Above-knee amputation in children
R. F. Baumgartner *
Based on a paper presented at the ISPO International Course on Above-knee Prosthetics, Rungsted, November, 1978.
Etiology
Five to 10 per cent of all amputees treated at Balgrist were amputated before the end of growth. In this group, the etiology is very different from that in adults. Arterial occlusion which is the cause of leg amputation in 80-90 per cent of adults is very unusual in children: haemorrhagic infarction due to meningococcal sepsis or anaphylactic reaction to drugs with necrosis of peripheral tissues are fortunately rare.
The major cause of amputation in children is trauma, which accounts for 75-80 per cent of cases. It is 2 1/2 times more frequent in boys than in girls and 3-4 times more frequent in the lower than in the upper limb. The distribution between above-knee and below-knee amputation is about even. There is a uniform age distribution in traumatic amputation in children from 2-16 years. The major causes of traumatic amputation in children are traffic accidents (40%) and agricultural machinery (30%). Railroad and traffic accidents often cause bilateral lower limb amputations.
Ten per cent of children are amputated due to malignancy. Progress in diagnosis however permits a more differentiated treatment, particularly local resection instead of amputation. Amputations due to malignancy are ten times more frequent in the lower than in the upper limb.
Osteomyelitis and tuberculosis used to be one of the major causes of amputation in children before the advent of antibiotics. They have now almost completely disappeared in countries with a high standard of living.
Growth problems
As in any other cortical bone, the proximal and distal epiphyseal growth plates are responsible for growth which takes place mainly at one end of the bone. In the femur, the contribution of the distal growth plate is about 70 per cent whilst only 30 per cent is provided by the proximal plate at the femoral head and the greater trochanter (Blount, 1954). The loss of the distal epiphyseal plate therefore greatly retards the growth in length of the femur. The younger the child at the time of amputation, the greater will be the disproportion between the length of the remaining femur compared with the amputated side. For example, an amputation between the middle and distal third at the age of 2 years will become a very short stump once the patient has reached maturity (Fig. 1 ).
However, a difference in length will also occur even where the distal growth plate can be preserved (Fig. 2 ). As in poliomyelitis, one of the consequences of amputation is a diminished blood supply since there are fewer cells to be served and there is less activity of the muscle tissues. The result is a significant slowing of overall growth not only in length but also in the other two dimensions. Not only the hip joint, but the entire pelvis becomes hypoplastic. This effect is the more marked the higher the level of amputation and the younger the child at the time of amputation. In one case of a bilateral high above-knee amputation at 2 years, the child developed after 13 years a subluxation of both hips which were perfectly normal before amputation (Fig. 3 ).
Stump revision due to overgrowth is unknown in the femur, however the end of the bone can become very sharp because of the lack of growth and it may be necessary to round this edge with a minimum of further shortening.
The question of improving the qualities of the femoral diaphysis by lengthening or enlarging is very delicate. The few bone grafts at the end of the femur seen at Balgrist were all resorbed leaving another scar at the site where the graft was extracted. More modern techniques of intradiaphyseal lengthening using the Wagner (1972) technique are worth considering but have not yet been attempted.
Soft tissue growth is not retarded as much as bone growth. There is, therefore, often an abundance of soft tissue around the hypoplastic femur. This may cause difficulties in fitting with a total contact prosthesis. However, resection of superfluous soft tissues should not be done as a routine since it always causes a further shortening of the stump. With modern prosthetic fitting using a total contact socket, this operation should only be performed in exceptional cases, for example when the skin flaps are in poor condition.
In some cases however, there might be a lack of soft tissues or formation of keloid scars. Plastic surgery with excision of the scar tissues and covering with Z-flaps is indicated. If possible, further skin transplants in children should be avoided. The regenerative power of the soft tissues in children is considerably higher than in adults ; even extended skin defects close spontaneously within a few weeks providing a scar with excellent qualities.
Through-knee amputation
Wherever possible, this level of amputation should be performed in children because the distal growth line of the femur can be preserved. It should be done even if the quality of the soft tissues is poor and the patella has to be removed. Also, this level provides a stump with full end bearing qualities which permits prosthetic fitting without an ischial seat (Fig. 4 ).
The short above-knee stump
The shorter the stump, the more important becomes the disproportion between the remaining muscle groups. In the frontal plane, the abductors between the pelvis and the greater trochanter always remain intact whilst the adductors always have to be partially removed. In the sagittal plane, the same discrepancy occurs between the flexor and extensor muscle groups. The shorter the stump, the more it will assume an abducted and flexed position. The question arises, whether a very short femoral stump is of any use and should not be completely removed. An even more conservative attitude is advocated to children than to adults. Even if the short femur goes into an abducted position of 60° or more, it can be actively moved and is most useful in sitting. In addition, if the soft tissue cover is sufficient, it can be fitted with an above-knee prosthesis instead of the Canadian hip disarticulation prosthesis (Fig. 5 ) which also accelerates the disproportion between the muscle groups of the femur.
Congenital limb deficiencies
At the above-knee level, even grossly deformed stumps from congenital limb deficiency can be superior to an amputation stump with regard to function. There is no scar formation and sensitivity and blood circulation are intact. A phocomelic foot should never be amputated but actively included in a prosthesis. Even if the bone and soft tissues between the pelvis and the foot look poor the stimulation of these tissues when using a prosthesis might give surprising results (Fig. 6 ).
Prosthetic fitting
The basic design of above-knee prostheses for children is not different from adults. Patients are fitted, as a rule, with total contact sockets with partial or full end bearing depending on the stump. End bearing in children is particularly important because it stimulates growth and acts against osteoporosis. It furthermore prevents chronic oedema of the end of the stump which often causes serious troubles in the years to come. In bulbous stumps or congenital deformities the double wall technique referred to in the paper on knee disarticulation is used (Fig. 7 ).
Above-knee Amputation in Children
In small children, a prosthetic knee joint is superfluous. A lockable joint is fitted at the age of about 4-5 to facilitate sitting. A single axis knee is usually fitted when the child enters school. It is sometimes difficult to find components small enough for children. The knee joints available are usually simple hinges and do not offer the comfort of a brake or swing phase control commonly used in adults. While the difficulties in miniaturizing knee joints and the relatively small need for them are realised, perhaps more could be done in this field by the manufacturers of prosthetic components.
Further Reading
Baumgartner, R, (1977). Amputation und Prothesenversorgung beim Kind. Ed. Baumgartner, R. Ferdinand Enke, Stuttgart.
Steinen, W. (1976). Erworbene Amputationen während des Wachstums. Inaugural Dissertation, Zurich.
References:
Blount, W. P. (1954). Fractures in children. William & Wilkins Co., Baltimore.
Wagner, H. (1972). Technik und Indikation der operativen Verkürzung und Verlängerung von Ober-und Unterschenkel. Orthopädie 1, 59-.
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