Amputation Levels and Epidemiology

Amputation levels are designated by eponymous procedures and descriptive terms. These are: partial toe (any part of a toe), toe disarticulation (at metatarsophalangeal joint), ray resection (toe and its associated metatarsal), transmetatarsal (at midsection of the metatarsal), tarsometatarsal disarticulation (Lisfranc), midtarsal (Chopart), calcaneotibial arthrodesis (Boyd or Pirigoff amputations depending on surgical approach), and ankle or foot disarticulation (Syme’s resection of distal fibula and medial tibial malleolus to level of inferior tibial articular surface, with distal reattachment of the heel pad). The terms below- and above-knee, though still in use, are more aptly respectively designated as transtibial and transfemoral. Knee and hip disarticulations occur through the respective joints. Hemipelvectomy involves the resection of a lower limb with variable resection of the hemipelvis (hindquarter). Hemicorporectomy is a resection below L4-L5.

In 2005, an estimated 975,000 persons in the United States were living with lower limb loss. Vascular conditions account for most amputations (54%), with two thirds having a secondary diagnosis of diabetes. Over half of dysvascular amputations are major (transfemoral, 25.8%; transtibial, 27.6%), with 42.8% involving more distal levels (partial foot, ray, toes). Most occur in people aged 60 years and older. In the United States, there are approximately 82,000 non-traumatic, diabetes-related lower limb amputations annually. Trauma is the next most common cause (22%), followed by tumors (5%). In children aged 10 to 20 years, neoplasm is the most common cause. Men outnumber women 2.1:1 for disease-related and 7.2:1 for trauma-related limb loss. The global incidence of lower limb loss is estimated at 5.8 to 31 per 100,000 in the total population, with significant variation existing based on regional reporting differences.

Amputation Surgery

Knowledge of surgical approaches permits better assessment of postoperative complications and prognostication of outcomes. In older techniques, resected muscles simply retracted and atrophied, positing problems for prosthetic ambulation and skin integrity. Newer techniques employ myoplastic or osteomyoplastic (myodesis) approaches. Myoplasties involve muscle-to-muscle attachment across fascial layers over the end of a transected bone, preventing unopposed contracture and atrophy, and preserving some muscle action for socket control. They are indicated in dysvascular cases to ensure distal muscle tissue viability. Osteomyoplasties anchor resected muscles at distal ends of long transected bones, improving control over their movement, leading to better socket tolerance and control. At the transtibial level, the anterior distal tibia should be beveled and the fibula should be resected (2 to 2.5 cm) more proximally than the tibia. Relative motion between tibia and fibula (known as “chopsticking”) in a socket may be uncomfortable and injurious. The Ertl osteomyoplasty attempts to control this by creating a tibiofibular synostotic bridge, purported to promote end weight-bearing on the residuum. Attention is paid to closure of osseous intramedullary canals and treatment of neurovascular structures to decrease arteriovenous formations and entrapment of nerve stumps in scar tissue. Aspects of this procedure can be applied, wholly or in part, to other levels. For the patient with little ambulatory potential, a knee disarticulation merits consideration over a transtibial amputation, decreasing long-term risk of knee flexion contractures and skin breakdown. In a patient with good ambulatory potential, a knee disarticulation may also merit consideration over a transfemoral amputation as initial surgery or revision from a lower level. The Mazet procedure involves resection of the distal femoral condyles, partial appropriation of the patella in the intercondylar space, and distal myodesis of the thigh musculature. It preserves distal weight-bearing and a longer lever arm, leading to improved stability and propulsion. Surgical planning for hip disarticulation and hemipelvectomy levels must ensure adequate musculocutaneous coverage of the amputation site for comfortable socket use.

Symptoms

Post-amputation symptoms may include pain, phantom limb sensations, phantom pain, and delayed recurrence of residuum pain. Patients may report uncomfortable socket use, residuum skin breakdown, worsening walking ability, and falls. Surgical site pain is common and should resolve within a few weeks of surgery. Incidence of chronic residuum pain has been reported between 10% and 25%. Several conditions cause residual limb pain including, but not limited to, edema, ischemia, radiculopathy, sympathetic pain, neuromas, osteomyelitis, bone spurs, bony overgrowth, heterotopic ossification, soft-tissue inflammation (stump bursitis), and fluid collections.

Phantom limb sensation is the perception of paresthetic or dysesthetic symptoms (tingling, prickling, numbness, heaviness, formication, itching) in that part of the limb that has been removed. Their frequency and intensity subside in the first year following surgery, aided by stump desensitization and initiation of shrinker and socket use. Patients typically describe intermittent, non-debilitating, phantom sensations thereafter. Some may experience a “telescoping” phenomenon, described as the perception that the extremity (i.e., the foot) is moving closer to the amputation site, occasionally in non-anatomic angles or positions.

Phantom limb pain is a distressingly painful perception in the absent body part. Patients may describe it as cramping, stabbing, burning, or icy cold. The reported incidence varies from 0.5% to 100% owing to differences in study methods and population. Recent studies suggest that up to 85% of people with amputations will experience phantom pain at some time. Newer studies are beginning to implicate the dorsal root ganglion as contributory to the maintenance of phantom limb pain from ectopic action of axotomized primary afferent neurons in this location. Low back or intact lower limb pain may follow a period of ambulation with an inappropriately fitting or aligned prosthesis, stemming from gait deviations.

Physical Examination

A patient’s cognitive ability to safely use and manage a prosthesis (involving hygiene, troubleshooting fit, and device maintenance) must be determined. Upper limb dexterity is examined for ability to independently don/doff and operate the prosthesis; noted impairments may influence the choice of suspension method, prosthesis controls, and of other assistive devices. Both lower limbs must be evaluated for strength, range of motion, deformities, or dynamic instability of joints and skin integrity. Muscle strength graded at least 4/5 is required for safe ambulation. Passive and dynamic malalignments in standing and walking should be assessed for scoliosis or lordosis of the spine, pelvic position (lateral or anterior tilt), and intact limb ankle hyperpronation or pes planus.

Contractures, in either lower limb, result from stiffening changes to periarticular connective tissue structures such as ligaments or from muscle shortening, compromising joint range of motion. Functional contractures result from sustained positioning, when joints are not taken through their full range of motion. For example, knee and hip flexion contractures may result from prolonged habitual sitting. Mechanical contractures result from unopposed muscle action. For instance, the transfemoral amputee may develop hip flexion and abduction contractures from the unopposed action of those firmly attached muscles against the resected and weakened hip adductors and hamstrings. Flexion contractures of up to 20 degrees at the knee (for the transtibial residuum) or hip (at the transfemoral level) can be accommodated in the prosthetic socket alignment; greater contractures make prosthetic fitting more challenging and ambulation less safe. Absence of contractures is related to better success in prosthetic ambulation.

Postoperatively, non-healing incisions are manifestations of ischemia, underlying hematoma, or abscess. Sutures may be removed to facilitate evacuation of an abscess or hematoma. Expressible purulent discharge should prompt imaging evaluation (with an appropriate modality) to assess extent of underlying involvement. Gram stain and culture should only be sent if samples can be acquired under the strictest aseptic technique. Probing of tracts by long-tipped cotton swabs should be avoided, to decrease risk of delivering surface contaminants to deeper tissues, unless performed following thorough cleansing of the wound surface.

In the mature residuum, adherent scar tissue may lead to poor socket tolerance. Residuum skin breakdown in a prosthesis user results from pressure or shear forces. Motion of the residuum against the socket wall or brim causes shear that can separate epidermal and dermal layers, manifesting serous or serosanguinous blisters. Non-blanchable erythema over a bony prominence is a pressure sore until proved otherwise. Sustained increased focal pressure may progress slowly through skin callousing and fissuring, or quickly through deep tissue injury and overlying skin compromise. It is important to examine the prosthetic socket and other components such as liners for corresponding wear and alleviating or offending modifications fashioned by the prosthetist or patient. The prosthesis should not be worn until lesions are healed and appropriate adjustments to the socket have been made.

Bruising of the distal residuum is indicative of poor fit, with increased contact at the bottom of the socket. Conversely, a choke phenomenon may occur whereby proximal constriction prevents the residuum to fully enter the socket, leading to lack of total contact distally. Lack of distal contact, with negative pressure between residuum and socket, leads to impaired venous and/or lymphatic outflow, chronic lymphedema, and subsequent formation of verrucous plaque hyperplasia. The latter carries a risk for secondary ulceration and infection. Verrucous plaques do not require harsh chemical, biochemical, or mechanical débridement, and are reversible when gentle compression (by appropriate shrinker or liner) and total contact with the socket is restored. Skin conditions affecting the residuum can also include, but are not limited to, contact dermatitis (to cleanser, skin product, or prosthetic material), bacterial folliculitis or cellulitis, ingrown hairs, dermatomycosis, and viral infections (molluscum contagiosum).

Residuum pain without signs or symptoms of infection should be evaluated for neuroma (palpation and percussion along the anatomic course of the peripheral nerves). Skin breakdown without congruent pain symptoms should prompt evaluation of the level and quality of sensation in the residual limb (to fine touch, temperature, and deep pressure). Unexpected deformity of bone, firmness with painful or painless palpation of periosseous soft tissues, should all prompt radiographic evaluation for spurs or heterotopic ossification.

Gait evaluation should be performed with the prosthesis and other assistive devices, as necessary, to ensure safety. Observational gait analysis should note deviations during stance, weight transfer, and limb advancement phases for intact and prosthetic limb. Apparent gait deviations should be correlated with physical exam findings and communicated to the prosthetist to help guide modifications, and to the physical therapist for individualized attention to functional gait impairments and balance retraining. History of falls should prompt evaluation of other systems such as vision, balance, other neurologic or musculoskeletal impairments, and of prosthesis malfunction.