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(602) 345-1818If you had a bad back, a prior concussion, or arthritis before your crash, the other driver’s insurance adjuster is already building a defense around it. Here is what most people do not realize: a preexisting condition does not disqualify a preexisting condition car accident claim in Arizona. Under Arizona law, it can actually expand the damages you are entitled to recover. This article walks through the eggshell plaintiff rule, the difference between aggravation and a new injury, how doctors prove causation, the medical-record traps adjusters set, and the deadlines that still apply. It fits into the broader picture of how Arizona car accident claims work.
You can recover for a car accident injury in Arizona even if the same body part was already damaged, degenerative, or symptomatic before the crash. What Arizona law compensates is the change the crash caused. If your neck hurt sometimes before the wreck and now it hurts every day and radiates into your arm, the delta is the claim. If you had a herniated disc that was quiet and the crash made it symptomatic and surgical, the crash-related worsening is compensable.
The insurance adjuster wants you to believe the opposite. That is a claim-value tactic, not a statement of Arizona law.
Arizona follows what is commonly called the eggshell plaintiff rule. The rule is simple: a defendant takes the plaintiff as they find them. If the person you rear-ended happened to have a fragile neck, a prior fusion, or a history of concussions, you are still liable for the full extent of the harm you caused, even if a perfectly healthy person would have walked away with a stiff neck for a week.
This is standard black-letter tort doctrine in Arizona and appears in the Revised Arizona Jury Instructions (Civil) on personal injury damages. Juries are told, in substance, that a defendant is responsible for aggravation of a preexisting condition, not just for injuries a hypothetical average person would have suffered.
Practically, that means three things for a Phoenix car accident case:
People confuse the eggshell rule with Arizona’s comparative negligence rule. They do different work.
Comparative fault (A.R.S. § 12-2505) reduces your damages by whatever percentage of the crash was your fault. If you are 20% at fault, your recovery is reduced by 20%.
The eggshell rule has nothing to do with fault. It says that being physically more vulnerable to injury does not reduce your damages at all. You do not get docked because your spine was already worn down. Those are separate doctrines, and adjusters sometimes blur them on purpose.
There are two distinct compensable categories in a preexisting-condition case, and treating clinicians need to document which one applies:
1. Aggravation or acceleration of a baseline condition.
You had degenerative disc disease at C5-C6. It was there, visible on imaging, occasionally sore. The crash made it symptomatic, worse, or surgical earlier than it otherwise would have become. That is aggravation.
2. A new injury superimposed on the same body region.
You had degenerative disc disease at C5-C6. The crash caused a fresh herniation at C6-C7 that was not there before. The new herniation is a new injury, even though it is in the same neck.
Both are compensable. But they document differently, they get valued differently, and they defend differently. A clean chart will say something like: “Patient has known multilevel degenerative disc disease. Post-crash imaging demonstrates a new C6-C7 herniation not present on prior 2022 MRI, along with acute worsening of preexisting C5-C6 symptoms.” That sentence is worth real money because it separates the two categories.
This is also where delayed injury symptoms after a crash become important. Aggravation cases often present with a slow escalation. The neck was manageable the day of the crash, then locked up over 72 hours, then radiated down the arm at week two. That timeline is normal, and it is documentable, but only if you are actually seeing providers and reporting symptoms as they emerge.
Prior medical records are not the enemy. They are the baseline. Without them, you have no way to prove what changed.
Here is the structure that wins these cases:
The National Highway Traffic Safety Administration’s Special Crash Investigations program uses a similar methodology. Its investigators combine crash-scene evidence, vehicle inspections, event data recorder downloads, interviews, and medical records to reconstruct what a specific crash actually did to a specific person (NHTSA, Special Crash Investigations, https://www.nhtsa.gov/research-data/special-crash-investigations-sci). The logic translates directly to preexisting-condition claims: you compare pre-event data to post-event data and attribute the difference to the crash mechanism.
If your only prior imaging is from 2019 and you had a lot of life between then and the wreck, that is fine. It still anchors the timeline. What you do not want is to walk into a case with no prior records at all and no clear story about what your baseline was.
Arizona law requires you to prove the crash was a substantial factor in worsening your condition. That is a causation question, and it is answered primarily by treating physicians and, in litigated cases, retained medical experts under Arizona Rules of Evidence 702.
A causation opinion in a preexisting-condition case usually addresses:
Physicians who treat car accident patients regularly know how to write these opinions. Physicians who do not may write vague notes that hurt the claim without meaning to. Part of what a lawyer does in a preexisting-condition case is make sure the treating clinician understands what needs to be in the record.
MRI reports on adults over 35 are full of things like disc desiccation, mild bulging, facet arthropathy, and small osteophytes. Federal medical resources on spinal cord and back conditions describe these degenerative findings as common in the general adult population, often present in people who have no symptoms at all (National Library of Medicine, Spinal Cord Injuries, https://medlineplus.gov/spinalcordinjuries.html). The legally meaningful question is not whether degenerative changes exist. It is whether the crash converted asymptomatic findings into a symptomatic injury, or made an already symptomatic condition materially worse.
An adjuster who points at a 2018 MRI and says “see, it was already there” is describing a finding, not a symptom. Findings and symptoms are different things.
Patterns we see repeatedly:
A prior concussion is one of the more important preexisting conditions to disclose. The Centers for Disease Control and Prevention’s guidance on mild TBI and concussion notes that people with a history of prior concussions can face a higher risk of injury from a subsequent head impact and can have longer, more prolonged recovery from a later mild TBI (CDC, About Mild TBI and Concussion, https://www.cdc.gov/traumatic-brain-injury/about/index.html). If you have any concussion history, tell your doctor and get a careful post-crash cognitive evaluation. This is covered more fully on our page about traumatic brain injury after a crash.
Getting evaluated is not being dramatic. It is protecting a real medical issue and, secondarily, protecting the record.
The adjuster script is predictable. It goes roughly:
The counter is not to hide anything. The counter is a documented before-and-after: baseline function vs. post-crash decline, with treating-provider opinions tying the change to the crash mechanism.
This is one of many reasons to be careful about recorded statements to insurance adjusters. A recorded statement given before you have thought carefully about your prior treatment history is where people accidentally minimize old injuries (“nah, my back was fine”) or overstate them (“yeah, my back has always been bad”), and either version gets used against them later.
Rule of thumb: tell your lawyer everything, and tell your treating providers everything. Concealment discovered later can destroy a case that would otherwise have been strong.
Adjusters and defense lawyers have access to broad medical databases and prior-claim indexes. If you had a workers’ comp claim for the same shoulder five years ago and you did not mention it, they will find it. When they do, your credibility on every other issue in the case takes a hit, even the issues where you are completely right.
Full disclosure works the other way too. When your attorney knows the whole history, the demand package can address the preexisting condition head-on, frame the aggravation properly, and take the wind out of the defense’s argument before they make it. This is basic case-preparation work, and it is dramatically easier when the client is not editing their own medical history on the way in.
When the other driver’s insurance company sends you a medical authorization, read what it says. Many of the forms adjusters send are effectively unlimited: any provider, any records, any time period, for any reason.
You do not have to sign that. The scope of a medical authorization should generally be limited to:
HIPAA generally allows patients to limit the scope of an authorization. Adjusters know this, and they still send the broad version by default. This is one of the more common places car accident claims quietly leak information that gets used against the claimant later.
A preexisting-condition case is still a personal injury case, and Arizona’s personal injury statute of limitations applies: 2 years from the date of the crash to file a lawsuit (A.R.S. § 12-542).
A common misconception: because the aggravation of a preexisting condition may take months to become clear, some clients assume the clock does not start until treatment escalates. In most cases, that is wrong. The clock generally runs from the crash date. If you spend 18 months in conservative treatment before it becomes clear you need surgery, you have burned most of your window without realizing it.
There are narrow exceptions and there are separate rules for claims against government entities, but the safe planning assumption is: 2 years from the crash, and start early. Specific deadlines depend on the facts of your case and should be verified with a lawyer.
Yes. Assume they will. They pull medical records, prior-claim indexes, and sometimes prior litigation. That is why full disclosure to your own attorney at the start of the case is the safer play.
Not automatically. Under Arizona’s eggshell plaintiff rule, the defendant is responsible for the full extent of the aggravation the crash caused. The valuation question is how much the crash changed your baseline, not whether you had a baseline.
Then your baseline is functional. If you were living, working, and doing your normal activities without treatment, and now you cannot, that is documentable through your work history, your family, and your post-crash treatment. Lack of prior treatment is not fatal to the claim.
Yes. Same body part is the most common preexisting-condition scenario. What matters is whether the crash aggravated the existing condition or produced a new injury in the same region. Both are compensable, and clinical records need to distinguish which is which.
Read it first. Broad, unlimited authorizations are common and are usually overreaching. You generally have the right to limit the scope to the body regions and time frames actually relevant to the claim. Talk to a lawyer before signing anything unlimited.
Almost never. The Arizona personal injury statute of limitations generally runs from the date of the crash under A.R.S. § 12-542, even if the aggravation of the preexisting condition takes months to become fully clear. Do not wait to see how bad it gets before consulting a lawyer.
A preexisting condition is not a reason to accept a lowball offer, and it is not a reason to sign a broad medical release. It is a reason to make sure the record is built correctly from the start.
Free case review: (602) 345-1818. We answer 24/7. No attorney’s fees unless we recover (case costs and fee terms depend on the written agreement).
By Jared J. Pehrson | Impact Legal Car Accident Attorneys