| On Stump Socket Lamination |
In Figures 4-25, the manual manufacturing technique of the soft liner socket for D.S.L.T. PTB prosthesis is shown. Before you start with any particular manufacturing step, you should read through all of this part of the manufacture, and all materials and tools required (see part 4) must be prepared.
For preparation in cutting the material for the soft liner you need the following
a circumference of widest knee joint part,
b circumference right above distal stump end,
c length from above (supracondylar) the knee joint up to end of stump.
PE foam material (PE-lite, Tepefoam etc., not Plastazote!) of 7 mm thickness is cut into a trapezoidal and symmetrical shape. The upper edge corresponds to circumference measurement "a" taken before.
The cut must be 100 mm (4 inches) longer than the length measurement "c" taken before. The width "b", however, is situated at a distance of "c" from the upper edge. This procedure makes the lower edge of the cut smaller than circumference "b" which is important for a proper fit of the liner.
Both oblique edges of the cut material must be chamfered. One edge is chamfered from the upper side and the other from the lower side.
If a sanding drum (or a grinding stone) is available, a thin wooden slat, used as a support, is put under the edge which should be ground to an equal width, without wrinkles or lacerations. The grinding width is about 15 mm (0.6 inches).
Please note: One edge to be ground from above. The other edge to be ground from below. Neat work is essential.
Please read text of Figures 1 and 6.
The wooden support for the cut must have the same thickness (20 mm, 0.8 inches) as the small wooden block on which the blade is fastened, otherwise the cut will not be correct.
Put the PE-lite along the edge of the support and now, simply push the blade along the edge. Tilting the blade (put underneath) can be advantageous for the cut. Practice with a piece of waste first.
Please note: Cut one edge from above. Cut the other edge from below. Neat work is essential. Cover the blade after use.
This working procedure using a shoemaker's knife is an alternative for the procedures shown in Figures 6 or 7. The criteria are the same, and the result must be the same.
This procedure is possible but needs expertise.
In case of difficulties, please proceed according to Figures 6 or 7.
Both chamfered edges are painted with a thin and equal layer of a flexible glue (Pattex or a similar type of glue). Before glueing together, be aware of the time needed for drying, which is given in the manufacturer's instructions.
Both glued edges to be painted with a thin and equal layer of glue.Avoid dirt and forming of bubbles.
Only a suitable glue to be used.Be aware of the time necessary for drying.
Fasten the glueing aid in a bench vice.Hammer in two thin nails in a way that:
a) the distance between them will be nearly the length of the glued edge,
b) their heads remain about 10 mm (0.4 inches) from the aid.
Remove the nail heads:
One glued edge should be laid along the aid with some slight stretching, and pressed through nails. Now, the piece is secured against slipping off. The second glued edge should be picked up, placed around, arranged, and pressed on, the mid part first. Rub towards the bottom accurately and without wrinkles. Rub towards top, accurately and without wrinkles.
Please note: The glued edges must be neatly arranged when one is put on top of the other. Working without wrinkles is necessary.
Glued edges of this kind maintain their stability due to the force of application during glueing. Forceful but careful hammering will stabilize the glued edges.
Please note: Avoid any damage of material.
This illustrates the finished cone to be used to make the soft liner.
The strength of the liner (material strength) is consistently the same, even within the glued edges. The edges should be perfectly glued ail over with no wrinkles, lacerations or other imperfections.
In the event the cone for the soft liner socket should show any manufacturing mistakes, the procedure must be repeated right from the beginning.
It is less costly and better to correct possible mistakes now, rather than to continue work with faulty results and be forced, later on, to start again.
The below knee (BK) stump has bony (little weight bearing capacity) and muscular (sufficient weight bearing capacity) parts. The bony parts are relieved in the socket whereas the muscular parts are mostly loaded. In order to relieve bony prominces therefore, reliefs within the socket are provided.
The soft tissue of different amputees vary from stump to stump. This diagram shows the areas which are generally relieved:
1. Medial (inner) edge of the femoral condyle: It can be palpated in thin patients and with flexed knees. Normally, it does not cause any difficulties since, when loading the prosthesis, in a standing position, it does not protrude. In some patients, though, it would be better to relieve this edge, the decision to do so will be dependent on the individual amputee.
2. Tuberosity at the medial (inner) head of the tibia. Mostly, the medial tuberosity is less pronounced than the lateral (outer). Therefore, it is not significant to relieve it for every patient but must be decided for each individual amputee.
3. Lateral (outer) tuberosity at the head of the tibia. This can be felt distinctly in almost all patients and therefore, it has (almost) always to be relieved.
4. The anterior (forward) protuberance of the tibial head which is also the beginning of the patellar tendon. Unlike the patellar tendon which can and should be loaded, this is a bony prominence which has to be relieved.
5. The cross-section of the tibia is triangular shaped. One of the edges protrudes anteriorly (forward). This edge, but only this edge and not the surface of the tibia, should be relieved. This edge is known as the tibial crest.
6. Bony (and muscular) end of the stump. Depending on the surgical techniques, the covering of soft tissues, the scars and possible nerve endings, the stump end is not well suited for weight bearing purposes, at best it can only be partly loaded. This can be determined by palpation and questioning of the patient. The decision of the amount of relief required will be dependent on the individual stump.
7. The head of the fibula protrudes distinctly in every patient. It must always be relieved.
8. For the end fibula, the same criteria are valid as mentioned under point 6.
The parts to be relieved are to be determined individually in every patient.
Important hints will be supplied by questioning and palpating the patient.
The relief pads shown correspond in their form and contour to the bony protuberances shown in Fig. 13. For preparation of the socket, they are applied on to the stump and later on, after completion of the socket, taken off. Thus, well defined free spaces for relief of the bony protuberances, are prepared.
Relief pads can be:
- Cuts from fast setting p.o.p. bandage (p.o.p. bandage is frequently available in developing countries) which is self-adhesive.
- A: Chamfered PE-lite pads, to be fixed with adhesive tape.
- A: Chamfered felt pads, to be fixed with glueing tape.
- A: Wax-like substances such as plasticine (or tissues soaked in bees wax) - self-adhesive.
- A: Clay or Loam - self-adhesive.
The pads must have their main thickness (about 3 mm) centrally, their thickness tapering off towards the edges. Their surfaces are slightly larger than the bony protuberances. In p.o.p. bandages, this can be accomplished by 4 somewhat larger basic layers and 4 identically shaped but smaller covering layers. The wet p.o.p. pad is fingermoulded and well stroked out towards the edges. With the other suggestions, this will be achieved by chamfering and grinding.
The procedures indicated by an "A" are alternatives in case p.o.p. bandages are not available. The procedure using p.o.p. cuts is the best solution. Thickness of relief pads is 3 mm centrally, tapering towards their edges. They should follow the contours of bony protuberances and their surface should be only slightly larger.
Due to possible pumping movements of the stump, they must be somewhat larger towards distal end. They must be well fixed. During subsequent procedures, their position must not change.
The best embedding and working position is a knee flexion angle of 30 to 40 degrees.
Two layers of cotton stockinette are put on to: a) act as protection from heat, b) secure the position of the relief pads.
The stockinette is pulled up to nearly half the length of the thigh, without wrinkles, well compressed, and fixed with glued tape.
The smooth textured side must be to the outside.
The stockinette must be free of wrinkles and well compressed.
There is an alternative for the stockinette. The stump can be wrapped with an elastic bandage or gauze bandage. Here, the edges must be secured with adhesive tape to avoid the bandage slipping during the subsequent working procedure.
All alternative procedures mentioned here are the second best solution only. Whenever stockinette is available, it should be used.
The stump covered by the stockinette must be well covered with talcum powder which serves as a sliding agent for ease of pulling on the soft liner.
In case an air circulating oven, a good baking oven or any other electrical source of heat is available, it can and should be used due to the possibility of regulating working temperature. For PE foam materials, a working temperature of 130 °C (270 °F) should be used. If these devices or an electrical supply are not available, a charcoal fire may be used for heating the thermoplastic material.
The cone used for the soft liner is placed on a broomstick or other similar stick, held above the glowing fire at a distance of about 300-400 mm (12 to 16 inches) and must be turned continually in order to heat it equally. Once it is soft, flexible and mouldable, the proper working temperature will have been reached. If its surface has become somewhat sticky, wait for the proper working temperature before continuing work.
Control of temperature is important for success of your work. The working temperature is achieved, once the cone
- becomes soft (easily to be compressed with your fingers),
- becomes flexible (could be=bent from side to side),
- becomes mouldable (possibility to widen the edge).
The material must be equally heated alI over. Sticky surface indicates over-heating.
Brown or wrinkled, hardened spots are burnt ones.
Do not continue working with burnt or partly burnt material as the padding effect and resilience will then be lost.
You are advised to learn this working technique with a test piece first.
Fig. 19: Additional talcum powder for sliding
Fig. 20: First applications of liner cone
The inside of the heated cone must be well powdered with talcum in order to assist it with sliding over the stump.
Pull the heated cone over the stump. -The position of glued edge should be posterior. This process should be carried out quickly but with great care. After the first heating, the cone can only maximally be pulled up to below the patella and therefore, it will have to be heated a second (and third) time in order to achieve its final position. On repeating it will lose some of its moulded form which, however, will be regained with the subsequent applications.
Do not continue work with possibly burnt material.
Do not work with overheated (sticky) material.
Do not continue working with cooled material as it cannot be moulded.
Do not pull the material if it is not sliding over the stump easily as its edges could be torn off.
Talcum powder must be applied before each application (of the cone).
Fig. 21: Final position after 2 to 3 healings
Fig. 22: Cutting of lower cone end
The final position of the cone must have a sufficient height such that, later on in the procedure, the brim forming will be achieved easily (Fig. 46 and 47). Please bear in mind that the inner liner will be 5 - 8 mm longer than the hard outer socket.
The applied height is sufficient once the inner and outer brim reach about the height of the upper patella edge. However, it would be much better if it can be pulled up to the supracondylar area. There it will form folds and bulge but this is of no significance since these parts will be cut off later on.
The distal end of the cone must enclose the stump well and must contact it all over, without any free space.
For postmoulding of the distal socket end:
- re-heat distal third of cone,
- pull the cone up and let the patient hold it,
- free spaces and wrinkles must be pushed off downwards,
- forming wrinkles below the stump is of no significance, as they will be cut off later on.
Do not twist the heated cone as this will form folds and wrinkles.
Do not overstretch the heated cone as this will result in differing liner thickness which would be weak spots in material.
Pull the proximal end of the cone as far up as possible. The distal closure must not have any free spaces.
The area of what is to be the final soft liner must be kept free of wrinkles. Position of the glued edge is always posterior. For other precautional measures see the description of Figure 20.
Draw a circular trim line at the distal end of cone, as far distal on the stump as possible, above the level of the folds. The distal cap, including all folds, is cut off. This cut edge must be even and smooth.
Pull cone off, distal end to be cut neatly (no peaks) in a circular way. Very sharp knife to be used.
The newly existing distal end should be chamfered. Use a sanding drum (perhaps grinding stone), or handrasp and sandpaper.
Please note: Distal brim to be chamfered evenly and smoothly. At any case, avoid laceration. Cone to be pulled on again.
Cut a square piece of PE foam, sufficiently large for closure of the distal opening, about 150 x 150 mm (6 x 6 inches). Heat it, hold it at the corners and, with slight stretching, pull it over the distal stump end. During this procedure it would be helpful to make use of an assistant. Attention must be taken that the distal end of the cone is not damaged. After pulling over, the piece should be well moulded with both hands and kept in position until cooled down. Then, it should be cut in such way that the chamfering on the cone is well overlapped. Mark the subsequent glue edge and the position.
The edges are painted with glue and the end fixed in its correct position.
Even and wrinklefree glueing of the end of the cone is necessary.
The soft liner is taken off again and now, the glued edge is chamfered from the outside. No wrinkles, lacerations or holes are to be seen at the neat closure of the distal end.
Frequently, a second layer of PE foam will be required in order to sufficiently pad the stump end. Check the material thickness of the distal closure.
Checking the Results
The completed soft liner is an essential part for a good functional interface of the stump with the prosthesis to be manufactured. All possible manufacturing faults affect either directly the interface with the stump, or else the life expectancy of the soft liner.
Thus, the liner must be examined carefully both on and off the stump.
Examination on stump:
- Is the glued edge situated posteriorly?
- Is the fit faultless?
- Is the liner sufficiently adjacent to the stump all over?
- Does it present no free spaces?
- Are the relief pads in the prescribed position?
- Is the proximal end sufficiently high?
- Is the distal end sufficiently padded?
Examination when taken off the stump
- No overhead or burnt parts?
- Do the glue edges adhere without wrinkles?
- No lacerations, wrinkles or holes?
- No weak spots along thickness of liner?
The soft liner should only be used if all points mentioned above are acceptable.
It is easier and less costly to manufacture a new soft liner right now than to ignore the faults which will lead to a faulty result.
In many cases, the patient needs two soft liners in order that they may be exchanged. In this case, the second should be manufactured now and, after completion and the measurements, compared with the first. Later manufacture will always bring different presuppositions (e.g. different relief pads for bony structures, etc.) and thus, a second liner which is manufactured later on will not fit with the prosthesis as well as one manufactured now.