Permanent disability & §4663 apportionment

Causation answers whether the injury counts. Permanent disability answers what is left when treatment has done what it can — and how much of that residual the employer is responsible for. The governing rule is §4663the Labor Code section requiring that permanent disability be apportioned to its causes; together with §4664 it caps the employer's liability to the percentage of permanent disability actually caused by the industrial injury.

This work happens at MMI — Maximum Medical Improvement, also called Permanent & Stationary (P&S) — the point at which the condition has stabilized and further treatment is not expected to materially improve it. At MMI the clinician does two things. First, the clinician assigns WPI (Whole Person Impairment) using the AMA Guides 5th edition, Chapter 14, which covers mental and behavioral disorders. Second, the clinician apportions the permanent disability between industrial causes and non-industrial or pre-existing causes — the §4663 step.

Which P&S form a clinician files depends on the date of injury, because two rating schedules coexist. The PDRSthe Permanent Disability Rating Schedule used to translate impairment into a disability rating comes in two editions: the 2005 schedule applies to dates of injury on or after January 1, 2005, and the 1997 schedule applies to earlier injuries. That single fact decides the form — a P&S report is a PR-4 under the 2005 schedule and a PR-3 under the 1997 schedule.

For Sofia, MMI brings the final clinical picture together: final GAF, a WPI rating per Chapter 14, and a §4663 apportionment of the residual permanent disability between her industrial trauma exposure and any non-industrial or pre-existing contribution — the disability analogue of the causation split rendered at diagnosis.