Splinting and immobilisation in the emergency department

Splinting and immobilisation are the procedural craft that closes almost every fracture and dislocation the emergency physician manages — the backslab for the reduced Colles, the Thomas splint for the femoral shaft, the collar and board for the suspected spinal injury, the sling for the clavicle. The Fellowship examiner tests three things together: the governing principle (immobilise the joint above and below the fracture), the layered application technique (stockinette, wool, plaster dipped in cool water and moulded in the position of function), and the complications the candidate must prevent and recognise — compartment syndrome with its 5 Ps, pressure sores over bony prominences, and thermal injury from the exothermic setting reaction. The central distinction that frames every SCQ is the backslab versus the circumferential cast: the backslab is non-circumferential, accommodates swelling, and is the ED acute-phase default; the circumferential cast is rigid, definitive, and belongs to orthopaedics, applied only after the swelling has resolved.[1][2] A candidate who has read only this topic could apply a Colles backslab in an OSCE, defend the Thomas splint in a viva, and answer any SCQ on splint choice and the cast complications.

Definition, classification and the governing principle

Immobilisation is the restriction of movement at an injury site to relieve pain, prevent further displacement and soft-tissue damage, and stabilise the limb for transport and healing. It splits into rigid (plaster of Paris, synthetic fibreglass, the circumferential cast) versus soft (sling, swath, collar, bandage), and into circumferential (the cast) versus non-circumferential (the backslab, the SAM splint). Plaster of Paris (POP) is calcium sulphate hemihydrate that sets to a rigid dihydrate when wetted — a heat-releasing (exothermic) reaction that is the mechanism of cast burns.[7][8]

The governing principle, recited aloud in every viva, is that a splint must immobilise the joint above and the joint below the fracture: a forearm fracture is splinted from the metacarpal heads to the proximal forearm (wrist and elbow controlled), a tibial fracture from the metatarsal heads to the mid-thigh (ankle and knee controlled), a femoral fracture requires traction from hip to ankle. A splint that spans only the fracture itself fails because movement at either adjacent joint displaces the fragment. [1]

Indications

The indications are the conditions in which immobilisation relieves pain, prevents secondary injury, or stabilises the limb pending definitive care: stable reduced fractures (the post-reduction Colles, the undisplaced ankle, the scaphoid suspected on clinical grounds, the buckle fracture of the child), severe soft-tissue injury (a grade II to III ankle sprain, a suspected ruptured Achilles held in equinus), pain control in the undiagnosed limb injury while imaging is obtained, prehospital extrication and transport, temporary stabilisation of a displaced fracture pending orthopaedic theatre, and post-reduction immobilisation after a joint is reduced. Splinting is also the bridge between reduction and definitive orthopaedic casting — the backslab holds the reduction through the swelling phase, and the conversion to a circumferential cast happens at fracture clinic days later, once the limb is "cold".[1][9]

Contraindications

There is no contraindication to some form of immobilisation in the injured limb — even the open fracture is splinted, in the position found, after irrigation, dressing and intravenous antibiotics. The contraindications govern the type of immobilisation and the setting.[2][3]

A suspected or established compartment syndrome contraindicates any new rigid immobilisation: any existing cast is split to skin immediately, and the limb is prepared for fasciotomy. An open fracture is irrigated, dressed and splinted in the position found, not reduced in the ED, with intravenous antibiotics and orthopaedic referral in parallel. A neurovascularly compromised limb is reduced or handed to vascular and orthopaedic surgery, not splinted and observed. A grossly contaminated wound is debrided before immobilisation. The uncooperative or unconsentable patient is sedated or the procedure deferred, with consent documented when feasible. [1]

Relevant anatomy and landmarks

The anatomy that matters for splinting is the joint above and below the injury, the bony prominences that ulcerate under pressure, and the position of function in which the limb is moulded while the plaster sets. The prominences that must be padded at every site are the malleoli, olecranon, ulnar and radial styloids, fibular head, metatarsal heads, heel and patella — an unpadded prominence under a rigid splint develops a pressure ulcer within hours.[9] The position of function varies by joint: the wrist in 15 to 20 degrees of extension with slight radial deviation, the ankle at 90 degrees neutral (never plantarflexed, which shortens the Achilles and the calf compartment), the knee in 15 to 20 degrees of flexion, the elbow at 90 degrees. Moulding the plaster in these positions while it sets is the difference between a splint that holds the reduction and one that loses it.

Equipment and the splint set

The plaster set holds a defined inventory the candidate must name at the OSCE: stockinette (the tubular cotton layer rolled onto the limb, cut to length, protecting the skin), soft wool padding (Softban, rolled cotton or synthetic padding, two to three layers, extra over the prominences), plaster slabs or POP bandages (10 to 12 layers for an adult backslab, pre-measured to the limb), crepe or conforming bandages to hold the wet plaster, adhesive tape (never circumferential tape — it constricts), a bowl of cool or tepid water (never hot), a sling, and gloves for the operator. The SAM splint is a thin sheet of aluminium sandwiched between closed-cell foam — folded into a longitudinal accordion for rigidity, versatile for the field immobilisation of a forearm, ankle or finger. The Thomas splint is a steel ring on a long side-iron, in sized sets from child to adult. The rigid cervical collar (Aspen, Malley, Stifneck) is sized to the patient by measuring the neck height from the trapezius to the chin. The spinal board is a flat rigid plank with head blocks and straps. [1]

Patient preparation, consent and analgesia

Preparation has four steps stated in order. Document the pre-procedure neurovascular status — distal pulses, capillary refill, sensation and active movement — before any splint is applied, because a deficit emerging afterwards must be attributable to the injury or to the splint. Obtain consent — the procedure, the expected duration in the splint, the fracture-clinic follow-up, and the complications (compartment syndrome, pressure sores, burns) the patient must watch for and return for. Provide analgesia — a splint applied to an acutely fractured limb is itself painful, and the reduction that precedes it more so; the Fellowship answer pairs the splint with appropriate analgesia or procedural sedation. Position the limb in the position of function, with the operator seated and the limb supported by an assistant, and prepare all materials before the plaster is wetted.[2]

Stepwise technique — the layered backslab application

The backslab is the default ED immobilisation, and the layered sequence is the technique the OSCE examiner watches. The discipline is stockinette, wool, plaster, bandage, with the plaster moulded in the position of function while it sets, and a documented neurovascular re-check once it has hardened.[2][9]

The structural errors the examiner deducts for are the hot dip-water or too-thick slab (a burn from the exothermic reaction), the unpadded prominence (an ulcer), the wrong position of function (a lost reduction — a wrist splinted in flexion loses a Colles), the fingertip dent in wet plaster (a pressure sore), the circumferential tape or bandage (constriction), and the omitted post-procedure neurovascular check (the missed compartment syndrome).[7][9]

Splint types by indication — the device set

The Fellowship candidate must match the device to the injury, and recite the rationale. The set below covers the seven splints named in the topic and the situations the SCQ trades on.[4][11]

Drug doses and local anaesthesia

Splinting itself is rarely painful enough to need local anaesthesia, but the reduction that often precedes it is, and the analgesia plan is part of the immobilisation answer. The agent set the Fellowship candidate names: nitrous oxide 50 per cent in oxygen (Entonox, self-administered) for the brief painful manoeuvre; intranasal fentanyl 1.5 mcg per kilogram for the child or the adult without intravenous access; intravenous morphine 0.1 mg per kilogram titrated or fentanyl 1 mcg per kilogram IV for the displaced fracture; procedural sedation (ketamine 1 mg per kilogram IV, propofol 1 mg per kilogram IV) to the full standard for the reduction that needs it. For a digital splint after a finger injury, a digital block with plain lidocaine 1 to 2 per cent (maximum 3 mg per kilogram plain, never adrenaline) precedes the buddy strap or aluminium foam splint. The dose is calculated before drawing up, and the patient is monitored throughout. [1]

Differential diagnosis — circumferential cast versus backslab

The central SCQ distinction in splinting is the backslab versus the circumferential cast, and the Fellowship answer must distinguish each by its rigidity, its accommodation of swelling, its setting, and who applies it. The discriminating question is whether the limb is still swelling — the acutely injured limb swells for 48 to 72 hours, and only a non-circumferential device is safe in that window.[1][2]

The clinical rule the candidate recites: a backslab for the acute, a cast for the cold. Any limb that may swell further gets a backslab; the circumferential cast waits for the swelling to resolve. [1]

Complications — compartment syndrome, pressure sores, thermal injury

The complications the Fellowship candidate must name, prevent, and recognise divide into the three named in the topic and the secondary group. Each has a defined mechanism, prevention, and rescue.[2][3][6]

Compartment syndrome is the limb-threatening complication of immobilisation and the one the examiner most wants recognised. The tibial fracture carries the highest risk — McQueen and Court-Brown identified the predictors as the tibial-diaphyseal fracture, the young male, and the high-energy mechanism — but any casted limb, especially the child's, can develop it.[3] The pathophysiology is a rise in pressure within a fascial compartment that exceeds capillary perfusion pressure, producing ischaemia; the cast or the swelling haematoma is often the precipitant. The classic 5 Ps are pain out of proportion (and pain on passive stretch — the earliest and most sensitive sign, present while the pulse is still palpable), pallor, paraesthesia, paralysis, and pulselessness (a late and pre-terminal sign — the absence of a pulse means the compartment is already infarcting). In the child, compartment syndrome may be silent — the child cannot report the pain and presents instead with increasing analgesia requirement, agitation, and anxiety on passive stretch; a child demanding escalating opioid analgesia in a cast is assumed to have compartment syndrome until proven otherwise.[6]

Pressure sores arise where a bony prominence presses against an unpadded rigid surface. The malleoli, the olecranon, the ulnar and radial styloids, the fibular head, the metatarsal heads and the heel are the high-risk sites. Prevention is meticulous wool padding over every prominence; recognition is localised pain under the cast (or, in the neuropathic or the child, the discovery at cast removal); treatment is relief of the pressure, local wound care, and orthopaedic review for the deep ulcer over a fracture.[9]

Thermal injury (cast burns) is a direct consequence of the exothermic setting reaction: calcium sulphate hemihydrate reacts with water to form the dihydrate and releases heat. The peak temperature rises with hotter dip-water, more plaster layers, and insulating synthetic composites, and the burn is a full-thickness injury often discovered only at cast removal. The original measurements of Gannaway (1983) and the plaster-synthetic composite work of Burghardt (2014) established that cool dip-water and a modest slab thickness keep the peak temperature below the burn threshold — the practice the candidate must recite.[7][8]

Pitfalls and practical tips

The pitfalls invert the discipline, and the Fellowship candidate must name them aloud. Circumferential casting of an acute fracture — the iatrogenic compartment syndrome. Hot dip-water or an excessive slab thickness — the exothermic burn. An unpadded prominence — the pressure ulcer. Splinting the wrist in flexion or the ankle in equinus — the lost reduction. A fingertip dent in the wet plaster — the focal pressure sore. Circumferential tape — the constriction that strangulates. A collar as sole immobilisation of the cervical spine — the missed secondary injury. Prolonged use of the spinal board — the pressure sore and the respiratory compromise. Missing compartment syndrome behind opioid sedation — the limbed patient discharged with "good analgesia". [1]

The practical tips are the mirror. Backslab, never circumferential cast, for the acute limb. Cool water, 10 to 12 layers, mould with the palms. Pad every prominence. Position of function, always. Split and spread a tight cast to skin at the first suspicion of compartment syndrome. Elevate the limb. Document neurovascular before and after, and at every review. Log-roll off the spinal board within 30 minutes. A sling, not figure-of-eight, for the clavicle. Re-image at fracture clinic at 5 to 7 days. [1]

Post-procedure care and disposition

After the splint is applied and the neurovascular check is documented, the limb is elevated (a sling for the upper limb, a pillow or footstool for the lower) to reduce swelling, and the patient is discharged with fracture-clinic follow-up at 5 to 7 days for the wrist, ankle and clavicle, sooner (24 to 48 hours) for the higher-risk paediatric forearm and the supracondylar fracture. The safety-net is explicit and written down: return immediately for increasing pain despite analgesia, swelling, numbness or tingling, cold or pale fingers or toes, burning under the cast, or an offensive discharge. The analgesia plan and the elevation instruction are reinforced at discharge, and the patient is advised to keep the splint dry and not to insert any object under it (the foreign-body and ulcer cause of "itching under the cast"). The splint that has been applied for a prehospital or transient reason (the SAM splint, the cervical collar pending clearance) is reviewed and converted or removed as the work-up proceeds. [1]

Special populations

The child is the population in whom compartment syndrome is silent — the child cannot report the pain and presents instead with analgesia-refractory agitation, anxiety on passive stretch, and a rising opioid requirement; any child in a cast demanding escalating analgesia has compartment syndrome until proven otherwise, and the threshold to split the cast is very low.[6] The paediatric forearm reduction is the commonest splinted injury, and the backslab is converted to a cast at clinic only after the swelling subsides. The elderly patient has fragile skin (the wool must be generous) and often anticoagulation, which enlarges a fracture haematoma and raises the compartment-syndrome risk; the anticoagulated limb is watched closely. The pregnant trauma patient on a spinal board is log-rolled with a left lateral tilt to relieve aortocaval compression, and immobilised with the standard devices. The polytrauma patient is splinted after the life-threats are addressed — the femoral traction splint is part of the secondary survey, not the primary, and the open fracture is dressed, splinted in position and given intravenous antibiotics in parallel. The neurologically impaired patient (the head-injured, the intubated, the intoxicated) cannot report pain under the cast, and the threshold to split and inspect is the same as for the child.

Evidence and regional guidelines

The evidence base for the cast-versus-backslab decision is Barvelink's 2024 study of redisplacement of reduced distal-radius fractures, which examined whether the type of immobilisation affects loss of reduction, and Jorgensen's 2022 assessment of casting complications in acute distal-radius fractures, which quantified the cast-related morbidity that drives the ED preference for a backslab.[1][2] The compartment-syndrome evidence rests on McQueen and Court-Brown's predictors study (the tibial fracture and the young male as the high-risk profile) and on Lee's report of silent compartment syndrome in children, which established the analgesia-refractory child as the alarm sign.[3][6] The thermal-injury evidence is the classic Gannaway study of casting-material temperatures and the Burghardt composite-cast exotherm work, which together established the cool-water, modest-thickness practice.[7][8] The Thomas-splint evidence is Chu's description of paediatric traction-splinting practice and Irajpour's comparison of simple versus traction splints showing reduced pain with traction.[4][11] The cervical-spine immobilisation evidence is Pandor's 2024 systematic review of prehospital and emergency immobilisation and the NAP7 airway-management data for the collared patient, which together support motion restriction over rigid immobilisation and the timely removal of the collar once cleared.[5][10] The clavicle evidence is Lenza's Cochrane review of conservative interventions, which found no benefit of figure-of-eight over a simple sling.[12]

Exam pearls

• "Joint above and below." State the principle aloud at every splinting answer — a forearm splint controls the wrist and the elbow, a lower-limb splint controls the ankle and the knee, a femur needs traction from hip to ankle.
• "Backslab for the acute, cast for the cold." The backslab is non-circumferential, accommodates swelling, is the ED default; the circumferential cast is orthopaedic, applied only after swelling resolves at 48 to 72 hours. Applying a circumferential cast to an acute fracture is the iatrogenic cause of compartment syndrome.
• The 5 Ps, in order of onset. Pain out of proportion and pain on passive stretch (earliest, pulse still present), then pallor, paraesthesia, paralysis, pulselessness (late, pre-terminal). The pulse is a late sign — never wait for it.
• Split a tight cast to skin. On any suspicion of compartment syndrome, split the cast, the wool and the stockinette down to skin and spread it, re-check neurovascular, keep at heart level, analgesia, call orthopaedics for fasciotomy.
• Cool dip-water, 10 to 12 layers, palms not fingertips. The exotherm is controlled by cool water and a modest slab; mould with the palms because fingertips dent the wet plaster and make pressure sores.
• A collar does not immobilise alone. Pair with manual in-line stabilisation, head blocks and straps; log-roll off the spinal board within 30 minutes.
• Sling, not figure-of-eight, for the clavicle. The Cochrane evidence shows no outcome benefit and more discomfort from figure-of-eight bandaging.
• The silent child. A child in a cast demanding escalating analgesia has compartment syndrome until proven otherwise — split the cast. [1]

Red flags