Transtibial prosthesis

A transtibial amputation (sometimes one sees transtibal amputation) is an amputation above the foot but below the knee.

Transtibial amputees have the greatest hope of regaining normal mobility. The knee is the part of the leg involving the most complex biomechanics; as this is intact for all transtibial amputees, the process of mimicking native leg movement becomes much easier for this population.

Additional recommended knowledge

How to quickly check pipettes?

What is the Correct Way to Check Repeatability in Balances?

Guide to balance cleaning: 8 simple steps

History

Prior to the 1980s, foot prostheses merely restored basic walking capabilities. These early devices can be characterized by a simple artificial attachment connecting one’s residual limb to the ground.

The introduction of the Seattle Foot (Seattle Limb Systems) in 1981 revolutionized the field, bringing the concept of an Energy Storing Prosthetic Foot (ESPF) to the fore. Other companies soon followed suit, and before long, there were multiple models of energy storing prostheses on the market. Each model utilized some variation of a compressible heel. The heel is compressed during initial ground contact, storing energy which is then returned during the latter phase of ground contact to help propel the body forward.

Since then, the foot prosthetics industry has been dominated by steady, small improvements in performance, comfort, and marketability. Also see: XT-9 Energy-storing prosthetic knees (ESPK) developed by Symbiotechsusa [1]

Design considerations

There are multiple factors to consider when designing a transtibial prosthesis. Manufacturers must make choices about their priorities regarding these factors.

Performance

Nonetheless, there are certain elements of foot mechanics that are invaluable for the athlete, and these are the focus of today’s high-tech prosthetics companies:

• Energy storage and return – storage of energy acquired through ground contact and utilization of that stored energy for propulsion

• Energy absorption – minimizing the effect of high impact on the musculoskeletal system

• Ground compliance – stability independent of terrain type and angle

• Rotation – ease of changing direction

• Weight – maximizing comfort, balance and speed

• Suspension - how the socket will join and fit to the limb

Other

The buyer is also concerned with numerous other factors:

• Cosmetics

• Cost

• Ease of use

• Size availability

Emerging technology

Most companies choose to focus on two areas of performance: energy capabilities and ground compliance. Two particular models exemplify the innovation in these areas: the Elite foot (Endolite) and the Venture foot (College Park Industries).

The Elite foot relies on a polymeric material with a very specific set of elasticity and resistance requirements in order to optimize energy storage and return. It also uses an unprecedented three-pronged foot, which allegedly allows the foot to closely mold to the contours of any surface.

In contrast, the Venture foot retains the common one-point contact with the ground, but seeks to maximize performance (in both energy and compliance) with a complex metal heel component. This heel is equipped not just with a standard compressible foam piece, but also hinges which allow rotation on three different axes, allegedly yielding superior comfort (ground compliance) and a more precise mimicry of native foot biomechanics (energy capabilities).

Many other foot prostheses employ other useful innovative technology and designs. No one foot is perfect for all transtibial amputees. Hopefully, however, each amputee can find a foot that is best for his or her particular pattern of physical activity.

Sources

• ‘Biomechanics of running: from faulty movement patterns come injury.' Sports Injury Bulletin.

• ‘The College Park Venture Foot.' College Park Industries.

• Edelstein, J. E. Prosthetic feet. State of the Art. Physical Therapy 68(12) Dec 1988: 1874-1881.

• Gailey, Robert. The Biomechanics of Amputee Running. October 2002.

• Hafner, B. J., Sanders, J. E., Czerniecki, J. M., Ferguson , J. Transtibial energy-storage-and-return prosthetic devices: A review of energy concepts and a proposed nomenclature. Journal of Rehabilitation Research and Development Vol. 39, No. 1 Jan/Feb 2002: 1-11.

• ‘Hexcel at SAMPE, Long Beach.' Hexcel Corporation.

• ‘Hexply Prepreg.' Hexcel Corporation.

• High Tech Prosthetics Brown University BI108 Webpage

• ‘Lower Extremities Products.' Endolite North America.

• `Energy-storing Prosthetic Products' Symbiotechsusa.

• SPARKy (short for Spring Ankle with Regenerative Kinetics) is a smart, active and energy-storing transtibial, or below-the-knee, prosthesis developed by Dr. Thomas G. Sugar at Arizona State University (http://robotics.eas.asu.edu/research.htm).