My views in this article reflect over 50 years of personal experience wearing upper-limb prostheses and almost a decade of experience specifically using adjustable, self-suspending, transradial socket designs. I am a 77-year-old healthy man with a short left transradial residual limb resulting from an amputation at age 22. I am a regular, full-time, body-powered and activity-specific prosthesis wearer, and I have experience with a wide variety of prosthetic suspension technologies. This article presents a review, comparison, and rating of various self-suspending prosthetic designs, addressing factors of socket fit suspension security, effective range of motion (ROM), and socket comfort in static and dynamic circumstances.
History of Self-Suspending Sockets
There are multiple goals in creating a self-suspending prosthesis: capturing the morphology of the medial and lateral epicondyles and the olecranon; improving suspension, socket security, and comfort; maximizing ROM; eliminating or reducing excess harnessing; and simplifying and improving the efficiency of the prosthesis. Self-suspending prosthetic sockets have primarily targeted very short, short, and mid-length forearm absence cases, where surface area anatomy for suspension is less available. The German-designed Muenster socket was probably the first successful achievement in self-suspending prostheses as early as the 1950s (Figure A), and it was just the beginning of the evolution of this type of suspension concept. The 1980s marked the development of new socket materials and liners when the Icelandic New York or ISNY concept, a two-component socket was introduced (Figure B). It used a rigid, laminated, outer shell with a softer thermoplastic-formed inner socket for improved comfort. Various full and partial sockets and liners were experimented with using more compliant, formable materials like Pelite, but rigid outer shell, laminated sockets predominated.
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Karl Fillauer, CPO/L, FAAOP, introduced the Fillauer Silicone Suspension Socket, or 3S System, which was the first custom-fabricated, reinforced, silicone-impregnated liner with a locking component on the distal end of the flexible sleeve (Figure C). A threaded stud embedded into the end of the sleeve secured into a shuttle lock mechanism that was built into the distal end of the inner socket. This roll-on locking liner concept was an exceptional improvement for suspension and comfort. It quickly progressed, using other materials like polyurethane and thermoplastic liners, which could be manufactured and sold in various sizes. Interestingly, the first thermoplastic liners used the same inexpensive olefin polymer elastomer materials that were being used to mold artificial fishing worms. These systems continued to develop into liners like the Össur Upper-X (Figure D) that added longitudinal stretch control, which I believe is essential for security and stability.
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Photograph courtesy Bob Radocy. |
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Notably, Randall Alley, BSc, CP, and John Miguelez, CP, FAAOP(D), while working on Hanger’s first upper-extremity specialists team in the early 2000s further investigated the anatomical aspects of the elbow and ways to optimize the design of self-suspending sockets. Miguelez published an article on the transradial anatomical contour describing this research.1 Alley thereafter presented his own opinions on the anatomical contoured and controlled interface.2 Both contributed to improved understanding of the anatomy of the elbow and how to most functionally use it for prosthetic suspension. Alley later contributed to the discussion further as he described residual limb containment with the High Fidelity Interface, as well as the compression/release stabilized designs he created that captured and controlled the soft tissues around the longer bones of the limb.3
For more than two decades, roll-on locking liners inside of rigid, laminated prosthetic shells dominated upper-limb prescriptions. Then, Joseph Mahon, CPO, realized the potential for creating adjustable compression socket technology. Taking a BOA reel system out of a ski boot, he fabricated what were to become the first ever cable-tension, adjustable, self-suspending prosthetic sockets. He patented the concept of using these reel-adjustable cable tension systems as kits for prosthetists to use. At that time, TRS and I as its president were simultaneously working with BOA to introduce the technology into the profession, collaborating with EXOS, and we introduced BOA component technology into the O&P market. Click Medical, a prosthetic accessory component manufacturer, ultimately took over the lead in making BOA high-performance cable closure systems for use in the profession.
During this period, I was working with Chris Baschuk, MPO, CPO, FAAOP(D), and Handspring while trying to transfer a prototype adjustable socket concept called the Rapid Adjustable Modular Prosthetic (RAMP) Socket into a complete prosthesis (Figure E). That design incorporated medial-lateral flexible brims and a crossover cable tension configuration that enclosed the entire remnant limb. Baschuk, alternatively, created an above-the-olecranon compression plate design that captured the limb by trapping the olecranon (Figure F). Baschuk constructed a medial side mount reel design enclosed by a cover plate. This design had significant advantages over a nonadjustable socket.
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Photograph courtesy Bob Radocy. |
Photograph courtesy Bob Radocy. |
Just before we entered the 2020s, I began working with Dave Rotter, CPO. Rotter was experimenting with perfecting a flexible brim design socket, resulting in a design that incorporated a BOA control mounted on the medial side of the prosthesis where crossover, cable tension controlled the movement of both the medial and lateral flexible socket brims. The suspension, comfort, function, and ROM were significantly improved. Recently, at my request, Rotter built another flexible brim design that placed the BOA control reel behind and above the olecranon (Figures H-K). This provided for a clean forearm design, simplified the mechanics of the crossover cable routing, and provided improved application for people with longer forearms to use the design. These designs are worthy of further investigation by practitioners.
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