THREE DIFFERENT INTERLOCKING INTRA-MEDULLARY NAILS FOR UNSTABLE REVERSE OBLIQUE INTER-TROCHANTERIC FRACTURES: A BIOMECHANICAL COMPARATIVE STUDY OF LOADING TO FAILURE

Abstract

Introduction: Unstable inter-trochanteric fractures are increasing in incidence and stable fixation can improve outcome by leading to earlier mobilisation and reduced mortality. The appropriate choice of implant is vital to ensure a satisfactory outcome.

Objectives: The objective of this study was to determine the load at which different intramedullary device constructs failed.

Materials and Methods: Nine identical 3rd generation composite Sawbones were used and prepared with reverse obliquity cuts made to the femoral necks. Three different types of trochanteric entry intramedullary nail were then inserted using manufacturer’s guidelines. The nine constructs were loaded to failure using a Dartec 9500 servo hydraulic testing machine.

Results: The average failure loads were 3954±952N for the DePuy nail, 2420±281N for the Synthes nail and 3810±377N for the Stryker nail. In eight of the nine constructs the Sawbone failed at the medial side of the fracture. One of the DePuy nails failed at 5041N in the area of the distal locking screws.

The Stryker nail constructs were significantly stronger than the Synthes constructs (p=0.008); although the DePuy constructs were similar in strength to the Stryker constructs (p=0.83) they were not significantly different from the Synthes constructs (p=0.098).

Conclusion: There must be a balance between movement at the fracture site to allow compression but enough stability that the fracture may heal.

Our study showed that the Synthes nail failed at a significantly lower load than the DePuy or the Stryker nails. The Synthes construct failed at a typical walking load, around three times body weight for an 80kg patient.