The employee appeals the compensation judge’s finding that the employee did not show that his need for surgery in 2013 was causally related to his 1998 work injury, as well as the related denial of his claims for temporary total disability benefits, permanent partial disability benefits, and the intervenors’ claims.  We affirm.

On June 24, 1998, Richard J. Svenningsen, the employee, sustained a work-related low back injury while working for Petty & Sons Timber Products, Inc., the employer.  The employer was insured for workers’ compensation liability by OneBeacon Insurance Group.  The employee was diagnosed with a herniated disc at L4-5, and underwent a laminectomy on April 9, 1999.  After a hearing before a compensation judge on May 27, 1999, the employee received permanent partial disability benefits, temporary total disability benefits from July 1998 through the date of the hearing, and medical expenses.^[1]

The employee was able to return to work for different employers in several types of work, including a landscaper, van driver, construction laborer, cement laborer, general laborer, and general maintenance.  The employee described these jobs as light to medium duty.  The employee did not seek additional treatment for his low back until June 2010 when he was treated at the Mercy Hospital emergency department for severe low back pain and was prescribed medication.  On July 8, 2010, the employee sought treatment at the St. Joseph’s Hospital emergency department and reported low back pain over the past four weeks.  In September 2010, the employee was seen at the Mille Lacs Health System clinic in Onamia for continued low back pain with radiation into his right leg.  Physical therapy was recommended.

On January 8, 2013, the employee treated with Dr. Rodney Hayes at the Mille Lacs Health System clinic for increasing low back pain and bilateral leg radiation.  A few months later, the employee sought treatment at the Mille Lacs Health System emergency department for incapacitating low back pain and was admitted into the hospital at the same facility.  A March 28, 2013, lumbar spine MRI indicated a broad-based left paracentral disc protrusion at L4-5, canal stenosis, and a broad-based left lateral disc bulge at L5-S1.  The employee was discharged from the hospital and was treated with a transforaminal steroid injection a few days later.  The employee returned to Dr. Hayes on April 8, 2013, reporting that the injection did not provide significant relief.  Dr. Hayes recommended a neurosurgical consultation.  The employee was again admitted to the hospital after being seen in the emergency department on April 19, 2013, reporting a long history of low back pain after a work injury.  He was treated with medications and discharged on April 25, 2013.

On the same day, the employee was seen by Dr. Gregory Sherr at the St. Cloud Hospital for a neurosurgical consultation.  Dr. Sherr recommended another MRI, which indicated a left paramedian extruded disc at L4-5 that encroached on the descending left nerve root and degenerative disc disease at other levels without encroachment.  On April 27, 2013, Dr. Sherr performed a “re-do” L4-5 laminectomy as well as a left L4-5 discectomy and foraminotomies.  The employee recovered well until May 22, 2013, when he experienced a sudden onset of left leg pain.  The employee returned to the emergency department on June 27, 2013, reporting severe low back pain and radiculopathy, and was transferred to the St. Cloud Hospital.  Dr. Sherr diagnosed a recurrent left-sided disc herniation and performed a L4-5 laminectomy, discectomy, and microscopy.  The employee reported relief and was discharged on June 29, 2013.

On July 1, 2013, the employee filed a claim petition for temporary total disability benefits and/or permanent total disability benefits from and after April 25, 2013, medical expenses related to the low back surgeries on April 27 and June 28, 2013, retraining benefits, and attorney fees.  The petition also reserved a claim for permanent partial disability benefits.  Mercy Hospital, Central Minnesota Neurosciences, Minnesota Department of Human Services, and Mille Lacs Health System intervened for medical expenses incurred by the employee.  The employer and insurer denied the employee’s claims.  The employee filed an amended claim petition in August 2014 for additional permanent partial disability benefits.

On May 21, 2014, Dr. Sherr opined that he could not determine whether the employee’s condition and need for surgery in 2013 was causally related to the employee’s 1998 work injury.  At the request of the employer and insurer, the employee underwent an independent medical examination with Dr. Stephen Barron on July 25, 2014.  Dr. Barron opined that the employee’s 1998 injury was not a substantial contributing factor to his need for surgery in 2013 and that the new disc herniation in 2010 was not a result of the employee’s 1999 surgery.  The employee was evaluated by Dr. Mark Halstrom on August 19, 2014.  Dr. Halstrom opined that the employee’s 1998 work injury was a substantial contributing factor in the employee’s need for treatment and subsequent surgeries in 2013.

A hearing was held on February 10, 2015.  The employee testified that he had continued to experience symptoms over the years as he worked at light to medium duty jobs.  He agreed that some of these jobs required him to lift and carry up to 50 pounds.  The employee also testified that he was never completely symptom free even though he did not seek treatment for his back.  The compensation judge’s Findings and Order served and filed March 26, 2015, included the following unappealed findings:

The Workers’ Compensation Court of Appeals will uphold the factual findings of the compensation judge if they are supported by substantial evidence and were reached through application of the correct legal standard.^[5]  Substantial evidence is such relevant evidence as a reasonable mind might accept as adequate to support a conclusion.^[6]  In reviewing for substantial evidence to support the judge’s findings, we do not make credibility determinations.^[7]  Where the evidence allows reasonable minds to differ as to whether the employee’s injuries remain a substantial contributing factor in the need for continuing medical treatment, the responsibility for that decision rests with the compensation judge.^[8]  With this standard of review in mind, we consider the employee’s argument that the record lacks substantial evidence to support the compensation judge’s findings that the employee’s low back condition from 2010 forward as well as the medical and indemnity benefits were not related to his 1998 work injury.

An employer and its insurer are liable for an employee’s medical expenses when the need for treatment is due in substantial part to the work injury.^[9]  The work injury need not be the sole cause of the need for treatment but may be a substantial contributing factor in the employee’s condition.^[10]  In the present case, the compensation judge was provided with multiple expert medical opinions as to whether the work injury and subsequent treatment were causally connected.  In his findings and order, the compensation judge considered the evidence in the record, which included the expert opinions of Drs. Barron, Halstrom, and Sherr.  As the trier of fact, the compensation judge has the discretion to choose between conflicting medical experts’ opinions.^[11]  The judge determined that the preponderance of the evidence failed to show the causal connection between the employee’s work injury in 1998 and his claim for medical and indemnity benefits after June 2010.  The employee challenges this conclusion, arguing that the compensation judge erroneously relied on a flawed medical opinion from Dr. Barron in making this determination.

Dr. Barron performed an independent medical evaluation on the employee and issued a written report dated August 7, 2014.   In response to specific questions, Dr. Barron wrote the following:

First, the employee argues that Dr. Barron’s opinion is based upon an inadequate factual foundation in that it relied on a credibility determination by the doctor that was contrary to the facts as found by the compensation judge.  An expert medical opinion is not competent if it is based on a series of assumptions that lack a factual basis or if it materially relies on the facts contrary to those found by the compensation judge.^[13]  Here, Dr. Barron found it medically significant that the employee had no medical treatment to his back for over a decade and inferred from the medical records from this period that the employee “did quite well following his discharge from surgery on April 9, 1999 up until June 14, 2010.”  Dr. Barron wrote in his report that he considered this inconsistent with the history that the employee had given him.

The employee points to the fact that the compensation judge expressly accepted the employee’s testimony that he experienced back pain between 1999 and 2010.  Specifically, the judge found that “[t]he employee had low back pain that would wax and wane between 1999 and June 14, 2010.  The pain would generally take one day to resolve and did not require treatment or medication.  This pain normally did not radiate into his legs.”^[14]  As this finding was based solely on the employee’s testimony, the employee maintains that the judge clearly found the employee’s testimony as to his ongoing symptoms credible. The employee argues that Dr. Barron’s observation that the history given him by the employee was inconsistent with the medical records constituted a credibility determination contrary to that made by the judge.  We are not persuaded by this argument.

Dr. Barron’s report recites what the employee told him, by way of history, that after the 1999 surgery “he never returned to work and he had no significant subsequent employment.  He did some temporary jobs such as cement work, tree work, medi-van driver and working for a temporary agency.  He had no subsequent injuries or aggravations.  However, he remembers having constant lower back and left leg numbness and pain on an ongoing basis ever since the surgery.  He told me this was at a low level.”^[15]  The question whether the employee had any ongoing symptoms was one part of the history that Dr. Barron considered inconsistent with the medical records during this period.  There was also a work ability component to the overall inconsistency perceived by Dr. Barron.  For instance, Dr. Barron specifically mentions that the employee had a pre-employment physical in 2003, which resulted in the determination that the employee had no medical conditions that would affect his continued ability to work.

We note, in fact, that the history by Dr. Barron states he was given by the employee is arguably itself inconsistent with the compensation judge’s findings as to the employee’s symptoms during this period.  The judge found that the employee’s episodes of low back pain waxed and waned, generally did not radiate into the employee’s legs, and would typically resolve without treatment after one day.  Although the employee argues that the doctor’s opinion was based on an improper foundation, there is no compelling reason in this case to believe that an “inconsistency” rose to the level of direct negation.  Here, the history Dr. Barron’s report attributes to the employee was of constant low back and leg pain on an ongoing basis.  The judge’s findings themselves can be considered to echo Dr. Barron’s view, in that the judge did not accept the level of constant low back and leg pain that the employee reported as history to Dr. Barron.

There is no dispute about the absence of medical treatment during this period or about the contents of the records of the employee’s 2003 pre-employment physical.  Dr.  Barron’s opinion relied principally on the medical inference he made from the lack of medical treatment during the interval between the 1999 surgery and the onset of the employee’s new disc herniation in 2010.  While Dr. Barron noted that the history the employee gave him of ongoing back and leg pain and leg numbness was inconsistent with the medical records, this view is not clearly nor directly in conflict with the judge’s finding on the extent of the employee’s symptoms during that period.  We therefore reject the argument that the compensation judge’s acceptance of Dr. Barron’s opinion was improper under the facts of this case.

Dr. Barron opined that he would generally consider a recurrence causally related to the work injury if it occurred within the first year post surgery, but that here, where the recurrence took place eleven years after the employee’s surgery, he attributed it totally to the natural progression of the employee’s pre-existing degenerative disc disease of the lumbar spine. The employee characterizes this opinion as a rejection of the legal principle that the natural consequences of an injury are compensable.^[16]  Quoting Larson, the appellant maintains that “[w]hen the primary injury is shown to have arisen out of and in the course of employment, every natural consequence that flows from the injury likewise arises out of the employment, unless it is the result of an independent intervening cause attributable to claimant’s own intentional conduct.”^[17]  The employee renews his argument that the judge erred by relying on the expert opinion of Dr. Barron.  Even if the employee’s characterization of Dr. Barron’s views were accurate, an expert’s misunderstanding or confusion over a legal principle does not render the expert’s entire opinion devoid of other evidentiary value.^[18]  Here, the compensation judge could reasonably interpret the language of Dr. Barron’s statement not as a rejection of this principle, but rather as an opinion over the medical interpretation to be given to the evidence, including the extended absence of treatment and the existence of an MRI scan which already showed pre-existing degenerative disc disease in 1998. Where an expert opinion is subject to more than one reasonable interpretation, its interpretation is a matter for the finder of fact and generally the judge’s finding will not be disturbed by our court under the substantial evidence rule.^[19]  The judge did not err by relying on the expert opinion of Dr. Barron.

Finally, in the compensation judge’s memorandum, we note the recitation of several other factors the judge considered and relied upon in addition to the medical opinion of Dr. Barron in reaching his findings on causation.  Among these were the employee’s ability to work, the lack of restrictions, the medical opinion on causation from Dr. Sherr, and the lack of treatment during the interval in question.  Given his own reconciliation of the competing evidence and ultimate resolution of the other evidence, the judge considered Dr. Barron’s opinion more persuasive than the views of the other experts. We conclude that the compensation judge did not clearly err by relying, in part, on the opinions of Dr. Barron in this case.  The decision is affirmed.