Abstract
Introduction: The Taylor Spatial Frame (TSFTM, Smith & Nephew, Memphis) has gained international recognition for the fixation of complex long bone fractures and deformity correction. It’s application with transverse wires can be difficult in some anatomic regions, and fixation of frames with half pins is gaining clinical popularity. Half-pins cause minimal transfixion of the surrounding soft tissues and can be inserted into anatomically safe areas.
Aims: This study aimed to compare the stiffness characteristics of a TSF frame fixed with transverse wires to fixation with half pins.
Materials and methods: Experiments were carried out in the biomechanics laboratory at Cardiff university. All mechanical testing was performed with a servo-hydraulic test frame (MTS-858 Mini Bionix II®, MTS Corp., Minneapolis). Custom built mounts were used to attach the bone rigidly to one end of the machine and TSF ring to the other. Rings were fixed with 1.8mm transverse wires or hydroxyapatite coated 6.5mm half pins with 45°, 60°, 75° and 90° divergence angles. Bone was loaded with axial load to 400N and torque to 20Nm. Load/displacement curve data were analyzed for slope and displacement.
Results: For larger diameter rings (180mm) there was no statistically significant difference in axial stiffness between the transverse wires (with 2 rings) and the half pins (p> 0.05). For 155mm diameter rings half pins provided statistically higher axial stiffness than transverse wires (p= 0.036). Half pins gave significantly more torsional stiffness for both ring diameters when compared to transverse wires (p< 0.05). As in axial stiffness, small diameter rings showed increased stiffness in torsion. There was an increase in axial and torsional stiffness as the divergence angle between the wires or pins increased (p< 0.05).
Conclusion and clinical relevance: Half pins provide greater stiffness to TSF frames and allow axial micro-motion as well. This work provides a rationale for clinical decision making in construction of a TSF frame.
Correspondence should be addressed to A.H.N. Robinson, BOX 37, Department of Orthopaedics, Addenbrooke’s Hospital, Cambridge University Hospitals NHS Trust, Hills Road, Cambridge. CB2 0QQ, England.
