Examiner expectations from 15 marks crps question in ms orthopaedics theory examination

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CRPS complex regional pain syndrome MS orthopaedics theory exam 15 marks expected answer

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Here is a comprehensive guide to what examiners expect in a 15-mark MS Orthopaedics theory question on CRPS, structured exactly as a model answer would be written.

CRPS - Examiner Expectations for a 15-Mark MS Orthopaedics Answer

What the Examiner Is Looking For

A 15-mark long essay in MS Orthopaedics requires you to cover definition, classification, pathophysiology, clinical features (with stages), diagnostic criteria, investigations, and management - with specific orthopaedic relevance throughout. Each major heading carries marks. Missing any section loses you 2-3 marks. Generic answers without orthopaedic context score poorly.

MODEL ANSWER

1. DEFINITION (1 mark)

Complex Regional Pain Syndrome (CRPS) is a chronic pain disorder resulting from autonomic and pain transmission dysregulation, causing peripheral sensitization with allodynia, dysesthesia, hyperpathia, and reduced pain tolerance in the affected area - disproportionate to any inciting event.

Previously known as: Reflex Sympathetic Dystrophy (RSD), Causalgia, Sudeck's atrophy.

2. CLASSIFICATION - IASP (International Association for the Study of Pain) (2 marks)

Type	Old Name	Defining Feature
CRPS Type I	Reflex Sympathetic Dystrophy (RSD)	No defined nerve injury; after musculoskeletal trauma/insult
CRPS Type II	Causalgia	Fulfills same criteria BUT with identifiable nerve injury
CRPS-NOS	-	Partially meets criteria; no better diagnosis explains it

Further subdivision into:

Sympathetically-Maintained Pain (SMP) - relieved by sympathetic block
Sympathetically-Independent Pain (SIP) - not relieved by sympathetic block
Warm subtype (early/acute) vs Cold subtype (late/chronic)

3. EPIDEMIOLOGY (0.5 marks)

Incidence: ~26 per 100,000 person-years
Female predisposition (F:M = 3-4:1)
Upper extremity most frequently involved
Associated with smoking
Peak age: 40-60 years
Most common triggers in orthopaedics: fractures (Colles' fracture, tibial fractures), crush injuries, TKA/THA, nerve injuries

4. PATHOPHYSIOLOGY (2 marks) - Commonly asked for separate marks

Three overlapping mechanisms:

a) Peripheral Sensitization:

Tissue injury → nociceptor sensitization → lower pain threshold
Inflammatory mediators (substance P, bradykinin, histamine) → neurogenic inflammation

b) Central Sensitization:

Wind-up phenomenon - repeated C-fiber stimulation → NMDA receptor activation → central hypersensitivity
Cortical reorganization/maladaptive neuroplasticity - affected limb representation area in somatosensory cortex shrinks

c) Sympathetically Maintained Pain (SMP):

Abnormal coupling between sympathetic efferents and nociceptive afferents
Catecholamine hypersensitivity (Cannon's law of denervation)
Sympathetic activation → noradrenaline release → activates silent nociceptors → vicious cycle

Additional factors:

Immune dysregulation - elevated cytokines (TNF-α, IL-6)
Genetic susceptibility (HLA-B62, HLA-DQ8)
Psychological contributors - anxiety, PTSD, catastrophizing (but not purely psychological)

5. CLINICAL FEATURES - BONICA'S THREE STAGES (3 marks) - Highest-yield clinical content

Stage	Name	Onset	Symptoms	Duration
Stage 1	Dysfunction	1-3 months	Burning pain beyond dermatomes (follows "thermatomes"), spasm, immobilization tendency, warm/red extremity, hyperhidrosis, allodynia	2-8 weeks
Stage 2	Dystrophy	3-7 months	Vasoconstriction, unilateral cold extremity, hair loss, weakness, tremor, spasticity (flexed arm, extended legs), osteoporosis beginning	2-4 months
Stage 3	Atrophy	>7 months	Irreversible trophic changes - brittle nails, thin glossy skin, muscle atrophy, severe osteoporosis, ankylosis, fixed dystonic posture	Permanent

Cardinal Features (CRPS mnemonic - PASTA):

Pain - burning, constant, disproportionate, non-dermatomal
Autonomic changes - temperature, color, sweating asymmetry
Sensory - allodynia, hyperalgesia, hyperesthesia
Trophic changes - skin, hair, nail changes
Activity/Motor - decreased ROM, weakness, tremor, dystonia

6. DIAGNOSTIC CRITERIA - BUDAPEST CRITERIA (2 marks) - Must know for full marks

(Harden et al., 2010 - validated, currently used clinically)

ALL FOUR criteria must be met:

Continued pain disproportionate to any inciting event
At least one symptom in 3 of 4 categories (clinical) or 4 of 4 (research):
- Sensory: hyperesthesia or allodynia
- Vasomotor: temperature asymmetry, skin color changes or asymmetry
- Sudomotor/Edema: edema, sweating changes or asymmetry
- Motor/Trophic: decreased ROM, motor dysfunction (weakness/tremor/dystonia), trophic changes (hair, nails, skin)
At least one sign at time of examination in 2 or more categories (same four categories as above)
No other diagnosis better explains the signs and symptoms

Key point: Symptoms are what the patient reports; Signs are what the examiner elicits. Both must be present.

7. INVESTIGATIONS (1.5 marks)

Investigations aim to support clinical diagnosis - no single test confirms CRPS.

Investigation	Finding
X-ray	Patchy osteoporosis (Sudeck's atrophy) - late finding
Three-phase bone scan (Tc-99m)	Gold standard imaging - Stage 1: increased uptake all 3 phases; Stage 3: decreased uptake. Sensitivity 60%, Specificity 85%
MRI	Marrow edema, soft tissue swelling; useful to exclude other diagnoses
Thermography	>1°C temperature asymmetry between limbs - supports diagnosis
QST (Quantitative Sensory Testing)	Assesses allodynia and hyperalgesia objectively
Sudomotor tests (QSART, resting sweat output)	Sweating asymmetry
Sympathetic blocks	Diagnostic + therapeutic - if pain relieved: SMP confirmed

8. MANAGEMENT (3 marks) - Orthopaedic exam expects multimodal approach

Principle: Multimodal, Multidisciplinary, with emphasis on FUNCTIONAL RESTORATION

A. Physiotherapy (First line - mandatory):

Desensitization exercises (graded)
Mirror visual feedback therapy - most evidence for central sensitization
Graded Motor Imagery (GMI) - 3 steps: left/right limb recognition → motor imagery → mirror therapy
TENS (Transcutaneous Electrical Nerve Stimulation)
Contrast baths, stress loading programs

B. Pharmacological:

NSAIDs - early inflammation
Anticonvulsants - Gabapentin, Pregabalin (first line for neuropathic pain)
Tricyclic antidepressants - Amitriptyline (neuropathic pain)
Bisphosphonates - Pamidronate, Alendronate - reduce bone turnover, proven benefit in RCTs
Calcitonin - analgesic + antiresorptive
Vitamin C - 500 mg/day perioperatively - reduces CRPS incidence post-Colles fracture
Corticosteroids - short-term in acute warm CRPS
Ketamine infusions - IV; for refractory cases
Free radical scavengers - DMSO (topical), N-acetylcysteine

C. Sympathetic Blocks (Interventional):

Stellate ganglion block - upper extremity
Lumbar sympathetic block - lower extremity
Both diagnostic (confirms SMP) and therapeutic
Intravenous Regional Sympatholysis (Bier's block with guanethidine) - used but evidence debated

D. Spinal Cord Stimulation (SCS):

Best evidence for refractory CRPS
Implanted paddle/lead electrode in epidural space
Reduces pain by ~50% in majority of patients
Current first-choice neuromodulation for CRPS not responding to conservative management

E. Psychological:

CBT (Cognitive Behavioral Therapy)
Pain acceptance therapy
Address catastrophizing, kinesiophobia

F. Surgical (rarely indicated, last resort):

Surgical sympathectomy - chemical or surgical; controversial, short-lived benefit
Spinal cord stimulator implantation
Intrathecal drug delivery (opioids, baclofen for dystonia)

9. PREVENTION IN ORTHOPAEDIC PRACTICE (0.5 marks) - Marks-earning bonus

Vitamin C 500 mg/day for 50 days post-wrist fracture reduces CRPS incidence (Zollinger et al.)
Early mobilization post-fracture/surgery
Avoid unnecessarily tight casts
Early diagnosis and treatment (<6 months - better prognosis)

10. PROGNOSIS (0.5 marks)

Early diagnosis (<6 months) = better outcome
~75% patients improve with treatment
~15% do not improve after 2 years - risk of permanent disability
Warm CRPS responds better than cold CRPS
Central sensitization with cortical changes indicates poorer prognosis

EXAMINER SCORING BREAKDOWN (15 marks)

Section	Expected Marks
Definition + Classification (IASP types I & II)	2
Pathophysiology (3 mechanisms)	2
Clinical features + Bonica's stages (table)	3
Budapest Criteria (all 4 points)	2
Investigations (bone scan + others)	1.5
Management (multimodal - physio, drugs, blocks, SCS)	3
Prevention/Prognosis	0.5-1
Total	~15

EXAMINER'S SPECIAL EXPECTATIONS

Budapest Criteria - not knowing these loses you 2 marks outright. Examiners consider this the "litmus test" of CRPS knowledge.
Bonica's 3 stages - tabular format is expected. Confusing stage 1 and 2 features loses marks.
Mirror therapy / Graded Motor Imagery - frequently expected in management; omitting it signals a shallow answer.
Vitamin C prophylaxis - specific, marks-earning fact after Colles' fracture. Mention Zollinger's RCT.
Sympathetically Maintained Pain vs. Sympathetically Independent Pain - classification within management shows depth.
Spinal Cord Stimulation - for refractory CRPS; examiners look for this as it shows awareness of current practice.
Do NOT confuse CRPS with peripheral nerve injury alone - emphasize the disproportionate, non-dermatomal nature of pain.
Orthopaedic context - mention Colles' fracture, TKA complications, crush injury. Don't write a generic pain medicine answer.

Primary source: Campbell's Operative Orthopaedics 15th Ed 2026, Chapter 67

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