Internal fixation of femoral neck fractures with posterior comminution: a biomechanical comparison of DHS® and Intertan nail®

Abstract

Background and purpose: Internal fixation is a therapeutic mainstay for treatment of undisplaced femoral neck fractures and fractures without posterior comminution. The best treatment for unstable and comminuted fractures, however, remains controversial, especially in older patients. The present study was designed to assess the utility of the Intertan Nail® (IT) for stabilization of comminuted Pauwels type III fractures compared to dynamic hips screw (DHS).

Methods: Randomized on the basis of bone mineral density, 32 human femurs were assigned to four groups. Pauwels type III fractures were osteomized with a custom-made saw guide. In 16 specimens the posteromedial support was removed and all femurs were instrumented with an IT or a DHS. All constructs were tested with nondestructive axial loading to 700N, cyclical compression to 1,400N (10,000 cycles), and loading to failure. Outcome measures included number of survived cycles, mechanical stiffness, head displacement and load to failure.

Results: Postoperative mechanical stiffness and stiffness after cyclical loading were significantly reduced in all constructs regardless of the presence of a comminution defect (p = 0.02). Specimens stabilized with the IT had a lower construct displacement (IT, 8.5 ± 0.5 mm vs. DHS, 14.5 ± 2.2 mm; p = 0.007) and sustained higher failure loads (IT, 4929 ± 419 N vs. DHS, 3505 ± 453 N; p = 0.036) than the DHS constructs.

Interpretation: In comminuted Pauwels type III fractures, the fixation with the IT provided sufficient postoperative mechanical strength, comparable rate of femoral head displacement, and a similar tolerance of physiological loads compared to fractures without comminution. The absence of the posteromedial support in comminuted fractures tended to reduce the failure load regardless of the fixation method.

Fig. 1

Custom-made saw guide and fracture geometry according to Windolf et al. [12]

Fig. 2

Postoperative radiographs in two planes (AP and axial) were obtained for each specimen after fixation, cyclical testing, and loading to failure to evaluate the position of the implant, the fracture dislocation, and the modes of specimen failure

Fig. 3

Regardless of the fixation method and the presence of the comminution defect, the postoperative and post-cyclical mechanical stiffness was significantly reduced compared to intact femurs (p = 0.02)

Fig. 4

Independent of the fixation method, at 50 cycles, all of the constructs sintered. At the end of cyclical loading, the construct displacement was higher in the DHS groups compared to the IT groups (p = 0.007)