A NEW MECHANICAL AIMING DEVICE FOR THE PLACEMENT OF DISTAL INTERLOCKING SCREWS IN FEMORAL NAILS

Although the free-hand technique remains the most popular method for d istal interlocking screw insertion, a proximally mounted ''radiation-i ndependent'' device which compensates for implant deformation has been developed. In 15 intact human cadaveric femora the same surgeon perfo rmed statically locked intramedullary nailing using the distal aiming system. Operation time, distal screw insertion, total radiation time a nd accuracy of the interlocking screw placement were measured using a radiation-independent distal aiming system. The average total operatio n time was 21.2 +/- 8.6 min, and the average distal locking time (2 sc rews) was 7.1 +/- 2.4 min. The total operation time and the distal loc king time declined over the first 10 cases. These times did not signif icantly improve in the subsequent 5 procedures. The average total fluo roscopy time was 28.1 +/- 16.6 s. None of the screw placements using t he distal aiming device required the use of fluoroscopy. Drill-nail co ntact was absent in 5 drillings, mild in 9 drillings, moderate in 16 d rillings, and severe in none. Measurement of screw damage showed in 55 of 60 measurements wear of less than 15 mu m. There were no failures or major complications. A minor complication related to distal locking was observed in one specimen. This study suggests that distal interlo cking screws can be placed successfully using a radiation-independent aiming arm-based system, which accounts for nail deformations. The dis tal aiming device (DAD) can be learned easily. The main advantages of the aiming arm include the elimination of radiation during distal inte rlocking and precise screw placement with little insertion-related har dware damage.