Before locking, the correct position of the nail and the rotation of the femur must be verified.
If no traction table is used (ie, using the freehand technique) the cable method may be used. In this approach, a line is drawn from the iliac spine across the patella to the cleft between the first and second toes. If rotation is correct, this line will pass over the mid line of the patella. The radiological landmarks of the center of the femoral head, the center of the knee and the center of the ankle joint should all be in line if the mechanical axis of the femur is correct.
Another method of assessing rotational reduction is to compare the cortical thickness above and below the fracture. If a shaft fracture is multifragmentary, the image intensifier cannot be used to assess the analogue cortical diameter on both sides of the fracture.
For distal locking, the image intensifier is brought into a strict lateral position. The distal hole must be seen as a perfect circle and the tip of a scalpel is projected into the center of the hole.
This guides the stab incision down to the femoral cortex.
Screw insertion technique
The radiolucent drive helps to position the drill bit so that the locking screw can be properly inserted. While the locking hole is drilled, the assisting surgeon must prevent the lower extremity from moving in order not to miss the target hole. The length of the locking screw is determined, using the appropriate depth gauge. Then the locking screw is inserted.
If a radiolucent drive is not available, the projection of the tip of the drill bit should be placed as centrally as possible (see image). Start drilling but assess the position of the tip of the drill bit repeatedly, with the drill temporarily uncoupled.
Pearl: secure screw using a suture
If the contact between the screw driver and the locking screw is lost, the screw may move within the soft tissue and become extremely hard to capture. To prevent this time-consuming complication, the locking screw should be lassoed with a strong absorbable suture.
Pitfall: trapped locking screw
If the screw holes are not perpendicular to the nail, the locking screw may become trapped and may not be advanced properly.
Second locking screw
The second locking screw is inserted into the distal locking hole. After distal locking, an axial blow to the knee region may be be used to reduce any fracture distraction.
Alternatively, when distal locking is completed prior to proximal locking, a slotted hammer can be used to pull back the locked nail and the distal fragment.
Completed distal locking
The image shows the distal locking completed.
Pitfall: screw loosening
Care should be taken to capture the far cortex in order to prevent toggling when the patient is mobilized. This would lead to early loosening of the locking screw. In the image shown, the proximal locking screw is of correct length, but the distal one is marginally too short.