You had a bad back before the crash. Maybe you managed it with physical therapy, an occasional muscle relaxer, or a few careful stretches each morning. You could still work, drive, and pick up your kids.
Then another driver hit you, and everything changed.
Now the pain wakes you up at night. Your doctor is talking about injections or surgery. And the insurance adjuster on the phone keeps returning to one question: “Didn’t you already have back problems?”
Many injured people hear that question and assume their claim is over before it starts. It usually isn’t. California law recognizes that people with prior injuries can be hurt worse than a healthy person in the same collision, and it does not let the at-fault driver off the hook simply because your body was already vulnerable.
What the “Eggshell Skull” Rule Actually Means
The name comes from an old law school example. If someone carelessly taps a person on the head, and that person has an unusually thin skull, the careless party is responsible for the serious injury that follows. They cannot argue that a “normal” person would have walked away with a bruise.
California courts have applied this idea for decades. A California appellate court put it plainly in Rideau v. Los Angeles Transit Lines (1954): the person who causes harm “takes the person he injures as he finds him.”
Today, two standard California civil jury instructions carry this principle into the courtroom.
| Instruction | What it tells the jury | What it means for you |
| CACI No. 3927, Aggravation of Preexisting Condition or Disability | You cannot recover for the condition you already had. If the defendant’s wrongful conduct made that condition worse, the jury must award damages that reasonably and fairly compensate you for that worsening. | You are not asking to be paid for your old back problem. You are asking to be paid for what the crash did to it. |
| CACI No. 3928, Unusually Susceptible Plaintiff | The jury must decide the full amount of damages caused by the defendant, even if you were more vulnerable than a healthy person and even if a healthy person would not have been hurt the same way. | The other driver cannot reduce your claim by arguing that a younger or healthier person would have been fine. |
Read together, these instructions draw a clear line. Your prior condition is not compensable. The harm the crash added to it can be.
That line sounds simple. In practice, it is where most of the fighting happens.
Sources: CACI No. 3927 (2026 ed.); CACI No. 3928 (2026 ed.)
How Insurance Companies Use Your Medical History Against You
An insurance adjuster’s job is to limit what the company pays. When an adjuster sees a prior back injury in your file, they often see an opportunity to argue that your current pain has nothing to do with their driver.
Here are the tactics injured people commonly encounter.
- “It’s all degenerative.” Many adults show some disc degeneration, bulging, or arthritis on an MRI, even if they never felt symptoms. Adjusters frequently point to these findings and claim your pain is simply the natural result of aging.
- “You were already hurt.” If you treated for back pain years ago, the insurer may argue that your current symptoms are a continuation of that old problem rather than a new injury.
- Requests for your entire medical history. An adjuster may ask you to sign a broad medical authorization that reaches back many years and covers unrelated conditions. This gives them more material to search for anything they can use.
- Recorded statements. Early in the claim, an adjuster may ask you to describe your health on the record. A casual comment like “my back has always been bad” can later be quoted to downplay the crash.
- Gaps in treatment. If you waited weeks to see a doctor, or stopped going to physical therapy, the insurer may argue that the crash did not hurt you much or that something else caused your symptoms.
- Low initial offers. Some insurers make a quick offer that only accounts for a short flare-up, hoping you accept before the full extent of your injury is clear.
None of these arguments automatically defeats your claim.
They do mean you should expect your medical history to be examined closely. The stronger your evidence of the difference between your life before and after the crash, the harder these arguments become to sustain.
How You Prove the Crash Made Things Worse
The central question in an aggravation claim is a comparison. What was your condition right before the crash, and what is it now? Your claim generally depends on showing that difference with evidence, not just your own description.
Aggravation can look different from person to person. Some people had steady, manageable pain that became severe. Others had a condition that showed up on old imaging but caused few or no symptoms until the collision. In both situations, the focus stays on the change.
Your Medical Records From Before the Crash
This surprises many clients. Your prior records can help you.
If your records show that your back pain had stabilized, that you finished treatment, or that you had not seen a doctor for it in a long time, they help establish your baseline. They show where you were before the collision.
Your Medical Records After the Crash
Post-accident records show what changed. Helpful details often include:
- New symptoms, such as pain radiating into your legs, numbness, or weakness
- New or different findings on X-rays, MRIs, or CT scans compared with older imaging
- A change in treatment, such as moving from occasional therapy to injections or a surgical consultation
- Your doctor’s notes describing how the crash affected your condition
Medical Opinions
In many aggravation cases, a physician’s opinion carries significant weight. A treating doctor or retained medical expert may compare your before and after records and explain whether, and how, the crash worsened your condition. Your attorney can help determine whether this type of opinion is needed in your case.
Evidence of Your Daily Life
Medical charts do not always capture how an injury changes your routine. Other evidence can fill that gap:
- Work records showing missed days, reduced hours, or changed duties
- Statements from family, friends, or coworkers who saw the difference
- Photos or videos of activities you could do before the crash
- A pain journal you keep after the accident
Honesty matters most here. Be truthful about your prior condition with your doctors and your attorney. Hiding a past injury can damage your credibility far more than the injury itself.
Steps to Protect Your Claim if You Had a Prior Injury
You cannot change your medical history. You can control how well your current injury is documented.
- Get medical care promptly. See a doctor as soon as possible after the crash, even if you think the pain is “just your old back acting up.” Prompt care creates a record that ties your symptoms to the collision.
- Tell your doctor about your prior condition. Explain what your back felt like before the crash and what feels different now. Specific comparisons, such as “I could walk two miles before, and now I can’t get through a grocery store,” give your provider useful information to record.
- Follow your treatment plan. Attend your appointments and therapy sessions. If you need to stop or change treatment, talk with your doctor and make sure the reason is noted.
- Be careful with the other driver’s insurer. You generally do not have to give the at-fault driver’s insurance company a recorded statement. Consider speaking with an attorney before you give one or sign any medical authorization.
- Gather your older records. Identify the doctors, chiropractors, or therapists who treated your prior injury. Those records help establish your baseline.
- Watch what you post online. Insurers may review social media. A single photo can be taken out of context to suggest you are not hurt.
- Talk to a personal injury attorney early. An attorney can help you collect the right records, communicate with the insurance company, and evaluate whether medical opinions are needed to support your claim.
What the Rule Does Not Do
The eggshell skull rule protects you. It does not end the debate over your injuries.
The defense may still argue that part of your current condition would have developed anyway, even without the crash. They may also hire their own doctors to review your records and offer a different view of what caused your symptoms. These disputes over how much harm the crash added are often where aggravation claims are won or lost.
That is why careful documentation and an early legal review matter so much. Every case turns on its own medical history and evidence, and no rule makes the outcome automatic.
Don’t Wait Too Long to Act
California sets firm deadlines for injury claims.
- Most personal injury lawsuits must be filed within two years of the injury under California Code of Civil Procedure section 335.1.
- If a government entity may be responsible, such as a city vehicle or a dangerous public road, a written claim generally must be presented within six months of the injury under Government Code section 911.2, well before the two-year lawsuit deadline.
Exceptions and special rules can change these timelines. An attorney can review the specific dates in your case.
Missing a deadline can bar your claim entirely.
Talk With a California Injury Attorney About Your Prior Condition
A prior injury does not erase your right to seek compensation. It does mean your claim will likely face extra scrutiny, and the insurance company will be prepared for that fight.
You deserve someone prepared for it too.
If a car accident made an old back injury, neck problem, or other condition worse, our team can review your medical history, explain how California’s aggravation rules may apply, and help you explore your options. Contact us today for a free, confidential consultation. There is no obligation, and you can get answers specific to your situation.
This article provides general information about California law and is not legal advice. Reading it does not create an attorney-client relationship. Every case depends on its own facts.