Fracture Immobilisation & Casting

Splinting and casting technique for a stable, low-risk fracture managed in general practice or urgent care. See Easily Missed Orthopaedic Fractures in the GP Setting for fracture-specific management and red flags.

Splint vs cast

A splint is a non-circumferential application of plaster or fibreglass — it accommodates the swelling of the acute inflammatory phase and can be loosened or removed easily. A cast is circumferential and rigidly immobilises the joint or fracture. Because of that circumferential constriction, casts are rarely applied in the acute setting; a fresh injury is splinted first and only converted to a cast once swelling has settled, typically at a follow-up review.

Assessment

Examine the injured area, the joint above and the joint below, and document neurovascular status before and after any splint or cast is applied. Obtain appropriate anteroposterior and lateral X-rays of the affected region — the Ottawa Knee and Ankle rules help decide when imaging is warranted for those joints. An open wound over or near the fracture needs antibiotics, wound irrigation and debridement or closure addressed before splinting, not after — it should be assumed a skin break communicates with the fracture even if not directly over it, and infection risk climbs sharply if antibiotics are delayed: in one study, giving them within three hours of injury tracked a 4.7% infection rate.

Contraindications are relative, not absolute. A neurosensory deficit or a vascular injury needs surgical evaluation before splinting, since splinting can mask or worsen compartment syndrome or a vascular complication in an already-compromised limb. Peripheral neuropathy and chronic peripheral vascular disease are not contraindications outright but raise the risk of an undetected pressure injury, since baseline sensation is already altered.

Equipment

Assemble everything before starting — stockinette, undercast padding, plaster or padded fibreglass (wider for the upper arm or lower leg, narrower for the forearm), a bucket of cool water, elastic bandage, and a sling for an upper-limb injury — to avoid the material starting to set before application. Cut materials to length in advance; plaster should be stacked 8–10 sheets thick for adequate strength, fewer in children. Ensure adequate analgesia first, both for comfort and to allow muscle relaxation during any reduction.

Technique

1. Apply stockinette circumferentially, extending beyond the splinted region at both ends.
2. Pad bony prominences — elbow, knee, calcaneus — with at least 1–2 cm of soft cast padding, then apply 2–3 circumferential layers of cast padding over the rest of the area.
3. Reduce any fracture, restoring length, rotation and alignment, before applying the splinting material. Activate the plaster or fibreglass in cool or room-temperature water (hot water risks a thermal skin burn from the exothermic setting reaction) and laminate the sheets together for strength.
4. Mould the material around the injury to resist the deforming force, and cut any circumferential overlap once it has set rather than leaving it fully encircling the limb.
5. Fold the stockinette back over the splint’s edges to protect the skin, then apply an elastic bandage circumferentially to hold everything in place while it hardens — never wrap the elastic bandage directly against bare skin.
6. Repeat the neurovascular check once complete; any deterioration means the splint comes off immediately for reassessment.

Upper-limb splints crossing the wrist should hold neutral dorsiflexion. Lower-limb splints crossing the ankle should sit in a neutral resting position, not plantarflexed, to avoid an Achilles contracture. A supracondylar elbow fracture in a child should never be splinted with the elbow flexed beyond 90° — this raises the risk of Volkmann ischaemic contracture.

Complications

Watch for loss of reduction, skin irritation or breakdown, and joint stiffness — minimised by a well-fitted splint with adequate padding that immobilises as few joints as possible. Compartment syndrome and neurovascular compromise are rare but serious, more often from a cast than a splint because of its circumferential nature; both need prompt removal of the immobilisation and reassessment. Warn every patient about return precautions: numbness, tingling, pallor, or increasing pain or swelling under the cast or splint need urgent review, not a scheduled follow-up. See Acute Compartment Syndrome for full recognition and management.

Follow-up

First review is typically at 7–14 days, before soft callus becomes hard callus, checking position and healing (clinically and, if needed, radiographically) and referring to orthopaedics if either is unsatisfactory. Further review follows at three or more weeks for an upper-limb fracture and four or more weeks for a lower-limb fracture. If the fracture site remains tender at review, continuing immobilisation for another 7–10 days before reassessing is reasonable. A splint intended as definitive treatment can be converted to a cast once early swelling has settled. Advise patients to keep the cast or splint clean and dry, elevate the limb to limit swelling, and return immediately for a wet cast or any change in sensation, colour or movement.

Referral

Refer to orthopaedics for an open, displaced or neurovascularly compromised fracture, one with significant rotation or malalignment, multi-trauma, or a fracture still not healed after about 10 weeks of primary-care management. Difficult-to-reduce, excessively shortened or comminuted fractures usually need operative fixation rather than definitive splinting or casting.