Reaffirming Nally Over Duvall in Successive-Injury Cases: Commentary on Ferrell v. City of Wilmington

I. Introduction

In Corey Ferrell v. City of Wilmington, No. 152, 2025 (Del. Dec. 4, 2025), the Delaware Supreme Court addressed a difficult workers’ compensation problem: how to allocate responsibility when a worker with a prior, fully-commuted work-related spinal injury suffers later symptoms while working for a different employer, and the prior carrier has been released from all future liability.

The case sits at the intersection of two important Delaware doctrines:

The recurrence vs. aggravation framework for successive work injuries and carriers articulated in Standard Distributing Co. v. Nally, 630 A.2d 640 (Del. 1993); and
The “substantial causation” rule for claimants with pre-existing conditions established in Duvall v. Charles Connell Roofing, 564 A.2d 1132 (Del. 1989).

Claimant Corey Ferrell, a firefighter, had:

A 2015 compensable thoracic spine injury while working part-time for Belvedere Fire Company;
A 2018 global commutation of that claim, expressly releasing Belvedere’s carrier from all “future benefit liability” for the 2015 injury;
A 2023 episode of severe thoracic/back pain while carrying two “high-rise packs” up stairs as a Wilmington firefighter.

The Industrial Accident Board (IAB) held that the 2023 episode was a recurrence of the 2015 injury, not an aggravation or new injury. Because the 2015 claim had been fully commuted and the original carrier fully released, that classification left Ferrell with no compensable claim at all. The Superior Court affirmed, and so did the Supreme Court.

The key legal issues were:

Which standard applies? Should the IAB have applied:
- Nally’s recurrence/aggravation rule for successive carriers; or
- Duvall’s “substantial cause” rule for work-related exacerbations of pre-existing conditions?
Was the Board’s factual determination supported by substantial evidence? Specifically, was there substantial evidence that:
- The 2023 incident was medically a recurrence (not a new injury or aggravation); and
- The staircase event was not an “intervening or untoward” event that proximately caused any new condition?

The Court held that Nally, not Duvall, controls cases about allocation of liability between successive employers/carriers, even when the earlier claim has been commuted and the result is a coverage gap. It further held that the IAB’s recurrence finding and its rejection of an “untoward event” were supported by substantial evidence.

II. Summary of the Opinion

A. Holdings

Correct legal standard: The IAB and Superior Court properly applied the Nally recurrence/aggravation framework. Duvall was inapplicable because this was a successive carrier allocation dispute, not a basic compensability dispute for a pre-existing condition.
Nature of the 2023 incident: Substantial evidence supported the IAB’s finding that:
- The 2023 symptoms were a recurrence of the 2015 thoracic injury; and
- Climbing stairs with two high-rise packs did not constitute an “intervening or untoward event” producing a new injury or true aggravation.
Effect of commutation: The fact that Ferrell had fully commuted the 2015 claim and released the original carrier from all future liability did not change the legal standard. The resulting gap in coverage is an unfortunate but legally irrelevant consequence of the commutation, not a reason to shift to the Duvall analysis.
Standard of review: The Supreme Court reiterated that it defers to the IAB’s factual findings, credibility determinations, and choice between conflicting expert opinions if supported by “substantial evidence.”

B. Practical Bottom Line

For Delaware workers’ compensation:

Successive injury / successive employer cases remain governed by Nally: the question is which carrier pays, not whether there is compensability at all.
The “substantial cause” rule in Duvall does not override or displace Nally in these allocation disputes.
A fully-commuted earlier claim may leave the worker without coverage for a later recurrence unless the later event qualifies as an untoward event causing a new injury or aggravation.

III. Detailed Analysis

A. Factual and Procedural Background

1. The 2015 Belvedere injury and commutation

In 2015, while working part-time for Belvedere Fire Company and also employed full-time by the Wilmington Fire Department, Ferrell was in a motor vehicle accident that caused thoracic and cervical spine injuries. Imaging revealed:

Thoracic disc bulges and herniations at multiple levels;
Central canal stenosis (narrowing of the spinal canal) at T6–7; and
Evidence of myelomalacia (spinal cord damage) and degenerative changes.

Ferrell pursued and received workers’ compensation benefits through Belvedere’s carrier. In 2017, based on those findings, a physician assigned (and he received a settlement for):

6% permanent impairment to the cervical spine; and
5% permanent impairment to the thoracic spine.

In 2018, Ferrell entered into a global commutation of his 2015 claim. In exchange for a lump sum (structured as a waiver of the carrier’s lien on a third-party recovery), he expressly:

released the workers’ compensation carrier from future benefit liability...

This commutation closed out all future entitlement for that injury against Belvedere’s carrier—medical, indemnity, and any other statutory benefits. Ferrell then continued working as a firefighter.

2. Intervening non-work 2021 car accident

In 2021, Ferrell was rear-ended in a non-work-related car crash. He experienced significant back pain and spasms and sought treatment from his family doctor, Dr. Tucker. Some care was recommended (during the COVID-19 pandemic), but Ferrell could not recall whether he completed all follow-up. This incident was not itself a workers’ comp claim and plays a limited doctrinal role in the opinion; it does, however, reinforce that Ferrell’s thoracic spine remained fragile and symptomatic after 2015.

3. The October 6, 2023 Wilmington incident

While on duty with the Wilmington Fire Department, Ferrell responded to a high-rise call. Firefighters must carry “high-rise packs” of hose and related equipment (30–40 pounds each). Ferrell:

Carried both his own pack and a supervisor’s pack up several flights of stairs;
Experienced sudden shortness of breath and chest pain;
Later reported back spasms and, at some point, reported feeling a “pop” in his back.

His cardiac workup at the hospital was negative; he was directed to follow up for his back. Subsequent imaging in December 2023 again showed:

Thoracic disc bulges and herniations at essentially the same levels as the 2015 MRI;
Findings consistent with progression of thoracic disc disease, including cord atrophy at some levels.

He received conservative treatment (including chiropractic care); an injection was recommended but declined. On March 6, 2024, he was placed on modified duty.

4. IAB proceedings and decisions

Wilmington denied the workers’ compensation claim. At the IAB hearing, the central dispute was whether the 2023 event:

Constituted a new injury unrelated to the 2015 injury;
Was an aggravation of the 2015 injury caused by an “intervening or untoward event”; or
Was merely a recurrence or manifestation of the 2015 injury’s ongoing pathology.

Evidence included:

Ferrell’s testimony that the 2023 pain was more intense than anything since 2015 and that he felt a “pop” in his back;
His report of minimal symptoms between 2015 and 2023, except for a symptomatic period after the 2021 non-work accident;
Expert testimony by Dr. Tucker (treating family physician) and Dr. Matz (orthopedic surgeon retained by Wilmington FD) offering conflicting etiological views.

The IAB:

Credited Dr. Matz’s testimony over Dr. Tucker’s;
Found that the 2023 imaging showed degenerative progression consistent with the natural history of the 2015 injury, not a new acute insult;
Concluded that climbing stairs with packs was part of Ferrell’s normal job duties and not a “genuine intervening event” that proximately caused a new condition;
Classified the 2023 episode as a recurrence of the 2015 injury.

Under Nally, that would normally place liability on the 2015 carrier, but because Ferrell had commuted and released that carrier from any “future benefit liability,” there was no responsible carrier. The IAB therefore denied the petition.

5. Superior Court and Supreme Court review

Ferrell appealed, arguing:

The IAB applied the wrong legal framework by using Nally instead of Duvall and by mischaracterizing the 2023 event as non-intervening; and
The IAB’s factual findings were unsupported by substantial evidence.

The Superior Court rejected both arguments and affirmed. Ferrell then appealed to the Delaware Supreme Court, which likewise affirmed.

B. Precedents and Doctrinal Framework

1. Standard Distributing Co. v. Nally – Successive Carrier Liability

Nally involved a beer delivery driver who:

Suffered a back injury when kegs fell on him, and received compensation from Carrier A;
Later, after the employer switched to Carrier B, experienced renewed back problems while unloading a keg.

The question was: which carrier—A or B—was responsible for the post-second-incident symptoms?

The Court in Nally articulated a clear allocation rule:

responsibility [is placed] on the carrier on the risk at the time of the initial injury when the claimant, with continuing symptoms and disability, sustains a further injury unaccompanied by any intervening or untoward event which could be deemed the proximate cause of the new condition. On the other hand, where an employee with a previous compensable injury has sustained a subsequent industrial accident resulting in an aggravation of his physical condition, the second carrier must respond to the claim for additional compensation.

Key definitions drawn from Nally (itself drawing on DiSabatino & Sons, Inc. v. Facciolo, 306 A.2d 716 (Del. 1973)):

Recurrence: “the return of an impairment without the intervention of a new or independent accident.”
Aggravation: a worsening of the condition caused by a new industrial accident, making the condition more severe than it was before.

Policy underpinnings:

In successive carrier disputes, compensability is conceded; the only issue is which carrier pays.
Liability should be fixed on primary responsibility for risks as they arise and, to avoid “delay and confusion,” continue “as long as the consequences of that injury are present.” (citing Pennsylvania Mfrs. Ass’n Ins. Co. v. Home Ins. Co., 584 A.2d 1209 (Del. 1990)).
The central test is whether there has been a “genuine intervening event” which is the producing cause of a changed physical condition.

2. Duvall v. Charles Connell Roofing – Abandoning the Unusual Exertion Rule

Duvall involved a roofer with a congenital spinal weakness who injured his back while unloading an 80‑pound bundle of shingles. Historically, Delaware applied an “unusual exertion” doctrine: a worker with a pre-existing weakness was denied compensation unless engaged in “unusual” effort at the time of injury.

The Supreme Court in Duvall abandoned that doctrine and adopted the “usual exertion” / substantial cause rule:

an injury is compensable if the ordinary stress and strain of employment is a substantial cause of the injury.

Important aspects of Duvall:

It addressed whether any compensation at all is payable when a work event interacts with a pre-existing condition.
It aimed to fulfill the core purposes of the Workers’ Compensation Law—prompt, non-fault compensation and reduced litigation (see Champlain Cable Corp. v. Employers Mut. Liab. Ins. Co. of Wisconsin, 479 A.2d 835 (Del. 1984)).
It held that pre-existing vulnerabilities do not bar compensation so long as work is a substantial cause of the injury—even if the effort was “ordinary.”

3. Other cited authorities

DiSabatino & Sons, Inc. v. Facciolo, 306 A.2d 716 (Del. 1973) – Origin of the “recurrence” definition as the return of impairment without a new accident.
Pennsylvania Mfrs. Ass’n Ins. Co. v. Home Ins. Co., 584 A.2d 1209 (Del. 1990) – Supports the policy that initial carrier liability should persist as long as the consequences of the original injury continue, to avoid uncertainty in successive carrier disputes.
Barkley v. Johnson Controls, 2003 WL 187278 (Del. Super. Jan. 27, 2003) – Explains that under Nally, the Board must first decide whether the later incident constitutes an “intervening or untoward event.”
Standard of review cases:
- Betts v. Townsends, Inc., 765 A.2d 531 (Del. 2000) – Substantial evidence standard on appeal from IAB.
- Elzufon, Austin, Tarlov & Mondell, P.A. v. Lewis, 309 A.3d 424 (Del. 2023) – Defines “substantial evidence” and reaffirms deference to the Board’s fact-finding; reiterates that adopting one expert over another can itself be substantial evidence.
- Breeding v. Contractors-One, Inc., 549 A.2d 1102 (Del. 1988) – “Substantial evidence” is more than a scintilla but less than a preponderance.
- Noel-Lisziewicz v. La-Z-Boy, 68 A.3d 188 (Del. 2013) – Confirms that assessing witness credibility and resolving conflicting testimony are within the IAB’s exclusive province.

C. The Court’s Legal Reasoning

1. Why Nally – not Duvall – governs this case

The Supreme Court’s first analytical move is to correctly classify the nature of the dispute:

This is a case about which employer/carrier, if any, is liable for a later work-related episode (2015 Belvedere vs. 2023 Wilmington).
It is not a case about whether a pre-existing non-compensated condition is covered at all.

Because the core issue is allocation of liability between successive work-related injuries and carriers, the Court holds that Nally is the controlling framework:

Nally governs “successive carrier responsibility in recurrence/aggravation disputes” when “an employee seeks compensation for a work-related injury that is causally related to an injury compensated by a previous employer or carrier.”
Duvall governs when the question is whether a pre-existing condition can be compensated at all when work substantially causes or exacerbates that condition.

The Court expressly notes that these frameworks respond to different policy concerns:

Duvall addresses fairness to vulnerable workers and the basic compensability threshold.
Nally addresses efficient and predictable allocation between carriers once compensability is conceded.

That Ferrell had a pre-existing spinal condition does not convert a Nally-type allocation case into a Duvall-type basic compensability case. Nor does the fact that Ferrell had a symptom-free period transform his compensated 2015 injury into a generic “pre-existing condition” for Duvall purposes. The Court emphasizes:

Ferrell received permanency ratings in 2017, explicitly acknowledging the sustained, permanent nature of his 2015 injury.
The commutation and permanency settlement reflected that the injury was recognized, compensated, and expected to persist to some degree.

Thus, the legal question remained squarely: Did the 2023 incident create a new injury or aggravation (imposing liability on Wilmington), or was it a recurrence for which Belvedere’s (now released) carrier would be responsible under Nally?

2. The three-step Nally analysis as applied

The Court crystallizes the Nally inquiry into three sequential questions for successive-injury cases:

Is the later condition a completely new injury unrelated to the prior compensable injury?
If yes, then Nally does not control; the later employer/carrier bears responsibility for a new injury.
If related, is it a recurrence or an aggravation of the prior injury?
This requires medical and factual analysis of the underlying pathology.
Was there an “intervening or untoward event” at the time of the second incident that proximately caused a new condition?
Even for an aggravation, the second carrier is liable only if such an event is the producing cause of a changed physical condition.

Applying that framework:

a. New injury vs. related injury

The Supreme Court characterizes the Board’s determination that the 2023 condition was related to the 2015 injury as “the most straightforward question.” Key supporting facts:

The 2015 and 2023 MRIs centered on the same thoracic levels (T5–T11);
The injury pattern (disc bulges, protrusions, stenosis, cord changes) was substantially similar;
Both experts agreed, at least broadly, that the 2023 imaging involved the same anatomical region.

Ferrell did not seriously dispute relatedness; his argument focused instead on aggravation vs. recurrence and on the nature of the 2023 event.

b. Recurrence vs. aggravation

The more difficult question for the IAB was whether the 2023 incident constituted a recurrence or an aggravation. The Court underscores an important doctrinal point from Nally:

[T]he analysis under Nally is not whether [the claimant’s] pain or other symptoms have returned but whether there has been a new injury or worsening of a previous injury attributable to an untoward event.

In other words:

The focus is on structural or pathological change, not merely increased pain.
A claimant’s subjective experience of more intense pain does not, by itself, convert a recurrence into an aggravation.

Here, the IAB adopted Dr. Matz’s view that:

Ferrell’s thoracic spine showed a degenerative, slowly progressive disc disease;
The changes between the 2015 and 2023 MRIs were consistent with expected progression over eight years given the pre-existing pathology and aging;
There was no convincing medical evidence that the October 6, 2023 staircase exertion produced a new structural injury beyond expected degeneration.

Because the IAB was entitled to choose between experts, and because Dr. Matz’s testimony was grounded in specific imaging comparisons and clinical reasoning, the Supreme Court held that this medical conclusion qualified as substantial evidence supporting the “recurrence” classification.

c. Was there an intervening or untoward event?

Even if one accepted some degree of worsening, Nally still requires that the later industrial event be an “intervening or untoward event” that is the proximate cause of the new condition before shifting liability to the later carrier.

The Court notes that the Board:

Considered Ferrell’s description of climbing the stairs with two packs; and
Highlighted Dr. Matz’s testimony that:
- The described activities were within the normal job duties and expected exertions of a firefighter;
- Ferrell did not report a fall, slip, being struck, or any discrete traumatic incident;
- He did not initially tell Dr. Matz that he had felt a “pop”; that account appeared later and was inconsistent with more contemporaneous medical records.

On that basis, the Board concluded that the 2023 staircase episode, though physically demanding, was not a “genuine intervening event” under Nally. The Supreme Court accepted that conclusion as factually supported and consistent with precedent.

3. Why Duvall does not control

Ferrell argued that his 2015 injury, having become asymptomatic for a significant period, should be treated as a pre-existing condition and that his 2023 work activity substantially caused an exacerbation, thereby bringing the case under Duvall’s substantial cause standard.

The Court rejected this for several reasons:

Doctrinal mismatch: Duvall addresses whether work is a substantial cause of an injury at all in the presence of a pre-existing condition, not which of two compensable injuries (and carriers) should pay.
Nature of the condition: The 2015 injury was not a latent, non-compensated predisposition; it was a fully recognized and compensated workers’ comp injury, confirmed as permanent through a permanency rating and settlement.
Symptom-free period not dispositive: Being relatively symptom-free for a period does not mean the previous work injury healed or became medically irrelevant. The permanency rating established that the injury persisted.
Policy continuity: Nally is specifically designed to allocate liability in serial work-injury cases and, as the Court notes, generally does not disadvantage claimants because one of the carriers is normally on the hook. The fact that Ferrell’s commutation left no carrier does not undermine the logic of Nally.

The Court thus preserves a clean doctrinal boundary:

Duvall = “Do I get any workers’ comp for this work-related event if I’m medically predisposed?”
Nally = “Assuming it’s compensable, which carrier/employer pays when there are serial work-related injuries?”

4. Substantial evidence and deference to the IAB

On Ferrell’s second argument—lack of substantial evidence—the Court reiterates well-settled principles:

Substantial evidence is “such relevant evidence as a reasonable mind might accept as adequate to support a conclusion,” more than a scintilla but less than a preponderance.
The IAB has exclusive authority to:
- Weigh evidence;
- Assess witness and expert credibility; and
- Resolve conflicts in testimony.
Choosing to credit one expert’s testimony over another’s can itself constitute substantial evidence if that testimony is grounded in the record.

Applying that standard:

The Board relied heavily on Dr. Matz’s detailed comparison of 2015 and 2023 MRIs, his degenerative-disease explanation, and his view that no discrete traumatic event occurred in 2023.
It expressly found Dr. Matz more credible than Dr. Tucker.

The Supreme Court therefore declined to reweigh the evidence, noting that Ferrell’s disagreement with the Board’s factual determinations is not a basis for reversal so long as reasonable evidence supports the Board’s view.

D. Impact and Implications

1. Clarifying the boundary between Nally and Duvall

This opinion provides important clarification for practitioners:

Nally remains the governing standard in successive work-injury / successive carrier disputes, even where the first injury has been fully commuted.
Duvall is not a catch-all “pre-existing condition” standard that applies whenever a claimant had any prior medical problem. It is confined to assessing initial compensability in the presence of pre-existing vulnerabilities.
Courts and the IAB must first classify the nature of the case—allocation vs. initial compensability—before selecting the governing doctrine.

2. Practical consequences for commutations

Perhaps the most striking feature of Ferrell is the outcome: applying Nally in the usual way produces an anomalous result where no carrier is liable because:

The original injury’s carrier has been fully released (via commutation); and
The later incident is only a recurrence, not a new injury or aggravation caused by an untoward event.

The Court expressly notes that Nally “does not typically leave a worker without compensation”; the gap here is a function of Ferrell’s earlier choice to commute:

Its application did so here only because of Ferrell's commutation. That unusual result does not mean that the Board applied the wrong standard.

For practitioners, this highlights:

Risk of future recurrences: When advising on global commutations of serious or permanent injuries—especially spinal injuries—counsel must warn claimants that:
- If later symptoms are merely recurrences of the original injury, those future episodes will remain, conceptually, the responsibility of the original carrier; and
- If that carrier has been released from all future liability, there may be no recourse against later employers or their carriers unless there is a distinct new injury or genuine aggravation.
Drafting and structuring settlements: Parties may seek to:
- Limit commutation to certain benefit types (e.g., indemnity only, preserving medical); or
- Enumerate how recurrences will be treated, though statutory rules like Nally will still govern carrier allocation.

3. Implications for claim classification and expert practice

The opinion underscores that:

The recurrence vs. aggravation label depends heavily on objective medical evidence (MRIs, clinical findings) and credible expert testimony—not simply subjective symptom severity.
Ordinary job activities (even relatively strenuous tasks like carrying heavy packs up stairs) may not constitute an “untoward event” if they fall within the worker’s regular duties and there is no discrete traumatic incident (fall, blow, twist, etc.).
Treating physicians and IME doctors must clearly articulate:
- Whether there is any structural change beyond expected degeneration;
- How the timing and nature of symptoms correlate with identified anatomical changes; and
- Whether the work event is, medically, the producing cause of any new pathology.

4. Potential for future litigation and legislative attention

While the Court faithfully applied existing law, Ferrell exposes a structural tension:

The Workers’ Compensation Act is designed to avoid gaps in coverage and to provide predictable, no-fault relief.
Yet fully-commuted claims, when combined with the Nally framework and degenerative injuries, can leave a subsequent employer’s carrier legitimately denying responsibility, even when an acute work episode triggers disabling symptoms.

This tension may:

Influence how often and how broadly global commutations are used for significant permanent injuries;
Encourage more nuanced settlement structures (e.g., partial commutations, limited releases); or
Prompt legislative review of how recurrences after commutations are to be handled (for example, whether and under what conditions later employers can be deemed primary payors for recurrences in heavily physical occupations).

E. Complex Concepts Explained

1. Commutation / global settlement

A commutation in workers’ compensation is essentially a buyout: the worker accepts a lump sum in exchange for giving up some or all future rights under the claim.

In Ferrell’s case, the commutation was described as “global” and expressly released the 2015 carrier from all “future benefit liability.” That means:

No further weekly wage loss benefits;
No further medical bills;
No further right to reopen the claim for recurrences, worsening, or additional permanency.

A critical consequence: if future symptoms are classified as a recurrence of that old injury, they are conceptually the original carrier’s responsibility—but practically non-compensable because that responsibility has been contractually extinguished.

2. Recurrence vs. aggravation

The distinction:

Recurrence – The original injury flares up or manifests again, but there is no new accident or structural change caused by a later work event. The condition is attributable to the original injury’s ongoing pathology.
Aggravation – A later work accident or incident makes the underlying condition worse in a medically meaningful way (e.g., new herniation, additional level involvement, increased cord compression), beyond natural progression.

In successive carrier cases:

Recurrence → Original carrier is liable.
Aggravation caused by an “untoward event” → Later carrier is liable.

3. “Intervening or untoward event”

Under Nally, to shift liability to the later carrier, there must be a work event that:

Is more than just the usual manifestations of the prior condition; and
Can be deemed the proximate (producing) cause of a new or worsened physical condition.

Examples that often qualify:

A fall or slip;
Being struck by equipment or debris;
Sudden twisting or lifting with immediate, clearly changed symptoms and new imaging findings.

In Ferrell, the Board concluded that climbing stairs with heavy packs, while strenuous, was still within the ordinary range of duties of a firefighter and not an unusual, discrete traumatic event that caused new structural damage.

4. Usual exertion vs. unusual exertion; substantial cause

Before Duvall, Delaware required “unusual exertion” for a worker with a pre-existing weakness to be compensated. Duvall rejected that rule and adopted the “usual exertion” standard:

Ordinary job activities can create a compensable injury if they are a substantial cause of the injury, even if the worker is medically predisposed.

That concept is distinct from the Nally inquiry. In Nally and Ferrell:

The threshold of basic compensability is already satisfied by a prior compensable injury;
The issue is instead whether a later event is a distinct, causative industrial accident that should shift liability to a new carrier.

5. Substantial evidence and appellate review

“Substantial evidence” is a deferential standard. On appeal from the IAB, courts do not:

Reweigh evidence;
Reevaluate witness credibility; or
Substitute their own view of medical disputes.

Instead, they ask:

Is there enough relevant evidence that a reasonable factfinder could rely on to reach the Board’s conclusion?

If yes, the Board’s decision stands—even if another factfinder could have decided differently on the same record.

6. Permanency ratings and degenerative vs. acute injuries

A permanency rating recognizes that a worker’s condition has stabilized but will not return to normal. It is assigned as a percentage of impairment to a body part or system and often forms the basis of a settlement.

In Ferrell’s case:

6% cervical and 5% thoracic permanency confirmed that his 2015 injury had lasting effects.

A degenerative condition (like progressive disc disease) tends to worsen gradually over time, whether or not distinct trauma occurs. An acute injury is tied to a specific incident.

Dr. Matz’s testimony that Ferrell’s MRIs showed expected degenerative progression, rather than new acute trauma, was central to the Board’s recurrence finding.

IV. Conclusion

Ferrell v. City of Wilmington does not radically alter Delaware workers’ compensation law; instead, it clarifies and reinforces the proper use of two existing doctrines:

Nally remains the controlling rule for allocating liability between successive employers/carriers when a subsequent work-related episode is causally related to an earlier compensable injury.
Duvall’s “substantial cause” standard continues to govern basic compensability questions for workers with pre-existing conditions, but does not displace Nally when the issue is which carrier pays.
A global commutation of a prior claim does not change the legal characterization of later symptoms as recurrence vs. aggravation; it only affects who, if anyone, remains financially responsible.
The IAB’s role as factfinder, especially in choosing between medical experts and reading imaging evidence, is entitled to strong deference under the substantial evidence standard.

The case serves as a cautionary tale about the long-term effects of commuting serious injuries, particularly spinal injuries, and as a doctrinal guidepost confirming that recurrence/aggravation analysis under Nally is the proper lens for successive work-injury cases—even when an earlier commutation leaves the claimant without a compensable avenue for a later flare-up.