Some aspects of litigation are highly reliant upon experts.  Medical causation is on of those areas.  The issues between experts should be clarified in the joint statement.  In Smith -v- Tesco PLC & Royal Free London NHS Foundation Trust [2016] EWHC 3252 (QB) David Pittaway QC considered a case in which an expert raised a new theory after the joint report. The late advancement of a new theory is rarely helpful to a party seeking to prove matters at trial.

The late advancement of this opinion is, in my view, very unsatisfactory and if a live issue should have been considered at a much earlier stage and permission sought to rely on urology evidence. It defeats the purpose of exchange of expert evidence and joint discussions between experts if experts raise new theories shortly before trial.”


The claimant was injured at work. One of the issues before the court was causation: the extent to which the accident caused an injury to the claimant’s back.


The judge commented on the differences between the doctors and the production of the joint medical report. There was, however, a subsequent development with a new theory being advanced by the doctor instructed on behalf of the defendant.

  1. The joint statement agreed that Mr Smith had symptoms of low back pain with radicular features affecting the left leg prior to the accident in 22ndMarch 2011 consistent with posterolateral disc protrusion. They are agreed that Mr Smith’s “onset of symptoms of severe low back pain and subsequent symptoms of cauda equina with an acute onset with rapid progression following the index event, are in keeping with [Mr Smith] having suffered a sequestered fragment at the time of the index event.”. They are agreed that the entries in the hospital records are contradictory and required clarification. No further witness evidence has been provided. Otherwise they maintained their respective positions on causation set out in their reports. There is no mention of urinary retention in the joint statement.
  2. Shortly before trial Mr Porter produced a further report in which he continued to maintain that the Mr Smith was already in the cauda equine syndrome before the accident on 22nd March 2011. His opinion, however, was based upon a new hypothesis, namely that the two episodes of incontinence after 0600 were in keeping with overflow incontinence and as a result Mr Smith had already entered cauda equine syndrome in retention some hours before the accident. He postulates that overflow incontinence will occur where patients have a bladder volume of 800-1000 mls some hours after the onset of bladder paralysis. He considers that it would take a number of hours to establish that level of urine. He considers that there would be distress at 400 mls of urine in the bladder and retention at 500 mls. He speculates that Mr Smith had a full bladder at the time of the index event. He defers to the opinion of an urologist but adds that a neurosurgeon is expected to recognise and manage immediate bladder problems associated with the condition. He considers that Mr Smith’s acute back pain immediately after the accident arose as a consequence of a further additional sequestered fragment of disc, which had no material effect on his outcome.
  3. Both experts are agreed that cauda equine is a very rare condition but that disc degeneration is very common as is disc prolapse. Mr Porter accepted that most people who suffer extrusion or sequestration do to not go on to develop cauda equine syndrome. He accepts that Mr Smith did not display symptoms until after the index event. Where he differs from Mr Sakka is his view that he developed urinary retention as a result of a sequestration of the disc before the accident, which was caused by another event or spontaneously to a vulnerable disc. He considers that the disc fragment move inferiorly compressed the central nerves at some point during the evening of 21st March 2011. He accepts that urinary retention is central to his opinion. He also accepts that at the time he prepared his first report urinary retention did not appear to him as central to the case. He also accepts that he has not met a case of this type in his clinical practice.
  4. After careful consideration I have preferred the evidence given by Mr Sakka to that of Mr Porter. The opinion in Mr Porter’s first report, in my view, is largely based on two factors that have turned out not to be correct, namely, the note made by the neurosurgical registrar at the Royal Free Hospital that Mr Smith was incontinent at midnight before the accident and his own history that Mr Smith was experiencing numbness in his buttocks at 0230. On any view the neurosurgical registrar’s note cannot be correct and must have been an incorrect transcription or relaying of the history that Mr Smith gave him. I have already concluded that Mr Smith probably incorrectly relayed his history to Mr Porter on 21st March 2015.
  5. There is no suggestion in Mr Porter’s first report that he considered that the Mr Smith was in urinary retention at the time of the accident. His opinion, as I think he recognises, is at the boundaries of his expertise when he gave evidence about the amount of urine that was required to be retained before it overcame the muscular controls of the body. The late advancement of this opinion is, in my view, very unsatisfactory and if a live issue should have been considered at a much earlier stage and permission sought to rely on urology evidence. It defeats the purpose of exchange of expert evidence and joint discussions between experts if experts raise new theories shortly before trial. It seems to me that Mr Sakka’s explanation is correct that by the time that Mr Smith’s urinary incontinence occurred the cauda equine syndrome was complete. There is an inescapable logic that when he went upstairs he was uncontrollably incontinent and once he had found the lavatory he was unable to pass urine because, at that time, there was no more urine to pass.


  1. In these circumstances I have reached the conclusion that Mr Smith, who was suffering from a vulnerable back, sustained a sequestered disc when the one or more wheels of the tug struck the sunken fire hydrant on 22nd March 2011. I reject the theory postulated by Mr Porter that Mr Smith was already in urinary retention by the time of the accident. There is nothing to suggest that he was suffering from red flag symptoms of cauda equine syndrome before the accident, or indeed, that he was unable to carry out his duties before that time. It follows that I am satisfied, on the balance of probabilities, that the accident caused Mr Smith’s cauda equine syndrome.”


Experts changing their minds

For another example of where an expert changed their minds after the joint report see:

Experts generally

The proving things series