Recently, the interlocking intramedullary nailing is being regarded as one of the best method using static or dynamic UTN(Unlearned Tibial Nail) in the treatment of the tibial shaft fractures. However it has made the locking screw break because the early weight bearing and exercise for the early bony union and the delayed removal of the static locked screw. Failure of the locking screw has not resulted in loss of reduction, but broken screw can make nail removal difficult.

The authors have clinically analysed 17 patients of open tibial shaft fractures treated with static or dynamic interlocking intramedullary nailing using UTN followed by more than 6 months at Chung Nam National University Hospital from January 1993. to February 1995.

1. In all 17 cases, nails were inserted via closed method and early weight bearing was encouraged.

2. Among 17 cases, 4 cases of proximal static screw were broken, and all screw failures were occurred in static hole of proximal portion of AO UTN.

3. Among 17 cases, secondary dynamization was tried at POD 4 wks for early bony union in only one case and that revealed good result.

So, We recommand that the locking screw of the proximal lowest hole should be removed before weight bearing because of its mechanical weakness, and that the start of weight bearing should be considered according to AO Groups principles including the character of the patient and fractures.