WO2002065942A2

WO2002065942A2 - Ankle-foot orthosis with plantarflexor torque assistance

Info

Publication number: WO2002065942A2
Application number: PCT/US2002/004298
Authority: WO
Inventors: Elizabeth T. Hsiao-Wecksler; Casey Kerrigan
Original assignee: Boston University; Spaulding Rehabilitation Hospital Corp
Current assignee: Boston University; Spaulding Rehabilitation Hospital Corp
Priority date: 2001-02-15
Filing date: 2002-02-14
Publication date: 2002-08-29
Anticipated expiration: 2003-08-15
Also published as: AU2002245432A1; WO2002065942A3

Abstract

An ankle-foot orthosis (10) (AFO) is disclosed for providing external torque that mimics the torque typically produced by the plantarflexor muscles of the leg when the ankle is dorsiflexed. The torque generated by the AFO (10) assists persons with weak platarflexor strength due to, for example, neurological weakness. The present invention may assist in improving the walking ability of patients who use the AFO (10). In one embodiment, the AFO (10) has a first orthotic member (12) which is adapted to be removably attached to a portion of a calf, and a second orthotic member (14) which is adapted to be removable attached to a portion of the wearer's foot. The second orthotic member (14) can be pivotably mated to the first orthotic member (12). The AFO (10) also includes at least one bias member (68) having a first end and a second end. The first end is mated to the first orthotic member, and the second end is mated to the second orthotic member. The bias member (68) is configured to provide resistance against dorsiflexion of the foot.

Description

ANKLE-FOOT ORTHOSIS WITH PLANTARFLEXOR TORQUE ASSISTANCE

FIELD OF THE INVENTION

The present invention relates to an ankle-foot orthosis (AFO) for limiting dorsi- flexion of the foot, and more specifically, to an ankle-foot orthosis which provides external torque that mimics the torque generated by the plantarflexor muscles of the leg.

BACKGROUND OF THE INVENTION

The term "gait" is used to describe walking and running, and the term "normal gait" is used to present those parameters that have been generalized across gender, age, genetic predisposition and anthropometric variables. In normal gait, the ankle joint goes through two phases: the stance phase and the swing phase. The stance phase is the period of time during which the foot is in contact with the ground. During the stance phase, the foot slowly progresses into dorsiflexion from early to midstance and then plantarflexes in terminal stance. The swing phase is the period of time in which the foot is off the ground and swinging forward. Immediately after toe-off during initial swing the ankle is plantarflexed and begins dorsiflexing in midswing and terminal swing.

Normal gait requires the proper functioning of the musculoskeletal system and the nervous system. Abnormalities in gait can arise due to, for example, neurologic weakness as a result of upper or lower motor neuron injury, such as stroke, cerebral palsy or spinal cord injury.

Abnormal gait can be mitigated, however, by conventional orthotic intervention, which varies with the level and type of lower-extremity dysfunction. Ankle-foot orthoses (AFOs), for example, are rehabilitation devices designed to support, align and improve the functions of the ankle and the foot. AFOs are commonly used to maintain proper foot alignment for patients suffering from foot slap or steppage gait, or spastic paretic stiff-legged gait, which is characterized by reduced knee flexion during swing. Currently, there are several different AFOs used to provide ankle stability for abnormal gait patterns. The most common type of AFO used for correcting abnormal gait is the rigid solid AFO, which is typically made of plastic and has an L-shaped configuration. A posterior support extends from a point below the knee to the heel of the patient, and includes a contoured lower element which conforms to the plantar surface of the foot. The rigid AFO prevents plantarflexion, which, in theory, prevents foot slap at initial contact during the stance phase and allows for clearance during the swing phase. This rigid design also prevents dorsiflexion. However, by not allowing movement, it does not effectively mimic the ankle plantarflexors which provide resistance while lengthening (eccentrically contract) from mid to terminal stance. While the rigid solid AFO can improve the ankle torque, it does not allow dorsiflexion, which impedes the ability to progress the body forward during these phases of walking.

AFOs are also available in an articulating construction, wherein the foot base portion is a separate member hingedly connected to the posterior leg support. The hinge is typically biased to limit plantarflexion movement of the foot, while allowing for unrestricted dorsiflexion. Articulating AFOs typically mimic the dorsiflexor muscles which control plantarflexion.

While conventional AFOs prevent plantarflexion, they do not assist in mimicking plantarflexor muscles, which provide resistance during dorsiflexion. Accordingly, there exists a need for an AFO which mimics the plantarflexor muscles.

SUMMARY OF THE INVENTION

The present invention is directed to an ankle-foot orthosis (AFO) which provides external torque that mimics the torque typically produced by the plantarflexor muscles of the leg when the ankle is dorsiflexed. The torque generated by the AFO assists persons with weak plantarflexor strength due to, for example, neurologic weakness. The present invention may help to improve the walking ability of patients who use the AFO.

An ankle-foot orthosis (AFO) is provided for generating external plantarflexor torque. The AFO has a first orthotic member which is removably attachable to a posterior portion of a wearer's leg adjacent the calf, and a second orthotic member which covers a portion of the bottom of the wearer's foot and extends in a transverse plane of the wearer's foot. The first and second orthotic members are pivotably joined to one another. The AFO also includes at least one bias member having a first end mated to the first orthotic member and a second end mated to the second orthotic member. The bias member according to the present invention can be a material capable of providing resistance to stretching, such as a spring, rubber cord, elastic strap, or a similar device. The bias member is configured to provide resistance against dorsiflexion of the foot. The first and second orthotic members can be hingedly connected along an axis of rotation of the wearer's foot. The first and/or second orthotic member can also include straps that enable the orthotic members to be attached to the wearer's leg or foot. In one embodiment, the bias member forms an inverted Y-shape having first and second lower ends. The first lower end is attached to the posterior-medial side of the second orthotic member, and the second lower end is attached to the posterior-lateral side of the second orthotic member. The bias member can be made from two cords partially joined in a sleeve to form an inverted Y-shape.

In another embodiment, the AFO includes first and second bias members, each bias member having first and second ends. The first end of the first bias member is mated to the posterior-medial side of the first orthotic member, and the second end of the first bias member is mated to the posterior-medial side of the second orthotic member. The first end of the second bias member is mated to the posterior-lateral side of the first orthotic member, and the second end of the second bias member is mated to the posterior-lateral side of the second orthotic member.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be more fully understood from the following detailed description taken in conjunction with the accompanying drawings, in which:

FIG. 1 illustrates the prior art anatomical planes and motions of a foot;

FIG. 2 is a lateral side view of a right ankle-foot orthosis having a bias member according to one embodiment of the present invention;

FIG. 3 is a rear view of a left ankle-foot orthosis having a bias member according to another embodiment of the invention;

FIG. 4 is a medial side view of the ankle-foot orthosis of FIG. 3;

FIG. 5 is a medial side view of a left ankle-foot orthosis according to yet another embodiment of the present invention; FIG. 6 is a medial side view of a left ankle-foot orthosis according to another embodiment of the present invention;

FIG. 7A is a lateral side view of a right ankle-foot orthosis according to another embodiment of the present invention;

FIG. 7B is a lateral side view of the right ankle-foot orthosis of FIG. 7A, illustrated in use with a foot in a dorsiflexed condition;

FIG. 8 A is a lateral side view of a right ankle-foot orthosis according to another embodiment of the present invention;

FIG. 8B is a lateral side view of the right ankle-foot orthosis of FIG. 8 A, illustrated in use with a foot in a dorsiflexed condition;

FIG. 9A is a lateral side view of a right ankle-foot orthosis according to another embodiment of the present invention;

FIG. 9B is a lateral side view of the right ankle-foot orthosis of FIG. 9 A, illustrated in use with a foot in a dorsiflexed condition;

FIG. 10 is a lateral side view of the right ankle-foot orthosis of FIG. 3, illustrated in use with a foot in a dorsiflexed condition; and

FIG. 11 is a lateral side view of a right ankle-foot orthosis according to another embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates an ankle-foot orthosis (AFO) which provides an external source of resistive plantarflexor torque that mimics the torque typically produced by the plantarflexor muscles of the leg when the ankle is dorsiflexed. As shown in Figure 1, dorsiflexion involves upward movement of the front of the foot in the sagittal plane toward the tibia. For reference purposes only, Figure 1 is a prior art illustration of the various anatomical planes and motions of the foot. Control of the plantarflexor muscles during dorsiflexion, and particularly during the mid to terminal stance of gait, is critical to maintaining forward propulsion and hence walking in general. The AFO of the present invention is particularly useful for assisting persons with weak plantarflexor strength due to neurological weakness caused by, for example, stroke, cerebral palsy or spinal cord injuries. The AFO of the present invention may help to improve the walking ability of patients who use the AFO.

In general, the AFO 10 according to the present invention includes first and second orthotic members 12, 14, and at least one bias member 16, 18, 22, 32, 34, 68, 70, 80, 90 mated to the first and second orthotic members, as shown in Figures 2-6. The first orthotic member 12 is pivotably mated to the second orthotic member 14 and removably attaches to a posterior portion of a wearer's leg adjacent the calf. A strap 28 can be provided on the first orthotic member 12 to removably attach the first orthotic member 12 to a posterior portion of the wearer's leg adjacent the calf. The second orthotic member 14 can also include a strap 52 (Figure 10) to secure the orthotic member 14 to the wearer's foot.

The first and second orthotic members 12, 14 can be formed from a rigid or semi-rigid shell, which may be a plastic, a light weight metal or metal alloy, or a composite material. Each orthotic member is preferably lightweight and shapeable to allow the members to conform to the wearer's leg and foot. In one embodiment, a polymer such as polypropylene, polyethylene, or the like, can be used to form the shell. The first and second orthotic members can be preformed in standard sizes corresponding to what might be ordinary foot and leg sizes, or can each be cast from an exact plaster replica of the patient's foot and leg.

The first orthotic member 12 wraps around the posterior portion of the wearer's calf and extends downward from the mid- or lower-calf to the ankle. In one embodiment, the orthotic member 12 is sufficiently rigid along an axially extending middle portion 44 (Figure 3) to maintain the first orthotic member 12 in an upright position adjacent the posterior portion of the wearer's calf. The outer sides 46, 48 (Figure 3) of the orthotic member 12 can be more resilient, but should be sufficiently pliable to allow the orthotic member 12 to be drawn into conforming engagement with the posterior calf portion of the wearer's leg.

As noted above, the first orthotic member 12 can include a strap 28 to removably secure the first orthotic member 12 in a desired position adjacent to the calf portion of the wearer's leg. One end of the strap 28 can be secured to one side 48 of the first orthotic member 12 and can extend across the anterior portion of the wearer's leg. The free end of the strap is removably secured to the other side 46 of the first orthotic member 12, and is tightened to hold the first orthotic member 12 snuggly in position against the wearer's leg. A buckle, snap, hook and loop fastener (e.g., VELCRO), or a similar closure device can be used to secure the free end of the strap 28 to the first orthotic member 12. The strap 28 can be manufactured from a variety of suitable materials, including those that are elastic, inelastic, or semi-elastic.

The second orthotic member 14 is a rigid foot-supporting shell which conforms closely to the shape of a portion of the foot and provides a light weight means of support for the bottom, sides and rear of the wearer's foot. The second orthotic member extends beneath the bottom of the wearer's foot and projects upwardly to intimately wrap around the heel and ankle areas of the wearer's foot. The lower portion of the second orthotic member 14 extends underneath and around the wearer's heel, and can extend forward underneath the wearer's foot toward the forefoot. The second orthotic member 14 can optionally include a strap 52, as shown in Figure 10, for securing the second orthotic member 14 to the wearer's foot. The strap 52 is similar in construction and purpose to strap 28.

The first and second orthotic members 12, 14 are joined together by articulating joints 36 on the medial and lateral side of the AFO 10, preferably at a location that corresponds to the position of the wearer's ankle. The articulating joints can be made from plastic or metal designs and may be mounted on each side of the AFO 10 along a common axis through the axis of rotation of the ankle joint to pivotally engage the first and second orthotic members 12, 14. The axis delineated by the articulating joints 36 allows the first and second orthotic members to rotate with respect to one another, and with the ankle, during dorsiflexion and plantarflexion. Any joint currently manufactured for AFOs can be used, including, for example, the Tamarack Flexure Joint, the Chamber Axis Hinge Kit, and the Oklahoma Ankle Joint, all manufactured by Becker Orthopedic (Troy, Michigan).

As shown in Figure 2, the first and second orthotic members 12, 14 are oriented such that a gap is provided between the lower portion 38 of the first orthotic member 12 and the upper edge 42 of the upward projection of the second orthotic member 14. One of ordinary skill in the art will appreciate that the first and second orthotic members can be constructed to prevent plantarflexion of the foot beyond a certain point. A stop can alternatively or additionally provide for limited plantarflexion.

One of ordinary skill in the art will further appreciate that the AFO 10 of the present invention can be designed to be worn above or under a stocking, and/or with normal footwear.

The bias member 16, 18, 22, 32, 34, 68, 70, 80, 90 of the present invention can be made from any material that is extensible and resilient. Preferably, the bias member 16, 18, 22, 32, 34, 68, 70, 80, 90 is made from a material that, while extensible, resists extension to some degree when tension is applied, and which returns to its natural dimensions and/or shape when tension is removed. Suitable materials and structures from which the bias member 16, 18, 22, 32, 34, 68, 70, 80, 90 can be made include elasticized straps or cords, springs, pneumatic pistons, electro-mechanical structures, metallic structures, and composite structures which generate a resistive force during dorsiflexion of the foot. The tension of the bias member can be selected or adjusted according to the particular patient's needs. When the foot and ankle are in the neutral position (90°), the bias member may be set so as to not generate a resistive force.

Figure 2 illustrates one embodiment of an AFO 10 having first and second orthotic members 12, 14 pivotably joined, and two bias members 16, 18 mated to the first and second orthotic members. The first orthotic member 12 is removably attached to a portion of a calf with a strap 28. The bias members 16, 18 are mated to the posterior-medial and posterior-lateral portions of the first and second orthotic members 12, 14. As shown in Figure 2, the bias members 16, 18 are elastic cords. In one embodiment, each bias member 16, 18 respectively has an origin point 55, 56 at the posterior-lateral and posterior-medial portions of the first orthotic member 12. The origin point 55, 56 is preferably positioned below the mid-calf. The termination point medial portion of the second orthotic member 14. The termination point is preferably disposed below and posterior to the pivot 36. The cords 16, 18 can be directly attached to the orthotic members 12, 14, or secured to pegs 54 disposed on the first and second orthotic members 12, 14. The cords can be made from any elastic material, such as, for example, natural rubber.

Figures 3 and 4 illustrate another embodiment of a bias member 22 that is attached between the first and second orthotic members 12, 14. The bias member 22 has an inverted Y-shape having a top end 23 at an origin point 62, and first and second lower ends 24, 26, each of which has a termination point 57, 58. The bias member 22 can be a single elastic cord split along a portion of the length of the cord, or two cords joined in a sleeve extending along a portion of the length of the cords. The origin point 62 of the top end 23 of bias member 22 is positioned on the posterior side of the first orthotic member 12, preferably at a location along middle portion 44 that is central to the width of the orthotic member 12. The origin point is preferably below the mid-calf region. The first lower end 24 of the bias member 22 is attached to the posterior-medial side of the second orthotic member, and the second lower end 26 is attached to the posterior- lateral side of the second orthotic member. The termination point 57, 58 of the first and second lower ends 24, 26 is preferably at a location that corresponds to the termination point discussed above with respect to bias members 16, 18. By way of non-limiting example, the first and second orthotic members can contain pegs or hooks 54 molded, screwed, or riveted into the plastic shell, or the bias member 22 can be attached to the first and second orthotic members with rivets, screws, or cement.

Figure 5 illustrates a further embodiment of an AFO 10 having two bias members 32, 34 attached to the medial and lateral posterior portions of the first and second orthotic members 12, 14. Bias members 32, 34 are similar in placement and operation to bias members 16, 18 discussed with respect to Figure 2. However, as shown in Figure 5, the bias members 32, 34 are springs encased in a protective material such as a plastic sleeve. The springs will provide tension when the ankle joint is dorsiflexed beyond the neutral position (90°). In Figure 6, another AFO 10 is shown having a single bias member 68 attached along the posterior portion of the AFO. Bias member 68 is attached to the posterior portion of the first orthotic member 12 just below the calf at origin point 62, and extends directly downward to the posterior portion of the second orthotic member 14 and attaches at termination point 66. An articulating joint 36 mates the first and second orthotic members 12, 14.

Figures 7, 8, and 9 illustrate alternative embodiments of the bias members according to the present invention. Bias members 70, 80, 90 are shown attached to the posterior portion of the first orthotic member 12 at origin point 62, and extending directly downward to the posterior portion of the second orthotic member 14 to termination point 66. While Figures 7, 8, and 9 illustrate a single bias member attached to the posterior portion of the AFO 10, two bias members can be attached to the medial and lateral posterior portions of the first and second orthotic members 12, 14.

In Figures 7A and 7B, bias member 70 is shown having an upper member 72 and a lower member 74. The upper member 72 is slidably mated with the lower member 74. The two members 72, 74 can be mated together with strap 78, band, or similar device disposed around both members 72, 74. The strap 78 provides resistance against slidable movement of the upper and lower members 72, 74, thereby providing resistance during dorsiflexion of the foot (shown in Figure 7B).

Figures 8A and 8B illustrate a bias member 80 attached to the AFO 10 at origin point 62 and termination point 66. The bias member 80 has a leaf-spring structure in the neutral position, as shown in Figure 8A. During dorsiflexion, as shown in Figure 8B, the bias member essentially forms a straight line, thereby generating tension and providing resistance against dorsiflexion.

In Figures 9A and 9B, another bias member 90 is shown mated to the AFO 10. The bias member 90 has an accordion-like structure, as shown in Figure 9A. The bias member 90 is tensioned during dorsiflexion, as shown in Figure 9B, to lengthen the accordion-like structure. The resistance against lengthening of the bias member 90 provides resistance to dorsiflexion of the foot.

In use, the bias members of the present invention provide an external, resistive plantarflexor torque that is generated during dorsiflexion. As shown in Figure 10, during dorsiflexion d of the foot, the bias member 22 provides a tension t which mimics the torque generated by the plantarflexor muscles. The resistance of the bias member(s) can be altered by changing the bias member(s) to provide either more or less resistance. The torque generated by the bias member 22 is intended to assist persons with weak plantarflexor strength, thereby improving walking ability.

Figure 11 illustrates another embodiment of an AFO 110 according to the present invention having a bias member 116. The bias member 112 can be a spring or similar device for providing a compressive force. The bias member 112 disposed within a slot 118 formed in the articulating joint 36. The slot 118 is positioned on the anterior-lateral side of the first and second orthotic members 12, 14. In use, a resistive torque is generated by the bias member 112 during dorsiflexion of the foot.

While figure 11 illustrates the bias member 112 positioned on the anterior-lateral side of the first and second orthotic members 12, 14, the bias member 112 can be positioned on the anterior-medial side of the first and second orthotic members 12, 14, or a bias member can be provided on both the anterior-medial side and the anterior- lateral side.

While the bias member of the present invention is illustrated with an articulating AFO, a person having ordinary skill in the art will readily appreciate that a variety of different orthotic support members having additional features can be use in conjunction with the bias member.

One of ordinary skill in the art will know, or be able to ascertain, using no more than routine experimentation, many equivalents to the specific embodiments of the invention described herein. These and all other equivalents are intended to be encompassed by the following claims. All publications and references cited herein are expressly incorporated herein by reference in their entirety.

What is claimed is:

Claims

1. An ankle-foot orthosis for providing external plantarflexor torque, comprising: a first orthotic member removably attachable to a posterior portion of a wearer's leg adjacent the calf; a second orthotic member pivotably mated to the first orthotic member, at least a portion of the second orthotic member extending in a transverse plane of a wearer's foot; and a bias member having a first end mated to the first orthotic member and a second end mated to the second orthotic member, the bias member being effective to provide resistance against dorsiflexion of the foot.

2. The ankle-foot orthosis of claim 1, wherein the first and second orthotic members are pivotably connected by first and second articulating joints.

3. The ankle-foot orthosis of claim 0, wherein the first and second articulating joints are disposed along an axis of rotation of the wearer's foot, each on opposite sides of the orthosis.

4. The ankle- foot orthosis of claim 0, further comprising a strap disposed on the first orthotic member for securing the first orthotic member to the wearer's leg.

5. The ankle- foot orthosis of claim 1, wherein the bias member is selected from the group consisting of elasticized straps, elasticized cords, springs, pneumatic-pistons, electro-mechanical structures, composite structures, and metallic structures.

6. The ankle-foot orthosis of claim 0, wherein the second orthotic member has a posterior-medial side and a posterior-lateral side, and wherein the bias member forms an inverted Y-shape having first and second lower ends, the first lower end being attached to the posterior-medial side of the second orthotic member, and the second lower end being attached to the posterior-lateral side of the second orthotic member.

7. The ankle-foot orthosis of claim 0, wherein the Y-shaped bias member comprises two cords partially joined in a sleeve.

8. An ankle-foot orthosis for providing external plantarflexor torque, comprising: a first orthotic member removably attachable to a posterior portion of a wearer's leg adjacent the calf and having a posterior-medial side and a posterior-lateral side; a second orthotic member pivotably mated to the first orthotic member and having a posterior-medial side and a posterior-lateral side, at least a portion of the second orthotic member extending in a transverse plane of a wearer's foot; and a first bias member having a first end and a second end, the first end being mated to the posterior-medial side of the first orthotic member, and the second end being mated to the posterior-medial side of the second orthotic member; and a second bias having a first end and a second end, the first end being mated to the posterior-lateral side of the first orthotic member, and the second end being mated to the posterior-lateral side of the second orthotic member; wherein the first and second bias members are effective to provide resistance against dorsiflexion of the foot.

9. The ankle-foot orthosis of claim 0, wherein the first and second bias members are selected from the group consisting of elasticized straps, elasticized cords, springs, pneumatic-pistons, electro-mechanical structures, composite structures, and metallic structures.

10. The ankle- foot orthosis of claim 0, wherein the first and second orthotic members are pivotably connected by first and second articulating joints.

11. The ankle-foot orthosis of claim 0, wherein the first and second articulating joints are disposed along an axis of rotation of the wearer's foot.

12. The ankle-foot orthosis of claim 0, further comprising a strap disposed on the first orthotic member for securing the first orthotic member to the wearer's leg.