"They say it's just arthritis."

What apportionment is

Labor Code § 4663 permits apportioning permanent disability between industrial and non-industrial causes. A physician must state what approximate percentage of the permanent disability was caused by the industrial injury and what approximate percentage by other factors.

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

Naming a cause is not an opinion. It is a conclusion. The question a valid report must answer is how the non-industrial factor produced this worker's permanent disability, and why that share is 40% rather than 15%.

Why "everyone your age has this" is a weak argument

Degenerative findings on imaging are extremely common in people with no symptoms and no disability at all. That is well established across the spine, the shoulder, and the knee.

Which cuts against the defense. If most people with those findings are not disabled, then the findings by themselves do not produce disability. What produced the disability is whatever converted an asymptomatic condition into a symptomatic, function-limiting one — and that is the industrial event or exposure.

Apportionment is to disability, not to pathology. That distinction is the whole answer, and it is a legal rule, not an argument.

The questions that decide it

Were you doing your full job the day before? A worker performing full duties without restriction, complaint, or accommodation had no disability from the pre-existing condition — whatever the imaging showed.

Did the evaluator review your pre-injury records? An opinion apportioning to a prior condition, written by someone who reviewed nothing from before the injury, has no factual basis.

Is there any prior treatment, complaint, or restriction? Not a prior finding — a prior disability.

What supports this percentage rather than another one? If the report cannot answer, it is not substantial evidence.

Two rules that constrain it

Prior findings are not the same as prior disability — but Lindh does not make that argument for you. 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 the defense still has to prove is that the condition caused part of this disability, on substantial medical evidence — and under Escobedo the physician must explain how and why, not merely name a prior condition.

And medical treatment consequences generally cannot be apportioned away. Under Hikida v. WCAB, where industrial medical treatment itself causes disability — a failed surgery, a post-operative complication — that disability is industrial. This matters enormously where a surgery made things worse, and it is regularly overlooked. But Hikida has been cut down, and the site that does not say so is out of date.* In County of Santa Clara v. WCAB (Justice) *(2020) 49 Cal.App.5th 605 [85 Cal.Comp.Cases 467] the Court of Appeal held that Hikida "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. Sole cause is a demanding test, and the rule is much narrower than it is usually described.

Where this comes up most

• Low backdegenerative disc disease
• Shoulderasymptomatic cuff tears in people over 60
• Kneearthritis and body weight
• Carpal tunneldiabetes and thyroid disease
• Hearing losspresbycusis, where the audiogram configuration answers it