sprain or fracture in the ankle or foot but does not have stage 1 disease. Unless the patient has sustained a fracture, the radiographs would be normal.
Stage 1 is the acute or developmental phase. The patient presents with an acute inflammatory process. Radiographs will show joint effusion, bone fragmentation, and joint subluxation.
Stage 2 is the subacute or coalescent phase, described as a decrease in warmth, redness, and swelling. Radiographs will show sclerotic bone surrounding the joint, resorption of intra-articular debris, and fusion of larger bony fragments.
Stage 3, or the reconstructive phase, is characterized by continued resolution of the inflammation. Radiographs will show remodeling of bone and some reformation of the joint architecture.