Comparison of mechanical rigidity between plate augmentation leaving the nail in situ and interlocking nail using cadaveric fracture model of the femur

Abstract

Thirteen matched pairs of cadaveric femurs were placed into two groups. In each group, a transverse fracture was created at a point 70% distal between the lesser trochanter and the adductor tubercle. One femur out of each matched pair was then stabilised with an interlocking intramedullary nail (nail only group) and the other femur was stabilised with plate augmentation after interlocking intramedullary nailing (plate augmentation group). The bending load to promote 5-mm displacement showed statistically significant differences between the plate augmentation group (mean 843.36 ± 409.13 N) and the nail only group (mean 315.02 ± 219.80 N) (p = 0.001). Torsional torque at the angle of 15 degrees showed statistically significant differences between the two groups; a mean of 2.09 ± 0.53 N·m for the plate augmentation group and a mean of 0.63 ± 0.46 N·m for the nail only group (p = 0.0001). We found a 2.6-fold increase in bending stiffness and a 3.3-fold increase in torsional stiffness in plate augmentation leaving a nail in situ compared to interlocking nailing only in the distal third fracture of femur.

Fig. 1

Fractures were created that were at 70% the length of the femur, measured from the lesser trochanter to the adductor tubercle. A femur of each matched pair was fixed with interlocking intramedullary nail and the contralateral femur was fixed with plate augmentation after interlocking intramedullary nail

Fig. 2

Four-point bending test performed until the fracture bent to 5-mm displacement

Fig. 3

A mounting jig was designed to keep the two holding fixtures for a subsequent torsional test (above). Each femur was rotated until an angle of 15 degrees or failure of the fixation (below)

Fig. 4

Plate augmentation after interlocking intramedullary nailing was significantly stiffer than the interlocking intramedullary nail alone in bending test (p = 0.001)

Fig. 5

The torsional stiffness showed that the plate augmentation group was 3.3-fold stiffer than the nail only group (p = 0.0001)