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.
Position the patient supine on a radiolucent table, slightly head down 10° to prevent sliding towards the foot of the table.
Place a small pad behind the knee to take pressure of the neurovascular structures. The pad also facilitates lateral x-ray images as this will lift the knee anterior to the contralateral side.
Also place a sandbag behind the same buttock to prevent external rotation of the leg.
The knee can be flexed to 90° by breaking the table. One of the reasons for flexing the knee is to aid fracture reduction. This will relax the tension in the gastrocnemius muscles, which pull on the posterior femoral condylar fragments.
Check that you can get good image intensifier pictures before starting the surgery.