Taylor Spatial Frame (2/2)
...go to previous page...bone-transfixing components: fine wires and/or half-pins. If a combination of half-pins and fine wires is used to transfix the broken bone segments to the TSF, it is common to refer to such a fixator as a hybrid. Fine wires are typically pretensioned in order to increase their stiffness response to axial loads (perpendicular to the wire major axis). They are clamped on the rings using slotted or cannulated bolts. Two wire types, based on section diameters, are available: 1.6 mm & 1.8 mm. Wires can be made either from stainless steel or titanium alloy. Half-pins are fixed onto the rings using stacks of rancho cubes. Three types of half-pins are available: 4 mm, 5 mm & 6 mm in section diameter. To allow for greater segment stability and transfixing component anchorage space, accessory rings can be mounted on either side of the TSF.
The TSF's unique parallel kinematics enables all six degrees of geometric freedom (three spatial and three rotational) to be altered via variation of the lengths of the struts simultaneously. This gives the surgeon complete freedom to correctly orient and align broken bone segments, which should in principle lead to improved healing. Moreover, as compared to other mechanisms, Stewart-Gough platforms are known to have generally high stiffness and strength to mass ratios, which should increase patient mobility and comfort.
The frame is mounted and defined with reference to a master tab (reference point). The reference point is always located on the proximal (top) ring. Looking from the top, or in the distal direction, the closest strut to the left from the reference point is strut 1 and to the right of it is strut 2. Struts 3-6 are labelled anticlockwise from strut 2. The struts are arranged in such a way that they form sides of trapezoids. The parallel parts of the trapezoids are ring segments between the struts. Typically, one ring segment is significantly shorter than the other one, and therefore the trapezoid is similar to a triangle. This arrangement of struts allows for greater stability of the frame.
The clinical application method of the TSF based fixators is very similar to that of the well-established Ilizarov fixator [4, 5]. Both Ilizarov and TSF fixators use rings located around the injured limb to provide anchorage space for bone-transfixing components and to distribute the load from wires/pins to the longitudinal elements of the frame. Ilizarov rings are made from stainless steel or more recently carbon fibre. Steel rings are radio-opaque while carbon fibre ones are radio translucent allowing clear visualization of the x-rayed fracture. The TSF rings are made from aluminium alloy and are only partially radio translucent. The same bone-transfixing components are used for both fixators. Typically, two wires or two half-pins are used per ring. Accessory rings can be mounted on either side of the fixators for greater stability and increased anchorage space. The standard straight Ilizarov configuration involves rings interconnected with four longitudinal elements (threaded rods). A hinge can be added to enable deformity correction with the Ilizarov fixator. However, deformity correction and fracture reduction using the Ilizarov fixator is complex and time consuming. Furthermore, it is hard (if possible at all) to correct deformity in more than one plane simultaneously. By contrast, the TSF's kinematics allow simple fracture reduction planning and execution in the full six degrees of freedom.
To sum up, there is a wide range of orthopaedic fixation devices available in the market today. The choice depends on location, type, severity and complexity of the fracture. Severe fractures have been treated successfully using the Ilizarov ring fixator over a number of years, but the TSF has yet further advantages and complications.Discuss this article, in our forum.
Taylor Spatial Frame references
1. Taylor HS and Taylor JC, Orthopaedic fixation device, Patent No: 5,702,389. 1997, Smith & Nephew Richards, Inc.: USA. p. 1-24.
2. Stewart D. A Platform with six degrees of freedom. Proceedings of Institution of Mechanical Engineers, Part I, 1965. 180(15): p. 371-386.
3. Gough VE and Whitehall SG. Universal tyre test machine. Proceedings, Ninth International Technical Congress FISITA(IMECHE), 1962: p. 117.
4. Ilizarov GA. The tension-stress effect on the genesis and growth of tissues: Part II. The influence of the rate and frequency of distraction. Clinical Orthopaedics & Related Research, 1989(239): p. 263-85.
5. Ilizarov GA. The tension-stress effect on the genesis and growth of tissues. Part I. The influence of stability of fixation and soft-tissue preservation. Clinical Orthopaedics & Related Research, 1989(238): p. 249-81.