Assembly of Figure-8 Harness

Purpose of the transhumeral harness

  • Suspend the prosthesis
  • Transfer excursion and force to operate the elbow and/or TD.

The harness designs most frequently used for transhumeral prostheses are modifications of the basic Figure-8 and chest strap patterns used with transradial prostheses.

Only use pencil on dacron, not sharpie or pen.

Lateral suspensor strap: 1) Provides suspension and 2) resists external rotation of the socket (from the control strap)

  • The main suspensor.
  • Originates at posterior upper portion of axilla loop and extends horizontally over the anterior support strap and over the acromion. May be attached at one or two locations on socket:
    • – Riveted to socket at point of rotation (lateral to the head of the humerus and ½” anterior to acromion).

Splits just medial to the acromion process and attaches to ant and post stabilizers at points of shoulder rotation.
Crosspoint

  • Located below the 7th cervical vertebra and toward the sound side.
  • Location of this junction affects the size of the axilla loop (which affects comfort) and directs the pathway of the control attachment strap (which affects excursion).
  • May use a NW ring or a BAHA ring.
Control strap

  • Originates at posterior intersection of axilla loop.
  • Resides over the lower 1/3- ¼ of scapula (midway between spine and inf angle).
  • Straight line from the cross to the center of the back of mid-humerus.
Anterior suspensor strap: 1) Suspends against axial loading and prevents rotation for the socket on the residual limb. 2) Attachment point for release of elbow lock.

  • Originates at axilla loop, passes over involved side, and inserts at anteromedial aspect of humerus just proximal to the turntable (medial to elbow lock cable).
  • 1” strap
    • o Proximal part of the strap is Dacron and distal part is elastic. Juncture of webbing and elastic starts at the axilla level.
    • o Located in the deltopectoral groove.
    • o Distally adjustable buckle attached with metal screw into the lamination just above the turntable. Should not interfere with turntable.
Elbow Lock Control Strap

  • 1/2” dacron/velcro strap that originates at the upper, nonelastic portion of anterior support strap (just inferior to clavical in the deltopectoral groove).
  • Attached through loop of elbow lock control cable.
  • Adjustable
Cross back strap: Often necessary to prevent the harness from riding up the back to increase efficiency of the harness to capture excursion. In addition, it helps alleviate pressure from axilla loop by offsetting the vertical force on the pecs, teres major, lats and neurovascular bundle.

  • Originates on axilla loop near posterior axillary fold
  • Extends horizontally slightly above the inferior angles to the distal end of the control attachment strap
  • Placed between the control attachment straps of the bilateral harness or the axilla loop and the control attachment strap of a unilateral harness system
Z Modification: a variation of the cross-back strap

  • Modification of the crossback strap used to enhance excursion capability

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Upper Limb Prosthetics and Orthotics: Techniques Copyright © by Sue Spaulding. All Rights Reserved.

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