CROSS-REFERENCE TO RELATED APPLICATIONS
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This application is a continuation of U.S. patent application Ser. No. 11/995,875, filed on Jul. 23, 2008, which is a 35 U.S.C. §371 application of PCT international application no. PCT/US2006/026837, filed on Jul. 12, 2006, which claims the benefit of, and priority to, U.S. Provisional Patent Application No. 60/701,189, filed on Jul. 20, 2005 and U.S. Provisional Patent Application No. 60/767,440, filed on Mar. 28, 2006, the entire contents of which are incorporated herein by reference.
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OF THE INVENTION
This invention relates generally to improvements in external or exoskeletal prosthetic devices and systems of the type utilizing an implanted, bone anchored mounting post having or carrying an externally protruding or externally exposed fixator structure for removable attachment to a prosthesis such as a prosthetic limb or the like. More particularly, this invention relates to an improved attachment system for coupling the external fixator structure to the prosthesis, wherein the attachment system includes a safety release mechanism adapted to release in response to an excess mechanical load applied to the prosthesis.
Socket type prosthetic limbs such as prosthetic arm and leg structures for use by amputees are generally well known in the art, wherein a prosthesis is constructed with an open-ended and typically padded socket structure for receiving and supporting the post-surgical stump of an amputated limb. By way of example, a socket type prosthetic leg includes such open-ended socket structure at an upper end thereof for receiving and supporting the post-surgical upper leg of a transfemoral amputee. Various straps and/or other fasteners are provided for securing the prosthetic leg to the amputated limb to accommodate walking mobility at least on a limited basis. Such prosthetic limbs can be an important factor in both physical and mental rehabilitation of an amputee.
However, socket type prosthetic limbs are associated with a number of recognized limitations and disadvantages. In particular, the socket style prosthesis inherently couples mechanical loads associated with normal ambulatory activity through a soft tissue interface defined by the soft tissue covering the end or stump of the amputated limb, but wherein this soft tissue interface is structurally unsuited for this purpose. While many different arrangements and configurations for the requisite straps and other fasteners have been proposed for improved transmission and distribution of these mechanical loads to bone structures to achieve an improved secure and stable prosthesis attachment, to correspondingly accommodate a more natural ambulatory movement, such arrangements have achieved only limited success. In addition, compressive loading of the soft stump tissue interface often results in blisters, sores, chafing and other undesirable skin irritation problems which have been addressed primarily by adding soft padding material within the socket structure. But such soft padding material undesirably increases the extent of the soft or non-rigid interface between the amputated limb and prosthesis, all in a manner that is incompatible with an optimally secure and stable prosthesis connection. As a result, particularly in the case of a prosthetic leg, traditional socket style connection structures and methods have generally failed to accommodate a normal walking motion.
In recent years, improved external or exoskeletal prosthetic devices have been proposed, wherein the external prosthesis is structurally linked by means of a bone anchored mounting system directly to patient bone. In such devices, a rigid mounting post is surgically implanted and attached securely to patient bone as by means of osseointegration or the like. This implanted bone anchored mounting post extends from the bone attachment site and includes or is attached to a fixator pin or post structure that protrudes through the overlying soft stump tissue at the end of the amputated limb. Thus, one end of the fixator structure is externally exposed for secure and direct mechanical attachment to a prosthetic limb or the like by means of a rigid linkage.
In such bone anchored mounting systems, mechanical loads on the prosthetic limb during ambulation are thus transmitted by the rigid linkage and through the external fixator structure and implanted mounting post directly to patient bone. As a result, conventional and undesirable mechanical loading of the soft tissue interface is avoided, and substantially improved and/or substantially normal patient movements are accommodated. In addition, the requirement for compressive loading of the soft tissue at the end of the amputated limb is significantly reduced, to correspondingly reduce incidence of blisters and other associated skin irritation problems. Moreover, by mechanically linking and supporting the prosthesis directly from patient bone, amputees have reported a significant increase in perception of the prosthesis as an actual and natural body part—a highly desirable factor referred to as “osseoperception”.
Although use of a bone anchored mounting system offers potentially dramatic improvements in secure and stable prosthetic limb attachment, and corresponding improvements in amputee lifestyle, major complications can arise when the prosthetic structure encounters a mechanical load that exceeds normal design parameters. More particularly, in the event of a tensile, bending, or torsion load exceeding structural design limitations, fracture-failure can occur. Breakage of prosthesis structures such as the implanted bone anchored mounting post often requires repair by surgery. Breakage of the patient bone at or near the interface with the implanted mounting post also requires surgical repair, and reseating or replacement of the implanted mounting post may not be possible. Both of these failure modes represent traumatic and highly undesirable complications.
There exists, therefore, a significant need for further improvements in and to external or exoskeletal prosthetic devices of the type utilizing a bone anchored mounting post, wherein an improved attachment system couples the prosthetic device to an externally protruding fixator structure in a manner accommodating substantially normal patient movement and a corresponding range of normal mechanical loads, but wherein the improved attachment system includes a safety release mechanism adapted to release in response to an excess mechanical load thereby preventing undesirable fracture failures. The present invention fulfills these needs and provides further related advantages.
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OF THE INVENTION
In accordance with the invention, an improved releasable attachment system is provided for use in combination with a bone anchored post and related external prosthesis such as a prosthetic limb or the like adapted for connection thereto. The bone anchored mounting post comprises an implant component adapted for secure and stable affixation to patient bone. This bone anchored mounting post carries or is connected to a fixator structure such as an elongated pin which protrudes through soft skin tissue and the like covering the end or stump of an amputated limb, and is adapted for secure and stable attachment to the external or exoskeletal prosthesis. The improved attachment system incorporates a safety release mechanism designed to accommodate substantially normal patient movement and a corresponding range of substantially normal mechanical loads. However, in the event of an excess mechanical load applied to the prosthetic structures and/or to the implant interface of the mounting post with patient bone, the safety release mechanism is designed to release or break away thereby preventing undesirable fracture failure modes. The safety release mechanism is designed for response to excessive bending, tensile, and/or torsion loads.
In a preferred form, the releasable attachment system is interposed between the prosthesis and the fixator structure, and is adapted for mechanical connection with a radially enlarged mounting flange on the fixator structure. The safety release mechanism includes an upper socket member lined by a plurality of spring-loaded jaw elements for releasable clamp-on, substantially snap-fit engagement with the fixator structure mounting flange. The socket member is coupled by a resilient tension band to a lower release clutch including a plurality of downwardly presented, radially open detent seats having a sawtooth geometry or the like for respectively receiving a plurality of radially projecting detent pins. The tension band normally draws and retains the detent pins securely within the detent seats.
Upon encountering a bending force exceeding a predetermined limit, the tension band accommodates relative movement between the upper socket member and the lower release clutch, while the spring-loaded jaw elements accommodate relative movement between the socket member and the fixator structure mounting flange. When the bending force exceeds a predetermined limit, the jaw elements will accommodate separation of the socket member from the fixator structure. Similarly, upon encountering a tensile force load exceeding a predetermined limit, the tensile band will elongate and/or the spring-loaded jaw elements will displace to accommodate similar relative motions between components of the attachment system. Upon encountering a torsion force load exceeding a predetermined limit, the tensile band will elongate sufficiently to accommodate relative rotational displacement between the detent pins and the detent seats.
In an alternative preferred form of the invention, the attachment system or unit comprises a bending force clutch for adjustably responding to a bending force overload condition, and a torsion force clutch for adjustably responding to a torsion force overload condition. The bending force clutch comprises a relatively large ball-shaped member having a peripheral groove for normally seated reception of an array of spring-loaded clutch balls. This ball member is coupled by means of a universal joint linkage with the torsion force clutch comprising a torque cartridge including spring-loaded detent balls carried within a generally cup-shaped unit housing. The ball member and the unit housing are adapted for connection between the bone anchored fixator structure and the prosthesis. The ball member is designed for angular movement relative to the housing in response to a bending force overload condition, whereas the torque cartridge is designed for rotational movement relative to the housing in response to a torsion force overload condition.
Other features and advantages of the present invention will become apparent from the following more detailed description, taken in connection with the accompanying drawing which illustrate, by way of example, the principals of the present invention.
BRIEF DESCRIPTION OF THE DRAWINGS
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The accompanying drawings illustrate the invention. In such drawings:
FIG. 1 is a somewhat schematic diagram showing the releasable attachment system of the present invention in combination with a bone anchored prosthesis mounting post for use in releasable external attachment to an exoskeletal prosthesis;
FIG. 2 is a somewhat schematic diagram illustrating an amputated upper leg portion of a transfemoral amputee, prior to implanted installation of a bone anchored mounting post;
FIG. 3 is a somewhat schematic diagram similar to FIG. 2, but showing the amputated upper leg portion following implantation of the bone anchored mounting post;
FIG. 4 is a fragmented perspective view showing the lower or stump end of the amputated upper leg portion, and illustrating a fixator structure protruding externally from the amputated limb;
FIG. 5 is a somewhat schematic diagram similar to FIG. 1, but depicting initial release and displacement of the attachment system in response to a bending force overload condition;
FIGS. 6 through 8 are diagrams similar to FIG. 5, and showing successively further release and displacement of the attachment system in response to a bending force overload condition;
FIG. 9 is another schematic diagram similar to FIGS. 1 and 5-8, illustrating initial release and displacement of the attachment system in response to a tensile force overload condition;
FIG. 10 is a somewhat schematic diagram similar to FIGS. 1 and 5-9, and showing initial release and displacement of the attachment system in response to a torsion force overload condition;
FIG. 11 is a perspective view showing the top, front and left sides of a releasable attachment unit constructed in accordance with one alternative preferred form of the invention;
FIG. 12 is a front elevation view of the releasable attachment unit of FIG. 11;
FIG. 13 is a left side elevation view of the releasable attachment unit of FIG. 11;
FIG. 14 is an exploded top perspective view of the releasable attachment unit of FIG. 11;
FIG. 15 is an exploded bottom perspective view of the releasable attachment unit of FIG. 11;
FIG. 16 is an exploded front view of the releasable attachment unit of FIG. 11;
FIG. 17 is an exploded saggital or medial-lateral sectional view of the releasable attachment unit shown in FIG. 16;