FRCA Notes

Post-Amputation Pain Syndromes

Phantom limb pain appeared as an SAQ in 2019 (53% pass rate), with examiners "surprised at the lack of knowledge" on elements such as clinical features or management.

It re-emerged as a CRQ in 2022 (47% pass rate), where candidates struggled with the practical aspects of pain management including drug classes used in its management.

Resources

  • In the UK the commonest indications for lower limb amputation are peripheral arterial disease and diabetes
  • Other indications include trauma, malignancy and CRPS

  • Approximately 3500 major lower limb amputations are performed annually in the UK; most patients are >65yrs, smokers or ex-smokers, and diabetic
    • 30-day mortality is 8.4% for transfemoral and 4.4% for transtibial amputation
  • Pain control is frequently poor: NCEPOD found only 23% of patients reported good pain control pre-operatively and 38% post-operatively
  • Amputation carries one of the highest rates of chronic post-surgical pain of any surgery, involving peripheral, spinal and cortical neuroplastic mechanisms

Acute stump pain

  • Immediate, largely nociceptive pain localised to the site of amputation, reflecting the tissue trauma of stump formation
  • Typically a constant aching, throbbing pain with erythema and oedema; may also have neuropathic features
  • Usually resolves within 14-21 days, but persists in approximately 10%

Chronic residual limb (stump) pain

  • Pain felt in the remaining part of the limb, often with an identifiable anatomical cause on careful examination
  • Commonly coexists with phantom limb pain
  • Causes include:
    • Surgical complications: infection, wound breakdown, osteomyelitis, haematoma; consider DVT at any time
    • Neuroma: occurs in up to 15%; tender on palpation with a positive Tinel sign, and a diagnostic local anaesthetic block proximal to it can help confirm
    • Prosthesis-related: poor fit causing corns, blisters, cysts or pressure ulcers; inadequate soft tissue padding over bone; bursitis
    • Bony: terminal bone overgrowth (spurs), heterotopic ossification (after traumatic amputation), fractures from disuse osteopenia
    • Primary pathology: ongoing ischaemia, tumour recurrence, painful diabetic neuropathy
    • Referred pain: from proximal joints or nerve root compression
    • CRPS: type 2 if a neuroma is present

Phantom limb sensation

  • Non-painful sensations (tactile, proprioceptive or kinaesthetic) perceived to originate from the absent limb
  • Near-universal early after amputation and rarely affects quality of life or function
  • It is important to distinguish sensation from pain to avoid unnecessary treatment, although the two may exist on a continuum

Phantom limb pain

  • Painful sensations perceived in the missing limb, which are intrusive and significantly affect quality of life and function

  • Reported prevalence ranges from 30-85%; more recent prospective studies suggest a lower incidence
    • At least 5-10% of amputees report severe phantom limb pain
    • Onset is usually within days of surgery; once established, intensity often remains constant for years

  • Usually projected to the distal parts of the missing limb e.g. foot or toes
  • Predominantly neuropathic descriptors: burning, stabbing, pricking
  • Nociceptive descriptors such as squeezing or crushing are also common
  • Episodes last seconds to hours, or may be continuous

Other

  • Chronic back pain and proximal joint pain due to altered gait biomechanics with a prosthesis; this is under-recognised

Diagnosis of chronic pain after amputation (ICD-11)

All of the following criteria must be fulfilled
Chronic pain (persistent or recurrent for >3 months)
Pain began or increased in intensity after the amputation
Pain is of higher intensity or has different characteristics compared with any pre-operative pain
Pain is located in the area of the amputation or referred into the amputated limb
Pain is not better explained by infection, malignancy, a pre-existing pain condition or another cause


  • Development and maintenance of chronic pain after amputation is multifactorial: biological, psychological, social and genetic
  • Understanding the mechanisms helps target treatment at the peripheral, spinal or cortical level

Peripheral mechanisms

  • Nerve transection causes tissue injury, inflammation and disruption of normal afferent input (deafferentation)
  • Neuromas form from uncontrolled axonal sprouting when proximal nerve ends cannot reconnect with their distal targets
  • Neuromas have increased sodium channel density and inflammatory mediators, giving reduced activation thresholds
    • This produces hyperexcitability and spontaneous ectopic discharges
    • May manifest as residual limb pain, phantom limb sensation or phantom limb pain
  • There may also be spontaneous discharge in the DRG and coupling to the sympathetic nervous system
  • Targets: local anaesthetics, NSAIDs, capsaicin and injection therapies

Spinal cord mechanisms

  • Central sensitisation in the dorsal horn:
    • Increased neuronal activity and spontaneous firing
    • Lower firing thresholds
    • Expansion of the neuronal receptive field

  • 'Wind-up': increased NMDA-receptor activity driven by substance P, tachykinins and neurokinins alters the firing pattern of central nociceptive neurones
  • Spinal disinhibition:
    • Reduced efficacy of GABAergic and glycinergic transmission
    • Loss of descending inhibitory control and local intersegmental inhibition
  • Targets: NMDA antagonists, gabapentinoids, antidepressants, opioids and neuromodulation

Central (brain) mechanisms

  1. Cortical reorganisation
    • The most cited mechanism for phantom sensation and phantom limb pain
    • Cortical areas representing the amputated limb are taken over by adjacent zones in the primary somatosensory and motor cortex
    • Functional imaging shows a correlation between the degree of reorganisation and phantom limb pain
    • Thalamic reorganisation also occurs; thalamic stimulation can evoke phantom sensations
    • More recent longitudinal imaging studies have challenged cortical reorganisation as the underlying mechanism

  2. Disturbance of the neuromatrix/neurosignature
    • Amputation eliminates input into a network of neurones integrating somatosensory, limbic, visual and thalamocortical information ('the neuromatrix')
    • This distorts the central representation of the self ('the neurosignature') and generates a phantom sensation
  • Targets: pharmacological agents, neuromodulation, graded motor imagery/mirror therapy and psychological therapies

Genetic

  • Single-nucleotide polymorphisms in GCH1 and KCNS1 may be associated with chronic pain after amputation


Risk factors for chronic pain after amputation
Pre-amputation pain, especially if severe or of long duration
Severe acute or subacute post-operative pain
Pre-operative anxiety and depression
High pre-operative opioid use
Lower limb and more proximal amputation
Residual limb pain and phantom limb sensations
Bilateral amputation or repeated limb surgery

Prevention

  • Identifying high-risk patients allows early referral to the chronic (or transitional) pain team
  • Reducing post-operative pain intensity is the most useful modifiable target
  • Regional techniques and pre-emptive neuromodulatory drugs reduce acute pain and opioid requirements
  • Careful surgical nerve handling aims to reduce symptomatic neuroma formation (see intra-operative)

  • No method has reliably been shown to reduce the incidence or severity of chronic pain after amputation

Assessment

  • Detailed history and examination to establish the type of pain and exclude differential diagnoses
  • Examine the residual limb carefully; check prosthesis fit, alignment and gait
  • Look for secondary sources of pain e.g. back pain, proximal joint pain

General principles

  • Interdisciplinary management: surgical, chronic pain and specialist prosthetic/rehabilitation teams
  • Pharmacological options remain the mainstay, although the evidence base is limited
  • Non-invasive options are preferred over invasive ones given risk, cost and availability
  • Physical and psychological therapies should be considered at all stages

  • Residual limb pain: identify and treat the source
    • Prosthetic modification to offload painful areas is often effective
    • Surgical refashioning if this fails
  • Phantom limb pain: managed as neuropathic pain; treatment options are more limited
    • Improving coexistent residual limb pain often improves phantom limb pain

Pharmacological


Drug class Examples and notes
Tricyclic antidepressants Usually first choice for neuropathic pain but limited by side-effects
SNRIs Duloxetine
Gabapentinoids Limited by dizziness, sedation and dependence
Sodium channel blocking anticonvulsants For refractory neuropathic pain
Opioids For mixed nociceptive/neuropathic pain, within safe long-term prescribing principles
NMDA antagonists For refractory pain
Sodium channel blockers (systemic) Lidocaine infusion or mexiletine for refractory pain
α2-agonists Clonidine
Non-opioid analgesics Paracetamol, NSAIDs
Cannabinoids Nabilone; unlicensed, monitored use only
Topical agents Capsaicin 8% patch or lidocaine 5% plaster

  • Salmon calcitonin (200IU SC daily) has mixed evidence for established phantom limb pain and no evidence for prevention

Injections and interventional

  • Steroid and myofascial trigger point injections: short-term benefit
  • Botulinum toxin A: reduces muscle spasm (intramuscular) and neurogenic inflammation (intradermal)
  • Neuroma-targeted:
    • Pulsed radiofrequency (DRG or peripheral); limited evidence but safer than neurodestructive options
    • Cryotherapy
    • Chemical or thermal neurolysis; risk of further nerve injury and neuritis

Neuromodulation

  • TENS: low-risk and easily available
  • Spinal cord and DRG stimulation: limited evidence, invasive, specialist centres only
  • Transcranial magnetic stimulation, motor cortex and deep brain stimulation: research tools or rarely offered

Surgical

  • Neuroma excision, targeted muscle reinnervation (TMR) or regenerative peripheral nerve interface (RPNI); recurrence is possible, especially after simple excision
  • Refashioning of the residual limb for bony overgrowth or inadequate soft tissue padding; high complication risk

Physical and psychological therapies

  • Graded motor imagery and mirror therapy: considered an essential part of rehabilitation with some evidence of effectiveness; require active participation
  • Immersive virtual reality
  • Biofeedback and multimodal sensory training
  • CBT and EMDR
  • Pain management programme

Rehabilitation

  • The goal is return to pre-amputation function; prosthetic ambulation is not achievable for all, particularly older, comorbid patients
  • Pain is a major barrier to prosthetic use; long-term follow-up with prosthetic rehabilitation and chronic pain teams is often needed

Perioperative Analgesic Management for Amputation Surgery


Assessment and optimisation

  • Pre-existing pain (ischaemia, infection, gangrene) is common; optimise the current regimen, usually including opioids and neuropathic agents
  • Document pre-operative opioid use (dose, preparation, duration, effectiveness) to plan post-operative analgesia
    • High pre-operative opioid use should trigger early, aggressive post-operative pain management
  • Identify patients at high risk of chronic pain

MDT involvement

  • Early acute pain team involvement
  • Early chronic pain team referral if long-term pre-existing pain; transitional pain services may bridge acute and chronic care
  • Pre-amputation counselling and education; consider referral to the prosthetics and amputee rehabilitation centre for elective cases
  • Address fear, anxiety, depression and distress

Pre-emptive analgesia

  • Pre-emptive epidural analgesia started 72hrs before surgery reduced phantom limb pain in the landmark Bach et al. (1988) study
  • These long-term benefits have not been reliably reproduced, and pre-emptive epidural use is now rare
  • Ultrasound-guided perineural catheters may be sited by the anaesthetist before surgery

Regional anaesthesia

  • Single-shot nerve blocks: sciatic ± femoral, with long-acting local anaesthetic or liposomal bupivacaine
    • Comparable, time-limited analgesia without catheter-related risks
  • Perineural catheters (sciatic for transfemoral, tibial for transtibial):

Anaesthetist-placed (proximal) Surgeon-placed (distal)
Ultrasound-guided, before surgery Under direct vision before neurectomy, threaded 10-20cm cranially
Analgesia from the start of surgery Higher success rate and less dislodgement
Theoretically wider nerve coverage; femoral catheter can be added Preferred by most UK vascular centres
Pre-operative sciatic catheter has not been shown to be superior to a surgically placed catheter

  • Epidural analgesia: consider for bilateral amputation or to deliver neuraxial adjuvants (opioids, clonidine); limited by anticoagulation

Systemic multimodal analgesia

  • Paracetamol and NSAID unless contraindicated
    • NSAIDs may reduce heterotopic ossification after traumatic amputation
    • Use cautiously in the elderly with renal, cardiovascular or GI disease
  • Opioids
  • ± Ketamine: bolus up to 0.35mg/kg, infusion up to 1mg/kg/hr; may be continued post-operatively
  • ± Lidocaine: 1.5mg/kg bolus, infusion up to 1.5mg/kg/hr
    • Consider cumulative local anaesthetic toxicity if regional techniques are also used
  • ± Magnesium
  • Neuropathic agents if neuropathic features

  • These adjuvants are opioid-sparing but may not reduce chronic pain

Surgical considerations

  • Traction neurectomy: nerves isolated and sharply divided under caudal tension so they retract cranially
    • Keeps the nerve end away from scar tissue and the prosthetic socket, reducing symptomatic neuroma formation
    • Applies to sensory nerves (e.g. saphenous) as well as major nerves
    • Sciatic nerve ligation is not encouraged
  • Bevel the cut ends of bone and avoid tension in myocutaneous flaps
  • Advanced nerve techniques:
    • Target deficient: burying the nerve end in muscle, bone or fascia
    • Target reassignment: TMR (coaptation to a distal motor nerve) or RPNI (implantation into a free muscle graft)
    • NICE recommends TMR only as a secondary procedure for established pain, not prophylactically

Analgesia

  • Regular paracetamol ± NSAID
  • Continue regional local anaesthetic infusion via catheter (electronic or elastomeric pump), ideally for 72hrs
  • IV PCA: morphine, or fentanyl/oxycodone depending on comorbidities such as renal dysfunction
    • Convert to oral immediate-release opioids as soon as feasible, with discharge advice on tapering
    • Opioid-tolerant patients need their baseline opioid plus supplemental analgesia; aim to return to the baseline regimen
  • ± Ketamine infusion
  • Lidocaine infusions only in monitored areas e.g. PACU or HDU
  • Neuropathic agents (amitriptyline, duloxetine) if neuropathic features
  • TENS reduces analgesic consumption

Worsening pain

  • Consider infection (purulent discharge, wound dehiscence), haematoma, wound breakdown and DVT
  • Infection is more common with diabetes, vascular disease and poor nutrition

MDT reviews

  • Acute pain service, with early chronic pain team referral if high risk
  • Psychological support
  • Therapy services and prosthetic rehabilitation