The employer and insurer appeal from the compensation judge’s determination that the employee’s work injury resulted in a permanent aggravation of his previously-diagnosed degenerative disc disease and spondylolisthesis at the L5-S1 level.  We affirm.

Mr. Harlon Tomford, the employee, whose career has included work in various construction and welding positions, began working for Mark’s Welding, the employer, on September 8, 2003.  His medical history includes treatment in the 1980’s for neck and low back symptoms resulting from a motor vehicle collision.  In March 1990, the employee sustained a work-related injury after falling approximately ten feet off a truck.  He fractured his left arm and wrist, left hip and left knee.  In May 2004 and April 2005, the employee received occasional chiropractic treatment, the need for which he attributed to the physical demands of his welding job.

On June 2, 2005, the employee was injured at work while welding a hay bale fork.  As he turned to balance the bale fork, which weighed approximately 250 - 300 pounds, the fork fell over onto him, striking both of his shins, and landing on top of both of his feet, with the bulk of its weight landing on his right foot.  The bale fork also knocked the employee backwards, causing him to land onto his back and buttocks on the concrete floor.

The employee experienced symptoms in his right foot and low back which limited his work.  He sought chiropractic treatment in June and July, and worked only a few days in June.  Although the employer provided the employee with light-duty work in early July 2005, the employee could only tolerate limited work hours, and he has not worked for the employer since August 2005.

On July 13, 2005, the employee consulted James Bergmann, a physician’s assistant (PA-C) at Centra Care, reporting low back and right foot pain.  The lumbar x-rays showed very mild scoliosis and early signs of arthritis but no obvious compression fractures, as well as L5 spondylolysis with spondylolisthesis, which was suspected to be chronic due to the sclerosis about the pars fracture lines.  Mr. Bergmann prescribed naproxen to treat inflammation, and confirmed that the employee’s chiropractor had assigned physical work restrictions.

The employee’s low back pain continued; his treating chiropractor, Dr. Michael Buffington, restricted the employee to a 20-pound lifting limit and advised that he should stand no more than four hours per eight-hour work day.  The employee continued to undergo periodic chiropractic treatments through at least February 2006.

On September 1, 2005, the employee filed a claim petition, seeking payment of temporary partial and temporary total disability benefits, as well as medical and chiropractic expenses.  The employer and insurer admitted primary liability for the employee’s right foot injury, but denied primary liability for his claimed low back injury, contending that the employee had a pre-existing low back condition and had not reported his low back condition until a few weeks after his injury.  He also filed a request for rehabilitation services.

On November 10, 2005, Dr. Richard Strand, orthopedist, examined the employee at the request of the employer and insurer.  Dr. Strand concluded that the employee had sustained no specific injury to his lumbar spine on June 2, 2005, and that any symptomatic exacerbation that the employee might have sustained would have resolved within a period of days.  Dr. Strand concluded that the employee needed no restrictions as a result of any injury in June 2005, that he had reached medical maximum improvement (MMI) from his alleged low back injury within a few days of the incident, and that any medical care and treatment beyond mid-July 2005 was due to his pre-existing low back condition.

The employee’s claim petition and rehabilitation request were consolidated for a hearing, which was held before a compensation judge in January 2006.  In findings and order issued following the hearing, the compensation judge awarded a portion of the employee’s indemnity claim and his claim for rehabilitation benefits.  The judge denied the employee’s claim for chiropractic benefits after November 30, 2005, determining that the employee had reached MMI from his work-related injuries as of that date and therefore any chiropractic or other medical treatment received thereafter was not reasonable, necessary, nor causally related to, the employee’s work-related injury.

Following the employee’s appeal, this court remanded the matter to the compensation judge for reconsideration of a portion of his decision.  Tomford v. Mark’s Welding, Inc., No. WC06-165 (W.C.C.A. Dec. 4, 2006).  In a decision issued on remand, the compensation judge concluded that the employee had not yet reached MMI from his work injury, and also awarded payment for chiropractic treatment the employee received in December 2005.  No further appeal was taken from that decision.

In June 2006, Dr. Sunny Kim, orthopedist, examined the employee and diagnosed chronic low back pain associated with isthmic spondylolisthesis at L5-S1.^[1]  He recommended conservative care, including physical therapy and a low back rehabilitation program.

In August 2006, the employee began working in maintenance for Central Bi-Products.  At that time, he continued to note low back symptoms, and resumed periodic chiropractic treatment in February 2007, which he continued throughout that year.  In September 2007, Dr. Strand re-examined the employee, and again diagnosed spondylolisthesis at the L5-S1 level, with periodic episodes of back pain.  He placed lifting restrictions on the employee’s work, based on his history of recurrent pain with activities.  X-rays and an MRI scan in October 2007 confirmed bilateral L5 spondylolysis with associated L5-S1 spondylolisthesis.

Dr. Deborah Rasmussen examined the employee in October 2007, who reported that he had experienced three or four flare-ups of his low back pain during each of the past two years.  Dr. Rasmussen referred the employee for a series of three epidural steroid injections for pain relief.  Also at her referral, the employee underwent a neurosurgical consultation with Dr. Anthony Bottini in November 2007; he recommended a trial of conservative medical management, including physical therapy.  Dr. Bottini also discussed the possibility of a discogram to determine whether the employee’s pain was isolated to one disk, and discussed the possibility of proceeding with an anterior lumbar interbody fusion at the L5-S1 level.  The employee opted for conservative care at that point.

The employee continued working until mid-February 2008.  Additional litigation ensued concerning the nature of the employee’s 2005 injury, and whether the employee was entitled to temporary total disability benefits, ongoing rehabilitation assistance, and approval for a discogram and potential fusion surgery.  Dr. Strand re-examined the employee in May 2008, and diagnosed mechanical back pain secondary to multiple level degenerative disc disease and instability of L5-S1 secondary to bilateral spondylitic defects and a Grade 1 spondylolisthesis.  Dr. Strand again concluded that the employee had sustained a temporary aggravation of his underlying spinal disease process while working for the employer and recommended against surgical intervention.  He also recommended work restrictions to try to prevent recurrent symptoms, but explained that those were unrelated to any injury the employee may have sustained in 2005.

Another evidentiary hearing was held on May 29, 2008, before the same compensation judge who presided at the 2006 hearing.  In his findings and order served and filed August 22, 2008, the compensation judge concluded that the employee’s 2005 injury caused a permanent aggravation of his pre-existing low back condition and that the employee continued to be restricted from lifting over 20 pounds as a result of that injury.  The compensation judge awarded a portion of the employee’s temporary total disability claim, provision of ongoing rehabilitation assistance, and payment for outstanding medical expenses.  The compensation judge determined that the employee’s claim for a discogram and surgery was premature, and therefore denied that claim.  No appeal was taken from those findings.

In December 2008, Dr. Kim reexamined the employee.  On the basis of the results from the employee’s MRI scan, Dr. Kim recommended a diagnostic and therapeutic bilateral L5 pars injection, advising that if the injection reduced the employee’s pain, he then would consider the employee to be a candidate for fusion surgery.

On February 2, 2009, the employee filed an additional claim petition, seeking approval for surgery recommended by Dr. Kim.  The employer and insurer denied the claim for surgery, contending that it was not reasonable, necessary, or causally related to the employee’s 2005 work injury.

On August 12, 2009, Dr. John Sherman, orthopedist, examined the employee at the employer and insurer’s request.  Dr. Sherman diagnosed an isthmic Grade 1 spondylolisthesis at L5-S1, which he concluded had pre-dated the employee’s June 2005 work injury.  He also concluded that the employee’s work injury temporarily aggravated his pre-existing condition, and that the employee reached MMI with three months of that injury.  As to the employee’s medical care for his low back, Dr. Sherman believed that such treatment had been reasonable and necessary, but was not causally related to the employee’s work activities in June 2005.  Dr. Sherman also agreed that the surgery proposed by Dr. Kim was a “reasonable consideration,” although he would prefer that the employee avoid surgery through a self-directed exercise program.  In Dr. Sherman’s opinion, the employee was capable of working on a full-time basis, within certain restrictions related to his age, multilevel disc degeneration and spondylolisthesis.

A hearing was held on September 10, 2009, before the compensation judge who had presided at the earlier hearings.  Issues addressed at the hearing included whether the employee’s 2005 work injury caused a permanent aggravation of the employee’s pre-existing spondylolisthesis at the L5-S1 level and whether the employee was entitled to temporary total disability benefits from December 2, 2008, to the present and continuing.

Also at issue at the 2009 hearing was whether an earlier finding, that the employee’s 2005 work injury caused a permanent aggravation of his pre-existing low back condition, was res judicata for future claims on that issue.  (See Findings and Order, August 22, 2008).  The employee contended that this earlier finding precluded a new determination of whether the employee’s work injury caused a permanent aggravation of the employee’s pre-existing spondylolisthesis at the L5-S1 level.  The employer and insurer contended that the judge’s earlier finding, that the work injury permanently aggravated the employee’s low back condition, was not adequately specific as it did not definitively address the potential aggravation to the employee’s spondylolisthesis.  They contended that the earlier finding therefore had no res judicata effect because it did not specifically identify which pre-existing condition (degenerative disc disease or spondylolisthesis) was permanently aggravated, nor did the earlier findings and order specifically state that the employee’s condition of spondylolisthesis was causally related to the employee’s work injury.

In his findings and order served and filed January 21, 2010, the compensation concluded that res judicata did apply.  He found that the August 22, 2008, findings and order were res judicata with regard to establishing that the employee’s work-related low back injury of June 2, 2005, caused a permanent aggravation of the employee’s pre-existing back condition, including both his degenerative disc disease and his spondylolisthesis at L5-S1.  The compensation judge also separately found that, assuming that res judicata was not applicable, the employee’s 2005 injury caused a permanent aggravation of both conditions.  In addition, the compensation judge determined that the recommended surgery, in the nature of a Trans 1 procedure at L5-S1, was reasonable, necessary, and causally related to the employee’s work-related injury of 2005.

On a separate issue, the compensation judge denied the employee’s claim for temporary total disability benefits from December 2, 2008, through the date of hearing, based on the lack of a reasonable and diligent job search during that period of time.  The employee did not appeal from the denial of temporary total disability benefits.

The employer and insurer, however, appealed from the compensation judge’s determination of the res judicata effect of the August 22, 2008, findings and order, and appealed the separate finding that the employee’s 2005 injury caused a permanent aggravation of his pre-existing degenerative disc disease and spondylolisthesis.^[2]

In his findings and order at issue in this appeal, the compensation judge found that the employee’s June 2, 2005, injury resulted in a permanent aggravation of the employee’s underlying low back condition and led to the employee’s need for surgery.  He made that specific finding after addressing the res judicata effect of his 2008 findings and order.  The compensation judge relied on the opinion of Dr. Kim, the employee’s treating orthopedic surgeon, in rendering his decision.  He referred to Dr. Kim’s October 1, 2009, report wherein he stated that the employee had been doing “quite well without having any significant low back pain,” until his work injury in June 2005, and that his injury rendered the pre-existing condition to be “permanently painful.”  On the basis of Dr. Kim’s opinion, the compensation judge concluded that the employee’s injury caused a permanent aggravation of the employee’s pre-existing back condition, which included both the employee’s pre-existing degenerative disease as well as the employee’s pre-existing spondylolisthesis at L5-S1.

The employer and insurer argue that the compensation judge did not state the basis for his conclusion that the employee’s work injury aggravated both pre-existing conditions, and that the compensation judge did not address the factors related to the determination of whether the aggravation was permanent or temporary.  They request a remand for specific findings related to these factors.

We agree that several factors are relevant to determining whether an injury is temporary or permanent, including (1) the nature and severity of the pre-existing condition and the extent of restrictions and disability resulting therefrom; (2) the nature of the employee’s symptoms and extent of medical treatment rendered 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 employee’s 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.”  Wold v. Olinger Trucking, Inc., slip op. (W.C.C.A. Aug. 29, 1994).  Contrary to the employer and insurer’s argument, however, these factors may be considered by the compensation judge; the compensation judge is not required to address all of these factors in determining whether an aggravation is temporary or permanent.  Heckel v. Crown, Cork & Seal, slip op. (W.C.C.A. Dec. 21, 1999) (employer and insurer argued that the compensation judge had erred by failing to apply all six of the factors listed in Wold).

The judge concluded that the employee’s June 2, 2005, work injury caused a permanent aggravation of the employee’s pre-existing spondylolisthesis at L5-S1 and his pre-existing degenerative disc disease.  The compensation judge certainly considered the nature of the employee’s symptoms and extent of medical treatment following the aggravating incident.  He specifically found, after reviewing the medical records, that both the employee’s spondylolisthesis at L5-S1 and his pre-existing degenerative disc disease have been symptomatic since the work injury.  The compensation judge also considered medical opinions related to the issue, and noted that Dr. Strand and Dr. Sherman’s reports suggest that both conditions became symptomatic and subject to recurrent exacerbations after that injury.

The judge also relied upon Dr. Kim’s opinion that the employee’s injury had rendered the pre-existing spondylolisthesis permanently painful.  In his report of October 1, 2009, Dr. Kim outlined his opinion that the employee has chronic low back pain associated with his spondylolisthesis, and that until the work injury in 2005 he was doing quite well without significant low back pain.  The employer and insurer argue that the compensation judge erroneously relied upon Dr. Kim’s opinion, asserting that his opinion is solely based on the employee’s pain complaints.  They rely on the opinion of Dr. Sherman, who concluded that the employee’s 2005 injury had only temporarily aggravated his pre-existing condition.

The compensation judge weighed all of the medical evidence and ultimately relied upon Dr. Kim’s opinion when concluding that, as a result of his work injury, the employee sustained a permanent aggravation of his pre-existing spondylolisthesis at L5-S1 and his pre-existing degenerative disc disease.  A compensation judge’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.  See Nord v. City of Cook, 360 N.W.2d 337, 342, 37 W.C.D. 364, 372 (Minn. 1985).  In this case, the facts underlying Dr. Kim’s opinion are supported by the medical records in evidence.

The employer and insurer also argue that there is no evidence of a structural change in the employee’s spondylolisthesis at L5-S1 based on the employee’s x-rays and scan from before and after the injury.  There is no requirement, however, for an employee to prove that a condition has structurally changed in order to establish that an aggravation was permanent.  The issue is whether the work injury resulted in a permanent aggravation of the employee’s pre-existing spondylolisthesis at the L5-S1 level.  We note that the employee has had an ongoing lifting restriction since his 2005 work injury, and that Dr. Kim has not yet released the employee to return to work since his examination in late 2008.  In addition, it was not until after the employee’s injury that any physician recommended surgery.

In reviewing factual determinations, it is this court’s role to review the entire record and to assess the substantiality of evidence supporting the decision of the judge.  Under our standard of review, supportive evidence is substantial if it is, in light of the record as a whole, “evidence that a reasonable mind might accept as adequate,” granting “due weight to the opportunity of the Compensation Judge to evaluate the credibility of witnesses appearing before the judge.”  Hengemuhle v. Long Prairie Jaycees, 358 N.W.2d 54, 59, 37 W.C.D. 235, 239 (Minn. 1984); Redgate v. Sroga’s Standard Serv., 421 N.W.2d 729, 734, 40 W.C.D. 948, 957 (Minn. 1988).  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).  In this case, there is substantial evidence to support the compensation judge’s finding that the employee sustained a permanent aggravation of his pre-existing degenerative disc disease and his pre-existing spondylolisthesis at L5-S1.  Accordingly, we affirm.

The employer and insurer have also appealed from the compensation judge’s determination that the August 22, 2008, findings were res judicata with regard to establishing that the employee’s 2005 injury caused a permanent aggravation of his pre-existing back condition, including both his degenerative disc disease and his spondylolisthesis at L5-S1.  Given our disposition of the employer and insurer’s appeal of the judge’s alternate finding on causation, we need not address the res judicata issue.