11.3 Amputations and prostheses

Amputation, from the Latin amputare (to cut away), can be considered as one of earliest surgical procedures. Initially performed as a punishment, surgical techniques have been improved, mainly pioneered by military surgeons during the great wars, to produce functional stumps to support prosthetic wear and rehabilitation.

Amputation of a limb may be indicated to relieve symptoms (e.g. ischaemic rest pain), to remove a non-viable part of a limb (e.g. gangrene or a crushed limb), to preserve life (e.g. malignant tumour), or to improve function and quality of life (e.g. neuropathic foot or congenital limb deficiency). The commonest cause for amputation in the United Kingdom remains vascular disease (67%), including arteriosclerotic large vessel disease, and diabetic vascular disease. Only 9% of amputations are due to trauma, mainly being performed late after limb reconstruction has failed. Rarer causes include infection (7%), tumours (3%), neuropathic (1%) changes, and congenital limb deficiencies. Upper limb loss is much less frequent with a greater majority being secondary to trauma. The subject of congenital limb deficiency has been considered in Chapter 13.14.

The purpose of amputation is not only to remove the diseased or damaged part of a limb to produce a healed stump, but equally to produce a new end-organ for locomotion (lower limb) or interaction with the environment (upper limb)(Box 11.3.1). Meticulous handling of the soft tissues is important to create a well healed functional stump. Tourniquet should be utilized in all cases except those with peripheral vascular disease.

If gross contamination or major sepsis is present at the time of amputation, a delayed primary closure after 5–10 days is wise. Good perioperative pain control is essential. There is some evidence that epidural anaesthesia and analgesia in the perioperative period may reduce subsequent phantom limb pain.

In general, amputations should be carried out at the most distal level at which healing can be achieved, though there are exceptions. An ideal stump for ‘prosthetic’ use of a lower limb should be of an appropriate length. In general, optimum femoral bone length is approximately 15cm proximal to knee joint level; for transtibial amputation residual bone length may be calculated as 8cm for every metre of height. Preservation of joints is important, though for prosthetic fitting adequate length and ‘clearance distance’, i.e. distance from the end of the amputation stump to the level of the contralateral joint line, is recommended. This is to ensure space to accommodate sophisticated prosthetic units and maintain level joints. Good end-bearing properties of through knee disarticulation, Gritti–Stokes amputation, or a Syme’s amputation may be crucial to maximize function but may present problems of satisfactory appearance of the prostheses. Prostheses for Syme’s amputation and knee disarticulation are cosmetically poor and these amputations should be avoided if ‘cosmesis’ is important.

Fixed contractures in proximal joints compromise alignment and leads to unsatisfactory gait and weight bearing. Excessive contractures may preclude prosthetic use. For patients who are likely to walk or stand to transfer, an attempt should be made to preserve the knee joint. However, if a patient is likely to remain bed- or chair-bound, a through knee disarticulation or Gritti–Stokes amputation may be preferable to ensure satisfactory end bearing and bed mobility.

In the foot, a metatarsal amputation requires a minimum of prosthetic help and produces minimal disability. Hindfoot amputations like Chopart and Lisfranc procedures, tend to result in an equinovarus deformity, are prone to skin breakdown and are difficult to fit with a prostheses that can be worn with a normal shoe. Through hip and hindquarter amputations are fortunately rare, normally as a result of malignant disease or severe trauma. The prosthesis is required to embrace the whole pelvis and mobility remains poor.

In upper limb amputation, especially in the hand, no prostheses can adequately replace an injured hand, and so as much of the hand as possible should be preserved.

The rehabilitation programme should ideally start before the amputation. If the amputation was an elective amputation and an ‘optional’ treatment rather than a ‘necessity’, a pre-amputation consultation with the rehabilitation team is strongly recommended. Success in rehabilitation depends on the input of a multi-disciplinary team.

Physiotherapy should start early and include general mobility in bed, transfers, exercises of the stump and proximal joint, supervision of wound healing, and physical measures to control postoperative oedema. A rigid plaster of Paris dressing provides protection and reduces postoperative oedema, but there are risks of ischaemia and infection and is best avoided in dysvascular amputations, except in specialized units. Lightly elasticated tubular bandages are used followed by use of elasticated and graduated pressure stump shrinkers (e.g. Juzo^™) once wound healing is ensured. Early walking aids (EWAs) allow the patients to stand and walk early with the physiotherapist and assist in control of stump oedema, improve standing and walking and morale. Commonly used types are the pneumatic post amputation mobilty (PPAM) aid (Figure 11.3.2) for the trans-tibial amputation with a maximum pressure of 40mmHg, or a Femurette^™ for a transfemoral amputation (Figure 11.3.3).

Following provision of an appropriate prostheses, gait re-education is essential. It may be particularly complex if the prosthesis prescribed has complex components like hydraulic or microprocessor-controlled prosthetic joints. Rehabilitation should be planned with targeted goals to help the patient achieve maximum potential. Their general medical condition and presence of comorbidity are obvious influencing factors.

Commonly used outcome measures are listed in Box 11.3.4. Less commonly used outcome measures are the Trinity Amputee and Prosthetic Scales (TAPES) and the Prosthetic Profile of the Amputee Questionnaire (PPA).

Laboratory gait analysis is generally reserved for research or complex gait problems.

The most important part of any prosthesis is the socket, as this provides the interface between the residual limb and the prosthesis; if the socket is not comfortable, the most sophisticated prosthetic componentry will be of no benefit. Although leather and aluminium alloy are still used for some sockets, the vast majority are now made either of thermoplastic materials like polypropylene or of laminate plastic construction with glass- or carbon-fibre reinforced acrylic or polyester resin. Considerable forces have to be transmitted through the stump–socket interface of lower-limb amputees—several times body weight during vigorous activities. With the exception of amputations through or very close to joints, amputation stumps will only tolerate slight pressure directly under the distal bone end, so traditionally most sockets have been mainly proximally load-bearing, through the ischial tuberosity in the case of transfemoral, or the patellar tendon in the case of transtibial amputations. Most sockets now are of total-contact type, so that weight-bearing is spread more evenly, although the plaster cast of the stump from which the socket is made is first ‘rectified’, to increase loading in these tolerant areas and to reduce loading over areas such as the distal femur and head of fibula which are intolerant of pressure. Most sockets are worn over a cotton, wool, or polyurethane gel sock, but self-suspending suction sockets are worn next to the skin.

Most lower-limb prostheses used in the United Kingdom are now of endoskeletal construction, in which the socket is linked to the foot by an internal tubular structure of carbon fibre or aluminium, and this together with the joints, if applicable, and devices for adjusting the alignment of the socket and foot, are enclosed in a soft foam cosmetic cover with an outer woven, PVC, or silicone skin. Most, but not all, endoskeletal prostheses are of so-called modular construction, in which the component parts, apart from the socket, are prefabricated and clamped or bonded together, making assembly and subsequent adjustment or repair easier and quicker. In exoskeletal prostheses, the outer visible part of the prosthesis is the structural component.

The majority of upper-limb prostheses are of exoskeletal type. Even though they are much lighter than the natural limb which they replace, almost all prostheses feel heavy to the user, even more so for elderly amputees, so the aim is always to make the prosthesis as light as possible, compatible with strength. However, the extra comfort, stability, or function provided by more sophisticated componentry or socket materials often carries a weight penalty; this is the main disadvantage of electrically powered upper-limb prostheses. Summary of prostheses in Box 11.3.5.

The two standard methods of fashioning a transtibial stump are the long posterior flap method (Figure 11.3.1), or the so-called ‘skew-flap’ technique (Figure 11.3.4). The difference is mainly in the skin flaps, as both employ a long posterior muscle flap, which is basically gastrocnemius, as most of the soleus should be removed distal to the level of bone section to avoid an excessively bulky distal stump. Both methods result in similar healing but the shape of the skew flap generally facilitates early limb fitting.

Most prosthesis for the transtibial amputation are endoskeletal construction and use a rigid plastic socket with cuff suspension and worn over a cotton sock. However, there is increasing use of silicone or gel liners which are worn next to the skin and also provide total contact and self-suspending properties (Figure 11.3.5). The figure describes this type of prostheses and not one with a cuff suspension.

The simplest type of prosthetic foot is the solid-ankle cushioned-heel (SACH) foot. More recently, various energy storage feet with different degrees of flexibility are available to suit different activity levels, including those for running.

The choice of skin flaps is less critical than for transtibial amputation, but usually equal anterior and posterior flaps are used. The anterior and posterior muscle groups are stitched over the cut end of the bone and if vascularity is not impaired, a myodesis is performed by suturing the muscles to holes drilled into the distal femur.

Most sockets (Figure 11.3.6) are ischial bearing or ischial containment, and there is increasing use of total-contact sockets. Distal soft tissue support improves proximal comfort and avoids venous congestion and chronic oedema. The anterior wall of the socket needs to be high to avoid the ischial tuberosity slipping off the posterior seating area.

The prosthetic knee may be a semi-automatic locked knee which locks itself on extension and thus ensures safety in a stiff knee gait. It is unlocked for sitting. Alternatively, an optional lock may be incorporated thus giving the individual the ‘option’ to walk with a locked knee over difficult and uneven terrain. Fitter individuals who can control a free knee require both stance and swing phase control for optimal gait. Stance stability is largely a function of the correct alignment of the prosthesis (the weight line should be slightly in front of the knee axis when the knee is extended), but mechanical ‘stabilized’ knees provide enhanced stability by locking on weight-bearing even in slight flexion (up to about 25 degrees). Polycentric knees provide stance control by ensuring that the knee extends fully (usually into slight hyperextension) even if weight is placed on a slightly flexed (up to 10–15 degrees) knee. Swing-phase control can be in the form of an extension assist spring, by controlled friction, or by means of an adjustable pneumatic or hydraulic damper. An electronically-controlled pneumatic swing phase unit can be used; this measures the swing rate of the knee, and then selects the most appropriate of three preset positions (or an intermediate position) of a needle valve, to provide the optimal setting for different walking speeds. More recently, electronic knee units are available where microprocessor controls are available for both the swing and the stance phase of gait. Heavy-duty hydraulic knees, which provide both stance and swing-phase control in one unit, suit the most active users, but are heavier than other types and most require more effort to drive them. Recently introduced hydraulic knees require less effort and suit a wider range of individuals. Polycentric knees are more compact, and are indicated when clearance above the level of the sound knee is limited. The choice of prosthetic feet is similar to those described for transtibial amputations.

Most upper-limb amputations are due to trauma, and in many cases this will determine the level of amputation and the site of the skin flaps; if there is sufficient healthy skin, equal length flaps on the flexor and extensor aspects are best.

Upper limb prostheses are generally of three types:

Even if the hand is severely injured, it is usually worth preserving as much of it as possible, although this may not apply if the remnant is devoid of sensation or if the wrist is immobile or flail. Even if only one digit remains, provided this has intact sensation, a simple opposition-type prosthesis can be fitted to give useful grip. Such a device would be needed if the thumb alone is lost (Figures 11.3.7 and 11.3.8), unless the index finger is to be pollicized. Loss of a single finger is not usually a great disability, except, for example, for a musician, but a minority do find this psychologically very disturbing and benefit from a silicone finger prosthesis, which can look very realistic. Recently, direct skeletal fixation of prosthetic fingers is being attempted. If all the digits are lost, a wrist-operated prosthesis can be fitted to provide useful grip.

Although a through-wrist amputation has the advantage over a transradial amputation of preserving pronation and supination, it is difficult to provide a prosthesis that is both functional and cosmetically acceptable, and the choice of prosthetic hands is much more limited. The lightest, easiest to operate, and most precise terminal appliance remains the split hook (Figure 11.3.9). This is connected by an operating cord to a loop around the opposite shoulder, and shoulder flexion or elbow extension will open the hook, which is usually closed by elastic bands (the number of bands determining the grip strength and the effort required to open the hook). These devices are described as ‘voluntary opening’; voluntary closing hooks may also be used. Many, but not all, split-hook users also have a readily interchangeable cosmetic hand, which is covered in a PVC or silicone glove. Body-powered hands are heavier, provide less precise grip, and need more effort to open than split hooks, but look more natural. Electric hands provide similar function, with the option of powered wrist rotation, but many amputees reject them on account of their even greater weight. They may be operated by a switch in the prosthetic harness, or myoelectrically using electrodes within the socket which pick up the electrical activity in the flexor and extensor muscles; this has the advantage, if a self-retaining supracondylar socket is used, of obviating the need for any harness or straps. A large variety of special attachments can be fitted to non-powered arms, such as tool holders, and appliances for driving, typing, or golf. Sockets are of rigid or flexible plastic, or leather, which is often favoured by those engaged in heavy work.

Loss of the elbow joint results in a much greater disability, and a more cumbersome and less cosmetic prosthesis, which is more difficult to operate. Therefore the elbow joint should be preserved if at all possible, and it is worthwhile considering skin grafts and free flaps if these would make this possible. Although anaesthetic skin is a considerable disadvantage, because the loads on the skin are much less than with a lower-limb amputation, it presents fewer problems in the upper limb.

A functional prosthesis is not usually helpful for through-shoulder or forequarter amputations. A lightweight cosmetic arm is possible using a hollow, rigid PVC hand, and a foam shoulder cap (extending only just distal to the shoulder) is valuable for the very disfiguring forequarter amputation and allows clothes to hang normally.

Recent developments being trialled include direct skeletal fixation using osseointegration or intraosseous transcutaneous amputation prosthesis for attachment of the prosthesis to the amputation stump.