Michael Saleh practices at the University of Sheffield, Great Britain. He has spent a lot of his time studying external fixation in the treatment of limb trauma.
From the concept of Ilizarov, he has been led to develop a device that brings together the biomechanical advantages of the existing systems: the Sheffield Hybrid Fixator.

 Maîtrise Orthopédique (M.O.): What prompted your interest in external fixation?

Michael Saleh (M.S.): I was training with Mr John Sharrard who then became Professor of Paediatric Orthopaedics. Nobody in Sheffield was really interested in external fixation and John discovered the Orthofix Fixator during one of his numerous trips abroad. That was during a visit to Verona where he had been impressed by the fact that patients were able to walk in the streets with this fixator. When he came back, he wanted one of his senior registrars to dedicate his time to this technique. That is how I became involved in this field and, as is often the case, it was pure coincidence.

M.O.: Which usual osteosynthesis method did you use at the time?

M.S.: We were just starting to use intramedullary nailing for leg fractures and we were coming off a long period of use of screws and plates. Overall we were very conservative in Sheffield and our teachers recommended that we use plaster as often as possible. As far as I was concerned, I was coming from Dundee in Scotland where there was a good school of biomechanics and the concept of external fixation is a logical application of biomechanics.

M.O.: Have you benefited from the experience of the Italian School of Verona?

M.S.: Yes, indeed, I have. Two surgeons from Verona visited us shortly afterwards and I became friends with them. Then I went myself to spend some time with them. I was very surprised by the speed with which they were treating complex trauma cases thanks to this external fixator. By comparison, it took them 3 hours in Verona to do cases which would have taken us a whole day in Sheffield.

M.O.: And what results did you obtain with this technique?

M.S.: Very satisfactory results. Of course, as with any new technique and with growing experience, one starts to realise the limits of the method. But precisely, what makes orthopaedics fascinating, is this constant need to keep pushing the limits further. Thus, when I became a consultant and was able to use this method for something other than fresh trauma, i.e. for what we call reconstructive surgery that includes pseudarthroses, malunions and shortenings, I felt the need to use other devices.

M.O.: Did you apply external fixation in all cases?

M.S.: No, we had selective indications. However, taking into account the fact that 60% of my referral pseudarthrosis cases were infected, it is obvious that I was more inclined to resort to external fixation rather than internal. Overall and consistently, I apply one implant for every two external fixators.


M.O.: External fixation has been blamed extensively for producing pseudarthroses…

M.S.: Yes, and that is why I was very interested in what De Bastiani called "dynamisation" with his fixator. We could criticise today his theoretical approach but there is no doubt that the system works and that there are very few pseudarthroses when this method is used. Often the critics of external fixation do not have much experience of it and use it in the worst case scenarios, which obviously reinforce their convictions. But this situation is currently changing and in difficult cases, surgeons today tend to refer the patient to a colleague specialising in this field.

M.O.: You seemed to be satisfied with De Bastiani's fixator. What made you change?

M.S.: That change resulted from a number of observations. When I was confronted with the Ilizarov method, I first thought that it was a primitive method, and a rather severe one for the patients. But with his tensioned wires Ilizarov managed things that we could not achieve with monolateral fixation. We had difficulty with fixation in metaphyseal bone and porotic bones with our screws. Since wires have a better hold in soft bone we realised that we would have to use a ring fixator. There were numerous systems on the market derived from the Ilizarov device, in France, the Séquoia can be cited as an example. With clinical experience, the strengths and weaknesses of monolateral devices such as the Orthofix and the ring systems such as the Ilizarov had become patent and several surgeons had the idea to combine the advantages of both methods. That is what led to the introduction of hybrid fixators that combined wires and screws.

M.O.: In France it seems that some surgeons have been disappointed by the Ilizarov method…

M.S.: In Great Britain, internal fixation is preferred wherever possible, but that is not always feasible. When a deformity calls for a very progressive correction, when cross-joint fixation is required and where infection is present, the results of internal fixation are poor and that is particularly true for nails in metaphyseal problems.

M.O.: Do you think that this type of method should only be reserved for a few specialised centres?

M.S.: This has been the trend until recently but things are changing because we increasingly see high energy trauma, bone and soft tissue loss and juxta-articular fractures. In Sheffield, where the surrounding countryside is very pleasant, there are many hikers and climbers at weekends and falls with complex fractures of the tibial plateau and pilon occur frequently. In the past, they would have been treated by internal fixation but with a lot of serious wound problems. Nowadays we can look after them so that there are hardly any with infection problems thanks to percutaneous approaches and good techniques of external fixation. The results are so satisfactory with this technique that it must become the standard method and that all general hospitals confronted with trauma should apply it, and not only specialised centres.

M.O.: Where did you learn the Ilizarov method?

M.S.: I tried his method on my own on 4 cases then I went to Kurgan to spend two weeks in the centre where Ilizarov worked. Later on I spent some time with Jean-Marie Hardy in Brive in the centre of France and I was so impressed by his work that I invited him to come to Sheffield. I also visited Spinelli in Rome. My accumulated knowledge came from all these centres.


O.: How long did it take you to come to the hybrid fixator?

M.S.: Quite a long time. I started using the Orthofix monolateral fixator in 1987 and the Ilizarov rings in 1988. In practice, while I was using one of these systems, I sometimes regretted not having the advantages of the other one, until I realised that the two systems were complementary. The wires were more effective in the metaphyseal region but not easy to place in the diaphysis. The efficacy of wires is due to their crossing angle that must be wide enough. This is difficult to achieve safely in the diaphyseal part of the leg. In addition, wires placed in the diaphysis often penetrate muscles. By contrast, the 6 mm screws of the Orthofix device were well tolerated in the diaphysis sometimes lasting up to 18 months without loosening. Thus, the technical requirements were as follows: wires that work well in the metaphysis and screws that work well in the diaphysis. Based on the number of hybrid systems that appeared, it seems that a lot of surgeons must have come to the same conclusion.

M.O.: Why do you say that wires are more effective than screws in the metaphysis?

M.S.: I realised it after a particular case. We had a woman who had been hospitalised for 18 months with a distal femur fracture and I had asked Jean-Marie Hardy to assist me in the application of a Séquoia External Fixator. Whilst inserting the first wire, I realised that it could be pushed into the bone practically without drilling. I told Jean-Marie "This will not work" and he replied "Just wait a bit, tension the wires and you will see". That is what we did and we inserted four distal femoral wires. Two days later, this woman walked and she consolidated her pseudarthrosis in four months. I tried to get an explanation for wire efficacy and the engineers I asked about the subject did not have a satisfactory explanation; on the contrary, they insisted that 6 mm screws should perform better than wires.

M.O.: What do you think about it?

M.S.: We have progressed on this question. A screw has a very strong fixation on a diaphyseal cortical bone but placed in a cell-like environment, as is the case in metaphyseal cancellous bone, its grip is mediocre. In addition to this mediocre grip, the screw of a monolateral fixator undergoes very severe cantilever stresses. Following the repetitive demands of cyclical loading during walking, it ends up loosening. In contrast, a transfixing wire connected on each side to a ring distributes stresses more evenly since the wire's elastic modulus is closer to that of metaphyseal bone. Thus wires allow better compliance between bone and metal and the assembly performs better.
The problem is more complicated: when screws attached to a monolateral bar are connected to wires on rings, the overall device does not always give good results and that is what we wanted to avoid. We wanted the stresses to be distributed evenly from each side of the fracture site. We came to the conclusion that the only way it could be achieved was to have rings on both sides: to fix the wires and to fix the screws. That is our true innovation and that is the reason for developing the Sheffield Hybrid Fixator.

M.O.: But why is a device with metaphyseal ring connected with two rods to diaphyseal screws not satisfactory?

M.S.: We have carried out a series of comparative biomechanical studies of various assemblies. Amongst all the variations reviewed, there was in particular an ideal Ilizarov assembly and a Sheffield Hybrid Assembly. The ideal Ilizarov assembly included four rings and with 2 wires crossing at 900 to each other on each ring placed between them, this formed an idealised device, which would not have been possible to do clinically due to the risks of neurovascular injury. The Sheffield Hybrid Assembly included a metaphyseal ring with wires and a diaphyseal ring with screws, both rings being attached by 3 reduction units. In other hybrid systems, the metaphyseal ring was connected to the diaphyseal screws by different configurations of rods. It appeared that the ideal Ilizarov and the Sheffield Hybrid outperformed all the other assemblies. When the others were loaded axially, they produced an angular deformity as a result of the cantilever stresses. The Ilizarov and the Sheffield devices did not produce any angulation when loaded and to the contrary, demonstrated an even distribution of stresses that we call "beam loading" support. Thus, hybrid systems that connect metaphyseal wires to diaphyseal screws with tubes or oblique rods do not escape cantilever stresses.

M.O.: And what about in clinical practice?

M.S.: Our experience is supportive. Patients that have had other fixators before the Sheffield were telling us that the latter was less heavy. At first this confused us because the weights were similar but in fact, the even distribution of load around the leg gives an impression of lightness and increased comfort.

M.O.: Do you think that the good clinical results are associated with a better distribution of stresses?

M.S.: In traditional fixators, the assembly can be so rigid that all the stresses go through the frame and there is no stimulation of the fracture site. However, assemblies such as the Ilizarov can also be very rigid but can nonetheless consolidate perfectly. The Ilizarov's rigidity seems to be due to the wires deforming under load. The more the assembly is loaded, the more the wires tend to deform. This provokes increased rigidity in the system and greater stability for the fracture. That is what we term the "self-stiffening" effect. The issue is to know what is the right amount of rigidity. In assemblies such as Ilizarov, since stiffness increases with the load, a feedback reaction may be taking place. This reaction makes the patient adjust the load going through the fracture site subconsciously. At the end of the day, experimentally, only assemblies such as the Ilizarov and Sheffield demonstrate this self-stiffening effect that does not exist with other hybrid assemblies. With other hybrid systems, rigidity decreases with load. I actually think that the Ilizarov magic lies in the even distribution of stresses, i.e. in beam loading, and in the self-stiffening effect of the assembly.

M.O.: What do you think of bone transport?

M.S.: This is a technique derived from the Ilizarov concepts of limb lengthening. Since bones can be lengthened by distraction, this principle could also be applied to make up for bone loss within a limb. By comparison with other techniques, this method is very attractive and has created a lot of enthusiasm but mastering the technique is a long process. I have dedicated a lot of my time to it and I use it as a salvage method in clinical situations which would have previously led to amputation.

M.O.: Have you ever met Ilizarov?

M.S.: I met him on many occasions. First at international congresses where I was not ready to accept the amazing things he was showing us. Then in Kurgan where it was more convincing to see him in his hospital. In particular, I remember an operation day when all theatres were in use but Ilizarov, who was not operating himself, went from one theatre to the other to give advice. He often approved with "Da, da" but there were also some "Niet, niet" when assemblies were either too stiff or or not stiff enough. He had charisma and seemed to understand straight away the type of problem and its solution. When I think about it retrospectively I realise how unstable assemblies caused pin site infections, which have been responsible for the bad reputation that external fixation has got. If things are managed as well as Ilizarov used to do it with stable mountings, pin site infections are rare.

M.O.: Was everything that Ilizarov presented to these congresses confirmed?

M.S.: I have seen quite a few clinical cases that confirmed his oral presentations at European congresses. I have also seen high level experimental work that would have merited publication in Western medical journals. Having said that, practice conditions in Siberia are peculiar and not always transferable to Western countries. The fixators often caused pain; patients stayed in hospital for long periods and practised a sort of group therapy with group exercises, adult and children together, to allow them to put up with their device. I do not think that our patients and health system could cope with the same prolonged hospitalisation.


M.O.: Have you got any tolerance problems with the Sheffield?

M.S.: We quickly noticed that patients used less analgesics with our fixator than with Ilizarov frames. This is probably due to diaphyseal screws as they do not transfix muscles. Then we had patients who cycled with their assembly on and who did not complain about it. One of them came back to see me six weeks later. He told me that I was going to tell him off because he had hit his fixator and there was no more space between the ring and the skin, as was the case after leaving the hospital. I knew that when the fixators fail the ring moves and may compress the skin but when trying to move this particular ring I did not manage it. I asked him what he had been doing for these past few weeks and he told me that, prior to the accident he had enjoyed cycling. He had not been able to ride since the accident. With the fixator on, his pain had reduced and he had started cycling and timing himself doing a circuit trying to go faster and faster. This is when I realised that the space between the skin and the fixator had disappeared because of muscle hypertrophy. I had never seen this before with muscle hypertrophy occurring in a patient with an external fixator Since then, apart from cases of articular fracture, we allow patients to go back to their normal routine. We have many examples such as this one. For example there was this climber who had sustained a very severe tibial pilon fracture and to whom, given the extent of the damage, I had suggested an arthrodesis of the ankle.
I did not know that dorsial flexion of the ankle was so important for climbers and the patient refused the arthrodesis and asked me what I would have done if the fracture were not so comminuted. I explained to him that I would have attempted to restore the joint surface of the tibial plafond and that I would have neutralised this fixation with a Sheffield Hybrid Fixator. He told me to try this plan on his fracture and we did. I then saw him again with pictures of himself climbing with his fixator. He consolidated in five months and took up his climbing vigorously once again - even climbing the difficult side which he had fallen off. His x-rays are not very good but the function is excellent. These anecdotes are not here to prove that I am a good surgeon but they demonstrate that when the fixation is good, patients can do their physiotherapy during the consolidation and rehabilitate quicker. That is really the surgical challenge of the 21st century: to give the traumatised limb its function back and the patient his independence and ability to work and achieve. The issue is not only to bend one's knee to 90° but it is also to be able go back to work without worrying about one's fracture while it is consolidating normally.

Maîtrise Orthopédique n°99 - 2000, december