Low-profile symes foot prosthesis

LOW-PROFILE SYMES FOOT PROSTHESIS

0002Background of the Invention; This invention relates to foot prostheses in gen¬ eral, and specifically to a prosthetic foot adapted for use by persons who have undergone what is known in the art as a Symes amputation. This amputation severs the foot from the leg near the ankle region. Because the Symes patient's calf and shin functions as the patient's stump for prosthetic purposes, any prosthetic device utilized by the patient must either be relatively compact so as to be attachable below the point of amputation, or must be configured to accommo¬ date the patient's shin and calf while attached thereto or higher up on the wearer's leg.

0003Prior art prostheses available to Symes patients typically include an artificial foot bonded or bolted onto the bottom end of a socket worn on the patient's stump. Examples of prior art Sy es-type prostheses include U.S. Pat. No. 3,874,004 to May, which teaches an artificial ankle joint which can pivot in simulation of a natural ankle, and U.S. Pat. No. 4,225,982 to Cochrane, which teaches an elon- gated socket secured to a rubber-filled cavity of a slipper member.

0004Other prosthetic foot devices include U.S. Pat. No. 3,335,428 to Gajdos, which attempts to duplicate the skeletal and skin structure of a natural human foot, U.S. Pat. No. 2,075,583 to Lange, which incorporates a rubber form mounted in operative relationship with a rigid metallic core, and U.S. Pat. No. 4,645,509 to Poggi, which teaches a prosthetic foot incorporating a monolithic keel or beam of relatively massive proportions intended to react to the load of an amputee's body during walking, running, jumping, and the like and to release the resultant stored energy to cre¬ ate foot lift and thrust complementing the amputee's natural stride. These and other prosthetic foot devices, however, have significant deficiencies; for example, the May '004 and the Cochrane '982 patents achieve relatively focused and limited stress response because of their structure and reliance on hardened rubber members for flexure. Moreover, the component parts of the prostheses are too heavy and too rigid, as in Lange, or are too massive and monolithic, as in Poggi, to respond properly to the nuances of stress-response gradients characteristic of the human foot. Certain of these performance deficiencies are overcome in U.S. Letters Patent No. 4,547,913 for my inven¬ tion relating to a "Composite Prosthetic Foot and Leg", United States Letters Patent No. 4,822,363 for my invention relating to a "Modular Composite Prosthetic Foot and Leg", and United States Letters Patent No. 5,037,444 for my inven¬ tion relating to a "Prosthetic Foot". Also, my pending application Serial No. 07/337,374 discloses a prosthetic foot device with similar preferred materials and methods of manufacture, and with corresponding benefits therefrom.

0005Each of my aforementioned inventions is character¬ ized by lightweight, elongated structures incorporating polymer impregnation of superimposed reinforcing laminae or fibers maintained in the desired configuration. Such configurations and constructions provide the desirable characteristics of strength and flexibility in the pros¬ thetic member, and achieve a simulation of the performance of natural feet which had previously not been attainable. Such prostheses may be provided in modular assemblies, whereby the particular performance characteristics of a given prosthesis may be adapted and readily adjusted to meet the needs and activity level of the individual patient.

0006None of my prior inventions, however, is readily utilized by Symes amputees, because of the various con- straints set forth above. Among other things, my prior prosthetic inventions are not configured to accommodate affixation to a Symes-type stump, in that the prostheses are not compact enough to be attachable below the point of ampu- ta ion, nor are they configured to accommodate the patient's shin and calf while attached thereto or higher up on the wearer's leg.

0007Objects and Advantages of the Invention;

0008It is, therefore, an object of my invention to provide a low-profile prosthetic foot suitable for use by Symes amputees, which foot incorporates the desirable lightweight, flexible, energy-absorbing and energy-storing performance of certain of my prior inventions.

0009It is a further object of my invention to provide a prosthetic foot of the aforementioned character which is of modular configuration, resulting in ready assembly and adjustability thereof. The foot of my invention preferably includes forefoot and heel portions that can be readily exchanged with correspondingly-constructed forefoot and heel portions to provide size adjustment or different spring rates to suit the size of foot of the amputee or the stride, height, weight, and activity level of the amputee. There¬ fore, a range of combinations of spring rate and size can be provided to the amputee, achieving a natural stride and resilience of gait, which has not been fully obtainable by prior art prosthetic devices.

0010In addition to bringing important benefits to Symes amputees, my invention may be utilized in connection with pylons by being operatively attached to the lower end thereof, and would thereby be useful to non-Sy es amputees in certain applications.

0011The preferred embodiment of the invention is char- acterized by its low profile, which permits utilization by amputees having very low Symes amputations. Moreover, my invention provides means for adjustability for desired and necessary planarflexion and dorsiflexion of the foot.

0012It is a further object of my invention to provide a low-profile prosthetic foot which is characterized by a forefoot portion incorporating an attachment section and an arch section and a toe section extending forwardly there¬ from, said attachment section being configured to be opera¬ tively positioned, retained and utilized below a wearer's stump; and a heel portion having an attachment section secured to said forefoot portion and a heel section extend¬ ing rearwardly therefrom. In a preferred, embodiment, the heel portion is demountably attached to the forefoot portion to permit heel portions having different spring rates to be secured to said forefoot portion of said foot.

0013An additional object of my invention is to provide a lower leg prosthesis having an attachment means for attaching the prosthesis below a wearer's stump,, in combina¬ tion with an elongated, substantially flat forefoot portion, said forefoot portion including an attachment section for operative alignment and retention of the prosthesis under the wearer's stump, and an arch section and a toe section extending forwardly therefrom.

0014It is a further object of my invention to provide a prosthetic foot of the aforesaid character which is fab¬ ricated from superimposed laminates maintained in operative relationship by an encapsulating polymer and susceptible to bending stress determined by the dimensions of the lami¬ nates, or from chopped fiber maintained in operative relationship by an encapsulating polymer and susceptible to bending stress determined by the cross-section of the respective heel and/or forefoot portions. Yet another object of my invention is the provi¬ sion of a prosthetic foot of the aforementioned character which may be utilized with one or more auxiliary support members to permit fine-tuning of the performance character¬ istics of the foot. Another object of my invention is the provision of a prosthetic foot of the aforementioned character having a forefoot portion of unitary structure which is continuous, integrally and simultaneously formed to provide spring stress generated energy storage, whereby the subjection of said toe section to bending moments will cause uniform transmission of spring stress through said arch and said toe sections to said attachment section.

0015The polymers utilized to encapsulate the fibrous laminae or chopped fiber are characterized by elasticity and flexibility so that the foot prosthesis deflects proportion¬ ally to the engagement of said prosthetic foot with an adja¬ cent surface, causing the resultant energy to be stored and subsequently released when the gait of the amputee incorpo- rating thrust and lift components results in the utilization of the stored energy and a consequent reduction of the energy.expended by the amputee.

0016In order to impart a cosmetic aspect to the pros¬ thetic foot, after proper fitting of the foot to insure that it is properly balanced and of appropriate size, the pros¬ thesis may be encapsulated in a suitably shaped cosmetic shroud. The shroud must be sufficiently flexible so as not to inhibit the free movement and flexure of the foot, but, because of the inherently resilient and stress-absorbing characteristics of said foot, little dependence is needed upon the ancillary cushioning action of the shroud.

0017Consequently, the foot of my invention is charac¬ terized by extreme light weight, instantaneous response to imposed loads and correspondingly instantaneous delivery of stored energy when the gait of the wearer indicates that such stored energy is to be released. The wearer of the foot may engage in a wide variety of activities which were precluded in the past, or in activities in which the wearer's enjoyment was limited, because of the structural limitations and corresponding performance of prior art pros¬ theses. Running, jumping and other activities are sustained by the foot and it may be utilized in substantially the same manner as the normal foot of the wearer. Another object of my invention is to provide a prosthesis of the aforementioned character that may be com¬ pletely or substantially disposed within the patient's shoe, thus providing an optimum cosmetic appearance.

0018An additional object of my invention is the provi- sion of a prosthetic foot of the aforementioned character in which the aforedescribed forefoot and heel portions may be manufactured by various expedients, including injection molding and/or the use of thermoplastic materials and pro¬ cesses, or any of a range of combinations thereof. Other objects and advantages of the invention will be apparent from the following specification and the accom¬ panying drawings, which are for the purpose of illustration only.

0019Brief Description of the Drawings;

0020FIG. 1 is a front elevation view of an alternative embodiment of a prosthesis constructed in accordance with the teachings of the invention;

0021FIG. 2 is a plan view of an alternative embodiment of a prosthesis constructed in accordance with the teachings of the invention;

0022FIG. 3 is a side elevation view, taken along line 3-3 of FIG. 2;

0023FIG. 4 is a side elevation sectional view, taken along line 4-4 of FIG. 2;

0024FIG. 5 is a partially sectional side elevation view of an alternative embodiment of the prosthesis of the invention, similar to the view shown in FIG. 3;

0025FIG. 6 is a side elevation view of yet another embodiment of the invention, similar to the view of FIG. 3;

0026FIG. 7 is a side elevation, partially sectional view of a preferred embodiment of the invention, similar to the view of FIG. 6 but incorporating an arcuate, adjustable attachment structure;

0027FIG. 8 is a sectional view of the prosthesis of FIG. 7, illustrating flexure of the forefoot portion during, for example, ambulation, and further illustrating the adjustment means positioned in a forward position as com¬ pared to FIG. 7;

0028FIG. 9 is a side elevation, partially sectional view of a preferred embodiment of the invention, illustrat- ing its utilization with a socket structure; and

0029FIG. 10 is a side elevation, partially sectional view of another embodiment of the invention, illustrating the use of an auxiliary support or spring means.

0030Description of Preferred Embodiment; The preferred embodiment of my invention is illus¬ trated in FIGS. 7-9, as more fully described herein, but many of the basic fabrication techniques and principles of operation of my invention are similar for the embodiments set forth in FIGS. 1-5. Those fabrication techniques and principles of operation are described in some detail in my co-pending application, Ser. No. 07/585,920, and are briefly reviewed here. Generally, the embodiments of FIGS. 1-5 include a foot prosthesis 10, FIG. 3, which includes a forefoot por¬ tion 12 and a heel portion 14 secured thereto. The forefoot portion 12 preferably includes an attachment section 22, a curvilinear ankle section 24, an arch section 26 and a toe section 28. The heel portion 14 preferably includes an attachment section 32 and a heel section 34 projecting rear- wardly therefrom. The various sections of the forefoot and heel portions, respectively, are preferably formed inte- grally with one another and simultaneously by the incorpora¬ tion of a plurality of laminae 16, FIG. 4, embedded in a hardened, flexible polymer, similar to the fabrication meth¬ ods taught in my above-noted patents.

0031Although the ankle section 24 of the forefoot por- tion 12, as best shown in FIGS. 3-5, is configured to permit juxtaposition thereof to a rearward surface 66 and a lower surface 68 of a socket associated with the wearer's stump, the preferred embodiment of my instant invention, FIGS. 7-9, provides a prosthetic foot with an even lower profile, thereby making it more useable by persons with even lower amputations or providing an alternative to the configura¬ tions of FIGS. 1-5. Moreover, the embodiment of FIGS. 7-9 may be readily adapted for use in connection with a wide variety of other prosthetic devices such as, for example, being mounted on the lower end of a known prosthetic pylon tube (not shown) .

0032Referring to the drawings, and particularly to FIG. 7 thereof, I show a foot prosthesis 100 constructed in accordance with the teachings of the invention and including a forefoot portion 112 and a heel portion 114 secured thereto.

0033The forefoot and heel portions of my invention, as well as the inventions of my above-noted patents, may be manufactured by any of a variety of expedients, including injection molding, resin-impregnation of laminates, the use of thermoplastic or thermoset materials and processes, or any of a range of combinations thereof.

0034Among other things, chopped fiber may be blended in a thermoplastic or thermoset resin and the resulting mix¬ ture injection molded into an appropriate configuration. Alternatively or additionally, thermoplastic laminae may be wound around an injection-molded core, or a thermoplastic resin may be injected between thermoplastic or thermoset laminae, whereby the laminates are bonded onto the injected material.

0035The forefoot portion 112 preferably includes an attachment section 116, and an arch section 118 and a toe section 120 extending forwardly thereof. In order to pro- vide the desired energy transmission characteristics of my invention, these sections are preferably formed integrally and simultaneously with each other, and may include lami¬ nates extending through the entire length of the forefoot portion 112. The forefoot portion (as well as the heel por¬ tion 114) may be tapered or altered in cross-section along its length, in order to modify the energy-storage and release performance of the prosthesis. The fibers or lami¬ nates imbedded in the prosthesis may also be fayed or tapered to assist in or accomplish the same result.

0036The heel portion 114 preferably includes an attachment section 122 and a heel section 124 extending rearwardly therefrom. In the preferred embodiment, the heel portion 114 is demountably attached to the forefoot portion through the use of nut, washer and bolt combinations 126 or similar expedient, although permanent attachment of the heel through the use of epoxy, resin, or simultaneous forming may be utilized with efficacy. Demountable attachment is pre¬ ferred, in that it permits the forefoot portion 112 to be selectably affixed to any of various heel portions 114 hav¬ ing different spring rates.

0037Pad members 128 may be affixed to the underside of the forefoot and heel portions, to create a profile for the bottom of the prosthesis 100 which corresponds to the inte- rior of a shoe. Such a profile orients the foot 100, when the foot is in an unstressed state, at an appropriate angle for wearing shoes.

0038As illustrated in FIGS. 7 and 8, the preferred embodiment of my invention is utilized in connection with an attachment plate member 130. The plate member 130 prefer¬ ably provides a curvilinear contact surface adjacent the attachment section 116, and is adapted to be incorporated into a socket 132, FIG. 9, or otherwise operatively attach- able to a wearer's stump. The aforesaid incorporation into a socket 132 may be achieved through simultaneous formation of the socket 132 and the plate member 130, subsequent lami¬ nation or adhesion therebetween, or other expedient.

0039Further in the preferred embodiment, the attach- ment plate member 130 is operatively attached to the attach¬ ment section 116 through the provision of attachment and adjustment means 134 such as nut, washer and bolt combina¬ tions 136 or similar expedient. The adjustment means 134 further preferably includes mounting slots or holes 138 in the attachment section 116, which are elongated or otherwise of large enough dimension to permit the nut and bolt combi¬ nations 136 to be selectively positioned therein.

0040Those skilled in the art will understand that alternative embodiments of the invention include permanent affixation of the plate member 130 to the attachment section

0041116, or even direct formation or incorporation of the attachment section 116 into the socket 132. They will also understand, however, that the preferred embodiment of FIGS. 7-9 provides a beneficial adjustability and individual customization of the prosthetic foot which would not be achievable in such alternative constructions.

0042Specifically, the aforesaid selective positioning of the nut and bolt combinations 136 in the mounting slots or holes 138 permits rotating attitude adjustment and align¬ ment of the prosthesis to accommodate an individual wearer's needs. The upper surface of the attachment section 116 may be radiused to correspond to the shape of the attachment plate 130 for this same purpose. In prototypes, this curva- ture has been utilized to permit an attitude adjustment of up to eight (8) degrees within a single prototype.

0043As shown in FIG. 8, the preferred assembly permits sliding movement of the plate 130 with respect to the attachment section 116, to and fro in the direction indi- cated by the arrow A. When a desired position is selected, the attachment means 134 may be appropriately tightened to provide frictional, non-sliding contact between the plate 130 and the attachment section 116. The abovedescribed incorporation of the attachment plate member 130 into the socket 132, through lamination or otherwise, is preferably accomplished so that the just- described adjustability of the attachment means 134 is nei- ther precluded nor interfered with. In short, the resulting socket 132 preferably has an outer profile which is config¬ ured to cooperate with its mating upper surface of the attachment section 116 in the manner described above.

0044The prosthesis of my invention further preferably includes cavity means 140 such as one or more cavities 142 correspondingly configured and positioned to receive any projecting portion of the adjustment means 134 during ambulation of said foot. Such ambulation and loaded condi¬ tion of the prosthesis is illustrated in FIG. 8, showing the reception of the nut and bolt means 136 in the cavity 142.

0045This cooperative relationship permits the attachment section 116 to be flexed downwardly, as shown by arrow B, FIG. 8, further than would be possible without the provision of the cavity 142. Such additional degree of flexure provides a corresponding additional degree of energy storage and release and improved performance of the prosthesis.

0046FIG. 6 illustrates an alternative embodiment of my invention. The heel portion 14 and the arch section 26 and oe section 28 of the forefoot portion 12 of FIG. 6 are also substantially the same as those illustrated in FIGS. 1-5. The embodiment of FIG. 6 differs from those of FIGS. 1-5, however, in that an attachment section 70, similar to attachment section 116 of FIGS. 7-9, is formed adjacent to and integrally with the arch section 26; the curvilinear ankle section 24 of FIG. 3 is not present in the embodiment of FIG. 6. Attachment means such as an attachment plate 72 and corresponding screws 74, FIG. 6, are provided adjacent the attachment section 70 to provide affixation to the wearer's socket, similar to socket 132 of FIG. 9.

0047The structure and method of this attachment may include, for example, any of those described in my copending application regarding attachment means 40 of FIGS. 1-4 or socket member 50 of FIG. 5. As indicated in FIG. 6, how- ever, the front edge 76 of the attachment plate 72 is preferably provided with a curvilinear surface to reduce stress concentration in that area during flexure of the prosthesis.

0048As an alternative to the nut and bolt combinations 136 of FIGS. 7-9, in order to maximize the amount of flexure available with the prosthesis of FIG. 6, button-head screws 74 or other low-profile attachment means are preferred. As indicated above, higher profile attachment means have the disadvantage of contacting the heel section 34, FIG. 6, dur- ing heavy loading, thus preventing desired further flexure of the components of the prosthesis.

0049As indicated above, the forefoot and heel portions 112 and 114 are preferably fabricated from superimposed laminates such as laminates 16, FIG. 4, maintained in opera¬ tive relationship by an encapsulating polymer and suscepti¬ ble to bending stress determined by the thickness of the laminates. The preferred materials and fabrication process are more thoroughly described and explained in my above- mentioned U.S. Patent Nos. 4,547,913, 4,822,363, and

00505,037,444 and include laminates such as carbon fibers and/or fiberglass or synthetic fibers such as Kevlar. Exemplary alternative methods and materials are described hereinabove. The construction of the forefoot and heel portions 112 and 114 of my invention thus preferably includes continuous, integrally and simultaneously formed sections 116, 118, and 120, and 122 and 124, respectively. The aforesaid sections are fabricated as unitary structures by polymer impregnation of the aforedescribed superimposed reinforcing laminae. As a result of the materials, design and construction of the prosthetic foot 10, the various sec¬ tions are capable of spring stress generated energy storage whereby the subjection of the prosthetic foot of my inven- tion to bending moments or other stress loading will cause transmission of spring stress through said sections.

0051It will be obvious to those skilled in the art that a virtually infinite variety of forefoot portions 112 and heel portions 114 may be fabricated, each having unique spring stress response characteristics determined by the configuration, composition and amount of the various compo¬ nent materials utilized therein. The aforementioned demountable connection of the heel portion to the forefoot portion therefore permits interchangeability of those por¬ tions to match the weight, stride and activity schedule of the wearer utilizing the prosthetic foot...

0052The foot 100 may be affixed to the wearer by any of several means. As described above, a socket 132 may be affixed directly to the foot 100. Alternatively, a tubular pylon (not shown) may be attached to the foot through the use of epoxy, glue, brackets or the like. For amputees who may utilize tubular pylons, however, a greater degree of energy storage and release may be provided by certain of my other aforementioned inventions.

0053The attachment section 116, when assembled with the attachment means 134, is substantially rigid and capable of sustaining torsional, impact, and other loads impressed thereupon by the wearer during use of the foot 100. In addition, the inherent rigidity of the attachment section prevents it from being distorted in any way and causes the effective transmission of the aforesaid loads imposed there¬ upon between the wearer and the prosthetic foot 100. A cosmetic shroud similar to the shroud 64, FIG.

00545, may be utilized to encapsulate the foot 10, in a manner more fully explained in my previously-described patents.

0055In addition to the foregoing, those skilled in the art will understand that auxiliary support or spring means 144 such as flexure members 146, FIG. 10, may be effica¬ ciously utilized in connection with any embodiment of the abovedescribed invention, without departing from the scope of the teachings hereof. Although a broad variety of aux¬ iliary spring means 144 may be utilized with efficacy, including a range of configurations and sizes and locations on the prosthesis 100, the embodiment of FIG. 10 is illus¬ trative.

0056In FIG. 10, the auxiliary support member 146 is configured similarly to the forefoot portion 112. Nut and bolt combinations 126 and 136, or similar expedient, are utilized to retain the various components in operative alignment. In order to permit the desired flexure of each of members 112 and 146 independently from each other, an oversized opening such as opening 148 is preferably provided in either or both of members 112 and 146. This ensures that, if the members are fixed with respect to each other at a location, for example, such as the attachment section 116, the remainder of the members 112 and 146 may slide with respect to each other when deformation of the prosthesis occurs (during ambulation or the like) .

0057As indicated above, those skilled in the art will understand that the auxiliary support members may be pro¬ vided by a wide variety of configurations, positioned to cooperatively function with the rest of the prosthesis 100. Such auxiliary support members may be attached at various locations and in various manners on the prosthesis 100 with¬ out departing from the scope of the invention.

0058Among other things, these auxiliary support mem- bers permit the energy-storage and -release characteristics of the foot 100 to be refined and fine-tuned. In that regard, the auxiliary support members 146 are preferably constructed from materials, and fabricated by techniques, similar to those from which and by which the other compo- nents of the foot 100 are constructed and fabricated.

0059An important aspect of the polymers and laminates referred. to hereinabove is that they are characterized by needed, but not excessive, flexural deflection under load, which characteristic permits the shock-absorption stress loading of the prosthesis 100 while maintaining sufficient stability to prevent the collapse of the prosthesis while loads are imposed thereupon.

0060To achieve the relatively thin construction of the forefoot and heel portions 12 and 14, the aforesaid polymers are preferably utilized in conjunction with various fibers and/or laminating materials.

0061There is a wide variety of fibrous reinforcements available at the present time, including such inorganic fibers as glass or carbon fibers.

0062The prosthetic foot of my invention can thus be provided in different sizes to correspond to the size of the natural foot of the wearer of the prosthesis 100. When such different sizes are provided, corresponding reduction or increase in the cross-section and/or the number of laminae and thickness of taper, if any, of the respective sections of the forefoot and heel portions 112 and 114 can be made to provide for the proper flexure of said sections.

0063Moreover, and as mentioned above, the flexibility of the prosthetic foot of my invention may be further increased, while still maintaining acceptable strength char¬ acteristics, by providing an auxiliary support member or auxiliary forefoot portion such as auxiliary means 144, FIG. 10. Such an auxiliary member or portion is preferably operatively positioned with respect to the forefoot portion 112 to provide the desired support while permitting some relative movement therebetween, thereby permitting the desired flexure. By such a construction, the same total thickness of supportive material is achieved in an assembly of overly¬ ing, juxtaposed, thin layers, which construction has much more flexibility than does a unitary forefoot portion of the same total material thickness. Such an auxiliary support member can be especially beneficial in the construction of FIG. 6-9.

0064The aforementioned flexure of the foot portions 112 and 114 provides the capacity for increased surface area contact between the bottom surfaces of the foot 100 and the adjacent surface, during both the energy impact and delivery phases of the prosthesis 100. It will be noted that the elongated structure of the portions 112 and 114, together with their aforesaid flexure capabilities, provides for a relatively extended lever arm which achieves stress storage and stress reaction.

0065The preferred method of manufacturing the forefoot and heel portions 112 and 114 of the prosthesis 100 is by a thermosetting molding process including the utilization of molds having properly shaped and sized cavities. The cavi- ties are designed to receive the requisite number of lami¬ nates or fibers and the proper volume of polymer, such that the portions 12 and 14 are respectively unitary structures, with the various sections thereof formed simultaneously within each respective portion.

0066Unlike prior art unitary devices, the fitting of the prosthesis 100 involves the judicious adjustment of the prosthesis by the proper combination of forefoot and heel portions 112 and 114. Only when the proper correlation has been accomplished, can the cosmetic shroud be installed upon the assembled, respective portions of the prosthesis 100.

0067By the prosthesis of my invention I provide-a foot prosthesis which can be carefully matched to the weight, stride and physical characteristics of the wearer. This is accomplished by carefully balancing the respective physical characteristics of the forefoot and heel portions 112 and 114 and. the various sections thereof.

0068Moreover, the assembled prosthesis is far lighter in weight than prior art prostheses since the inherent de- sign and structure of the prosthesis, the materials used and the careful calculation of stress factors of the components of the prosthesis permit fine-tuning of the prosthesis to the needs of the wearer thereof. The prosthesis of my invention has been described with some particularity but the specific designs and con¬ structions disclosed are not to be taken as delimiting of the invention in that various obvious modifications will at once make themselves apparent to those of ordinary skill in the art, all of which will not depart from the essence of the invention and all such changes and modifications are intended to be encompassed within the appended claims.