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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]

From: The Charcot foot: a pictorial review

 

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