Last Updated on October 4, 2025
A plaster cast is a rigid external device applied to immobilize a limb or body segment after fracture, dislocation, osteotomy, or soft-tissue repair. The primary purpose is to maintain the reduction of fracture fragments or to restrict joint motion until healing occurs. By controlling movement, the cast provides stability, reduces pain, and facilitates biological repair.
Historically, plaster of Paris has been the traditional material used, hence the term “plaster cast.” In contemporary practice, synthetic alternatives such as fiberglass are widely employed, but the principles of immobilization and molding remain the same.
In orthopaedic practice, plaster casts may serve as a temporary measure, providing pain relief and swelling control before definitive treatment, definitive treatment, especially for undisplaced or successfully reduced fractures, or as an adjunct to internal fixation, when additional external support is required.
Despite being one of the oldest techniques in fracture management, cast application remains a core orthopaedic skill. Proper technique is essential to avoid complications such as loss of reduction, pressure sores, or even compartment syndrome.
Indications of Plaster Cast
The decision to use a plaster cast depends on the fracture pattern, soft-tissue status, and overall treatment plan. Broadly, indications can be divided into temporary, definitive, and adjunctive uses.
Temporary Immobilization
- Pain relief and muscle relaxation immediately after injury
- Reduction of swelling before definitive fixation
- Initial stabilization of fractures or dislocations in the emergency setting
- Immobilization after manipulation while awaiting operative fixation
Definitive Treatment
- Undisplaced or minimally displaced fractures that are inherently stable
- Fractures reduced by closed methods and maintained by cast molding (e.g., pediatric forearm fractures, distal radius fractures)
- Some ligament injuries (e.g., ankle sprains, medial collateral ligament injury), where external support aids healing
Adjunct to Internal Fixation or Soft-Tissue Repair
- To supplement fixation after osteotomies or unstable internal fixation constructs
- To protect the repairs of tendons, vessels, or nerves by blocking joint motion
- As an external support in cases where internal fixation alone may not tolerate early loading
Difference Between Plaster Slab and Plaster Cast
Immobilization can be achieved either with a circumferential plaster cast or a partial plaster slab. The choice depends on the clinical situation, especially the risk of swelling and the degree of stability required.
Plaster Cast
A plaster cast is a circumferential application of plaster bandages. The cast is stronger being circumferential than slabs, controls the reduction of fragments better, and withstands mechanical stresses better. Most of the closed reductions of the fractures require a cast application.
Plaster Slab
A plaster slab (commonly called a “backslab”) is a non-circumferential support applied to one or more aspects of the limb and secured with a bandage.
- Allows room for swelling, reducing the risk of vascular compromise.
- Where there is swelling or a poor skin condition that needs to be observed
- Temporary measure while waiting for definitive treatment.
- Frequently used in the acute setting (first 48–72 hours), after internal fixation
- Many undisplaced fractures are treated by slab application.
Sometimes, two slabs may be applied, for example, one anterior and the second posterior, for better strength and control.
Materials Used in Plaster Cast
Orthopaedic casts can be made from plaster of Paris (POP), fiberglass, or hybrid combinations of both. Each material has distinct physical properties, advantages, and limitations that guide clinical use.
Traditionally, plaster casts made from Plaster of Paris are used. That is why these are called plaster casts. But the name plaster cast is used interchangeably for casts from other materials.
Plaster of Paris (POP)
- Composition: Derived from gypsum (calcium sulfate hemihydrate). On mixing with water, it rehydrates to crystalline calcium sulfate dihydrate in an exothermic reaction.
- Advantages:
- Excellent molding properties, conforms to anatomy
- Easy to apply and inexpensive
- Radiolucent, allowing clear X-ray assessment
- Plaster of Paris is extremely safe and does not produce allergies.
- It is cheaper in comparison with more modern materials.
- The cast strength depends upon the thickness of the plaster and the shape of the cast
- Limitations:
- Heavy and less durable
- Weak when wet. The optimum strength is achieved when it is completely dry. The plaster takes a long time to dry fully (36–72 hrs, depending on thickness and climate). Drying can take 7 days for a hip spica, especially if the atmosphere is moist and cool.
- Risk of thermal burns if the water is too hot or thick layers are applied
Fiberglass (Synthetic Casts)
- Composition: Glass-fiber reinforced plastic impregnated with polyurethane resin.
- Advantages:
- Lighter and stronger than POP cast- Three times stronger and one-third the weight of POP
- Resistant to water damage and more durable
- Available in various colors (often improves compliance in children)
- Sets rapidly (within minutes)
- Limitations:
- Less yielding to molding,
- Hygroscopic [absorbs water] and setting time decreases with humidity and warmth.
- More expensive
- Radiodensity can obscure some fine fracture lines
Casts made of this material require less maintenance.
Hybrid Techniques
This involves a POP inner layer for molding and a fiberglass outer layer for strength. It combines the molding ability of POP with the strength and lightness of fiberglass. However, it is tedious and requires greater preparation for one plaster, and is more time-consuming.
Principles of Plaster Cast Application
The effectiveness of a plaster cast depends not only on immobilizing joints but also on the quality of reduction and molding. Correct technique ensures stability while minimizing complications.
General Principles
- Immobilize the joint above and below the fracture.
- Apply adequate padding to protect skin and accommodate swelling.Padding serves to prevent sores, increase comfort, and act as a spacer to aid removal.
- Position the limb according to the functional position of the affected joint.
- Apply bandages with uniform overlap, avoiding folds or ridges.
- Smooth with wet hands to adapt to contours.
Molding Techniques
Molding is critical in maintaining reduction and preventing redisplacement.
- Three-Point Molding: Essential for angulated fractures (e.g., distal radius). Pressure is applied at two points on one side and one counterforce on the opposite side.
- Interosseous Mold: Used in forearm fractures; compresses the radius and ulna together to prevent rotational displacement.
- Varus/Valgus Control: Cast contouring at the fracture site to counteract deforming forces (e.g., supracondylar humerus).
- Rotational Control: Achieved by extending molding proximally and distally around the limb contours.
Types of Plaster Casts
The type and extent of a plaster cast are determined by the fracture location, the joints that need immobilization, and the forces that must be neutralized. The guiding principle is to immobilize the joint above and below the fracture while applying appropriate molding for stability.
Upper Limb Casts
- Short Arm Cast: Extends from the distal palmar crease to just below the elbow. Used for distal radius, carpal, and metacarpal fractures.
- Long Arm Cast: From the distal palmar crease to the upper arm, immobilizing the elbow. Indicated in proximal forearm and elbow fractures, or unstable distal radius requiring elbow control.
- Thumb Spica Cast: Short or long arm with inclusion of the thumb. Used for scaphoid, first metacarpal, or UCL injuries.
- Shoulder Spica Cast: Includes torso and affected upper limb; rarely used today but historically applied for proximal humerus or shoulder stabilization.
Lower Limb Casts
- Short Leg Cast: From base of toes to just below the knee. Used for ankle fractures, severe ankle sprains, and metatarsal injuries.
- Long Leg Cast: From base of toes to mid-thigh, immobilizing the knee and ankle. Indicated in tibial shaft, unstable ankle fractures, and pediatric femoral shaft fractures (in select cases).
- Cylinder Cast: Extends from the groin to the ankle but leaves the ankle free. Used for knee injuries, patellar fractures, or post-operative stabilization.
- Hip Spica Cast: Encompasses the trunk and one or both lower limbs. Common in children for femoral shaft fractures or congenital hip dislocation.
Trunk and Body Casts
These are rarely used now and have been replaced by braces:
- Body Jacket Cast: Encases the trunk; used for spinal stabilization (rare now, replaced by braces).
- Shoulder/hip spica variants: Provide immobilization across trunk and limb junctions.
How to Apply a Plaster Cast?
Extent
Plaster cast application aims to block a joint above and below the fracture. This is done as a movement of either joint can cause movement in fracture fragments.
Different types of casts based on the extent of the plaster are
- Long Arm Plaster Cast: From distal palmar crease anteriorly and to covers the lower two-thirds of the arm. Aims to immobilize the forearm and elbow
- Short Arm Plaster Cast: From the distal palmar crease to the proximal third of the forearm. Aims to immobilize the wrist and distal forearm.
- Long Leg Plaster Cast: From the base of the toes to the middle of the thigh. A cylinder cast has a similar upper extent but ends at the ankle.
- Short Leg Plaster Cast: a cast that extends from the base of the toes to the below knee
- Body Casts: Body casts are those casts that also include the trunk. The examples are shoulder Spica, hand ip spica [used in case of femur fracture in very young children and in cases of congenital hip dislocations.
Plaster Cast Application – Procedure
Document the procedure and give cast care instructions.
Preparation
Explain the procedure to the patient and obtain consent. Position the limb comfortably, with the fracture held in the desired alignment by an assistant or traction. Protect clothing and the surrounding area from plaster slurry.
Stockinette and Padding
Apply a stockinette layer extending beyond the cast edges. Add uniform padding (orthopaedic wool/felt) with extra thickness over bony prominences. Avoid creases or ridges.
Plaster Bandage Application
Immerse one bandage roll at a time in lukewarm water. Remove when bubbling stops, gently squeeze from ends to avoid loss of plaster. Warmer water accelerates setting, colder water prolongs working time.
Unroll evenly, overlapping each turn by one-third to half. Shape and smooth continuously to match limb contours.
Molding
Apply three-point molding or interosseous molding as required to maintain reduction. Molding of the bandages to the contours of the limb should be done by constant smoothing with the palms of the wet hands. Ensure functional position (e.g., forearm in neutral/pronation, ankle at 90°).
Completion
Fold back stockinette edges and cover with the final plaster turns. Trim excess for joint mobility at uninvolved segments. Hold until plaster sets (usually 3–5 minutes).
After Setting
Support cast while drying (24–72 hours for POP, a few hours for fiberglass). Check circulation, sensation, and movement of exposed digits. The cast does not fully dry out until 36 to 72 hours after application. When a dry plaster cast is tapped with the knuckles, it gives a crisp, clear sound, but the damp cast gives a dull sound.
Plaster Slab Preparation and Application (Backslab)
Slab is a rapid, safe immobilization that accommodates swelling in the acute phase. It can be completed to a circumferential cast once swelling settles. It is similar to the POP cast for material requirements.
Slab Preparation
Measure the limb segment and decide the slab’s extent. Unroll bandages to the required length and fold them back on themselves on a flat surface to build the slab. The typical thickness is 12–16 layers, adjusted to patient size and required support. Keep all layers co-extensive in length and width.
Application
Immerse the slab as a unit in lukewarm water until bubbling ceases. Lift by the ends and gently squeeze toward the center to express excess water without stripping plaster. Lay the wet slab back on the flat surface and smooth with the palms to remove air pockets, wrinkles, and ridges.
With stockinette and uniform padding in place (extra over bony prominences), transfer the slab to the limb in the desired position. Contour with the palms; avoid fingertip indentations. Fix with a crepe/cotton bandage using even, gentle tension. Re-smooth the surface and check that skin is visible at the margins for inspection.
Confirm comfort and position. Record neurovascular status (pulses, cap refill, motor/sensation) after application.
For additional control, consider an anterior counter-slab or convert to a circumferential cast once swelling subsides.
Pearls
Lukewarm water moderates set and reduces exotherm risk; hotter water accelerates the setting and heat. Maintain uniform thickness to avoid pressure points; ridges and folds cause sores.
Aftercare of Plaster Cast
Effective follow-up is as important as correct application. Monitoring helps detect complications early and ensures fracture stability until union.
Immediate Post-Application
- Document neurovascular status (pulses, capillary refill, motor and sensory exam).
- Elevate the limb to reduce swelling and discomfort.
- Reassess circulation and pain within the first 24 hours, especially in acute fractures.
Follow-Up Schedule
- Early check (24–48 hours): For acute fractures, to assess swelling, cast tightness, and comfort.
- Radiographic check:
- Children: at 5–7 days, then 2 weeks, depending on fracture type.
- Adults: at 1–2 weeks, then as clinically indicated.
- Subsequent reviews are timed according to expected healing (every 2–3 weeks in children, 3–4 weeks in adults).
Ongoing Monitoring
- Look for signs of compartment syndrome, pressure sores, or loosening.
- Ensure patient is mobilizing free joints (fingers, toes, proximal limb joints).
- Reinforce cast edges or overwrap if breakdown occurs.
Discharge Advice (Core Summary)
- Keep cast dry and protected.
- Return immediately if severe pain, numbness, color change, or swelling occurs.
- Weight-bearing is permitted only if permitted and after the cast has reached full strength.
Complications of Plaster Cast
Although plaster casts are widely used and generally safe, improper application or inadequate monitoring can result in significant morbidity. Awareness of complications is essential for early recognition and timely intervention.
Pressure Sores and Skin Problems
- Caused by inadequate padding, wrinkles, or indentations in the cast.
- Present with localized pain, burning, or foul odor.
- May progress to ulceration or infection if unrecognized.
It is a dictum to inspect the cast for any pain that is unrelenting. It could be skin ulceration or infection.
Compartment Syndrome
- The most feared complication of tight casts.
- Rising intracompartmental pressure compromises perfusion and nerve function.
- Clinical features: severe pain disproportionate to injury, pain on passive stretch, paresthesia, pallor, pulselessness (late).
- Management: Immediate cast bivalving or removal, fasciotomy if symptoms persist.
Thermal Injury
- May occur if bandages are soaked in hot water, applied in very thick layers, or allowed to set without ventilation.
- More common with plaster of Paris than fiberglass.
- Risk increased in children and patients with neuropathy.
Cast Syndrome or Superior Mesenteric Artery syndrome
It is seen with body casts (e.g., hip spica, body jacket) and occurs due to duodenal compression by the superior mesenteric artery, causing nausea, vomiting, abdominal pain, and obstruction. application of body casts in slight hip flexion and avoiding excessive lumbar extension.
Joint Stiffness and Wasting
Prolonged immobilization leads to disuse muscle wasting and a restricted range of motion. It can be prevented by encouraging movement of free joints and timely rehabilitation after cast removal.
Other Complications
- Venous thromboembolism: Especially in lower limb casts.
- Cast breakage or loosening: Reduces effectiveness and may necessitate replacement.
- Psychological discomfort: Anxiety, claustrophobia, especially in long spica or body casts.
Cast Modification Techniques
Plaster casts often require modification during treatment, either to accommodate swelling, adjust alignment, or allow inspection of soft tissues. These techniques are essential in preventing complications and ensuring the cast continues to serve its intended purpose.
Bivalving
Bivalving is splitting the cast along both medial and lateral (or anterior and posterior) aspects, then re-securing with bandages. The plaster is divided into two halves. It is done to relieve pressure in cases of swelling, suspected compartment syndrome, or circulatory compromise.
Splitting (Univalving)
Splitting is cutting the cast along one side only. It provides partial pressure relief or prepares the cast for expansion into a bivalve if needed. Always spread the cut edges adequately; a cut without separation does not relieve pressure.
Cast Wedging
It is used for controlled correction of the angulation of fracture fragments after cast application. The angulation may be due to inadequate reduction or slippage of fragments after the reduction.
It is done by cutting the cast, creating a wedge, and re-securing. It is of two types, depending on the side of angulation- closing wedge and opening wedge.
- Closing Wedge: It removes a wedge of plaster to close the gap and correct alignment. It is done on the convex side of angulation (where there is an open gap)
- Opening Wedge: It involves opening the cast, inserting a spacer to open one side and realigning the fracture. It is done on the concave side of the deformity.
The wedging is done close to the fracture site. The correction is measured on x-ray.
Cast Window
A section of cast is cut out to allow inspection or access. It is done to check wounds, skin flaps, surgical drains, or neurovascular status. After the checking, the window is re-covered with the removed piece or padding to prevent localized pressure.
Cast Removal
Plaster casts are removed once the fracture has healed sufficiently or if complications require early discontinuation. Removal should be performed carefully to avoid skin and soft-tissue injury.
The oscillating cast saw is the standard tool in modern practice. The blade oscillates rather than rotates, reducing the risk of deep cuts. For cutting, apply gentle pressure from one end of the plaster to the other. Avoid bony prominences and areas with thinner skin. In a synthetic cast, an additional cut may be needed as if bilveing, because this cast is very unyielding.
Plaster Shears / Cast Scissors can be used to further cut the plaster and remove it.
Precautions During Removal
- Protect the underlying skin by avoiding pressure at one point.
- Beware of thermal injury from saw friction—common in children, anxious patients, or those with thin casts.
- Provide adequate support during the removal of weight-bearing casts to prevent fracture displacement.
