Abstract
Introduction and Objective
Intramedullary nails are frequently used for treatment of unstable distal tibia fractures. However, insufficient fixation of the distal fragment could result in delayed healing, malunion or nonunion. The quality of fixation may be adversely affected by the design of both the nail and locking screws, as well as by the fracture pattern and bone density. Recently, a novel concept for angular stable nailing has been developed that maintains the principle of relative stability and introduces improvements expected to reduce nail toggling, screw migration and secondary loss of reduction. It incorporates polyether ether ketone (PEEK) inlays integrated in the distal and proximal canal portions of the nail for angular stable screw locking. The nail can be used with new standard locking screws and low-profile retaining locking screws, both designed to enhance cortical fixation. The low-profile screws are with threaded head, anchoring in the bone and increasing the surface contact area due to the head's increased diameter.
The objective of this study was to investigate the biomechanical competence of the novel angular stable intramedullary nail concept for treatment of unstable distal tibia fractures, compared with four other nail designs in an artificial bone model under dynamic loading.
Materials and Methods
The distal 70 mm of thirty artificial tibiae (Synbone) were assigned to 5 groups for distal locking using either four different commercially available nails – group 1: Expert Tibia Nail (DePuy Synthes); group 2: TRIGEN META-NAIL with Internal Hex Captured Screws (Smith & Nephew); group 3: T2 Alpha with Locking Screws (Stryker); group 4: Natural Nail System featuring StabiliZe Technology (Zimmer) – or the novel angular stable TN-Advanced nail with low-profile screws (group 5, DePuy Synthes). The distal locking in all groups was performed using 2 mediolateral screws. All specimens were biomechanically tested under quasi-static and progressively increasing combined cyclic axial and torsional loading in internal rotation until failure, with monitoring by means of motion tracking.
Results
Initial nail toggling of the distal tibia fragment in group 5 was significantly lower as compared with group 3 in varus (p=0.04) or with groups 2 and 4 in flexion (p≤0.02). In addition, the toggling in varus was significantly lower in group 1 versus group 4 (p<0.01). Moreover, during dynamic loading, within the course of the first 10,000 cycles the movements of the distal fragment in terms of varus, flexion, internal rotation, as well as axial and shear displacements at the fracture site, were all significantly lower in group 5 compared with group 4 (p<0.01). Additionally, group 5 demonstrated significantly lower values for flexion versus groups 2 and 3 (p≤0.04), for internal rotation versus group 1 (p=0.03), and for axial displacement versus group 3 (p=0.03). A trend to significantly lower values was detected in group 5 versus group 1 for varus, flexion and shear displacement – with p ranging between 0.05 and 0.07 – and versus group 3 for shear displacement (p=0.07). Cycles to failure were highest in group 5 with a significant difference to group 4 (p<0.01).
Conclusions
From a biomechanical perspective, the novel angular stable intramedullary nail concept with integrated PEEK inlays and low-profile screws provides ameliorated resistance against nail toggling and loss of reduction under static and dynamic loading compared with other commercially available intramedullary nails used for fixation of unstable distal tibia fractures.
