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https://www.msdmanuals.com/professional/injuries-poisoning/h…

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I now have comprehensive information from authoritative textbook sources (Rockwood & Green's Fractures and Pye's Surgical Handicraft) plus the MSD Manual. Here is the full step-by-step guide:

Medical Plaster Cast Application - Step by Step

Equipment Needed

Stockinette (appropriate width)
Synthetic wool / cotton padding
Plaster of Paris bandages (or fiberglass bandages)
Bowl of lukewarm water (~35°C / 95°F)
Gloves
Bandages for securing a slab

Part 1: Preparation

Step 1 - Position the patient Position the patient so you have full, comfortable access to the injured extremity. The limb must be in the correct anatomical alignment for the specific injury before anything is applied.

Step 2 - Reduce the fracture If displaced, reduce the fracture first. An assistant must hold the fracture in the reduced position throughout the entire casting procedure until the material hardens.

Step 3 - Decide: slab or full cast?

If swelling is present or anticipated (e.g., acute injury), apply a slab (backslab/splint) only - NOT a full circumferential cast. Swelling inside a rigid full cast can cause compartment syndrome.
A full cast is applied once swelling has subsided (usually several days later).

Part 2: Stockinette

Step 4 - Apply stockinette Choose stockinette of the appropriate width - form-fitting but not constricting circulation. Apply it so it extends approximately 5-10 cm beyond the anticipated proximal and distal extent of the cast. This will be folded back later to create smooth, finished edges.

Part 3: Padding

Step 5 - Apply wool/cotton padding Wrap padding circumferentially from distal to proximal, overlapping each layer by 50% (half the width of the padding). Apply it firmly against the skin without gaps, but not so tightly that it restricts circulation.

Step 6 - Protect bony prominences Add extra non-circumferential pieces of padding over and around bony prominences (e.g., malleoli, radial styloid, olecranon, fibular head). This prevents pressure ulcers.

Step 7 - Extend padding past the cast Padding should extend approximately 3-5 cm past the anticipated edge of the plaster material.

Step 8 - Smooth the padding Smooth out any protrusions, lumps, or wrinkles. Tear away small pieces of padding in wrinkled areas to make it lay flat.

Tip: Too much padding allows fracture redisplacement; too little risks pressure sores and compartment syndrome. Ideally two layers of wool, each with 50% overlap.

Part 4: Soaking the Plaster

Step 9 - Immerse the casting material Submerge the plaster bandage roll in lukewarm water (~35°C). Hold the roll with one hand and the free end with the other. Wait until bubbles stop emerging from the ends of the roll.

Step 10 - Squeeze out excess water Gently squeeze by rotating the ends - do not wring plaster. Wringing removes too much water and prevents proper setting. For a slab, draw it slowly through the water, hold it vertically to let excess water drain off.

Part 5: Applying the Material

If applying a SLAB:

Step 11a - Apply the pre-cut slab of appropriate length to the correct surface of the limb (e.g., posterior surface for a backslab). Mold it to conform to the limb contours.

Step 11b - Secure with a wet gauze bandage (wet bandage has already reached its maximum shrinkage, reducing the risk of constriction as it dries).

If applying a FULL CAST:

Step 11c - Apply the casting material circumferentially from distal to proximal, overlapping the underlying layer by half the width of the bandage. Keep bandages flat - any fold creates a pressure point.

Step 11d - Use 8-10 layers of plaster of Paris, or 2-4 layers of fiberglass for adequate strength.

Part 6: Molding and Setting

Step 12 - Smooth and mold Use the palms of your hands (not fingertips) to rub the plaster and bond the layers together. Fingertip pressure creates indentations that cause pressure ulcers. Conform the cast to the contour of the extremity.

Step 13 - Mold the fracture While the material is still soft, use gentle three-point molding where appropriate to maintain fracture reduction. Do not indent the cast material.

Step 14 - Finish the edges Fold back the extra stockinette and cotton padding at the outer margins of the cast to cover the raw edges of plaster. Secure under the last layer of casting material for a smooth, comfortable edge.

Step 15 - Hold position until set Maintain the extremity in the correct position until the cast hardens sufficiently - typically 10-15 minutes for plaster of Paris. Plaster sets faster in warmer water; fiberglass sets faster overall.

Part 7: Post-Application Checks

Step 16 - Neurovascular check Immediately check:

Capillary refill distally
Distal sensation
Distal motor function (e.g., finger/toe movement)

Step 17 - Check joint mobility Ensure any joints that should remain free to move are not obstructed by the cast.

Step 18 - If swelling is present: split the cast If there is significant swelling, the cast should be split (bivalved) along its length to relieve pressure.

Step 19 - Obtain X-rays After application, take radiographs to confirm the fracture remains in acceptable position.

Part 8: Aftercare & Patient Instructions

Give verbal and written instructions including:

Do not get the cast wet
Do not put objects down the cast
Elevate the limb to reduce swelling
Seek immediate medical care if numbness, tingling, increased pain, or tightness develop - these are signs of compartment syndrome
Arrange appropriate follow-up (fracture position can shift as swelling resolves over 1-2 weeks)

Key Rules for Cast Length

As a general rule from Pye's Surgical Handicraft: the joint above and the joint below a fracture must be incorporated in the cast to achieve adequate immobilization. This rule may occasionally be relaxed when the fracture is very close to one end of a long bone.

Common Errors to Avoid

Error	Consequence
Applying full cast to swollen limb	Compartment syndrome
Padding too tight	Compartment syndrome
Using fingertips when smoothing	Indentation -> pressure ulcer
Not smoothing layers together	Weak cast (layers don't bond)
Water too hot (>24°C) or cast too thick (>8 sheets)	Thermal burn from exothermic reaction
Improper joint positioning	Contractures
Insufficient follow-up	Missed fracture displacement

Sources: Rockwood and Green's Fractures in Adults, 10th ed. (2025), Table 10-4; Pye's Surgical Handicraft, 22nd ed., pp. 200-201; MSD Manual - How to Apply a Cast

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