Phantom Limb Pain and Amputation Pain

Phantom limb pain is pain perceived in the absent limb. It arises from maladaptive cortical reorganisation after limb loss and is distinct from the two other pains of the amputee, residual limb pain and stump neuroma pain. Separating the three allows targeted prevention and treatment rather than generic opioid escalation.

The painful stump neuroma - the peripheral driver that feeds the cortical reorganisation, and the target of TMR and RPNI - has a dedicated page: Neuroma Management. This page is the pain syndrome (central and peripheral); that one is the peripheral lesion itself.

How common. Among major limb amputees:

• Phantom pain - 50-80%
• Residual limb pain - 20-50%, often prosthetic-related
• Stump neuroma pain - 10-25%, focal and surgically treatable
• Telescoping - 30-50% report the phantom limb shortening over time

What it costs. Pain is the leading cause of prosthetic non-use. Chronic pain is strongly associated with depression and anxiety, repeated surgical interventions bring a risk of opioid dependence, and the effect on employment and social function is profound.

Where it arises. Phantom pain has mechanisms at every level from the cut nerve to the cortex, and a psychological one besides:

• Peripheral - ectopic firing from transected nerves and neuromas
• Spinal - central sensitisation and disinhibition in the dorsal horn
• Cortical - reorganisation of the S1 map, with loss of inhibitory control
• Psychological - the memory of pre-amputation pain, and emotional processing

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Cortical reorganisation. After amputation the primary somatosensory cortex reorganises rapidly: the map of the missing limb is invaded by the representations of adjacent body parts, the face and trunk. This maladaptive plasticity generates phantom sensations and pain, and functional imaging shows that the degree of reorganisation correlates directly with phantom pain intensity. Mirror therapy and TMR work by restoring appropriate cortical input, preventing or reversing the change.

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Central sensitisation. In the dorsal horn the activation threshold falls and transmission strengthens while descending inhibition weakens. Once established, the pain persists without any peripheral generator, which is why a technically perfect neuroma excision can leave it unchanged.

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The neuroma. After transection the distal axon undergoes Wallerian degeneration while Schwann cells form Büngner bands to guide regrowth. With no distal target the sprouting axons coil into a tangled mass with ectopic pacemakers, the neuroma, and mechanical provocation of it generates paraesthesia felt distally (the Tinel sign). Both TMR and RPNI are designed to redirect this disorganised regeneration.

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Residual limb pain has local causes: ischaemia, scar tethering and prosthetic pressure, the last from shear forces on the skin, a bony prominence or poor suspension.

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An examiner discriminator the rest of this topic assumes: not every phantom phenomenon is painful. Three things must be separated.

Sub-types of non-painful phantom sensation worth naming in a viva:

• Exteroceptive - touch, temperature, itch or pressure felt in the phantom
• Kinetic - a sense of (often involuntary) movement of the phantom
• Kinaesthetic - the perceived size, shape and posture of the phantom, including telescoping, in which the phantom hand or foot is felt to retract gradually towards the stump. Telescoping is a clinical marker of the cortical reorganisation that also drives phantom pain

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Classification by mechanism directs therapy: cortical for phantom pain, mechanical for residual limb pain, surgical for neuroma pain.

History. Establish the timing (immediate or delayed onset after amputation), the location (the absent limb, the stump or one focal point), the quality (burning, cramping, electric, aching) and the triggers (prosthetic use, weather, emotional stress, pressure). Then ask what has already been tried: mirror therapy and compliance with it, medications, surgery.

Examination. Inspect the stump for healing, skin quality, prosthetic fit and volume, and palpate it for a Tinel sign over a neuroma, a bony prominence and scar tethering. Assess the prosthesis (suspension, alignment, pressure points), the phantom (position sense, telescoping, movement control) and the neurology (allodynia, hyperalgesia, sensory mapping).

Telling the three apart. Ask the patient to point to the exact site of the pain. In phantom limb pain the patient points to the space where the limb used to be, often to cramping or burning in the phantom hand or foot, and stump palpation does not reproduce it. Residual limb pain is felt within the stump tissues themselves, often mechanical and worse with prosthetic donning or weight-bearing, and there may be skin breakdown or ischaemic features.

Stump neuroma pain is highly focal. A positive Tinel sign produces electric paraesthesia in the phantom distribution, and light touch or socket pressure at one point may trigger it.

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Mostly clinical. Imaging is rarely required for diagnosis: most diagnoses are clinical, imaging is adjunctive, and the key is accurate pain mapping by the patient. The first-line work-up is clinical mapping:

1. Pain diagram - the patient draws the pain on a body outline (phantom, stump or focal)
2. Tinel mapping - mark every site that produces phantom paraesthesia
3. Prosthetic review - socket fit, suspension and alignment, by the prosthetist

Ultrasound, if a neuroma is suspected. Focal Tinel-positive pain is the indication. Ultrasound confirms the neuroma's morphology, a hypoechoic mass in continuity with the transected nerve. It confirms the neuroma anatomy when surgical intervention is planned and guides targeted injection or surgical planning.

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Functional MRI, for research or complex cases. It quantifies cortical reorganisation before and after mirror therapy or TMR, showing the lip or face representation shifted into the deafferented limb area. It is a research tool demonstrating the cortical basis of phantom pain rather than a clinical decision-making instrument.

Prevent first. Once phantom pain is established complete resolution is difficult, and late interventions have lower success rates. Always address the three pain syndromes separately rather than treating all post-amputation pain as a single entity.

PreventionEstablished Phantom PainNeuroma and Residual Pain

At the time of amputation the aim is to stop maladaptive cortical reorganisation and neuroma formation becoming established. Early perioperative interventions, particularly TMR and optimised analgesia, significantly reduce incidence.

1. Before surgery - pre-emptive epidural or continuous peripheral nerve block; counsel the patient about the risk of phantom pain and the mirror therapy plan; plan TMR or RPNI at the primary amputation when feasible
2. At surgery (TMR) - identify the major peripheral nerves (median, ulnar, radial, tibial, peroneal) and coapt their ends to motor branches of the residual (target) muscles, which prevents neuroma and provides intuitive prosthetic control signals
3. Days 0-14 - continue regional analgesia for 5-7 days minimum; start mirror therapy on day 1, 15 minutes twice daily; rigid dressing or an immediate post-operative prosthesis

Prevention Pearl

Targeted muscle reinnervation performed at the time of amputation is the single most effective intervention to reduce both phantom pain and neuroma pain. When TMR is not available, continuous regional analgesia for at least 5 days combined with immediate mirror therapy significantly lowers incidence compared with opioid-only regimens.

Where the analgesia evidence stands. The two randomised trials of perioperative analgesia conflict. Nikolajsen 1997 found that pre-emptive epidural blockade did not reduce phantom or stump pain; Karanikolas 2011 found that optimised analgesia started 48 hours before surgery reduced phantom pain at 6 months. The magnitude of prevention remains debated, and the 5-7 day duration commonly quoted is pragmatic, not trial-defined.

The aim is to reverse cortical reorganisation through sensory input and pharmacological modulation. Avoid long-term opioids and use multimodal analgesia.

1. Non-pharmacological - mirror therapy, 15-30 minutes daily; desensitisation by graded tactile stimulation of the stump; graded motor imagery, laterality recognition then imagined movement
2. Pharmacological - gabapentin or pregabalin first line, titrated to effect; duloxetine or amitriptyline second line for the neuropathic component; ketamine infusion for severe refractory pain, and memantine, as adjuncts. Gabapentinoids, SNRIs and membrane stabilisers act by inhibiting ectopic firing
3. Interventional - peripheral nerve stimulation for focal residual or neuroma pain; spinal cord stimulation for selected refractory phantom pain; TMR revision, since even late TMR can reduce established neuroma pain

Mirror therapy is the first-line non-pharmacological treatment. A mirror placed parasagittally between the legs reflects the intact limb into the visual position of the missing one, so the brain 'sees' two normal limbs while the intact limb moves. The restored visual feedback helps reverse maladaptive cortical reorganisation, and randomised evidence supports it (Chan 2007). Desensitisation exploits the same cortical plasticity.

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The aim is to eliminate ectopic neuroma firing and optimise the prosthetic interface.

Reinnervation surgery. TMR or RPNI is used for established neuroma pain. TMR is indicated for established neuroma pain or failed conservative management: the symptomatic neuroma is identified and coapted to a nearby motor branch; published series report 70-80% significant pain reduction, and the transfer also provides intuitive myoelectric signals for advanced prosthetics.

Prosthetic optimisation works on four fronts:

• Volume management - shrinker socks, silicone liners, serial casting
• Socket design - total surface bearing, flexible inner sockets
• Alignment - correct any gait deviation causing shear or pressure
• Skin and scar - silicone or gel liners, antifungal management, scar management

Algorithm

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The first 30 days. The first 30 days after amputation are the critical window for cortical reorganisation. Early intervention within the first month yields the greatest reduction in long-term pain burden, and interventions after the window have diminishing returns.

Prognostic factors. The best prognosis follows TMR at the index amputation, pre-emptive regional analgesia for more than 5 days, immediate mirror therapy, a compliant patient and no chronic pain before the amputation. Delayed presentation beyond 6 months, multiple failed neuroma excisions, opioid dependence, untreated depression and a poor prosthetic fit all predict a poor one.

Both can be performed at the time of amputation (preventive) or later for an established symptomatic neuroma. Both outperform simple traction neurectomy or repeated neuroma excision, which leave the nerve end without a target and tend to recur.

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