# 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 **Clinical Interpretation:** This patient has **superimposed infection on Charcot arthropathy** of the knee: **Evidence for Charcot Arthropathy:** - Type 1 DM with longstanding peripheral neuropathy (loss of protective sensation) - Minimal pain despite severe joint destruction (neuropathic) - Classic radiographic 5 D's: Density, Debris, Destruction, Disorganisation, Dislocation **Evidence for Superimposed Infection:** - Systemic inflammatory response (WCC 18.5, CRP 185) - Low-grade fevers - Positive labelled WBC scan (differentiates from pure Charcot) - Previous metalwork is a nidus for infection **Critical Finding:** BSL 47 mmol/L indicates diabetic ketoacidosis or hyperosmolar state - this is a medical emergency requiring immediate endocrinology involvement and intensive care monitoring. **Key Point:** Minimal pain with destructive arthropathy should always raise suspicion for neuropathic joint (Charcot). > **Consultant Tip:** The triad of diabetes + minimal pain + severe destruction = Charcot. Superimposed infection makes management extremely difficult. **Eichenholtz Classification for Charcot Arthropathy:** | Stage | Name | Clinical Features | Radiographic Features | |-------|------|-------------------|----------------------| | **0** | Prodromal | Warmth, swelling, laxity | Normal X-ray (MRI shows oedema) | | **I** | Development/Fragmentation | Acute inflammation, instability | Fragmentation, debris, subluxation | | **II** | Coalescence | Reduced swelling, improving stability | Absorption of debris, sclerosis | | **III** | Reconstruction/Consolidation | Stable deformity | Fusion, ankylosis, remodelling | **This Patient:** Stage I (Development/Fragmentation) with superimposed infection. **Relevance:** - Stage determines management approach - Surgery in Stage I has high complication rates (active inflammation) - Prefer to operate in Stage II/III when inflammation subsided - Infection changes everything - cannot wait for natural progression > **Consultant Tip:** Eichenholtz staging guides timing of intervention. Surgery in active Charcot (Stage I) has higher failure rates. **Immediate Priorities (First 24 hours):** | Priority | Action | Rationale | |----------|--------|-----------| | 1 | **Endocrinology referral** | BSL 47 = medical emergency (DKA/HHS) | | 2 | **ICU/HDU monitoring** | Fluid resuscitation, insulin infusion | | 3 | **Blood cultures x2** | Before antibiotics | | 4 | **Joint aspiration** | MC&S, cell count, crystals | | 5 | **IV antibiotics** | Broad spectrum after cultures (e.g., flucloxacillin + gentamicin) | | 6 | **Offloading** | Splint knee, non-weight-bearing | | 7 | **Vascular assessment** | Ensure adequate perfusion for healing | **Multidisciplinary Team:** - Endocrinology (glycaemic control) - Infectious diseases (antibiotic management) - Orthopaedic surgery (definitive management) - Vascular surgery (if arteriopathy suspected) - Physiotherapy/rehabilitation - Diabetes nurse educator **Investigations to Add:** - Ankle-brachial index ± arterial duplex - MRI lumbar spine (exclude spinal cause of unilateral neuropathy) - Echo if prolonged fever (endocarditis screening) > **Consultant Tip:** This is NOT primarily an orthopaedic problem initially. Medical stabilisation comes first. **Surgical Options for Infected Charcot Knee:** | Option | Considerations | Challenges | |--------|----------------|------------| | **Staged debridement + antibiotic suppression** | Temporising, may allow medical optimisation | Does not address underlying instability | | **Knee arthrodesis** | Creates stable painless limb | High non-union rate in diabetics (40-60%), infection recurrence, may require multiple procedures | | **Two-stage revision arthroplasty** | Rarely feasible in Charcot | Poor bone stock, high reinfection rate, neuropathy causes wear | | **Above-knee amputation** | Definitive, eliminates infection, predictable rehabilitation | Significant functional loss, psychological impact, short stump risks | **Factors Favouring Amputation:** - Severe bone loss (unable to achieve stable fusion) - Uncontrolled diabetes (poor healing) - Poor nutrition (albumin 25) - Recurrent/persistent infection - Life-threatening sepsis **Factors Favouring Limb Salvage:** - Localised infection - Good vascular supply - Patient preference (if realistic expectations) - Adequate bone stock for fusion **For This Patient:** Given poor diabetic control, previous metalwork infection, extensive bone destruction, and young age, an honest discussion about outcomes is essential. Knee arthrodesis has a high failure rate but preserves the limb. Above-knee amputation may be more predictable. > **Consultant Tip:** All salvage options have significant limitations in young diabetics. Honest counselling about realistic outcomes is essential. **Knee Arthrodesis Technique:** **Preoperative:** - Optimise glycaemic control (HbA1c target <9% ideally) - Complete antibiotic course (6 weeks IV for MRSA osteomyelitis) - Repeat inflammatory markers (CRP trending down) - Nutrition optimisation (albumin >30 g/L) **Surgical Principles:** | Step | Details | |------|---------| | **Exposure** | Anterior approach, remove all previous hardware | | **Debridement** | Radical debridement of infected/necrotic tissue | | **Bone preparation** | Resect to bleeding bone, create flat surfaces | | **Fixation options** | Intramedullary nail (preferred), external fixator, plate fixation | | **Bone grafting** | Consider if significant bone loss | | **Position** | 5-7° valgus, 10-15° flexion, neutral rotation | **Fixation Options Comparison:** | Method | Advantages | Disadvantages | |--------|------------|---------------| | **IM nail** | Load-sharing, early WB | Difficult with short segments, reaming risks | | **External fixator** | No internal implant (lower reinfection) | Pin site problems, patient compliance | | **Plate** | Stable fixation | Load-bearing, not ideal for osteoporotic bone | **Postoperative:** - Protected weight-bearing for 3-6 months - Serial X-rays for fusion assessment - Continue diabetic management - Lifelong surveillance > **Consultant Tip:** Knee fusion in diabetics has 40-60% complication rate. IM nail provides best mechanical environment but requires adequate bone stock. **Counselling Points:** **1. Natural History:** - Without treatment: progressive destruction, persistent infection, risk of sepsis - This is a limb-threatening AND life-threatening condition **2. Realistic Outcomes:** | Option | Success Rate | Functional Outcome | |--------|--------------|-------------------| | Knee fusion | 40-60% union in diabetics | Stiff knee, limp, may require multiple surgeries | | AKA | >90% wound healing | Good prosthetic function, return to walking in 3-6 months | | Non-operative | Ongoing infection, limited mobility | Wheelchair-dependent, risk of systemic sepsis | **3. Lifestyle Modifications:** - Lifelong glycaemic control essential - Smoking cessation mandatory - Regular podiatry/foot surveillance - Protected weight-bearing for extended periods **4. Risks of Limb Salvage:** - High reoperation rate - Non-union requiring revision or amputation - Wound complications - Contralateral limb at risk (bilateral neuropathy) **5. Quality of Life Considerations:** - Young patient (38 years) - long life expectancy - AKA prosthesis allows good functional recovery - Multiple failed surgeries may be worse than early amputation - Patient preferences and social support > **Consultant Tip:** In complex reconstructive cases, shared decision-making with realistic outcome data is essential. Don't promise what you can't deliver. --- ## 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 1. **Medical stabilisation first** - glycaemic control, sepsis management 2. **MDT approach essential** - endocrinology, ID, vascular, orthopaedics 3. **MRI spine for unilateral Charcot** - exclude spinal pathology 4. **All surgical options have high failure rates** - honest counselling 5. **Consider early amputation** - may be most reliable option 6. **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