properties which can occur in seemingly the same composite. The importance of quality control of the raw materials was also emphasized.

Dr. P.J. Fydelor (Royal Military College of Science, Shrivenham) gave a brief history on the use of synthetic plastics for replacements in the cardiovascular system. The present ‘state of the art’ was discussed together with some exciting predictions for the future.

The development of a special epoxy-based carbon fibre reinforced material for fracture fixation plates was the subject of the paper presented by Dr. G.W. Hastings (Bio- medical Engineering Unit, Medical Institute, Stoke-on-Trent). He discussed the potential advantages of using plates having a stiffness comparable to that of bone. Mr. K.J.J. Tayton (Department of Orthopaedic Surgery, University of South Wales, Cardiff) showed some promising clinical results in which the carbon fibre composite plates had been employed. He believed that, in order to facilitate fracture healing, it was important to transmit forces through the fracture site and not to bypass the forces around the site, as more usually occurs with the less flexible metal plates. A further significant, although unexplained advantage he had found in using the carbon reinforced plates was that they could be employed satisfactorily in cases where infection was apparent.

The diversity of the mechanical properties obtained using composite materials was ably demonstrated in the final paper presented by Dr. D.A. Ryder (U.M.I.S.T., Manchester). Unlike the previous speaker, Dr. Ryder has produced a composite material which had a very high stiffness. The aim had been to develop an ultra stiff metal composite pin for use in compression arthrodesis. Dr. Ryder claimed that the currently employed stainless steel pins deflected excessively in use, which resulted in the pins becoming jammed in the side clamps.

As well as having a discussion period at the end of the meeting, the programme was arranged such that each paper was discussed at length immediately following its presentation If, as I believe, the depth of the discussion which ensued is an indicator of the interchange of ideas, then clearly the objective of the meeting was realized. Perhaps, therefore, conference organisers could learn from this format. To further facilitate the flow of information, the meeting was free and was also an open one; that is to say none of the work presented will be formally reported in the lnstitu- tion’s proceedings. However, interested readers who would like to obtain further information on the work presented should contact the appropriate speaker.

Keith W.J. Wright

Electrie~ Effect in Biolo~c~ systems

The increasing importance of this subject has been emphasized recently by two well-attended meetings. The first, held at Stoke-on-Trent on 9 May 1980, was the third in a series of symposia on ‘Methods and Materials for

Fracture Fixation’and was organized jointly the B.E.S., the Biomedical Engineering Unit of the North Staffordshire Polytechnic and the Orthopaedic Department of the North Staffordshire Hospital Centre. It was entitled ‘Electrical Stimulation of Bone Healing’.

The second was organized by the Electrochemical Group of the Royal Society of Chemistry and was entitled ‘Electrochemistry in the Control of Biological Growth’. This took place in Oxford on 1-2 July, 1980.

Overlap of some subjects and speakers occurred at the two meetings but the emphases were different. At Stoke, the meeting was biased towards clinical work but there was a supporting content of basic scientific study, the aim being to present the different methods of using electrical and magnetic stimulation for the treatment of non-unions, and to assess these against the use of other methods of treat- ment. Laboratory studies showed the increasing body of scientific knowledge on electrical properties of tissue and the effects of electrical fields upon it, although these were not necessarily related to clinical studies,

In contrast, the Oxford meeting mainly emphasized the effects of electrical energy at cellular level. Clinical papers were included, describing the use of the main systems, but the meeting was directed primarily to the fundamental studies.

(A full report appears in J. Eiomed. Engng. 2,4, 19801

TREATMENT OF FRACTURE NON-UNIONS

A series of presentations at both meetings reviewed the clinical position and gave the opportunity to contrast the differing methods and to evaluate the results. There are two main approaches as far as technique is concerned. One of these uses electromagnetic stimulation, the energy being applied to the fracture site by means of external coils. These are usually supplied with a pulsed current and many results from iaboratory studies seem to indicate that there may be a specific relationship between pulse characteristics and the mechanism of stimulation, though the precise nature

is not yet clear. The Bassett method of electromagnetic stimulation,

employing Helmholtz-aiding coils on the outside of the POP cast, was exemplified by Mr. W.J.W. Sharrard, Sheffield, who spoke at both meetings; the main emphasis of his paper was the two important factors of electrical stimulation and correct orthopaedic management. Typical treatment is a 7 Ejhlday period of stimulation extending over 5.5 months.

E.M. Downes and J. Watson from Swansea (‘Treatment of delayed union using pulsed magnetic fields’) have used a G-shaped electro-magnet located on each side of the POP cast. A 1 Hz frequency is used. Patients are treeted on an outpatient basis and although the 66% success rate is lower than Bassett’s, this may result from shorter treatment time.

J.R. Corfield and E.R.L. Jones (Kent and Cancerbury Hospital) uses an air-cored system devised by themselves and the main characteristic of the pulse is a fast rise time and low fall time. A 15 Hz frequency is used. Results from 20 patients were presented and the advantage claimed is outpatient treatment with low-cost equipment.

Siomaterials f980, Voi ? October 227

The alternative approach has evolved from work at the University of Pennsylvania in Carl Brighton’s group, and Dr. Jonathan Black spoke at Oxford on this work. Electrodes supplied with direct current are inserted into the fracture site. These are cathodic and deliver 20pA of direct current to the fracture site for 12 weeks. The power pack is incorporated into a non-weight-bearing cast and a skin anode is used. 78-80% solid union is claimed for the University of Pennsylvania series. Mr. John King (The London Hospital) reviewed his clinical results with this system and although convinced of its value, believes there should be more study of reasons for failure.

A deliberate contrast to these methods of treatment was given in the Stoke meeting in a paper by J.K. Webb (Queens Medical Centre, Nottingham) ‘The place of internal fixation in non-unions’. The aim of internal fixation is union with perfect function at the end of it, with the avoid- ance of joint stiffening. Satisfactory repair of hypertrophic non-union by internal fixation was possible with a good success rate, from some centres almost 100%.

With this paper, stimulation methods are seen as another option for treatment of a difficult clinical problem, but one that still needs careful evaluation. There are important differences between the Philadelphia group’s method and the magnetic field systems.

BASIC SCIENCE

Several of the papers were addressed to the question of the way in which electrical fields influenced bone cell activity and whether the electrochemistry of the membrane was a factor. Dr. G.W. Hastings, reviewing the nature of the electromechanical properties of bone, reported that at Stoke they had concluded that bone, since it exhibits ferro-electric properties, is a piezo-electric material and that the charged dipoles are arranged in domains.

Professor A. Pilla (Bio-electrochemistry Laboratory, Orthopaedic Research Laboratories, College of Physicians and Surgeons, Columbia University, New York) spoke at both meetings on the electrical modulation of cell surface phenomena. He described experiments using weak pulsating currents inductively applied to modulate cell and tissue function. This was essentially a study of non-Faradaic chemistry, i.e. not involving oxidation or reduction processes. This is an important distinction for the electrode insertion methods where the electrode reactions cannot be excluded. Although the reactions may be highly unspecific in terms of the end result, a more specific interaction of pulse with membrane electrochemistry may be anticipated. This was further elaborated by Dr. S. Fitton-Jackson (Cambridge) who reported on the biological responses of chondrogenic and osteogenic tissues to pulsed magnetic fields.

Dr. Jonathan Black presented a second paper at Oxford, ‘Physical mechanisms in DC stimulation of osteogenesis’. Reviewing earlier observations that for electrodes inserted at a fracture site, bone forms when the electrode is cathodic, he developed the concept that the cathode is an oxygen ‘getter’. This produces local oxygen deficiency and increased pH and in fact oxygen tension in healing fractures is low for the first 25h post-operatively. Thus an intermediate physicochemical effect appears to produce bone stimulation. The interest lies in trying to reconcile these electrochemical observations with those of Pilla’s and other groups.

Professor R.J.P: Williams in the concluding paper at Oxford summarized the physical characteristics of stimulation and proposed a possible synthesis of the differing results and mechanisms. Stimulation affects all types of cells, deals with cell growth, is an electrical process nothing to do with electrons but rather with ionic processes. All ion gradients are pumped and he proposed that all effects are due to Ca2+ movements. Ca*+ being divalent is particularly active in terms of binding proteins. The input channel for calcium is triggered in viva by electrical pulses. Inside the cell there may be a high calcium flux and the multiple membrane systems in the cell and high storage capacity for Ca*+ contribute to an automatic amplifier system.

Considerable interest derived from these meetings particularly since it was possible to hear both the clinical results and the scientific experiments which were attempting to underpin them. It is still undoubtedly a controversial area as the results from the Swiss group with magnetic stimulation show. There is little question that bone does show electrical characteristics and also that there is an effect on biological systems when studied in the laboratory. However, one could conclude that the clinical picture is not quite so certain. The fact that many of the patients for whom the method has been successful have in the past received a variety of treatments does not always mean that these have been the most effective for that particular case. The clinicians who spoke have all emphasized the need for correct orthopaedic treatment for their patients and the need for complete immobilization of the fracture, which could be the determining factor.

It should be noted that in discussion a word of warning was entered regarding observation on the adverse effects on major organs remote from the site of magnetic stimulation when prolonged treatment is given.

There is a difference in mechanism between DC stimula- tion with electrodes and magnetic effects and more work is clearly needed. The involvement of the electrochemical group of the Royal Society of Chemistry is an encouraging sign for the advancement of the scientific studies.

G.W. Hastings

228 Biomaterials 1980, Vol 1 October