TERI J. PARKER, Employee/Respondent, v. FOLEY LOCKER, INC., and RAM MUT. INS. CO., Employer-Insurer/Appellants, and INTEGRACARE CLINIC, CONSULTING RADIOLOGISTS, INST. FOR LOW BACK & NECK CARE, CENTRACARE SURGERY CTR., BLUE CROSS BLUE SHIELD OF ALA., ST. CLOUD ORTHOPEDICS, CENTRACARE HEALTH CLINIC RIVER CAMPUS, and REJUV MED., Intervenors.

The employer and insurer appeal from the awards of temporary partial and permanent partial disability benefits, and from the judge’s determination that the employee’s claimed medical expenses were reasonable, necessary, and causally related to her injury of March 12, 2015. We affirm.

The employee, Teri Parker, started working for employer Foley Locker^[1] in 1998. In her capacity as Retail Manager, she was responsible for waiting on customers, packaging meat products, and carrying boxed meat orders weighing from 70-100 pounds to customer vehicles. The employee sustained an admitted work injury on March 12, 2015, when she slipped and fell in the employer’s freezer landing on her buttocks and back.

The employee was taken by ambulance to the hospital on the date of injury with complaints of severe low back pain radiating into both legs. CT scans showed a possible nondisplaced left sacral fracture and a disc bulge at L4-5 with mild spinal canal stenosis and mild left neural foraminal narrowing. The employee was diagnosed with a pelvic fracture and taken off work for four weeks.

On March 18, 2015, the employee began treatment with Dr. Timothy Hiesterman at St. Cloud Orthopedics. She reported symptoms over the sacral areas and at the low back area, with pain, numbness and tingling radiating down the legs. Physical therapy was initiated and the employee was released to work with light-duty restrictions. The employer accommodated her restrictions, but she earned less because her hours were reduced. By June 3, 2015, Dr. Hiesterman concluded that the sacral fracture had healed and that the employee’s ongoing pain was related to the low back. He recommended a lumbar MRI.

The MRI, performed on July 7, 2015, showed minor spondylolisthesis at L4-5 with facet degeneration and right joint effusion, associated with minor bulging and mildly narrowed nerve root canals. After reviewing the scan, Dr. Hiesterman noted that, although the employee had some facet arthropathy and degenerative changes prior to the fall,^[2] she had previously been completely asymptomatic. He concluded that the fall had likely exacerbated the existing pathology with new disc bulging and foraminal narrowing.

Dr. Hiesterman referred the employee to Dr. Joel Shobe, who saw her on August 11, 2015. The employee reported constant low back pain with intermittent leg pain over the past five months. Facet injections were administered, but did not help. On October 13, 2015, Dr. Shobe noted that a minor trauma can often stir up an inflammatory process and cause ongoing symptoms.

The employee was referred to the Institute for Low Back and Neck Pain on November 6, 2015. On November 16, 2015, Dr. Richard Salib performed a lumbar bilateral medial branch block which provided minimal relief.

On December 3, 2015, the employee reported continuing bilateral low back pain with radiation to the tailbone, as well as pain, numbness, and tingling radiating down the legs in a multi-dermatomal distribution. A second set of bilateral medial branch blocks at L4-5 and L5-S1 was administered by Dr. Sabers of CentraCare on December 18, 2015. Following the injections, the employee had immediate relief which lasted for weeks. The pain then returned to the former level. Since then, she has been treated with a variety of conservative treatments including physical therapy and ongoing chiropractic care.

The employee had a neurological evaluation in January 2016 by Dr. Shelly Larson-Peters on referral from a physician’s assistant at CentraCare. After EMG testing proved negative, Dr. Larson-Peters stated that the symptoms might be due either to a contusion or stretch injury to the nerves in the low back and/or lumbosacral plexus as a result of the work injury.

Dr. David Fey performed an IME in January of 2016. He opined that the employee’s sacral fracture would have been expected to heal within three months of the March 2015 work injury or by about June 15, 2015. He thought the fall might have resulted in a temporary soft tissue sprain of the low back, which also would have resolved within three months. He did not believe that there was objective evidence to demonstrate that the work injury accelerated, modified, or changed the employee’s pre-existing degenerative disease. He rated 0% permanent partial disability due to the work injury.

Dr. Robert Wengler examined the employee on March 28, 2016, at the request of the employee’s attorney. He characterized the employee’s condition as a degenerative disc at L4-5 which flattens the ventral thecal sac, resulting in moderate bilateral neural foraminal stenosis, with radicular symptoms primarily in the left, and an absent left ankle reflex. He opined that when the employee fell, she destabilized the motion segment because such a fall causes the calcium deposits along the margin to dislodge, causing the disc to become unstable and symptomatic.^[3] Dr. Wengler testified that, given the fracture to the sacral alar, which is a fairly large bone, it is reasonable to expect the spine to have absorbed enough energy in the fall to irritate and destabilize the existing degenerative changes. He concluded that the employee’s medical treatment had been reasonable and necessary. He assigned a PPD rating of 13% for spinal stenosis.

In a claim petition filed on March 30, 2015, the employee alleged entitlement to various workers’ compensation benefits, including reimbursement of certain medical expenses, temporary partial disability compensation for certain periods, and permanent partial disability compensation for a 13% permanent partial disability rated pursuant to Minn. R. 5223.0390, subps. 4.E and 4.E(1).

At the hearing below, the parties stipulated that the employee had sustained a compensable injury to her pelvis and low back on March 12, 2015. However, relying on the opinion of Dr. Fey, the employer and insurer contended that the employee’s work injury was temporary in nature and had resolved within three months of the injury with no permanent partial disability. They accordingly attributed the employee’s ongoing symptoms, medical treatment, restrictions and wage loss following that date to pre-existing low back problems.

Following the hearing, the judge found that the 2015 work injury remained a substantial contributing cause of the employee’s ongoing symptoms, need for medical treatment and loss of earning capacity. The judge found that the medical care at issue was reasonable and necessary, except for treatment at IntegraCare subsequent to August 26, 2016. The judge found that the employee had sustained a 13% permanent partial disability as a result of the work injury. Benefits were ordered payable consistent with these findings. 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(3). 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).

A decision which rests upon the application of a statute or rule to essentially undisputed facts generally involves a question of law which the Workers’ Compensation Court of Appeals may consider de novo. Krovchuk v. Koch Oil Refinery, 48 W.C.D. 607, 608 (W.C.C.A. 1993), summarily aff’d (Minn. June 3, 1993).

The compensation judge found that the employee had shown a loss of earning capacity and lost earnings attributable to the work injury, and awarded temporary partial disability. The judge further found that certain medical treatment was attributable to the employee’s work injury, and awarded payment of the associated medical expenses. Finally, the judge found that the employee’s work injury was a substantial contributing factor to a 13% permanent partial disability.

The appellants contend that these findings, and the resulting orders awarding benefits, are contrary to law and unsupported by substantial evidence. The appellants’ principal argument, applicable to all three issues on appeal, is that the compensation judge should have found that the employee’s work injury on March 12, 2015, was temporary in nature and had resolved within three months of the injury with no permanent partial disability and no restrictions attributable to the work injury. They attribute the employee’s subsequent medical treatment, permanency, restrictions, and disability to the effects of her pre-existing low back problems. The appellants relied primarily on the expert medical opinion of Dr. Fey.

The employee in this case had a pre-existing back condition in the form of degenerative disk disease. However, it is not necessary that the employment be the only cause of the condition for which benefits are sought, and an injury is compensable if it can be shown that the employment is a substantial contributing factor in the employee’s condition.^[4] An injury is also compensable if the employment is a substantial contributing factor to the aggravation or acceleration of a pre-existing condition.^[5]

The compensation judge accepted the expert medical opinions of Dr. Hiesterman and Dr. Wengler as more persuasive that the opinion of Dr. Fey. These doctors offered the opinion that the work injury aggravated the employee’s pre-existing degenerative low back condition, which had previously not been disabling. This court must defer to the fact-finder’s choice of expert opinion unless the facts assumed by the expert in rendering an opinion are not supported by the evidence.^[6] The appellants have not made such a showing with respect to the expert opinions adopted by the compensation judge in this case.

Whether the employment aggravated the pre-existing condition is a question of fact.^[7] Factors to consider in determining whether a work-related incident is a temporary or permanent aggravation of a pre-existing condition may include, but are not limited to (1) the nature and severity of the pre-existing condition and the extent of restrictions and disability resulting therefrom; (2) the nature of the symptoms and extent of medical treatment prior to the aggravating incident; (3) the nature and severity of the aggravating incident and the extent of restrictions and disability resulting therefrom; (4) the nature of the symptoms and extent of medical treatment following the aggravating incident; (5) the nature and extent of the employee's work duties and non-work activities during the relevant period; and (6) medical opinions on the issue. Which of these factors are significant in a particular case and the weight to be given to any factor is generally a question of fact for the compensation judge.^[8]

The compensation judge’s determination on this issue was also supported by the employee’s testimony about her injury and her symptoms, both before and after the injury. The compensation judge’s memorandum notes that the judge found the employee’s testimony on these points to be credible. It is well-settled that the assessment of the credibility of a witness is the unique function of the trier of fact.^[9] We see no basis on which to reverse the judge’s credibility determination.

The judge reasonably considered a number of other factors in reaching his determination on this issue as set out in the memorandum. These included the non-disabling nature of the employee’s symptoms and the absence of restrictions prior to the 2015 work injury as compared to the subsequent imposition of medical restrictions, the nature of the work injury, which involved sufficient force to fracture the employee’s sacrum, the worsened nature of subsequent symptoms, and the employee’s greater need for ongoing medical treatment subsequent to the work injury.

Viewing the record as a whole, we conclude that the compensation judge’s finding regarding the permanent nature of the work injury was adequately supported by substantial evidence, and affirm.

The appellants do not dispute the specifics of the employee’s wage loss or restrictions as found by the compensation judge. Their argument on appeal disputes only the causal relationship with the 2015 work injury. As discussed above, we have affirmed the compensation judge’s finding of a continued causal relationship between the employee’s medical condition, restrictions and disability, and her need for treatment.

The appellants argue that the employee had reached maximum medical improvement no later than the date of Dr. Fey’s examination in January 2016. They argue that the compensation judge erred in failing to make findings as to whether the employee had reached MMI; they further seem to argue that such a finding would have the legal effect of terminating the employee’s entitlement to various benefits, specifically including temporary partial disability compensation.

We see no error in the compensation judge’s failure to address the question of whether the employee had reached MMI. At the inception of the hearing, the compensation judge listed the issues presented and asked the parties whether there were any additions or corrections. MMI was not one of the issues listed, and no party objected.^[10] While the issue of entitlement to temporary partial disability benefits was before the compensation judge, a determination regarding MMI was not relevant to that issue, as the attainment of MMI does not terminate an employee’s entitlement to temporary partial disability compensation.^[11]

We accordingly conclude that the compensation judge properly awarded temporary partial disability compensation, and we affirm.

With respect to the issue of the medical expenses awarded, the appellants again argue that the treatment was causally unrelated to the 2015 work injury. As discussed above, we have affirmed the compensation judge’s finding of a continued causal relationship between the employee’s medical condition, restrictions and disability, and her need for treatment. The appellants have not offered any further reason why the judge’s order for reimbursement of medical expenses should be reversed. Thus we affirm the award of medical expenses.

On this issue as in those previously discussed, our affirmance of the judge’s finding of a causal link between the employee’s work injury and the employee’s ongoing condition and associated permanency is determinative of the appellants’ argument that the permanency award should be reversed on the basis of a lack of a causal link between the injury and the permanency.

With respect to the extent of any permanent partial disability (PPD), the compensation judge accepted the expert medical opinions of Dr. Wengler, Dr. Hiesterman, and Dr. Milbauer, all of whom proffered a 13 percent PPD rating for the effects of the work injury. Dr. Fey provided a rating of zero percent for a healed sacral fracture that he did acknowledge to have been sustained in the work injury, but did not provide an opinion as to a rating for the employee’s ongoing disability, which he attributed solely to a pre-existing condition.

The employer and insurer note that Dr. Wengler, in his deposition testimony, stated that he had rated the employee based on Minn. R. 5223.0390, subps. 4.E. and 4.E.(l), which he considered to be the rule most closely representing the employee’s condition. That rule applies to rating a radicular syndrome in the lumbar spine. The appellants argue that the medical evidence, taken as a whole, fails to adequately support a 13 percent PPD rating pursuant to this rule, which, in pertinent part, provides as follows:

The appellants, again relying on Dr. Fey’s opinion, contend that the employee did not sufficiently show radicular findings and that such findings as were relied on by Dr. Wengler in rating the employee’s disability were not correlated with direct MRI findings of nerve root impingement. In his deposition, Dr. Wengler explained his opinions regarding causation, his diagnosis, and the mechanism of the radicular impingement associated with the employee’s injury. Dr. Wengler noted that he had observed an absent left ankle reflex on examination, which he considered an objective indication of significant nerve root entrapment. His examination also noted a positive straight leg raising test, limited range of motion, and instability with percussion, which he testified could be characterized as objective findings. In his deposition testimony, Dr. Wengler testified that, in his opinion, the MRI findings and the absence of the ankle reflex on straight-leg raising supported his PPD rating. In his opinion, the employee’s injury had destabilized the L4-5 motion segment, such that it subsequently exhibited translational instability. He explained that this instability, in combination with the stenotic lesions shown on the employee’s scans, were causing radicular symptoms through irritation of the nerve roots.

While the absent left ankle reflex noted by Dr. Wengler was not reported during a number of prior examinations with different physicians, Minn. R. 5223.0390, subp. 4.E. does not require persistent objective findings. Thus a rating under that rule does not require that an absent reflex was found repeatedly on exam.

Taking the evidence as a whole, we conclude that substantial evidence supports the compensation judge’s adoption of the rating offered by Drs. Wengler, Hiesterman, and Milbauer, and we affirm.