The appellants, M.E. Robinson and EMC Insurance Company, appealed the compensation judge’s finding that the employee’s September 17, 2008, injury was a temporary aggravation of his preexisting lumbar spine condition that resolved by December 17, 2008.  Finding substantial evidence to support the finding, we affirm.  The cross-appellants, Osseo Brooklyn School Bus Company and SFM Mutual Insurance Company, appealed the compensation judge’s calculation of the employee’s weekly wage on their date of injury.  Concluding the compensation judge erred in the method used to compute weekly wage, we reverse and remand.

Robert L. Lensegrav, the employee, has had multiple injuries to his low back.  On July 22, 1989, he sustained a personal injury to his low back while moving an adult resident of Mission Farms Nursing Home into a wheelchair.  Within a month, the employee experienced low back pain extending into both legs.  An EMG study was interpreted as showing evidence for an L5 radiculopathy, however, a lumbar MRI scan in March 1990 was normal.  The employee missed time from work following the injury and received a substantial amount of conservative care.  He was compensated for a 3.5% permanent partial disability due to the personal injury.  By some point in 1991, the employee’s low back and leg symptoms had resolved almost completely and caused only infrequent symptoms thereafter.

On May 12, 1995, the employee sustained a second personal injury arising out of his employment with M.E. Robinson, then insured by EMC Insurance Company (EMC).  On that date, the employee twisted his low back while catching a case of oil that was tossed at him.  The employer and insurer admitted liability for the injury.

The employee was seen at the Mork Clinic on May 16, 1995, with complaints of low back and left leg pain.  Following conservative treatment, the employee initially improved.  However, in April 1996, the employee sought treatment from Dr. Bocklage, an orthopedic surgeon, complaining of low back and left leg pain.  An MRI scan revealed a moderate-sized disc herniation at L5-S1 on the left with nerve root compression.  Dr. Bocklage referred the employee to his associate, Dr. Crowe, who performed a laminotomy and disc excision in May 1996.  Initially, the surgery provided relief of the employee’s pain but within a few months the employee’s low back and left leg pain recurred and worsened.  An MRI scan on November 5, 1996, showed scar tissue in the left lateral recess at L5-S1 without a new herniation.  The employee continued to complain of significant symptoms and Dr. Crowe ordered another MRI scan.  This scan, obtained on July 21, 1997, again showed post-operative scarring without a new herniation.  Thereafter, Dr. Crowe released the employee to return to work with restrictions.

In September 1997, Dr. Paul Wicklund examined the employee at the request of the appellants.  The doctor diagnosed a left L5-S1 disc herniation, treated surgically with an average result.  Dr. Wicklund noted the employee continued to have low back pain but opined there was no recurrent disc herniation and further treatment was not necessary.  The doctor opined the employee had reached maximum medical improvement (MMI), was able to work subject to restrictions, and had a 14% whole body disability which he apportioned 20% to the 1989 injury and 80% to the 1995 injury.  M.E. Robinson and EMC paid the employee for a 10.5% permanent partial disability.

The employee was unable to return to his pre-injury occupation, and in 1997, began working as a school bus driver for Laidlaw Bus Company.  He testified he did his best to keep his activities within his restrictions, but stated he had ongoing low-level low back symptoms that he self-treated.  In 2007, Osseo Brooklyn School Bus Company took over the contract with the school district.  The change did not affect the employee’s employment status or duties.

In May 2006, the employee saw Dr. Brett Oden at the Buffalo Clinic after slipping on the stairs.  The employee complained of low back pain with radiation into the left leg and foot.  Dr. Oden diagnosed a lumbar strain with radiculopathy and prescribed a Medrol Dosepak with Vicodin for pain.  An MRI scan again showed status post left L5-S1 hemilaminectomy with scarring but no evidence of a recurrent disc herniation.

On September 17, 2008, the employee sustained an injury to his low back while working for Osseo Brooklyn School Bus Company, then insured by SFM Mutual Insurance Company (SFM).  On that day, the employee pulled on the emergency brake of a bus and experienced increased low back pain.  The employer and insurer accepted liability for a personal injury and commenced payment of benefits.

The employee saw Dr. Thomas Ahrens at the Buffalo Clinic on September 24, 2008, complaining of low back pain off and on for a week.  The doctor prescribed Flexeril and recommended physical therapy.  On October 3, 2008, the employee saw Dr. Dale Lawrence who diagnosed back pain with radiculopathy and recommended chiropractic treatment.  An MRI scan in October 2008 showed degenerative disc disease at L5-S1 and was unchanged from the May 2006 MRI scan.  The employee returned to see Dr. Lawrence in November 2008 with complaints of continued back pain.  The doctor noted the employee was then receiving physical therapy at Sister Kenny but was still unable to work.

In December 2008, Dr. Paul Biewen, an orthopedic surgeon, prescribed a L5-S1 epidural injection which provided no significant relief.  An MRI scan in January 2009 was unchanged from the October 2008 scan with no evidence for a new disc herniation or stenosis.  The employee returned to see Dr. Lawrence in January 2009 complaining of tingling and numbness in his right foot.  An EMG showed minimal findings consistent with a right peroneal nerve lesion with no radiculopathy.

The employee saw Dr. Garry Banks at Advanced Spine Associates in May 2009 with complaints of persistent low back and left leg pain.  On examination, the employee had normal motor and sensory testing in both legs with a decreased left ankle reflex.  After reviewing the employee’s MRI scans, Dr. Banks recommended a discogram to determine if the employee was a candidate for fusion surgery.  The employee did not proceed with a discogram because, at that time, he did not want surgery.

The employee saw Dr. Mark Janiga at Minnesota Interventional Pain Associates in June 2009 to evaluate his left leg pain.  The doctor recommended diagnostic facet joint injections which resulted in 50 to 75% pain improvement but this was not considered to be a positive result.  Thereafter, the employee received sacroiliac joint injections which did not improve his condition.  Dr. Janiga stated the only other option was a discogram.

Dr. John Dowdle examined the employee in October 2009 at the request of SFM.  The doctor diagnosed mechanical low back pain and L5-S1 degenerative disc disease following a laminectomy and disc excision at L5-S1.  He noted the employee had no new structural lesions after the September 2008 incident, and the 2008 MRI scan when compared to the 2006 MRI scan showed no significant changes.  Dr. Dowdle concluded that the employee’s 1989 injury was not a contributing factor to his current condition, and opined the employee had an onset of pain in September 2008 without a specific injury.  He opined the employee sustained, at most, a temporary aggravation of his preexisting degenerative condition from which the employee had recovered by December 17, 2008.  The doctor stated the employee required further care and treatment for his low back condition, but opined the September 2008 injury was not a contributing cause to the need for additional medical care.  Dr. Dowdle stated the employee was able to do only minimal activities and was not then able to be gainfully employed.

Dr. Jeffrey Gerdes, a neurosurgeon, examined the employee in July 2010.  The doctor stated that surgical intervention for low back pain would be a fusion which Dr. Gerdes felt was too aggressive at that time.  The doctor made arrangements for the employee to be seen at the Center for Pain Management.

In July 2010, Dr. Wicklund reexamined the employee.  The doctor stated he disagreed with Dr. Dowdle’s opinion that the September 17, 2008, injury was a temporary aggravation, stating the employee’s symptoms since that date had permanently worsened.

Also at issue at the hearing was the employee’s weekly wage with Osseo Brooklyn School Bus Company on September 17, 2008.  A representative of the employer prepared a wage information document relative to the September 17, 2008, work injury, Petitioner’s Exhibit A.  The exhibit states the employee’s wage rate on the date of injury was $13.85 an hour and that the employee normally worked forty hours per week and was paid bi-monthly.  The exhibit sets out gross pay for the pay period ending on September 30, 2007, through the pay period ending October 15, 2008, together with the number of days worked during each payroll period.  The exhibit reflects that during the summer of 2008, the employee’s earnings were less than they were during the regular school year.  The employee testified his earnings were lower because he did not have a guaranteed five hour run that he had during the regular school season.  During that summer, he drove bus for a summer school route and extra activities, as well as training drivers on an as-needed basis, a job activity that was just starting to get going.  The employee testified he believed that, beginning in the summer of 2009 and in the summers to come, he would be working full time because he would be training drivers on a regular basis.

The claims of the parties were heard before a compensation judge.  In a Findings and Order filed October 11, 2010, the judge found that on September 17, 2008, the employee sustained a temporary aggravation of his preexisting low back condition that resolved by December 17, 2008.  During this three month period, the compensation judge found the employee was totally disabled and found Osseo Brooklyn School Bus Company and SFM solely liable for that disability.  Thereafter, the judge found the employee continued to be totally disabled and found that disability was the sole responsibility of M.E. Robinson and EMC.  Finally, the compensation judge found the nature of the employee’s job with the school bus company changed in late summer 2008 from full time during the school year and part time during the summer months to a full-time, year-round job, and held the employee’s wage on September 17, 2008, was forty times his hourly wage or $554.00 a week.  M.E. Robinson and EMC appealed the compensation judge’s finding that the September 17, 2008, injury was temporary.  Osseo Brooklyn School Bus Company and SFM appealed the compensation judge’s calculation of the employee’s weekly wage on the date of their injury.

The appellants contend substantial evidence does not support the compensation judge’s finding that the employee fully recovered from the September 17, 2008, injury by December 17, 2008.  They argue the judge’s determination that liability for the employee’s continuing disability suddenly shifted on December 17th from SFM to EMC is inexplicable and unfounded.  Rather, the appellants argue the apportionment opinion of Dr. Wicklund should be adopted by this court.  We are not persuaded.

There are a number of factors which a compensation judge may consider in determining whether an aggravation of a preexisting injury or condition is permanent or temporary.  These factors include the nature and severity of the preexisting injury and the extent of the medical treatment prior to the aggravating incident; the nature and severity of the aggravating incident and the extent of restrictions and disability resulting therefrom; the nature of the symptoms and the extent of medical treatment following the aggravating incident; the nature and extent of the employee’s work duties and non-work activities during the relevant period; and medical opinions on the issue.  McClellan v. Up North Plastics, slip op. (W.C.C.A. Oct. 18, 1994).

The employee testified his symptoms changed and worsened after his 2008 injury.  He was able to work prior to September 2008 and had had little medical treatment for ten years prior thereto.  Since the 2008 injury, the employee has had extensive medical treatment and has been totally disabled.  Dr. Wicklund opined the 2008 injury was a substantial contributing cause of the employee’s current disability.  This evidence, we acknowledge, would support a different result in this case.  On appeal, however, the issue is not whether the evidence will support a different result but whether findings of fact are “clearly erroneous and unsupported by substantial evidence in view of the entire record as submitted.”  Minn. Stat. § 176.421, subd. 1(3); Hengemuhle v. Long Prairie Jaycees, 358 N.W.2d 54; 37 W.C.D. 235 (Minn. 1984).

The employee had a significant injury with lasting results arising from his May 12, 1995, injury with M.E. Robinson.  As a result of this injury, the employee underwent an L5-S1 laminotomy and disc excision from which Dr. Wicklund opined the employee obtained only an average result.  Initially, the surgery provided relief of the employee’s pain, but within a few months his low back and left leg pain recurred.  Dr. Crowe released the employee to return to work, but imposed significant restrictions that precluded the employee from returning to his pre-injury occupation.  The employee was paid for a 10.5% whole body disability secondary to his 1995 personal injury.

Dr. Dowdle stated the 2008 incident caused no new structural lesions and that the 2008 MRI scan when compared to the 2006 scan showed no significant changes.  The doctor maintained that 15% of patients who have a laminectomy and disc excision will go on to have progressive disc degeneration and persistent symptoms that fail to respond to conservative treatment.  Dr. Dowdle opined the 2008 injury was a temporary aggravation of the employee’s preexisting injury that resolved by December 17, 2008.  Dr. Dowdle further opined the employee’s May 12, 1995, injury was a contributing cause of the employee’s current condition and symptoms and need for treatment.

The compensation judge accepted the opinions of Dr. Dowdle. Where a compensation judge’s determination is based upon a choice between differing medical opinions, this court must affirm where the opinion relied upon had adequate foundation.  See Nord v. City of Cook, 360 N.W.2d 337, 37 W.C.D. 364 (Minn. 1985).  Dr. Dowdle reviewed the employee’s medical records, obtained a history from the employee, and examined the employee.  The opinions of Dr. Dowdle are not inconsistent with the facts as found by the compensation judge, and are well-founded.  The judge did not err in relying of Dr. Dowdle’s opinions.

Nor do we find inexplicable the judge’s finding that the employer and SFM were 100% liable for the three months from September 17 to December 17, 2008, and the employer and EMC were 100% liable thereafter.  The employee had an ongoing, underlying disability as a result of the 1995 injury.  It was not unreasonable for the judge to conclude that the employee’s disability was primarily and substantially a result of the 2008 aggravation from the date of the injury until the injury resolved.  When the effects of the temporary aggravation subsided, the effects of the 1995 injury were again a substantial contributing cause of the employee’s disability.

There is substantial evidence to support the compensation judge’s decision and we, accordingly, affirm.

The compensation judge stated, at the start of the hearing, that the parties disagreed which method - - of four proposed - - should be used to calculate the employee’s pre-injury weekly wage.  (T. 7-8.)  The judge accepted the employee’s claim that his future full-time earning capacity had been impaired by the injury and that his weekly wage should based on a forty hour week times his hourly wage.  We disagree.

The employee worked full time during the 2007-2008 school year.  During the summer of 2008, the judge found the employee drove school bus but was not guaranteed full-time work and his summer earnings were about one-third of his school year earnings.  The employee testified that, during the summer of 2008, his supervisors talked to him about getting a drivers’ training certificate so he could train other school bus drivers.  The employee anticipated he would be working full time in the summer of 2009, and in the years to come, as a bus driver and as a certified driver trainer.  (T. 40-46.)  The compensation judge concluded the employee had a full-time, year-round job by the time of the injury in September 2008, and computed his weekly wage at forty times his hourly wage of $13.85, or $554.00 a week.  Osseo Brooklyn School Bus and SFM contend there was no evidence the employer had offered the employee year-round, full-time employment as of the date of the injury, and whether year-round, full-time work would have been available in the future was speculative.  Accordingly, the cross-appellants ask that the case be remanded to recompute the employee’s weekly wage.

Entitlement to temporary total wage loss benefits is based on the employee’s “weekly wage at the time of the injury.”  Minn. Stat. § 176.101, subd. 1.  “Weekly wage at the time of injury is a relatively concrete quantity, and the statutory method for measuring weekly wage for purposes of temporary [total] compensation and for the general purpose of fixing the benefit rate is the same.”  Jellum v. McGough Constr. Co., Inc., 479 N.W.2d 718, 46 W.C.D. 182 (Minn. 1992)(citing Minn. Stat. § 176.011, subds. 3 and 18).^[1]  The potential post-injury availability of full-time work is irrelevant for the purpose of determining of an employee’s weekly wage “at the time of injury.”  The employee’s weekly wage is not based on what the employee’s earning capacity might have been had he continued in the same job, but is based on the employee’s actual earnings - - that is, the wages the employee actually earned prior to and on the date of injury.  Cf. Erdrich v. Ford Motor Co., 49 W.C.D. 528 (W.C.C.A. 1993).  Wages that an employee anticipates or theoretically could earn in the future are speculative and generally cannot be used to compute the pre-injury weekly wage.  Stadick v. United Parcel Serv., 47 W.C.D. 9 (W.C.C.A. 1992).  While the employee anticipated full-time employment during the summer of 2009, on the date of his injury he had not been so employed.  We, accordingly reverse the judge’s calculation of the employee’s pre-injury weekly wage based on potential full-time work in 2009.

The issue remains, however, as to how best to calculate the employee’s pre-injury earnings.  Three additional methods for computing the weekly wage were listed by the compensation judge: the statutory twenty-six week averaging method; a modified calculation based on the Sawczuk case; or dividing the employee’s annual earnings by 52 weeks.

Under the statute, the daily wage is to be computed first by dividing the total amount the employee actually earned in the last 26 weeks by the total number of days in which the employee performed any of his work duties.  Minn. Stat. §176.011, subd. 8a; Sawczuk v. Special Sch. Dist. No. 1, 312 N.W.2d 435, 34 W.C.D. 282 (Minn. 1981).  Weekly wage “is [then] arrived at by multiplying the daily wage by the number of days . . . normally worked in the business of the employer for the employment involved.”  Minn. Stat. §176.011, subd. 18.  In this case, the pre-injury wage information provided by the employer permits the inference that the employee’s earnings were irregular over the 26 weeks preceding the injury and the information is sufficient to permit calculation of the daily wage during that time frame.  This amount would then be multiplied by the number of days normally worked in the business of the employer for the employment involved.

The employee contends the statutory 26-week calculation understates the earning capacity lost by the employee as a result of the injury and argued, at the hearing, that the employee’s pre-injury weekly wage should be calculated in accordance with principles set forth in Sawczuk.  The employee in Sawczuk worked full time in the school cafeteria during the school year.  The compensation judge included in the 26-week period the 9 weeks the employee worked from the beginning of the school year to her injury in November, and the 17 weeks of employment prior to the end of the previous school year.  Noting the object of wage determination is to “arrive at a fair approximation of [the employee’s] probable future earning power which has been impaired or destroyed because of the injury,” the supreme court affirmed the compensation judge’s exclusion of the summer weeks the employee was off work on the basis that the “last 26 weeks” of employment refers to the last 26 weeks in which the employee actually performed work for the employer.  The employee in this case asserted there were a number of weeks during the 26 calendar weeks prior to the injury in which the the employee did not work at all, and argued that these weeks should be excluded from the weekly wage calculation.

The final method proposed is to calculate the employee’s annual earnings and compute the weekly wage on a 52-week basis.  While weekly wage is usually based upon a 26-week period, “there are various circumstances which make the claimant’s actual earnings during a particular period an unreliable measure of his future earning power.  As Professor Larson has stated, ‘sometimes it is as important to reject as it is to accept a brief recent-wage experience, if a realistic approximation of future wage loss is to be obtained.’”  Bradley v. Vic’s Welding, 405 N.W.2d 243; 39 W.C.D. 921 (Minn. 1987)(citing 2 A. Larson, The Law of Workers’ Compensation § 60.21[c], now 5 A. & L.K. Larson, § 93.02[2][c])(emphasis added).  When, in unusual fact situations, application of the statutory wage calculation formulas creates a result that does not fairly reflect the earning capacity lost due to an injury, the finder of fact may substitute any reasonable method of calculation which achieves this statutory objective.  Loberg v. Northhome Healthcare Ctr., 57 W.C.D. 113 (W.C.C.A. 1997).  See, e.g., Newbauer v. Pepsi Bottling Group, 43 W.C.D. 339 (W.C.C.A. 1990).  “[I]f the statutory period designated by the by [statute] happened to be an abnormal one, it is plainly not fair and reasonable to follow [the formula] slavishly, whether the wages for the period were abnormally high or abnormally low.”  5 Larson, supra, § 93.01[1][e].  In this case, the employee worked full-time three-quarters of the year.  However, one-half of the 26 calendar weeks prior to the injury encompass the summer months when the compensation judge found the employee’s earnings were about one-third of his school year earnings.  A 52-week calculation may, arguably, be a “fair[er] approximation” of the future earning power impaired as a result of the work injury.

Calculation of the employee’s pre-injury wage requires determinations of fact which are the province of the compensation judge.  We, therefore, remand this matter to the compensation judge for computation of the employee’s weekly wage.