The employer and insurer appeal from the compensation judge’s finding that the employee’s need for proposed knee surgery is causally related to the employee’s work injury.  We affirm.

The employee was employed by Central Bi-Products Rendering Service [the employer] on January 6, 2005, when he slipped and fell, striking his right knee on a peg of a container at work.  He experienced immediate pain in that knee and sought treatment the next day from a physician assistant, Mark Helgeson, at Broadway Medical Center.  He reported having injured his knee the day before and having experienced progressive pain and difficulty ambulating.  He also reported a prior football injury to that knee but indicated that he had had no residual problems.  X-rays of the right knee taken on that date revealed severe degenerative changes but no fractures.  He was placed in a knee immobilizer.

The employee continued to treat with Mr. Helgeson until an MRI, recommended by Mr. Helgeson on March 7, 2005, was read as showing a possible tibial plateau fracture.  Mr. Helgeson then referred the employee to an orthopedist, and the employee was seen by Dr. Dennis A. Weigel at Alexandria Orthopedic Associates on March 16, 2005.  At that time, the employee reported a burning, sharp, and throbbing pain in the entire right lower leg, rating the pain as a 9 on a scale of 1 to 10.  Dr. Weigel noted in his records that the employee had moderate to severe radiographic changes in the right knee but had been asymptomatic until the injury at work.  It was Dr. Weigel’s goal to get the employee back to his pre-injury status.  The employee was treated with work limitations, therapeutic exercise, and cortisone injections.

The employee was seen by Dr. Dana J. Harms at Little Falls Orthopedics on August 8, 2005, for a second opinion.  Dr. Harms concluded that “the only way I can potentially alleviate his discomfort is a total knee arthroplasty.”

At a September 28, 2005, appointment, Dr. Harms noted that the employee’s right knee osteoarthritis was significant, and the doctor told the employee that his knee condition was advanced enough that a knee replacement would be reasonable.  The employee, however, indicated that he would like to try to continue with work restrictions.

The employee was seen by Dr. Ross Paskoff, for an independent medical examination [IME], on March 7, 2006.  Dr. Paskoff’s report of that date included a reference to an April 29, 2002, medical record from Parker’s Prairie Medical Center, where the employee was seen for right knee pain that he attributed to entering and exiting his truck 30 times a day.  Dr. Paskoff opined that the employee was suffering from moderate to severe osteoarthritis and synovitis of the right knee.  He also diagnosed a contusion, resulting in a posterior lateral tibial plateau compression fracture of the right knee, which had by that point healed.  It was Dr. Paskoff’s opinion that the osteoarthritis was due to genetics and wear and tear through the course of “physiologic loading.”  He also felt that the synovitis was related to the work injury.  At that time it was Dr. Paskoff’s opinion that “the severity of the above incident was such that it did significantly impact the knee for some time and that the current symptoms are residual of that injury.”  He did not, however, feel that the injury had any effect on the arthritis in the employee’s knee.

On October 15, 2007, the employee began treating with Dr. Phillip L. Prosapio at Little Falls Orthopedics.  New x-rays obtained on that date showed moderate degenerative arthritis, and Dr. Prosapio indicated that a total knee arthroplasty would be a “good viable option in the future.”

The employee was also seen by Dr. Loren Vorlicky for an IME on April 29, 2008.  In his report dated May 5, 2008, the doctor issued opinions related to the left knee only.  In an addendum report dated September 23, 2008, issued after he reviewed additional medical records, Dr. Vorlicky addressed the claim that the employee’s proposed right knee replacement was work related. It was Dr. Vorlicky’s opinion that the employee was a reasonable candidate for a right total knee replacement and that knee replacement was the only surgical option that would treat the employee’s osteoarthritis.  It was his opinion, however, that the employee’s osteoarthritis preceded the work injury and that the work injury “had no bearing on his need for a knee replacement at this time.”

On October 13, 2008, the employee returned to Dr. Prosapio for follow up, presenting with significant swelling and pain in the right knee.  Dr. Prosapio opined that,

A claim petition and medical request, filed by the employee, were consolidated by order of August 29, 2008, and came on for hearing on October 21, 2008.  Issues included causation.  In findings filed on January 20, 2009, the compensation judge found, in relevant part, that the employee’s need for the proposed right total knee arthroplasty was causally related to the January 6, 2005, work injury.  The employer and insurer appeal.

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 (2008).  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, 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 evidence or not reasonably supported by the evidence as a whole.”  Northern States Power Co. v. Lyon Food Prods., Inc., 304 Minn. 196, 201, 229 N.W.2d 521, 524 (1975).

In their appeal from the compensation judge’s decision on causation, the employer and insurer make several arguments as to why the compensation judge erred in relying on the opinion of Dr. Prosapio.  We are not persuaded by any of these arguments.

The employer and insurer first contend that Dr. Prosapio’s opinion has an inadequate factual basis because Dr. Prosapio was not personally involved in the employee’s treatment until October of 2007.  This argument has no merit whatsoever.  Specialists are often not brought into a case until other avenues of treatment have been exhausted.  While the employer and insurer argue that the “causation opinion of Dr. Prosapio necessarily relied on other information such as treatment records as the factual basis for his opinion,” exactly the same can be said of independent medical examiners.  In the instant case, the employer and insurer’s examiner, Dr. Paskoff, did not examine the employee until fourteen months after the injury, and Dr. Vorlicky, also their examiner, did not examine the employee until more than three years after the injury.  Doctors are not disqualified from rendering opinions on grounds of the timing of their examinations or treatment.

The employer and insurer’s second complaint is that Dr. Prosapio did not review all relevant treatment records.  In this regard, they point to Dr. Prosapio’s October 13, 2008, chart note, where he recorded, “[the employee] has also had what sounds like an IME.  I don’t have any records in that regard from the IME or from Alexandria to review.”  The employer and insurer further allege that Dr. Prosapio did not have any records regarding the employee’s treatment at Alexandria Orthopedics.  Dr. Prosapio’s office note of October 15, 2007, states, however, that the employee had an IME “which I have had a chance to review.”  The referenced IME would have been Dr. Paskoff’s IME report, and, in that report, Dr. Paskoff itemized the employee’s treatment with Dr. Weigel and Alexandria Orthopedics from March 16, 2005, through July 8, 2005, including references to x-ray and MRI findings.  As such, while Dr. Prosapio might not have had the actual records from Alexandria Orthopedics, he certainly had knowledge of their contents.  And, while it is possible that Dr. Prosapio did not have the IME report of Dr. Vorlicky, that report does not contain any additional relevant information on the issue of causation.^[1]

The employer and insurer next contend that Dr. Prosapio’s opinions are lacking in foundation because “there is nothing in the record to show that Dr. Prosapio was aware that Employee had sought treatment for right knee pain before the work incident of January 5, 2005, or that he was aware of the ‘extensive degenerative change’ findings of the right knee x-rays taken the day after the work incident.”  We note initially that the evidence received at hearing contains only two actual records from treatment that preceded the employee’s work injury, both of which are from Parkers Prairie Medical Clinic.  The first is dated April 29, 2002, when the employee was seen for right knee pain, with an entry indicating that “he does give a past history of having a right knee dislocation as a teenager playing football.”  The employee was diagnosed as having a right knee strain with tendonitis and was taken off work for four days.  The second entry is dated May 6, 2002, at which time the employee called the clinic to report that “his knee is now 100%.”  Dr. Prosapio apparently did not have these records for review.  However, as mentioned above, Dr. Prosapio did review Dr. Paskoff’s report, which details the employee’s treatment on January 7, 2005, including a reference to “a prior football injury,” the x-ray report of that date, and the specific findings of Dr. Richard Eiser, who read the x-ray.  In addition, Dr. Paskoff’s report details the April 29, 2002, visit to Parkers Prairie Medical Center for right knee pain.  Dr. Paskoff’s report adequately summarized the treatment in question.

Finally, the employer and insurer contend that Dr. Prosapio did not review or compare x-rays in order to evaluate the worsening of the degenerative changes.  However, we are not persuaded that his failure to do so invalidates his opinions.  The employee testified that he was not experiencing right knee problems at the time of his work injury, and the compensation judge found, in an unappealed finding, that, following the injury, “the employee has continually experienced right knee pain, which has gradually worsened.”  Furthermore, prior to the work injury, the employee had gone without right knee treatment for more than two and a half years, during which time he worked without restrictions or time off work related to his right knee.  The knee did not become symptomatic again until the date of the work injury and has worsened since then.  Dr. Prosapio acknowledged, in his opinion report of October 13, 2008, that the employee had preexisting degenerative arthritis, but he noted that the employee had landed hard on his knee at the time of injury and that pain, swelling and disability continued thereafter, concluding that “it is certainly reasonable that that has exacerbated and worsened his degenerative changes in the knee.”

A trier of fact’s choice between experts whose testimony conflicts is usually upheld unless the facts assumed by the expert in rendering his opinion are not supported by the evidence.  Nord v. City of Cook, 360 N.W.2d 337, 37 W.C.D. 364 (Minn. 1985).  In the instant case, Dr. Prosapio was apparently aware that the employee sustained an injury to his right knee while a teenager, that he sought treatment for the right knee on one occasion in 2002, and that x-rays taken at the time of the injury showed severe degenerative changes of the right knee.  Dr. Prosapio was also aware that the employee had not experienced ongoing right knee problems until the January 6, 2005, work injury and that his symptoms continued thereafter.  The employer and insurer have pointed to no facts assumed by Dr. Prosapio that were not supported by the record.  In addition, the compensation judge noted in his memorandum that the employee testified credibly that his right knee was essentially asymptomatic prior to the work injury, and, in an unappealed finding, the judge found that the employee’s knee pain has gradually worsened since that injury.  Credibility assessments are a unique function of the trier of fact.  Even v. Kraft Inc., 445 N.W. 2d 831, 42 W.C.D. 220 (Minn. 1989).

In that the record supports the conclusion that the employee had been asymptomatic for some time prior to the work injury, he sustained a blow to the knee sufficient to cause a compression fracture of the tibia, he has had pain in his right knee since that date, which has gradually worsened, and Dr. Prosapio has opined that the need for a right total knee arthroplasty is causally related to the work injury, there is substantial evidence to support the judge’s findings, and we affirm.