Prosthesis (i.e. – artificial body members) – parts thereof – or ai – Implantable prosthesis – Bone
Reexamination Certificate
2000-05-31
2001-11-20
McDermott, Corrine (Department: 3738)
Prosthesis (i.e., artificial body members), parts thereof, or ai
Implantable prosthesis
Bone
C623S021110, C623S018110
Reexamination Certificate
active
06319284
ABSTRACT:
FIELD OF THE INVENTION
The present invention is directed to a toe implant. More specifically, the present invention is directed to a double-stemmed toe implant that is used to supplement a first metatarsal phalangeal joint arthroplasty of the great toe.
BACKGROUND
It is well know that some people have problems with one or more joints in their feet. Examples of problems include a rigid or limited range of motion in one or more joints, painful rheumatoid arthritis in one or more joints, deformed bones associated with arthritis, and/or unstable or painful joints from previous surgeries.
Several procedures have been developed to treat these conditions. For example, intra-articular soft tissue procedures, arthrodesis, and Keller arthroplasty have been developed for the first metatarsal phalangeal joint. An intra-articular soft tissue procedure involves reconstructing the joint utilizing soft tissue structures within and around the joint. An arthrodesis procedure involves the fusion of the bones of the joint. A Keller arthroplasty procedure involves the reconstruction of the joint after removal of a portion of the bone from the joint.
Unfortunately, none of these procedures or treatments is completely satisfactory. For example, intra-articular soft tissue procedures are successful for only a limited range of patients. Arthrodesis is effective in eliminating pain but at the expense of joint immobility, load transfer complications, and limited shoe wear options. Keller arthroplasty frequently relieves pain but sometimes results in an unstable toe and loss of toe purchase due to muscle weakness and imbalance.
An alternate solution to the problem includes the use of a double stemmed implant to combat the destructive processes in the joints of the foot. One type of implant
10
P is illustrated in
FIGS. 1A and 1B
. In particular,
FIG. 1A
illustrates the implant
10
P in a relaxed condition, while
FIG. 1B
illustrates the implant
10
P (partly in phantom) positioned in a first metatarsal phalangeal joint
12
P of a great toe
14
P. In
FIG. 1B
, the toe
14
P is flexed. Additionally, the sesamoid apparatus
15
P is illustrated in FIG.
1
B.
The implant
10
P includes a proximal stem
16
P, a distal stem
18
P, a hinge
20
P and a pair of metal grommets
22
P. The proximal stem
16
P is inserted into the metatarsal
24
P while the distal stem
18
P is inserted into the proximal phalanx
26
P. The implant
10
P is designed to flex at the center of the hinge
20
P. The grommets
22
P are positioned on opposite sides to the hinge
20
P. The implant
10
P is sold by Wright Medical Technology, Inc. located in Arlington, Tenn., under the trademark “SWANSON®”.
Unfortunately, the results obtained with the implant
10
P illustrated in
FIGS. 1A and 1B
are not entirely satisfactory. More specifically, the implant
10
P must deform to accommodate the anatomy of the first metatarsal phalangeal joint
12
P. As a result thereof, the implant
10
P limits the range of motion of the joint
12
P, increases the stress at the joint
12
P and/or alters the normal flexing of the toe
14
P.
Further, the deformation of the implant
10
P can cause binding in the joint
12
P. Moreover, referring to
FIG. 1B
, the grommets
22
P can contact during flexing of the toe
14
P.
Furthermore, the cuts to metatarsal
24
P and/or the proximal phalanx
26
P required to make space for the implant
10
P can interfere with the sesamoid apparatus
15
P or the flexor hallucis brevis attachment (not illustrated in FIG.
1
B). This can significantly influence how the toe
14
P functions with the implant
1
OP.
In light of the above, it is an object of the present invention to provide a toe implant for the first metatarsal phalangeal joint for the great toe that provides increased available range of motion. Another object of the present invention is to provide a toe implant that allows the toe to move in a fashion that better simulates the natural motion of the first metatarsal phalangeal joint. Still another object of the present invention is to provide a toe implant that does not significantly increase the stress at the joint or alter the normal flexing of the toe. Yet another object of the present invention is to provide a toe implant that does not interfere with the sesamoid apparatus or the flexor hallucis brevis attachment. Another object is to provide a toe implant that provides relatively good joint mobility, relatively good load transfer, relatively good toe stability, and relatively good toe purchase. Still another object is to provide a toe implant that is relatively easy to insert into the first metatarsal phalangeal joint.
SUMMARY
The present invention is directed to a toe implant that satisfies these objectives. The toe implant is particularly useful as a first metatarsal phalangeal joint between the proximal phalanx and the metatarsal of a great toe. The toe implant includes an implant body having a proximal stem, a distal stem, and a hinge. The hinge is positioned between and connects the proximal stem to the distal stem. The hinge includes a hinge center, a proximal hinge buttress and a distal hinge buttress. The proximal stem extends away from the proximal hinge buttress and the distal stem extends away from the distal hinge buttress.
Uniquely, the implant body is designed to accommodate an axis of motion at an area that is not at the hinge center when toe implant is inserted in the toe. More specifically, the implant body is designed to accommodate an axis of motion near the proximal hinge buttress. With this design, the toe implant maintains the proximal phalanx in the correct anatomic position relative to the metatarsal during bending and flexing and allows the toe to move in a fashion that simulates the natural motion of the first metatarsal phalangeal joint.
The proximal stem includes a proximal axis and the distal stem includes a distal axis. Importantly, the distal axis is offset relative to the proximal axis. More specifically, the distal axis is positioned below the proximal axis. Further, the proximal hinge buttress is axially offset from the distal hinge buttress. With this configuration, the distal stem is better able to match and provide a better anatomic fit in the medullary canal of the proximal phalanx. Additionally, the toe implant is better able to match and maintain the natural position of the proximal phalanx relative to the metatarsal during movement of the toe. As a result thereof, there is less stress created by the toe implant and the toe implant does not alter the normal flexing of the toe.
Additionally, the proximal hinge buttress is preferably at an angle of between approximately forty-five degrees and seventy-five degrees relative to the proximal axis. Further the distal hinge buttress is preferably at an angle of between approximately sixty-five degrees and eighty-five degrees relative to the distal axis. With this design, the cuts required to the metatarsal and the proximal phalanx to make space for the toe implant do not interfere with the sesamoid apparatus or the flexor hallucis brevis attachment. This feature also allows the toe to move in a fashion that simulates the natural motion of the first metatarsal phalangeal joint.
The hinge includes an upper cutout and a lower cutout that allow the implant body to flex through a range of motion through plantar flexure and dorsal flexure of between at least approximately seventy-five degrees and ninety-five degrees. This feature allows the toe implant to provide a relatively good available range of motion in the first metatarsal phalangeal joint, without significantly increasing the stress at the joint or altering the normal flexing of the toe.
Additionally, the hinge can include a strength rib that is positioned in the lower cut-out. The thickness of the strength rib can be varied along the length of the strength rib to influence the bending characteristics of the toe implant. For example, the strength rib can be thicker near the hinge center of the hinge than near the edges of the hinge. With this design, the strength rib adds materi
Lawrence Bruce R.
Rushdy Jamal
Barrett Thomas
Futura Biomedical LLC
McDermott Corrine
Roeder Steven G.
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