O&P professionals have an involved understanding of prosthetic socket fabrication. There are many ways to fabricate a definitive prosthetic socket, but how can we make the outcome more effective? One way is to focus more attention on the check socket.
A check socket is a temporary socket used to determine the optimal fit and dynamic alignment for an amputee’s definitive socket.
Most amputees experience drastic volume fluctuations following trauma and amputation. Many experience long-term volume fluctuations, nerve disturbance, phantom pain and fitting challenges. Fabricating a definitive prosthetic socket too early in the rehabilitation process may result in a socket that loosens quickly, leaving the amputee feeling uncomfortable and unstable. Many check and/or definitive sockets could be fabricated over an amputee’s lifetime. The sooner the fit and function are optimized for the amputee’s current situation the sooner they achieve maximum mobility and confidence in their prosthesis.
This is the first of a series of articles that will focus on basic transtibial hard check sockets using a variety of techniques.
The check socket is used to diagnose an amputee’s socket fit, dynamic alignment and function. It allows the prosthetic team to easily adjust these critical factors as most sockets are easily adjusted using a heat gun to optimize comfort and function. An accurately fitting socket in proper dynamic alignment can help to make the amputee more comfortable, stable and enable them to expend the least amount of energy required to ambulate. An uncomfortable fit or poor alignment would have an obvious negative effect on the amputees’s comfort, stability, energy consumption and confidence in their prostheses.
Check sockets can be laminated but are often formed using thermoplastics. Check sockets fabricated using clear thermoplastic materials allow the clinician to visually inspect surface contact in static and dynamic applications. Non transparent sockets can be used by placing inspection openings in strategic locations. In all instances the amputee’s involvement and communication is imperative.
Check socket design and modification should be established under the direction of a certified prosthetist and/or qualified prosthetic technician. The socket’s life span should be predetermined by the experienced prosthetic technician/prosthetist using proven materials, components, techniques and procedures.
I recently requested of James Little CP(c), owner of Vancouver Island Prosthetics, a very basic overview of cast modifications. He advised the following based on an article that appeared in Artificial Limbs by James Foort:
1. Reduce cast in pressure tolerant areas such as the popliteal fossa, patellar tendon, pre-tibial area and, tibial flare.
2. Smooth cast down to compression value measurements (circumferences).
3. Apply buildups to relieve pressure sensitive areas 1/8 (3 mm) at tibial crest, fibular head, distal cut end of fibula and 1/2 (12 mm) at distal tibia, allow sloping relief to hamstrings tendons where they exit popliteal shelf.
4. Smooth cast.
Our next consideration will be to decide on the thermoplastic material to be used for fabricating our check socket. The most common material used for check socket fabrication is co-polyester, or polyethylene terephthalate modified with cyclohexanedimethanol (PETG), often marketed under a multitude of other private labels.
Styrene-buta-1, 3-dieen copolymer thermoplastic is also available for fabricating check sockets. Higher initial costs can be justified by performance and ecological benefit. Currently, seam draping this material may not be practical unless a mechanical fastening technique is implemented. Using this material in a seamless application is preferable. It can outperform PETG, offer biodegradable characteristics, and when properly processed become more cost-effective than PETG.
The thermoplastics mentioned above offer us a clear check socket. Laminations and a variety of opaque or solid colored thermoplastics are sometimes applied. They do not offer the ability to visually inspect pressure points and/or gapping. If not chosen or processed properly thermoplastics can deform and fail under repetitive stress situations.
These materials are available in various thicknesses and are processed using two basic techniques. Always follow the manufacturer’s specifications and record optimal and inferior performances based on your material, equipment, techniques and procedures.
This is a technique in which the thermoplastic sheet is vacuum formed over the positive cast and a seam is present. Once the socket is formed, the plaster model is broken out leaving the socket intact. In certain instances the socket can be removed without destroying the modified cast. The seam must be reinforced or mechanically fastened. This technique is often inferior to a bubble formed (seamless) check socket unless it is adequately re-enforced. A simple synthetic casting wrap can be effective but, in my opinion, is not adequate for more than a static assessment in parallel bars. The socket integrity will always be dependent on adequate re-enforcement of the seam. If component attachment has not been considered in initial stages they must be addressed after the socket has been formed. Techniques used for this will be addressed in future articles.
This is a technique in which the thermoplastic socket is vacuum formed over the positive cast and is seamless. The thermoplastic material of the appropriate thickness is suspended in a frame and formed over a modified positive cast. Following the manufacturer’s specifications, the material is allowed to droop into a bubble shape and then formed over a prepared cast. If component attachment has not been considered in initial stages they must be addressed after the socket has been formed.
We have now formed a clear check socket and must consider component selection, alignment and cosmetic expectations. This will be based on the amputee’s prosthetic demographics that will be discussed in future articles.
For more information:
- Foort J. The patellar-tendon-bearing prosthesis for below-knee amputees, a review of technique and criteria. Artificial Limbs. Spring 1965; 9; 4-13
Patrick J. Myrdal, RTPO(c), FCBC is the owner of Myrdal Orthopedic Technologies in Winnipeg, Manitoba and vice president of the Orthotic and Prosthetic Technological Association. He can be reached at email@example.com.