Introduction: Internal fixation of diaphyseal fracture of shaft of femur in an adult by Kuntscher nail is the most common operative method of treatment in Nepal where operative facilities for the same exist. Since the complete range of K-nail sizes and length are not available in most operation theatres in Nepal, most orthopaedic surgeons assess the size and length of the K-nail pre-operatively by various methods and keep one size above and below the assessed length for the planned surgery.

Materials and Methods: The following measurements were taken in five hundred people involved in the study:

Measurement No. 1: Tip of the greater trochanter to lateral knee joint line minus 2cms.

Measurement No. 2: Tip of the olecranon process to the tip of little finger, and

Measurement No. 3: Tip of the greater trochanter to the upper pole of patella.

An average of all three lengths were analysed to see if there were any differences in their mean lengths.

Results: Analysis showed that there were significant differences between the mean lengths measured by the three different methods. The average length of measurement no: 2 was 3 cm longer than the average length of measurement no: 1, which is the reference pre-operative length of K.nail.

Conclusion: However, in practice since measurement no:2 is more convenient to perform and can also be used when the patient has sustained bilateral fractures of femur, an accurate pre-operative K-nail length assessment can be done by subtracting 3 cm from measurement no:2, i.e. the tip of the olecranon process to the tip of the little finger.