by Victoria Tremblett March 12, 2022 3 min read

Personal injury cases, including those for medical negligence or malpractice, will almost always require the evidence of expert witnesses to determine damages. Often, the plaintiff(s) and defendant(s) will each retain their own experts to provide their opinion for the purpose of litigation.  However, in some cases, there may be neutral, non-party experts who may give opinion evidence while participating in the events at issue (e.g. treatment of the injured party).

What is Different About a Non-Party Expert?

Unlike a litigation expert who is retained by a party, a non-party expert does not have to provide a written expert report to be filed and served upon each party in advance of trial. This is because the non-party expert’s opinion is typically contained within the medical records or other documentation obtained in the course of the discovery process, so each party has advance notice of the expert’s opinion.

If, however, the non-party expert’s opinion goes beyond their observations and participation in the events, they will be required to provide a written report in accordance with Rule 53.03 just the same as a litigation expert. If the non-party expert fails to provide a report in accordance with Rule 53.03, they may be limited to providing oral evidence in relation to their original observations and opinions.

Recent ONCA Case Considering Non-Party Expert Evidence

The ONCA recently considered the law pertaining to the evidence of non-party experts in St. Marthe v O’Connor,2021 ONCA 790.  The underlying action to this appeal was for injuries sustained by the plaintiff construction worker when he was hit by a motor vehicle while riding his bicycle.

At trial, the plaintiff called Dr. Mussett, an orthopedic surgeon, as a non-party expert. Dr. Mussett had performed an assessment of the plaintiff approximately 4 years before trial, at the request of the plaintiff’s accident benefits insurer.

In his report, Dr. Mussett stated that the plaintiff’s ongoing right upper back and arm pain “resulted in the inability to perform expected duties at work without experiencing pain and discomfort.” Dr. Mussett’s report also stated that in his opinion, the plaintiff had “sustained an impairment as a direct result” of the accident, and that the plaintiff required additional treatment in order to decrease his pain and improve his strength and range of motion. However, his report did not contain any comment on the plaintiff’s ability to return to work as a construction worker.

In the course of cross examination by defence counsel, Dr. Mussett agreed that the plaintiff’s injuries were not disabling. The plaintiff took issue with this and brought a motion to discharge the jury, arguing that cross-examination was “seriously unfair, unexpected and elicited opinion evidence from Dr. Mussett on matters that were not included within his report,” which “irreparably damaged the [plaintiff’s] principal claim that he was no longer able to work in construction.”

The trial judge ultimately granted the order dismissing the jury and awarded the plaintiff damages in the amount of $205,662.23 at the end of trial. 

The Court of Appeal upheld the decision of the trial judge, noting that at no time prior to cross-examination was Dr. Mussett asked to opine on the plaintiff’s ability to return to work. Dr. Mussett’s report only stated that the plaintiff was unable to engage in strenuous activity without experiencing pain or discomfort. Dr. Mussett’s opinion regarding the plaintiff’s ability to return to work went beyond the scope of his previous observations and assessment of the plaintiff and was inadmissible. In coming to their conclusion, the Court highlighted the important policy to avoid trial by ambush.

The Court also noted that the probative value of Dr. Musset’s opinion evidence on this matter was minimal, as Dr. Musset was unaware of the plaintiff’s current condition, and had only conducted one assessment, over 4 years before trial. Moreover, it was quite prejudicial as it undermined the plaintiff’s principal claim for loss of income.

The trial judge was in the best position to assess the potential effect of Dr. Mussett’s testimony on the jury with respect to the plaintiff’s claim for loss of income. The Court of Appeal held that there was no reason to interfere with his determination that a caution to the jury would not suffice.

Takeaway From the Case

St. Marthe v O’Connor,2021 ONCA 790, demonstrates the strict limits of non-party expert testimony. In light of that, it is important that parties carefully assess the quality of non-party expert evidence well in advance of trial and determine whether litigation experts must be retained to supplement the non-expert evidence.


NOTE: A blog post is never a substitute for legal advice tailored to your situation. Wise Health Law represents professionals in a variety of proceedings, including civil litigation. 

To learn more about Wise Health Law and our services, please contact us!

Also in Blog

man consulting doctor for surgery
Greater Access to Gender-Affirming Surgery in Ontario

by Mina Karabit April 25, 2024 4 min read

The Divisional Court confirms the rights of transgender and non-binary individuals to receive funding for gender-affirming care that aligns with their non-binary experiences of gender.
Physiotherapy clinic
Regulated Health Professionals can be Held Accountable for Business Practices

by Mina Karabit April 20, 2024 2 min read

The Divisional Court confirms that Colleges can have jurisdiction to consider the business practices of regulated health professionals.
Two physicians discussing licence revocation due to conduct during COVID-19 pandemic
Conduct During the COVID-19 Pandemic Results in Licence Revocation

by Mina Karabit March 12, 2024 4 min read

CPSO revokes physician’s certificate of registration revoked based on findings he was unprofessional, incompetent and ungovernable during the pandemic.