12 Socket Impression Technique

1. Before patient arrives

• Create action plan
• Gather materials

2. Patient evaluation

Review ICF factors to identify appropriate functional goals. For this socket design, specifically evaluate the patient’s limb including

• ROM, strength,
• tissue compressibility (pinch test),
• muscle bunching,
• muscle tendons (pectoralis),
• sensitive areas,
• residual limb shape, and
• areas of potential skin irritation.

Predict how to balance the triplanar forces and counter-forces during both static and dynamic activities.

3. Preparation

Communicate with the patient about the process and what they might expect.  Ask if they have any questions, so they can relax.

Lengths:

• Residual limb:
  • Acromion to distal end
  • Acromion to distal end, slightly compressed
  • Axilla to distal end (Ritz stick or mark lateral side)
• Contralateral side
  • Acromion to lateral humeral epicondyle
  • Lateral humeral epicondyle to distal tip of thumb
• Measure old prosthesis too

Circumferences:

• Residual limb
  • at axilla level
  • and 3-4 levels below axilla level
  • Snug – tape is snuggly wrapped around limb
  • Snugger – skin is compressed somewhat tightly
• Contralateral limb
  • at locations to match circumferences
  • hand size

• Mark a location for your measurement that will be transferred to the mold, such as the deepest spot in the deltopectoral groove and just below the spine of the scapula. Use calipers with rounded tips to measure the dimension, compressing slightly.

Measure M-L dimension:

• Place a Ritz stick in the axilla and measure from the pectoralis tendon to the latissimus tendon. Do not compress.

Use a gown and towels/sheet to cover the patient’s torso, clothing, and shoes.

Don stockinette or nylon.  Cut one leg off the nylon, then place the nylon on the pts limb.  Twist the bottom of the nylon, tie off and reflect back up onto the limb.

Apply a liberal amount of Vaseline/separator to hair and place plastic wrap over the area.

Cut one splint for the proximal section using 5” or 6” plaster.  The length of the splint should extend from the medial border of the scapula to 2-3 inches past the deepest portion of the deltopectoral groove.  Make this splint 6-10 layers and cut so that it is not a continuous length of plaster.

Cut the second splint about 5-6″ long using 5″ plaster. Make this 4 layers.

Optional: cut splint to cover distal end.

(1) Medially:  One hand is placed in the axilla, while the opposite hand compresses softly from the lateral aspect of the residual limb. The hand in the axilla should avoid compression into the neurovascular bundle. If the fingers are too thick in the axilla, use a small dowel or 10mm thick sheet of soft foam.

(2)  Anteriorly:  Place your thenar or hypothenar eminence in the deltopectoral groove, avoiding pressure on the clavicle or the humeral head. Posterior aspect:  The fingers lie on the scapula in the same plane as the scapula.

UCLA pages 244-249

• Locations of the fingers/palm relative to the bony landmarks, and the right thumb marking acromion
• Angles of the hands matching the anatomy

4) Capture the impression 

ML pressure (1st part)

Begin by wrapping circumferentially at midpoint of the limb and moving distally.

Use about 3 layers of elastic, 3 layers of rigid plaster.

After wrapping the limb with plaster circumferentially, place a splint over your inside hand. The palm of your hand rests against the chest wall, the dorsal side of your palm touches the plaster wrap, and the top of your fingers press comfortably in the axilla.

• Notice that the plaster is longer on the dorsal side of the hand.

Place the inside hand comfortably in the pts axilla. Its only purpose is to locate the height of the axilla and location of tendons. Be sure to have plaster over the tips of your fingers. Do not flex the fingers of the medial hand – this may create undo pressure at the neurovascular bundle.

The opposite hand presses medially parallel to the other hand. The palm of the hand is moves proximally starting from just above the distal-lateral end moving towards the acromion to create a smooth lateral wall.

After the circumferential wrap has set, reposition the plinth and practice your AP hand placement again.

Recheck your trimlines and the length of the splint.

• Extend from 1” distal to level axilla to clavicle and spine of scapula.
• Extend ~3” medial from the axilla or middle of clavicle.

Wet the splint material and lay on pt so that the top of the splint is at the clavicle and the spine of the scapula. You want to be able to identify the clavicle and the spine of the scapula in your cast.  Place the winkles of the plaster bandage laterally.

Check Alignment

• Pt should be seated comfortably with arm relaxed at his/her side.
• Neutral frontal plane and sagittal plane alignment
• If casting with patient in too much abduction, the anterior/posterior stabilizers will not be positioned accurately.

Apply significant AP compression:

• Posteriorly:  your fingers are below the spine of the scapula and in the plane of the scapula. This hand is stabilizing the anterior force.
• Anteriorly:  Your thenar or hypothenar eminence is pressing posteriorly in the deltopectoral groove. Do not press on the coracoid or the head of the humerus or clavicle.

5. Review

Before removing cast: Mark landmarks and alignment lines

• Measure the A-P dimension while the plaster is on the limb. Mark a location anteriorly and one posteriorly. Use the outside calipers to measure the A-P dimension. This dimension will likely change as the cast is removed and you can use this measurement to reset the cast to the proper dimension.
• Mark the carrying angle in the frontal plane, 1” lateral to hip.
• Mark the handing angle in the sagittal plane.

Gently remove the cast and inspect the residual limb

Inspect the cast:

• Captured the anatomical landmarks: clavicle, spine of the scapula and axilla.
• Shape is relative to the shape of the residual limb.
  • o Is the deltopectoral groove in the “right” location?
  • o Is the plane of the scapula in the right plane?
• Captured the AP dimension from deltopectoral groove to scapula.

Review functional goals and purpose with the patient.