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Only one benefit can be apportioned: permanent disability; medical treatment, temporary disability, and death benefits cannot be apportioned.

SB 899 (see Reforms) made major changes to apportionment of permanent disability:  Labor Code §4663 was revised to provide
"Apportionment of permanent disability shall be based on causation." The leading Escobedo en banc case defined "other factors" to  include "pathology, asymptomatic prior conditions, and retroactive  prophylactic work preclusions, provided there is substantial medical evidence establishing that these other factors have caused permanent disability."

SB 899 added Labor Code §4664 to announce the policy that "The employer shall only be liable for the percentage of permanent disability directly caused by the injury arising out of and occurring in the course of employment." If there was a prior permanent disability award, "it shall be conclusively presumed that the prior permanent disability exists at the time of any subsequent industrial
injury." This was intended to prevent claims of rehabilitation as a way to avoid apportionment. The Kopping decision held that defendant has the burden of proving overlap if claiming a deduction for a prior award.

Body regions were listed, so that awards over a lifetime could not exceed 100 percent, unless the case fell under Labor Code §4662. Regions E., F., and G. ((E)The upper extremities, including the shoulders. (F) The lower extremities, including the hip joints. G) The head, face, cardiovascular system, respiratory system, and all other systems or regions of the body not listed in subparagraphs (A) to (F), inclusive) appear Draconian. If a worker injured shoulders in the past, developed ulnar neuritis from a later injury, then lost a hand in the third injury, this all gets lumped together. Even worse is G., which lumps together many unspecified regions or conditions in addition to the head and face. Nonetheless, under Kopping, defendant has the dual burden of proving the exisitence of the prior award and the overlap of factors of disability between the prior award and the current award.

The fifth edition of the AMA Guides states:

 "Apportionment analysis in workers' compensation represents a distribution or allocation of causation among multiple factors that caused or significantly contributed to the injury or disease and resulting impairment. The factor could be a preexisting injury, illness, or impairment. In some instances, the physician may be asked to apportion or distribute a permanent impairment rating between the impact of the current injury and the prior impairment rating. Before determining apportionment, the physician needs to verify that all the following information is true for an individual:

1. There is documentation of a prior factor.

2. The current permanent impairment is greater as a result of the prior factor (ie, prior impairment, prior injury, or illness).

3. There is evidence indicating the prior factor caused or contributed to the impairment, based on a reasonable probability (> 50% likelihood).

The apportionment analysis must consider the nature of the impairment and its possible relationship to each alleged factor, and it must provide an explanation of the medical basis for all conclusions and opinions." (pp. 11-12)

The permanent disability reduced by the apportionment stands alone when calculating the dollar value. As the Supreme Court held in the Brodie decision, "The tables in section 4658 are for compensating the current injury only."

Permanent disability ratings also require that a workers' compensation judge "determine whether the apportionment is inconsistent with the law" (8 CCR 10163).

See, too: Attacking Causation, Causation, Evidence, Permanent Disability, PD Rating

For apportionment of liability, see Contribution & Joinder

Label Item Links Comments
Labor Code (a) Apportionment of permanent disability shall be based on causation.
   (b) Any physician who prepares a report addressing the issue of permanent disability due to a claimed industrial injury shall in that report address the issue of causation of the permanent disability.
   (c) In order for a physician's report to be considered complete on the issue of permanent disability, the report must include an apportionment determination. A physician shall make an apportionment determination by finding 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, including prior industrial injuries.... 
LC §4663   
  A previous award of permanent disability is conclusively presumed to exist at the time of a later injury, etc. (see above).
LC §4664  
Regulations/Rules Various regs mention apportionment: see 8 CCR 10162, 8 CCR §10163 (Apportionment Referral)

Cases  Granado v. WCAB: cannot apportion other than PD

Escobedo: Leading case on apportionment.

Kopping v. WCAB: "The burden of proving overlap is part of the employer's overall burden of proving apportionment, which was not altered by section 4664(b), except to create the conclusive presumption that flows from proving the existence of a prior permanent disability award."

Brodie v. WCAB addressed this issue: "When a worker suffers an industrial injury that results in permanent disability, how should the compensation owed based on the current level of permanent disability be discounted for either previous industrial injury or nonindustrial disabilities?" The Supreme Court concluded that "The tables in section 4658 are for compensating the current injury only."

Benson v. WCAB (2009) 170 Cal. App. 4th 1535: "We hold that the Wilkinson doctrine is inconsistent with the apportionment reforms enacted by Senate Bill No. 899. We agree with the Board that a system of apportionment based on causation requires that each distinct industrial injury be separately compensated based on its individual contribution to a permanent disability. We also agree that there may be limited circumstances, not present here, when the evaluating physician cannot parcel out, with reasonable medical probability, the approximate percentages to which each distinct industrial injury causally contributed to the employee's overall permanent disability. In such limited circumstances, when the employer has failed to meet its burden of proof, a combined award of permanent disability may still be justified."
Granado v. WCAB

Escobedo en banc


Brodie v. WCAB

Benson v. WCAB

Benson v. The Permanente Med. Group (en banc) 2007
Practice Tips Certain law enforcement officers are exempt from apportionment

See sample letter to client concerning effect of Benson on a case involving multiple injuries to same body parts with same employer but different insurers
Labor Code §4663(e)

Sample Letter
Articles Apportionment: Case law update focusing on themes, trends, and problem areas: handout from DWC 21st annual educational conference 2/14

Keys to Proving Apportionment: The Bullet Proof List

Inextricably Intertwined – Benson Revisited by Robert G. Rassp, Esq.

SB 863 and Benson by Robert G. Rassp, Esq.

Green v. City of Los Angeles: Refresh of Apportionment: Rejection of the Black Box Approach by Charles Edward Clark, Esq.




Keys to Proving

Rassp on Benson

Rassp on Benson & SB 863

Clark on Green

Magazine Articles Apportionment: Science or Science Fiction? by Marjory Harris, Esq.

Apportionment of Orthopedically Produced Permanent Psychiatric Disability: Bruce T. Leckart, Ph.D.

Carving Up PD: Part I by Marjory Harris, Esq.

Carving Up PD: Part I by Marjory Harris, Esq.
Science or Science Fiction?

Ortho-produced psyche PD

Carving Up PD I

Carving Up PD II

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