**Core Concept**
A tube (cylinder) cast is a type of orthopedic cast used to immobilize and stabilize long bone fractures, particularly those of the tibia (shinbone) and fibula. This cast is applied to provide compression and support to the affected area, promoting healing and reducing the risk of complications.

**Why the Correct Answer is Right**
The tube cast is specifically designed for mid-shaft fractures of the tibia and fibula, where it provides excellent compression and support to the affected area. The cast is typically applied with the knee in 10-15 degrees of flexion to reduce tension on the surrounding soft tissues and promote healing. The compression provided by the cast helps to reduce the risk of compartment syndrome, a potentially life-threatening condition that can occur when pressure builds up in the muscles and nerves.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because a long leg cast is typically applied for fractures of the femur, which is a different type of fracture that requires a more extensive cast.
**Option B:** This option is incorrect because a splint is a lighter, more flexible form of immobilization used for minor injuries or temporary support, rather than a long bone fracture.
**Option C:** This option is incorrect because a back slab is a type of cast used for fractures of the spine or pelvis, which requires a different type of immobilization.

**Clinical Pearl / High-Yield Fact**
When applying a tube cast, it is essential to ensure that the knee is in 10-15 degrees of flexion to reduce tension on the surrounding soft tissues and promote healing.

**Correct Answer: C.