In a recent decision, Zak v. State of Minnesota, No. WC25-6629 (W.C.C.A. May 12, 2026), the Minnesota Workers’ Compensation Court of Appeals reaffirmed two important principles in Minnesota workers’ compensation law: (1) compensation judges are not required to make separate credibility findings regarding every witness who testifies, and (2) whether a work injury constitutes a temporary or permanent aggravation of a pre-existing condition remains a fact question largely dependent upon the compensation judge’s weighing of the evidence.
Background
The employee had an extensive history of low back problems predating the injury at issue. Most notably, he was diagnosed with childhood spondylolisthesis at L5-S1, with bilateral lytic pars defects. In 2007, he suffered a low back injury with imaging supporting the pars defect, mild arthropathy, and potential for synovitis.
In 2020, he sustained a significant low back injury while working for Lakeville Collision, Inc (Lakeville). That injury ultimately resulted in lumbar fusion and decompression surgery. Although the surgery reportedly resolved his radiating leg symptoms, the employee continued to experience chronic low back complaints.
The 2020 claim was resolved through settlement, with only future low back surgery remaining open.
Following the 2020 injury, the employee changed employers and eventually began working as a cook for the Minnesota Department of Veterans Affairs. On July 22, 2024, he slipped on a wet floor while working and sustained an admitted work injury. Subsequent medical imaging revealed fractured and loosened pedicle screws associated with his prior lumbar fusion.
The employee underwent revision surgery in December 2024. During that procedure, surgeons noted that the original fusion hardware remained solid while newer screws were loose and fractured. Following surgery, the employee continued to report bilateral leg symptoms despite imaging showing no clear neural impingement.
The primary dispute centered on causation and duration of injury. The employee’s treating surgeon opined that the employee had not yet reached maximum medical improvement and that the July 2024 work injury remained a substantial contributing factor in his ongoing condition. Conversely, the employer and insurer’s independent medical examiner, Dr. Dunn, opined that the July 2024 injury represented only a temporary aggravation of the employee’s longstanding lumbar condition and that the aggravation had fully resolved approximately six weeks after the revision surgery.
The Compensation Judge’s Findings
The employee and his mother both testified at the hearing.
The compensation judge described the employee’s testimony as “earnest but unreliable” and no credibility determinations were made for the employee’s mother. Ultimately, the judge adopted Dr. Dunn’s opinions. Based upon that medical evidence, the judge concluded that the July 22, 2024, work injury constituted a temporary aggravation of the employee’s pre-existing low back condition, that the aggravation resolved by February 6, 2025, and that the employee reached maximum medical improvement on that date.
As a result, responsibility for medical treatment through February 6, 2025, was apportioned between the two injury dates, while treatment after that date was attributed solely to the prior 2020 injury. Temporary total disability benefits were awarded only through the date the temporary aggravation was found to have resolved.
The employee appealed.
The Appeal
On appeal, the employee argued that the compensation judge committed reversible error by failing to consider the testimony of the employee’s mother and to make an express credibility determination regarding it.
The employee further challenged the compensation judge’s determination that the July 2024 injury was merely a temporary aggravation rather than a permanent worsening of his condition.
The W.C.C.A. rejected both arguments and affirmed.
Credibility Findings Need Not Address Every Witness
The Court first addressed the employee’s argument concerning his mother’s testimony.
The W.C.C.A. acknowledged that compensation judges are often required to assess witness credibility. However, the Court explained that a judge is not required to make a separate, explicit credibility determination for every witness who testifies.
Here, the mother’s testimony largely corroborated the employee’s own account of his symptoms and limitations. Because her testimony did not provide independent evidence regarding a separate factual issue, the compensation judge’s assessment of the employee’s credibility effectively addressed the substance of her testimony as well.
Accordingly, the Court concluded that the absence of a separate credibility finding regarding the mother’s testimony did not constitute reversible error.
Temporary Versus Permanent Aggravation Remains a Fact Question
The Court next addressed whether substantial evidence supported the compensation judge’s determination that the July 2024 injury was only a temporary aggravation.
The W.C.C.A. reiterated that determining whether an aggravation is temporary or permanent is generally a factual question entrusted to the compensation judge. In making that determination, judges may consider both medical evidence and non-medical evidence, including the employee’s medical history, treatment course, symptom progression, and functional abilities.
While the treating surgeon believed the employee had not yet reached maximum medical improvement and continued to attribute ongoing symptoms to the July 2024 injury, the compensation judge was entitled to rely upon Dr. Dunn’s contrary opinion.
The Court found Dr. Dunn’s opinion adequately founded and persuasive. Her conclusion was tied to a specific recovery period following the revision surgery and was consistent with the employee’s lengthy history of chronic low back complaints predating the July 2024 injury.
Because substantial evidence supported the compensation judge’s reliance on Dr. Dunn’s opinion, the W.C.C.A. affirmed the finding that the July 2024 work injury was a temporary aggravation that resolved by February 6, 2025.
Practical Takeaways
Zak serves as a useful reminder that appellate review remains highly deferential to compensation judges on issues involving credibility and causation.
First, compensation judges are not required to issue separate credibility findings regarding every witness. Where testimony merely corroborates another witness’s account and does not provide independent evidence on a separate factual issue, a detailed discussion of that testimony may be unnecessary.
Second, temporary aggravation disputes continue to be heavily dependent upon the quality and foundation of the competing medical opinions. Even where a treating physician supports ongoing causation, a well-founded IME opinion may provide substantial evidence supporting a finding that a work injury has resolved.
Finally, the decision underscores the importance of developing a complete medical history in cases involving significant pre-existing conditions. Here, the employee’s longstanding lumbar problems, prior surgery, and prior workers’ compensation claim provided critical context supporting the conclusion that the 2024 injury represented only a temporary aggravation rather than a permanent worsening of his condition.
For employers and insurers, Zak provides another example of the W.C.C.A.’s continued willingness to affirm compensation judges who rely upon adequately founded IME opinions to distinguish between the effects of a temporary work injury and the natural progression of a pre-existing condition.