Place the patient supine on a radiolucent table. A small bolster can be placed beneath the buttock to prevent external rotation of the lower extremity.
The supine position with the knee flexed 30° provides good support for the knee and relaxes the tendency of the gastrocnemius muscle to pull the condyles into hyperextension. It has the disadvantage that, for lateral image intensifier use, the limb may need to be lifted up.
The supine position on a split table fully extends the knee and relaxes the knee extensor muscles. This is useful when vastus lateralis has to be retracted forwards. It is also the position of choice for patellar fractures and disruptions of the extensor mechanism.
The supine position with unilateral leg support offers excellent image intensifier access for the lateral views. It also allows the surgeon to vary the degree of flexion of the knee at different stages of the procedure. A surgical assistant is needed to hold the lower leg in the correct position throughout the operation.
In the supine position with the knee flexed 90° it is fully supported, which helps the surgeon who has little, or no, intraoperative assistance. It tightens the extensor muscles and limits vastus lateralis retraction. It is well suited to procedures requiring lateral patellar dislocation. Beware prolonged pressure on the popliteal neurovascular bundle.