Liberty Mutual denied my workers' comp claim for a herniated L4-L5 disc from lifting a 90-lb compressor at work claiming it was 'pre-existing degenerative disease' even though I had no prior back complaints in 12 years of employment. Won permanent partial disability rating of 18% body as a whole using the AMA Guides 6th Edition, an IME challenge, and Wisconsin's preponderance-of-evidence standard. The aggravation-of-pre-existing-condition framework

Sharing this because the "pre-existing degenerative disease" defense is the single most common carrier tactic for denying workers' compensation back injury claims, and the legal framework for overcoming it is well-established in nearly every jurisdiction but is poorly understood by most injured workers. Background: I am 47 years old and have worked as an HVAC service technician for 12 years for a commercial mechanical contractor in southeastern Wisconsin. In December 2025 I was lifting a 90-pound rooftop compressor onto a delivery cart when I felt an immediate sharp pain in my lower back radiating down my right leg. I reported the injury to my supervisor that day, completed the WKC-12 incident report the following morning, and was seen at occupational health within 48 hours. The MRI obtained 9 days later showed a right paracentral L4-L5 disc herniation with nerve root impingement at the L5 nerve root, consistent with the clinical presentation of right L5 radiculopathy with foot drop and decreased sensation in the lateral calf and dorsum of the foot.

Liberty Mutual denied the workers' compensation claim through Helmsman Management Services (their TPA) on the basis that the MRI also showed multilevel degenerative disc disease at L3-L4 and L5-S1 with mild facet hypertrophy and that the L4-L5 herniation was therefore "pre-existing degenerative disease unrelated to the alleged work incident." The denial relied on an Independent Medical Examination performed by an orthopedic surgeon retained by the carrier who opined that the disc herniation was a degenerative process that "would have occurred regardless of the alleged lifting incident" and that the work incident was at most a "temporary aggravation that has resolved within the expected timeframe." This is a textbook example of how carrier-retained IMEs systematically discount the contribution of work incidents to symptomatic spine injuries by reclassifying acute disc herniations as degenerative processes.

The aggravation-of-pre-existing-condition framework. First, the legal standard in nearly every state including Wisconsin. The Wisconsin Worker's Compensation Act (Chapter 102) and the substantial body of case law interpreting it establish that a work injury is compensable if it "precipitates, aggravates, or accelerates" a pre-existing condition beyond its normal progression, even where the pre-existing condition is the underlying anatomic basis for the symptoms. Lewellyn v. ILHR Department (Wis. 1972) is the controlling Wisconsin case establishing this rule. The carrier's burden is not to show the existence of pre-existing degenerative disease (which exists in essentially every spine MRI of a 47-year-old) but to show that the work incident did not aggravate or accelerate the pre-existing condition. That burden is rarely met where the worker had no prior symptoms, no prior treatment, and an acute symptomatic event temporally linked to a specific work activity. Second, the IME challenge. The carrier's IME report must be challenged on multiple grounds: the reviewer's lack of treatment relationship, the failure to address the pre-incident asymptomatic status, the failure to apply the controlling legal standard (aggravation/acceleration rather than sole cause), and the failure to engage with the contemporaneous medical records documenting acute onset.

Third, the AMA Guides 6th Edition impairment rating. For permanent partial disability claims involving spine injuries the AMA Guides to the Evaluation of Permanent Impairment, 6th Edition (the controlling impairment rating methodology in Wisconsin and most states) uses the Diagnosis-Based Impairment (DBI) methodology with grade modifiers for functional history, physical examination findings, and clinical studies. An L4-L5 disc herniation with documented radiculopathy and surgical intervention typically rates Class 2 (moderate impairment) with grade modifiers based on residual symptoms, with whole person impairment ratings commonly running 13 to 22 percent body as a whole depending on the specific clinical presentation. The treating spine surgeon and the independent rating evaluator both produced reports supporting an 18 percent rating. The Wisconsin Department of Workforce Development - Workers' Compensation Division held a hearing in April 2026 where the ALJ found that the work incident was the precipitating cause of the symptomatic disc herniation under Lewellyn, that the IME report was unpersuasive because it failed to engage with the asymptomatic pre-incident status, and that the 18 percent permanent partial disability rating was supported by the preponderance of the medical evidence. Total recovery: $94,300 in PPD benefits plus the original medical and TTD benefits that had been disputed.