On Appeal from Superior Court, Washington Unit, Civil Division Helen M. Toor, J.
Patricia K. Turley and Stephen L. Cusick of Zalinger Cameron & Lambek, P.C., Montpelier, for Plaintiff-Appellee.
Stephen D. Ellis and William J. Blake, IV of Ellis Boxer & Blake PLLC, Springfield, for Defendant-Appellant.
PRESENT: Reiber, C.J., Dooley, Skoglund and Robinson, JJ., and Durkin, Supr. J., Specially Assigned
¶ 1. This appeal follows a dispute over an order based on a worker’s compensation agreement. Claimant injured his back in 2002. Claimant received an 8% whole-person impairment rating, with 6% of that rating referable to a previous injury. Based on this rating, claimant executed an Agreement for Permanent Partial Disability Compensation (Form 22) with his employer, the State, which the Commissioner of the Department of Labor then approved. Six years after the commissioner ordered the award, claimant underwent two more permanency evaluations with different doctors who both used a method that the first doctor had not used. Each of the subsequent evaluations resulted in higher whole-person impairment ratings before consideration of the portion attributable to any pre-existing impairment. Based on the higher ratings, claimant made a claim for additional benefits related to the 2002 injury. Claimant asserted that the award should be modified because his medical condition had worsened, or, alternatively, that the parties had based their Form 22 agreement upon a material mistake of fact. The commissioner ruled in the State’s favor. Claimant then appealed to the superior court, which reversed the decision of the commissioner and awarded claimant additional benefits after a bench trial. We vacate the decision of the superior court as to the issues on appeal.
¶ 2. The following facts were found by the commissioner and the superior court and are undisputed, unless noted otherwise. Claimant worked at the Vermont State Hospital as a psychiatric technician and ward aide. His duties involved lifting and dealing with patients who could be combative. Claimant suffered work-related injuries on three separate occasions in 1987, 1992, and 1997. All of these claims related to low back pain in the L5-S1 region of his spine, with radicular symptoms down claimant’s left leg. Claimant underwent surgery after each of these injuries and returned to work. After the 1992 injury, claimant’s surgeon rated him with a 10% permanent impairment to his spine, and the State began paying permanent partial disability benefits. There was no new rating for the 1997 injury.
¶ 3. In June 2002, claimant assisted a coworker in restraining a self-abusive patient. At one point, the patient lifted both legs off the floor, putting his entire weight on claimant and his coworker. Claimant immediately experienced low back pain, with sciatic pain radiating down both legs. Claimant’s symptoms after the 2002 injury differed from the previous three injuries in that low back pain predominated over radicular pain, and he experienced radicular symptoms on both sides rather than just his left side. Following the 2002 injury, claimant did not have surgery and did not return to his job at the hospital and was evaluated for a new work-related injury claim.
¶ 4. In a report issued in 2003, Dr. Maurice Cyr, claimant’s treating chiropractor, concluded that claimant had reached a medical end result and assigned a whole-person impairment rating of 5-8% for claimant’s lumbar spine injury. On the basis of this report, the parties entered into a Form 22 settlement agreement that identified claimant’s lumbar spine impairment as 8% whole person, from which was apportioned 6% on account of claimant’s permanent partial disability award for his 1992 injury.  See 21 V.S.A. § 648(d) (“An impairment rating determined pursuant to this section shall be reduced by any previously determined permanent impairment for which compensation has been paid.”). The commissioner approved the agreement on February 3, 2004, and awarded claimant benefits for the agreed-upon 2% permanent impairment rating.
¶ 5. Claimant continued to experience low back pain and radicular symptoms. In November 2004, an MRI revealed an L4-5 disc herniation. The injuries from 1987, 1992, and 1997 had all involved the L5-S1 area of claimant’s spine. An MRI taken in 2002 in connection with the injury did not reveal any disc herniation at the L4-5 level. Claimant sought legal representation and in July 2008, consulted with Dr. Sikhar Banerjee. Dr. Banerjee concluded that claimant’s worsened symptoms related to the 2002 work injury and to the L4-5 disc herniation despite the results of the 2002 MRI and assessed a 13% whole person impairment rating. Initially, Dr. Banerjee evaluated claimant using the diagnosis-related estimate (DRE) method, the same used by Dr. Cyr in 2002 to evaluate whole person impairment. Subsequently, Dr. Banerjee conducted a second evaluation using the range-of-motion (ROM) method and assessed a whole-person impairment rating of 25%. Dr. Banerjee subtracted the 8% previously rated and paid in accordance with Dr. Cyr’s impairment rating, leaving 17% additional whole-person impairment attributable to the June 2002 injury. 
¶ 6. The State’s expert, Dr. William Boucher, reached a different result. Dr. Boucher concluded that because claimant had prior lumbosacral injuries and multiple surgeries, the ROM method-not the DRE method-was the appropriate evaluation method for determining claimant’s impairment for the 2002 injury. Dr. Boucher applied this method to the 2002 injury evaluation conducted by Dr. Cyr and Dr. Banerjee’s initial evaluation that used only the DRE method. Dr. Boucher concluded that claimant likely had an 18 % whole-person impairment as of May 2002. Dr. Boucher concluded claimant had a 20 % whole person impairment in 2010. Based on a series of assumptions about the likely range-of-motion deficits he thought claimant would have experienced after his 1997 surgery, Dr. Boucher concluded that claimant had an 18 % whole-person impairment prior to his June 2002 injury. Subtracting 18% from 20%, Dr. Boucher concluded that claimant’s impairment from the 2002 injury gave rise to an additional whole-person impairment of 2%. Using an entirely different method, Dr. Boucher reached a result that agreed with Dr. Cyr’s rating of 2% relating to the 2002 injury. Dr. Boucher’s result-2% impairment attributable to the 2002 injury-was consistent with the Form 22 agreement executed by the parties and approved by the commissioner. 
¶ 7. Given the differences in the methods used and results of the three whole-person impairment evaluations, claimant sought an award of additional benefits relating to the 2002 injury. Claimant argued to the commissioner that the award in the 2004 Form 22 agreement should be modified because his condition had worsened. Alternatively-and primarily at issue on appeal-claimant argued that the Form 22 agreement should be reformed under the mutual mistake doctrine and that Dr. Banerjee’s rating should be substituted for Dr. Cyr’s rating, as Dr. Cyr should have used the ROM method rather than the DRE method in making the determination upon which the Form 22 was based. The commissioner concluded that claimant had failed to prove that his worsened condition after 2008 related to his 2002 injury. Thus, the commissioner decided in favor of the State and declined to modify the award on the ground of a change in condition.
¶ 8. The commissioner also decided in favor of the State with regard to claimant’s alternate argument that the Form 22 approved in 2004 was based on a material mistake of fact. The commissioner noted “that the ‘material portion’ of the Form 22 at issue here concerns only the impairment rating to which the parties agreed-8% whole person-not the methodology used to derive it.” Neither claimant nor the State introduced any evidence of what claimant’s impairment rating would have been in 2002 had he been evaluated using the ROM method at that time. As the commissioner stated, based on the evidence presented at the administrative hearing, “[ i ]t is impossible to know... whether the 8% permanency to which the parties ultimately agreed would have been higher, or lower, or perhaps just the same.” The commissioner added that even if Dr. Cyr’s interpretation ...