Introduction: The success of interlocking nail is due to proximal and distal locking, giving stability to nail. For proximal locking authors have inbuilt aiming system in jig, but distal locking is done free hand. Free hand method is associated with radiation exposure and time taking. In this study authors emphasized the importance of mechanical aiming system for distal locking. Objective: The study is a comparative study between, distal locking by free hand method and distal locking by proximally mounted mechanical distal aiming device (DAD) with respect to radiation exposure and time taken. Methods: It was a prospective study conducted over a period of one and a half years. Cases under study were patient with mid-shaft femur fracture (type32a simple). Comparison was done for c-arm shots and time required for distal locking. Results: A total of 140 patients were assessed. There were 70 patients in free hand group and 52 patients in DAD group. There was dramatic decrease in radiation exposure (free hand group-13.5 c-arm shots, DAD group-2 c-arm shots) and time required (free hand group-22.4 min(mean), DAD group-7.8 min (mean)) for distal locking. There was also decrease in drill bit/nail graze in DAD group. Conclusion: Distal locking by free hand method is time taking and associated with radiation exposure. There is a learning curve for distal locking in free hand technique. But distal locking by DAD is user friendly just like proximal locking with decrease in locking time and radiation exposure.

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