Pre-Existing Conditions and California Workers' Compensation

What does California law actually say about pre-existing conditions?

Pre-existing conditions do not bar a workers' comp claim, but the insurer can argue apportionment to reduce the permanent disability award by the non-industrial share.

California workers' compensation does not require an injured worker to be in perfect pre-injury health. The no-fault liability rule under California Labor Code §3600 applies regardless of the worker's medical history: an injury that arose out of and in the course of employment is compensable, even if the worker had prior conditions that made the body part vulnerable. The question is not whether the worker was perfectly healthy before, it is whether the work injury caused new disability or aggravated an existing condition.

What pre-existing conditions can do is reduce the permanent disability award through apportionment. Apportionment under California Labor Code §4663 lets the insurer attribute part of the worker's final permanent disability to non-industrial causes, aging, prior injuries, genetics, pre-existing degenerative changes, or other unrelated medical conditions. The percentage attributable to those causes is deducted from the rating.

How does apportionment actually work in California?

The QME or AME assigns a percentage of the worker's permanent disability to non-industrial causes, and the indemnity award is reduced by that share.

Apportionment under California Labor Code §4663 is built on top of the AMA Guides 5th Edition impairment rating under California Labor Code §4660. The QME or AME under California Labor Code §4062.2 first assigns a whole-person impairment percentage based on the worker's current condition, then analyzes how much of that impairment is industrial and how much is non-industrial. A 30% permanent disability rating that is 40% apportioned to pre-existing degenerative disc disease drops to 18%. The dollar impact is significant, apportionment is the single largest place where insurers cut California cases.

The employer carries the burden of proof on apportionment

California Labor Code §4663 places the burden of proof on the employer. The insurer must produce substantial medical evidence, typically from the QME or AME, showing that part of the worker's current disability is attributable to non-industrial causes. Vague references to "degenerative changes" or "aging" are not substantial medical evidence; specific clinical reasoning is required.

The Brodie rule on asymptomatic findings

The California Supreme Court held in Brodie v. WCAB (2007) that asymptomatic pre-existing imaging findings, alone, are a weak basis for apportionment. The relevant question is whether the worker was symptomatic before the work injury, not whether the MRI shows abnormality. Most adults over 35 have some degree of degenerative findings on lumbar or cervical imaging; the law does not allow an insurer to use those findings to apportion away the case absent evidence that the findings were producing symptoms or limitation before the injury.

Combination injuries and aggravation

When a work injury aggravates a pre-existing condition, the worker is entitled to compensation for the entire current disability, but apportionment can deduct the portion attributable to the pre-existing condition. The math depends on whether the pre-existing condition was symptomatic before the work injury and whether the work injury caused new functional limitations beyond what the worker had before.

What kinds of pre-existing conditions actually come up in California cases?

Prior back surgery, old knee injury, degenerative disc disease, prior workers' comp claims to the same body part, and arthritis are the most common triggers.

The most common categories are spine conditions (degenerative disc disease, prior disc herniations, prior fusions, spondylosis); joint conditions (osteoarthritis, prior shoulder or knee surgeries, meniscal degeneration); psychiatric conditions (prior depression, anxiety, PTSD diagnoses); cardiac and metabolic conditions (hypertension, diabetes, prior heart events); and prior workers' compensation claims to the same or adjacent body parts. Each category has its own apportionment dynamics, and a specialist attorney prepares the medical record differently depending on what the defense is likely to argue.

How does a specialist fight unfair apportionment?

Challenging the substantial-medical-evidence basis, demanding specificity on percentages, and producing alternate medical opinions through a QME or AME report.

A specialist attorney challenges apportionment on five fronts. First, by selecting the right QME panel specialty under California Labor Code §4062.2, apportionment opinions vary widely by physician specialty. Second, by preparing the worker for the exam so the medical history accurately reflects pre-injury function (often the worker was working full duty without complaint and the defense argument collapses on that fact). Third, by submitting supplemental medical evidence showing the worker was asymptomatic pre-injury, coworker statements, pre-injury employment records, the absence of prior medical treatment for the body part. Fourth, by deposing the QME to expose apportionment opinions that rest only on imaging without symptomatic history (the Brodie rule). Fifth, by filing a Petition for Reconsideration within 25 days of service by mail (or 20 days from electronic service) under California Labor Code §5903 if a judge accepts a flawed apportionment at trial.

What about a worker who had a prior workers' comp claim to the same body part?

A prior claim does not bar the new case; apportionment may reduce the indemnity, but the worker still recovers medical care and the post-injury permanent disability share.

A prior workers' compensation claim to the same body part complicates the analysis but does not bar the new claim. Apportionment under California Labor Code §4663 can attribute part of the current disability to the residuals of the prior claim, based on the rating from that prior case. If the prior claim resolved by Compromise and Release, the medical care for that claim was closed out, but the new injury is fully compensable as a new claim. If the prior claim resolved by Stipulated Award, the worker may be able to petition to reopen for new and further disability under California Labor Code §5410 within five years of the prior date of injury, in addition to pursuing the new claim.

Related on yazdchilaw.com: California workers' compensation lawyer pillar · what to do if you can't go back to work after a workers' comp injury · what happens if the workers' comp judge mishears your testimony · can you keep workers' comp if you move out of state · California Labor Code §3600 explained.