To Crack or Crumble: Use of the Thin Skull and Crumbling Skull Rules

The psycholegal and medicolegal assessment of injury-related physical and psychological impairments and disabilities is fraught with difficulties, including assessing for physical and psychological risk factors. In the injury litigation context, in Canada, issues related to pre-injury physical and psychological risk factors are best captured by the thin skull and crumbling skull rules. A review of court cases in which these rules have been considered suggests that the rules are not applied consistently. This inconsistency in the application of these rules has contributed to conflicting determinations of cause and damages across trial court, appeal court, and Supreme Court cases. This article provides operational definitions of the thin skull and crumbling skull rules, presents a case that involves a series of court decisions that exemplify the difficulties associated with the application of these rules, and provides recommendations for more effective application of the two rules.