CIM Case: Charcot Foot

Clinical Scenario

Patient: 60-year-old female Presentation: Right foot swelling and redness developing over 1 week, minimal pain, has been walking on it, noticed "warm feeling" in foot Relevant history: Type 2 diabetes for 15 years, on oral hypoglycaemics and insulin, HbA1c 9.2% (poorly controlled), peripheral neuropathy diagnosed 5 years ago, bilateral cataracts (diabetic retinopathy), previous left foot ulcer healed with conservative treatment Examination findings:

Right midfoot significantly swollen and erythematous
Increased warmth compared to left foot (>2°C difference by infrared thermometer)
Loss of medial longitudinal arch (early rocker-bottom deformity)
Peripheral pulses palpable bilaterally (dorsalis pedis, posterior tibial)
Absent protective sensation (10g monofilament negative at all sites)
Absent ankle reflexes bilaterally
No open wounds or ulceration
No purulent discharge
Probe to bone not applicable (no wound)
Able to weight-bear but with antalgic gait
Left foot shows healed plantar ulcer scar

Investigations Provided

Laboratory Results

Test	Result	Normal Range	Interpretation
Hb	118 g/L	115-160 g/L	Normal
WCC	8.2 ×10⁹/L	4-11 ×10⁹/L	Normal (argues against infection)
Platelets	245 ×10⁹/L	150-400 ×10⁹/L	Normal
ESR	18 mm/hr	<20 mm/hr	Normal
CRP	12 mg/L	<5 mg/L	Mildly elevated (can occur in acute Charcot)
HbA1c	9.2%	<6.5%	Poorly controlled diabetes
Fasting glucose	11.2 mmol/L	3.5-5.5 mmol/L	Elevated
Creatinine	145 μmol/L	60-110 μmol/L	Mildly elevated (diabetic nephropathy)
eGFR	48 mL/min	>90 mL/min	Stage 3a CKD
Uric acid	0.38 mmol/L	0.15-0.45 mmol/L	Normal (excludes gout)
Procalcitonin	0.1 ng/mL	<0.5 ng/mL	Normal (argues against bacterial infection)

Imaging

Image 1: Weight-bearing AP and Lateral Foot Radiographs

Radiological features:

Fragmentation of the tarsometatarsal (Lisfranc) joints
Subluxation at tarsometatarsal articulation
Subchondral sclerosis and bone debris
Joint effusion with soft tissue swelling
Early collapse of medial longitudinal arch
No sequestrum or involucrum (favours Charcot over osteomyelitis)
No gas in soft tissues

Anatomical location: Midfoot (Brodsky Type 1, Sanders/Frykberg Pattern II)

Image 2: MRI Foot with Gadolinium (if obtained)

MRI findings:

Bone marrow oedema in navicular, cuneiforms, and metatarsal bases
Periarticular soft tissue oedema
Joint effusions at Lisfranc joints
No rim-enhancing fluid collection (argues against abscess)
No sinus tract
Subchondral bone changes without cortical destruction pattern typical of osteomyelitis
Ghost sign negative (intact cortex)

Questions & Model Answers

What is the differential diagnosis and how do you distinguish Charcot neuroarthropathy from infection?

Describe the classification systems for Charcot neuroarthropathy.

What is the pathophysiology of Charcot neuroarthropathy?

How would you manage this patient's acute Charcot foot?

The patient presents 2 years later with a rocker-bottom deformity and recurrent plantar ulcer. What are your surgical options?

What is the prognosis and how do you counsel this patient about long-term outcomes?

Key Teaching Points

Pattern Recognition

This pattern suggests Charcot Neuroarthropathy:

Diabetic patient with peripheral neuropathy
Warm, swollen, erythematous foot
Relatively painless (neuropathy)
Intact skin (no ulcer or wound)
Midfoot involvement
Normal or only mildly elevated inflammatory markers
Radiographic fragmentation without sequestrum

Distinguish from Osteomyelitis:

Feature	Charcot	Osteomyelitis
Skin integrity	Usually intact	Usually wound/ulcer
Probe to bone	N/A	Positive
WCC	Normal	Elevated
Procalcitonin	Normal	Elevated
Location	Midfoot most common	Under ulcer

Critical Management Points

Early diagnosis is key - before significant collapse occurs
Offloading is the mainstay - TCC or non-removable walker
Don't confuse with infection - both can have warmth and erythema
Long treatment duration - 6-12 months offloading
Lifelong surveillance - contralateral foot at risk
Surgery for deformity/ulceration - not primary treatment

Common Examiner Follow-ups

Q: "How do you monitor response to treatment?"

Monitoring parameters:

Temperature difference: Should decrease to <2°C
Swelling: Progressive reduction
Serial X-rays: Transition from fragmentation to coalescence
Clinical examination: Resolution of acute signs

Transition to Stage 2 (coalescence) typically takes 3-6 months. This is when gradual weight-bearing can begin.

Q: "What is the evidence for bisphosphonates in Charcot?"

Evidence for bisphosphonates:

Theoretical rationale: Reduce osteoclast activity, prevent bone resorption
Jude et al. (2001): Pamidronate reduced bone turnover markers
Recent trials: Mixed results, no clear clinical benefit demonstrated
Current practice: Not routinely used, consider in refractory cases

The mainstay of treatment remains offloading. Bisphosphonates are not standard of care.

Q: "What if MRI shows changes consistent with both Charcot and osteomyelitis?"

This is challenging - "overlap" cases:

Charcot with secondary osteomyelitis: Can occur if ulcer develops
Ghost sign: Absent bone marrow on T1 with absent cortex suggests osteomyelitis
Sinus tract: Strongly suggests osteomyelitis
Response to offloading: Charcot improves; osteomyelitis progresses

If doubt:

Bone biopsy for culture and histology
Consider tagged WBC scan
Trial of offloading with close monitoring
Multidisciplinary discussion

Q: "How does Charcot affect surgical planning for foot and ankle procedures?"

Considerations:

Higher non-union rate - impaired bone healing
Higher infection rate - diabetic microvasculature
Need for super constructs - extend fixation, use stronger implants
Longer healing times - extended non-weight-bearing
Risk of triggering Charcot - any surgery can trigger acute Charcot in at-risk feet

Prophylactic measures:

Optimise glycaemic control preoperatively
Prolonged non-weight-bearing
Close monitoring post-surgery
Consider protected weight-bearing longer than standard protocols

Diabetic Foot Ulcers
Osteomyelitis
Midfoot Arthrodesis
Peripheral Neuropathy
Total Contact Casting
Diabetic Foot Infections

Charcot Foot