England and Wales Court of Appeal (Civil Division) Decisions

IN THE COURT OF APPEAL (CIVIL DIVISION)
ON APPEAL FROM Birmingham District Registry
His Honour Judge Owen QC

		Royal Courts of Justice Strand, London, WC2A 2LL
		23/10/2015

Dame Janet Smith:

Introduction

1. This is an appeal from the order of HHJ Owen QC, sitting as a High Court Judge, dated 16 May 2014. On a trial of two preliminary issues, the judge held that the claimant, June Evans, had demonstrated that the defendant, Royal Wolverhampton Hospitals NHS Trust, by its consultant surgeon Ejaz Mughal, had been negligent in his conduct of her total hip replacement and that she had suffered injury as a result.
2. The respondent, Mrs Evans, underwent a left total hip replacement in January 2010. After the operation, it was found that her left leg was numb and she could not move her left foot. A post-operative X-ray showed the presence of a large piece or 'blob' of the cement which had been used to secure the acetabular prosthesis in position. This cement was removed at a second operation; it was found to have been in contact with the left sciatic nerve. Despite prompt removal of the cement, the sciatic nerve had been permanently damaged. The respondent sued, alleging that the surgeon had been negligent in allowing the blob of cement to be retained and had suffered damage as a result. Eventually, causation was conceded and the only live issue for the judge at trial was breach of duty. The judge held that the surgeon had been negligent in failing to see and remove the cement. The NHS Trust appeals against that decision with the permission of Sir Stanley Burnton.

The hip replacement procedure as carried out by Mr Mughal.

3. Arthritic degeneration of the hip joint is a common complaint leading to pain and restricted movement. Nowadays total hip replacement is a routine procedure. Its objective is to replace both the ball and socket parts of the hip joint with prostheses thereby providing smooth surfaces over which the joint can articulate easily. Usually the socket prosthesis is made of plastic and the ball is made of metal. Generally, the operation produces excellent results although there are risks of some well-recognised complications about which patients must be advised. One such complication is the possibility of nerve damage, which can occur in a number of ways.
4. Over the years since hip replacement was first practised, more than one operative technique has been developed. I shall describe only the technique used at the appellant hospital which was followed by Mr Mughal. I shall focus on the stage of the operation with which this appeal is concerned, which is the fixing of the plastic cup prosthesis into the acetabulum.
5. Initially, the surgeon opens the hip capsule and cuts through the soft tissues to expose the ball and socket hip joint. The ball is the head of the femur or thigh bone. The socket or acetabulum is part of the pelvic structure. After exposing the hip joint and applying traction devices to hold back the soft tissues, the surgeon dislocates the joint and saws off the femoral head. He then prepares the acetabulum (which was described to the court as being like half a lemon) by reaming out all the arthritic bone. He then drills several holes inside the acetabulum in order to improve the penetration of the cement which he is about to use to secure the cup in position. Once the cavity has been cleaned and dried, it is ready for the cement. When the cement is first mixed, it is quite soft. As soon as it has been mixed, it will begin to polymerise and harden gradually. This process takes approximately 15 minutes. It is an exothermic reaction. The cement begins to give off significant heat after about 8 to 10 minutes and continues until about 14 to 15 minutes after mixing, after which it will begin to cool down.
6. The surgeon places a quantity of cement inside the cavity and presses it down manually into the prepared surface. At this stage, the cement has the consistency of soft dough. Then, using a tool called an introducer (or a positioner), he places the plastic cup onto the cement in the prepared cavity. It is important that the cup is in the right position and orientation. Also, the cup must be held quite still until the cement has set. As soon as the cup is pressed into place, some of the cement begins to extrude around its rim. This is to be expected. If there were no extrusion, it might mean that insufficient cement had been used to create a complete cement mantle between the acetabulum and the cup.
7. It is important that any extruded cement should be removed. There are at least two reasons for this. One is that cement retained within the joint might cause wear and tear and interfere with the smooth operation of the joint. The other, which is germane to this appeal, is that retained cement might disappear into the soft tissues surrounding the hip. Although such retained cement does not usually cause harm, there is a risk that it might do so; for example there is a recognised risk that it might damage a nerve such as the sciatic nerve which runs through the soft tissues behind the hip joint. Such damage could be caused by pressure on the nerve or by the heat generated during polymerisation or by a combination of the two.
8. It is possible to begin the process of removal of extruded cement while the introducer is in place. However, the tool severely restricts the view which the operator has of the rim. In any event, there will be more extrusion to come because, after a while, when the cement has thickened to some extent, the operator will put down the introducer and use a much smaller tool, called a pusher, to maintain manual pressure on the cup to keep it in place. When the pusher is used, there will be more cement extrusion. There will also be a further opportunity to remove it. Because the pusher is much smaller than the introducer, the surgeon has a better view of the rim. However, he still does not have a complete view; he cannot clearly visualise the part of the rim under the pusher. When polymerisation is complete or almost so, the pusher can be put down and the operator then has a clear view of the whole of the rim. This is his final opportunity to ensure that all the extruded cement has been removed.
9. I must mention one particular factor relating to the removal of extruded cement. There is particular tendency for a significant quantity of cement to extrude at the bottom of the acetabulum through what is called the acetabular notch. The acetabulum is not a perfect hemisphere. At the lower edge of the cavity, there is a depression. The word 'notch' is not entirely apposite in that the depression is not narrow or sharp-edged; it is gradual and smooth. It was sometimes described in evidence as a bony defect. When the plastic cup (which has a circular rim) is placed in position, there is a gap underneath the cup at the position of the depression or notch. This gap is partially filled by the transverse acetabular ligament which runs across the depression. But the ligament does not completely fill the gap and more extrusion may be expected at this position than elsewhere on the rim. This is the part of the rim which is partially obscured while the pusher is being used. So, although the operator can remove much of the extruded cement while he is using the pusher, he may not be able to see clearly all the extrusion coming from the area round the notch until he has finished with the pusher. When that is removed, the operator has a complete view of the rim and can ensure that all extruded cement is dealt with.
10. I should mention that identifying all the extruded cement might not be entirely straightforward, particularly in the region of the acetabular notch. That is because there will be a tendency for blood to accumulate in that area. It can be removed using a sucker. Also, in this area, the soft tissues will be immediately adjacent to the rim so that an extrusion might well hang over the edge of the rim and become hidden in the soft tissues. However, such a piece would remain attached to the body of cement at the rim unless and until it was cut off. It seems to have been common ground that extruded cement would not break off spontaneously.
11. Once the plastic cup is secured within the acetabulum, the surgeon fits the femoral head prosthesis. I need say no more about this aspect of the operation as it was carried out successfully by Mr Mughal.
12. When Mr Mughal performed the operation on the respondent, he was quite unaware that anything untoward had occurred. His operation note described a routine procedure. It made no reference to the removal of extruded cement, let alone any reference to a problem arising in association with the cement. He moved on to another operation. The post-operative X-ray of the respondent's hip showed the presence of a large piece of cement in the soft tissues some distance below or behind the hip joint. When the respondent recovered from the anaesthetic, her left leg was numb and she could not move her foot. Mr Mughal was informed and he consulted his senior colleague. He was advised to and did carry out a second operation to locate and remove the piece of cement. He found the cement lying in contact with the sciatic nerve although not apparently adherent to it. Mr Mughal removed the blob of cement 'atraumatically' as he recorded in his note of the second operation. He did not keep the blob; nor did he photograph or measure it. Nor did he record whether or not it was still attached at the rim. In evidence at the trial he said that the piece of cement was of irregular shape, approximately 2 by 2.5 centimetres in size. It was flattened rather like a piece of ravioli. He said it was not connected to the acetabular rim.

The proceedings

13. Mrs Evans sued, alleging that Mr Mughal had been negligent in failing to see and remove the large blob of cement and to prevent it from being retained in the soft tissues adjacent to the sciatic nerve. The defence denied negligence and also causation, although this issue was conceded shortly before trial.
14. Mr Mughal's witness statement described the conduct of the operation as a whole in some detail but, in relation to the extrusion of cement and its removal, he said only that, when he had pressed the acetabular component into the reamed area of the acetabulum, he "then removed any cement which extruded from around the flanged edge". He said nothing about looking for or removing any extrusion at a later stage, for example when he was using a pusher or after he had finished doing so.
15. This paucity of detail meant that the experts instructed to advise had little factual information on which to base their opinions on the adequacy of what Mr Mughal had done. Each party had instructed an orthopaedic surgeon with long experience of hip replacement operations. Mr Simon Bridle was the claimant's expert and Mr Terence Cain was instructed for the defendant. Despite their limited information, the experts gave their opinions, relying mainly on their own experience of conducting the operation and what usually happened. It was not until the trial, when Mr Mughal had given evidence and had provided some further information about his conduct of the operation that the experts were able to refine their opinions.
16. There was a good deal of common ground between the experts following exchange of their reports and a discussion between them. It was agreed that a substantial quantity of cement is to be expected to extrude especially when the component or cup is first inserted and pressed into the acetabulum. It was agreed that, in this case, cement had probably extruded at the inferomedial part of the acetabular rim at the area of the transverse acetabular ligament; it was common for cement to extrude at this point. It was agreed that some extruded cement would have migrated into the soft tissues and would not have been visible to the surgeon even when he could visualise the entire rim. Mr Bridle was of the view that, when the surgeon checked the rim, he should have realised that some of the cement he could see might be connected to more cement which had migrated into the soft tissues and was not visible. He should have confirmed the extent of the extrusion and removed it. His failure to do so amounted to evidence of substandard care. Mr Cain thought that the surgeon would not necessarily be aware that cement had extruded into the soft tissues. Both experts agreed that, if identified, extruded cement should be removed but Mr Cain added a caveat that he thought it was potentially hazardous to attempt to remove cement which could not be seen.
17. Mr Cain drew attention to studies published in the medical literature which suggested that retention of cement was common; in one study, extruded cement had been seen on the post-operative X-rays in 45% of the cases considered. It was common ground between the experts that not all of those cases could have entailed negligence on the part of the surgeon. Accordingly, the fact that this extruded cement had been missed was not in itself evidence of substandard care.

The hearing

18. Mr Mughal was the only witness of fact and went first. He adopted his written statement as his evidence in chief. Thus it was not until cross-examination that Mr Mughal first gave a detailed description of how the relevant stage of the operation had gone and exactly what he had done. Unsurprisingly, it was apparent that he could not remember the operation in detail and was having to reconstruct what had probably happened from his usual practice in conducting this type of operation and his recollection of where he had found the blob of cement at the second operation.
19. He said he was aware of the need to apply a rigorous surgical technique in removing all extruded cement and claimed that he had done so. He pointed to the absence on the post-operative X-ray of any signs of extrusion retained round the rim of the acetabulum itself. He accepted that the most common route for cement to extrude was through the gap or channel at the acetabular notch. He stressed the difficulties of visualising the whole rim (and in particular that area) while using an introducer or pusher. He stressed the impossibility of seeing cement which had migrated into the soft tissues. It was at quite a late stage of cross-examination that he seemed to acknowledge that the piece of cement must have 'broken off' while he was using his curette to remove extrusions. In re-examination, he eventually acknowledged that the only logical explanation for what he had found at the second operation was that he must have severed, at the rim, a bridge or ribbon of cement which had a quantity of hidden cement attached to it and which had then dropped away into the soft tissues. At no stage did he suggest that this cement could have dropped away without being severed. The two experts both regarded that explanation as plausible and for the rest of the trial it was assumed that that is what had happened. Because Mr Mughal was unaware that that is what he had done, he cannot have known at what stage he had done it. However, he asserted that he had looked at the rim with great care at every stage when he had the opportunity to do so. He asserted that it would not be right for him to go searching below the soft tissues to find hidden extrusions.
20. In essence, (and I paraphrase long sections of evidence) Mr Bridle's opinion was that because rigorous removal was important and because it was common for cement to extrude at the acetabular notch, a surgeon should examine that area with particular care. It was, he accepted, the most difficult area to visualise. Moreover the surgeon must be aware of the possibility that some cement might have migrated into the soft tissue and would no longer be visible; it would however still be attached to cement which was visible. It was incumbent on the surgeon to identify the presence of hidden cement and remove it if at all possible. He described how this could be done, if necessary by dividing any tissues which might be impeding removal. Not knowing exactly when Mr Mughal had severed the bridge or link to the retained cement, he suggested that this must have happened either while the pusher was in use, in which case Mr Mughal must have used his curette in a part of the rim of which he had an imperfect view. He should not have done that. Alternatively, if he had severed the link after he had ceased to use the pusher, at which time full visualisation was possible, Mr Mughal could not have looked carefully enough at what he was cutting and had failed to identify the fact that there was some hidden cement attached to the part he was cutting. Mr Bridle was of the view that, either way, Mr Mughal's practice on this occasion fell below an acceptable standard.
21. The main attack on Mr Bridle's evidence was based on Mr Cain's reliance on the published studies which showed that retention of extruded cement was very common and rarely caused any problems. So common was it that it was clear that retention must occur quite frequently without negligence. It was put to Mr Bridle that he was drawing an inference of substandard practice from the fact that a large piece of cement had been retained. This was impermissible in the light of the published studies. Mr Bridle's response to this (and again I paraphrase quite lengthy sections of evidence) was to accept that one could not infer substandard care from the mere fact of retention of a large piece of cement. He pointed out incidentally that the studies did not relate to recent practice and he thought that techniques had improved since then. But in answer to the allegation put to him, he said that the size of the piece was relevant to his conclusion (this piece was very much at the top end of the size of the retained pieces reported in the studies) as was the fact that it had extruded from a part of the acetabular rim from which extrusion was to be expected and which was the most difficult to see. These factors, he said, meant that particular care was required on the surgeon's part. It was put to him that he could not identify any aspect of Mr Mughal's operative technique which was substandard or that made Mr Mughal different from the many other surgeons (reported in the published studies) who had allowed cement to be retained but had not been negligent. Mr Bridle repeated that Mr Mughal should have examined the area with care and should have identified the piece of cement which was extending into the soft tissues. However, at one stage, towards the end of cross-examination, when it was put to him yet again that he was, in truth, drawing an inference of substandard care from the fact that the large piece of cement had been retained, he said that the drawing of such an inference "would not be unreasonable". He also conceded that he probably would not have been critical of Mr Mughal if the piece of retained cement had been small. At that stage, Mr Thomas sat down, no doubt satisfied with the answers he had just elicited. The judge took up the questioning and gave Mr Bridle the opportunity to restate his opinion about the need for careful examination of the whole of the rim.
22. Mr Cain relied heavily on the published materials to support his view that Mr Mughal's performance of the operation had not fallen below acceptable standards. As Mr Cain's opinion was rejected by the judge and there was no real challenge to his reasons for doing so in the appeal.

The judgment

23. The judgment set out the evidence and arguments in great detail. I have attempted to condense this material in the foregoing paragraphs. The judge's reasoning begins at paragraph 99 where he reminded himself that the burden of proof rested on the claimant. He said that the primary facts did not, without more, give rise to any inference of negligence. There was no shifting of an evidential burden of proof to the defendant. In particular, the fact of the cement extrusion or the size of that extrusion did not of itself imply any lack of care by Mr Mughal and did not require him to provide an explanation for the presence of the blob of cement lying on the sciatic nerve, which was consistent with no breach of duty on his part
24. The judge found that a substantial cement extrusion probably occurred in the area of the transverse acetabular ligament and that it probably occurred at a time when Mr Mughal could not see it happening because of the presence of the tool he was using. That such extrusion occurred was not indicative of sub-standard technique. He found that Mr Mughal knew or ought to have known that extrusion might occur while he was using a tool and that the extent of the extrusion could not be predicted. He held that Mr Mughal should have adopted a rigorous surgical technique which demanded vigilance and careful examinations of the rim for extrusions at all times when it was capable of being visualised. Although the fact of an extrusion might not be evident to the surgeon until after it had occurred, the consistency and state of the cement was such that it would have extruded in a single form extending at and over the rim edge and, depending on its size, possibly below the tendon or soft tissues. Thus, until severed by a curette, the extrusion would be a continuous piece from the point of extrusion at the acetabular edge or rim to its mass at the distal end. Whilst the cement could not have been seen by Mr Mughal as it was extruding, it could and should have been visualised after the pusher stage when there was no 'blind spot'.
25. The judge further found that Mr Mughal had probably severed the extrusion using his curette. The judge thought it was likely that this occurred at a time when the whole of the rim was visible (after use of the pusher had ceased). If so, the judge was of the view that Mr Mughal had cut the extrusion without taking rigorous care to check whether it extended into the soft tissues. In the alternative, it was possible that Mr Mughal had severed the extrusion at an earlier stage while using the pusher, that is at a time when he had a restricted view and could not properly see what he was clearing away. In either case, his performance or technique fell below acceptable standards. The judge observed that Mr Mughal had been unable satisfactorily to describe any steps he had taken to deal with the risk of extrusions. The extrusion was 'there to be seen'. The judge thought that it was not irrelevant that the operation note did not address this part of the operation at all. Further, the witness statement provided no detail of this part of the procedure. Having heard the oral evidence, the judge was not satisfied that the necessary minimum degree of vigilance had been exercised.
26. The judge explained why he had preferred Mr Bridle's opinion to that of Mr Cain. Mr Bridle's views had been logical and internally consistent. He had not (as alleged) rested his opinion simply on the fact and size of the blob of extruded cement. His criticism was based on the substantial size of the extrusion and the fact that it had come from a site known to give rise to extrusions in circumstances when the size of the extrusion could not be predicted. That was why vigilance was required when the rim was capable of being visualised and care had to be taken to ensure that all extruded cement was removed.
27. On the other hand, the judge felt unable to rely on the opinion of Mr Cain, who, the judge thought, had a mind-set which appeared to assume from the outset that the injury had occurred without the possibility of any failure in technique. The judge admitted that he had been influenced to some extent by Mr Cain's belated change of mind on the issue of causation. Mr Cain had sought to explain this but the judge was wholly unconvinced by this explanation. Further the judge observed that Mr Cain had not engaged with the factual issues surrounding the mechanism by which the extrusion had come to be where it was found. He had made a number of points but none of them dealt with the real issue of what Mr Mughal should have done in order to avoid the risk of severing and losing a partly concealed piece of cement.
28. The judge concluded that the respondent had made out her case.

The appeal to this court

29. The written argument in this appeal (I cannot call it a skeleton argument) is 27 pages long. I regret to say that it complicates what should be a fairly simple set of grounds of appeal. In it Mr Thomas advances four reasons (Grounds A-D) why the judge's decision was wrong and a further argument (Ground E) that the decision had been unjust on account of a serious procedural irregularity. Possibly due to interventions by the court at an early stage, in oral submissions, Mr Thomas did not follow the structure of his grounds or written argument; rather he tackled what he accepted was the nub of the appeal, namely whether the judge's central findings of fact, inferences and conclusion were properly supported by the evidence. Before turning to that argument, however, I will address Mr Thomas's first ground.
30. Mr Thomas submitted that, although the judge had purported to direct himself that the burden of proof lay on the respondent, in fact the judge had treated the case as one where the appellant, through Mr Mughal, had to prove that he had conducted the surgery with reasonable skill and care. This was not a case where any inference of negligence could arise from the circumstances themselves and therefore there never was a prima facie case for Mr Mughal to answer.
31. I have already summarised, at paragraph 23 above, the self-direction which the judge gave. It is manifestly correct as Mr Thomas accepts. The suggestion is that he did not comply with it. It was common ground that the published materials showed that retained cement extrusion was a common finding and that no inference of negligence could be drawn from it. As I understand it, the argument was that the judge should not have based his conclusions on Mr Mughal's evidence; without it, the respondent would have had no prima facie case. The reliance the judge placed on this evidence shows that he had, in effect, shifted the burden of proof onto Mr Mughal.
32. In my view, this argument is without merit. In the first place, even if Mr Mughal had chosen not to give evidence, the respondent would have had a prima facie case. Mr Bridle would have given evidence in accordance with his report and this would have amounted to a prima facie case.
33. Of course, Mr Mughal chose to give evidence and, by agreement between counsel, was the first witness. This is in accordance with modern practice in cases of this kind. It enables the experts to give their opinions after the factual evidence has been heard. Once Mr Mughal had given evidence, it was before the court for all purposes. The judge is not expected to exclude his evidence from consideration while deciding whether there is a prima facie case.
34. This first ground was not pursued at any length and, in my view, for good reason. It is clear that the judge's direction of law on the burden of proof was correct. He correctly said that he could draw no inference of negligence from the fact that an extrusion had been retained, not even a large extrusion like this one. He correctly identified the question he had to answer which was whether, on the facts of this particular case, the respondent had proved that Mr Mughal's performance of the operation had fallen below the acceptable standard. It appears to me that he then went on to consider and answer that question. I would reject this first ground of appeal.
35. Most of the remainder of Mr Thomas's submissions focussed on the issue identified by the court at an early stage, which was whether the judge's findings and holding were supported by the evidence. He submitted that they were not.
36. Perversity is always a difficult furrow for an appellant to plough. Appellate courts are reluctant to interfere with factual findings where they depend to any significant extent on the impression a witness has made on the judge. The appellate court can of course analyse the transcript to see whether the words uttered by the witnesses support the judge's conclusions. But it cannot assess a witness's demeanour or know the extent to which that demeanour has influenced the judge. Before one begins any analysis of the evidential basis of the judge's findings and holdings in this case, it must be noted that he formed a favourable view of Mr Bridle and an unfavourable view of Mr Cain. The judge gave his reasons for those views and they can be analysed but we cannot factor in the effect which their demeanour had on him.
37. Mr Thomas's attack on the judge's holdings focussed mainly on Mr Bridle's opinion. His main argument was that, despite his protestations to the contrary, Mr Bridle had in truth drawn an inference of negligence from the fact that a large piece of cement had found its way into the soft tissues. Second, Mr Bridle had failed to take on board the significance of the published studies which showed that retained cement was a very common finding and must in many cases have occurred without negligence. There was, he submitted, a fundamental inconsistency between Mr Bridle's assertion that Mr Mughal had fallen below the standard of care expected of a reasonably competent surgeon and the need to accept that retention often happened without negligence. Mr Bridle had, submitted Mr Thomas, been unable to point to anything that Mr Mughal had done or failed to do which made him different from those other non-negligent surgeons.
38. I will deal with that second argument first. The studies do indeed record that retained cement was found on the post-operative X-rays in a substantial proportion of cases. In the oldest study, published in 2002, the proportion was 45%. Mr Bridle pointed out that this was some ago and that today one would expect to find a much lower incidence. Be that as it may, he did accept that some of those incidents of retention must have occurred without negligence. The point is, however, that the study was not concerned to investigate whether the retention had been due to negligence; nor did it seek to discover how or from where the retained cement had come. The only conclusion which could safely be drawn was that which Mr Bridle accepted (and the judge adopted) that one could not infer negligence from the mere fact of retention. Apart from that, the studies tell one nothing about whether there has been negligence in a particular case. There might and there might not have been. The question can only be decided by close examination of the circumstances of the particular case. That is what the judge had done.
39. In support of his first submission, Mr Thomas took us to a number of points in Mr Bridle's report and evidence where he referred to the size of the retained piece of cement. These showed, submitted Mr Thomas, that in criticising Mr Mughal, Mr Bridle had been strongly influenced by and had drawn an inference of negligence from the size of the retained piece of cement, whereas at other moments he had acknowledged that the size of the piece was irrelevant to the issues of breach of duty. The high point of his submission was that, shortly before the end of cross-examination, Mr Bridle had said that it was not unreasonable to infer breach of duty from the fact that a large piece of cement had been missed and retained. Also he had said that he probably would not criticise Mr Mughal for missing a small piece. As I observed, having secured those answers, Mr Thomas had ended his cross-examination. He submitted to this court that those answers made his point.
40. Mr Roussak, who appeared for the respondent before this court but not at trial, acknowledged that these answers from Mr Bridle did cause him some difficulty. He described them as Mr Bridle's 'wobble'. He submitted that these two answers were out of line with the rest of his evidence, both written and oral. At all other times, Mr Bridle had given a consistent opinion that his criticism of Mr Mughal was his failure to see and identify the piece of extruded cement which was 'there to be seen' and then to remove it, including the part which was initially hidden under the soft tissues. He could not explain why Mr Bridle had succumbed to Mr Thomas's final questions in the way he had but, he submitted, these isolated answers should not be allowed to undermine the solid line of argument and opinion he had advanced throughout.
41. I have read the whole of Mr Bridle's evidence. There are times when he expressed himself in a slightly infelicitous way. But despite that, I would accept Mr Roussak's submission that his views came over clearly and consistently. His criticism of Mr Mughal was not dependent on the size of the retained piece of cement; it was based on Mr Mughal's failure to see the visible part of that piece, which must have been there to be seen at a part of the rim where extrusion was to be expected and where a particularly careful examination was needed because of the potential difficulties of visualisation. I would reject Mr Thomas's submission that Mr Bridle's opinion was logically flawed and inconsistent with the published studies.
42. It seems to me that it cannot possibly said that, on the basis of the evidence before him, the judge's decision was wrong. His findings of primary fact were, by the end of the hearing, virtually common ground. A substantial extrusion had occurred in the area of the transverse acetabular ligament, probably at a time when Mr Mughal could not see it because of the tool he was using. Although extrusion was to be expected, its extent could not be predicted. That too was common ground as was the judge's statement that the consistency and state of the extruding cement was such that it would be in a single form extending over the rim and depending on its size, possibly over into the soft tissues. It was Mr Mughal's own evidence that this must have happened in the present case. It was also Mr Mughal's own evidence that the only logical explanation for what had happened was that he had cut through the extrusion with his curette and it had fallen away into the soft tissues. As he did not realise he had done this, he cannot have known at what stage he did it. None of those findings of primary fact were or could sensibly be open to challenge.
43. The judge did not make a definite finding as to when Mr Mughal had severed the extrusion. He considered two possibilities; first that he had severed it while still using the pusher and second that he had done it after he had finished using the pusher. Mr Thomas did not suggest that the judge was wrong to do that. The judge also held that, at the time the extrusion was severed, it formed a single piece or strand of cement, party visible and partly hidden. That finding was not challenged; indeed it seems to me to follow inevitably from the acceptance that the cement would not break off spontaneously.
44. The judge's holdings as to the extent of the duty or the standard of care to be expected were almost entirely based on common ground. The experts agreed that the risk of extrusion (particularly from the acetabular notch) was well known and that it was important to remove the extrusion so far as possible. The judge said that Mr Mughal knew or ought to have known of the risk that an extrusion might occur and that its extent could not be predicted. That was uncontroversial; Mr Mughal did not disagree with it. Both experts (and Mr Mughal) agreed that a 'rigorous surgical technique' was required in the removal of extruded cement. This expression came directly from one of the published studies on which the appellant relied. The judge said that Mr Mughal should have adopted a technique which demanded vigilance and careful examination of the rim at all times when it was capable of being visualised. That was uncontroversial. Mr Mughal himself agreed with that; his case was that he had adopted such a technique. But, he said, he had not been able to see the part of the extrusion below the soft tissues and could not go searching below the soft tissues to see what might be there.
45. That aspect of the surgeon's duty was to some extent controversial and it was here that the judge had to examine and rely on the expert opinions. As I have said, Mr Bridle said that a reasonably careful surgeon had to examine the rim very carefully at each stage when he had a view of it. Mr Cain did not disagree with that. Mr Bridle said that the surgeon should not make a cut into an extrusion that he could not clearly visualise and if he could not see the whole of an extrusion, he should ascertain its extent and pull it out, rather than cutting what he could see and letting go of the hidden part. Mr Cain did not disagree with the proposition that the surgeon should not make a cut where he could not see but he did not deal fully or really at all with what the surgeon should do if faced with a piece of cement which extended partly below the soft tissues. He did say that one might do more harm than good by pulling out an extrusion which had become lodged in the soft tissues. Mr Bridle did not disagree with that but thought that such occasions would be rare and that an attempt to lift and remove the hidden part should be made. In any event that dispute was not relevant as Mr Mughal had not been faced with the dilemma of what to do about a hidden piece of cement; he had never been aware there was one. Neither expert sought to support the idea that a surgeon should just cut off the extrusion and allow the hidden section to fall away.
46. Accordingly, the areas of dispute which the judge had to decide were very small. Mr Mughal had cut the extrusion without realising it; he said he had been very careful in his examination of the rim. Mr Bridle said that a surgeon should not cut where he could not clearly see what he was doing; if Mr Mughal had used his curette to cut cement underneath the pusher where he could not see properly, that would be substandard technique. If he had cut the cement after the pusher had been removed, he ought to have seen and examined it before cutting. It seems to me that the judge cannot possibly be faulted for holding that, if Mr Mughal cut the cement after he had put down the pusher, he cannot have looked at it properly; if he had he would have realised that it extended below the tissues. One way or the other, Mr Mughal had failed to meet the standard to be expected.
47. In my view, the judge was entitled to form an unfavourable view of Mr Mughal's failure to deal with the issues surrounding the retention of extruded cement in his witness statement (saying only that he had 'removed any extruded cement') and claiming by way of explanation for this failure that he had not realised that he was expected to give a detailed account of what had happened. To my mind, it is most surprising that a consultant surgeon, in receipt of legal advice, would not realise that he was supposed to give a detailed account of the operation in his witness statement which was prepared at a time when the issues in the case were clear. The result was that Mr Mughal could not provide any detail about what he had done at the time. Indeed, he seemed never to have thought about the detail of what had happened until he was in the witness box. In my view, it is unfortunate that he did not write an addendum to his first operation note after he had performed the second operation and knew that a large (and damaging) piece of cement had been retained. But he did not and it is not surprising that the judge was unimpressed by his evidence.
48. For these reasons, I would reject all those grounds of appeal by which it is contended that the judge's decision was wrong on the evidence. That leaves only the argument that the trial was unfair due to a serious procedural irregularity. Mr Thomas submitted that Mr Mughal had not had the opportunity to deal with the allegation that he had negligently cut the cement extrusion at a time when he did not have a complete view of the rim because of the presence of the pusher. This, submitted Mr Thomas, was a different allegation from saying that he had failed to look carefully enough for cement which was there to be seen.
49. I would reject this ground of appeal. First, Mr Mughal's function was that of witness of fact. He was there to describe what he had seen and done. He was not there in the capacity of an expert whose function it was to give an opinion on breach of duty. So, strictly speaking, it would not have been proper to ask Mr Mughal whether or not it would be negligent if he had cut the cement while using the pusher. I would accept that, in clinical negligence cases, where the person criticised often has a high degree of expertise, this distinction can become blurred. But it cannot be a serious procedural irregularity not to put to a witness of fact that a particular action amounted to substandard practice.
50. It is true that, after he had admitted that he must have cut the cement, Mr Mughal was not asked at what stage he had done so and whether he had done so while his view was restricted by the pusher. The judge found that he might have cut the cement at that stage or he might have done it later, after he had finished with the pusher. I do not see how any criticism could be made of Mr Richard Seabrook who appeared for the claimant below for not asking that question. It was only at a late stage of cross-examination that Mr Mughal made the admission that the cement had fallen away while he was using his curette. Even then, it was only in re-examination that he admitted that the only logical explanation was that he must have cut the extruded cement. The person best placed to ask any questions supplementary to that answer was Mr Thomas himself. But I can understand why the point was not pursued. It was clear that Mr Mughal did not know that he had cut the cement and I can see little point in asking him whether he had done that while he was using the pusher or afterwards. He would not know.
51. In my judgment, this case was conducted thoroughly and fairly and there was no procedural irregularity at all, let alone one which could undermine the fairness of the process.
52. For those reasons, I would dismiss this appeal.

Lord Justice Underhill:

53. I agree.

Lord Justice Dyson:

54. I also agree.