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Plaster of Paris in Orthopedics

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1. History

• Seutin (Belgian surgeon) introduced rigid dressings that could be maintained for longer periods.
• Pirogov (Russia) and Mathijsen (Holland, 1851, Haarlem Military Hospital) introduced POP bandages just prior to the Crimean War — an era when effective fracture treatment had become critical due to Napoleonic-era war injuries.
• In the United States, Sayre, Stimson, and Scudder promoted POP bandages.
• Lorenz Böhler of Vienna was a key proponent, advocating accurate reduction, skintight casts, and intensive physiotherapy.
• Sarmiento later advanced the concept of functional bracing for tibial fractures, permitting early joint mobilization.
• In 1927, hard-coated POP rolls were developed, incorporating a binder to improve adhesion to cloth.

— Rockwood and Green's Fractures in Adults 10th ed., p. 315–316; Pfenninger and Fowler's Procedures for Primary Care, p. 1283

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2. Chemistry and Physical Properties

Gypsum (calcium sulfate dihydrate) is heated to approximately 128°C, driving off most of the water of crystallization, leaving a fine white powder — Plaster of Paris.

When water is added, the reaction reverses: POP recrystallizes by incorporating water molecules back into the calcium sulfate dehydrate crystalline lattice. This is an exothermic reaction — heat is produced as the cast hardens.

• Facilitates easy application
• Helps maintain proper molding during setting
• Adds structural support to the finished cast/splint

— Roberts and Hedges' Clinical Procedures in Emergency Medicine, p. 1334; Rosen's Emergency Medicine, p. 1394

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3. Advantages and Disadvantages

Advantages of POP over fiberglass

Disadvantages of POP

— Pfenninger and Fowler's, p. 1284; Rockwood and Green's, p. 321

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4. Indications

• Stable, undisplaced, or minimally displaced closed fractures
• Reduced fracture-dislocations requiring immobilization
• Soft tissue injuries: ligament sprains (e.g., grade III ankle sprain), Achilles tendon disruption, tendonitis refractory to other therapy
• Congenital deformities (e.g., correction of clubfoot/talipes equinovarus)
• Postoperative stabilization of vascular, tendon, or nerve repairs
• Acute phase management of unstable fractures (before definitive treatment)

— Pfenninger and Fowler's, p. 1284

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5. Types of POP Casts and Slabs

Slabs vs. Full Circumferential Casts

• Slabs (back-slabs/half-casts): Applied when post-injury swelling is anticipated. Safer acutely as they allow expansion. Secured with bandages.
• Full casts: More effective immobilization; applied once swelling has subsided.

Upper Limb

Lower Limb

— Rockwood and Green's Fractures in Adults 10th ed., pp. 329–337

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6. Equipment Required

• Rubber gloves, gown, shoe covers, draping
• Stockinette (2-, 3-, 4-inch widths)
• Cast padding/wool (felt, soft cotton Webril, or synthetic polyester bandages)
• POP rolls/slabs (avoid >10 ply to prevent thermal injury)
• Water source (with plaster trap in drain; water temperature <24°C/75°F)
• Elastic (Ace) bandages
• Cast spreader, cast saw, cast cutter
• Scissors, slings, Chinese finger traps, leg stand

— Pfenninger and Fowler's, p. 1283–1284

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7. Application Technique (Step-by-Step)

1. Reduce the fracture (if displaced); assistant holds position.
2. Measure and apply stockinette — should extend ~10 cm beyond proposed cast ends.
3. Apply wool/cast padding distal → proximal, 50% overlap between turns.
4. Protect bony prominences with extra padding (malleoli, fibular head, olecranon, radial styloid).
5. Submerge POP in water, then squeeze to remove excess water.
6. If swelling anticipated → use a slab; apply, mold, then bandage.
7. If full cast → apply POP bandages in circumferential layers.
8. Hold fracture in reduced position until cast hardens; mold as appropriate.
9. Fold stockinette and wool padding back; apply second cast bandage to seal.
10. Ensure proximal and distal joints can mobilize adequately.
11. Cut the cast if swelling is present or anticipated.
12. Obtain post-application radiographs to confirm position.
13. Warn the patient about potential complications.

— Rockwood and Green's, Table 10-4, p. 329

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8. Thermal Considerations

• Water temperature >24°C (75°F)
• Cast thickness >8–10 sheets/plies
• Inadequate ventilation of the newly applied cast
• Immersing plaster for too short a time or squeezing out too much water (incomplete hydration → more heat generated)
• Resting the wet cast on an impermeable surface (e.g., rubber pillow) during setting

Rule: Use lukewarm water, apply ≤10 plies, ensure ventilation, and rest cast on breathable material while setting.

— Rosen's Emergency Medicine, p. 1394; Roberts and Hedges', p. 1334; Pfenninger and Fowler's, p. 1284

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9. Cast Wedging (Correcting Malunion Within the Cast)

• Radiographs or fluoroscopy identify fracture site and direction of deformity.
• Cast is cut at the fracture level, leaving a hinge of 2–3 cm intact (hinge position depends on direction of correction).
• Example: Valgus fracture → medial hinge left intact → varus force applied to distal cast to open the window.
• A wooden wedge or doweling is inserted to maintain position while supplementary POP is applied.
• Rotational deformity: cast is cut at the fracture level, rotation corrected — though position is difficult to maintain and reapplication is sometimes preferable.

— Rockwood and Green's, p. 330, Fig. 10-12

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10. Complications

Management of a tight/symptomatic cast

Bivalve the cast — cut the cast and padding on each side, remove half the cast at a time, using the other half as a mold to keep the extremity immobile. The bivalved cast can then be held together with bias-cut stockinette or elastic bandaging.

— Rosen's Emergency Medicine, pp. 1394–1396; Rockwood and Green's, p. 329

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11. POP vs. Fiberglass: Summary

POP casts remain widespread globally — inexpensive, easily applied, and well suited to initial/acute-phase immobilization.

— Rockwood and Green's, p. 321

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12. Special Notes

• COVID-19 pandemic experience: There was a documented return to nonoperative/POP management during lockdowns, including for distal radius fractures, with generally acceptable outcomes — demonstrating the continued relevance of POP.
• Padding and fracture stability trade-off: Too much padding allows secondary displacement; too little increases compartment syndrome/skin risk. Two layers of wool with 50% overlap is the accepted standard.
• Skin care instruction to patients: Keep cast dry; do not insert objects under the cast; seek review urgently for pain, tingling, swelling, or color change of digits.
• Sink trap required: Plaster waste must not enter drains without a trap — it hardens and blocks plumbing.

— Rockwood and Green's, pp. 328–330; Pfenninger and Fowler's, p. 1284

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• Rockwood and Green's Fractures in Adults, 10th ed., 2025 — Chapter 10: Nonoperative Fracture Management
• Roberts and Hedges' Clinical Procedures in Emergency Medicine — Chapter 50: Splinting
• Rosen's Emergency Medicine: Concepts and Clinical Practice — Chapter 41: Orthopedic Procedures
• Pfenninger and Fowler's Procedures for Primary Care, 3rd ed. — Chapter 187: Cast Application
• Gray's Anatomy for Students — Bone fractures