“A fighting force both consistent and compassionate on a scale’s a 5 all around.”
Rachael Hall
✦ Certified Specialist in Workers’ Compensation Law — Certified by the State Bar of California, Board of Legal Specialization ✦
Serving injured workers across California. Board-certified specialist; no fee unless we win.
By Eman Yazdchi, Esq. · Certified Specialist in Workers' Compensation Law, State Bar of California Board of Legal Specialization
In California, a pre-existing condition does not bar a workers' compensation claim — but apportionment under §4663 can reduce the permanent disability award by the percentage attributable to non-industrial causes. The employer carries the burden of proof. Yazdchi Law, a Certified Specialist in Workers' Compensation Law firm, fights apportionment. Request a free case review.
One of the most common ways California workers' compensation insurers reduce a claim's value is by pointing at a pre-existing condition — a prior back strain a decade ago, an old shoulder X-ray showing arthritis, a known psychiatric history, a previous accident that left lingering symptoms. The insurer argues that some percentage of the worker's current disability comes from those non-industrial sources rather than the work injury, and the award gets cut accordingly. This is apportionment, and it is one of the most contested issues in every California permanent disability rating.
This guide walks through how California treats pre-existing conditions under workers' compensation, what apportionment actually is, the leading case law that limits the defense, and how a specialist attorney fights flawed apportionment to keep the worker's award intact. It is written for a worker whose QME report has just come back with a 40% apportionment number and who is trying to understand whether that number is fair.
The short version: California law does not let an insurer cut the case just because an MRI shows degenerative findings. The relevant question is whether the worker was symptomatic before the work injury — and that is a question the employer has the burden of proving.
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.
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.
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 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.
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.
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.
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.
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.
Injured at work? Call (661) 273-1780
Tap to call →A QME apportionment finding is not the end of the case — it is a number to challenge. The worker has time to supplement the record, depose the QME, and litigate the apportionment at trial. The three priorities are documentation, medical-record supplementation, and a free consultation with a specialist.
The single strongest defense to apportionment is contemporaneous evidence that the worker was symptom-free and working full duty before the injury. Pre-injury performance reviews, coworker statements, the absence of prior medical treatment for the body part, regular fitness or recreational activity records — each piece supports the Brodie argument that pre-existing imaging findings alone are not a basis for apportionment. The history must be honest; a misrepresented history can damage the case worse than the apportionment itself.
The QME's first report is often the version most favorable to the defense — particularly on apportionment. Supplemental reports, depositions, and AME reviews routinely move the apportionment percentage down on the same underlying facts. A settlement built on the first report leaves money on the table. California settlements require WCAB judicial approval, and the judge has independent authority to push back on apportionment that does not have substantial medical evidence behind it.
California workers' compensation attorneys work on contingency under California Labor Code §4906 — typically 15% of any settlement, paid only if the case recovers. A free consultation costs nothing, and a Certified Specialist in Workers' Compensation Law, certified by the California Board of Legal Specialization, State Bar of California, evaluates the apportionment opinion against the medical record and the case law within days. Yazdchi Law handles California apportionment disputes from the firm's office in Palmdale.
Last reviewed by Eman Yazdchi, Esq., May 2026.
Ready to discuss your case? Schedule a free consultation.
Schedule Free ConsultationRead more testimonials →“A fighting force both consistent and compassionate on a scale’s a 5 all around.”