UNIQUE APPLICATIONS FOR CUSTOM SILICONE LINERS
Sandra Ramdial, C.P.(c); Otto Bock Health Care, Oakville, Ontario Scott Simmons, C.P.(c); Northern Alberta Prosthetic & Orthotic Services Ltd., Edmonton, Alberta John Sowerbutts, C.P.(c); Colman Prosthetics & Orthotics Inc., Calgary, Alberta
Silicone suction sockets have become the optimal suspension for upper and lower extremity prostheses. There has been a vast array of off-the-shelf liners from various manufacturers. These liners were designed to fit amputees with a "standard" shape. Up until now there has not been a good suspension option for those individuals with unusual shapes such as congenital amputees.
This paper will cover two specific cases where Otto Bock's custom silicone liners offered unique solutions to optimize these prosthetic fittings. The 1st case is Ian, a five year old boy with PFFD and the 2nd case is Megan, a four year old girl with a metacarpal complete deficiency.
Case 1 is Ian who was born in April 1998 and was diagnosed with left PFFD, Aitken Type D and complete tibial hemmimelia. A very short femoral segment was present which was flexed and abducted. There was a complete absence of tibia although a "knee joint" was present. The fibula was short and had a five toed foot attached. The foot was rotated such that the toes pointed towards the ischium.
After a Symes amputation in early 1999, Ian was fit with a prosthesis and needed a hip joint and pelvic band to aid in suspension.
He had a revision in September 2000 where his hip was released to allow more hip extension and the fibula was fused to the distal end of the femur. Ian was fit with a new prosthesis incorporating ischial weight bearing and a Silesian belt. Suspension was the main problem. In sitting, the leg would pop off due to excessive flexion of the residual limb. He could ambulate quite well with a walker and seemed to tolerate the prosthesis.
In Ian's most recent fitting, a new socket design was investigated. Since the conventional silicone off-the-shelf liners did not fit his shape, a custom liner was requested from Otto Bock to allow distal pin suspension, and control rotation without a Silesian belt or other strap. When Ian was sitting, even with full flexion of the residual limb the liner would stay on! The liner fit so well that Ian felt the prosthetic leg was a part of him!
Lycra was also incorporated on the outside distal aspect of the liner for ease of donning into the prosthesis. However the entire proximal 2 to 3 inches of the liner did not have any Lycra and the silicone was left exposed – this was done to offer some rotational control because of the increased friction between the silicone and the socket. The silicone Otto Bock uses is a very durable material – it's much stronger than any silicone currently used in prosthetics! Traditionally, the silicones that we used in our labs were laminated onto a positive model and are room temperature cured. These silicones are not very durable and we used to integrate a matrix or stockinet to increase the strength. Whereas the silicone used for these clients are cured in the oven, and because of the chemical structure of the material (having longer chains and lots of cross links) it's extremely durable. Also, because of this strong silicone, the proximal edge of the liner was feathered to less than a millimeter. This thin edge prevents the skin shearing problems associated with the sharp edge of a thicker liner.
For Ian's prosthesis, all Otto Bock components were used except for the foot, modular locking aluminum knee and pylon and a Child's Play foot. It was very difficult, actually, virtually impossible to engage the shuttle lock. Even with the use of a larger pin – up to 2 inches – nothing worked! The shape of the residual limb made the approach to the lock at the wrong angle. The decision was made to cut out a wedged section of the lateral wall of the prosthesis – because of the banana shaped residual limb – to allow easier donning. A piece of spring steel was used as a hinge and Velcro straps kept the door in place. The patient was easily able to don the leg and engage the lock completely.
Ian has been seeing his Physical Therapist twice a month. She has noted some excellent gains in his function since he has received his new prosthesis in November 2002. Ian wears his prosthesis all day and is choosing to walk more frequently than crawl when at home. He is progressing to the use of only one crutch and has just begun this in March of this year. Ian is able to get from the floor to standing without support and is reported to stand alone for several minutes. He continues with Physical Therapy in the community.
Case 2 is Megan , who was born in May 1999 with a right metacarpal complete deficiency.
She was initially fit with a passive prosthesis with supracondylar suspension – a standard Northwestern style socket. Megan was fit with her 1st myoelectric prosthesis in 2001, again with supracondylar suspension.
One concern with this type of fitting is that the anterior brim was trimmed down low to facilitate donning of her long residual limb however, the suspension was compromised. At clinic, various options for freeing the elbow and improving suspension, without affecting the total length of the prosthesis were discussed.
The chosen solution was to fit Megan with an Otto Bock custom silicone liner for her myoelectric prosthesis.
Like Ian, Megan's congenital limb shape required a custom liner. Our goal was to design a suspension system that would not add any additional length to the prosthesis – in order to match the length of the sound side as closely as possible.
This liner suspended the prosthesis without extending above the elbow , allowing for greater ROM. A rectangular cut out was made in the liner for proper electrode contact. The electrode is mounted in the usual manner in the laminated socket to keep the electrode cables between the socket and forearm.
The main feature of the liner is the unique locking button on the side. This was used instead of a distal shuttle pin suspension, to achieve our goal of keeping the length of the prosthesis the same as the sound side. Also, a custom pattern was incorporated into the liner as Megan loves butterflies!
The prosthesis consisted of an Otto Bock System 2000 hand, electrode and external battery. The socket was fabricated by taking a cast over the silicone liner and laminating over the positive model. A hole was cut out for the side button to pop into for suspension and rotational control. A corresponding hole was made in the forearm so that Megan can press a button to release the mechanism and doff the prosthesis. This worked very well, she has a normal ROM at the elbow and the socket suspension is excellent. Megan prefers this type of design, and as a result, a passive prosthesis was made using the same silicone liner – so she can interchange her passive and myoelectric prosthesis with the one liner!!
We'd like to thank Ian, Megan and their families for allowing us to share their cases with you. These are just 2 examples where the Otto bock Custom Silicone liners allowed both Ian and Megan to have excellent suspension and to optimize these prosthetic fittings.
Sandra Ramdial, CP ( c)
Manager, Custom Silicone Services
Otto Bock Healthcare
2897 Brighten Road
Oakville, ON L6H 6C9