The employer and insurer appeal from the compensation judge’s determination that the employee’s work resulted in a Gillette^[1] injury to the employee’s low back, culminating when the employee fell and experienced a rupture of the disc at the L4-5 level on December 4, 2008.  We affirm.

Johnathon Shoemaker was born October 9, 1980, and was 21 years old on the date of the hearing.  He began working for the employer, Route 52 Truck & Car Wash, in February 2007.  The employee left the job in August 2007 but was rehired a month later.  He worked there until December 8, 2008.  His duties included cleaning livestock trucks and semi-trailers, refrigerated trailers, hauling trailers, grain trailers, tankers, pickup trucks and automobiles.  In addition, the employee sometimes performed maintenance work on washers, ladders, and hoses and assisted in pumping out a septic tank.  He occasionally also answered phones, did store cleanup, took out trash, operated a computer, and performed customer checkouts.

Vehicle exteriors were cleaned with brushes, hand mitts and hoses.  There were extension handles, ladders and platforms to assist with cleaning the exteriors of large trucks, but parts of the job required bending and reaching.  Stooping was required to clean wheels and hub caps.

The parties largely agreed that the most physically demanding part of the employee’s job was cleaning out the inside of double-decked livestock trailers and that this job was more difficult in winter, when the layers of manure that accumulated on the deck floors during livestock transport were frozen.  The employee used scrapers, hammers and chisels to dislodge the frozen manure, but it then had to be shoveled or carried out of the trucks by hand.  In the summer, more of the manure could be removed with heavy flood hoses and hatches in the truck floors were accessible and could be used for removing the manure.  In winter, the hatches were frozen and inaccessible.  However, even in the summer, the manure tended to clog the drains in the cleaning bays unless it was frequently shoveled out of the drain pit and removed, sometimes with a skid loader, but usually by filling and carting off wheelbarrow loads by hand.  Depending on how many people were working and how many vehicles were being cleaned, there might be three workers involved in cleaning a cattle trailer, or as few as one.

The parties disagreed about the weights that were lifted, what motions and postures were required to clean out cattle trailers, and what percentage of the employee’s time was typically involved in this part of the work.

The employee, his brother, Jason, who had also worked at the truck wash, and Matthew McMahon, a co-worker, testified that the trailer decks were not high enough to stand upright so that cleaners had to work in a stooped position while shovelling and lifting 25-100 pound loads.  The working height in the trailer was reduced by several inches of manure caking the floors.  Loads of frozen manure were often irregular in shape and tended to slide off the shovels, and the footing on the frozen manure was slippery and uneven.  Sometimes heavier loads would need to be carried because some large chunks of frozen manure could not be broken up easily.  The employee and his witnesses testified that sometimes a shovel-load of frozen manure would weigh as much as 200 pounds.  In the summer it would take from 45 minutes to an hour to clean out a large cattle trailer, but in winter it could take from one to five hours.  The employee stated that about 30 to 40 percent of his time in winter was spent cleaning trailers and, while on a slow day there could be from one to five trailers being cleaned at the truck wash, on a busy day as many as 12 to 15 trucks needed to be cleaned.

The employer and insurer offered testimony contradicting some particulars of the description of the work offered on behalf of the employee.  The employer’s owner, Brian Haugen, testified that job logs indicated an average of only about 20 to 30 percent of his employees’ time was spent cleaning cattle trailers.  He didn’t think more than two or three trucks were cleaned in a shift.  Troy Kaus was a manager at the truck wash, although he never supervised the employee.  He testified that the heaviest weights lifted in cleaning a cattle trailer would not have exceeded about 100 pounds.  He considered it unlikely that more than about 50 pounds could be lifted on the plastic shovels provided to the employee without the shovels breaking, and characterized the job as one of pushing the manure out the truck doors with the shovels.  Mr. Kaus testified that he was 5’11" tall and that he was usually able to stand upright inside the cattle trailers.  He thought that only about 25 percent of the time cleaning trailers would have to be spent in a crouching position.  James Hennig, the employer’s sales, marketing and human resources manager during the period the employee worked at the truck wash, also testified describing the layout and operation of the truck wash, the kinds of livestock trailers washed, and his observations of the employee and others doing the work.  The employer and insurer also offered testimony disagreeing with the employee over the weight of a grate, the frequency with which a skid loader was available on site, and other similar points of detail regarding the work.

The employee testified that he began to have back pain at work almost from the start of his job but he considered a sore back to be the normal result of hard physical labor.  After a while, he began to have back pain each morning when he woke up that would improve as he moved around and loosened up.  He testified that he mentioned having a sore back now and then to his prior supervisor and then to James Hennig after Hennig began to work there.  Hennig, in his testimony, denied ever having heard the employee complain of back pain at work.  The employee testified that working hunched over in cattle trailers for hours could cause back pain that lasted all the next day.  Co-employee Matthew McMahon and the employee’s brother both testified that they had been aware that the employee was having back problems at work from his comments and movements while they were working with him.

On April 30, 2007, the employee was seen at the Fairview Zumbrota Clinic by Dr. Abraham D. Tatpati.  The employee reported back pain on and off for two weeks across his lower back that was worse when he was doing his work as a truck washer.  The doctor noted that the employee’s job involved heavy lifting.  On examination, the employee’s midline low back and paraspinal areas were non-tender, but straight leg raising on the right produced sharp pain in the low back without sciatic signs.  The employee was diagnosed with a lumbosacral sprain and prescribed ibuprofen.  Home exercise was recommended and he was given a referral for possible physical therapy.  According to the employee’s testimony, he had the impression that there was nothing he could do about his ongoing back pain at work, so he did not continue treatment.

The employee sustained a work injury on March 4, 2008, while washing the second floor or deck of a livestock trailer, when he tripped on an open floor hatch and caught himself on his elbow.  He was treated at the Fairview Zumbrota Clinic the following day for pain in the left clavicular area and a sore elbow with a cut.  No low back injury or symptoms were reported or treated in association with this injury.  A first report of injury for this incident indicates that the employee sustained a strained ligament in the shoulder and neck on the left.

The employee testified that when he fell on March 4, one of his legs fell through the trap and the other did not.  His initial pain was in the collarbone and elbow but a few days after treating for those problems and returning to work, he began to notice brief periods of numbness from his back, down the right buttocks and into his right leg.  His right leg would sometimes “give out,” particularly with lifting or with pulling a heavy hose.  He also noticed sharp pain down the leg at times while bent over inside trailers.  The employee stated that he had mentioned to James Hennig on various occasions at work that his leg had given out.  This was denied by Mr. Hennig in his testimony.

The employee was treated again at the Fairview Zumbrota Clinic on August 25, 2008, for pain at the right cervical spine and trapezius which had started when the employee jumped off a skid loader at work and felt a pop, straining his right neck area.  Again, no low back symptoms were reported or treated.  The employee testified that this incident did not increase his low back pain or injure his low back.

The employee testified that his leg symptoms continued to worsen in October and November 2008.  However, he did not seek medical attention for his leg giving way as it was then happening only with heavy lifting and he was not particularly alarmed since he thought it was probably just a normal physical response to the heavy lifting.

Early in December 2008, the employee went to Iowa with his brother to scout out some sites for possible bow hunting later that year.  The employee stated they had parked near a place called Buffalo Creek Bottom and got out of the car and started walking.  After walking about 150 yards, they were crossing the snow-caked and frozen Des Moines River when the employee’s right leg simply gave way and he fell on his buttocks.  He had an onset of severe back pain.

The employee saw a local chiropractor, Dr. Merle Tigges, on December 8, 2008, which was either the day of the fall or shortly after.  In his notes, Dr. Tigges recorded that the employee had slipped on ice and had landed on his tailbone.  He diagnosed low back pain with possible buttock and right leg pain.  There was tenderness on the right side at the lower lumbar spine.  X-rays of the lumbar spine were read as showing foraminal encroachment or swollen disks from L4-5 and L5 to the sacrum with subluxations.  Dr. Tigges treated the employee with spinal manipulation on December 8 and 9, 2008.  He discharged the employee with recommendations that he rest and ice his back and then return to work on December 10, 2008.

The employee continued to have severe back pain, and on returning to Minnesota he went to the Fairview Red Wing Medical Center for treatment where he was seen by Dr. Thomas Meyer on December 10, 2008.  Dr. Meyer’s history was that the employee had been “hunting in Wisconsin” [sic] and fallen on the ice, landing on his buttock and experiencing severe pain.  The next day he had increasing pain and “saw a chiropractor in Iowa where this happened.”  Chiropractic care did not improve the employee’s symptoms and he had been “unable to sleep due to excruciating pain.”  The employee described numbness and paresthesias radiating to his right leg, mostly down the posterior aspect into his calf.  He had also noticed a lack of muscular strength in his right leg which made it a bit more difficult to walk.  On examination, the employee was noted to be in extreme pain and virtually unable to ambulate.  There was marked paraspinal spasm and loss of lumbar lordosis.  Straight leg raising caused severe lower back pain at even the slightest degree of elevation.  Deep tendon reflexes were diminished in the lower legs.

An MRI scan was performed and showed a very large L4-5 disc herniation with marked impingement of the spinal cord and a free fragment apparently impinging on the right-sided L5 nerve root.  The employee was admitted to the hospital and a consultation was requested from an orthopedic surgeon, Dr. Matthew Eich.

Dr. Eich saw the employee the next day.  He noted that the employee, now 20, had worked washing trucks since high school and that the work there was heavy and could involve moving material weighing 100 pounds and more.  The doctor noted that the employee’s work was often done in cramped spaces in which he could not stand up straight and required bending while chipping and moving manure.  The employee gave a history of back pain that had been intermittent but progressive over the past several months, and was accompanied by increasing tingling and numbing in his leg.  More recently, the employee had slipped on the ice and landed on his buttocks, after which he had further increased symptoms.  Straight leg raising was positive at less than 10 degrees causing spasms of pain up the back and leg; sensation was intact to the lower legs but with some tingling in the L5 calf area and at the lateral border of the right foot.  Dr. Eich reviewed the MRI and noted it showed a very large ruptured disc at the L4-5 level with about 85 percent occlusion of the canal.  The discs above were normal and well hydrated, as was L5-S1.  The anterior aspect of L4-5 was still hydrated as well.  Dr. Eich recommended immediate surgery due to the massive size of the herniation.  That same day, Dr. Eich performed an L4-5 exploration foraminotomy and removal of the extruded disc at L4-5. His surgical report recorded that “the disc was enormous in size and has significant pressure and tension on the neural elements.”

On January 19, 2009, Dr. Eich saw the employee in follow-up and the employee told him that coverage had been denied by the employer’s workers’ compensation carrier on the basis that the injury was not work-related.  Dr. Eich reviewed his notes and, as he later explained in deposition testimony, noted that some of the material in his rough notes from his initial consultation with the employee on December 11, 2008, were transcribed out of context and with transcription errors; he testified that this might have given rise to some confusion regarding the etiology of the employee’s problem.  He reiterated his understanding that the employee had been having problems with his back going back at least a year or more while working at the Route 52 truck wash facility, which was associated with heavy physical activities in that work, and which included an onset of severe back and right leg symptoms.  Although the employee’s leg gave out when he was walking in Iowa and his symptoms increased after he fell onto thin ice, he had already had symptoms of right leg radiculopathy and weakening.  Dr. Eich did not believe that a slip and fall such as described would be capable of causing a severe herniated disk in a muscular and healthy 20-year-old male.  He stated in his chart notes that the employee’s injury was work-related.

On July 16, 2009, Dr. Eich noted that surgery had given the employee good improvement and that he was working driving a truck, although vibration and sitting for long periods in that work was difficult.  He suggested that the employee would need retraining in the future and should have less physical work.  Maximum medical improvement had been reached.  In a letter report dated July 27, 2009, Dr. Eich concluded the employee had sustained a Gillette injury from repetitive overloading of his spine as the result of working flexed forward with heavy and awkward lifting and twisting, such that the ligaments were weakened to the point that a rupture was finally able to occur.  He rated the employee as having an 11 percent permanent partial disability.

The employee also engaged an ergonomist, David J. Dixon, Ph.D., to review the employee’s job activities.  In a report dated July 31, 2009, Dr. Dixon concluded that the employee’s job activities performed in cleaning out trucks contributed substantially to his back injury.  He noted in particular that the weights exceeded maximum weights recommended by the National Institute of Occupational Safety and Health, and were performed in a stooped posture which greatly increased the compressive forces on the intervertebral disks.  He also pointed to several other aggravating factors, including the frequency of the lifts, the lack of recovery time between lifts, awkward postures while lifting, and a cold environment which he believed increased the risks of back injury.

The employer and insurer had the employee examined on their behalf by Dr. John Sherman on September 3, 2009.  Dr. Sherman opined that the employee was likely genetically predisposed to early disc degeneration, presumably had pre-existing degenerative disc problems at the time he fell, and that the herniated disc would not otherwise have occurred from the employee’s fall in Iowa.  Dr. Sherman did not believe that the employee’s work activities had caused either the herniation or the presumed pre-existing disc degeneration.

Dr. Eich was deposed on September 21, 2009.  In his deposition testimony, he disagreed with Dr. Sherman’s opinion and explained in still greater detail the basis for his view that the employee’s work activities had caused repetitive injury to the employee’s back ligaments and permitted his L4-5 disc to bulge, and that due to the weakened condition of the employee’s back the disc finally ruptured when his leg gave way and he fell in Iowa.  He did not agree with Dr. Sherman’s presumption that the employee had pre-existing degenerative disc disease from genetic factors, noting that there was no evidence of any degenerative disc disease at any other level on any of the radiological studies.

At the hearing, in addition to the lay testimony by the employer’s owner, office manager and a supervisor, the employer and insurer also presented the testimony of Dr. Charles Edward Bain, identified as a consultant in biodynamics.  Dr. Bain had a general medical degree and a degree in chemical engineering and testified that, based on his study of the causation of back injuries, repetitive work activities were not a significant cause of low back injuries.  Instead, disc herniations were primarily the result of genetic factors which predisposed some individuals to back problems.  He testified that, in his view, neither the employee’s fall in Iowa nor his work activities had been a substantial contributing cause of the L4-5 disc herniation.  The employer and insurer also offered Dr. Bain’s affidavit discussing his analysis of the employee’s case, and a large number of attached medical journal articles which Dr. Bain alleged supported his position.

Following the hearing, the compensation judge adopted the opinion of Dr. Eich, and found that the employee’s disc herniation was causally related to his work activities for the employer.  The employer and insurer appeal.

The employee claimed at the hearing that he had sustained a Gillette injury as a result of his work activities for the employer.  The injury began with in increasing back pain and leg weakness over the course of his employment and started a process that culminated in a disc herniation when his right leg gave out and he fell on his buttocks in Iowa.  In support of this claim, the employee relied on his own testimony and that of his brother and another co-worker as to the strenuous nature of his job and the employee’s symptoms prior to the date of the culmination of the injury, as well as on the expert medical opinion of Dr. Eich and on an ergonomic analysis of the back injury risk potential of the employee’s job duties conducted by Dr. Dixon.

The employer and insurer presented two lines of defense against the employee’s claim.  First, they introduced evidence to counter the employee’s description of his job.  They relied on testimony by the employer’s owner, office manager, and a supervisor disputing the employee’s account of the extent to which his work had involved strenuous and repetitive labor.  These witnesses also disputed the employee’s testimony that he had been having back and leg problems at work by denying having heard or seen anything from the employee or in his demeanor that would have suggested that.  The employer and insurer also relied on the absence of ongoing medical treatment for low back problems, the employee’s failure to seek medical treatment for his right leg giving out, and the wording of the initial medical records following his fall in Iowa, to suggest that the employee did not in fact have low back and leg problems prior to the date of his fall away from work.

The employer and insurer also relied on the medical opinion of Dr. Sherman and the biomechanical analysis of Dr. Bain to offer an alternative explanation for the employee’s low back problems that the employee’s work duties did not contribute to the development of those problems.  This alternative explanation was not based on a claim that the employee’s fall in Iowa was the cause of his low back problems but that his disc herniation was largely the result of genetic factors personal to the employee, with the fall in Iowa either playing a very significant further role (Dr. Sherman) or a very minor role (Dr. Bain).

The case as presented by the parties was thus one involving principally the resolution of a number of factual disputes.  In resolving those disputes, the compensation judge specifically noted that she found the employee’s testimony to be credible.  A close review of the judge’s findings and memorandum indicates that while she did not adopt every part of the employee’s testimony, she accepted those parts of the testimony of the employee which were consistent with the testimony of his co-worker and his brother as to the frequency, nature and difficulty of the lifting activities the employee performed at work.  She did not accept the testimony of the employer’s witnesses that the work was substantially less strenuous.  The compensation judge also accepted the testimony of the employee and his supporting witnesses that the employee had been having low back and leg problems on the job before the fall in Iowa.

On appeal, the employer and insurer make a number of arguments based on the testimony of their witnesses on the questions of the weights lifted by the employee, the height inside cattle trailers, whether the employee would frequently have lifted in a stooping position, and whether the employee mentioned or displayed signs of back and leg problems at work.  The assessment of witness credibility is a matter uniquely within the province of the compensation judge, and findings based on that assessment will generally not be reversed in the absence of clear error.  Even v. Kraft, Inc., 445 N.W.2d 831 at 835, 42 W.C.D. 20 at 22, (Minn. 1989), citing Brennan v. Joseph G. Brennan, M.D., P.A., 425 N.W.2d 837, 839-40, 41 W.C.D. 79, 82 (Minn. 1988).  No compelling reason has been shown why the compensation judge’s adoption of the testimony of the employee or his supporting witnesses over that of the employer and insurer’s witnesses was inappropriate.  We note further that other evidence offered by the employer and insurer directly contradicted their contention that cattle trailers were generally of sufficient height to stand upright while working in them.^[2]  This further supports the judge’s rejection of the testimony offered by the employer and insurer’s witnesses on that issue.

The employee’s claim was that of a Gillette injury.  A Gillette injury is a result of repeated trauma or aggravation of a pre-existing condition which results in a compensable injury when the cumulative effect is sufficiently serious to disable an employee from further work.  Gillette v. Harold, Inc., 257 Minn. 313, 321-22, 101 N.W.2d 200, 205-06, 21 W.C.D. 105, 111-13 (1960); see also Carlson v. Flour City Brush Co., 305 N.W.2d 347, 350, 33 W.C.D. 594, 598 (Minn. 1981).  In order to establish a Gillette injury, an employee must “prove a causal connection between [her] ordinary work and ensuing disability.”  Steffen v. Target Stores, 517 N.W.2d 579, 581, 50 W.C.D. 464, 467 (Minn. 1994).  While evidence of specific work activity causing specific symptoms leading to a disability “may be helpful as a practical matter,” determination of a Gillette injury “primarily depends on medical evidence.”  See id., citing Marose v. Maislin Transp., 413 N.W.2d 507, 40 W.C.D. 175 (Minn. 1987).  Ultimately, questions of medical causation fall within the province of the compensation judge.  Felton v. Anton Chevrolet, 513 N.W.2d 457, 50 W.C.D. 181 (Minn. 1994).

Since there was a disagreement between the two medical experts in this case,^[3] Dr. Sherman and Dr. Eich, the judge’s resolution of the central question in the case necessarily rested heavily on her choice between the medical opinions.  The judge adopted Dr. Eich’s opinion over that of Dr. Sherman.  Where there is adequate foundation for the opinion adopted by the judge, this court must uphold the compensation judge’s choice among medical experts.  See Nord v. City of Cook, 360 N.W.2d 337, 37 W.C.D. 364 (Minn. 1985).

The employer and insurer argue that Dr. Eich’s opinion was based on an erroneous view of the employee’s work activities, but their argument is essentially based on the points of disagreement between the witnesses for the employee’s case and those for the employer and insurer regarding the employee’s work duties that were principally resolved in the employee’s favor by the compensation judge.  Since the facts assumed by Dr. Eich that were material to his opinion were consistent with the factual resolution reached by the compensation judge, we must consider Dr. Eich’s opinion well-founded.  Grunst v. Immanuel-St. Joseph’s Hosp., 424 N.W.2d 66, 40 W.C.D. 1130 (Minn. 1988); Schulenberg v. Corn Plus, 65 W.C.D. 237 (W.C.C.A. 2005).

Many of the arguments raised by the employer and insurer on appeal discuss why they believe that the evidence they submitted would have provided substantial support for a contrary finding denying a causal link between the employee’s work activities and his low back and leg problems and a consequential L4-5 disc herniation.  However, our standard of review is whether the findings made by the compensation judge have substantial support in the record, and not whether the evidence might have provided substantial support to some other hypothetical result.  Land v. Washington County Sheriff’s Dep’t, slip op. (W.C.C.A. Dec. 23, 2003); Manthei v. Layne Minn., 65 W.C.D. 18 (W.C.C.A. 2005).

The compensation judge gave a very detailed explanation of her reasons for rejecting the opinion of Dr. Sherman and the supporting opinion of Dr. Bain.  Among those reasons, she noted that neither had provided any explanation or discussion of facts present in the case to support their assertion that the employee had a personal genetic predisposition to low back injury.  She also failed to find Dr. Bain’s qualifications sufficiently strong to qualify him as an expert on the question of genetics versus environmental factors in back injury.  And, she noted that the journal articles which were offered as support for Dr. Bain’s views did not in fact give support to his conclusions.  Based on the evidence, we are not able to state that the compensation judge erred in her findings.

The compensation judge’s decision is affirmed.