If the leg cannot be straightened, what should be used?

When dealing with a leg injury where the leg cannot be straightened, a bent knee splint is an appropriate choice because it provides support while accommodating the natural position of the leg. This type of splint allows for the maintenance of the injured leg's position without forcing it into a straightened alignment, which could potentially cause further injury or discomfort.

The use of a bent knee splint ensures that the joint is stabilized, while the bend can help in reducing tension on the muscles and ligaments that may be affected by the injury. This support can also allow for some mobility in the case of transport and can be adjusted to fit the specific needs of the patient, making it a versatile option for when full leg extension isn’t possible.

In contrast, options like a full leg cast or a straight leg splint would not address the situation appropriately, as they would require the leg to be straightened, which is not feasible in this case. A knee immobilizer provides support but lacks the adjustability of a bent knee splint and may not provide the same level of comfort for a patient unable to straighten the leg. Therefore, a bent knee splint is the most suitable choice when the leg cannot be straightened.