The crumbling skull rule is a well-established

legal doctrine A legal doctrine is a framework, set of rules, procedural steps, or test, often established through precedent in the common law, through which judgments can be determined in a given legal case. A doctrine comes about when a judge makes a ruling ...

used in some

tort law A tort is a civil wrong that causes a claimant to suffer loss or harm, resulting in legal liability for the person who commits the tortious act. Tort law can be contrasted with criminal law, which deals with criminal wrongs that are punishabl ...

systems. It holds that where a plaintiff had a condition or injury that predates the tort and would have naturally deteriorated or worsened over time (e.g. a crumbling skull), the defendant is not responsible to the degree that the condition or injury would have naturally worsened over time. A defendant is only liable for the degree the injury was worsened or the hastening or acceleration of the damage caused by the tort. The crumbling skull rule should not be confused with the related thin skull rule. The concept is sometimes applied without specific reference to the crumbling skull rule, instead being expressed as a non-absolute application of the thin skull rule.

References

{{Law-stub Tort law Legal doctrines and principles