The AO distal locking aiming device: an evaluation of efficacy and learning curve

The AO nail mounted 'distal locking aiming device', developed to obtain radiation independent distal locking, has an unproven efficacy in a large clinical setting. This prospective study compares the efficacy and learning curve of the distal aiming device with the popular 'free hand technique'.

Distal locking in thirty cases of statically locked intramedullary femur nailing using the distal aiming device for rotationally stiff unslotted AO SUN nails was prospectively compared with the same number using the free-hand technique with regard to duration, radiation exposure, accuracy of screw placement, and learning curve.

For the free-hand technique and the distal aiming system respectively, the average distal locking time was 35.8+/-18.6 versus 19.3+/-9.8 minutes, and the average number of images taken to achieve distal locking was 11.5+/-3.4 versus 3.8+/-3.5. The decrease in average distal locking time by 46.1% and in radiation by 70.0% with the distal aiming system is statistically significant at P<0.001. There were three failures of the distal aiming device and these were converted to the free-hand technique. The learning curve for the distal aiming device was shorter and more predictable than that with the free hand technique. We also analyse the failures and associated pitfalls with the system.

We found the AO distal locking aiming device to be an accurate, radiation-independent jig with a short and predictable learning curve.