Ambulation Of Congenital Bilateral Lower Extremity Amelias And/Or Phocomelias
Cameron B. Hall, M. D.
Although every lower-extremity child amputee presents a problem which is to some degree novel and difficult in regard to prosthesis design, fitting and subsequent ambulatory training, none offer as knotty a complex of challenges as the amputee with congenital bilateral lower extremity amelias or phocomelias.
The complexity of the problem is due in part to the fact that, in most cases, these bilateral lower extremity deficiencies are accompanied by one or more upper extremity anomalies. A further complication is introduced with the frequent occurrence of bizarre muscle structures at the sites of the anomalies.
The Child Amputee Prosthetics Project (CAPP) at the University of California at Los Angeles is providing assistance to seven child amputees with congenital bilateral lower extremity amelias and/or phocomelias. The youngest is eight months old; the oldest, twelve years. Of these patients, only two exhibit normal upper extremities. The remaining five have congenital upper extremity anomalies of varying degrees of severity; there are two bilateral amelias; two bilateral hemimelias, transverse; one unilateral hemimelia, upper left, elbow disarticulation, with upper right synostosis, metacarpals, 4th and 5th.
Although this number represents only 4% of the total active patient population, this small group has provided sufficient data for the initiation of an organized program of research and assistance.
Physical and X-ray examinations revealed a relatively normal lumbo-sacral spine consistent with the patients' chronological age. No gross deficits of iliolumbar musculature have been detected; all patients can sit erect with pelvic stabilization provided by external support in the immature or neuromuscular balance in the more advanced. The major pelvic skeletal defects consist of anomalies of the acetabulum and the proximal femoral focal deficiencies so well discussed by Dr. George T. Aitken and Dr. Richard E. King. These seven cases with fourteen ilio-femoral joints present a surprising display of the various major types described by them; none reveal a normal hip joint.
Accompanying the skeletal aberrations, however, are palpable rudiments of functioning extra-pelvic musculature which allow gross "stump" or extremity movement of sufficient power to permit upright balance and ambulation of sorts. Patterns of motion are bizarre and utilization for prosthesis activation, even where a relatively long extremity is present, often is less than satisfactory. Several of the lower extremities are completely flail; some reveal sufficient voluntary control to stabilize the patient in a standing weight-bearing attitude. None reveal a complete range of voluntary powerful hip joint motion in the quadrants ordinarily considered as normal. All present severe problems of prosthetic stabilization and control.
Orthopedic therapeutic measures have included the use of molded and wedged serial plaster casts in often futile attempts to correct knee flexion contractures and gross hip displacement. The amount of improvement has been minimal -- hope springs eternal, however, and faced with similar contractures in the future, we would probably use plaster again as a preliminary procedure. Surgery for stabilization of proximal femoral focal deficiencies has proven unsatisfactory in our experience and none has been attempted in these particular cases.
As would be expected, the most successful surgical procedure has been a combination of conversion plus knee stabilization. A shortened, two-segment lower extremity, with an anomalous foot can be subjected to knee fusion preserving the distal femoral and proximal tibial epiphyses (see case #165). Ankle disarticulation then converts this resultant long stable segment to an end-bearing, easily-fitted, above-knee amputee.
Pre-existing hip flexion contractures of a severe nature have prevented this procedure in one case (#179). In. another, however, rather severe contractures melted away under the activity of the long lever arm in stubby prostheses and at some future time we may reconsider the application of the procedure to case #179. Terminal humeral overgrowth has required several stump revisions in one case (#57). The construction of musculoskeletal tunnels for socket stabilization, after Dr. J. Warren White's famous case, has been considered but a satisfactory anomaly has not yet been found.
In this program, which is directed toward the goal of adequate ambulation for the bilateral lower extremity amputee, CAPP utilizes the skills of an orthopedist pediatrician, medical social worker, pros-thetists, engineers, physical therapist and occupational therapist. Empirical evidence has indicated that such an interdisciplinary team may best fulfill the demands of the program.
The interdisciplinary effort is initiated with the preliminary investiga tions of the medical social worker. An accurate analysis of the familial situation, plus a successful effort by the social worker in guiding the parents to a realistic acceptance of the problem is of considerable value to the other members of the team in their own planning.
The diagnoses and recommendations of the orthopedist and pediatrician provide the basis for whatever specific plan of treatment the individual case requires. In staff discussions the other team members offer recommendations; the physical therapist, for example, may have observed opportunities for motor activities designed to promote general muscular development and coordination and to prevent contractures and deterioration of vestigial limbs.
The prosthetics staff at CAPP has made use of existing prosthesis designs, and has also modified existing designs as well as developing new ideas which indicated promise. One such novel design was the rocker-base prosthesis. (See Fig. 2 and Fig. 6 )
CAPP prosthetists and engineers, working with the Engineering Department of the University of California at Berkeley, have designed and built prostheses in which were incorporated 1) a socket to hold the body, 2) pylons to elevate the child above the floor, and 3) rockers to serve as a base in the attempt to provide security and movement.
The Rocker-Base Prosthesis
Two pelvic socket designs have been used in conjunction with these rocker bases. The closed pelvic socket encloses the pelvic area, and is designed in such a way as to allow sufficient space for listing to shift the center of gravity for prosthetic control and to provide close contact with areas which must transmit impulses intended to move the prosthesis. Growth factors are a major design problem. In addition, the closed socket, fully enclosing the pelvis as it does, creates a heat problem which can be partially alleviated by as many socket perforations as is ructurally permissible.
The open pelvic socket is essentially a frame on which the child sits and to which the other prosthetic components are attached. Weight is supported through the ischial tuberosities on a saddle-like seat. Mediolateral counter-pressures are provided in that portion of the frame which encircles the anterior haLf of the pelvis. These extensions also serve as points of suspension for the joint system, control straps, and joint stops. The socket, entered from the back, is anchored by a band around the waist.
Theory of the Rocker Design
The rocker used on these prostheses may be compared to the section of the rim of a wheel.
To move the rocker from a position of equilibrium requires an expenditure of energy; to maintain the new position requires a further expenditure.
The radius of curvature of the rocker directly influences the amount of stability the rocker will provide, and also the amount of energy required to move it from its position of equilibrium; i.e., the larger the radius of curvature the shallower the curve of the rocker will be, while at the same time the more energy will be required to move it.
The height of the center of gravity of the child-prosthesis unit depends on 1) the clearance needed for rudimentary limbs, 2) the length of stride required, and 3) cosmetic requirements.
Once the height of the center of gravity has been determined, the rocker must be designed to insure stability by positioning the center of curvature above the center of gravity. How high above the center of gravity the center of curvature is positioned depends on how well the child can control the rocking action of the prosthesis.
The closer the center of gravity is to the center of curvature, the more the rocker will shift position on the floor as a result of a change in the position of the center of gravity; consequently, the greater the change in position of the rocker on the floor, the greater are the demands on the child for voluntary control. But the more voluntary control he can exercise, the less dependent he is on the mechanical characteristics of the prosthesis, and rockers with small radii of curvature help to condition musculature by requiring more musclé control. Thus the radius of curvature of the rocker will be decided by the balance between two factors -- the child's need for mechanical stability and his ability to control the prosthesis.
Stops (elevations placed at the an-terior and posterior edges of the rocker undersurface) are used to establish the range over which the rockers may act, and the placement of these are dependent upon the child's ability to control his prosthesis and maintain satisfactory balance.
Mediolateral Stability and Control
If the rockers are rigidly attached to the socket, the action in using them is as follows: the child shifts his weight laterally on the prosthesis; as he does so, the load on the opposite rocker is reduced or removed. He then uses a pivoting action to bring the unloaded rocker forward. By repeating this action alternately on each rocker, he uses this "tacking" procedure to propel himself forward.
In this effort, energy is expended in 1) the lateral impulse used to unload the rocker to be moved, and 2) the twisting action used to pivot the unloaded rocker against the resistance offered by the floor. These expenditures of energy may be lessened by bringing the lines of action closer together, provided they are not so close as to endanger stability.
Less energy is required when the underside of the rocker is slightly curved on the lateral edge. The rocker thus presents two undersurfaces, one of which serves as a stable base when the wearer stands e-rect, while the incurvated portion facilitates the leaning and pivoting actions.
The Mechanical Hip Joint
The twisting action used to pivot one rocker around the other requires greater energy expenditure than the lateral leaning action. This twisting action can be eliminated by the addition of a joint for flexion and extension. When the unloaded rocker leaves the ground, an elastic strap impels it forward to the new position. As the child shifts weight on this rocker, it propels him forward and the elastic strap is reloaded. By alternately leaning from side to side, he moves forward.
To function successfully, the prosthesis must be stable at the joint in stance phase and the rocker must clear the floor sufficiently in swing phase.
Evaluation of the Rocker-Base Prosthesis
With this prosthesis, the bilateral lower extremity amputee can achieve limited unassisted ambulation. However, as the child grows, and the center of gravity rises accordingly, balance becomes more difficult, then precarious, and the old prosthesis must be redesigned.
Even though a reasonable amount of balance and stability can be achieved on rockers, the rate of progression is so slow that the child experiences considerable frustration and may prefer to revert to movement by pelvic rotation alone.
The great energy expenditure required limits the child to ambulation on a smooth, even surface. Unable to achieve any perceptible amount of vertical lift, the wearer is unable to negotiate any obstacle, even the edge of a rug, the rise of a sill, or irregularities in a floor.
The substitution of SACH feet for rockers provides less ability to move about, but may be preferred for cosmetic reasons.
One CAPP case may serve to illustrate both the advantages and disadvantages of the rocker-base prosthesis. Case No. 57 (D. F.), was referred to CAPP at age 5. The patient, a girl, has congenital bilateral lower extremity amelias and congenital bilateral upper extremity hemimelias, transverse above elbow. Prior to her referral to CAPP, she used only forearm crutches and a pelvic socket on a small wheeled platform.
She was first fitted with Standard Above-Elbow prostheses with Dorrance 10X hooks, and trained in the use of these. At age five years, nine months she was fitted with a lower extremity prosthesis which consisted of a pelvic platform with molded leather socket, short pylons and SACH feet. She adapted very well to these, and soon could ambulate with some degree of independence. However, high energy requirements and limited ambulatory capability has led to its discard. She was provided with a 3-wheeled scooter and two crutches with leather sockets which could be fitted to the upper extremity stumps, and with these devices her mobility was excellent. This appears the most satisfactory device to date and is not materially different than the original bucket and casters!
At age six years, seven months she was fitted with a Canadian hip disarticulation type split socket prosthesis of limited flexibility; i.e., free knee joints, weak hip flexion control straps, and functional solid ankle feet. She experienced considerable difficulty with these: her balance was poor and she could not control the knee joints. Knee locks were inserted and she received intensive training in muscle strengthening and coordination exercises for trunk rotation and pelvis elevation, in addition to gait training.
At seven years, six months she was provided with a closed pelvic socket, fitted without knee joints, with pylons hinged to the anterior surface of the socket in the manner of the Canadian hip disarticulation type, and rockers. A set of interchangeable feet were also supplied for cosmesis. Crutches were provided, and were held by the upper extremity prostheses, but she was soon able to ambulate quite well and did not use them.
At eight years, eight months the child's growth had made a new prosthesis necessary; this one was of the same general design, with only slight modifications. A few months later she received an electric wheelchair with a special ring control which was operated by the right upper extremity prosthesis. At ten years, three months another lower extremity prosthesis, similar to the previous one, was required.
At eleven years, a new socket for the prosthesis was provided, and at the same time she received a specially designed three-wheeled cart which could be pushed about with crutches. This cart consisted essentially of a bucket-type seat mounted on a triangular frame with three casters. The cart and her prosthesis were used interchangeably; the cart provided a greater radius and speed of function, while the prosthesis was employed for cosmesis. At the present time, at age 12, the child continues to employ these devices with good results. (See Fig. 7 )
The three-wheeled cart, as described above, appears to be very satisfactory, at least from the point of view of freedom and speed of movement in open areas. When properly positioned in this cart, the child can propel himself by means of crutches with considerable ease. In it, however, he cannot go up or down steps, and inclined planes are dangerous, since the mechanism, as presently designed, has no braking device; but on a level surface, locomotion is relatively easy, rapid and satisfying to the child.
Modified electric wheel chairs also offer a satisfactory means of locomotion with relatively little expenditure of energy. There are models, commercially available, which have been specially designed and balanced for bilateral lower-extremity amputees. This means of locomotion is being considered for one CAPP patient with congenital bilateral upper extremity amelias and bilateral lower extremity phocomelias. This child displays considerable skill and agility in the use of the one functional lower vestigial limb, suggesting its possible use in operating the control mechanism of a specially designed wheelchair of this type.
The Role of the Therapist
CAPP experience indicates that satisfactory balance and muscle control, prerequisites for successful ambulatory efforts, is best fostered by the integrated planning and assistance of the CAPP therapists, the parents, and whatever trained personnel the child's school may provide. A continuous program of general physical conditioning progress appears to be essential. Instruction and assistance in mastering the control motions required to propel the prosthesis components, and subsequent gait training, can also be accomplished best by such an integrated effort.
The limited success thus far achieved with the rocker-based prosthesis in its various modifications illustrates a basic design problem which has not yet been solved satisfactorily: at best, a child's energy sources are limited, his output small. The severe limitation thus placed on prosthesis design indicates that the most satisfactory solution to the problem of ambulation for bilateral lower extremity amputees may lie in the utilization of outside power sources. Successful upper extremity prostheses have been fabricated in which an outside power source was utilized, and it may be that certain of these principles of operation can be employed for lower extremity prostheses, thus combining the advantages of freedom and rapidity of movement, now provided only by the three-wheeled cart and the power-driven wheelchair, and the cosmesis of presently-employed ambulatory devices.
Cameron Hall is Orthopedic Consultant, Child Amputee Prosthetics Project, School of Medicine, University of California at Los Angeles