The employee appeals from the compensation judge’s findings that the employee failed to prove that his chronic pain disorder, anxiety, and/or depression are a result of his admitted August 4, 1989, left knee injury; that the employee failed to prove the August 4, 1989, left knee injury was a substantial contributing factor to his permanent total disability from and after November 15, 2011; and that the employee failed to prove his work activities as a professional football player with the Minnesota Vikings Football Club caused, aggravated, or accelerated his traumatic brain injury/cognitive impairment, chronic traumatic encephalopathy and/or dementia.  We affirm.

There is minimal dispute as to the underlying facts in this case.  The employee began playing football in high school.  He then played as a defensive end for the University of Michigan for five years.  He graduated with a degree in speech communication and enrolled for one year in graduate school to study urban planning.

The employee was drafted into the National Football League (NFL) and began his professional football career in 1980 playing defensive end for the St. Louis Cardinals.  He transferred with the team in 1988 when the Cardinals became the Arizona Cardinals.  In March 1989, the employee signed with the Minnesota Vikings.  His playing time with the Vikings consisted of participation in two mini-camps in April or May 1989, and four to six days of training camp before he injured his left knee on August 4, 1989.  The employee underwent an arthroscopic diagnostic examination on August 15, 1989, and was started on a rehabilitation program, but his left knee never regained sufficient function to return to play.  His contract was terminated by the Vikings in September 1989.

During mini-camp, there were team meetings in the morning followed by 2½ hours of full contact drills in the afternoon.  There was conflicting evidence as to whether the mini-camps were three days or five days in length.  Training camp consisted of practicing full contact drills twice a day for 2½ hour sessions, six days a week.  Approximately 65 plays were run per practice session.  In an unappealed finding,^[1] the compensation judge found the employee practiced with the Minnesota Vikings a total of 10 to 12 days over a span of three to four weeks, 6 days of which consisted of partial days during mini-camp.

In October 1990, the employee began working for Anheuser-Busch as an assistant branch manager of a distribution operation.  In 1993, he purchased an independent distributorship of Anheuser-Busch in New Jersey.  He was president and CEO of the distributorship until 2002 when Anheuser-Busch hired him as their director of government and industry affairs.  He left Anheuser-Busch on November 15, 2011, due to performance issues related to cognitive problems and memory loss.

As a defensive lineman, the employee engaged in head-to-head, helmet-to-helmet collisions with offensive linemen.  The medical reports reference a number of concussions during the employee’s years playing football.  In 1978, while at the University of Michigan, the employee was brought to the emergency room after receiving a blow to the head and losing consciousness.  He was diagnosed with a mild closed-head injury.  In September 1980, while playing for the St. Louis Cardinals, the employee sustained a severe concussion and was taken from the game by ambulance.  He was hospitalized for 7 or 8 days and was on injured reserve until October 10, 1980.  The employee suffered another concussion in 1984 and was taken off practice for a week.  He sustained another concussion in 1985 during a game.  The employee also self-reported, to medical evaluators in 2012, a concussion in 1989 while playing for the Vikings, but in testimony at the hearing stated he could not recall whether he ever sustained a concussion while with the Vikings.  There was no medical record of a concussion in 1989.

The employee also testified that over his entire football career he would “get his bell rung” where he saw stars, got dizzy and disoriented, and would need a moment to catch his breath and get himself back together before continuing practice or playing in the game.  The employee wasn’t able to quantify how often it occurred, but stated that as time went on, it became more prevalent.  He agreed on examination that it occurred once a week, but less than once a day, but also agreed with the statement that, during mini-camp and during training camp with the Vikings, it was probably more than ten.  It is apparent from reading the employee’s testimony that he had little or no independent memory of the extent of any “bell ringers” he may have experienced during his 10 to 12 days with the Vikings.

The employee sustained multiple injuries during his career as a defensive lineman in the NFL.  All of the injuries, except the August 4, 1989, left knee injury, occurred during the 8 years the employee played for the St. Louis, and later Arizona, Cardinals.  The medical reports are somewhat inconsistent, but it can be concluded that the employee sustained injuries to his hands, fingers, and thumbs bilaterally, both elbows, both shoulders, toes on both feet, and multiple ankle and wrist sprains.  In 1985, the employee experienced right knee pain and swelling which was treated with arthroscopic surgery in December 1985.  He missed the remainder of the season.  In 1986, he reinjured the right knee in training camp and was again treated with arthroscopic surgery.  He was placed on injured reserve for the 1986 season.  The employee was placed on injured reserve due to problems with his low back radiating into the legs for the entire 1988 season.

In 2012, the employee reported chronic back pain, bilateral knee pain, and bilateral hip pain. He experiences intermittent pain in his neck and both shoulders.  He has a tingling sensation that runs bilaterally down his arms to his fingers with aching pain in his hands.  He experiences swelling in both of his wrists and ankles and pain in his toes.  The employee has used a cane since 2010 which he carries in his right hand and uses for balance and to keep the pressure off his knees.

On August 24, 2012, the employee filed a claim petition seeking permanent total disability benefits arising out of a specific injury to the left knee on August 4, 1989, sustained while playing football for the Vikings, and alleged Gillette injuries^[2] to the head/brain, and to the low back, neck, left shoulder, both elbows, both thumbs, bilateral hips, right knee, bilateral ankles, and/or bilateral great toes culminating on August 4, 1989.  The employee also contended that these injuries separately, or in combination, resulted in a consequential psychological injury in the nature of depression, anxiety, and/or chronic pain disorder.

The employer and insurer admitted the employee sustained a left knee injury on August 4, 1989, while playing for the Vikings, and also stipulated the employee had been permanently and totally disabled since November 15, 2011.

In a Findings and Order served and filed on February 21, 2014,^[3] the compensation judge found, among other things, that

In reviewing cases 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).  Where evidence conflicts or more than one inference may reasonably be drawn from the evidence, the findings are to be affirmed.  Id. at 60, 37 W.C.D. at 240.  Similarly, “[f]actfindings are clearly erroneous only if the reviewing court on the entire evidence is left with a definite and firm conviction that a mistake has been committed.”  Northern States Power Co. v. Lyon Foods Prods., Inc., 304 Minn. 196, 201, 229 N.W.2d 521, 524 (1975).  Findings of fact should not be disturbed, even though the reviewing court might disagree with them, “unless they are clearly erroneous in the sense that they are manifestly contrary to the weight of the evidence or not reasonably supported by the evidence as a whole.”  Id.

The compensation judge found the employee suffers from depression, anxiety, and chronic pain disorder due to his cognitive deficits and the multiple physical injuries he sustained while playing professional football.  The judge further, found, however, that the employee failed to prove the left knee injury of August 4, 1989, was a substantial contributing factor to his psychological condition.

The employee contends the evidence, including the employee’s testimony, overwhelmingly indicates the employee’s left knee injury was his most significant injury and remains one of his most significant conditions.  Thus, the employee argues, although the medical experts opined the employee’s psychological condition is a result of his injuries in combination, the employee is not excluded from recovery based on such a distinction given the undeniable significance of his left knee condition.

An adequately founded medical opinion is necessary to establish a causal relationship between an employee’s physical injury and an alleged consequential psychological injury.  Rindahl v. Brighton Wood Farms, Inc., 382 N.W.2d 855, 856, 38 W.C.D. 473, 475 (Minn. 1986).  Dr. Greenzang, a psychiatrist, diagnosed a cognitive disorder not otherwise specified, depression, and anxiety.  He attributed the employee’s psychological condition to his physical symptoms and cognitive deficits.  The doctor stated that the employee’s emotional reaction to his many physical injuries was inextricably entwined to such a degree that he could not attribute it to any specific injury or injuries.  Dr. Hoover, a psychologist, diagnosed major depression, anxiety disorder, pain disorder, and cognitive disorder not otherwise specified.  She opined the employee’s depression and anxiety was likely interrelated with multiple factors including chronic pain, fatigue, psychosocial stressors, and organic brain changes.  Neither doctor connected the employee’s psychological problems specifically to his left knee injury, and neither opined that the 1989 left knee injury was a substantial contributing factor to the employee’s psychological condition.

The compensation judge did not accept the employee’s testimony that his left knee condition was the most disabling of his many injuries and conditions.  It is the role of the finder of fact to assess the credibility and probity of a witness’s testimony.  Redgate v. Sroga's Standard Serv., 421 N.W.2d 729, 40 W.C.D. 948 (Minn. 1988).  The judge’s conclusion is not inconsistent with the medical evidence and the testimony presented.  Substantial evidence supports the compensation judge’s finding that the employee failed to meet his burden of proving that the 1989 left knee injury, specifically, is a substantial contributing cause of his psychological condition and we affirm.

The employee contends the compensation judge erred in failing to specifically determine whether the employee was permanently and totally disabled as a result, in part, of his depression, anxiety, and/or chronic pain disorder.  The issue before the judge was whether the “[August] 4, 1989, work injury [is] a substantial contributing factor to the permanent total disability.”  (Findings & Order, February 21, 2014, Issue 6.)  As previously discussed, the compensation judge found the employee failed to prove causation for a consequential, psychological injury related to the August 4, 1989, left knee injury.  The compensation judge also found the employee failed to prove a Gillette injury culminating on August 4, 1989.  Because the compensation judge decided the employee did not sustain a compensable psychological injury consequential to the claimed 1989 work injuries, it was not necessary to address the issue of whether the employee’s psychological condition contributed to his permanent total disability.

The employee also asserts the compensation judge appears to state the employee’s permanent total disability is due solely to his cognitive disorder relying upon the report of Dr. Yelena Usmanova, the employer and insurer’s medical expert, and if so, that is a misstatement of Dr. Usmanova’s opinion.  Dr. Usmanova explained that the employee’s chronic pain disorder, sleep apnea, and depression are significant compounding factors that contribute to his memory dysfunction and create cognitive difficulties.  The compensation judge found the reason for the employee’s inability to continue employment at Anheuser-Busch was his cognitive and memory problems.  This finding is not inconsistent with Dr. Usmanova’s opinion.

The employee contends the evidence does not support the compensation judge’s determination that the employee did not sustain a Gillette injury to his head/brain as a result of his work activities as a defensive end for the Minnesota Vikings.  There appears to be agreement that the employee does have cognitive problems likely related to injuries to the head while playing professional football.  The question is whether the employee’s time with the Minnesota Vikings was a substantial contributing factor to this condition.

The employee takes issue with the compensation judge’s comparison of the employee’s brief tenure with the Vikings with the significant head trauma documented in medical records during the employee’s previous years of playing football.  A Gillette injury by definition requires repetitive injury over time, and the amount of repetition and extent of injury are permissible factors for the judge to consider.  The employee played four years of high school football, five years of college football, and nine years of professional football with the NFL.  Of his 18-year football career, the employee spent 10 to 12 days playing football for the Vikings.  Six of those days were partial practice days during mini-camp.  The compensation judge properly considered the length of time the employee played for the Vikings in reaching her decision regarding whether a Gillette injury to the head/brain occurred on or about August 4, 1989.

The employee also takes issue with the compensation judge’s determination that the employee’s testimony was general, conclusory, not particularly detailed, speculative, inconsistent, and without independent memory of the extent of injuries he sustained while with the Vikings.  Counsel for the employee reminds the court that the employee suffers from a cognitive disorder.  Assessment of the credibility and probative value of a witness’s testimony is the unique function of the trier of fact.  Brennan v. Joseph G. Brennan, M.D., P.A., 425 N.W.2d 837, 839-40, 41 W.C.D. 79, 82 (Minn. 1988).  That a witness’s testimony may be unreliable due to mental difficulties is not a basis for reversing a judge’s decision.  Even v. Kraft, 445 N.W.2d 831, 834-35, 42 W.C.D. 220, 225-27 (Minn. 1989).  The employee also asserts his testimony should have been accepted because it was “unrefuted.”  The evidence presented to the court included extensive medical reports, all of which included various histories provided by the employee.  The compensation judge analyzed these reports at length in her memorandum and clearly reviewed all of them.  The evidence was conflicting and the compensation judge properly exercised her judgment in weighing the evidence and making a determination.

Finally, the employee argues the report of Dr. Steven LeBow, who provided an expert opinion on behalf of he employee, should have been accepted over the report of Dr. Usmanova, the independent medical examiner (IME).  The employee does not argue that Dr. Usmanova is not qualified to provide an expert opinion but argues, instead, that the doctor failed to adequately explain her opinion.  Such an argument goes to the persuasiveness of the opinion and not the foundation for the opinion.

Dr. Usmanova noted the employee had a history of documented concussions while playing for the University of Michigan and as a professional football player in 1980, 1984, and 1985.  The employee reported head-to-head collisions during practices with the Vikings as he had in the past when playing with other football teams, but received no treatment for such incidents.  Dr. Usmanova stated that, neurologically, the employee has evidence of cognitive impairment not otherwise specified, and that his history of concussions places him at risk of developing memory disorders and dementia.  The doctor maintained the medical records do not show any evidence of head injuries sustained while playing for the Minnesota Vikings, and that, in her opinion, there is no convincing medical data to support the conclusion that playing for the Vikings was a substantial contributing factor to the cognitive difficulties the employee is now experiencing.

Dr. LeBow provided two brief opinions supporting the employee’s claims.  In the second opinion, Dr. LeBow assumed the employee did not sustain a concussion which involved loss of consciousness while playing for the Vikings but did sustain head trauma that involved visual changes, bell ringing, dizziness, and/or headaches.  Dr. LeBow concluded that such symptoms comprised definitive evidence that there were concussive effects, and stated that one does not need a complete loss of consciousness to document concussion.  Therefore, to the extent the employee sustained such injuries while playing for the Vikings, Dr. LeBow was of the opinion that the employee’s time with the Vikings was a substantial contributing factor to his chronic, post-traumatic cognitive disorder.

Given the lack of reliable evidence that the employee sustained a concussion while playing for the Vikings or the extent of any “bell ringers” experienced by the employee during his time with the Vikings, the compensation judge found Dr. LeBow’s opinion was less persuasive, and, relying on the opinion of Dr. Usmanova, found the employee failed to prove his work activities for the employer caused, aggravated, or accelerated the employee’s cognitive and memory impairments.  Pursuant to Nord v. City of Cook, 360 N.W.2d 337, 37 W.C.D. 364 (Minn. 1985), this court must give deference to a compensation judge’s choice of medical expert provided the expert’s opinion has adequate foundation.  The compensation judge’s determination is supported by substantial evidence and is, accordingly, affirmed.