5a. Triceps Pad and Humeral Cuff Fabrication

Below-elbow hinges connect the socket to the cuff or pad on the upper arm and are important for suspension and stabilization of the prosthesis on the limb. There are three major types of hinges: flexible, rigid, and step-up. The selection depends primarily upon the level of amputation, residual limb condition and the individual’s level of activity.

In this section, you will find directions for fabrication of 1) flexible hinges and triceps pad and 2) humeral cuff for the rigid hinges.^[1]

Flexible Hinges and Triceps Pad

The flexible hinges and triceps pad provide suspension to the socket while allowing elbow and forearm motion. Once fitted, the patient should be able obtain 50% of their residual pronation/supination with flexible hinges. Flexible hinges are fitted with a triceps pad, which allows for the attachment and transmission of force for cable operation.

Process to Fabricate and Fit Triceps Pad (7 steps)

1) Fabricate pattern for triceps pad

1. 1. Gather supplies:  paper, scissors, pencil, measurement sheet
   2. Find the circumferences just above (a) and below (b) the belly of the biceps and the length between them (c).
   3. Fold a piece of paper in half and mark the length between the circumferences along the fold (c).
   4. Determine ¼ of the circumferences and mark this spot perpendicular to the fold. Draw the line that connects the two spots.
   5. Curve the line inside the lines drawn to a pattern similar to the drawing below.
   6. Cut out the pattern

2) Assess triceps paper pattern on patient with elbow at 90’

• Position the cuff pattern on the patient so the proximal edge is at the level of the deltoid insertion. The distal M/L corners may lay over the epicondyles or allow more clearance, based on pt preference.
• Trim the pattern to allow unrestricted elbow flexion.

3) Fabricate the flexible hinges and cross hanger

• Gather supplies: ½” Dacron for hinges, 1” Dacron for crosshanger, screws for attachment to distal end of forearm, rivets or buckles for attachment to triceps pad.

• 

  Hinges:

  • Purpose: Provide suspension and allows pronation/supination of the prosthesis
    • Flexible hinges may be fabricated from various materials:
      • Dacron webbing – lightweight, inexpensive and comfortable
      • Leather – may stretch over time
      • Cable – durable for heavy-duty use, may add weight and may limit some pronation/supination.
  • Fabrication: Cut two lengths of ½” Dacron, each a little more than twice the distance from wrist to 4-5 cm proximal to epicondyle. (In clinical practice, double the length and sew together to provide more durability.)
    • Distal location: 2.5cm proximal to wrist unit (to allow maximum pronation/supination). Burn two holes through the distal ends of each flexible hinge. Fasten the flexible hinges to the prosthesis with cadmium plated No 6 binding head sheet metal screws, using two in each hinge. Make sure that the screws do not penetrate through the inner socket.
    • Proximal Location: 1 cm proximal to distal medial/lateral edges of triceps cuff. In class, you may use buckles to allow for adjustability. The metal part of the buckle should not touch the patient. Burn holes through the proximal ends of each flexible hinge to allow quick adjustments. (In clinical practice, punch holes in the leather and rivet the flexible hinges to the triceps cuff.)
• Cross hanger:
  • Purpose: The cross hanger keeps the hinges from bridging the elbow during flexion and maintains the position of the hinges through the axis of the epicondyles.
  • Fabrication: Cut 1” Dacron, about 3cm more than twice the topographical distance from medial to lateral epicondyle posteriorly.
    • You may sew the cross hanger to the flexible hinges ahead of time or assess the location on the patient before sewing it in place.

4) Attach buckles to the proximal anterior edges of the triceps pad for attachment to the inverted-y.

• Avoid any metal contact on the skin by riveting the strap so that the entire buckle lies on the triceps pad.

5) On the patient, check the location of hinges relative to elbow joint center.

• Location: The hinges should extend from just proximal to the wrist unit to the cuff. The hinges should pass through the elbow joint center throughout the ROM.
  • The cross hanger is located at the proximal edge of the socket.
  • The line of action of the flexible hinges should go through the epicondyles as the elbow is flexed and extended.

Humeral Cuff for the Rigid Hinges

Rigid hinges and humeral cuff provide stability and protection to the elbow joint and the residual limb. They are often used for short transradial cases where no voluntary pronation or supination is present. They are also used for patients with all levels of transradial amputation who will be lifting heavy loads or involved in activities that create greater than normal forces on the residual limb. The rigid hinges provide resistance to the transverse plane rotational forces that occur between the socket and the residual limb. Additionally, the full cuff provides more protection at the distal end of residual limb by transferring the load from the residual limb to the upper arm, thereby protecting the limb.

Rigid hinges can be fitted with a half humeral cuff or a full cuff. Two types of rigid hinges are available: single pivot and polycentric. The mating gear teeth on the polycentric hinge impart a displacing action to the socket during elbow flexion and provide clearance for bunching of flesh in the cubital fold, a common problem for individuals with fleshy arms.

Full Cuff Fabrication: provides maximum protection of the residual limb

1. Follow guidelines for fabrication of the half humeral cuff.
2. Add an anterior portion to the cuff. This may be fabricated from 1/8” polyethylene.
3. Secure fit around upper arm with a Velcro strap or other method.

Process to Fabricate and Fit Humeral Cuff (9 steps)

1) Fabricate pattern for humeral cuff

1. Gather supplies: paper, scissors, pencil, measurement sheet
2. Fold piece of paper in half
3. Find the circumferences at the deltoid insertion and 25mm proximal to olecranon.
4. Mark the length between the circumferences along the fold
5. Determine ¼ of the circumferences and mark this spot perpendicular to the fold. Draw the line that connects the two spots. This is, approximately, where the hinges will attach.
6. Curve the lines to extend the pattern about 2.5cm anterior to the hinge line.
7. Cut out the pattern.

2) Assess humeral cuff paper pattern on patient with elbow at 90’

• Position the cuff pattern on the patient so the proximal edge is at the level of the deltoid insertion and the distal edge is 25mm proximal to olecranon.
• The cuff should extend 25mm anterior to midline of the arm so that the uprights attach at the midline of the arm.
• Trim the pattern to allow unrestricted elbow flexion.

3) Construction of the Humeral Cuff

• Use pencil or pen to trace the pattern onto plastic. Trim out and smooth. Form the plastic to the shape of the person’s arm.
• Attach crossbar assembly to the center of the cuff

4) On the patient, re-assess location of hinges relative to elbow joint center.

• Location: The axis of the hinges goes through the epicondyles when elbow is flexed and extended. The uprights extend along the midline of the upper arm.

5) Check fit of humeral cuff, with elbow positioned at 90’.

• Location of cuff: Position the cuff at the lowest possible point on the humerus leaving enough room between the distal edge of the cuff and the posterior socket brim. Ensure that no tissue will be pinched at full flexion and full extension. Allow 25mm between the olecranon and the humeral cuff.

6) Determine location where the bars attach to cuff.

• Position the cuff so there is even pressure of the cuff against the posterior aspect of the arm.
• While holding the cuff and the lateral upright, ask the patent to flex and extend their elbow joint.
  • Note the movement of the bar in relation to the lower edge of the cuff in the anterior-posterior plane.
    • If relatively little motion occurs, trace along the bars.
    • If motion of the bars does not exceed 6mm, mark the center of the two extremes of motion for attachment.
    • If motion exceeds 6mm, investigate the socket fit. The probable cause is the anterior brim.
  • Mark the location of the bar with hatch marks.
• Repeat the process to assess the location of the medial bar.

7) In the lab, attach hinges to cuff

• Contour the joint uprights so that they lie evenly and follow the contour of the upper arm along the humeral cuff and midline of the arm.
• Rivet the bars to the humeral cuff. At the proximal end, use the same rivet to attach the buckles to the bars and the humeral cuff.

8) Finish: Ensure that all edges and rivets are smooth on the inside and the outside of the cuff.

9) On the patient, check the location of hinges relative to elbow joint center and the position of the humeral cuff as the patient flexes and extends their arm.