Page 209 - WSAVA2018
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Principles and Clinical Application of Tension Band Wiring
Tension Band Wiring is a means of converting the distractive forces acting at the fracture site into compressive forces between the fragments. Such distractive forces are generally caused by a tendon or ligament being attached to an avulsed bone fragment. Conversion of these forces to create compression at the fracture surfaces will generate to stability and lead to bony union.
Technique
Fig. 1: A/B/C
Clinical Applications
The main indications for Tension Band Wiring is the treatment of avulsion fractures such as those involving the olecranon, greater trochanter, patella, tibial tuberosity malleoli, calcaneus.
In all this avulsion fractures the fragment is distracted by the muscle, tendon or ligament which originates/inserts on it.
The tension band is placed so that counteracts the tensile forces acting on the fragments and redirects it to compress the fragment against the adjacent bone. Tension band wiring is also used to repair osteotomies, for example trans-olecranon osteotomy in the caudal approach to the elbow joint or osteotomy of the greater trochanter in the dorsal approach to the hip joint.
Case Example
The treatment of an avulsion fracture of the tibial tuberosity is used here a an example of tension band wiring (Fig 2). This injury is quite common in Greyhounds and Terrier breeds and the fracture occurs through the growth plate. The tibial tuberosity is distracted by the tensile forces exerted by the quadriceps muscle group through the straight patellar tendon.
The fracture is initially reduced and fixation is achieved with two K wires driven through the tuberosity into the metaphysis. The idea behind placing two K wires is that they suppose prevent rotation of the fragment. In reality a well reduced avulsed fragment attached to the tendon has very little tendency to rotate particularly once is under compression, therefore o single pin in in most of the cases more than adequate for the purpose. If the choice lies between one large and two smaller pins the latter is the best choice. A hoe is drilled transversely through the tibia distal to the fracture site.
A length of orthopedic wire is passed through the hole, it is very important to pay attention to use the correct diameter of the wire. As a general indication:
For patients over 20 kg of bodyweight use 18 Gauge (1.2 mm diameter)
For patients below 20 kg of bodyweight use 20 Gauge (1.0 mm diameter)
Avulsion fragments can be effectively stabilized using the pin and tension band wire technique.
The fragment is initially stabilized using either 1 or 2 k-wires. To protect this implant from being pulled out or bent by the forces exerted by the pull of the attached ligaments or tendons a cerclage wire is placed to oppose the tensile forces. An additional and very significant benefit of this technique is that the pull in the ligament and the counter-pull in the wire convert these tensile forces to compressive forces across the fracture
In principle the use of two small parallel pins is better than a single bigger pin, however the number of pin size and it size will be defined by the size of the fragment.
Once the fragment is reduced the pin/s are driven perpendicular to the fracture plane and parallel to each other. If possible they should penetrate the trans-cortex (Fig 1 A). To anchor the tension band wire a hole is drilled transversely across the main fragment on the surface away from the ligament or tendon. This hole is usually located approximately the same distance below the fracture line as the pins are above the fracture line. It is important to ensure when drilling the hole that sufficient bone is purchased to prevent the wire from cutting through it and causing a ‘stress riser’ point that could potentially result in a pathological fracture.
The wire is passed through the hole in the bone, brought across to the original side of the bone, around the ends of the pins and back to the other end of the wire on the starting side of the bone. This creates a figure of eight pattern
(Fig 1 B).
Twist knots are commonly used for tension band wires. To effectively tighten a tension band wire with one knot, the slack in the arm opposite the one with the knot must also draw in by the tightening process. This is very difficult in bigger wire sizes. To avoid this, a twist knot can be tied in both arms of the figure of eight.
Once the wire is tightened, the ends of the K-wire are bent over so that they lie flat against the bone (Fig 1 C).
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