Infected Charcot Knee in Type 1 Diabetic
CIM Case: Infected Charcot Knee in Type 1 Diabetic
Clinical Scenario
Patient: 38-year-old man with Type 1 diabetes mellitus Presentation: Progressive right knee swelling and deformity over 3 months, minimal pain despite severe clinical appearance, low-grade fevers Relevant history: Type 1 DM for 25 years, very poor compliance (HbA1c 12%), previous tibial plateau fracture 5 years ago (ORIF), known peripheral neuropathy, visual impairment from retinopathy, no previous ulceration Examination findings:
- Grossly swollen right knee with significant effusion
- Varus deformity with instability in all planes
- Surprisingly minimal pain with manipulation (neuropathic)
- Warm joint with mild erythema
- No draining sinus
- Peripheral neuropathy confirmed (loss of protective sensation - 10g monofilament negative)
- Palpable dorsalis pedis and posterior tibial pulses
- BSL at presentation: 47 mmol/L (severe hyperglycaemia)
Investigations Provided
Laboratory Results
| Test | Result | Normal Range | Interpretation |
|---|---|---|---|
| BSL | 47 mmol/L | 4-8 mmol/L | ↑↑↑ Severe hyperglycaemia |
| HbA1c | 12% | <7% | ↑↑ Very poor diabetic control |
| WCC | 18.5 ×10⁹/L | 4-11 ×10⁹/L | ↑ Leucocytosis |
| CRP | 185 mg/L | <5 mg/L | ↑↑ Markedly elevated |
| ESR | 95 mm/hr | <15 mm/hr | ↑↑ Elevated |
| Creatinine | 145 μmol/L | 60-110 μmol/L | ↑ Diabetic nephropathy |
| Hb | 98 g/L | 130-170 g/L | ↓ Anaemia of chronic disease |
| Albumin | 25 g/L | 35-50 g/L | ↓ Poor nutrition/chronic illness |
Imaging
Image 1: AP and Lateral Radiographs of Right Knee
Radiological features:
- Severe joint destruction with loss of normal architecture
- Previous ORIF hardware (plateau) with significant bone loss around implants
- Dense subchondral sclerosis with fragmentation
- Large joint effusion
- Osteophyte formation with debris
- Subluxation of tibiofemoral joint
- Classic Charcot changes: 5 D's (Density increased, Debris, Destruction, Disorganisation, Dislocation)
Image 2: MRI Right Knee
MRI findings:
- Extensive bone marrow oedema in distal femur and proximal tibia
- Large joint effusion with synovitis
- Complete destruction of articular cartilage
- Soft tissue enhancement concerning for infection
- Difficult to differentiate Charcot from infection (both cause marrow oedema)
Image 3: Labelled WBC Nuclear Scan
Findings:
- Increased uptake in right knee consistent with infection
- Differentiates infection from pure Charcot arthropathy (Charcot alone = bone scan positive but WBC scan negative)
Questions & Model Answers
What is your interpretation of the clinical and investigation findings?
What is the Eichenholtz classification and why is it relevant?
What is your immediate management plan?
The patient is medically stabilised. Cultures grow MRSA. What are the surgical options?
If you proceed with arthrodesis, describe your surgical approach.
What factors would you discuss when counselling this patient?
Key Teaching Points
Pattern Recognition
This pattern suggests Infected Charcot Arthropathy:
- Diabetic with longstanding peripheral neuropathy
- Minimal pain despite severe joint destruction (neuropathic)
- Radiographic 5 D's: Density, Debris, Destruction, Disorganisation, Dislocation
- Superimposed infection evidenced by systemic inflammatory markers and WBC scan
Distinguish Charcot from Septic Arthritis:
| Feature | Charcot | Septic Arthritis |
|---|---|---|
| Pain | Minimal (neuropathic) | Severe |
| Destruction | Progressive over weeks-months | Acute destruction |
| Systemic | May have low-grade inflammation | Usually febrile, unwell |
| WBC scan | Negative (unless infected) | Positive |
Key Point: BSL 47 mmol/L is a medical emergency requiring immediate treatment before any orthopaedic intervention.
Critical Management Points
- Medical stabilisation first - glycaemic control, sepsis management
- MDT approach essential - endocrinology, ID, vascular, orthopaedics
- MRI spine for unilateral Charcot - exclude spinal pathology
- All surgical options have high failure rates - honest counselling
- Consider early amputation - may be most reliable option
- Optimise before surgery - HbA1c, nutrition, vascular status
Common Examiner Follow-ups
Q: "Why would you MRI the spine in unilateral Charcot?"
Unilateral Charcot is unusual - bilateral expected with diabetic peripheral neuropathy. Unilateral involvement suggests:
- Spinal cord lesion (syringomyelia, tumour)
- Lumbosacral plexopathy
- Unilateral nerve root lesion MRI of spine mandatory to exclude these causes.
Q: "What is the difference between Charcot and osteomyelitis on imaging?"
| Feature | Charcot | Osteomyelitis |
|---|---|---|
| Bone scan | Positive | Positive |
| Labelled WBC scan | Negative | Positive |
| MRI marrow oedema | Present | Present |
| Cortical destruction | Subchondral | May be focal |
| Soft tissue abscess | Absent | May be present |
Key: WBC-labelled scan helps differentiate - negative in pure Charcot, positive in infection.
Q: "What are the risk factors for wound complications after surgery in diabetics?"
| Risk Factor | Impact |
|---|---|
| HbA1c >8% | Increased infection, poor healing |
| Albumin <30 g/L | Poor wound healing |
| Peripheral arterial disease | Ischaemia |
| Smoking | Vasoconstriction, poor healing |
| Neuropathy | Unrecognised trauma |
| Immunosuppression | Infection risk |
Related Topics
- Diabetic Foot Disease
- Neuropathic Arthropathy (Charcot Joint)
- Above-Knee Amputation
- Knee Arthrodesis
- Perioperative Diabetic Management