Adaptive Sports Ankle Prosthetics

Abstract

Participating in sport at all levels is gaining a dedicated following and this is also apparent in individuals with an amputation. Currently, there is a wide variety of ankle prostheses available which attempt to provide function, control, and comfort, as well as good aesthetic appeal. Participation in sport, however, increases the demands placed upon ankle prostheses. This can compromise function and performance, and constrain the opportunities of participation in various outdoor and water sports. In acknowledging this limitation and the need to develop more versatile ankle prostheses, this article introduces the evolution of a prototype ankle prosthesis referred to as “Adaptive Sports Ankle.” The ankle prosthesis, which is compatible with any foot pyramid adapter, offers the same range of motion as the normal human ankle joint and is made up of components that are chemical and corrosion resistant. These design features that are specifically created to accommodate below-the-knee amputees provide an ideal prosthesis for those wishing to lead an active lifestyle and participate in aquatic (i.e. swimming, surfing, and scuba diving), snowboarding, and equestrian activities. Although it is acknowledged that there is a need to establish research on the Adaptive Sports Ankle, its introduction to the market will enhance and expand opportunities of those individuals with a lower limb amputation to lead an active and healthy lifestyle.

Clinical relevance

The introduction of the Adaptive Sports Ankle Prosthesis provides versatility in terms of motion of the device and robust material. Although in its infancy, clinicians should be aware of the potential of this product for individuals who have had a below-the-knee amputation and express a desire to participate in water sports and other outdoor activities.

SC:

How did Adaptive Sports Ankle Prosthetics come about? Can you sum up its evolution in 300 words?

DL:

Well, the complete story is presented in the web site www.adaptivesportsankle.com under the tab “Why the Ankle Was Created,” but I’ll give you the 300-word version.

I am a below-the-knee amputee, active in all things fun and exciting, namely, activities in the water, snow, and saddle, notably in the world’s most interesting places. I travel the globe extensively in my profession, and I take my three daughters with me exposing them to as much activity and adventure in nature as they can stand. I had experienced prosthetic component failures, thus having to travel with spare parts. Frustrated, I designed my own ankle with the capability to adapt to various uses, dependent on the activity at hand, that is, aqua, snow, or equestrian use. I chose to make it from Grade 5 Titanium so that salt water, sand, dirt, mud, industrial chemicals, and whatever else wouldn’t affect the ankle causing corrosion or breakage. I designed the ankle, so that the rotating side elements could be interchangeable for specific use. My intention was to make an ankle for myself, so that I could keep up with my three daughters as they grew up. My wife and friends thought it was such a good design; it was suggested that I should share it with other amputees who desire an active lifestyle. I produced a prototype to confirm functionality, set up a web site to gauge interest, presented technical papers to the International Triathlon Union (ITU) and International Paralympic Committee (IPC), entered an international design contest, conducted a personal field trial, and cold-called on the US Military Wounded Warrior programs to launch the ankle product all accomplished in a 12-month period! The next steps are to discover the mystery of marketing and distribution. There you have it in 295 words.

SC:

In comparison to other prostheses, how is the Adaptive Sports Ankle different?

DL:

The Adaptive Sports Ankle is the only ankle in the market of its kind. There is no other ankle prosthesis that can be compared to it in like design, material, and features. For comparison, there is a plastic ankle in the market, designed only to achieve a 70° plantar flexion orientation, manually fixed in position, and designed for K1 (ambulation of level surfaces) activity only.

The Adaptive Sports Ankle is designed utilizing the Principles of Universal Design for activity K1–K4 (ambulation on level surfaces (K1) to enhanced levels of ambulation (K4)). All load-bearing components are made from Grade 5 Titanium, dynamic components from 300 series stainless steel, and the rotating bearings from thermoplastic polymer all parts are corrosion and chemical resistant. The Adaptive Sports Ankle is designed to provide the same range of motion as a normal ankle: 15° of dorsiflexion, 50° of plantar flexion, 15° of inversion, and 10° of eversion.

The Adaptive Sports Ankle is designed so that the initial ankle positioning is achieved by pushing the anterior pushpin button with the heel of the opposite foot or by lifting the posterior guide pin plunger with the use of a hand. Transition back to a neutral (walk) orientation is hands free and dynamic (accomplished without having to stop your activity). Activity-specific side elements are interchangeable about the ankle central core with the use of a hex-end wrench and simple removal of the base pyramid receiver mounting screws. The Adaptive Sports Ankle is designed to be top-mount compatible with a titanium 30-mm tube clamp pyramid receiver or a titanium 30-mm tube clamp pyramid receiver and bottom-mount compatible with a titanium four-hole female pyramid receiver with countersunk base. The Adaptive Sports Ankle is compatible with any foot with pyramid adapter (attachment component).

SC:

In terms of the Adaptive Sports Ankle, how have you applied the Seven Principles of Universal Design?

DL:

Table 1 provides an overview of the seven principles.

Table 1.

The seven principles of universal design.

Principle 1 of universal design: equitable use.	The Adaptive Sports Ankle is designed to accommodate lower limb amputees with multiple activity interest which require ankle movements in the dorsi, plantar, medial, and lateral orientation, such as aquatic activities that involve swimming, scuba diving, surfing, and equestrian activities.
The design is useful and marketable to people with diverse abilities.	The Adaptive Sports Ankle is designed so that the initial ankle positioning is achieved by pushing the anterior pushpin button with the heel of the opposite foot or by lifting the posterior guide pin plunger with the use of a hand. Transition back to a neutral (walk) orientation is hands free and dynamic (accomplished without having to stop your activity). Activity-specific side elements are interchangeable about the ankle central core with the use of a hex-end wrench and simple removal of the base pyramid receiver mounting screws.
	The Adaptive Sports Ankle is designed for aquatic use in which the ankle components can be exposed to chlorinated and/or salt water and be articulated to achieve a normal ankle’s range of motion of 50° plantar flexion. When exiting the water, simply press the bottom of the attached prosthetic foot against any surface that can reciprocate a reaction force, such as the pool floor/step/ladder, beach shore, or boat ladder, thus returning the ankle to the neutral orientation, and walk, run, or climb out of the water.
	The Adaptive Sports Ankle is designed for equestrian use in which the ankle can be articulated to achieve a “heels down” orientation requiring the normal ankle’s range of motion of 15° dorsiflexion. The specially designed wobble connector components enable the active amputee to have a normal ankle’s range of motion of 15° medially and 10° laterally. This design is prosthetic industry unique in that the foot remains flat on the saddle stirrup (or a surfboard), while the ankle is movable in the dorsiflex mode. Removal of the compressive force on the foot returns the ankle to its neutral orientation.
	The Adaptive Sports Ankle is designed and produced from materials that can withstand rigorous use by active amputees with diverse abilities when used for static or dynamic activity in any marine/dry environment. Materials of construction are corrosion and chemical resistant Titanium, 300 series Stainless Steel, and maintenance-free Thermoplastic Polymer bearings.
	The Adaptive Sports Ankle is appealing to all prosthetic foot users, in which the base is designed to mount to any foot with a pyramid connector, and the 30-mm top pylon can be fitted with either a 30-mm tube clamp female pyramid receiver or tube clamp pyramid.
Principle 2 of universal design: flexibility in use.	The Adaptive Sports Ankle is designed so that activity-specific side elements are interchangeable about the ankle central core.
The design accommodates a wide range of individual preferences and abilities.	The Adaptive Sports Ankle is designed for use on any side, which accommodates right- or left-handed access and use.
	The Adaptive Sports Ankle is designed so that the initial ankle positioning is achieved by pushing the anterior pushpin button with the heel of the opposite foot or by lifting the posterior guide pin plunger with the use of a . Transition back to a neutral (walk) orientation is hands free and dynamic (accomplished without having to stop your activity). Activity-specific side elements are interchangeable about the ankle central core with the use of a hex-end wrench and simple removal of the base pyramid receiver mounting screws.
	The Adaptive Sports Ankle is appealing to all prosthetic foot users, in which the base is designed to mount to any foot with a pyramid connector, and the 30-mm top pylon can be fitted with either a 30-mm tube clamp female pyramid receiver or tube clamp pyramid.
	The Adaptive Sports Ankle design takes into consideration the user’s accuracy and precision when activating ankle articulation by incorporating a large button head on the anterior pushpin and a pull ring on the posterior guide pin plunger. Another available option is the addition of a lanyard attached to the posterior pull ring for users where body flexibility/reach needs to be accommodated.
	The Adaptive Sports Ankle design provides adaptability to the user’s pace or choice of activity and need for ankle movement sensitivity by offering the use of soft or firm compression springs for the guide pin plunger and the wobble connector. For example, the guide pin plunger compression spring used for aqua activity is firmer than the compression spring used for equestrian riding. The wobble connector spring-loaded set screws are offered in soft and firm compression springs to enable optional sensitivity for side-to-side movements depending on leg strength.
Principle 3 of universal design: simple and intuitive use.	The Adaptive Sports Ankle design eliminates unnecessary complexity by utilizing one touch actuation, hands-free transition, and maintenance-free materials.
Use of the design is easy to understand, regardless of the user’s experience, knowledge, language skills, or current concentration level.	The Adaptive Sports Ankle has instructions for use that are visually and literally communicated in English, Spanish, French, and German to accommodate a wide range of literacy and language skills.
Principle 4 of universal design: perceptible information.	The Adaptive Sports Ankle design does not convey any perceptible data or feedback via electronic controls or screens; all actions/reactions are mechanical orientations.
The design communicates necessary information effectively to the user, regardless of ambient conditions or the user’s sensory abilities.
Principle 5 of universal design: tolerance for error.	The Adaptive Sports Ankle design minimizes hazards by rounding all edges so that sharp edges are eliminated.
The design minimizes hazards and the adverse consequences of accidental or unintended actions.	The Adaptive Sports Ankle instructions for use provide warnings of a possible pinching hazard. The risk associated with pinching is nonexisting when the ankle is in use as intended within a complete lower limb prosthesis; however, when being held by hand, in the uninstalled condition and being articulated, the risk of getting a finger pinched is possible.
	The Adaptive Sports Ankle design provides the following fail-safe features:
	In the extreme unlikely event, the guide pin experiences catastrophic failure during dorsiflexion mode, maximum dorsiflexion is physically constrained at 15°.
	In the extreme unlikely event, the guide pin experiences catastrophic failure during plantar flexion mode, maximum plantar flexion is physically constrained at 50°. In the unlikely event, the guide pin fails only in one side element during dorsiflexion mode, movement is mechanically constrained by the normal operation of the opposite side.
	In the unlikely event, the guide pin fails only in one side element during plantar flexion mode, movement is mechanically constrained by the normal operation of the opposite side.
	The wobble connection assembly is redundantly mechanically fastened to the pyramid with a self-locking implanted cotter pin and spring-loaded set screws.
	The Adaptive Sports Ankle assembly is mechanically fastened at the base with a pyramid receiver by four mounting screws.
	If during equestrian use, the stirrup presses the anterior pushpin button affecting an unconscious action, simply remove the anterior pushpin, ankle articulation is then affected by lifting the posterior guide pin plunger.
Principle 6 of universal design: low physical effort.	The Adaptive Sports Ankle design allows the user to maintain a neutral body position when engaging the ankle for articulation and during transition back to the neutral (walk) orientation. For example, during aquatic use, walk, run, or jump into the water and simply tap the anterior pushpin with the heel of the opposite foot to engage ankle articulation and simply step down on the attached prosthetic foot for a balanced and safe transition out of the water without assistance. A user engaged in equestrian activity can activate the ankle while seated in the saddle by lifting a lanyard tab within a comfortable hands reach located on the top backside of the riding boot while maintaining a balanced and safe seated position.
The design can be used efficiently and comfortably and with a minimum of fatigue.	The Adaptive Sports Ankle design minimizes repetitive actions by utilizing a one-push/pull engagement for enabling ankle rotation, either dorsal or plantar flexion.
Principle 7 of universal design: size and space for approach and use.	The Adaptive Sports Ankle design provides a clear line of sight to important elements for any user by offering push/pull engagement, anterior and posterior access, and upright/seated manipulation.
Appropriate size and space are provided for approach, reach, manipulation, and use regardless of user’s body size, posture, or mobility.

SC:

Is it made for particular sporting activities?

DL:

The Adaptive Sports Ankle is designed to accommodate lower limb amputees with multiple activity interest, which require ankle movements in the dorsi, plantar, medial, and lateral orientation, such as aquatic activities (Figures 1 and 2) that involve swimming, scuba diving, surfing, snow ski and snowboard activities, and equestrian activities.

Figure 1.

Aqua Sports Ankle, shown as a complete unit consisting of a central core, interchangeable rotating side elements attached. The central core top connection to the socket/leg is capable of utilizing either tube clamp pyramid adapter or tube clamp pyramid receiver. The side element pair base utilizes a four-hole rotating pyramid receiver compatible with any foot with pyramid adapter .

Figure 2.

The illustration shown is an ankle prosthetic unit for the lower leg amputee triathlete during a swim event. The diagram shows an example of the ankle assembly in swim position (50° of plantar flexion). Transition back to a flat orientation is easily acquired; no assisted handlers would be needed, thus allowing the Paralympian to compete independently.

The Adaptive Sports Ankle comprises a central core with interchangeable side elements for specific sport use. The side elements offered are as follows:

• Dorsi-Manual Plantar-Manual (DMPM): Designed for scuba diving and swimming where the ankle is easily articulated by depressing the front kick pin or lifting the rear Plunger Pin; torsion springs will rotate the ankle to a 50° plantar orientation, and be held at that position until the plunger pin is lifted, and a force is applied to the foot sole, thus rotating the ankle to a neutral (walk) orientation. It’s great for scuba diving, where the ankle is fixed so that extreme leg kicking with fins on the feet will not affect the foot/ankle orientation.

• Dorsi-Dynamic Plantar-Manual (DDPM): Designed for adaptive snowboard and Paraequestrian use, where there is a need to plantar flex the foot to fit into a boot and dorsiflex simply by pressing or leaning forward on the foot sole, the ankle rotates to 15° dorsi (effectively a toes up or heels down orientation). Compatible with a wobble component which is bottom mounted, allows for 15° medial flexion and 10° lateral flexion.

• Dorsi-Dynamic Plantar-Dynamic (DDPD): Designed for adaptive wave and wind surfing. Complete hands-free operation, just press on the foot to manipulate the ankle. Compatible with a wobble component which is bottom mounted, allows for 15° medial flexion and 10° lateral flexion.

• Plantar-Dynamic (PD): Designed for swimming use on the beach or lake, so that the user can progress into and out of the water without having to manually manipulate the ankle orientation from neutral to 50° plantar (swim), back to neutral. Complete hands-free operation, just press on the foot to manipulate the ankle.

SC:

Adaptive Sports Ankle Prosthetics has a global interest for use in Paratriathlon and Paraequestrian; do you have any scientific (and clinical) evidence to support such interest?

DL

Interest is not evidenced by scientific/clinical data collection, the interest for using the Adaptive Sports Ankle in IPC events such as Paratriathlon and Paraequestrian is evidenced in the facts that Adaptive Sports Ankle Prosthetics was selected to be a speaker and presenter at the 2011 ITU First World Congress to initiate the prospect of changing the rules to allow use of prosthesis during the swim event, selected to be a speaker and presenter at the 2011 IPC VISTA Conference to feature the ankle use in aqua and Paraequestrian events, and from the direct correspondence I receive via web site email enquiries.

SC:

How is the Adaptive sports Ankle unique in its use by the Paraequestrian?

DL:

The most important aspect of achieving equestrian dressage performance excellence is maintaining postural alignment in the saddle and stirrup. The objective of the multiaxis ankle is to provide the rider with angular flexibility in a three-dimensional orientation, thus obtaining the balance of weight and pressure in the saddle seat and stirrups that are required to establish correct postural alignment such that the rider’s center of gravity passes directly through and works in conjunction with the horse’s. It is proper body angulations that establish the contact between horse and rider. The ideal riding position is with the body weight evenly distributed over the centerline of the foot, with the ball of the foot flat on the stirrup iron with heel slightly lower the foot transversely rotated in the same plane as the femur. It is critical that the rider keeps even pressure across the foot, rather than pushing on the inside or outside of the stirrup iron. Incorrect distribution of the rider’s weight may cause a miscommunication between horse and rider, and may disturb the horse’s balance and rhythm, thus creating a less than desired performance or an unsafe situation (Figures 3 and 4).

Figure 3.

The Adaptive Sports Ankle is preride transverse aligned specifically for rider preference. It can either be manually placed in action (dorsiflexion/plantar flexion), ideal for trail riding, or can be dynamic, so that by pressing on the stirrup with the foot, the ankle will rotate to a “heels down” orientation. Remove pressure from the foot, and the ankle will rotate back to a flat position.

Figure 4.

The multiaxis ankle prosthetic component is designed to allow for the following angular movements: dorsiflexion 15°, plantar flexion 50°, inversion 15°, eversion 10°, and transverse alignment ±15°.

SC:

Can you provide more information on Wounded Warriors at US Military for the rehabilitation programs you are currently involved in?

DL:

The attributes of the Adaptive Sports Ankle have been presented to the United States Marine Corps (USMC) Wounded Warrior Battalion Quantico, Walter Reed National Military Medical Center (WRNMMC), and the US Naval Medical Center San Diego. The Adaptive sports Ankle received a warm reception, and is currently supplying prosthetic ankle components to WRNMMC for military Wounded Warriors.

SC:

What advice do you give to researchers and clinicians seeking to use Adaptive Sports Ankle Prosthetics for a particular sport?

DL:

The side elements can be used in a manual or dynamic (hands free) mode, I like to know how the client wants to perform before supplying. For example, a scuba activity is better suited for a manual mode where the ankle is held in the 50° plantar position until released to the neutral (walk) orientation, the fin motion will not affect the ankle position. A dressage rider on the other hand requires a light pressure on the foot to acquire a 15° dorsiflex (heels down) orientation. For a swimmer, I want to know if they are using a pool or walking in from the beach, maybe the dynamic mode is better suited for the beach if the surf or landing is rough. Main advice, use it and abuse it, it will not break, enjoy.

SC:

Have you undertaken any research using the Adaptive Sports Ankle Prosthetics that involve elite level athletes?

DL:

None.

SC:

How does the analysis differ from the “everyday” analysis they may be performed on a more sedentary individual?

DL:

I wouldn’t test any differently. The International Organization for Standardization (ISO) testing protocol regarding external lower limb components is based on normal walking stride, heel-to-toe strike, for a certain weight over 2 million repetitions. There really isn’t a testing methodology or specification that is applicable to the loads and angles of pressure and torque that are experienced in sport use.

SC:

What do you think are the key challenges faced by Paralympians compared to the novice and evolving athlete with disability?

DL:

Obtaining sponsorship. I won a lotto entry to participate in the Ironman World Championships at Kona in 2011, but could not do it without a corporate sponsor, the equipment cost and time away from employment were financially overwhelming.

SC:

You state that you have “personal experience” of being an amputee, how does the knowledge and skills learned at Adaptive Sports Ankle Prosthetics assist training and performances of sporting individuals assist the everyday/recreational athlete?

DL:

I have learned how to avoid getting injured.

SC:

What features do you perceive as the “key” to determining optimal performance in terms of training and minimizing injury risk with Adaptive Sports Ankle Prosthetics?

DL:

I believe the key feature is the assurance that the ankle will not break. Confidence in your prosthesis components is key to mental performance. If I am worrying about the structural/mechanical integrity of my prosthesis, I’m not going to perform at the optimum level.