Table 1.
MRI features for differentiating an active Charcot foot from osteomyelitis. Information collected from Ahmadi et al. 2006 [25], Donovan and Schweitzer 2010 [29], Ergen et al. 2013 [2], Johnson et al. 2009 [28], Martín Noguerol et al. 2017 [30], Mautone and Naidoo 2015 [24], Schoots et al. 2010 [3], and Toledano et al. 2011 [20]
| Active Charcot foot | Osteomyelitis | |
|---|---|---|
| Location of bone marrow abnormality (edema shown in fluid sensitive sequences, and reduction of fatty bone marrow shown in T1 sequences) |
○ Pattern tends to be periarticular ○ Usually involves several joints and bones (mostly tarso-metatarsal joints and metatarsophalangeal joints) |
○ Tendency to involve a single bone with diffuse marrow involvement ○ Usually affects weight-bearing surfaces of the toes, metatarsal heads, calcaneus, malleolus, and a special area in Charcot: cuboid (in rocker-bottom deformity) ○ Develops almost exclusively by continuous spread of infection from skin ulcerations and sinus tracts |
| Sinus tracts | o Usually not present | o Often present |
| Skin ulceration (technician should mark the exact ulcer location) | o Can be present |
o Often present o Often relationship to sinus tract |
| Fluid collections |
o Present o Usually smaller than in case of infection, unless sinus tract is present |
o Present o Usually larger than in active Charcot foot, unless a sinus tract exists over which the collection is drained (paradoxical decrease of size of fluid collection) o Diffusion-weighted imaging (DWI) might help in differentiation abscesses from non-infected fluid collections |
| Subcutaneous fat | o Dorsal often with edema, plantar often normal | o Often disappears due to presence of cellulitis |
| Subchondral cysts |
o Typical image feature in chronic Charcot foot o The presence of subchondral cysts indicates the absence of infection |
o Tendency to disappear in case of infection/osteomyelitis o Best recognized if regular previous follow-up studies are present, which demonstrate the disappearance of the cysts |
| Intraarticular bodies | o The presence of intraarticular bodies indicates the absence of infection | o Often disappear in the setting of infection due to dissolution or obscureness by surrounding inflammation |
| “The ghost sign” | o Negative: a neuropathic joint without infection will not demonstrate the “ghost sign” because the bones are definitely destroyed and will look destroyed on all sequences | o Positive: bones that “disappear” on T1-weighted images and “reappear” (outline of the bone becomes visible again) after contrast administration (or on T2-weighted images)—suspicious of osteomyelitis—Fig. 21 |