§4663 Apportionment Fight — A California Workers' Comp Case Study

How the statutory framework applied

An apportionment opinion that relies on imaging alone, without a supported medical explanation of how the pre-existing condition caused disability, is legally insufficient.

Several California Labor Code sections and controlling case-law principles layered together on a California Labor Code §4663 apportionment fight.

The §4663 apportionment statute

California Labor Code §4663 requires every permanent disability rating to account for non-industrial causation where supported by substantial medical evidence. The statute reads that apportionment of permanent disability shall be based on causation, and a physician's report addressing apportionment shall include an analysis explaining what approximate percentage of the permanent disability was caused by the direct result of injury arising out of and occurring in the course of employment and what approximate percentage of the permanent disability was caused by other factors both before and subsequent to the industrial injury.

Brodie v. WCAB and the substantial-medical-evidence standard

The California Supreme Court's decision in Brodie v. WCAB (2007) and related cases set the standard for what counts as substantial medical evidence on apportionment. A bare statement that "50% is due to degenerative changes" does not meet the standard. The physician must explain how and why those non-industrial factors contributed to the disability, the specific medical reasoning, and the basis for the percentage assigned. Conclusory apportionment findings without medical reasoning are routinely struck down at the WCAB and the appellate level.

Asymptomatic imaging findings are not automatically apportionable

Pre-injury MRI evidence of degenerative changes does not, by itself, support apportionment under California Labor Code §4663. The medical-legal question is whether those pre-existing findings were causing disability before the industrial injury, not whether they merely existed on imaging. Many adults have degenerative spinal findings on MRI that are asymptomatic; if those findings were not causing disability before the work injury, they generally do not support apportionment after the work injury. The QME's apportionment must be grounded in actual pre-injury impairment, not in pre-injury imaging alone.

The supplemental request route under §4062.2

California Labor Code §4062.2 controls the QME selection and exam process. When the QME report contains apportionment findings that lack the substantial-medical-evidence analysis required under Brodie, the worker's attorney can submit a supplemental request to the QME for clarification, asking the QME to explain the medical reasoning, the specific pre-injury impairment relied upon, and the basis for the percentage assigned. A well-drafted supplemental request often produces either a revised report with reduced apportionment or a deficient response that supports striking the apportionment at trial.

Litigating apportionment at the WCAB

When the supplemental request route does not resolve the apportionment, the case proceeds to trial at the WCAB. The worker's attorney challenges the QME's apportionment as not based on substantial medical evidence, cross-examines the QME if a deposition is taken, and submits briefing on Brodie and the related case law. The workers' compensation judge can adopt, modify, or reject the QME's apportionment finding based on the substantial-medical-evidence analysis. A successful apportionment challenge can restore the full California Labor Code §4660 permanent disability rating.

Petition for Reconsideration under §5903

If the workers' compensation judge issues a Findings and Award adopting the contested apportionment, the worker can file a Petition for Reconsideration under California Labor Code §5903 within 25 days of service by mail (or 20 days from electronic service). The Petition for Reconsideration is heard by the WCAB en banc panel and is the route to challenge apportionment findings that lack substantial medical evidence. Adverse Reconsideration outcomes can be reviewed by the California Court of Appeal under a Petition for Writ of Review under California Labor Code §5950.

DWC's 2024 Audit Report logged 12,463 cases reviewed by Audit Unit auditors, with a defendant-paid penalty rate above the historical baseline, a reminder that the §5814 25% self-imposed late-payment increase is enforced, not theoretical.

Related reading: California pillar guide · §4663 explainer.

Related on yazdchilaw.com: California workers' comp settlement pillar · California Labor Code §4061.1 explained · California Labor Code §4663 (apportionment) · What happens at a mandatory settlement conference in california workers comp.