34th Annual Scientific Meeting proceedings

Objective
To compare the mechanical behavior of straight (STRT) and bent (BENT) interlocking nails under eccentric compressive loads.

Study Design
Experimental.

Sample Population
Tibial gap fracture models simulating a comminuted mid-diaphyseal fracture stabilized with either an STRT or BENT I-Loc interlocking nail (n=5/group).

Methods
Constructs were mounted in a servo-hydraulic loading frame using proximal and distal custom designed unconstrained couplings in both groups. Cyclic compressive loads were applied eccentrically to mimic in vivo loading conditions of the tibia. Ramp tests were then conducted until failure. Outcome measures consisting of construct compliance, yield point (0.1% offset), maximum resistive torque, and failure load were statistically compared using Student’s t-test (P<0.05). Failure modes were described.

Results
Compliance was ~50% lower in BENT (17±2 [10-4]mm/N) vs STRT (29±1 [10-4]mm/N) constructs (P<0.05). Yield point (616.3±23.9N vs 476.7±27.5N) and failure loads (1065.7±45.7N vs 968.6±49.2N) were significantly greater in BENT than STRT constructs. In contrast, there was no difference in resistive torques between groups (P>0.05). Construct failure occurred via plastic deformation at the nail isthmus in both groups.

Conclusion
Bending I-Loc nails provided mechanical advantages in resisting eccentrically applied compressive loads in a tibial fracture gap model. Bending however, had no influence on the failure mode and maximum resistive torques sustained by the constructs.

Clinical Significance
Tibial interlocking nail yield failure in bending has been anecdotally reported with straight nail. The prevalence of this complication may be reduced by pre-bending the interlocking nail. Surgeons should consider pre-operatively contouring I-Loc nails prior to implantation for tibial osteosynthesis.