WAX CHECK SOCKET FIT FOR RI-MD HINGE

When single pivot or polycentric rigid hinges are to be used, additionalprocedures must be performed, Procedures relating to trim for pronationand supination are excluded.

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The proximal trim line is outlined asshown. Sufficient material must coverthe medial and lateral humeral condyleswhere the joint spacer will be placedon the joint axis. The posterior trimshould be one inch proximal to theolecranon.

When rigid hinges are used additionalflare and trim at the cubital foldshould sometimes be made to permit 13s’of elbow flexion and to keep the tis-sues from forcing the socket off thestump.

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The posterior trim should be proximalto the olecranon.and without excessivepressure against the triceps tendon at10° of elbow flexion. Ample socketmaterial over the humeral gn

Locate the axis of rotation for the rigid hinges joint center with a pair of. pointed outside calipers. Select points over the medial and lateral epicon-

dyles of the humerus. Put the points of the calipers into the outer surfacesof the check socket. This can be done with the socket off the amputee afterthe points have been selected. Be careful not to change the medig and lat-eral dimensions. This procedure should be carried out with care and preci-sion to avoid motion between the mechanical joints and the stump in the fin-ished prosthesis.

Begin the procedure as illustrated,with elbow flexed 90°, and the calipersnearly parallel to the humerus.

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Lightly pull the socket upwards whilethe amputee slowly extends his arm toapproximately 30' and returns it togo*.

Observe the motion of the calipers atthe point illustrated. If properlyplaced, no motion will be observed.

If no relative motion exists betweenthe calipers and the arm, have thepatient slowly flex his elbow to approx-imately 130’. Use a goniometer ifnecessary, maintaining the check socketon the stump with the opposite hand asshown.

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Change the direction of the calipersuntil they are perpendicular to thehumerus as illustrated. Repeat theprocedure with the amputee flexing andextending his elbow within the parame-ters established in the previous step.

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When the calipers do not exhibit medio-lateral wobble or the points do notmove in a semicircle in both caliperpositions, the rotation center has beenlocated.

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Hold the calipers as i l lustrated. Ifthey move medially or laterally, thejoint centers are too anterior orposterior.

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Again hold the calipers perpendicularas illustrated. If they move mediallyor laterally, the joint centers aretoo distal or proximal.

The elbow joint centers may or may not fall over the epicondyles. If in theabove steps, the calipers move, the points of the calipers must be repositionedon the wax check socket. Observe both points of the calipers as follows.

Distal

Anterior

Proximal

If the point of the caliper moves in an arc as shown by (A) in the above diagram,then the point must be moved posterior on the socket toward the true center ofrotat ion (@). If the point of the caliper moves in an arc, (IS), then the pointmust be moved distally. If the point moves in an arc, (C), then the point mustbe moved anteriorly and proximally.

As described above, reposition the points of the calipers and observe their move-ment, as shown on steps (1) and (2) until the calipers no longer move with elbowmotion. Now the elbow joint centers have been located. If the cam action ofsome elbow joints or excessive soft tissues prevent exact placement over the cen--

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ters, a compromise must be made.

-Provide clearance of 1/4-inch overthe medial condyle of the humerus.

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Repeat the above over the lateralepicondyle allowing clearance o f3/16-inch.

The fitted check socket is shown.Mark the correct joint axis center.

With a pair of inside calipers, meas-ure the medial-lateral width at thejoint centers and record it on theprbsthetic information sheet. Thiswill be needed when the joint spacersare installed.

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Single Joint Spacer

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Joint spacers hold rigid hinges in alignment until lamination procedures arecomplete. Immediately after the fitting, the joint spacers are installed in thecheck socket. The joint spacers must be carefully installed so that the checksocket is not distorted. (SeeChapter IV, Materials, for details).

The complete spacer assembly is shown,with a cutting- tool for making thespacer holes in the check socket.(See Chapter IV, Materials on how tomake a cutting tool.)

Set the inside calipers to the widthof the medial-lateral distance ofthe socket.

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Punch the joint spacer holes. Re-check the medial-lateral distance withthe calipers. If the distance changedwhen the spacer holes were being made,reset the distance.

Set the joint spacer to the approxi-mate medial-lateral width. Do notinclude the steel spacer washer inthe setting because it is used todetermine the lamination thickness.

Slide the spacer through the holes.

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Align the face of thebrass spacer. The steelspacers have been removedfor i l lustrat ive purposesonly . The wall of thecheck socket is usuallvon an angle to the faceof the spacer. Place theface end of the spacerjust inside the deepestpoint of the angle. Whenthe lamination model ismade the brass spacerwi l l pro ject out o f themodel approximately l/U-inch at its lowest point.

Loosen the lock nuts andadjust the length untilthe above procedure isrepeated on the oppositewal l .

Recheck the medial-lateral width.Tighten the lock nuts on the spacerbo l t . The spacer should now be heldin true alignment by the threads. Ifthe spacer heads wobble, replace thethreaded bolt with a longer one. Puta parting agent on the spacer.

Breakout Mold

Materials:

plaster

mandrel

knife

sandpaper or screen

parting agent for the mold

Seal the holes in the check socket and make a breakout mold as described in ChapterIV, Materials. Insert a mandrel in the plaster for holding the mold.

When the plaster has set, carefullyremove the wax check socket by cutting,heating and peeling it off the mold.

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Smooth the mold, especially the triml ines; they should be round enough toform a comfortable rolled edge on theplastic socket. Apply a parting agentto the mold for the plastic lamination.

Plastic Socket -

Materials :

dacron felt

nylon stockinette (approximately 2 inches wide)

PVA and iron

polyester resin, catalyst, promoter and color pigment

masking tape

string

Flexible Hinge

Make a dacron bag and pull it over themold. Sew across the end of the nylonstockinette and pull it over the mold.Make one layer of dacron and two lay-ers of nylon stockinette. Now startthe lamination.

Rigid Hinge

Materials in addition to above:

single pivot or polycentric hinge

bending irons

lamination spacers

When the wax check socket is removed,the single steel spacer washers willproject out of the model. This deter-mines the thickness of the socket. Ifa heavy duty prosthesis is desired,add additional washers.

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Apply one or two dacron layers andtwo layers of nylon stockinette onthe lamination.

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Cut small slits over each of the spa-cer heads as illustrated.

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Assemble the joints to the model.First apply a lamination spacer (seemanufacturers ’ instructions) o_ver thesteel spacer washer and then the lowerjoint straps. Bend the straps off themold until they lie parallel to theaxis of the stump with 1/8 to 3/16=in-ches of space under the straps. Donot tighten the straps against thymodel because the resin will notpenetrate underneath.

Fill the space between the stockinetteand the straps with dacron felt.

Align the straps parallel to the ulnaor the posterior aspect of the model.T h i s w i l l preflex the jo ints 15’. Ifmore flexion between the upper armcuff and the socket is needed, movethe end of the stump model upwardsfrom the strap until the additionaldegrees are obtained. A simple wayto check the alignment is illustrated:when both joints rest on the vicejaws the joints are parallel. Tightenthe holding screws.

The lamination washers project proxi-mally on a 15’ angle to the lowerstrap. Put two layers of nylon stock-inette over the straps so that theywill be imbedded in the plastic socket.

Tie thestring.

stockinette at the bottom with

Make a PVA bag to fit over the mold(see Chapter IV, Materials). Dampenit and pull it down tightly until allwrinkles have disappeared. Tie thebag to the mandrel.

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Mix polyester resin with its promoter,catalyst and color pigment (see page

) Pour the resin into the top ofthe &A bag and work it into the sotck-inette. Tie off the top of the bag toremove excess resin.

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FOREARM EXTENSION

Flexible and Rigid Hinge Prostheses .

To establish the length of the below elbow prosthesis9 a filler between the end ofthe stump and the wrist unit must be provided. This is the holding receptacle forthe terminal device. If the amputation is unilateral, the overall length includingthe terminal device equals the length of the elbow to the thumb tip on the soundarm. This is standard procedure but variations do occur, such as congenital anom-a l ies , or special occupational requirements. If the fitting is for a bilateralpatient, consult the anthropometrical chart on page .

Materials used to form the extension vary according to stump length and the natureof the prosthesis, exoskeletal or endoskeletal,

Wrist Disarticulation: the extensionis minimal and therefore exoskeletal.

Short Below Elbow: the extension can be either exoskeletal or endoskeletal as shown.

Alignment: Standard practice is to make the forearm strafght, similar to the norm-al forearm. Certain advantages can be gained by preflexing the forearm and cantingthe wrist unit. Canting is described as an alternate method in the following steps.Preflexion is described in detail for the Muenster prosthesis in this chapter.

Forearm Extension Alignment

To determine the length of the forearm, take the lateral epicondyle to thumb tipmeasurement from the prosthetic information form. (The olecranon to thumb tipmeasurement may also be used.) From this measurement subtract the length of theterminal device to be used. (If the prescription calls for more than one terminaldevice, use the length of the longest device.) This remaining amount will be thelength of the forearm.

Draw a line on the posterior socket. For a flexible hinge prosthesis, make theline parallel to the long shaft of the ulna. For a rigid hinge prosthesis, drawthe line perpendicular to the joint spacer.

Place the socket in a holding device. In the picture below, an alignment jig isused. Any suitable holding fixture may be used.

Adjust the holding device to the length of the forearm determined above. Measurefrom the flat level surface up to the mark (olecranon, epicondyle or the jointspacer, whichever method is being used).

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No canting of the terminal device: Position the socket so that the long axis isperpendicular to a flat level surface. Use the reference line drawn on the socket.

viewed from t,h.e posterior viewed from the side

Canting the wrist unit: From the prosthetic information form determine to whatdegree and direction the terminal device will be prepositioned from the long axisof the stump. Using the reference line as a guide,, align the socket as follows:

Viewed from the posterior position.To bring the terminal device inwardtoward the body (ulnar flexion), tiltthe socket so that it leans toward thebody at the proximal end. A left armprosthesis is i l lustrated. The direc-tion is opposite for a right armprcsthesis.

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Viewed from the side (medial or lat-eral) . To bring the terminal deviceinward and upward, in addition to thestep above, position the long axis sothat it appears to lean toward theanterior at the proximal end of thesocket. Recheck both angles with aprotractor. It is important that theyare correct; an error here could ruinthe prosthesis. Secure the holdingdevice so that it will not move.

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Center the wrist unit under the longaxis of the stump as illustrated andscribe the position.

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viewed from the side

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viewed from the posterior

If an oval wrist unit is to be used,rotate it internally until it appearsto hang at a natural angle (about 20’).A wrist unit at this angle also makesit easier for the amputee to work on aflat wurface with a terminal device.

Mask the threaded hole and seal thevital parts with clay or playdough.Cover the knurled portion with maskingtape to keep it clean for subsequentlaminating.

Make a cone for the forearm extension(see Chapter IV, Materials). Attachit securely to the wrist unit. Inthe i l lustrat ion , polyurethane isused.

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Temporarily replace the wrist unit andcone into the scribed position pre-viously marked. Adjust it for sizeand length desired in the buildup.

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Fasten the wrist unit and cone so thatit will not move. Clay is satisfac-tory if additional support is pro-vided during the foaming action.

An elaborate holding device isi l lustrated.

Prepare the foaming mixture (see Chap-ter IV, Materials) and pour it into thecone. Observe all safety precautionswhen working with polyurethane (seeChapter IV, Materials).

Use more material than necessary forthe buildups. Ample material is need-ed for shaping.

Remove the cone from the buildup. Itshould appear smooth and contain amplematerial for shaping.

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Shape and contour the foam to matchthe sound side as much as possible;the wrist unit will limit this some-what. Be sure to remove all foam atthe proximal trim line of the socket.

Paint all of the model except thewrist unit with mixed polyester resin.This will seal the foam and eliminateair bubbles during lamination.

Sand the model until it is smooth;the final lamination will then bond.

Mask off the end of the wrist unit.

Final Lamination: Make a layup oftwo layers of nylon stockinette.Double one piece of stockinette backover the model and tie it at thegroove in the wrist unit. For a heavyduty prosthesis add more layers ofstockinette.

Kake a PVA bag, mix the resin, andlaminate the model.

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Fitting and Harnessing

Materials:

rubber mallet-

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sander

terminal device

pattern of triceps pad or arm cuff

polyethylene or flexible polyester plastic

flexible hinges

rigid hinges

cable and large cable housing and liner

diagonal shears

swivel terminal

retainer

swaging tool or soldering kit

adjustable hanger and allen key

For rigid hinges only, uncover thejoint portion of the lower strap andtrim the plastic to remove the lamin-at ing spacer. Use a heat gun tosoften the plastic.

After the final lamination has set andcured, break out the mold and trim thesocket to the lines made from the waxcheck socket. The edges should berounded, and the inside very smooth.For the rigid hinge prosthesis, removethe elbow joint spacer from the sock-et by loosening the joint spacer nutsand pulling out the spacer assembly.

Typical trims for the rigid and flex-ible hinge prosthesis are illustrated.For more detail, see page .

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Prepare the flexible hinges (see page , Chapter IV, Materials). The patient witha flexible hinge prosthesis is now ready for fitting and harnessing. Turn toPage l

For a rigid hinge prosthesis, proceed to the next page.

- Remove al 1 excess resin that may haveadhered to the joint surface. Suff i -cient clearance should exist betweenthe joint head and the socket so thatthe upper joint strap will not bind.Clean and lubricate the wrist unit.

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-Assemble the joints and wrist unit.They should move freely withoutbinding.

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Prepare the control system assembly..

Attach the terminal device and thecable assembly forearm base plate.(An APRL hook requires an extra baseplate on the posterior forearma)

Make the upper arm cuff from the pattern that was drawn when the prosthetic infor-mation was obtained (see page 9 Chapter IV, Materials).

Apply the prosthesis using stump socks,if any. If the check or trial fittingsocket technique is used, the prosthe-tic socket should be a perfect fit.There is no need to trim or carve thesocket.

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Observe the relation of the straps tothe upper arm. They should lie evenlyalong the skin. In some cases no bend-ing is necessary. If space does exist9measure the distance of the straps fromthe upper arm. Make sure the socket isproperly oriented on the stump.

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Bend the straps. If sharp bends orconsiderable offset are needed, removethe upper straps from the prosthesiswhile shaping the straps.

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Locate the half cuff at the lowestpossible point on the humerus. Leaveenough room between the distal edge ofthe cuff and the posterior socket brimso that the tissues will not bepinched at full extension.

Adjust for even pressure against theposterior aspect of the arm. Foldthe cuff and the top end of the upperbar, and ask the patient to flex andextend his elbow joint. Note themovement of the bar in relation to thelower edge of the cuff in the anter-ior-posterior plane. Adjustment canalso be made by temporarily attachingthe top of the bars to the cuff. Ifrelatively l i tt le exists , scribe alongthe bars. If motion of the bars doesnot exceed 1/4-inch, mark the centerof the two extremes of motion. Dri l lholes in the upper straps and rivetthe cuff to the straps. If the motionexceeds 1/4-inch, investigate thesocket f it . The probable cause is the

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anterior brim.