Immobilisation of the lower limb is a key aspect of managing fractures, ligamentous injuries, and post-operative recovery in Trauma and Orthopaedics. Proper immobilisation supports healing, protects injured structures, reduces pain, and allows safe mobilisation during the early phases of recovery. This article provides an overview of the common lower limb immobilisation methods used in clinical practice, outlining their indications, advantages, and essential principles to guide junior doctors in delivering safe and effective patient care.

Casts

Backslab and Full Casts

Both a backslab and a full cast are made of natural gypsum (calcium sulfate dihydrate), more commonly known as Plaster of Paris (POP). Once mixed with water, the compound hardens and is used to immobilise a limb.

A backslab is when the hardened POP is applied only to one side of the limb and secured with bandage. The limb is wrapped in wool beforehand to protect the skin. Backslabs are commonly used in acute injuries to allow for soft tissue swelling.

In contrast, a full Plaster of Paris cast encases the limb circumferentially, providing greater stability. It can be used in acute injuries if the fracture pattern requires more support than a backslab can provide; in these cases, the cast is usually split to accommodate soft tissue swelling.

Fig 1: Above knee backslab (blue) applied to lower limb which has already been covered in wool layer and stockinet to protect skin. Image Source – https://surgeryreference.aofoundation.org/orthopedic-trauma/pediatric-trauma/proximal-tibia/basic-technique/splinting

Synthetic Lightweight Cast

A synthetic lightweight cast is an alternative to a full POP cast, made from modern materials such as fibreglass or polyester. These casts are lighter, stronger, and more durable. Patients with fractures managed non-operatively are often changed from a backslab or full POP cast to a synthetic cast at fracture clinic review 1–2 weeks after injury.

Fig 2: Below Knee Synthetic Cast. Image source – https://fineartamerica.com/featured/short-leg-cast-in-synthetic-plaster-david-parker.html

Cricket Pad Splint

A cricket pad splint, also known as a straight-leg splint or Richard’s splint, is a fabric splint applied with its midpoint over the knee and extending from the mid-thigh to the upper calf. It is used to keep the knee fixed in extension, and patients are usually allowed to weight bear while wearing it. This type of splint is commonly applied in A&E for suspected soft tissue knee injuries—such as ACL or meniscal injuries, or quadriceps tendon rupture—as knee flexion typically exacerbates pain. The splint provides comfort and temporary stabilisation while swelling settles. Patients are then reviewed in fracture clinic for further clinical assessment and appropriate investigations, such as MRI, to guide definitive management.

Fig 3: Cricket Pad Splint. Image Source – https://beagleorthopaedic.com/tri-panel-economy/

Hinge Knee Brace

A hinge knee brace is a rigid or semi-rigid support that encases the knee and has adjustable hinges on either side to permit movement. It is used to stabilise the knee joint while permitting a safe range of flexion and extension, depending on the injury. Hinge braces are commonly prescribed for ligament injuries (e.g., ACL, PCL, MCL), post-operative rehabilitation, or significant soft tissue injuries. By controlling movement, the brace helps protect healing structures, reduce pain, and allow early mobilisation. Patients are typically reviewed in fracture or orthopaedic clinics, where the range of allowed movement is gradually increased as recovery progresses.

Fig 4: Hinge Knee Brace. Image Source – https://www.chaneco.co.uk/product/paediatric-post-op-pin-knee-brace/

Walker Boot

A walker boot, also known as a controlled ankle motion (CAM) boot, is a rigid, adjustable boot designed to immobilise and protect the foot and ankle while allowing partial or full weight bearing. It is commonly used for stable fractures of the foot and ankle, tendon injuries, or post-operative recovery. The boot reduces pain, controls swelling, and provides support while permitting some degree of mobility, which can help prevent deconditioning. Patients are typically reviewed in fracture or orthopaedic clinics, where the duration of use and progression to regular footwear are determined based on healing and clinical assessment.

Fig 5: Air Walker Boot. Images Source – https://orthotix.co.uk/products/ultra-air-walker

Further Reading

Baylor R, Al-Migdad A, Obeidat N, Melhem M, Abu-Ashour S, Gamage JC, et al. Revolution in orthopedic immobilization materials: a comprehensive review. Heliyon. 2023;9:e13640. doi:10.1016/j.heliyon.2023.e13640.

Written by Mr Amar Sidhu (CT2 in Trauma and Orthopaedics)