Pre-Existing Conditions and the Eggshell Plaintiff Rule: Aggravation, Apportionment, and Your Rights

# Pre-Existing Conditions and the Eggshell Plaintiff Rule: Aggravation, Apportionment, and Your Rights

Insurance adjusters love to discover a pre-existing condition. The moment they find a prior back injury, an old surgery, or a history of arthritis, they often argue: "You were already hurt — this accident did not cause your problems." It sounds persuasive, and it scares many injured people into accepting far less than they deserve. But the law is squarely against this argument, thanks to one of the oldest and most plaintiff-friendly doctrines in tort law: the eggshell plaintiff rule.

This guide explains how pre-existing conditions interact with a personal injury claim, what the eggshell rule means, the difference between aggravation and pre-existing harm, and how apportionment works.

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The Core Principle: You Take Your Victim As You Find Them

A defendant who negligently injures someone is responsible for the full extent of the harm they cause, even if an ordinary person would have been hurt less. This is the eggshell plaintiff rule (also called the "thin skull" rule).

The classic illustration: if a defendant negligently strikes a person whose skull is as fragile as an eggshell, the defendant cannot escape liability by arguing that a normal person would have suffered only a bruise. The defendant must compensate for the actual, full injury — fractured skull and all.

Applied to real cases, this means:

• A minor collision that would barely bother a healthy 25-year-old but causes a serious herniation in a 60-year-old with degenerative disc disease is still **fully compensable**.
• A defendant cannot reduce damages merely because the victim was unusually susceptible to injury.

The rule reflects a simple policy choice: between the innocent victim and the negligent wrongdoer, the wrongdoer bears the risk of the victim's hidden vulnerabilities.

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The Critical Distinction: Aggravation vs. Pre-Existing Harm

The eggshell rule does not make a defendant pay for conditions they did not cause. The dividing line is aggravation.

• A defendant **is** liable for *aggravation* — the worsening, acceleration, or "lighting up" of a previously dormant or stable condition.
• A defendant **is not** liable for the pre-existing condition *itself*, only for the additional harm the accident caused.

So if you had mild, manageable arthritis before a crash and the crash makes it severe and disabling, the defendant owes you for the difference — the new pain, the new treatment, the new limitations — not for the arthritis you already had.

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Apportionment: Dividing the Harm

When a victim has a relevant prior condition, courts and juries may apportion damages — separating the harm caused by the accident from the harm that pre-dated it. The general rules:

• If the harm can be **reasonably divided**, the defendant pays only for the portion they caused.
• If the harm **cannot be divided** — for example, the accident and the prior condition combine into a single indivisible injury — many courts hold the defendant responsible for the **entire** result.

This indivisibility argument is powerful. If your treating physician cannot meaningfully separate the new pain from the old, the defendant may be on the hook for all of it.

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How Medical Evidence Wins or Loses These Cases

Pre-existing condition cases are won and lost on medical documentation and physician testimony. Key proof points:

1. **Baseline function.** Records showing you were working, active, and stable before the accident are gold. If you had not treated for the old condition in years, that supports aggravation.
2. **Change after the accident.** New symptoms, new imaging findings, or a new need for surgery demonstrate the worsening.
3. **A clear medical opinion.** Your physician should state, to a reasonable degree of medical probability, that the accident aggravated the prior condition.
4. **Honest disclosure.** Hiding a prior condition is the single biggest mistake an injured person can make.

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Why You Must Disclose Your History

The instinct to conceal a prior injury is understandable but disastrous. Defense lawyers routinely subpoena years of medical records. If you denied a prior back problem and the records prove otherwise, your credibility collapses — and credibility is often worth more than any single piece of medical evidence. Disclosing a prior condition and explaining the aggravation is far stronger than being caught hiding it.

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Practical Steps to Protect Your Claim

• **Tell your doctors the truth** about your full history and exactly how the accident changed things.
• **Tell your lawyer everything**, including conditions you think are irrelevant.
• **Gather pre-accident records** that show your prior baseline and function.
• **Keep treating consistently** so the worsening is documented.
• **Let your attorney frame the narrative** of aggravation rather than trying to minimize your history yourself.

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Pre-Existing Condition Claim Checklist

A pre-existing condition is not the end of your case — in the hands of a skilled attorney, the eggshell plaintiff rule turns the insurer's favorite argument into a losing one. The key is honesty, strong medical evidence, and a clear story of aggravation. If an adjuster is using a prior injury to devalue your claim, consult a licensed personal injury attorney in your state. Most offer a free consultation and can evaluate how the eggshell and apportionment rules apply to your situation at no upfront cost.