UNSTABLE PROXIMAL TIBIA FRACTURES: A BIOMECHANICAL EVALUATION OF THREE FIXATION METHODS AND INITIAL CLINICAL RESULTS

Abstract

Introduction: Unstable, extra-articular, proximal, tibia fractures are difficult clinical problems often complicated by mal-alignment and soft-tissue breakdown.

Aim: To evaluate the biomechanical properties of a traditional double plating (DP) technique, the Less Invasive Stabilization System (LISS) and hybrid external fixation. Secondarily, the clinical outcomes of an initial series of 20 fractures treated with the LISS system were to be evaluated.

Methods: The axial stiffness and biaxial tilt (varus/valgus and anterior/posterior) of the three systems were tested. Five synthetic tibiae per system were loaded in sequence under the following conditions of instability:

1)Intact.

2)1 cm medial wedge osteotomy (proximal metaphysis).

3)1 cm gap osteotomy.

Twenty proximal tibial fractures treated with the LISS system were reviewed to assess union rates, complications, knee motion and secondary procedures.

Results: There were no significant differences between the different systems when they were used on the intact specimens. The DP system was significantly stiffer axially and in varus tilt than the LISS and the hybrid systems for the wedge osteotomy for all loads. The LISS was significantly stiffer in varus tilt than the hybrid with the wedge at maximal loading. With the gap osteotomy, all three systems were significantly different from each other in both stiffness aspects (DP> LISS> hybrid). The hybrid exhibited axial gap closure at approximately one third of the force of the other systems. No implant failed or exhibited plastic deformation. In the clinical review all fractures united and only three required bone grafting. No fixation failed but there were three deep infections. Over 80% of the cases had knee motion of 90 degrees or better.

Conclusions: The DP was significantly stiffer than both the LISS and the hybrid system for axial displacement and varus tilt at comparable loads for the wedge and gap models. The LISS was significantly stiffer than the hybrid in the completely unstable gap model. The tibial LISS system gave encouraging initial clinical results.