ORIGINS AND EVOLUTION IN HUMAN AND VETERINARY ORTHOPAEDICS Professor Gavriil Abramovich Ilizarov (1921-1992) was Director of the Institute of Traumatology and Clinical Orthopaedics in the city of Kurgan, in Siberia. Ilizarov started applying his orthopaedic technique about 50 years ago and it has been used in Europe and in North America since 1981. Ilizarov developed his apparatus in 1951 following an accident. In fact, by mistake a patient turned the nuts of the connecting rod between the rings of an orthopaedic system the wrong way, causing distraction of the bone instead of compression. Ilizarov saw that this distraction generated new bone tissue which could be seen on X-ray. He understood the potential of this and started a series of experiments on groups of animals, mainly dogs. The basic principle and innovation of Ilizarov’s, strategy (circular external fixation), subsequently proven by numerous technical and experimental studies at his Institute, is that the distraction tension on tissue exerted by the apparatus creates conditions similar to those of natural growth. More recent research by Aronson has confirmed this principle.
Ilizarov’s method marks the birth of an innovative and original theory regarding osteoinduction and new growth of bone tissue, which developed from the practical application of this new transosseousosteosynthesis technique in the field of orthopaedics and traumatology. Ilizarov himself carried out experiments on the technique from 1947 and clinical documentation dates from 1968. The most interesting cases taken from Ilizarov’s publications are:
- compound comminuted leg fracture;
- forearm deformity treated without bone grafting;
- loss of bone substance of the tibia treated with a fibulapro-tibia technique;
- femoral non-union and simultaneous lengthening with correction of the axis;
- congenital non-union of the tibia with severe angulation;
- correction of humerusvarusand simultaneous bone lengthening;
- foot reconstruction and lengthening;
- lengthening of the upper and lower limbs in achondroplastic dwarfism;
- severe congenital malformation of the tibia with 32 cm shortening, re-establishing the length and normal conformation of the limb.
These varied clinical cases show the great potential of Ilizarov’s apparatus which, in humans, can be applied to any bone segment. In 1978, Ilizarov received the Lenin Prize for Medicine for his contribution to orthopaedic surgery with his innovative theories and techniques.
In 1980 Carlo Mauri, an Italian explorer, consulted Professor Ilizarov in Kurgan to cure an infected non-union of the tibia which over the previous 10 years had been treated by a number of doctors with a variety of techniques, none of which had proven successful.
In 6 months Ilizarov cured Mauri’s tibial non-union, osteomyelitis and equinus foot enabling rapid functional recovery. After having been healed, Mauri returned to Lecco and showed extensive photographic documentation of the clinical results he had seen in Kurgan to doctors at the hospital. Professor Ilizarov was, therefore, invited to present his apparatus at the 22nd Italian AO Congress in Bellagio in 1981. In order to demonstrate his technique, Ilizarov also performed a tibial lengthening at Lecco Hospital. Among those present in the operating theatre, mention should be made of the Italian surgeons Cattaneo (head of the Institute of Orthopaedics and Traumatology at Lecco Hospital), Bianchi Maiocchi (Milan), Benedetti (Bergamo), Villa (Lecco), Catagni (Lecco) and Tentori. The theme of the congress was “Prophylaxis and treatment of bone infections”. Ilizarov demonstrated the three main uses his apparatus: treatment of compound fractures, treatment of post-traumatic osteomyelitis and bone lengthening.
After the congress, and following a period of training with Ilizarov in Kurgan, the abovementioned Italian surgeons started to use the technique in the Traumatology and Orthopaedic Unit at Lecco Hospital. Ilizarov continued to work with the hospital for many years. In 1982, the Association for the Study and the Application of the Methods of Ilizarov (ASAMI) was founded in Lecco, with Cattaneo as its President. The following year the association started organizing courses in the theory and practice of Ilizarov’s technique which began being used elsewhere in western Europe. Affiliated associations were founded in the 1990s in various countries: France, Germany, Belgium, Spain, Portugal, Brazil, India, Korea, Croatia, Japan, the Netherlands, Norway, Great Britain, the Caribbean, the USA and Canada. There are now over 2,000 members of the ASAMI worldwide with 400 in Italy. In 1994 there was an historic meeting in Bergamo between two of the greatest orthopaedic surgeons of the 20th century, Professor Ilizarov and Professor Muller, the founder of the AO Foundation.
The first Italian ASAMI Congress in 1983 was attended by two American orthopaedic surgeons, Sarmiento and MacEwen. Then two other surgeons, Paley and Aronson, came to Lecco to learn the new technique which, with improvements made by Italian surgeons, became used and appreciated also in North America.
Ilizarov tested his system on more than 100 dogs to demonstrate his theories of osteogenesis and to optimise the configuration of the apparatus itself. This experimental model was reproduced by Deloix in Brussels and by Aronson in the United States. In 1984, Ferretti, a veterinary surgeon from Legnano, near Milan in Northern Italy, started using Ilizarov’s technique of circular external fixation in dogs and cats. The patients tolerated the apparatus well and the first clinical results were very encouraging, such that Ferretti continued, and still continues today, to use this technique in many orthopaedic cases not only in small animals but also in large animals, especially horses. However, circular external fixation is not an easy technique to apply and so it is currently used by a limited number of veterinary orthopaedic surgeons in Italy.
The intrinsic versatility of Ilizarov’s apparatus, together with a skilled surgeon, enable to achieve excellent results in cases in which other more conventional orthopaedic techniques cannot be used. In particular, an Ilizarov procedure is one of the treatments of choice for limb length disorders and limb deformities.
ILIZAROV’S APPARATUS
Ilizarov’s apparatus, being a circular external fixator, differs from axial external fixators in that, before being applied, it is ‘built’ by the surgeon according to specific criteria for the desired treatment. The surgeon takes into consideration not only the dimensions of the bone segment to be treated but also a whole series of other variables. Circular external fixators are, therefore, made up of many elements which can be assembled in an unlimited number of configurations. The determinant factor in the choice of arrangement of the apparatus to be used is, obviously, the pathology to be treated.
The components of the apparatus can be divided into main elements and secondary elements.
MAIN ELEMENTS. These are the standard components used to secure the skeleton and skeletal fragments to the apparatus: transosseous wires with or without olive stops, pins, rings, half-rings, carbon fibre half-rings, arches, wire fixation and wire locking bolts, and adjustable buckles.
SECONDARY ELEMENTS. These are the standard components needed to assemble the various parts of the apparatus:threaded rods, telescopic rods, graduated telescopic rods, slotted rods, straight, curved and twisted plates, posts, sockets, washers, bushings, nuts, and bolts. These elements also include the dynamometric wire tensioner, and various types of angled and straight wrenches.
The equipment needed to apply Ilizarov’s apparatus includes: wires/pins; fixation, support, connection, assembly and sliding elements; tensioning devices; and wrenches.
Wires and pins
The thin wires used in an Ilizarov’s circular external fixator have a diameter between 1.0 and 1.6 mm for animals and between 1.5 and 2 mm for humans. The 1.0 mm wires are used in dogs weighing under 10 kg, the 1.2 mm wires in dogs weighing 10-20 kg, and the 1.5 mm wires in dogs weighing more than 20 kg. The wires differ not only in diameter, but also by having two different types of tip: bayonet and trocar. The bayonet tip is used for fixation in the diaphyseal zone (cortical bone) while the trocar tip is used in the metaphyseal zone (cancellous bone). Furthermore, the wires can be of the same diameter along their whole length (‘simple’ wires) or have a wider part half way along. These latter are called ‘olive’ wires because the oval-shaped widening serves as an olive stop. Once inserted these wires can be used to put the bone segment or stumps under tension, by exerting traction on the other end of the wire to the olive once this has come into contact with the cortical bone. This allows various corrections of the position of the fracture stumps and, in the case of an oblique fracture, compression can be exerted on the stumps by using two olive wires on opposite sides of the bone shaft. This type of wire is, therefore, used to prevent translation of bone fragments during lengthening, providing stability and allowing interfragmentary compression. Alternatively, to obtain the same functional mechanism, a simple wire can be used folding it back on itself or shaping a “U”. Obviously this manual modification makes the wire weaker and consequently, often renders it more difficult to remove.
Pins are self-tapping elements with a tapered thread and a blunt or pointed tip. They are used in situations in which it is not possible to apply full rings attached by ordinary wires. Thus, they are used for the proximal parts of the limbs where the large muscle mass requires the use of partial rings. They are also used in hybrid fixation techniques.
Fixation elements (bolts, washers and bushings)
Bolts are used to fix wires to the main and secondary supports of the apparatus. There are various types:
- Cannulated wire fixation bolt
This has an elongated head and a central hole through which the wire is fixed to the ring. The wire can obviously only be fixed centrally, but this provides firmer fixation than a slotted bolt.
- Slotted wire locking bolt
This has an eccentric groove which allows lateral fixation of the wire. The wire can be put under tension without using wire tensioners.
- Cannulated bolt with threaded head (female)
This type of bolt has a bigger head with a threaded hole which takes the threaded connection rod thus avoiding the use of extra holes in the ring. This type of bolt is not often used in orthopaedic surgery.
The wires must be kept straight in order to prevent the apparatus from moving, the wires themselves from breaking, stress to the bone and a potential fracture while tightening the wires.
Washers can be used in addition to bolts when the wire is not on the same plane as the ring.
Bushings are fixation elements with holes. They can be hexagonal or cylindrical. The former are used to extend threaded rods or to stabilize the connection to rings or arches (within a limited distance). The latter can be used, together with rings or short plates, to produce distraction or compression at different levels on a horizontal plane. They can also be used to fix pins to rings.
Washers are used to adjust the support planes of secondary elements. They can be simple, slotted or conical. Simple washers can be used to raise wire fixation bolts so that the wire lies correctly on the ring. Slotted washers have a groove to fix the wire in particular conditions in complex assemblies. Finally, conical washers are always used in pairs, one on top of the other. They are used to ensure the rings are parallel to each other.
Support elements (rings, posts, hinges, plates)
The rings most commonly used in veterinary orthopaedic surgery have a diameter between 40 and 120 mm.
Ilizarov’s original apparatus included:
- Holed arches
Arches have a larger diameter than half rings. They have a double row of holes at the ends. In human orthopaedics they are used above all for the humerus and proximal femur.
- Full (closed) rings
Full rings are not as versatile as half rings but, on the other hand, they have more holes available to fix the wires and bars. Full rings are used for distal bone segments where there is not such a large volume of muscle.
- Half rings
Half rings can be used singly, usually close to joints so as not to limit the range of movement. Alternatively, a half ring can be attached to another half ring of the same diameter to make a full ring. Two bolts with suitable nuts are used to join the half rings together. The connection bolts provide reference points to align the rings with each other and to align the fixation system with anatomical structures.
In order to have a precise anatomical reference point, some half rings have notches corresponding to the goniometric anatomical scale. Half rings can be made of steel or carbon fibre. Carbon fibre has the advantages of being lighter and is radiologically transparent.
- Half rings with curved ends
These are also called “W” rings and are placed close to joints to preserve articular mobility.
- 5/8 half ring
This is another type of ring which is used close to joints.
Posts are essential elements in Ilizarov’s apparatus for building secondary supports for stabilisation, rotation and correction of deformities. They are bars 12 mm thick of variable length (25, 35 or 45 mm). They have a variable number of holes and a rounded end. The other end has a thread which can be male or female. A male end is fixed with a nut while a female end is fixed with a bolt. To increase stability, two posts can be arranged on the ring at 180° from each other, in order to fix a third wire, called a support wire. If a wire is positioned obliquely to the plane of the ring, creating a difference of more than 10 mm, a post can be used for fixation of the ring itself. Bolts are used for the connections, as for fixation to a ring. By placing a slotted washer to the base of the post, two nails can be fixed at two different levels using only one hole in the ring. Two posts, one with a male thread and one with a female thread, can be positioned either side of a single hole of a ring to increase fixation with the placement of two or more wires on two or more planes. Furthermore, the posts can be used to join a plate to a ring or to construct a hinge or joint.
Hinges are made of two special posts with a single hole connected by a nut and bolt. They are essential and innovative components since they enable correction of axial deformities and allow protected joint movements. There is also a particular type of hinge (90° joint) in which a female threaded post connected to a threaded rod is used. This structure allows passage from a perpendicular plane to a vertical plane and the transmission of forces in a variety of directions. There are also pre-assembled hinges (‘universal joints’) which can be used in the same way as the posts, but are much easier to apply.
The plates are support elements. They are available in different lengths and with different types of end and are chosen according to where they are going to be used in the apparatus and their intended function.
- Long and short connection plates
These are of variable length and have different numbers of holes. The space between the holes may always be the same or there can be a larger space between the first and second holes. Short plates are used to lengthen the ends of half rings or, together with hinges and clamps, act as secondary lateral supports. Long plates, employed with hinges, can be useful for strengthening the whole apparatus. In human orthopaedics they are frequently used for foot fixation systems.
- Connection plate with threaded end
This is a standard plate with a threaded rod at the end. It allows gradual movement along the axis of the plate itself and, when fixed to two rings, can be used to construct other secondary supports.
- Twisted plate
This type of plate has a 90° twist in its middle part. It performs the same function as 90° hinges, allowing the passage from a horizontal plane to a vertical one.
When it is fixed to a ring with a clamp, two posts can be connected to transmit the forces along the threaded rods.
- Curved plate
This has three holes and is used to lengthen half rings or other straight plates. It provides extra holes to fix the wires and can be used to create structures which can adapt to different, and sometimes complex, anatomical profiles.
Connection elements (rods)
Rods are used to connect support elements. They include threaded and telescopic rods. The diameter of the rods (or bars) depends on the size of the other parts of the Ilizarov apparatus. Usually rods with a 4, 6 or 8 mm diameter are used with threads of 0.66, 0.8 and 1 mm, respectively. Rods of 5 mm can be used in dogs and cats of all sizes, whereas 6 mm rods are used in humans and in medium, large and giant breeds of dogs.
The original Ilizarov apparatus included several types of rods:
- Threaded rod
This is the simplest type of rod for connecting all the principal and secondary elements and is essential to the biomechanical properties of the apparatus. Rotating the nuts which fix the rod to the structure produces a compression or distraction force, depending on the direction in which the nuts are turned. The thread of the rod is made in such a way that every complete (360°) rotation of the nut corresponds to a 1 mm translation along the longitudinal axis.
The rods, together with other components of the apparatus, transfer the forces generated to the bone. For biomechanical reasons, long connection rods are sometimes replaced by a greater number of shorter rods.
Sometimes in order to reduce a fracture, threaded rods with grooves are used which, together with olive wires, allow interfragmentary compression or gradual distraction forces to be applied.
- Telescopic rod
These rods, like the threaded ones, are used to connect the elements of the apparatus together. The base is made in such a way as to have an internal diameter which allows placement of a partially or completely threaded rod. The head of the rod has two holes: one in its axis to position the threaded rod, the other horizontal and threaded to position the bolt used to fix the threaded rod inside the tube.
When there is a relatively large distance between two rings (150-200 mm), a telescopic rod is used to increase the stability of the structure. Furthermore, for lengthening, the telescopic rod allows the structure to be expanded from the inside. To carry out the lengthening procedure, the bolt of the telescopic rod is unscrewed and the nut is moved to the head to obtain the desired distancing.
- Graduated telescopic rod
This new device was developed recently in Italy. It makes the lengthening procedure easier to perform and control. The aluminium tube has a grooved window with a metric scale to measure the forward movement of the threaded rod inside the cylinder. The head of the telescopic rod is replaced by a rotating head. Depending on the direction of rotation of the head, the threaded rod is moved in such a way as to apply a compression or distraction force.
- Slotted threaded rod
This threaded rod has a 20 mm longitudinal groove at one end. A wire can be placed in the groove and held in place by two bolts. The rod can be used with an olive wire to apply tension forces for interfragmentary compression or bone transport. These rods are attached to the structure by secondary elements and have the great advantage of allowing forces to be applied at any level and in any direction.
In a standard assembly, the free end of the rod is fixed to a hinge or support with two nuts. A second hinge or support is used for fixation to the structure.
Assembly elements (nuts and bolts)
These are essential for assembling the support and connection elements. They include hexagonal headed bolts and both simple nuts and triangular nuts (with progressively numbered faces to facilitate manipulation during the lengthening procedure).
Sliding elements (adjustable sliding buckle)
The buckle is made of a plate with two small threaded rods and a plate with two threaded holes; these two components are attached to each other by two nuts. The upper plate has a threaded hole. This component is essential for the assembly of fixed or mobile secondary elements to rings or connecting plates.
Tensioning devices (wire tensioners)
There are two types of wire tensioners: simple and dynanometric.
- Simple wire tensioner
The wire is introduced into the canal in the centre of the wire tensioner and is fixed with a bolt; the wire tensioner must then be attached to the ring to avoid it sliding. The wire is tightened by turning the lever clockwise. This exerts traction but does not calculate how much traction is exerted, which is why a dynamometric wire tensioner is usually preferred. Sometimes a simple wire tensioner can be used to remove olive wires which have become trapped in the bone.
- Dynamometric wire tensioner
A dynamometric wire tensioner is extremely important because it puts wires under tension, calculating exactly how much force is exerted, and thereby increases the stability of the entire bone-apparatus structure. Wires are put under a force of 30-150 kg. The amount of force is proportional to the body weight of the animal on which the fixator is assembled and also depends on the condition of the bone, the type of treatment involved (fracture, lengthening, deformity) and the structure of the apparatus. The transosseous wires can be tightened further both during surgery and in the post-operative period. To enable this, the ends of the wire must be left long enough (at least 4 cm) to use a wire tensioner. The dynamometric wire tensioner is made up of three parts: a hand-grip to apply tension (using circular movements), a dynamometric scale (to show the force in kg), and fixed and mobile buckles.
Wrenches
Differently shaped wrenches (angled, straight and for telescopic rods) are used to assemble the various components of the apparatus. The most frequently used wrenches are 7, 8 and 10 mm.
BIOLOGICAL PRINCIPLES OF THE ILIZAROV METHOD
Between 1969 and 1985 Ilizarov published numerous articles on techniques of bone lengthening using circular external fixators. According to his method, weight-bearing by the limb being lengthened is not only allowed, but is actually preferred. Much more significant lengthening is achieved and no primary or secondary bone input is necessary. Ilizarov developed a complete method based on considerable clinical and experimental research. Knowledge of these experimental studies facilitates understanding of the method and the practical applications of Ilizarov’s ideas. The scientific principles underlying Ilizarov’s innovative method and above all the concept of osteogenesis induced by distraction were derived from these studies (Fig. 4). All the experiments were carried out on the tibiae of dogs. Ilizarov’s preliminary studies explored the role of fixation, the role of osteogenic tissue and vessels, the potential of bone marrow and vessels, and the effect of longitudinal traction on osteogenesis. In particular, it was seen that it is possible to obtain newly formed bone through an appropriate amount of traction in relation to the condition of the bone marrow and the osteogenic tissue. Distraction osteogenesis is mechanical induction of the formation of new bone as a result of a tension-stress effect: gradual traction exerted on viable tissues creates stress which stimulates tissue growth and regeneration. The callus tissue, subjected to slow, regular traction, is metabolically activated. The bone regeneration process in the distraction gap is influenced by numerous factors: the stability of the fixator, an adequate blood supply, non-traumatic surgery, correct distraction rate and rhythm and physiological use of the limb. The applications of these theories are based on the intrinsic regenerative capacity of the bone tissue and make it possible to “control” the processes of healing and remodelling. According to Ilizarov, the tension-stress effect induces an increase in biosynthetic activity also in the region’s soft tissues (skin, muscles, fasciae, vessels and nerves) inducing their gradual lengthening. Ilizarov’s original technique of distraction osteogenesis involved a corticotomy with conservation of the bone marrow blood vessels and stable fixation. The corticotomy is followed by a period of 3-7 days during which a bridge of fibrous tissue is formed in the gap. There then follows a distraction phase during which the columns of newly formed bone extend in the gap. Under optimal biological and mechanical conditions, the bone is formed through pure membranous ossification. Under other conditions, the biological sequence is altered, resulting in non-union or delayed consolidation.
Ilizarov studied the importance of the osteotomy technique, the conservation of intramedullary and periosteal vascularisation, the latency period, the extent and rhythm of distraction, and the stability of the fixation for bone regeneration. In a series of experiments on dogs, he evaluated the effects of different strategies of distraction on the histogenesis of bone tissue, vessels, periosteum, muscle, bone fascia and skin. Both the quantity and the quality of the newly formed bone were better when very stable fixation systems were used, with an osteotomy technique that preserved intramedullary, periosteal and extraosseous blood supply, and with a protocol of regular, greatly fractioned distraction.
Stability of the structure
Stable fixation is guaranteed by a circular external fixator which allows immediate weight-bearing on the limb. The configuration of the fixator and the use of wires placed under tension create axial micromovements (or a pump effect) which stimulate and intensify the formation of regenerated bone and its corticalisation. Instability results in fractures in the osteogenic zone and inhibits osteogenesis. The most common cause of translational fractures is unstable fixation of bone segments during the distraction. This is sometimes due to slackening or incorrect regulation of the nuts holding the rings to the connecting rods. The diameter, the number and the size of the rings along with the orientation and the tension of the wires are the most important factors contributing to the stability of the structure. If the structure is not stable, the wires can move and infections can develop along them, compromising the stability of the osteogenic area. In experimental conditions, this instability results in atrophic non-union, with disorganized neovascularisation and cartilaginous areas.
Corticotomy/osteotomy
Ilizarov believed that it was essential to preserve the periosteal and intramedullary bone marrow supply in order to obtain the best results from distraction osteogenesis. He developed a technique of subperiosteal osteotomy (‘corticotomy’) in which the osteotome is used to cut the anterior, lateral, and medial parts of the cortex leaving the bone marrow vasculature intact. The posterior part of the cortex is fractured manually (osteoclasia) by applying a twisting force to the bone. Although Ilizarov demonstrated the importance of preserving the vasculature with this technique, some recent studies have shown that the bone marrow vascular network recovers quickly after conventional osteotomy. Therefore, on the basis of present knowledge, Ilizarov’s method produces good results both with corticotomy and with traditional osteotomy. The periosteum must be preserved as much as is possible with both techniques.
Latency
Latency is the period of time between the osteotomy and the start of distraction. The period of latency allows organization of the haematoma and early vascularisation of the fibrous matrix. The duration of the latency period is determined by a number of factors: the patient’s age, the site of the osteotomy, the extent of soft tissue trauma, the primary pathology, and whether the procedure involves simple lengthening or bone transport.
If the latency period is too long, it becomes impossibile to perform distraction because the gap becomes completely filled with new bone, i.e. there is premature consolidation of the bone. In contrast, if the latency period is not long enough, the quality and quantity of the regenerated bone may not be adequate or non-union may occur.
It is important to remember that metaphyseal osteotomy requires a shorter latency period than that required for diaphyseal osteotomy.
In veterinary orthopaedics, it is recommended that the latency period should be 2-3 days for growing animals and 5-7 days for adults.
Distraction rate
The total lengthening performed in one day is based on similar considerations as those described for latency.
The amount of distraction in veterinary medicine ranges from 0.75 mm to 2.0 mm a day. A similar range is also used in human orthopaedics. It is obvious that angular distraction will induce osteogenesis at different rates.
Like latency, the distraction rate is also influenced by a variety of factors: the patient’s age and the type and site of the osteotomy. If the distraction rate is too slow the gap will close too quickly; this is what happens in the normal process of fracture healing. However, too fast a distraction rate can lead to soft tissue contractures, joint subluxation or inadequate mineralisation in the gap (because the advancement of the new blood supply is not so fast). It is, therefore, essential to establish the appropriate distraction rate to prevent premature consolidation of the regenerated bone and to preserve the integrity of joints and soft tissue.
Weekly X-ray monitoring is helpful to identify the most appropriate distraction protocol for each individual case.
In human orthopaedics, accurate measurement of the fibrous interzone length by quantitative computer tomography is sometimes used instead of X-ray. If the length of the fibrous interzone is less than 2 mm, the distraction rate should be increased. Contrariwise, if the distraction rate is over 4 mm, a decrease is advised.
Rhythm
Rhythm is defined as the number of lengthenings performed in one day. According to Ilizarov, the distraction rhythm influences the quantity and the quality of the newly formed bone tissue and the preservation of soft tissue integrity during the lengthening. A distraction of 1 mm a day in a single session inhibits osteogenesis significantly. In veterinary orthopaedics, a distraction rhythm of 2 or 4 times a day is recommended (distractions of 0.5 mm twice a day or 0.25 mm four times a day). Automatic distractor devices are now available which allow an overall daily lengthening of 1 mm to be subdivided into 60 fractions. However, these are more widely used in human orthopaedics than in veterinary practice.
Consolidation
As soon as the distraction phase is stopped, the fibrous interzone starts to mineralise and the central area becomes radiographically sclerotic. Over the following weeks, the columns of newly formed bone acquire a more homogeneous density because lamellar bone replaces the woven bone. In domestic animals, the formation of new cortical bone and the bone marrow cavity takes 8-12 weeks. The healing index used in humans is calculated as the total duration of treatment (lengthening and consolidation) in months divided by the total bone lengthening in centimetres. The index for long bones in the limbs of humans is usually 1.2-1.5 months/cm. Marcellin-Little et al. reported a healing index of 0.53 months/cm in young dogs which underwent correction of limb deformities with hinged fixators. Many factors influence consolidation. The rate of consolidation is slower in patients who do not subject the limb to adequate loads because they are afraid, in pain or have contractures. Circular external fixators enable dynamisation of the regenerated callus, which promotes consolidation.
Bone transport
Soft tissues are limiting factors for distraction osteogenesis. Both experimentally and clinically, lengthening over 20% often results in an increase in complications involving peripheral nerves, muscles and tendons. Although intensive physiotherapy during the lengthening phase can reduce the severity of joint contractures and help to prevent joint disorders, there are other techniques that can be used to avoid or reduce these complications. One of these techniques is double level osteotomy. This consists of two osteotomies followed by distraction osteogenesis at two levels. The central bone fragment is stabilised with one ring of the fixator and the two adjacent bone segments are subjected to distraction in opposite directions, producing two different areas of regeneration. With two sites of regeneration for lengthening, the total time needed for the lengthening and consolidation is reduced to approximately half of that needed for the same amount of lengthening at a single site. Furthermore, the forces to which the myotendinous structures are subjected are distributed along the whole muscle system, thus reducing degenerative effects.
BIOMECHANICS OF A CIRCULAR EXTERNAL FIXATOR
The mechanical characteristics of a circular external fixator influence the characteristics of the “microenvironment” in which bone regeneration takes place. A circular external fixator has biomechanical characteristics that optimise the conditions for fracture healing and for distraction osteogenesis. A circular external fixator uses small diameter wires placed under tension rather than traditional nails to connect bone to the apparatus. The use of small diameter wires under tension seems to offer less stability than the large diameter nails used in traditional external fixator systems. However, a 1.6 mm diameter Kirschner wire correctly tightened, subjected to flexion at three points has the same rigidity as 4.0 mm diameter nails.
A circular external fixator allows axial micromovements at the osteotomy (or fracture focus) without compromising the stability of the fixator. Compared to unilateral fixators, cranio-caudal flexion and torsional stresses are distributed horizontally and minimised, while there is greater transmission of axial movement during compression. In other words, all fixators in which the connection between the bone and apparatus lies on the same plane have “dynamic or elastic” movements which are reflected on the bone as compression movements, but also as angulation movements. According to numerous studies, these latter movements are “parasitic” and have a negative effect on bone healing. The real advantage of all circular fixators is that they used transosseous wires that minimise “parasitic” movements (angulation and rotation) without compromising the elasticity which, according to many biomechanical studies, promote bone healing. In fact, controlled axial micromovements of bone segments seems to stimulate the formation of callus at the fracture focus or distraction gap. Experimental and clinical studies, evaluating the effects of a daily intermittent load, have shown the application of controlled axial micromovements is associated with significant improvement in the healing process.
The biomechanical characteristics of circular external fixators were first identified by Ilizarov through his initial experiments on the tibiae of dogs. Ilizarov understood that the configuration of the apparatus had to allow complete weight-bearing and a full range of movement of the adjacent joints in order for the limb to have normal physiological function during the treatment.
When evaluating the Ilizarov apparatus “system”, that is, the stability of the fixator-connection-bone, the following variables should be considered:
1. The rigidity of assembly;
2. The connections between the apparatus and the bone;
3. The intrinsic (or internal) stability of the segment involved.
These variables can also be defined as extrinsic and intrinsic biomechanical factors and determine the mechanical properties of a circular external fixator.
Extrinsic biomechanical factors
There are numerous extrinsic factors (depending on the fixator) which influence the biomechanical characteristics of a circular external fixator. These factors include the diameter of the ring, the material from which the rings are made, the configuration of the “ring block”, the number of wires, the diameter of the wires, the tension to which the wires are subjected, the orientation of the wires and the type of wire.
Intrinsic biomechanical factors
The intrinsic stability of the structure is also influenced by various factors: extension, length and modulus of elasticity of the tissues at the fracture site or distraction gap, contact surfaces of the bone stumps and the tension of the soft tissues surrounding the bone segment being treated.
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Extrinsic biomechanical factors |
Intrinsic biomechanical factors |
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Table 1. Intrinsic and extrinsic biomechanical factors of a circular external fixator.
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Variables DIRECTLY proportional to the stability of the system |
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Table 2. Biomechanics of the circular external fixator. Variables directly proportional to the stability of the system.
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Variables INVERSELY proportional to the stability of the system |
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Table 3. Biomechanics of the circular external fixator. Variables inversely proportional to the stability of the system.
CLINICAL APPLICATIONS OF ILIZAROV’S METHOD
According to Ilizarov, circular external fixation can potentially be used in all conditions and resolve any problem in the field of orthopaedics. In reality, the use of this technique depends on the advantages and disadvantages that the system has with respect to other techniques of osteosynthesis, whether internal or external. It is well known that no surgical technique is ideal in every circumstance, but that it is the evaluation of each individual case that enables the orthopaedic surgeon to select the most suitable treatment option. In making a decision, the surgeon must also consider factors which may appear to be secondary, such as the patient’s collaboration, post-operative management of the patient by its owner, and the owner’s economic resources. A brief description of the main advantages, problems and possible applications of Ilizarov’s method compared with traditional external fixators is given below. Subsequently, the orthopaedic problems for which a circular external fixator represents one of the best treatment options are analysed.
Besides providing fixation, a circular external fixator contemporaneously also reduces fractures or corrects deformities. It allows closed treatment of fractures and non-union, while cases of angular deformity or abnormally short bones require limited surgery sufficient to carry out corticotomy or osteotomy. The use of transosseous wires of very small diameter results in less damage to soft tissue, and in particular, to the vascular system, than the use of the nails employed in traditional external fixation. The immediate dynamisation resulting from the limited compression rigidity allows axial micromovements in the fracture focus or osteotomy site. These micromovements stimulate osteogenesis and are one of the main characteristics differentiating circular external fixators from linear external fixators. The use of conventional fixators to correct angular deformities and severe limb length anomalies often leads to serious complications. Circular external fixation offers the best compromise between efficacy (lengthening of between 9 and 70 mm can be achieved) and fixator rigidity (no risk of wires, rods or rings breaking).
The configuration of circular external fixators in animals means that they can be used distally to the elbow and to the knee. A circular external fixator is ideal for use on the tibia, radius and ulna, metacarpus and metatarsus since there is space to position the rings. Hybrid fixation, combining some of the typical characteristics of linear fixators together with other features exclusive to circular external fixators, is used to treat the humerus and femur. The orthopaedic surgeon must have a solid knowledge of biomechanics and anatomy to use this method. Planning the surgical intervention is lengthy and demanding, especially in the case of treatment of angular deviation or loss of substance. The surgical intervention itself is also more complicated than that of conventional external fixation.
The main uses of circular external fixation in small animals can be defined by examining a publication by Latte who reported on 75 cases, the highest number of patients treated with Ilizarov’s method. Latte did acknowledge that some of the more simple cases could have been treated by other methods of internal or external osteosynthesis.
The uses of circular external fixation can be divided into five categories:
- fractures;
- complications of fractures;
- bone deformities;
- loss of bone substance;
- other orthopaedic pathologies (miscellaneous).
Latte’s study did not include cases of treatment of loss of bone substance (after trauma or following excision of a neoplasm). Although experience in this context is still limited, it is thought that bone transport (in line with Ilizarov’s philosophy) to regenerate substantial tissue deficits is potentially better than traditional techniques.
Fractures
There are numerous osteosynthesis techniques, each with its own indications for use. Circular external fixation is an excellent treatment option for comminuted and/or exposed fracture (even with small metaphyseal or epiphyseal fragments) (Figs. 5, 6 and 7). This is because:
- the tightened wires take up little space and provide excellent stability of the fragments;
- many different configurations can be used;
- use of olive wires means that large fragments can be moved in the direction desired (without open surgery);
- there is no further trauma to the fracture focus from surgical interventions;
- trauma to surrounding soft tissues is minimal.
Complications of fractures
Circular external fixation is also used in the treatment of non-union, delayed consolidation and mal-union. Not only is it possible to use and put weight on the leg, but this should in fact be encouraged since the elasticity in compression, which is a typical characteristic of a circular external fixator, stimulates the formation of callus.
In hypertrophic non-union, the focus is still biologically active and stabilisation, with or without compression, is therefore sufficient to promote bone healing. In contrast, a biological stimulus is necessary for the treatment of atrophic non-union, such as corticotomy adjacent to the non-union or an autologous cancellous bone graft. Autologous cancellous bone grafting was not part of Ilizarov’s original technique. In order to accelerate healing, additional steps can be taken, such as cycles of compression-distraction at the site of the non-union, the use of olive wires to increase interfragmentary compression, modifying the bone extremities and excision of the infected bone (in cases of septic non-union).
Bone deformities
The treatment of bone deformities due to growth anomalies is one of the most outstanding uses of circular external fixation.Given its remarkable geometric flexibility, a circular external fixator can b
e used to treat angular abnormalities and abnormally short bones. The use of strategically positioned hinges enables correction of considerable angular deviations; furthermore, by acting on the connection rods, lengthening can be achieved through distraction osteogenesis. This technique has the advantage of being extremely precise because the correction is achieved gradually over the weeks following surgery. The intrinsic biomechanical characteristics of a circulator external fixator and minimal surgical trauma facilitate excellent bone healing. The clinical results of treatment of limb deformities using this method are excellent.
Loss of bone substance
The newly formed bone obtained with the distraction method can replace loss of bone tissue secondary to trauma, resection of neoplasms or sequestration due to infection. To achieve this, a technique of bone transport (single or double) technique is used in which a short segment of bone, obtained by osteotomy of one of the two extremities of the bone, is gradually distracted to fill the bone deficit until union with the bone end beyond the gap.
Limb sparing is one of the treatment options for osteosarcoma of the appendicular skeleton. One of the techniques described is based on neoplastic resection followed by bone regeneration by distraction through segmental bone transposition. Careful initial evaluation is essential in order to decide whether a case is suitable for this type of treatment. Likewise, correct oncological surgery and strict observance of the principles of Ilizarov’s technique are fundamental.
Miscellaneous
Circular external fixation is sometimes used in carpal or tarsal arthrodesis in combination with chondral resection and cancellous bone grafting.
Circular external fixation is also considered a possible treatment option for dislocations, since it maintains normal joint alignment once the dislocation has been reduced. In particular, Latte reported on the use of a circular external fixator to treat congenital elbow dislocation.
Other rare uses of circular external fixation reported in the literature include treatment of mandibular brachygnathia, metatarsal rotation, plantigrade anomalies, radial haemimelia and ectrodactyly.
COMPLICATIONS DURING AND AFTER SURGERY
There are many different ways of classifying the complications associated with the use of external fixation. They are usually classified as local or systemic and as intraoperative, early or late. Use of circular external fixation can result in the same complications as those experienced with conventional fixation methods as well as those due to the lengthening process by distraction osteogenesis which involve the bone tissue itself and the surrounding soft tissues. Thus, there are two further categories of complications: those during distraction and those during fixation.
Since circular external fixation induces daily physiological alterations to the bone and surrounding tissues, some difficulties can arise during the periods of distraction and fixation. The surgeon must be ready to intervene quickly and appropriately. Often adjustments to the apparatus, not included in the pre-operative plan, can resolve complications before the apparatus is removed.
Paley has proposed three subcategories of difficulties that can arise during lengthening: problems, obstacles and complications.
Problems are those difficulties than can be resolved without requiring further surgery; they are resolved within the treatment period through non-surgical techniques.
Obstacles are potential, expected difficulties that require further surgery; they are resolved within the end of the treatment period through surgical interventions.
Complications are difficulties that remain unresolved even at the end of treatment. These can be local or systemic and intra-operative or peri-operative. These are further subdivided into minor and major complications.
Most difficulties occurring during the correction of deformities are secondary to:
Errors in surgical technique
- Incorrect bone alignment;
- Thermal trauma to the bone;
- Vascular or neurological damage during surgery.
Weakness of the fixation structure (sometimes excessive rigidity)
- Too few rings;
- Insufficient tensioning;
- Unsuitable wire diameter.
Inappropriate post-operative management
- Latency period is too short;
- Rapid distraction;
- Low frequency of distraction;
- Muscle contraction not diagnosed early enough.
Having identified the most frequent causes of the difficulties that can occur when using Ilizarov’s technique, the problems, obstacle and complications are considered individually below.
For obvious reasons, the difficulties which arise during the treatment of fractures are less serious than those occurring during correction of deformities. Complications of the use of circular external fixators for fracture healing are very similar to those found with traditional external fixation.
Problems
Problems are difficulties which do not require surgery and which, if dealt with promptly and appropriately, do not compromise treatment results. According to Paley, they are due to the “labour-intensive nature of the procedure”. They include muscle contractures, self-limiting vascular lesions, skin irritation and leakage of exudate from along the course of the wires.
Obstacles
Obstacles require further surgery but, if well managed, do not compromise treatment results. Obstacles include breakage of the system, bone fracture, premature consolidation diagnosed early and serious vascular lesions.
Complications
Complications are harmful effects that circular external fixation may have on the patient. These can be local or systemic and intra-operative or post-operative. They are also subdivided into major and minor.
Minor complications include axial deviation, persistence of the bone length abnormality, temporary denervation, bone infection and a reduced range of movements of adjacent joints. Minor complications are those which do not cause the patient significant problems although they may make the treatment more difficult and prolong its duration.
Major complications are early consolidation that is diagnosed late, mal-union following loss of fixation, non-union, dislocation or subluxation of adjacent joints and neurological lesions. Some of these complications are permanent and the objectives set for surgery may not be met.
PROGNOSIS
The clinical results of treatment using Ilizarov’s circular external fixation have been reported in various publications. Latte reported excellent or good results in 55 of 75 applications (73%), including 13 fractures, 18 complications of fracture and 38 growth deformities. The average bone lengthening achieved was 28 mm (maximum 60 mm). The mean healing index was 8 weeks. Complications occurred in 39% of cases and 12% had a negative outcome.
According to the experience of Marcellin-Little, the average duration of treatment was 7 weeks. The healing of comminuted fractures treated with a closed technique is surprisingly fast. Use of a hinged circular external fixator to treat deformities enabled an angular correction of as much as 48° and compensation of length deficit of up to a maximum of 30% of the original bone length.
Although reports of large series of patients are limited, current experience shows that the use of Ilizarov’s method in veterinary medicine is very encouraging, even in very complex cases. Lengthening by distraction ostoegenesis and progressive, gradual correction of deviations are the innovations that circular external fixation have brought to the field of human and veterinary orthopaedic surgery. The strongest indication for this technique is the treatment of growth deformities, since it improves the prognosis for both two-legged and four-legged patients.
Suggested readings
- Aronson J: The biology of distraction osteogenesis. In A.S.A.M.I. Group (Bianchi Maiocchi A, Aronson J): “Operative principle of Ilizarov”; Medicalplastic, Milano, 1991, pg 42-52.
- Bianchi Maiocchi A: Historical review. In A.S.A.M.I. Group (Bianchi Maiocchi A, Aronson J): “Operative principles of Ilizarov”; Medicalplastic, Milano, 1991, pg 4-8.
- Bianchi Maiocchi A: Instruments and their use. In A.S.A.M.I. Group (Bianchi Maiocchi A, Aronson J): “Operative principles of Ilizarov”; Medicalplastic, Milano, 1991, pg 9-32.
- Bianchi Maiocchi A: Materials and Methods. In Catagni MA: “Treatment of fractures, nonunions, and bone loss of the tibia with the Ilizarov method”; Medicalplastic, Milano, 1998, pg 9-24.
- Catagni MA: Biomechanics of the Ilizarov Apparatus. In Catagni MA: “Treatment of fractures, nonunions, and bone loss of the tibia with the Ilizarov method”; Medicalplastic, Milano, 1998, pg 21-24
- Ferretti A: The applications of the Ilizarov Technique to Veterinary Medicine. In A.S.A.M.I. Group (Bianchi Maiocchi A, Aronson J): “Operative principle of Ilizarov”; Medicalplastic, Milano, 1991, pg 551-576.
- Frierson M, Ibraim K, Boles M, Boté H, Ganey T: “Distraction Osteogenesis. A comparison of corticotomy Techniques”. Clin Orthop; 301:19-24, 1994.
- IlizarovGA: “Clinical Application of the Tension-Stress Effect for Limb Lenghtening”. Clin Orthop; 250: 8-26, 1990.
- IlizarovGA: “The Tension-Stress Effect on the Genesis and Growth of Tissues: part II. The influence of the rate and frequency of distraction”. Clin Orthop; 239: 263-283, 1989.
- Innes JF, McKee WM, Mitchell RAS, Johnson KA: “Surgical reconstruction of ectrodactyly deformity in four dogs”. Vet Comp Orthop Traumatol; 14:201-209, 2001
- Latte Y: “Application of the Ilizarov method in veterinary orthopaedic surgery (part 1)”. EJCAP; 2: 26-50,1997.
- Latte Y: “ 75 Applications of the Ilizarov method (part 2)”. EJCAP; 8: 64-82,1998.
- Latte Y: “Bilan de 75 applications de la méthode d’ Ilizarov : deuxième partie”. Prat. Med Chir Anim Comp; 30:141-160, 1995.
- Latte Y: Methode d’Ilizarov. In Latte Y, Meynard JA: “Manuel de Fixaton Externe”; PMCAC, Paris, 1997, pg 355-366.
- Latte Y: Applications du fixateur externe circulaire. In Latte Y, Meynard JA: “Manuel de Fixaton Externe”; PMCAC, Paris, 1997, pg 425-490
- Lesser AS: “Segmental Bone Trasport for the Treatment of Bone Deficits”. J Am Anim Hosp Assoc; 30:322-330, 1994
- Lewis DD, Bronson DG, Samchukov, Welch RD, Stallings JT: “Biomechanics of Circular External Skeletal Fixation”. Vet Surgery; 27:454-464, 1998
- Lewis DD; Radassch RM, Beale BS, Stallings JT, Welch RD, Samchukov ML, Lanz OI: “Initial Clinical Experience with the IMEXTM Circular External Fixation System - Part I: Use in Fractures and Arthrodeses”. Vet Comp Orthop Traumatol; 12:108-117, 1999.
- Lewis DD; Radassch RM, Beale BS, Stallings JT, Welch RD, Samchukov ML, Lanz OI: “Initial Clinical Experience with the IMEXTM Circular External Fixation System - Part I: Use in Fractures and Arthrodeses”. Vet Comp Orthop Traumatol; 12:108-117, 1999.
- Marcellin-Little DJ: “Clinical Applications of the Ilizarov Method”. 7th ASAMI Veterinary Course , Cremona, Italy, November19-22, 2002
- Marcellin-Little DJ: “Ilizarov Method:Frame preassembly”. 8th ASAMI Veterinary Course , Cremona, Italy, November 25-27, 2004
- Paley D: “Problems,Obstacles, and Comlications of Limb Lenghtening by the Ilizarov Technique”. Clin Orthop; 250:81-104, 1990.
- Paley D: Problems, obstacles and complications of limb lenghtening. In A.S.A.M.I. Group (Bianchi Maiocchi A, Aronson J): “Operative principle of Ilizarov”; Medicalplastic, Milano, 1991, pg 352-366.
- RahalSC, Volpi RS, Vulcano LC, Ciani RB: “Use of the Ilizarov Method of Distraction osteogenesis for the treatment of radial Hemimelia in a dog”. JAVMA; 226:65-68, 2005.
- Rovesti GL, Bascucci M, Schmidt K, Marcellin-Little DJ: “Limb Sparing using a Double Bone-Transport Technique for Treatment of a Distal Tibial Osteosarcoma in a Dog”. Vet surgery; 31:70-77, 2002.
- Stallings JT, Lewis DD, Welch RD, Samchuvoc M, Marcellin-Little DJ: “An introduction to distraction osteogenesis and the principles of the Ilizarov Method”. Vet Comp Orthop Traumatol; 11:59-67, 1998
- Welch RD, Lewis DD: “Distraction osteogenesis”. Vet Clin North Am Small Anim Pract; 29:1187-1205, 1999
- VIDEO
- Bianchi Maiocchi A, Catagni (in collaborazione con ASAMI): “Il fissatore esterno circolare di Ilizarov”; Medi Surgical Video, Milano, 1998
- WEB
- http://www.imexvet.com/(Intramedullary and External Skeletal fixation devices for veterinary surgeons)
- http://www.asami.org/asp/(Association for the Study and Application of the Method of Ilizarov International and External Fixation)
- http://www.ilizarov.org.uk/biog.htm(Biografia di Ilizarov)
- http://www.ilizarov.org/(Applicazioni del metodo di Ilizarov in ortopedia umana)
- CD ROM
- Catagni MA: “Fratture e Pseudoartrosi-Trattamento con Fissatore Esterno Circolare di Ilizarov”. Medi Surgical Video, Milano, 1998.