| On Stump Socket Lamination |
Figures 26-57 show the manual manufacture of the hard outer socket for the D.S.L.T. PTB prosthesis. Before continuing with the particular manufacturing steps, you should acquire a comprehensive view, and all tools and materials required (see part 4) should be well prepared.
In spite of careful mixing of resin, hardener and accelerator it develops warmth during its setting process. With faulty mixing it can become hot. The stump of the patient is protected from this warmth by two layers of stockinette and by the soft liner. Care should be taken that the thigh must also be protected against this warmth although this should not be necessary since the resin should not reach this height. However, it is better to take a lot of care in order to absolutely ensure that the patient is not burned. The following steps must be taken:
- wrap the proximal liner with a gauze bandage or elastic bandage,
- with the rest of the bandage, the distal third of the thigh is bandaged with overlapping,
- the bandage must be secured with adhesive tape.
The PVA sleeve, moistened in a wet towel, and the soft liner are powdered with talcum which serves to aid the PVA to slide on to the stump.
The PVA sleeve is put on. It will be pulled proximally as far as possible, displacement of the heat protection bandage is to be avoided at any rate. The sleeve must well compress the soft liner all over and be free of wrinkles. If the sleeve is too dry, it is not elastic and difficult to be pulled on, whereas a sleeve which is too moist will be torn.
Wear no jewellery (rings), and the edges of fingernails must be well trimmed and smooth. Be careful that the sleeve is moistened correctly.
The sleeve should be pulled up as high as possible.
Avoid displacement of heat protection bandage.
Avoid damage to the sleeve.
A damaged sleeve must be replaced by a new one.
Once the PVA sleeve is completely pulled up and fixed at the proximal end, the wrinkles at distal end can be mostly eliminated by pulling out downwards, ensuring that the soft liner is well compressed all over. The sleeve must be tied tightly with a double thread at the distal end making sure that the PVA film is not damaged. Cut off the excess PVA film at the end of the sleeve.
Now, the sleeve entirely encloses the soft liner, compressing it and with no wrinkles other than several small ones at the distal end. Wrinkles in the area of the thigh are of no significance.
Sleeve to be pulled up without wrinkles compressing all the soft liner.
At stump end, sleeve is to be tied and cut off.
Damage of sleeve must be avoided. A possibly damaged sleeve is to be replaced by new one. Avoid displacement of heat protection bandage.
An alternative for the PVA sleeve is given by any PE film (e.g. film of plastic shopping bags). However, PVC film must not be used as polyester resin does not harden when in contact with PVC.
PE film is not as elastic as PVA film and is difficult to make into a conical bag form. Thus, it is applied by wrapping it into the stump, or by laying it on the stump and turning over in one piece, care being taken to ensure that it is as wrinkle-free as possible. However, this procedure is not possible without wrinkles. The edges must overlap and are to be fixed with adhesive tape in order to reliably avoid penetration of the resin into the soft liner. Do not apply PVC glue tape (see above).
All alternative procedures mentioned above are second best solutions. Whenever PVA sleeve is available, this should be used, and not PE film.
Do not apply PVC film and PVC adhesive tape.
Wrinkles within the soft liner caused by film wrinkles must be smoothed off later on and could possibly lead to inaccuracies of the fit.
For lamination, a total of 6 layers (3 double layers) of stockinette will be pulled on. Nylon stockinette is more stable but where not obtainable, it could be replaced by cotton stockinette. Stockinette pieces of double length are pulled above the knee, the distal end is either tied or turned around once, then turned over and pulled up above the knee. Both upper ends of the final double layer are cut at their anterior and proximal part (on the thigh) for about 20 - 30 mm (0.8 to 1.1 inches) and knotted firmly with each other. Thus, the stockinette is pulled up in a wrinkle-free and compressing manner.
If glass mat or fibre glass is available, this can be used for reinforcing the lamination. For each of the two last layers, take one piece of glass mat, the size of palm of a hand and push them medially and laterally underneath the layers. This is especially indicated in heavy or active patients although it is not absolutely necessary. Use of an entire glass mat is contraindicated as:
- processing of the brim will be much more difficult,
- thermoplastic re-moulding will be more difficult,
- during the pouring procedure you cannot judge whether the resin has completely soaked the stockinette layers under the glass mat reinforcement.
Six layers of stockinette to be put on.
Stockinette must compress without wrinkles.
Stockinette must be fixed so that no displacement occurs.
Final appearance of completed laminated stump.
There is an alternative to the application of stockinette: The use of medical cotton gauze bandages. These bandages are wrapped,with good tension and must overlap each other. There should be at least six layers in order to achieve the required liner thickness.
The bandage ends must be well secured.
The alternative procedure mentioned above is always a second best solution. Whenever stockinette is available, this should be used, and not the gauze bandage.
The outer PVA sleeve, well moistened in a wet towel, is pulled up.
Be careful that the sleeve is moistened correctly. Avoid damage to PVA sleeve.
A possibly damaged sleeve is to be replaced by a new one.
Sleeve must be pulled up well compressing the stockinette. Do not cut the distal sleeve end.
Fig. 36: Outer PVA sleeve in final position
Fig. 37: Preparation of compression pads
As described already (Fig. 13) some weight bearing surfaces of the stump must be in good contact with the liner, in particular the muscular parts must be compressed in order to take up weight. Due to the relief pad applied on the crest of the tibia, the soft liner as well as the stockinette tend to gap medially and laterally to the crest and thus are not in contact as required.
This can only become corrected from the outside by the following means: medial and lateral compression pads made from PE foam are prepared and, after moulding and compressing, applied there.
Size and form of compression pads to be determined individually. Parts to be chamfered towards the edges in order to avoid impression of edges.
The lateral compression pad extends around behind the stump for about 30 mm.
Application of pads is described under Figure 43.
During its setting reaction, resin develops warmth or even heat. The heat is dangerous to the patient. Therefore, by application of less amounts of hardener and accelerator than usual the heat development is reduced so that it only becomes warm. A desired side effect of using less amounts of hardener and accelerators is prolongation of setting time and, thus, simplification of the entire pouring procedure.
Due to the fact that resins from different manufacturers will require different percentages of hardener and accelerator, absolute details cannot be given here; But the following is always valid:
A maximum of 2/3 of the normal hardener amount is to be applied.
A maximum of 2/3 of the normal accelerator amount is to be applied.
Never use a resin on a patient if the relation of mixture and type of reaction are not exactly known. Never use unknown resins.
Danger of burning exists.
Acrylic resins need no accelerator. Some polyester resins have been pre-accelarated already and need no accelerator. Acrylic resins are more suitable, but polyester resins are quite applicable.
Before applying the resin, the stump outlines are palpated once again. For a good result the following areas should be noted: - bony contour of patella, - bony distal edge of patella,
- the tendon of patella (see drawing),
- bony contour of tibial head,
- bony contour of tibial crest,
- medial bony surface of tibia,
- bony small head of fibula,
- muscular surface, lateral to tibial crest,
- compressibility of calf muscle,
- popliteal flexor tendons,
- concave curvature of popliteal area.
Test application of moulding tool. It has two moulding sides, one of which should fit. But this must be, checked and, if necessary the tool re-adjusted.
All items mentioned above will be considered later on during socket manufacture in order to achieve a good functional result.
Turn over PVA sleeve brim so that it cannot be torn, fill with resin mixture. The sleeve is kept in the illustrated position until the air enclosures (larger air bubbles) have escaped.
Is the relation resin: hardener correct?
Do not throw away the mixture cup for resin, it will still be needed.
After the air bubbles have escaped, the resin will be pressed slowly into the stockinette material, evenly soaked from distal toward proximal part. Unsoaked ‘isles', must be avoided. For the present, the resin is not to be distributed higher than a level under the base.
Resin is only to be pressed up to under the knee.
Adhesive tapes are available in order to close quickly any possible holes in the PVA sleeve. This procedure can be carried out slowly as hardening will still take about one hour.
The sleeve is tied below the resin reserve (without any trapped air) in such a way that the knot can be reopened without damaging the PVA film (do not use a thin thread but a thicker string or shoe lace). The sleeve end is to be turned over and tightly tied (thin tread) in order to avoid unnecessary dripping. Now, with a shoe lace, the resin is slowly and carefully distributed up to the resin boundaries presented on the sketch. Powdering of . the sleeve with talcum will ease this work. Do not exceed the resin boundaries given, otherwise you cannot pull off the socket later on.
- Under the film, due to trapped air, parts with uneven resin distribution are seen. It helps to make several small holes by means of a needle into the part concerned. Massage the trapped air out of these holes, until only resin appears. Wipe this part neatly and close it with adhesive tape.
- Under the film surplus resin can be seen. The surplus resin should be massaged into the resin reserve at the stump end by means of the shoelace.
Open the shoelace at stump end again and let the resin surplus run back into the PVA film hose. After ensuring that the resin is evenly distributed with no puts bearing too little or too much resin the sleeve will be finally tied as close as possible to the stump end.
When pricking the film, splashing danger exists as the resin is under pressure.
Eye protection to be worn.
Be careful of the proximal resin boundaries. Eliminate trapped air.
Clean work is necessary - resin may cause skin damage.
Spilled resin must be cleaned immediately.
Check again the PVA film with regard to tightness. Any leakages have to be closed by adhesive tape. The distal sleeve end should be cut off below the knot. Film end must be wiped clean. The remains of the resin in the cut-off sleeve are poured back into the mixing cup.
Wait until the resin begins to set.
Due to the higher resin concentration, this will occur first with the remains in the mixing cup. Watch the cup and as soon as it gets warm, the next procedure will start.
Start fixing the compression pads in their intended position by wrapping them with an elastic bandage. Avoid any stringy (bandage) wrinkles. The bandage must not be wrapped higher than required. Fix the bandage securely by means of adhesive tape.
With one hand:
Apply the moulding tool. Its concave edge applies pressure on the patellar tendon and outlines the contour appearance of the patella area. However, it must not press onto the bony structures. Faults in application of the moulding tool will result in high pressure points in the prosthesis.
With the other hand:
The other hand is located on the posterior side of the stump. Intermittently, it presses carefully on the calf, flattening it, and the finger tips mould the proximal, posterior socket brim at the popliteal region and the flexor tendons area. Do not apply pressure onto the flexor tendons.
The functional moulding, with intermittent pressive hand positions, is kept up until the resin is so hard that its shape will not change anymore.
Alternatively, instead of application of a PVA outer sleeve, the resin could also be applied by brush onto the stockinette layers.
The alternative procedure mentioned above is always the second best solution only. Whenever PVA sleeve is available, it should be applied.
After application of the alternative procedure in Figure 44, the resin is massaged by means of a metal spatula into the material in order to ensure its thorough distribution through it. Simultaneously, the resin surplus is pressed out again. The surplus resin should be collected in the mixing cup which must be held underneath.
If a PVA outer sleeve is not available, the functional moulding procedures presented in Figure 43 will be difficult or made impossible. The functional moulding corrections must then be performed later, which is much more difficult, and imprecise in its result.
This diagram shows the position of the cut edge of the socket brim from both an anterior and a lateral view. The patella is covered between 1/3 to 1/2 of its height. Laterally, the socket brim rises about 20-30 mm (according to size of patient) above the mid patella at a position of about 2/3 of the lateral leg width. Then, slightly slanting, it runs relatively steeply down, posteriorly. The measurements given are approximate only. The brim slope is specific to each patient, and differs individually.
1. shows the undulating form of the posterior socket brim. Its mid-height corresponds to about the height of the midpatellar tendon support bar on the anterior side.
2. shows relief of the lateral flexor tendon.
3. shows relief of the medial flexor tendon.
Here, the soft liner is wrapped around the posterior brim in order to act as protection from pressure and also when the leg=is flexed (sitting position). The medial flexor tendon must have more relief than the lateral one. Forming the posterior brim requires skill and careful check of the result with the cooperation of the patient.
4. shows a concave impression in the distal popliteal area. This acts as a counter support (popliteal pad) in order to firmly secure the position of the patellar tendon opposite patella support bar. Above this impression, though, the socket brim is bulged outwards.
The soft liner must be 5-8 mm higher than the brim of the hard socket.
The socket brim shape, as indicated in Figures 46 and 47, are cut with strong scissors.
Exact contours are formed by a handrasp. Here, rasping for medial flexor tendon is shown. Subsequent smoothing is done with sandpaper.
Be careful when forming the brim.
It is easy to remove material, but once removed it can not be patched on again.
The soft liner is 5-8 mm higher than the hard socket brim.
For fitting and for subsequent processing, the socket is inserted into a block of light wood, inserting it to a depth of about 40 mm (1.5 inches). It is glued with a mixture of resin and sawdust.
The wood fibres run in vertical direction. This time, the resin should be prepared with normal hardener amount. Position and arrangement of socket can be seen in Figures 51-53.
Alignment of the socket depends on the individual stump position. For adducted stumps, alignment is adducted, for abducted stumps, it is abducted, and for stumps in neutral position, sockets will be aligned in neutral position. Deviation from anatomical and biomechanical considerations will cause pressure sores by the socket.
Frequently, with the normal anatomical shape, medium length stumps appear to be in an adduction of about 5°, whereas extremely short stumps appear to be, or are really in a position of abduction. Compare with the form of your own lower leg, at different heights below your knee joint.
Fig. 52: The result - posterior view
Same alignment of socket (here, in neutral position), posterior view. Here again, the position of the brim is made clear.
Fig. 53: The result - lateral view
The lateral view shows a flexed position (forward tilt) of the socket, of about 5°; this slightly flexed position is essential in order to achieve a good force distribution and force acceptance by the patellar tendon. A more flexed position is possible, but an extended or hyperextended position is contraindicated.
Looking from above into the socket, a cross-section of a triangle with almost equally long sides is to be seen. One side forms the anterior, medial tibial edge, the next stands for the anterior lateral muscle surface, and the third side for the flattened calf.
This functional shaping prevents rotations of the prosthesis around the stump and simultaneously corresponds to the anatomical biomechanical requirement of the BK stump.
It is not possible to functionally modify the D.S.L.T. socket to such a degree as would have been the case with a positive p.o.p. model. Alteration in shape or volume, though, may be carried out to a possibly required extent, without real difficulties.
With a cone-shaped metal nozzle turned upside down and put on a charcoal fire (e.g. a petrol funnel), certain parts of the socket may be point heated in order to re-mould these parts thermoplastically.
Fig. 56: Point heating by means of lighter
Minor shape alterations, e.g. Iimited pressure points, can be heated with a normal gas lighter.
Fig. 57: Manual moulding alteration
Thermoplastic corrections are performed manually. A moist cloth protects against burning the fingers and, simultaneously, cools down the desired result more quickly.
Example on picture:
Increasing the position of the posterior, distal popliteal pad (with more pressure into the socket) and, simultaneously, greater bulging outwards of the posterior proximal socket brim.