Apportionment

Apportionment is the single largest variable in a California permanent disability case, and it is decided by a paragraph in a medical report that most injured workers never read carefully.

The rule that governs all of it:

Apportionment is to permanent disability, not to pathology, not to imaging findings, not to risk factors, and not to history.

And under Escobedo v. Marshalls (WCAB en banc), a physician must explain the how and why. A report that names a condition — arthritis, degeneration, diabetes, age, obesity, a prior injury — and attaches a percentage without reasoning is not substantial evidence, and it cannot support an apportionment finding.

What the statute requires

Labor Code § 4663 makes apportionment based on causation. A physician who addresses permanent disability must make an apportionment determination and must state:

• What approximate percentage of the permanent disability was caused by the direct result of the injury, and
• What approximate percentage was caused by other factors, including any prior industrial injury.

And the physician must be able to say that the opinion is held to a reasonable medical probability, with the reasoning stated.

Labor Code § 4664 adds two separate things:

The employer is only liable for the percentage of disability directly caused by the industrial injury.

And where there is a prior award of permanent disability, that disability is conclusively presumed to still exist — which is a real and often harsh rule in a worker with a documented prior award. It applies to a prior award, not to a prior injury.

The four questions that decide it

1. Were you doing your full job the day before?

A worker performing full duties, without restriction, accommodation, or complaint, had no disability from the pre-existing condition — whatever an image showed. This is the strongest single fact in most apportionment fights, and it is a factual question you can answer.

2. Did the evaluator review your pre-injury records?

An opinion apportioning to a prior condition, written by a physician who reviewed nothing from before the injury, has no factual basis for the percentage. Ask what records were reviewed — the report has to list them.

3. Does the report tie the prior condition to this disability?

Be careful here: under City of Petaluma v. WCAB (Lindh) (2018) 29 Cal.App.5th 1175, a pre-existing condition that never disabled anyone can support apportionment — prior disability is no longer a prerequisite. What § 4663 still requires is causation of this disability, proved by substantial medical evidence. A report that names a degenerative finding and stops has not done that.

4. What supports this percentage rather than another one?

Why 50% and not 20%? If the report cannot answer that with reasoning tied to the record, it does not satisfy Escobedo.

The arguments you should expect

Three rules that limit apportionment

Medical treatment consequences generally cannot be apportioned away. Under Hikida v. WCAB (2017), where industrial medical treatment itself causes permanent disability — a failed surgery, a post-operative complication, a nerve injury during a procedure — that disability is industrial. This matters enormously where a surgery made things worse, and it is regularly overlooked. But Hikida was narrowed.* County of Santa Clara v. WCAB (Justice) *(2020) 49 Cal.App.5th 605 [85 Cal.Comp.Cases 467] holds that it "precludes apportionment only where the industrial medical treatment is the sole cause of the permanent disability." Where pre-existing pathology also contributes, §§ 4663 and 4664 apportionment still applies.

There is no such thing as "vocational apportionment." In Nunes v. State of California, Dept. of Motor Vehicles (WCAB en banc, June 22, 2023), the Board held that only reporting physicians may determine apportionment under § 4663, and that there is "no statutory provision for 'vocational apportionment.'" A vocational expert cannot substitute a 0% vocational apportionment for a physician's medical apportionment. Nunes II affirmed it. What vocational evidence can do.

And § 4664(b)'s conclusive presumption requires an actual prior award. A prior claim that settled by Compromise and Release without an award of permanent disability is not a prior award. This gets asserted more often than it applies.

What to do about a bad apportionment opinion

Read the paragraph. It is usually short, and it usually states a conclusion rather than reasoning. That is the defect.

Check what records were reviewed. If the list does not include pre-injury records, say so.

Get your own pre-injury records — primary care, urgent care, chiropractic, anything paid through your own health insurance. Their absence of complaint is evidence.

Document the full duty history. Job description, performance record, attendance, and the absence of any accommodation.

And raise it before the mandatory settlement conference. Under § 5502(d)(3) discovery closes there, and a supplemental report or a deposition of the evaluator obtained afterward is generally inadmissible. The full timeline.

Frequently asked questions

What people actually ask about apportionment

• They say it's just arthritis, not my job.
• I have two different injuries.and why they do not simply add
• I had a workers' comp case before.
• My other side started hurting.