LawShelf courses have been evaluated and recommended for college credit by the National College Credit Recommendation Service (NCCRS), and may be transferred to over 1,500 colleges and universities.

We also have established a growing list of partner colleges that guarantee LawShelf credit transfers, including Excelsior College, Thomas Edison State University, University of Maryland Global Campus, Purdue University Global, and Touro University Worldwide.

For a limited time: Purchase a course multi-pack for yourself or a friend!

Aggravation and Pre-Existing Conditions-Module 6 of 6

See Also:

Aggravation and Pre-Existing Conditions


          Pre-existing conditions can make it more difficult for the court to determine which party should be liable, how much of the total disability a specific injury caused, and how much benefits a worker should be entitled to. Pre-existing conditions can affect a claim in two ways: first, when a work-related injury aggravates a pre-existing condition, and second, when a pre-existing condition aggravates a work-related injury. Furthermore, liability may shift depending upon whether the pre-existing condition occurred in a worker’s personal life, with a prior employer, or with the current employer. This module addresses the major questions surrounding liability and pre-existing conditions. How does a claimant prove aggravation? Who should be liable, and how much compensation should be paid?  

How to Prove Aggravation of a Pre-Existing Condition

To prove aggravation, a claimant must understand the definition of “aggravation,” collect the specific evidence necessary to support an aggravation claim and confirm that any necessary notice requirements are met.

“Aggravation” is more than merely the coincidence, or “stacking” of a pre-existing condition and a subsequent work-related injury. Instead, the worker must demonstrate that either the pre-existing condition was made worse by the subsequent work-related injury, or that the work-related injury was made worse than it otherwise would have been due to the pre-existing condition. The natural deterioration or progress of a pre-existing condition is insufficient.

For example, California law distinguishes aggravation from a mere flare-up, recurrence, or exacerbation of the pre-existing condition. An aggravation is treated as a new injury, usually causing increased disability (whether permanent or temporary), the need for new medical treatment, or a change in the otherwise anticipated course of treatment.[1] A mere exacerbation, flare-up, or recurrence of a pre-existing condition however, is not treated as a new injury, and does not cause increased disability, the need for new medical treatment, or a change in the anticipated course of treatment. When there is only an exacerbation, the employer at the time of the exacerbation will not be liable. Instead, the employer at the time of the original injury may be liable for a change in condition, if the original injury was work-related. Alternatively, if the original injury was not work-related, liability will fall upon the worker.[2]

Some states require specific types of evidence to prove aggravation. For example, South Carolina requires that aggravation be shown via objective medical evidence, including expert medical opinion, medical records, and diagnostic tests. Testimony from the injured worker or other lay witnesses is not enough, as it is often subjective as compared to expert medical testimony and diagnostic records.[3]

Other states require that the employee give notice of the pre-existing condition to the employer at some point before the aggravation occurred. The required timing, content, and form of notice (written or verbal) varies by jurisdiction. Some states require notice be given at the time of hiring, while others may require no notice at all.[4]

Who Should Be Liable and How Much Compensation Should Be Paid?

Jurisdictions use several different methods to determine liability in cases of pre-existing conditions. Some states may use a combination of different models based upon the specific situation: where a pre-existing condition is not work-related; where multiple injuries occur with different employers; and where multiple injuries occur with the same employer. Although various rules can be applied or combined differently by each state, the most common models are: the Full Responsibility Rule, apportionment, the Last Injurious Exposure Rule, and subsequent injury funds.

Full Responsibility Rule

Traditionally, employers took workers “as they found them.”[5] In general civil litigation this is referred to as the Eggshell Plaintiff Rule, which makes the defendant liable for the plaintiff’s unforeseeable and uncommon injuries.[6] This philosophy also underpinned the Full Responsibility Rule, which made employers responsible for the employee’s entire disability, including the portion related to a non-work-related pre-existing condition.[7] While the Full Responsibility Rule ensured that workers were compensated for their true level of resulting disability, it also forced employers to pay for that portion of a worker’s disability not caused by their work-related accident.[8]

While the burden of the Full Responsibility Rule initially appears to fall upon the employer who must pay higher workers’ compensation rates, workers may have in fact ultimately shouldered the cost. Employers could simply off-set the higher cost of workers’ compensation by lowering employee’s wages. Alternatively, employers could simply avoid hiring workers who they knew or suspected of having pre-existing conditions, including the disabled, handicapped, and elderly. With time however, state legislatures realized the social value of encouraging employment for workers with pre-existing conditions, and many state laws began to change.[9] The concept of apportionment developed.


Apportionment is a tool used by employers and their insurance carriers to avoid liability for disability unrelated to their employment. Many states, including New York[10] and California[11] have instituted systems of apportionment.[12] However, there are some jurisdictions, such as Arkansas, Florida, Wyoming, and Georgia that have historically not applied apportionment and instead simply cut off a worker’s ability to receive benefits if a pre-existing condition is involved.[13]

Where apportionment is allowed, state law usually limits it to only pre-existing conditions of a specific quality. For example, New York law states that apportionment is only allowed where the pre-existing condition was either a compensable work-related condition, or disabling, meaning more than merely symptomatic.[14] Other jurisdictions may not require that the pre-existing condition was a compensable work-related injury, but only that there was some sort of loss of earning capacity evaluation of the previous injury. Usually the pre-existing condition and the subsequent work-related injury also must be to the same body parts.[15]

In an apportionment system, the judge bases his award upon the physician’s report, which must state what percentage of the worker’s disability is due to the industrial accident, and what percentage is due to the pre-existing condition.[16] States may have different requirements as to what specific information the physician’s opinion must be based upon and what information must be included in the medical report. For example, in California if a judge is to apply apportionment, the physican’s report must meet five criteria, it must:

·       “Make a specific apportionment determination, using percentages”;

·       “Analyze permanent disability based on causation of disability (rather than causation of injury);

·       “ ‘Not be speculative, [but] … be based on pertinent facts and on an adequate examination and history’ ”;

·       “ ‘Be based on ‘reasonable medical probability’ ”; and

·       Explain why and how the physician arrived at the conclusion.[17]

States may also vary as to what types of benefits will be apportioned. Some states may only apportion permanent disability benefits, while others may also apportion temporary benefits and medical benefits. The exercises in this module will only address calculation of permanent disability benefits.[18]

Some jurisdictions only apply apportionment to particular instances. For example, some states apply apportionment to determine benefits when a pre-existing condition is not work-related,[19] while some apply it when there were multiple injuries with the same employer, or multiple injuries with different employers.[20] Some jurisdictions apply apportionment in all of these situations or a combination of one or more of them.

Last Injurious Exposure Rule

The last injurious exposure rule (also known as the Last Employer Rule) states “that liability for an occupational injury or illness falls to the employer who exposed the worker to the injurious substance just before the first onset of the disease or injury.”[21] Put another way, liability falls upon the employer “at the time of the most recent injury that bears a causal relation to the disability.” However, if the second injury is really just a recurrence of the first, then the employer at the time of the first injury would instead be liable for the recurrence.[22]

While some jurisdictions may only apply the rule to occupational diseases, others may also apply it to multiple or successive injuries of the same type.[23] Clearly, apportionment and the last injurious exposure rule are mutually exclusive. Therefore, if your jurisdiction applies apportionment to a particular situation, it cannot also apply the last injurious exposure rule to that situation. For instance, while South Carolina may apply apportionment in cases where the pre-existing condition was not work related, it would not apply the last injurious exposure rule in those situations. Furthermore, if South Carolina applies the last injurious exposure rule to successive injuries with different employers, it would not apply apportionment in those cases.[24]

When the last injurious exposure rule is applied to occupational disease cases, the last employer often pays full benefits to the injured worker. However, some jurisdictions may apply apportionment after the worker is awarded benefits, as between the list of multiple employers. This would allow the last employer to recoup from previous employers that portion of benefits paid by him that could actually be attributed to exposure by prior employers.[25] If the last employer has no way of recouping for that portion of the disability that he did not cause, then the result of the last injurious exposure rule would effectively be a return to the full responsibility rule.

When apportionment is determined as between multiple employers after the fact, it allows the worker to obtain quicker compensation than would otherwise result if apportionment had to be determined prior to an award. Many occupational diseases take years to develop. For instance, asbestosis can take twenty or more years to develop. As you can imagine, evidence related to apportionment as between multiple employers would be extensive, including employment records, tax records, and medical records, assuming such evidence can still be located after twenty or more years. Also, when apportionment is determined as between multiple employers in an occupational disease case, liability may be assigned based upon how long the employee worked for each employer, rather than upon a physician’s opinion regarding what percentage of the worker’s end disability can be attributed to the exposure that occurred with each employer.[26]

Subsequent Injury Funds

As time passed and more states began using apportionment to calculate workers’ compensation benefits, increasing numbers of workers with non-work-related pre-existing conditions were left without full compensation for their total level of disability. To cover these workers, some states established subsequent injury funds, referred to as second injury funds in some states. In 1991, forty-nine states had second injury funds, but more recently that number has declined. As of 2011 only thirty-one states still had such funds.[27]

These funds can obtain resources from either the state’s general taxation funds, or by assessing fees directly from employers or insurance carriers. For instance, North Carolina’s second injury fund is supplied by assessing fees against employers and carriers based upon the number of particular work-related permanent injury cases occur in their workplace or under their coverage each year.[28]

Generally, states with second injury funds determine what portion of a worker’s end disability is attributable to a permanent, pre-existing disability that was not work-related, and what portion is attributable to the on-the-job injury. The state fund pays that portion of disability attributable to the non-work-related pre-existing condition, and the employer at the time of the subsequent injury is liable for that portion of the total disability caused by the second accident.[29] Often in jurisdictions where a subsequent employer is forced to be liability under the last injurious exposure rule or the full responsibility rule for a non-work-related disability, that employer will pay benefits to the injured worker in the first instance and later seek from the second injury fund reimbursement for the liability paid for the non-work-related injury.[30] Therefore, depending upon the rules in your state, a second injury fund can provide benefits to either an injured worker or an employer and his insurance carrier.

There are many state-to-state variations in the administration of second injury funds, including when the funds must or simply may provide reimbursement to employers; whether there is reimbursement for wage compensation benefits alone, or medical benefits as well; and what type of pre-existing conditions are covered.[31]

For instance, South Carolina simply requires that for reimbursement to be paid, the end disability of the worker must have been “substantially greater than that which would have resulted from the subsequent injury alone.” End disability can be made substantially greater either through mere coincidence of the two injuries (or “stacking”), or by aggravation.[32] Furthermore, the pre-existing disability can be due to any type of injury, no matter the body part injured, and no matter whether the injury is work or non-work related.

In comparison, North Carolina only requires that the second injury fund compensates employers where both the original injury and the subsequent injury were at least twenty percent of the whole member (body part); or where the pre-existing disability is due to loss of a hand, arm, foot, leg, or eye. However, statutes define other specific situations in which the fund may provide benefits, “in its discretion.”[33]

California law only provides second injury fund reimbursement where the end disability is seventy percent or more, among other things.[34] Additionally, some subsequent injury funds may only function to reimburse for certain types of pre-existing conditions.[35]

Clearly, the laws applying to pre-existing conditions vary greatly state-to-state. However, the growing, modern trend has been toward apportionment. Although a large number of states still have second or subsequent injury funds, in recent years many states have ended or moved to phase out such funds.[36] This may be to end the burden of funding them via taxpayer or employer dollars.

[1] California Department of Human Resources (2018, July). Workers’ compensation preview (p. 7). Retrieved from https://www.calhr.ca.gov/Documents/workers-compensation-preview.pdf

[2] Id.

[3] Beard, G. L., Poteat, S. T., Lamar, M. J., Sumwalt, V. R., Bluestein, M. M., & Sullivan, A.P. (2012). The law of workers’ compensation insurance in South Carolina sixth edition (p. 103-104) (citing Ellison v. Frigidaire Home Products, 371 S.C. 159, 638 S.E.2d 664 (2006). Columbia, S.C.: South Carolina Bar Continuing Legal Education; S.C. Code Sect. 42-9-400(a));S.C. Code 42-9-35(D) Evidence of preexisting injury or condition (South Carolina Code of Laws (2016 Edition).

[4] Beard at 103-104; Hancock at 532-533.

[5] American Bar Association (2007, May/June). From John Burton’s workers’ compensation resources: workers’ compensation policy review [Vol. 7, Issue 3, p. 6]. Retrieved from http://www.americanbar.org/content/dam/aba/administrative/labor_law/meetings/2011/ac2011/087.authcheckdam.pdf

[6] Black’s Law Dictionary (Seventh Edition, 1999). Definition: eggshell-skull rule, p. 533. St. Paul, Minn.: West Group.

[7] ABA at 6.

[8] Beard at p. 375 (citing A. Custy, The second injury fund: encouraging employment of the handicapped worker in South Carolina, 27 S.C.L. Rev. 661 (1976)).

[9] Beard at 375-376.

[10] Rasul, T. (2016, April 13). New York, Workers’ Compensation. Apportionment: how it can reduce exposure in certain workers’ compensation claims. New York, NY: Lois Law Firm, L.L.C. Retrieved from http://lois-llc.com/new-york/apportionment-how-it-can-reduce-exposure-in-certain-workers-compensation-claims/

[11] Commission on Health and Safety and Workers’ Compensation (May 2004). Background paper on workers’ compensation causation and apportionment. Retrieved from www.dir.ca.gov/chswc/Causation_and_Apportionment_Final_May_2004.pdf

[12] ABA at 6.

[13] COH&S, at 16-17.

[14] Rasul.

[15] Ockander, B. (Sept. 27, 2012). How apportionment relates to a new workers’ compensation claim. Retrieved from https://workerscompensationwatch.com/2012/09/27/how-apportionment-relates-to-a-new-workers-compensation-claim/

[16] Califoria WCAB Noteworthy Panel Decisions Reporter (Feb. 25, 2013). California: keys to proving apportionment: the bullet  proof list. Retreived from www.lexisnexis.com/legalnewsroom/workers-compensation/b/reform-legislation/archive/2013/02/25/california-keys-to-proving-apportionment-the-bullet-proof-list.aspx?Redirected=true

[17] Id.

[18] Staver, Mathew D. (Summer 1995). Liberty University, Faculty Publications and Presentations, Liberty University School of Law. Apportionment and contribution of workers’ compensation benefits. Retrieved from digitalcommons.liberty.edu/cgi/viewcontent.cgi?article=1007&context=lusol_fac_pubs  

[19] Beard at 375-376.

[20] Rasul, T. (April 13, 2016). New York, Workers Compensation. Apportionment: how it can reduce exposure in certain workers’ compensation claims. Retrieved from lois-llc.com/new-york/apportionment-how-it-can-reduce-exposure-in-certain-workers-compensation-claims/ 

[21] Black’s Law Dictionary (Seventh Edition, 1999). Definition: last-employer rule, p. 887. St. Paul, Minn.: West  Group.

[22] Beard at 382.

[23] Rasul; Beard at 381.

[24] Beard at 381-382.

[25] Rasul.

[26] Rasul.

[27] Hancock, T.R. (2011). Wyoming Law Review [Vol. 11, pp. 525-547 at 533 n. 72 listing the thirty-one states with second injury funds as of 2011]. Apportionment between preexisting conditions and work-related injuries: why Wyoming needs a second injury fund. Retrieved from https://www.uwyo.edu/law/_files/docs/wy%20law%20review/v11%20n2/13%20hancock.pdf

[28] North Carolina Workers’ Compensation Law Annotated (2011 Edition). Section 97-40.1 (a), p. 330. Charlottesville, VA: LexisNexis.

[29] Hancock at 532.

[30] Beard at 377.

[31] N.C. Workers’ Comp.Law, Sect. 97-40.1(b), (c), pp. 330-331.

[32] Beard at 377-378.

[33] N.C. Workers’ Comp. Law, Sect. 97-40.1(b)(1) and (2), pp. 330-331.

[34] Penny, T. A., Dubrawski, P., & Davis, Y. (2013). California: workers’ compensation compendium [26. What are the criteria for establishing a “second injury” fund recovery?] Los Angeles, CA: Haight Brown & Bonesteel LLP (citing Cal. Lab. Code Sect. 4751; see also Subsequent Injuries Fund v. Indus. Accident Comm’n, 366 P.2d 496 (Cal. 1961)). Retrieved from http://www.hbblaw.com/files/Publication/48acc5bc-8067-4bf7-908c-84d59ff10574/Presentation/PublicationAttachment/2a5514e7-68e6-434a-9fe9-962cd135626e/Penny%20-%20ALFA%20WC%20Compendium%20Update%202013.pdf

[35] Beard at 377.

[36] ABA at 6; Haancock at 531 n.58.