Charcot joint, also known as a neuropathic joint or Charcot (neuro/osteo)arthropathy, refers to a progressive degenerative/destructive joint disorder in patients with abnormal pain sensation and proprioception.
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Epidemiology
In modern Western societies by far the most common cause of Charcot joints is diabetes mellitus, and therefore, the demographics of patients match those of older diabetics. Prevalence differs depending on the severity of diabetes mellitus 1:
~0.1% in general diabetic population
~15% in high-risk diabetic population
~30% in patients with peripheral neuropathy
Clinical presentation
Patients present insidiously or are identified incidentally, or as a result of investigation for deformities. Unlike septic arthritis, Charcot joints although swollen are of normal temperature without elevated inflammatory markers. Importantly, they are painless.
Pathology
The pathogenesis of a Charcot joint is thought to be an inflammatory response from a minor injury that results in osteolysis. In the setting of peripheral neuropathy, both the initial insult and inflammatory response are not well appreciated, allowing ongoing inflammation and injury 1.
Charcot joints are typically unilateral but are bilateral in ~20% (range 5.9-39.3%) of cases 10. There are two patterns of Charcot joint: atrophic and hypertrophic.
Atrophic form
most common form
occurs earlier 2
has an acute progression
characterized by reabsorption of the ends of the affected bone
joint destruction with resorption of fragments
an absence of osteosclerosis and osteophytes
mainly occurs in non-weight-bearing joints of the upper limb
Hypertrophic form
only sensory nerves affected
slow progression
joint destruction with periarticular debris/bone fragmentation
initially widened then narrowed joint space
presence of osteosclerosis and osteophytes
absence of osteoporosis (unless the joint is infected) 3
Etiology/location
Sensorimotor and autonomic neuropathies of various etiologies are the primary predisposing factors. The most common etiology varies by the involved joint 10:
diabetes mellitus (most common cause overall and in the foot and ankle; most commonly affects the foot and ankle)
syringomyelia (most common cause in the upper extremity and shoulder)
neurosyphilis/tabes dorsalis (more common in the past; most commonly affects the knee)
traumatic spinal cord injury (most common cause in the spine) 11
alcoholism
tumors compressing or involving the spinal cord or peripheral nerves
steroid use (intraarticular or systemic)
familial dysautonomia (Riley-Day syndrome)
Less established causes:
Some of these can be recalled with the "S" mnemonic.
Classification
See: Eichenholtz and Brodsky Classification of Charcot foot
Radiographic features
Plain radiograph and CT
Charcot arthropathy appears as a destructive and disorganizing process centered in the joint and affecting surrounding bones, which may mimic severe osteoarthritis or septic arthritis 10. Manifestations depend on stage 14:
development/fragmentation/dissolution: subchondral osteopenia is the earliest finding 10, followed by bony fragmentation (with the formation of debris seen as intraarticular loose bodies) and joint malalignment (subluxation or dislocation due to ligamentous laxity)
coalescence: bony consolidation begins with subchondral sclerosis, periosteal bone formation, and fusion of the larger fragments and absorption of the smaller fragments
reconstruction/reconstitution: remodeling occurs with rounding of fragments and ankylosis, making deformity permanent
resorption of the metatarsal heads leads to the licked candy stick appearance.
in the spine, fragmentation of the vertebral body occurs, along with bone formation and debris. This process may be extensive and lead to "tumbling building block spine" and "jigsaw vertebra" appearance 18.
General characteristics may be recalled with the six Ds mnemonic.
MRI
MRI plays an important role in diagnosing complications, assessing the extent of the disease, and the presence of osteomyelitis.
-
T1
involved joints appear diffusely swollen, showing decreased signal intensity
fat planes adjacent to ulcerated skin show decreased signal intensity
if superinfected with a gas-producing organism, there will be a loss of signal intensity
subchondral microfractures and cysts 17
in later stages, joint dislocation and destruction
intra-articular loose bodies 17
T1 C+ (Gd): inflammatory areas show enhancement, with central non-enhancing necrotic areas
-
STIR
early stage: increased signal intensity due to marrow edema, typically in a periarticular distribution around the tarsometatarsal and metatarsophalangeal joints 17
joint effusions
later stages: loss of demarcation of cortical outline and cortical destruction
History and etymology
The French pathologist and neurologist Jean-Martin Charcot (1825-1893), the "father of neurology", was the first person to give a detailed description of the neuropathic aspect of this condition in 1868 in a patient suffering syphilis 15.
Differential diagnosis
Imaging differential considerations include:
-
advanced osteomyelitis
can co-exist (especially in the foot) 4,5
can have similar pattern of bone marrow signal on MRI 16
tuberculous spondylitis or Pott's disease (in the spine)
chondrosarcoma (shoulder): chondroid matrix instead of bony debris
inflammatory osteoarthritis/arthritis: in early stages can resemble Charcot joint
Practical points
Useful MRI features that support superimposed osteomyelitis on a Charcot joint include 4:
sinus tract
diffuse marrow signal abnormality
replacement of soft tissue fat
thick rim enhancement
joint erosion
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