Over 70% of amputees have postamputation pain in the residual limb, which can severely limit function, impair quality of life, and significantly impede rehabilitation. Residual-limb pain should be evaluated and treated aggressively because some causes can be dangerous. Phantom-limb sensation is a desirable, nonpainful sensory abnormality that can improve proprioception and is distinct from phantom pain.
Causes of residual-limb pain include
Postoperative surgical pain
Deep tissue infection (eg, osteomyelitis, vascular graft infection)
Pressure points with or without skin breakdown
Postoperative surgical wound pain typically resolves as tissues heal, typically over 3 to 6 months. Pain continuing beyond that time has numerous causes, including infection, wound dehiscence, arterial insufficiency, hematoma, insufficient muscle padding over cut ends of bone, and a poorly fitting preparatory prosthesis. Treatments are directed at the cause and may also include prosthesis modification, discontinuance of prosthesis use until healing, and analgesics.
Neuropathic pain is common in amputees and is usually described as a shooting or burning pain and typically develops within 7 days of amputation. It can go away on its own but is often chronic. It can be unrelenting and severe, or intermittent. It often is the result of nerve damage from an injury or the severing of nerves during the amputation. Treatment of neuropathic pain is multimodal (eg, psychologic treatments, physical methods, antidepressants, or antiseizure drugs).
Deep tissue infection may be more difficult to diagnose because focal swelling and erythema may not become apparent until pain has been present for some time; systemic manifestations such as fever or tachycardia may appear first and should not be ignored.
Painful neuroma can occur in any severed nerve (from surgery or trauma) and may cause a focal or enlarged area of pain that can be temporarily blocked (as a diagnostic maneuver) by local anesthetic injection. The diagnosis of a neuroma is suggested by history and physical examination. Pain from a neuroma may have neurogenic characteristics such as feeling electrical, shooting, tingling, sharp and stabbing, or prickly. The pain typically does not involve the phantom limb but can. Other symptoms that suggest neuroma include unusual and unpleasant sensations that occur without stimulation or upon contraction of residual-limb muscles and a disagreeable sensation (dysesthesia) that occurs with light palpation of skin. Neurogenic pains that occur while using the prosthesis and disappear quickly or slowly upon removal of the prosthesis suggest a neuroma. The longer the neuroma is irritated, either mechanically by the prosthesis or from muscle contraction, the longer it takes to dissipate. Magnetic resonance imaging and/or ultrasound can be used to confirm the diagnosis of neuroma. In severe cases, surgical neurectomy may be advised.
Patients whose amputation was necessitated by ischemic peripheral vascular disease are at risk for further ischemia, which can be difficult to diagnose but may be suggested by a very low transcutaneous O2 tension (< 20 mm Hg) on the skin of the distal limb.
If there is no medical disorder causing the pain, massaging and light tapping combined with elevating the residual limb may help relieve the pain. If this is ineffective, mild analgesics (eg, nonsteroidal anti-inflammatory drugs [NSAIDs], acetaminophen) can be used. If pain persists, referral to a pain management specialist may be helpful.
Amputees also can experience pain in other limbs, joints, back, and neck due to the compensatory body movements done to make up for the lost function of the amputated part. The prosthetist should regularly evaluate static and kinematic efficiency of the prosthesis and make adjustments as necessary. In addition, regular stretching and strengthening exercises help balance the body and relieve pain. A physical therapist can help design an appropriate exercise program.
Most patients experience phantom pain at some time. The phantom aspect is not the pain, which is real, but the location of the pain—in a limb that has been amputated. The mechanism is believed to involve peripheral and central factors. Onset and duration typically is within days following amputation but could be delayed months to years. Terms used to describe phantom pain include tingling, shooting, stabbing, throbbing, burning, aching, pinching, clamping, and vise-like squeezing.
Phantom pain is often more severe soon after the amputation, then decreases over time. Postsurgical desensitizing therapies are available and recommended to reduce pain during initial weight-bearing in the prosthesis. For many patients, phantom pain is more common when the prosthesis is not being worn, for example, at night. The risk of having this pain is reduced if both a spinal anesthetic and a general anesthetic are used during surgery.
Other nonpharmacologic therapies may be tried to relieve the pain, including transcutaneous electrical nerve stimulation (TENS), acupuncture, and spinal cord stimulation.
Most patients experience phantom sensation, which is the feeling that the amputated part is still present. Phantom sensation must not be misinterpreted as phantom pain. Phantom sensation can be a particular problem with lower limb amputees during nighttime trips to the bathroom. They believe their limb is still there and take a step and fall or injure their residual limb. A protective device can be worn while sleeping to prevent injury.
History and physical examination are often adequate to evaluate residual-limb pain, but sometimes testing is needed.
Pain accompanied by skin changes (eg, erythema, ulceration) suggests skin irritation or infection. Expanding painful and tender erythema suggests cellulitis. In patients with known vascular disease, ulceration may also be due to recurrent ischemia.
Constant pain without skin changes suggests neuropathy, complex regional pain syndrome, deep tissue infection, and in patients with known vascular disease, recurrent ischemia. If the pain increases with compression and/or there are systemic manifestations (eg, malaise, fever, tachycardia), there may be deep infection.
Intermittent pain without skin changes that occurs with use of the prosthesis and resolves with removal suggests fit problems, neuroma, or bone spurs. Dysesthesia and/or a neuropathic quality to the pain suggests neuroma. Intermittent pain unrelated to use of the prosthesis and with no skin changes suggests various underlying possibilities including neuroma, disuse atrophy of muscles with trophic changes in vessels, reduced blood supply, and deep bone ache due to open bone marrow.