Proximal Femoral Focal Deficiency:
The Patient Friendly Functional Device
Alternatives to Surgery in the Treatment of
Proximal Femoral Focal Deficiency:
The Patient Friendly Functional Device
Mark R. Moseley, C.P., D.C.
This case study and twelve year follow up explore the advantages of using the ankle of certain femorally deficient children to power the lower segment of a modified prosthesis in a below-knee fashion, without the necessity of a rotation plasty procedure.
Though a preliminary fitting of this design was attempted with only one child, clinical observations strongly suggest that this technique will prove useful in the treatment of patients with a variety of P.F.F.D. conditions. Beginning with a discussion of P.F.F.D. classifications and a brief historical overview of treatment options, this presentation will then utilize video recordings to illustrate the following advantages of the P.F.F. Device and unrotated ankle: 1) increased knee stability, due to inherent factors of alignment, 2) vastly improved body awareness, or proprioception, 3) spontaneity of use due to the fact that the unrotated ankle is positionally and functionally analogous to the knee in virtually all aspects of gait, and 4) developmental advantages, both physiologic and psychosocial, concerning the maintenance of intact body image.
Alternatives to Surgery in the Treatment of
Proximal Femoral Focal Deficiency:
The Patient Friendly Functional Device
This paper offers a prosthetic alternative to the Van Ness Rotation Plasty for those children with deficient femurs. The following method allows for the voluntary control of a lower leg prosthetic segment while avoiding a costly, traumatic course of surgeries.
There are at least three major systems for the classification of P.F.F.D. presently in use in the United States. The simplest and most widely used delineates four categories and was developed by George Aitkin, a surgeon from Grand Rapids, Michigan. Another system, by UCLA’s Harlen Amstutz, adds a category and several subclasses. A third system, by Arthur Pappas of the university of Massachusetts, describes nine categories ranging from complete femoral absence (Class One) to a slight hypoplastic femur (Class Nine).
A system’s usefulness often depends on the number of choices it offers. A limited number of diagnoses may suggest a limited number of alternatives. It is important that every child with P.F.F.D. be considered as an individual.[1]
Each child with a deficient femur should therefore be treated on the assumption that he or she is dealing with a unique set of circumstances. It may be obvious that a slight shortening of the femur should not be treated with amputation and knee fusion, but should instead be corrected with a shoe lift or lengthening. What may be less apparent is that a patient with a more severe shortening can use the natural knee and fitted with a BK-type prosthesis whether the foot has been removed or left intact. Though the knee will be high on the affected side, the below-knee function is very desirable and the gait can be extremely good. [2]
The remainder of this paper will focus on those children who will have an ipselateral or effected-side foot that will, upon maturity, reside somewhere near the contralateral knee. These children would currently be treated in one of four of the following ways:
1. No surgery. The prosthesis is designed around the presence of the foot. The advantage is that with the foot intact, its weight-bearing characteristics can be utilized with or without a prosthetic device. A very short femoral segment will probably do best with an above-knee type fitting. The disadvantage is one of cosmesis.[3]
2. Arthrodesis of the knee without removing the foot. The advantages are the same as above, however, the bothersome flexion of the natural knee within the socket of the prosthesis is eliminated. This procedure also adds functional length if the segment is short, and the increased stress at the hip will favor acetabular formation. The disadvantage is limitations to knee joint placement due to increased length, again a matter of cosmesis.[4]
3. Arthrodesis of the knee with removal of the foot. Fitting the patient as an above-knee amputee, this is currently the most commonly used treatment. The advantages are those of a traditional Symes amputation as well as a prosthesis that enjoys both end-bearing and self-suspending potential, and is much easier to fit. The disadvantage lies in a decreased ability to ambulate without a prosthetic device.[5]
4. The Van Ness procedure. First reported in 1950 by C.P. Van Ness, this procedure consists of bisecting the tibia, and fibula if present, and rotating the lower-leg section 180 degrees. The purpose is to more easily disguise the foot within the calf section of a prosthesis. In theory, this surgery should allow an almost BK-type function, enabling the patient to voluntarily control the lower leg section by plantar and dorsiflexion of the ankle, ie: the ankle would serve as a knee. Beyond the obvious physical, emotional and financial costs are numerous functional disadvantages that will be analyzed within the remainder of this paper. One must also remember that, often, repeated surgeries are necessary due to derotation tendencies in the growing child.[6]
Dr. C.P. Van Ness was the first to report on a rotation plasty, or turn plasty, procedure on children with P.F.F.D.. The rotation plasty procedure, however, has a more lengthy history.
In 1930, Dr. J. Borggreve reported a similar procedure on an adult patient with a severe infection of the femur that necessitated the removal of the distal section of that bone. Dr, Borggreve, understanding the limitations of a short, above-knee amputee, decided to make the best of a difficult situation. After removing the infected femur distally, he surgically rotated the lower leg 180 degrees and fixed it to the remaining femur. This left the foot at a level close to that of the contralateral knee, but facing backwards.
This procedure is still used today when a tumor necessitates the removal of a large section of the distal femur. The Van Ness and Borggreve rotation plasty procedures are similar in that they both involve the 180-degree rotation of the foot and lower leg. There are, however, important functional differences.[7]
Hip Stability - A functioning hip and intact abduction mechanism allow for a smooth, narrow, natural-appearing gait, as well as increasing the opportunity for end-weight bearing. Many P.F.F.D. patients, however, do not have sound hips.
Intact Fibula - The patient treated by Dr. Borggreve demonstrated no obvious congenital defects. His ankle was intact and thereby retained its full 35 degrees - 55 degrees of balanced motion. Many P.F.F.D patients are also fibular hemimelias.
Fibular Hemimelia - When the fibula is missing, or hypoplastic, the slight varus obliquity of the ankle is reversed and increased many fold. The ankle will then demonstrate a distinct valgus inclination. In such cases, a balanced ankle motion is more difficult to achieve. [8]
Level of Rotation - The muscles that power the ankle all originate on the proximal tibia of fibula, and most distal aspect of the femur. When the rotation is done through the femur, as in the case reported by Dr. Borggreve, these muscles are left largely intact.[9]
When the rotation is done through the tibia, and or fibula if present, the muscles that power the ankle must be twisted around these bones, jeopardizing the nervous and circulatory systems within, as well as severely decreasing the overall range of motion at the ankle. All too frequently, these children must endure a series of surgical procedures due to the body's tendency to derotate a rotated limb. A seven year-old patient seen at the UCLA clinic underwent four rotation surgeries up to the time of my departure, the first when he was 18 months old.
When derotations do occur they happen slowly, a fraction of a degree at a time. Only a few degrees of aberrant knee rotation is necessary to severely hinder ambulation and the intersocket pressures increase as the rotation continues. Eventually, meaningful knee flexion becomes impossible and the surgery is repeated. [10]
This Device appears much like the Van Ness-type prosthesis, the foot, however retains its anatomical position. Standard components are used and no new materials are needed. The knee joint (BK uprights) are positioned as far as possible to mimic the motion of the ankle/knee joint. A thigh shell or thigh lacer is fitted above the ankle/knee and a foot socket below. Foam, a foot, and a Silesian bandage complete the list of components.[11]
Alignment - The great majority of P.F.F.D. children experience, to some degree, end-bearing within the prosthesis. In normal ambulation, most of the weight is taken on the heel, some 60 % of this being borne at heel strike. Assuming this to be at least partially true for the P.F.F.D. patient, a rotation plasty places the heel, the greatest weight bearing area of the foot, in a position anterior to the mechanical knee joint. Upon contact with the floor, a Van Ness-type prosthesis will tend to break or flex at the knee. Conversely, the non-rotated P.F.F. Device places the heel posterior to the mechanical knee, thereby insuring a stable knee at floor contact. Beyond theory, experience shows this to be true. The Van Ness patients seen at the UCLA clinic all walked on their prosthetic toe, trying to correct for their inherently unstable knee. The child with the P.F.F. Device walks confidently, with an efficient heel-to-toe gait.[12]
Spontaneity - Few would argue against the value of spontaneity in the use of a prosthetic device. Indeed, spontaneity of use may well define a successful prosthetic user. With this in mind, a comparison of the relative motions and positions of the normal ankle and knee during the various cycles of gait argues strongly in favor of the P.F.F. Device. There is a striking similarity of the knee and ankle positions. Starting at heel strike, the foot is plantarflexed as the knee flexes. Then the anterior muscle group dorsiflexes the foot, and the knee extends shortly thereafter. At heel off, the knee flexes and the ankle plantarflexes almost simultaneously.
These are the natural muscular, neuronal, and skeletal patterns during the phases of gait. Knee flexion and extension is positionally equivalent to platarflexion and dorsiflexion respectively, as well as being contemporaneous. These patterns and reflexes are taken full advantage of when using the P.F.F. Device. For example, the unconscious dorsiflexion reflex of the foot at heel strike will spontaneously extend the knee in the device and help to ensure knee stability at heel strike. If the foot is turned 180 degrees, these patterns must necessarily be reversed; neurologic signals to the appendage must also therefore be reversed. This can only be done by conscious effort, and spontaneity will suffer as a consequence.[13]
Cosmesis - All the surgeries for P.F.F.D. mentioned above, with the exception of the knee fusion, are done solely for the sake of cosmesis. The rationale is that, upon plantarflexion, the rotated foot within the prosthesis is easier to conceal beneath a stocking or trouser leg. The Symes amputation is designed to make the residual limb resemble an above-knee amputation, and the rotation plasty strives to imitate a below-knee amputation. It is certainly questionable whether these attempts at cosmetic improvement are equal to the price paid in comfort and function. Finally, a prosthetic device is not worn at all times and the unrotated foot is a far more useful and visually appealing appendage
In order to gain the full range of ankle motion, the foot must be dorsiflexed when the knee is extended. This could mean that upon reaching full growth, the horizontal foot might prove more conspicuous than an amputated or rotated one. If, however, a sacrifice of some range of motion is made by slightly plantarflexing the foot, a more cosmetic situation would occur while still allowing for adequate function. There may be other ways of ameliorating the cosmetic difficulties. For example, when casting the P.F.F. Device, it is possible to position the foot and lower leg more posteriorly. This would accomplish three things:
1. it divides the length of the foot, half in front of the contralateral knee and half behind;
2. it increases slightly the downward slant of the foot, providing easier concealment within the confines of a pant leg;
* and, when the foot is moved posteriorly, the mechanical knee must likewise move posteriorly. This has the effect of further increasing the inherent stability of the knee.
It is of interest to note that in a twelve-year follow-up with the patient fitted with the P.F.F. Device, the leg on the affected side attained only 2/3s the growth of its partner, making the cosmetic issue essentially mute.
All conclusions, hypotheses and predictions were based on observation of a single child over a one-year period. The child is now fifteen and has enjoyed thirteen years of uninterrupted use. As a front-page story in the Southern California Orange County Register on Aug. 4, 1999 will attest, Rob is strong, confident, and a star basketball player. He has exceeded the expectations of his family and friends, and intends to seek a career in professional basketball, all of this despite the absence of an articulated hip joint.
Note from PFFDvsg Webmaster: see Rob's story at www.oandp.com/private/usa/ca/perform/valor.htm
Note from PFFDvsg Webmaster: For more information contact:
Dr. Mark Moseley
PERFORMANCE PROSTHETICS
AND ORTHOTIC SPECIALISTS
2820 Santa Monica Blvd.
Santa Monica, CA 90404
(310) 829-2322
www.oandp.com/private/usa/ca/perform/index.htm
E-mail Dr. Moseley at mosewin@aol.com
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