Why prior conditions come up
Insurers routinely review medical history. If a person who was hurt in a crash had back pain years earlier, the insurer may argue that current symptoms are from the old problem, not the accident. The injured person may respond that the accident made a stable condition worse. Resolving that dispute is often a central issue in the claim.
Aggravation of a pre-existing condition
Many jurisdictions allow recovery when an accident aggravates (worsens) a pre-existing condition. The general principle is that the at-fault party is responsible for the additional harm they caused, but not for the condition the person already had. In practice, this means comparing the person’s condition before and after the accident: frequency of treatment, symptoms, work ability and daily activities.
Before a fall, Sam had occasional knee pain managed with exercise and saw a doctor once in two years. After the fall, imaging shows a new tear, Sam needs surgery and misses two months of work. Records showing the stable “before” and the changed “after” are what make the aggravation clear. If, instead, Sam had been scheduled for knee surgery before the fall, the analysis of what the fall added would be more complicated.
The eggshell plaintiff principle
A long-standing principle in tort law, often called the eggshell skull or eggshell plaintiff rule, is that a defendant “takes the plaintiff as they find them”. If someone is unusually vulnerable — for example because of a prior condition — and suffers a more severe injury than an average person would from the same incident, the at-fault party can be responsible for the full extent of the harm caused. This principle concerns the extent of harm once liability is established; it does not make the defendant responsible for the pre-existing condition itself. How it is applied, and how juries are instructed, varies by jurisdiction.
Apportionment
Where both the prior condition and the accident contribute to current symptoms, the parties may argue about how much of the harm (and the associated costs) to attribute to each. Some jurisdictions instruct juries to separate the two where possible; medical opinion is often decisive.
Disclosing medical history honestly
Concealing prior injuries is a serious mistake. Insurers can usually obtain prior records, and a claimant who denied a history that later appears in records may lose credibility for the entire claim. Accurate disclosure, together with records that show the change, is generally the stronger position.
Evidence that helps clarify the change
- Records from before the accident showing the frequency and nature of any treatment.
- Records after the accident showing new findings, new symptoms or increased treatment.
- A treating doctor’s explanation of whether and how the accident changed the condition.
- Work and activity records, and statements from people who saw the change.
The Evidence Checklist includes space to note which records exist. Keep detailed medical history out of web forms; the tool only needs general notes.
Sources and references
- Legal Information Institute: “Eggshell skull rule” (opens in a new tab) — the rule that a defendant takes the plaintiff as they find them
- Legal Information Institute (Cornell Law School): “Damages” (opens in a new tab) — general definitions of compensatory damages