Causation is the second element a plaintiff must prove in an Ontario medical malpractice claim, after standard of care and before damages. The plaintiff must show that the defendant’s negligence caused the injury, ordinarily by satisfying the “but for” test: but for the negligent act or omission, the injury would not have occurred. The Supreme Court of Canada confirmed this approach in Clements v Clements, 2012 SCC 32, [2012] 2 SCR 181, while recognizing a limited “material contribution to risk” exception in narrow circumstances.
In medical cases, causation is often the most contested element. A plaintiff who proves a clear breach of the standard of care may still lose at trial if expert evidence cannot bridge the gap between the breach and the injury. Lost-chance arguments, delayed-diagnosis fact patterns, and cases involving multiple potential causes raise some of the hardest causation questions in Canadian tort law.
Posts tagged Causation analyze how Ontario courts have approached these issues across obstetrical, oncology, emergency, and surgical fact patterns, including appellate decisions that shape how trial judges instruct themselves on the test.
A settlement on behalf of a 40-year-old woman whose hysterectomy was described as uncomplicated but resulted in injuries to both ureters and chronic disability.
A 17-day birth injury trial. Battery, informed consent, five negligence allegations, and causation all addressed and rejected. A multi-ground defence dismissal.
The Court of Appeal affirmed plaintiff causation in a stroke malpractice case, holding that defendants cannot rely on evidentiary gaps their own negligence created.
A settlement on behalf of a woman in her 60s whose family physician dismissed three years of GI symptoms despite a known family history of colon cancer.
The Court of Appeal affirmed a $12 million plaintiff verdict for catastrophic maternal brain injury, rejecting the defence theory of amniotic fluid embolism.
A failed obstetric epidural with a fractured needle did not prove substandard technique. The British Columbia court rejected outcome-based reasoning on both grounds.
The Court of Appeal affirmed the dismissal of a medical negligence claim alleging failure to report child protection concerns. The causation chain failed at multiple links.
A delayed Lyme disease claim against two Ontario physicians dismissed on multiple grounds, including the most fundamental: the plaintiff failed to prove he had Lyme disease.
Composite card pairing the Medico-Legal Society of Toronto crest with the title Causation in Systemic Medical Negligence, on Paul Cahill’s navy brand panel.
An Ontario orthopaedic surgeon was found liable after removing clavicle hardware six weeks early without revisiting his own documented treatment plan.
A young mother left in a permanent vegetative state after C-section. The court found anesthesiology negligence but accepted that an amniotic fluid embolism was the unavoidable cause.
On December 1, 2023, the Ontario Superior Court of Justice dismissed a medical malpractice lawsuit brought by a young woman who suffered a stroke after taking birth control medication provided by her family physician who allegedly failed to advise her of the increased risk of stroke associated with that particular brand of birth control pill (Yaz).
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