The employee appeals the compensation judge’s finding that the employee did not prove that he sustained a Gillette^[1] injury while working for the employer.  We affirm.

On July 11, 2005, Robert Lowrey, the employee, began working as a full-time pipe insulation installer for Gagnon Insulation, the employer, which was insured for workers’ compensation liability by Liberty Mutual Insurance Company, the insurer.  The employee has worked as an insulation installer since 1974, as a union member since 1981.  Over the years, the union has sent the employee to work for many different employers.  He has worked in many different states, but resides in Missouri.

The employee was hired by the employer to work as a pipe insulator at the Flint Hills Refinery in Minnesota.  Before he was hired by the employer, the employee had not experienced any pain, tingling, or numbness in his hands, fingers, or wrists, had never been diagnosed with carpal tunnel syndrome, and had not undergone any treatment for any such condition.  According to the employee, he did not undergo a pre-employment physical before working for the employer, and was not under any physical restrictions or limitations.  His work for the employer involved using his hands to measure, cut, carry, and install insulation and fasteners on pipes, using hand tools, and climbing ladders; as compared to many worksites, the employee’s work for the employer involved more climbing up and down ladders.

The employee testified that he noticed symptoms in his hands and wrists, including numbness, stiffness, and tingling, approximately two weeks after starting work for the employer.  He was climbing a ladder the first time he noticed these symptoms.  A few weeks later, his tingling symptoms had worsened, he had no feeling in his hands, and he was dropping things while working. The symptoms continued intermittently.  The employee noticed that climbing ladders and using tin snips made his symptoms worse.  The employee did not report any of these symptoms to his supervisors at work.  The employee noticed that his grip had weakened and that he changed how he worked by being more careful to keep his tools in his tool pouch, by working more slowly, and by being more careful while climbing ladders.

The employee quit working for the employer on October 6, 2005, to return to Missouri to care for his wife while she recovered from back surgery.  He testified that his symptoms continued for awhile and then resolved while he was off work.  On October 21, 2005, the employee began working for Cherne Contracting in Illinois, a job he again obtained through his union and which was similar to his work for the employer, but with less ladder climbing.  The employee testified that his hand and wrist symptoms recurred about two weeks after he began working for Cherne.  The employee also developed an additional symptom of pain in his hands, wrists, and forearms.  He sought treatment for these symptoms for the first time on November 7, 2005, while at a check-up appointment with his family physician, Dr. Frances McKinney.  She referred him to an orthopedic specialist, Dr. William Feinstein, who examined him and, in a chart note dated November 11, 2005, noted that the employee reported bilateral hand pain, numbness, and tingling, and that the symptoms were severe enough to wake him at night.  Dr. Feinstein suspected that the employee had severe bilateral carpal tunnel syndrome and referred him for an EMG of both arms.  Dr. Daniel Phillips, a neurologist, performed an EMG on November 21, 2005, and interpreted the findings as showing bilateral sensory motor median neuropathies across the carpal tunnels, moderate on the right and mild on the left.

Upon review of the EMG results, Dr. Feinstein diagnosed bilateral carpal tunnel syndrome; he recommended surgery and proceeded to schedule the employee for surgeries to both wrists in late December 2005 and early January 2006.  After Cherne advised the employee and his co-workers of a pending seasonal layoff, the employee agreed to be laid off by Cherne in December since he was anticipating undergoing carpal tunnel surgery and to allow another worker with less seniority to retain his job.  At that time, the employee was still able to perform his regular job duties, although his hand and wrist symptoms had increased.  As of December 26, 2005, Dr. Feinstein restricted the employee from work until after he could undergo carpal tunnel surgery.

The employee evidently sought authorization from his union health insurance provider for the recommended surgeries.  According to the employee, the Heat and Frost Insulators Welfare Fund, which provided him with medical insurance, considered the employee’s carpal tunnel condition to be work-related, and would not pay for the recommended surgery until after the employee filed a workers’ compensation claim in Illinois against Cherne and had been denied.

The employee instituted a claim for workers’ compensation benefits in Illinois seeking benefits related to his work for Cherne Contracting.  In January 2006, during the pendency of the Illinois litigation, the employee was evaluated by Dr. Michael Beatty, a hand surgeon, who diagnosed bilateral carpal tunnel syndrome, and opined that that the employee’s symptoms were “consistent with causation on a work-related basis.”

The employee’s claim was addressed at a hearing on April 26, 2006, before an arbitrator with the Illinois Workers’ Compensation Commission.^[2]  At that hearing, the employee testified that while working in Minnesota, he developed generalized soreness in his hands, arms, legs and back, and “was sore all over.”  He attributed his stiffness and tight forearm muscles to the climbing that he did while working with the pipe racks in Minnesota, and also to “old age.”  The employee testified that his hands bothered him in Minnesota but he differentiated the symptoms he experienced while working between June and October 2005, in Minnesota, from those he experienced while working between late October and December 2005, in Illinois. He described his symptoms in Minnesota as being “just like working out, a stiffness of your muscles,” which he attributed in part to the climbing required of his work in Minnesota.  By contrast, the symptoms that developed while working for Cherne were “a sharp pain, a numbness, loss of mobility,” “a tingling, a sensation like I cut myself,” and “no feeling” in his hands, which made it difficult for him to hold on to items.

According to a decision issued on May 25, 2006, the Illinois arbitrator denied the employee’s claim for compensation, concluding that the employee’s bilateral carpal tunnel syndrome was not causally related to his employment with Cherne between late October and early December 2005.  The arbitrator’s decision was based, in part, on the employee’s testimony, on testimony provided by Dr. Beatty (which was not included in the Illinois transcript nor in the Minnesota hearing record), and a portion of the employee’s medical records.

On July 10, 2006, the employee underwent right wrist surgery, performed by Dr. Feinstein, and on July 24, 2006, he underwent surgery on his left wrist.  The employee remained off work between his second surgery until he returned to full-time work with no restrictions on October 1, 2006.

The employee later retained a Minnesota attorney, and his medical records were reviewed by Dr. David Falconer, an orthopedic surgeon.  In a March 2007 report, Dr. Falconer opined that the employee’s work for the employer in Minnesota was a significant contributing factor in the development, onset and manifestation of his bilateral carpal tunnel condition.  He based this on the nature and progression of the employee’s symptoms, the time spent working for the employer in Minnesota, and the findings on the employee’s EMG study.  Dr. Falconer also ruled out diabetes as a contributing factor of the employee’s condition.^[3]

On May 9, 2007, the employee filed a claim petition in Minnesota for workers’ compensation benefits.  The employer and insurer denied the employee’s claim, arguing that the employee’s condition was not causally related to his work for the employer.

On July 7, 2008, Dr. Scott McPherson, an orthopedic surgeon, reviewed the employee’s medical records at the employer and insurer’s request.  Dr. McPherson concurred with the diagnosis of carpal tunnel syndrome, and that the employee had sustained a Gillette injury.  He concluded, however, that the employee’s work for the employer for three months did not represent a substantial contributing factor of the employee’s carpal tunnel syndrome because that work was of short duration, and because his  symptoms did not worsen until after he began working for Cherne.  Dr. McPherson commented that the employee had been performing his insulator work for 30 years and, therefore, “a less than three-month time period [would] be a very small portion of this timeframe.”  Dr. McPherson concluded that the “ultimate breakdown or disability” date of the employee’s carpal tunnel condition was December 5, 2005 - - the date on which the employee consulted Dr. Feinstein and was diagnosed with bilateral carpal tunnel syndrome and was referred for surgery.  Dr. McPherson also noted that the employee’s weight and diabetes would be predisposing factors for carpal tunnel syndrome.

An evidentiary hearing was held on August 29, 2008, to address the employee’s Minnesota claim petition.  In her findings and order, the judge denied the employee’s claim, concluding that the employee’s symptoms did not cause objective external consequences and did not constitute disablement sufficient for a finding of a minute trauma injury arising out of the employee’s work for the employer between July 11 and October 6, 2005.  Even though she denied the claim, the compensation judge found that the employee had provided the employer with timely notice in 2007 of his claimed 2005 injury, as he had no reason to believe he had sustained a Minnesota work injury until Dr. Falconer issued his report on causation in March 2007.  The compensation judge accepted Dr. McPherson’s opinion that the employee’s work for the employer did not represent a significant contributing cause of his carpal tunnel syndrome.  Included in the judge’s analysis was her finding that the employee’s hand and wrist symptoms while working for the employer were not serious enough to cause him to lose time form work or seek medical treatment at that time, and that he was able to work his regular job with only minor changes by the time he stopped working for the employer in October 2005.  The compensation judge also found the employee’s testimony regarding the timing and description of his symptoms while working for both employers in 2005 to be inconsistent and not a reliable source of information.

The employee appeals.

The compensation judge found that the employee had not proven that he sustained a minute trauma injury, in the nature of bilateral carpal tunnel syndrome, as a substantial result of his work for the employer between July 11 and October 6, 2005.  The employee appeals, arguing that the evidence, including the medical report of Dr. Falconer, demonstrates that he sustained a Gillette injury while working for the employer, and contends that the compensation judge erred by denying the employee’s Gillette injury claim on the basis that he had not sustained a “legally sufficient disablement.”  The employee argues that this legal standard has been limited in applicability to occupational disease cases, and that the compensation judge erred by applying that legal theory to this case.  The employee further argues that he has satisfied the appropriate legal standard applied in cases addressing Gillette injuries, as he has presented medical support that shows a causal nexus between his work activities and subsequent disability.  See Steffen v. Target Stores, 517 N.W.2d 579, 50 W.C.D. 464 (Minn. 1994).

The employee also contends that the judge’s application of the incorrect standard led to her erroneous conclusion that “symptoms must cause objective, external consequences before a minute trauma injury occurs” and her conclusion that the employee did not prove the occurrence of any ascertainable event that could be determined as demonstrating a Gillette injury.

A Gillette injury is a gradual breakdown of a body part or an aggravation of a pre-existing condition as the result of repetitive, minute trauma in the performance of an employee’s ordinary work activities.  Gillette v. Harold, Inc., 257 Minn. 313, 101 N.W.2d 200, 21 W.C.D. 105 (1960).  To establish a Gillette injury, the employee must “prove a causal connection between [his] ordinary work and [the] ensuing disability.”  Steffen, 517 N.W.2d at 581, 50 W.C.D. at 467.  The determination of a Gillette injury “primarily depends on medical evidence.”  Id. (citing Marose v. Maislin Transp., 413 N.W.2d 507, 40 W.C.D. 175 (Minn. 1987)).

Earlier cases involving Gillette injuries required an employee’s cumulative trauma to be sufficiently serious to disable him from work in order for the injury to be compensable.  See  Carlson v. Flour City Brush Co., 305 N.W.2d 347, 350, 33 W.C.D. 594, 598 (Minn. 1981).  Minnesota courts since have recognized several other “ascertainable events” that can establish the date of “ultimate breakdown,” which is the time when repetitive micro-trauma becomes a compensable injury.  It is not mandatory that an employee be totally disabled from all work activity or suffer a wage loss in order to determine that a Gillette injury has occurred.  Johnson v. Lakeland Bean Co., 39 W.C.D. 884 (W.C.C.A. 1987).  The date of injury should “be determined on all the evidence bearing on the issue,” including other “ascertainable events” evidencing disability.  Schnurrer v. Hoerner-Waldorf, 345 N.W.2d 230, 233, 36 W.C.D. 504, 509 (Minn. 1984).  Ascertainable events may include the initiation of medical treatment, the imposition of work restrictions and modification of work duties, or the last date of employment.  See Dillon v. Pennco Constr., No. WC08-127 (W.C.C.A. Sept. 5, 2008).  There may be multiple dates that could be the date of culmination, and the date might not be determined to have occurred at the earliest ascertainable event.  See Simonson v. Zupanich Bros., slip op. (W.C.C.A. Jan. 27, 2000).

Liability may not be imposed on an employer unless the period of employment at issue was a substantial contributing cause of the employee’s disability.  Tannahill v. Mid-American Lines, 40 W.C.D. 726 (W.C.C.A. 1987).  In this case, the employee has worked as a pipe insulator, which is a physically challenging occupation, for approximately 35 years, and during his career he has worked, through his union, for various employers.  The employment period of time at issue here was from July 22 to October 6, 2005; the employee testified about the onset of his symptoms during that period of time, and also about the recurrence of his symptoms later in 2005 while he was employed by Cherne Contracting.  The compensation judge concluded that the employee did not sustain a Gillette injury as a result of his work for this employer in 2005, citing to various factors she considered had led to “no legally sufficient disablement . . . for purposes of finding a minute trauma injury.”

We are troubled, however, by that particular wording and by what we perceive is an incorrect legal standard - - one that resembles the standard set forth in Reese v. North Star Concrete, 38 W.C.D. 63 (W.C.C.A. 1985).^[4]  The Reese standard has been supplanted by the one outlined by the Minnesota Supreme Court in Steffen that requires an employee, in the case of Gillette injury claims, to “prove a causal connection between [his] ordinary work and ensuing disability,” and that “the question of a Gillette injury primarily depends on medical evidence.”  Steffen, 517 N.W.2d at 581, 50 W.C.D. at 467.  Despite our concern, however, about the judge’s reference to “no legally sufficient disablement,” which is the wording that forms part of the basis for the employee’s appeal, it is clear that the compensation judge based her ultimate conclusions on her review of the medical evidence, as required by Steffen.

The record contains conflicting medical opinions on the issue of causation.  Drs. Beatty, Falconer and McPherson agreed that the employee’s condition was work-related.  Dr. Falconer concluded that the employee sustained a Gillette injury while working for the employer in Minnesota; Dr. Beatty did not assign liability to a particular period of employment. Dr. McPherson determined that the employee’s injury culminated in December 2005 but that it did not result from his work for the employer in Minnesota.  The compensation judge reviewed the various medical records and opinions, and specifically accepted Dr. McPherson’s opinion that the employee’s three-month period of work for this employer was not a substantial contributing factor of the employee’s carpal tunnel syndrome.  It is the compensation judge's responsibility, as trier of fact, to resolve conflicts in expert testimony.  Nord v. City of Cook, 360 N.W.2d 337, 342, 37 W.C.D. 364, 372 (Minn. 1985).  As we have held in other cases as well, this court will generally affirm a compensation judge’s decision which is based on a choice between competing medical opinions.  Perry v. ADB Constr., Inc., 68 W.C.D. 491 (W.C.C.A. 2008).

The compensation judge also reviewed the employee’s testimony, and found that the employee was not a reliable source of information given the inconsistencies in his testimony regarding the nature and extent of his symptoms, when they developed, and how they affected him.  The assessment of witness credibility is the unique function of the trier of fact.  Dille v. Knox Lumber/Div. of Southwest Forest, 452 N.W.2d 679, 680, 42 W.C.D. 819, 821 (Minn. 1990).  While we do not believe that the employee’s testimony concerning the onset and progression of his symptoms was so obviously inconsistent between his Illinois and Minnesota hearings, the compensation judge had the opportunity to hear the employee’s testimony, and this court must give due weight to the compensation judge’s opportunity to judge the credibility of a witness.  As we have repeatedly held, this court must uphold the judge’s credibility determination unless it is manifestly contrary to the evidence as a whole.  Even v. Kraft, Inc., 445 N.W.2d 831, 834-35, 42 W.C.D. 220, 225-26 (Minn. 1989).

On appeal, the Workers’ Compensation Court of Appeals must determine whether “the findings of fact and order [are] clearly erroneous and unsupported by substantial evidence in view of the entire record as submitted.”  Minn. Stat. § 176.421, subd. 1.  Substantial evidence supports the findings if, in the context of the entire record, “they are supported by evidence that a reasonable mind might accept as adequate.”  Hengemuhle v. Long Prairie Jaycees, 358 N.W.2d 54, 59, 37 W.C.D. 235, 239 (Minn. 1984).  We concur with the employee that there is evidence in the record to support his claim of a Gillette injury.  Under our standard of review, however, where evidence is conflicting or more than one inference may reasonably be drawn from the evidence, the compensation judge’s findings are to be affirmed.  Id. at 60, 37 W.C.D. at 240.  The issue on appeal is not whether the record would have supported a different date of injury, or any Gillette injury at all, but whether the judge’s decision is supported by evidence that a reasonable mind might accept as adequate.  Reel v. Loftness Specialized Farm Equip., slip op. (W.C.C.A. Feb. 3, 2004).  In this case, the compensation judge reviewed the evidence and testimony submitted into the record and concluded that the evidence did not establish a Gillette injury during the employee’s approximately three months’ employment in 2005 with the employer.  While a contrary result could have been reached in this case, the compensation judge’s finding, that the employee did not sustain a Gillette injury while working for this employer, is supported by adequate evidence in the record as a whole, and we must, accordingly, affirm.