Home > Case Summary > Case Summary – Cross Examination of an Expert – St. Marthe v. O’Connor, 2021 ONCA 790

Case Summary – Cross Examination of an Expert – St. Marthe v. O’Connor, 2021 ONCA 790

The Allowable Scope of Cross Examination of an Expert

The Court of Appeal provided some helpful guidance on expert evidence, and striking a jury, in the recent decision of St. Marthe v. O’Connor, 2021 ONCA 790.

The Plaintiff, Peter St. Marthe was injured in a motor vehicle accident on November 9, 2011.  He suffered soft tissue injuries that led to chronic pain and prevented him from working in the construction industry.  In 2019 the case went to trial, and the trial judge found in favour of the injured plaintiff.


Why did the Defendant Appeal the Trial Judgment?

The Defendant appealed on two issues.  The first dealt with the admissibility of expert evidence from one of the plaintiff’s accident benefits assessors.  As part of its case, the Plaintiff led evidence from an orthopedic surgeon, Dr. Mussett, who was retained by the AB insurer.  In cross-examination, defending counsel cross-examined Dr. Mussett in a manner that required him to comment on matters not contained within his report (and in particular, about his ability to work).  Plaintiff’s counsel objected to the questioning (which was upheld by the trial judge) and later brought a motion to strike the jury based on the prejudice suffered by the plaintiff in the eyes of the jury (the second issue on appeal).  The trial judge granted the motion and finished the trial as a judge sitting alone.


What was the Result at Trial?

The trial judge awarded damages to the plaintiff in the amount of $205,662 plus costs and disbursements.  The insurer appealed.


What was the Result at the Court of Appeal?

The appeal was dismissed. In dismissing the appeal, the Court of Appeal reaffirmed the following principles of expert evidence:

  • An expert retained by a party (i.e. a litigation expert) must, among other things, provide a report that sets out the expert’s opinion and anticipated testimony;


  • In this respect, litigation experts are different than non-party experts (i.e. experts not retained by a party but who have special skill, knowledge, training or experience to give opinion evidence as long as the opinion is given as part of their participation in the case and was disclosed to the other party);


  • If opinion evidence of a non-party expert goes beyond the witness’ participation in a particular case and was not formed while observing material events, that expert must comply with the requirements in Rule 53;


  • It is not an error for a trial judge to prevent a non-party expert from giving opinion evidence that goes beyond the expert’s participation and comments in their report if that opinion was not disclosed well in advance of trial; and


  • On top of the above principles, trial judges must still apply the White Burgess criteria for the admission of expert evidence.


How did the Court of Appeal Apply the Law to the Facts?

In this case, the Court of Appeal found that Dr. Mussett was never asked to assess the plaintiff’s ability to return to work.  Rather, for the first time at trial, defence counsel sought to elicit an opinion from Dr. Mussett that the plaintiff’s condition was not disabling.  Compounding this attempt was the fact that, by the time of trial, Dr. Mussett had not seen the plaintiff in four years and had not reviewed updated medical records. This all occurred on top of the fact that even when Dr. Mussett had originally seen the plaintiff he had only ever reviewed a few insurance forms regarding the plaintiff, and had seen no medical records whatsoever.  This meant that when he gave his evidence on cross-examination, his evidence on the plaintiff’s ability to work, therefore, was not only in violation of Rule 53, but its prejudicial effect far outweighed its probative value.


What about Striking the Jury?

On the second issue on appeal, the Court also upheld the trial judge’s decision to discharge the jury.  It reaffirmed basic principles concerning the striking of juries and that discharging a jury is a ‘drastic remedy’.  That said, it also agreed with the trial judge in this case that:


  • Mussett was an impressive witness whose evidence “would have had a significant impact” on the jury;


  • He was seen as a neutral non-party expert, who, at least in part, supported the plaintiff in other areas, which would have added to his credibility about the extent of the plaintiff’s disability and employability, thus compounding the effect of the inadmissible evidence;


  • There was no advance warning that the defendant would solicit opinions beyond the scope of his report. If she had given notice, a voir direwould have been held on the scope and admissibility of his assessment, and the trial judge could have given a mid-trial instruction;


  • His opinion evidence on cross-examination at trial that the plaintiff could work would have a serious adverse impact on the plaintiff’s central claim for income loss, based on his employability as a construction worker; and


  • If the trial judge gave a corrective instruction, it would have to be a strong one, and he would have to comment on the conduct of trial counsel for the appellant. This would be his second instruction about her conduct and might cast the counsel in an unfavourable light with the jury, causing the jury’s view of her for the balance of the trial to be unfairly compromised. The trial judge determined that granting a mistrial would cause significant delay.


On top of these factors, the Court highlighted the need to avoid trial by ambush and that defence counsel had previously been rebuked for conduct in front of the jury, making any further corrective instruction prejudicial to her.

In the end, the Court found that the trial judge properly exercised his discretion to strike the jury and dismissed the appeal.


About the Authors

Joseph Dart is a partner at Bergeron Clifford LLP. He graduated from Yale University in New Haven, CT., in 200. He graduated from Queen’s University Law School in 2005. Joseph joined Bergeron Clifford in 2015, and represents plaintiffs in negligence, medical malpractice and auto cases.

Joseph was called to the bar in 2006, and began his legal career as a crown prosecutor in the Crown Attorney’s Office, first in Scarborough, and later in Belleville, where he worked on various high-profile criminal cases. During his time with the Crown’s Office, Joseph litigated many cases in both the provincial and superior courts of Ontario.

Joseph and his family moved to Kingston and he joined a local firm in 2011, where he gained tremendous experience while practicing civil litigation in a variety of areas, including personal injury. Know More

Warren Whiteknight_headshot_Personal Injury LawyerWarren WhiteKnight is a Lawyer and Partner at Bergeron Clifford LLP. He is based in the firm’s Kingston office but travels throughout Eastern Ontario each week as clients’ needs require. He holds a Certified Civil Litigation Specialist designation by Law Society of Ontario.

Warren is a Queen’s Law graduate where he achieved top 10% standing all three years, and received numerous course prizes and scholarships. He has been the Past President of the Frontenac Law Association.

Warren regularly represents his clients in court and tribunal proceedings and has an excellent track record of achieving results both in court and in out of court settlements. Know More

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