Pre-Existing Conditions & the Eggshell Rule

You were already dealing with a bad back. Or an old neck injury. Or controlled diabetes. Then someone else's negligence made everything worse — and now the insurance company says your injuries are just "pre-existing conditions."

This is one of the most common—and most misleading—insurance company tactics. Oklahoma law is clear: defendants take plaintiffs as they find them. Your pre-existing condition doesn't let the wrongdoer off the hook.

The Eggshell Plaintiff Rule

The legal principle is called the "eggshell plaintiff" (or "thin skull") rule: a defendant is liable for all injuries caused by their negligence, even if the plaintiff was unusually vulnerable.

The Classic Example

If someone with a normal skull is struck and suffers a minor bruise, that's the injury. But if someone with an unusually thin skull (an "eggshell skull") is struck with the same force and suffers a devastating fracture—the defendant pays for the devastating fracture. You don't get to choose your victims.

How It Applies

In practice, this means:

• Prior back problems don't eliminate liability for aggravating those problems
• Pre-existing diabetes doesn't prevent recovery for delayed healing complications
• An old injury that was manageable doesn't give defendants a free pass when they make it unmanageable

Defendants take plaintiffs as they find them.

What Oklahoma Jury Instructions Say

Oklahoma juries are specifically instructed on pre-existing conditions. The standard instruction tells jurors:

If you find that the plaintiff had a bodily condition at the time of the [collision/incident] that made plaintiff more susceptible to injury than a normal person, and those injuries were aggravated or made worse by defendant's negligence, then defendant is liable for any aggravation and for any injuries that were directly and naturally caused, even though, without such condition, the consequences might have been less serious or might not have occurred at all.

In plain English: you can recover for making a bad situation worse. This instruction — drawn from the Oklahoma Uniform Jury Instructions for Civil Cases — is one of the most important principles in Oklahoma personal injury law. It's the legal foundation that prevents insurance companies from writing off your injuries as "pre-existing" and walking away.

Understanding how Oklahoma uses comparative negligence alongside this rule is also important. Under 23 O.S. § 13, your recovery may be reduced by your percentage of fault — but that fault calculation is about who caused the accident, not about your pre-existing vulnerability. Your comparative fault percentage has nothing to do with whether you had a bad back before the crash.

The "Aggravation" Framework

Damages for pre-existing conditions follow a straightforward analytical structure, even though proving them requires careful evidence-building.

The first step is establishing the baseline — what was your condition actually like before the incident? Were you working full-time? Could you handle daily activities without significant limitation? Was your pain controlled with routine treatment, or was it already debilitating? The answers to these questions define the starting point against which everything else is measured.

The second step is documenting what changed. After the accident, did you develop new symptoms or experience a dramatic increase in severity? Did you lose the ability to work, exercise, or care for your family? Was pain that had been manageable suddenly uncontrollable? Did your treatment regimen go from routine checkups to surgery, injections, or long-term physical therapy?

The final step is valuing the difference. The defendant owes you the gap between your baseline and your current condition — the aggravation, acceleration, or worsening caused by their negligence. If you were managing a back condition with occasional physical therapy and could work full-time, and after the accident you needed spinal fusion and can't work at all, the defendant doesn't get credit for the fact that your back wasn't perfect. They owe you for taking functional to non-functional.

Insurance Company Tactics

Defense attorneys and insurance adjusters have a playbook for pre-existing conditions:

"All Your Problems Are Pre-Existing"

The claim: everything you're experiencing now is just your chronic condition, not accident-related.

The reality: If you were functioning before the accident and aren't now, that change is compensable—regardless of prior conditions.

"You Didn't Disclose This"

The claim: you "hid" your pre-existing condition from doctors.

The reality: Emergency rooms ask about immediate symptoms, not complete medical histories. Failing to volunteer unrelated history doesn't undermine your claim.

"You Were Already Going to Need This Treatment"

The claim: the surgery, therapy, or treatment you needed was inevitable anyway.

The reality: Even if degeneration would have eventually required treatment, if the accident moved up the timeline, you can recover. Acceleration is compensable.

"You're Exaggerating"

The claim: your prior condition proves you're prone to complaining.

The reality: Having a documented medical history can actually help—it establishes what your baseline was and shows the change caused by the accident.

Building Your Case

Overcoming pre-existing condition defenses requires building a comprehensive evidentiary record that makes the before-and-after contrast undeniable.

The foundation is complete medical records — not just from after the accident, but from before it. You need records showing what treatment you were receiving, how frequently, what your symptom levels were, and whether you were improving or stable. These records establish the baseline that the insurance company is trying to blur. If you were seeing your doctor every six months for maintenance and suddenly needed weekly visits, injections, and surgery after the accident, those records tell a powerful story.

Equally important is comparative evidence that shows the contrast between your life before and after the incident. This includes function levels, pain severity, medication needs, and activity restrictions. If you were hiking, playing with your grandchildren, and working overtime before the accident — and now you can barely get through an eight-hour day — that transformation is the heart of your aggravation claim. Employment records, gym memberships, social media posts showing activity, and witness testimony from family and coworkers all help paint this picture.

Medical expert testimony ties the evidence together. Your treating doctors can explain how the accident aggravated your condition, why your current symptoms are categorically different from your pre-accident baseline, what portion of your current problems relate to the accident versus the underlying condition, and what your prognosis would have been without the crash. In complex cases, independent medical experts or life care planners may be needed to quantify the long-term impact.

Finally, credibility evidence counters the inevitable attacks on your honesty. Insurance companies will comb through your medical history looking for inconsistencies — a visit where you didn't mention pain, an activity they'll claim contradicts your reported limitations. Building credibility means maintaining consistent reporting across all providers, identifying witnesses who observed you before and after, preserving employment records that document your function levels, and keeping photos or videos that show what you could do before the accident that you can't do now.

Special Situations

Asymptomatic Pre-Existing Conditions

Sometimes imaging shows degenerative changes you didn't know about—a disc bulge or arthritis that wasn't causing symptoms. If the accident makes these silent conditions symptomatic, the full injury is compensable.

Conditions You Were Managing

If you were successfully managing a chronic condition and the accident undoes that management—requiring more treatment, causing flare-ups, making the condition uncontrollable—that's a compensable injury.

Mental Health Conditions

Prior anxiety or depression doesn't prevent recovery for accident-related psychological injuries. The aggravation of mental health conditions follows the same rules as physical conditions.

What Defendants Must Prove

Remember: you don't have to prove you were perfectly healthy. The defendant has to prove what portion of your injury is unrelated to the accident. That's their burden—not yours.

If they can't apportion damages, they may owe you everything.

We Handle Cases With Pre-Existing Conditions

Having a pre-existing condition makes your case more complex—but not weaker. Insurance companies use prior medical history to frighten people away from valid claims.

If you've been injured in an accident and you're hearing that your pre-existing condition disqualifies you, contact us for a free consultation. We'll explain how Oklahoma law protects you and build the evidence to prove your aggravation claim.

The strength of pre-existing condition cases often depends on what happens in the first 72 hours after the accident — establishing that baseline medical documentation early creates the before-and-after contrast that wins these cases. And understanding how much your case is worth requires a full picture of how the accident changed your life relative to your prior condition, which is why settling too quickly almost always undervalues aggravation claims.

Frequently Asked Questions

What is the eggshell plaintiff rule in Oklahoma?

The eggshell plaintiff rule — also called the "thin skull" rule — holds that defendants are liable for the full extent of injuries they cause, even if the victim was unusually vulnerable. If you had a pre-existing back condition and an accident made it significantly worse, the defendant pays for the full aggravation, not just what a "normal" person would have experienced.

Can the insurance company deny my claim because of a pre-existing condition?

No. A pre-existing condition does not bar recovery in Oklahoma. The insurance company may try to attribute your symptoms to prior problems, but the law entitles you to compensation for any aggravation, acceleration, or worsening caused by the accident. The defendant's burden is to prove what portion of your injury is unrelated.

What if I had a degenerative condition I didn't know about before the accident?

Asymptomatic pre-existing conditions — like a disc bulge or arthritis that wasn't causing symptoms — are fully protectable under the eggshell plaintiff rule. If the accident made a silent condition symptomatic, you can recover for the full injury. The defendant cannot escape liability by pointing to imaging findings you were unaware of.

How do I prove my injuries were aggravated by the accident?

The strongest approach is "before-and-after" evidence: medical records showing your baseline condition, your treatment history, your function level before the accident, and how all of that changed after. Your treating doctors can provide expert testimony explaining the difference between your pre-existing condition and the accident-related aggravation.

Does Oklahoma's comparative negligence reduce my recovery for pre-existing conditions?

No. Comparative negligence addresses fault for causing the accident (e.g., who ran the red light), not vulnerability to injury. Your pre-existing condition has nothing to do with fault allocation. Even if you bear some fault for the accident itself, that is separate from the eggshell plaintiff analysis.

What if the insurance company claims I was already going to need surgery?

Even if your condition would have eventually required treatment, the defendant is liable if the accident accelerated that timeline. This is called "acceleration of treatment." If you would have needed surgery in five years but now need it immediately because of the crash, the defendant owes you for the accelerated timeline and all associated costs.