The employer and the insurer Grinnell Mutual Group appeal from the compensation judge’s determination that the employee’s July 10, 1986, personal injury to the ankle was not a substantial contributing cause of the employee’s need for surgery to the knee, and that Grinnell Mutual Group is solely liable for payment of the expenses for the employee’s right knee replacement surgery.  We affirm.

Robert A. Ornberg, the employee, worked for Beckman’s Appliance & TV, the employer, for 25 years, from 1972 until 1997.  His job duties included TV, refrigeration, and appliance repair, TV antenna installation and service, and appliance delivery.

On July 10, 1986, the employee sustained an admitted personal injury to his right ankle.  The employer was then insured by Travelers Group.  The employee sought treatment from Dr. Leitch at the Litchfield Clinic reporting persistent problems after spraining his right ankle at work.^[1]  X-rays were taken that suggested possible old, chronic changes in the posterior joint of the ankle.  Dr. Leitch diagnosed a possible ligamentous ankle injury and treated the employee conservatively.  The employee then received treatment at Litchfield Chiropractic from August to September 1986, after which point the employee was released from care, to return as necessary.

On May 21, 1992, the employee sustained an admitted personal injury to his right knee.  The employer was then insured by Grinnell Mutual Group.  The employee testified that while carrying an air conditioner or microwave, he tripped and fell forward onto the knee.  The employee was initially seen at the Litchfield Clinic by Dr. Detert on May 26, 1992.  The doctor diagnosed traumatic patellar tendonitis, prescribed icing and nonsteroidal anti-inflammatory medication, and released the employee to return to work with no deep knee bending or squatting.

The employee continued to have problems with the knee and was referred to Dr. Iverson, an orthopedic surgeon.  Dr. Iverson examined the employee on September 1, 1992.  He diagnosed possible post-traumatic chondromalacia of the patella,^[2] and treated the knee with a corticosteroid injection.  The employee did not improve, and on December 3, 1992, Dr. Iverson performed surgery on the knee consisting of a partial lateral meniscectomy, arthroscopic debridement of the patellofemoral joint, and an open lateral retinacular release.  In the operative report, the doctor noted a complex posterior tear of the lateral meniscus, a flap on the articular surface of the tibia, and significant grade II chondromalacia in the patellofemoral joint.  In follow-up on December 22, 1992, Dr. Iverson noted the employee was doing very well, referred the employee for physical therapy, and released him to return to work effective January 4, 1993.

The employee returned to see Dr. Iverson on January 19, 1993.  The employee’s knee was responding well and he had returned to work.  The employee, however, reported increased pain in his right ankle while rehabilitating the knee.  X-rays of the ankle revealed significant osteochondritis dissecans involving the dome of the talus.^[3]  The employee was advised to stop rehabilitation and anti-inflammatory medications were prescribed for the ankle.

In letters to USF&G (now Travelers) dated August 19 and September 26, 1994, Dr. Iverson stated that x-rays taken on May 14, 1986, showed a fair amount of osteochondritis dissecans in the right ankle with early degenerative changes, not significantly advanced in 1993.  In Dr. Iverson’s opinion, there was no causal relationship between the employee’s 1986 ankle injury and the employee’s 1992 knee sprain.  In a final follow-up examination on October 18, 1994, Dr. Iverson noted the employee’s knee was doing reasonably well, and the employee’s main complaint was disabling ankle pain.

On January 20, 1995, the employee was seen by Dr. Schmidt, an orthopedic surgeon, for an opinion regarding ankle surgery.  The employee reported knee and ankle problems following a work injury in 1986, and stated his ankle condition had gradually worsened over the years.  The doctor reviewed x-rays of the right knee and ankle taken in October 1994.  Views of the knee showed early degenerative arthritis but no severe joint space narrowing or medial joint line changes.  The knee was stable with a little increased valgus,^[4] but with basically full motion and no definite crepitance.  The right ankle x-rays revealed an extremely large area of osteochondritis dissecans involving the entire dome of the talus.  Dr. Schmidt stated the employee’s ankle was so severely involved that the only treatment that made sense was an ankle fusion.  Dr. Schmidt performed the ankle fusion surgery on March 20, 1995.  The fusion was not successful, and on October 23, 1995, a second surgery was performed, consisting of a re-fusion of the ankle joint with a bone graft and an external fixator.

In a letter report to USF&G/Travelers dated February 8, 1995, Dr. Schmidt opined the 1986 ankle injury was a causative factor in his right ankle condition.  The doctor stated the association of the employee’s right knee problems with his ankle injury was “more problematic.”  (Resp. Ex. 3, Fairview Southdale.)

On October 31, 1995, the employee was examined by Dr. Wicklund at the request of Grinnell Mutual.  The employee told Dr. Wicklund his 1992 knee injury had resolved, and the doctor’s examination findings for the right knee were unremarkable.  Dr. Wicklund found “no connection” between the ankle and knee problems.

On December 18, 1995, the external fixator was removed in outpatient surgery.  Dr. Schmidt noted the fusion seemed stable and the foot was in satisfactory position.  In May 1996, Dr. Schmidt noted a valgus-type deformity in the ankle, and referred the employee for shoe corrections and orthotics.  By June 17, 1996, the employee had a solid fusion.  At the employee’s final visit on July 1, 1996, Dr. Schmidt observed the ankle was “in just a little valgus” but generally in satisfactory position, and that with an orthotic in his shoe, the employee “walks very satisfactorily.”^[5]  (Resp. Ex. 3, Fairview Southdale.)

The employee did not see Dr. Schmidt again until January 13, 2000.  The doctor then noted a deformity through the subtalar joint^[6] and a very definite valgus deformity of the right foot.  No further treatment was undertaken at that time.  The employee returned for follow-up on November 9, 2000.  Dr. Schmidt again noted very significant valgus at the heel and pronation in the foot causing difficulty walking.  The employee also reported some problems with his right knee that seemed to be related to his foot problem.  On examination of the knee, the doctor noted some early arthritic changes and and a little valgus in the knee.  Dr. Schmidt stated the employee’s biggest problem was the foot/ankle deformity, and referred the employee to Dr. Coetzee, a foot and ankle specialist at the University of Minnesota, for evaluation.

Dr. Coetzee examined the employee on January 5, 2001, and recommended surgery to correct the overall alignment of the right ankle.  The employee underwent the surgery, consisting of a corrective osteotomy of the distal tibia^[7] and a subtalar fusion, on February 22, 2001.  The employee had ongoing problems with pain control following the surgery, and on July 2, 2001, Dr. Coetzee diagnosed a non-union in the ankle.  On July 11, 2001, Dr. Coetzee performed a revision of the ankle fusion using a blade (fixation) plate, and implantation of an internal electrical bone stimulator.  The employee was advised he would have to be nonweight bearing for at least six weeks.

Dr. Coetzee, on September 24, 2001, noted the fusion was progressing satisfactorily and the ankle appeared well-aligned.  The employee’s right leg was about 2.5 cm shorter than the left, so the doctor ordered a rocker bottom shoe and orthotics to accommodate the fusion and equalize the leg lengths.  The employee continued to report significant pain and difficulty walking, and was taking a significant amount of narcotic medication.  In December 2001, Dr. Coetzee suggested a below the knee amputation, which the employee rejected.  In February 2002, Dr. Coetzee stated the ankle fusion appeared to be completely stable with no signs of nonunion.  The employee was referred to a pain clinic for evaluation.

On May 2, 2002, Dr. Monsein conducted a chronic pain consultation.  The employee reported mostly sedentary and somewhat limited activities, and that he had applied for Social Security disability benefits.  Dr. Monsein’s impression was chronic pain syndrome and depression with significant opioid tolerance issues.  Although recommended, the employee did not enter the pain rehabilitation program as he was diagnosed with a lymphoma in the summer of 2002.

The employee returned to see Dr. Monsein in September 2003.  The doctor noted the cancer was in remission, but the employee’s dose of narcotic medications and tolerance to opiates had increased significantly.  He recommended a gradual attempt to wean the employee off opioid medications.  The attempt was not successful, and the employee was then treated at Minnesota Advance Pain Specialists (MAPS), beginning in 2004, where he was diagnosed with complex regional pain syndrome/reflex sympathetic dystrophy (CRPS/RSD) secondary to the ankle injury.  He continued to treat at MAPS until February 2006, when he began receiving treatment for chronic right ankle/foot pain and CRPS/RSD from Dr. Todd Hess at the United Pain Center.  The employee’s treatment included pool therapy for conditioning and weight loss and the prescription of methadone, oxycodone, and other medications for pain control.  The employee continued to be followed at the United Pain Center on a quarterly basis through the date of hearing.

The employee testified his right knee did not really begin to bother him until after about 2005, but he did not go to see a doctor right away.  In October 2007, Dr. Hess noted the employee’s right knee also had been quite bad recently.  There was significant crepitus in the knees bilaterally and difficulty with range of motion in the right lower extremity.  The doctor’s impression was very significant arthritis in both knees, right worse than the left.

In May 2008, the employee developed a spontaneous septic infection in the right knee requiring hospitalization.  On May 23, 2008, Dr. Kaus performed an arthroscopic irrigation and debridement of the knee and insertion of a drain.  In the operative report, the doctor noted severe tricompartmental degenerative arthritis in the knee.

On October 8, 2008, the employee was seen by Dr. Nessler, an orthopedic surgeon, for evaluation of the right knee.  The doctor noted severe crepitation, lateral laxity of the knee, and quite a bit of pain from the knee.  X-rays showed advanced arthritis and valgus collapse of the right knee.  The doctor additionally noted same-sided problems with the ankle and subtalar joint, and chronic narcotic use.  Dr. Nessler believed that knee replacement surgery was the only reasonable option for the employee, but felt surgery should be deferred until the infection had definitely cleared.  Dr. Nessler further opined that “the underlying arthritis which is the cause and need for his knee arthroplasty is certainly related to his 1992 injury and subsequent treatment requiring a lateral meniscectomy since this clearly is progression of lateral arthritis to tricompartmental arthritis in his knee.”  (Pet. Ex. B.)

The employee, unfortunately, had a recurrence of sepsis in his right knee in December 2008, and was again hospitalized with a second arthroscopic operation, including extensive debridement of the knee.^[8]  On February 23, 2009, Dr. Kuhl found no sign of infection, and the employee was referred back to Dr. Nessler.

On March 25, 2009, the employee was seen by Dr. Wicklund for an evaluation at the request of the employer and Grinnell Mutual.  The doctor confirmed a history of an ankle sprain in 1986 with a subsequent diagnosis of osteochondritis dissecans of the talus, and a knee sprain in 1992 with subsequent surgery.  Dr. Wicklund noted the ankle was stable with a well-healed pantalar ankle fusion and subtalar fusion.  With respect to the right knee, the doctor diagnosed end-stage degenerative arthritis, status post meniscectomy and lateral retinacular release, status post septic arthritis.  It was Dr. Wicklund’s opinion that the employee could not, at that time, undergo a joint replacement of the knee due to his two recent knee infections which would place the employee at high risk.  It was further his opinion that the May 21, 1992, injury was not a substantial contributing factor to the recommended knee replacement.  The doctor maintained the need for the surgery was due to an underlying valgus configuration of the knee contributed to by the valgus configuration of his right ankle, as well as the two infections leading to premature loss of joint surface cartilage.  Finally, Dr. Wicklund stated the valgus configuration of the ankle, corrected by Dr. Coetzee in 2001, lead to increased pressure along the lateral joint line which may have played a small role in the pain over the lateral joint of the right knee, but played only a minor role, less than 10%, in any need for knee surgery.

The employee returned to Dr. Nessler’s office on February 26, 2010.  At that point, the employee had been off antibiotics and infection free for one year and wanted to proceed with the arthroplasty.  Dr. Nessler referred the employee to Dr. Severance, an infectious disease specialist, for evaluation and clearance for surgery.  The doctor stated there was no evidence to support an active infectious process, and, on March 29, 2010, Dr. Nessler scheduled the employee for a right knee total arthroplasty.  Authorization for the surgery was denied on the basis the surgery was not reasonable.

The employee filed a claim petition on April 13, 2010, seeking approval of a right knee arthroplasty, listing both the 1986 injury and the 1992 injury.  On June 10, 2010, the employee was evaluated by Dr. Wyard on behalf of the employer and USF&G/Travelers.  Dr. Wyard performed an examination and a medical records review, including both reports of Dr. Wicklund and the October 8, 2008, examination note of Dr. Nessler.  The doctor’s impression was (1) osteochondritis of the right ankle, post two failed ankle fusions with subsequent subtalar fusion and distal tibial osteotomy, healed in acceptable position and alignment, with 2.5 cm shorter right leg; and (2) valgus right knee secondary to prior right knee surgery with lateral meniscectomy with progressive subsequent arthritis.  Dr. Wyard agreed with Dr. Nessler that the need for the knee replacement was causally related to the employee’s 1992 knee injury.  The doctor further opined that the 1986 ankle injury was not related to the proposed arthroplasty.

On June 21, 2010, Dr. Nessler provided a letter report, stating:

Following a hearing, the compensation judge found the proposed knee surgery was reasonable and necessary, that the May 21, 1992, injury to the right knee was a substantial contributing cause of the employee’s need for knee surgery, and that the July 10, 1986, injury to the right ankle was not a substantial contributing cause to the need for surgery.  The judge, accordingly, ordered the employer and Grinnell Mutual to pay for the right knee replacement surgery.

The employer and Grinnell Mutual have appealed solely from the finding that the July 10, 1986, right ankle injury was not a substantial contributing cause of the need for surgery.  No appeal was taken from those portions of the decision approving the surgery or determining that the 1992 knee injury was a causative factor in the need for the surgery.

The employer and Grinnell Mutual contend the preponderance of the evidence supports the conclusion that the July 10, 1986, work injury to the ankle was a substantial contributing cause of the employee’s need for knee surgery.  The appellants assert the compensation judge’s findings do not accurately reflect the evidence as a whole, and the opinions relied upon by the judge lack adequate foundation.  We are not persuaded.

We note first, that the “preponderance of the evidence” standard applies to the determination of disputed issues of fact by a compensation judge.  See Minn. Stat. § 176.021, subd. 1a.  The standard for review by this court is set forth in Minn. Stat. § 176.421, subd. 1(3).  Under this statute, review on appeal is limited to a determination of whether the compensation judge’s findings and order are “clearly erroneous and unsupported by substantial evidence in view of the entire record as submitted.”  Id.  This court is not a finder of fact and may not “retry” the factual issues before the judge; thus “it is irrelevant whether different conclusions than those found by the compensation judge could also be reached on the evidence.”  Land v. Washington Cnty. Sheriff’s Dep’t, slip op. (W.C.C.A. Dec. 23, 2003).  This court may not “substitute its view of the evidence for that adopted by the compensation judge if the compensation judge’s findings 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).

In determining that the 1986 ankle injury was not a substantial contributing cause of the employee’s need for knee surgery, the compensation judge accepted the opinions of Dr. Iverson and Dr. Wyard.  The employer and Grinnell Mutual argue that Dr. Iverson’s opinion is non-responsive to the issue in this case, and lacks the six-year history of treatment for the ankle between 1995 and 2001.

Dr. Iverson, an orthopedic surgeon, operated on the employee’s knee in 1992.  The doctor opined, in 1994, that there was no causal relationship between the employee’s 1986 ankle injury and his 1992 knee injury and surgery.  Dr. Wicklund, in 1995, also found no connection between the employee’s ankle injury and his knee injury.  While it is true Dr. Iverson lacked the employee’s more recent history of ankle surgeries and treatment, his reports were issued after the employee’s diagnosis of osteochondritis dissecans in the ankle, and do provide an opinion regarding causation more or less contemporaneous with the injuries themselves.  Accordingly, while the doctor’s opinion may not be conclusive, his reports do have some bearing on the issue of the relationship between the two conditions at the present time, and were properly considered by the compensation judge.

The appellants additionally assert that Dr. Wyard relied on Dr. Nessler’s opinion, incorrectly concluding that Dr. Nessler believed the need for surgery was solely related to the 1992 ankle injury, and that Dr. Wyard’s opinion is, accordingly, lacking in foundation.  We disagree.

Dr. Wyard took a history from the employee, performed a physical examination of the employee, and reviewed the employee’s medical records with respect to both the ankle and the knee.  As a general rule, this level of knowledge is sufficient to establish foundation for a doctor’s expert opinion.  See Grunst v. Immanuel-St. Joseph Hosp., 424 N.W.2d 66, 68, 40 W.C.D. 1130, 1132-33 (Minn. 1988).  Dr. Wyard was clearly aware of, and discussed, the treatment received by the employee for his right ankle, including the ankle surgeries.  The doctor concluded the 1986 ankle injury was “in no way related to the proposed arthroplasty.”  The doctor explained that “[t]he knee problem was going to go on to a valgus knee as a result of the injury in 1992 and subsequent surgery by Dr. Iverson with a partial lateral meniscectomy and lateral release for a subluxing patella.  Mr. Ornberg would have gone on to a valgus knee and arthritis in spite of any ankle injury.”  (Resp. Ex. 1.)

Dr. Wyard also noted that Dr. Wicklund felt the ankle injury played a minor role only, less than 10%, and that “Dr. Nessler feels it is not related and I agree with Dr. Nessler.”  We acknowledge that Dr. Nessler did not, in fact, state the 1986 ankle injury was not related.  On the other hand, what Dr. Nessler did say was that the “underlying arthritic process” was “multifactorial,” including “malalignments at the knee and ankle.”  He did not reference the 1986 ankle injury, or state, one way or the other, whether the ankle injury was a factor in - - or substantial contributing cause of - - the employee’s need for knee replacement surgery.  Dr. Wyard’s assessment and opinions have an independent basis in his examination and medical records review, and we cannot conclude that the compensation judge erred in relying on his opinion regarding causation with respect to the role of the 1986 ankle injury.

Finally, the appellants argue the greater weight of the evidence supports a determination that the 1986 ankle injury is a substantial contributing cause of the employee’s need for surgery.  It is impossible, they assert, to separate the employee’s long-standing ankle problems from his knee arthritis.  The employer and Grinnell Mutual point to references in the medical record indicating the employee’s ankle problems were affecting his knee, and maintain the medical records require a finding that the ankle injury is a contributing factor to the development of arthritis in the knee leading to the need for knee surgery.

We acknowledge that different inferences could be drawn from the evidence in this case.  However, it is the compensation judge’s responsibility, as the trier of fact, to judge the credibility of witnesses, to weigh the evidence, and to resolve conflicts in expert medical testimony.  See Nord v. City of Cook, 360 N.W.2d 337, 342, 37 W.C.D. 364, 372 (Minn. 1985); Hengemuhle, at 59-60, 37 W.C.D. at 237-240.  It is not the role of this court to re-evaluate the probative weight of the evidence.  “Whether we . . . might have viewed the evidence differently is not the point, but whether the findings of the compensation judge are supported by evidence that a reasonable mind might accept as adequate.”  Redgate v. Sroga’s Standard Serv., 421 N.W.2d 729, 734, 40 W.C.D. 948, 957 (Minn. 1988).  Having carefully reviewed the record, we conclude the evidence is adequate to support the decision of the compensation judge, and affirm.