Prosthetic Stimulation of Femoral Growth Following Knee Disarticulation
DENNIS S. WEINER, M.D.
For many years it has been a generally accepted premise that pressure across a human joint, most preferably of an intermittent nature, is an essential physiological phenomenon. This pressure is considered necessary not only to allow the proper diffusion of nutrients to enter and to distribute throughout the articular cartilage, but also to stimulate the epiphyseal growth plate to make its appropriate contribution to longitudinal bone growth. Retardation of longitudinal bone growth is almost an inevitable concomitant in limbs deprived of normal forces acting across a joint containing adjacent growth plates. In humans the forces delivered to articular joint surfaces and to epiphyseal growth plates are derived from muscle contraction, gravity, loading, or weight-bearing.
Strobino 4 , Blount 1 , Salter and Field 3 , Gelbke 2 , and Trueta 5 are but a few of the investigators who have shown that continuous strong compression, if applied for a sufficient period of time, will retard and subsequently will totally arrest growth from the epiphyseal growth plate. In this circumstance the cessation of the growth plate's contribution to long-bone growth is probably linked to interference with its vascular supply. It is likely that the growth plate can recover if total closure does not occur and if the pressure is removed. Partial closure commonly will lead to angular and rotational deformities. Conversely, the failure to provide adequate pressure to stimulate epiphyseal growth plates has been studied experimentally in animals and has been observed routinely in human disease states. Paralyzed limbs in children, for example, will routinely be shorter than the opposite normal member and smaller in girth.
A likely explanation for this discrepancy is a lack of normal pressure to stimulate the growth plates, i.e., diminished muscle activity, diminished gravity loads, and sometimes even lack of weight-bearing. A reduction in the amount of blood supplying the epiphyseal growth plates in paralyzed limbs has not been definitely established to date, but certainly appears logical.
It is seemingly paradoxical that we have recently seen in our juvenile amputee clinic three youngsters who have presented with prosthetics problems that we believe are directly related to the stimulation of epiphyseal growth by pressure. Prior to this experience we had assumed that if the child had the opposing portion of a lower-limb joint removed, i.e., disarticulation at the ankle or disarticulation at the knee, the remaining epiphyseal growth plate would still contribute to long-bone growth but not nearly as substantially as the opposite normal limb. Although gravity and weight-bearing loads on the prosthetic side would likely be nearly identical to those on the normal side, there would he little pressure stimulation from actual muscle contraction when the prosthesis was being worn and none at all when the prosthesis was removed. Interestingly all three youngsters, functioning at a knee-disarticulation level, have maintained a femoral segment length on the amputated side equal to that of the opposite side. In one adolescent, epiphysiodesis of the distal femoral epiphysis was performed in an effort to shorten the femur sufficiently to allow better prosthetic fitting with an above-knee-type joint. With multiple-axis knee joints now commercially available, however, raising the knee center by additional surgery does not seem warranted for the knee-disarticulation patient.
C.L., a 12-year-old Caucasian female, had previously undergone a knee disarticulation on the right side at approximately one year of age for a congenital hypoplasia of the right leg, ankle, and foot. Her initial prosthesis was originally fitted when she was approximately 3 months of age, and she had been a consistently proficient wearer. By the age of 12 years she was in a total-contact end-hearing knee-disarticulation prosthesis with rigid outside knee hinges. The length of her right femoral segment was identical to that of the unaffected side and precluded the use of internal, more sophisticated, above-knee prosthetic knee joints. It was decided to proceed with epiphysiodesis of the distal femoral epiphysis in November 1974, in an effort to gain the desired shortening necessary for a change in prosthetic fitting. Previously an attempted conversion to an ischial weight-hearing prosthesis over an 18-month period had, of course, no effect on femoral length.
It is readily apparent, in these children at least, that a sufficient amount of load or pressure was delivered through the prosthesis to the epiphyseal growth plates of the amputated limb so that its femur was clinically equal in length to that of the sound limb. There seems little doubt that, where possible, disarticulations in children are preferable to transections of long bones, particularly as a means of avoiding bony overgrowth. Fortunately, presently available prosthetic hardware and techniques preclude the need for surgical revisions to accommodate the mechanical knee joint, and effective knee-disarticulation prostheses can be applied with only minor cosmetic difficulties.
1. Blount, W.P., and U. R. Clarke, Control of bone growth by epiphyseal stapling. J Bone and Joint Surg, 31-A:464, July 1949.
2. Gelbke, H., The influence of pressure and tension on growing bone in experiments with animals. J Bone and Joint Surg, 33-A:947, October 1951.
3. Salter, R.B., and P. Field, The effects of continuous compression on living articular cartilage. An experimental investigation. J Bone and Joint Surg, 42-A:1:31-49, 76, 90, January 1960.
4. Strobino, L.J., P.C. Colonna, R. L. Brodey, and T. Lëinbach, The effect of compression on the growth of epiphyseal bone. Surg Gyn Obstet, 103:85, July 1956.
5. Trueta, J., Studies on the Development and Decay of the Human Frame. Chapter 16, 118. W. B. Saunders Co., Philadelphia, 1968.