The self-insured employer and its administrator appeal from the compensation judge’s finding that the employee’s injury at work to her left lower extremity on March 24, 2005, arose out of her employment.  We affirm.

Brenda Anderson has worked for Smead Manufacturing Company from 1972 to 1978 and then again from 1986 to the date of the hearing herein on July 9, 2008.  She has a history of minimal treatment to her left knee prior to March of 2005, having evidently injured it on August 21, 1995, and been treated thereafter by Dr. Paul Yellin and Dr. Jack Drogt.  There are no contemporaneous medical reports in evidence regarding this treatment,^[1] nor is there evidence that the employee obtained any treatment or worked under any restrictions after October of 1995 prior to March of 2005.On March 24, 2005, Ms. Anderson [the employee] was working for Smead Manufacturing Company primarily as a machine operator.  Her duties as a machine operator involved primarily the operation of dye cutting and printing machines to create office file folders.  Prior to that date, the employee and two of her co-workers had begun also to alternate job duties on a weekly basis.  Under this arrangement, the employee would work as a machine operator for two weeks and then as a “packer” for one week.  A packer pulled the front and back sections of folders from a conveyor and stacked them on waiting skids, which stood on either side of where the packer worked.  The employee described stacking a hundred folder sections at a time, to heights reaching five feet.  This required her to turn repeatedly to her right and to her left in the course of her work shift.  While working either as machine operator or as a packer, the employee wore tennis/athletic shoes and stood on a concrete floor covered by a rubber mat.

While working as a packer on Thursday, March 24, 2005, the employee sustained an injury to her left knee.  She subsequently related that, as she turned to her right, the upper part of her body moved but her feet did not turn with her body, and she felt immediate pain up and down on the medial side of the knee.  She sat for a few minutes and then reported the incident to her supervisor.  The employee completed her shift that day and also worked the following day.  She experienced some relief in her symptoms over the weekend, but upon her return to work on Monday, March 28, 2005, her pain worsened.  On the date of her injury, the employee was fifty-two years old and was earning a weekly wage of $706.40, and Smead Manufacturing Company’s workers’ compensation claims were administered by Gallagher Basset Services, Inc. [hereinafter referred to jointly as the employer].

The employee received initial medical attention for her injury on April 14, 2005, at the Allina Medical Clinic in Hastings.  Dr. Aubrey Schock saw her and diagnosed “internal derangement of the knee soft tissue.”  He prescribed icing and physical therapy and restricted the employee from working for two weeks.  The doctor’s office records on that date note,

When the employee returned to see Dr. Schock on April 28, 2005, she reported that she was financially unable to participate in physical therapy because the employer had denied liability for her injury.  Dr. Schock reiterated his recommendations of physical therapy and icing, suggesting also that she elevate the leg as much as possible and bear weight on it as tolerated.  About ten weeks later, on July 11, 2005, the employee reported to Dr. Schock that her left knee had worsened following some twisting and turning activity at work over the previous two days.  Dr. Schock diagnosed knee pain due to a probable meniscal strain, and at a visit the following week he recommended obtaining an MRI scan and an orthopedic evaluation.

The employee was seen in consultation by orthopedist Dr. Paul Yellin on July 27, 2005.  According to the history obtained by Dr. Yellin, the employee was injured at work in March of 2005, when “[s]he had a twisting episode at work and had immediate pain along the inner aspect of her knee.”  Dr. Yellin reviewed the employee’s MRI and noted that it “indicates a complex tear at the posterior horn and body of the medial meniscus.  It shows some reactive edema with a sprain at the MCL and tricompartmental mild degenerative arthritis no greater than grade 2 throughout all 3 compartments of the knee.”  With respect to a plan for the employee’s treatment, Dr. Yellin stated:

On August 5, 2005, Dr. Yellin performed arthroscopic surgery on the employee’s left knee.  In his operative report, Dr. Yellin noted that the employee had a complex flap and cleavage tear of the medial meniscus and grade III to IV changes of the patellofemoral joint.  The employee was totally disabled from work between August 5 and August 31, 2005, and she returned to work without restrictions on September 1, 2005.

On February 19, 2008, the employee filed a claim petition for workers’ compensation benefits, alleging that she sustained an injury to her left knee while in the course and scope of her employment for the employer on March 24, 2005, and requesting payment of her outstanding surgical expenses and temporary total disability benefits during the period of her surgical disability.  The employer denied liability for the employee’s alleged injury, contending that the employee’s injury did not arise out of her work activities.  The claim petition was later amended to include a claim for 3% permanent partial disability.

In a letter to the employee’s attorney dated March 3, 2008, Dr. Yellin opined that the employee had not reached maximum medical improvement with regard to her left knee condition and, in fact, would eventually require a “total knee.”  Dr. Yellin believed that the employee was entitled to a minimum permanent partial disability rating of 3% of the whole person, based on the excision of more than 50% of her meniscus.^[2]

The employer arranged for an evaluation by orthopedist Dr. Edward Szalapski, Jr.,  on May 20, 2008.  Dr. Szalapski obtained a history, reviewed the employee’s medical records, and performed a physical examination.  In a report dated May 29, 2008, Dr. Szalapski noted that, at the time of her alleged injury, the employee had been packaging press boards onto a skid.  The employee had reported to him that she experienced a sharp pain in her left knee as she was doing her job.  She had turned her body but not her feet.  Dr. Szalapski diagnosed end-stage osteoarthritis of the left knee, noting that he did not believe that the employee’s meniscal pathology was related to any work incident.  It was his opinion that the employee’s condition was “due to her morbid obesity and the fact that she was beginning to undergo a global degenerative process in her knee.”  Dr. Szalapski attributed the symptoms that the employee experienced at work to her underlying degenerative condition, not to the work itself.  He concluded that the employee’s work activities on March 24, 2005, were not a substantial contributing factor in the employee’s need for medical treatment, restrictions, or disability.

The employee’s claim for benefits came on for hearing before a compensation judge on July 9, 2008.  The issues in dispute were whether the employee had sustained a work-related injury to her knee on March 24, 2005, and, if so, the nature and extent of that injury.  In a findings and order issued August 15, 2008, the compensation judge found that ‘[t]he preponderance of the evidence is that the employee did sustain a personal injury on March 24, 2005, at least, in the nature of a meniscal tear which required greater than 50 percent removal of the meniscus, in the left knee.”  The judge awarded temporary total disability benefits for the period of time during which the employee was off work because of her left knee surgery, less short-term disability benefits received during that time.  He also awarded compensation for a 3% permanent partial disability as claimed, together with payment of the unpaid balance at Summit Orthopedics related to the employee’s surgery.  The employer appeals.

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).  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).

In his memorandum, the compensation judge explained that the employee credibly testified that she sustained trauma to her left knee while performing her work duties for the employer.  He accepted her testimony that she experienced immediate pain in her left knee when she turned at her work station and her left leg did not turn with her body as anticipated.  The judge stated that “pressure/torquing on her knee at that time, although it may have been minimal, was a substantial contributing factor to the injury,” and he found that “[the employee] was at an increased risk distinct from the general public as she was at her work station using a mat on a concrete floor which was directly involved in the occurrence of the incident.”  Based on the employee’s testimony and the opinions of the treating physician, the judge concluded that the employee had proved that her injury arose out of and in the course of her employment.

Citing Foley v. Honeywell, Inc., the employer argues that there was nothing unique about the employee’s job duties that would allow this court to find that the employee’s injury followed “as a natural incident of the work . . . as a result of the exposure occasioned by the nature of the employment.”  Foley v. Honeywell, Inc., 488 N.W.2d 268, 271 (Minn. 1992), quoting Hanson v. Robitshek-Schneider Co., 209 Minn. 596, 598-99, 297 N.W. 19, 21, 11 W.C.D. 463, 466 (1941), quoting Novack v. Montgomery Ward, 158 Minn. 495, 498, 198 N.W. 290, 292, 2 W.C.D. 156, 159 (1924).  While acknowledging that the employee was performing her job when she injured her knee, the employer contends that the evidence does not support a conclusion that, due to her employment activities, the employee was exposed to any “increased risk” related thereto, as required under case law.  The employer argues that the only connection between the employee’s employment and her March 24, 2005, injury was the fact that  the incident occurred on the employer’s premises during the hours of the employee’s work shift.  The employer contends also that the employee’s simple turning movement could have been performed anywhere and at any time and that such an activity was neither exclusive nor unique to her employment.  They argue that any increased risk for injury to the employee’s knee was created not by her work environment but by her obesity.  We are not persuaded.

In order to be compensable under Minnesota workers’ compensation law, a personal injury must be one “arising out of and in the course of” the worker’s employment.  Minn. Stat. § 176.011, subd. 16.  It is uncontested that the employee’s injury in this case occurred “in the course of” the employee’s employment, in that it occurred on the employer’s premises during the employee’s working hours.  The supreme court has established the following guideline for use in determining whether an injury “arises out of” employment:

The issue under this court’s standard of review is not whether the facts will support findings different from those made by the compensation judge, but, rather, whether substantial evidence supports the findings of the judge.  Hengemuhle v. Long Prairie Jaycees, 358 N.W.2d 54, 59, 37 W.C.D. 235, 239 (Minn. 1984).  We conclude that the judge’s decision is amply supported by the record and must be affirmed.

The employee in this case testified that her job as a packer required her to stand throughout her work shift and to repeatedly turn to her left and to her right in stacking folders onto skids.  She testified further that she experienced an immediate pain in her left knee when she turned to her right and her left leg did not turn with her body as anticipated.  The compensation judge found the employee’s testimony to be credible, and we defer to that finding.  See Brennan v. Joseph G. Brennan, M.D., 425 N.W.2d 837, 839-40, 41 W.C.D. 79, 82 (Minn. 1988) (assessment of a witness's credibility is the unique function of the trier of fact).  Moreover, the employee’s medical records, particularly those of Dr. Paul Yellin, support the judge’s determination regarding causation.  Dr. Yellin opined that the employee’s incident at work was a substantial cause of her medial meniscus tear, and, unlike Dr. Szalapski, he did not believe that the employee’s degenerative arthritis or obesity were the cause of the disability and medical treatment at issue in this case.  A compensation judge’s choice between  conflicting medical opinions is generally upheld if the facts assumed by the expert are supported by the record.  Nord v. City of Cook, 360 N.W.2d 337, 342-43, 37 W.C.D. 364, 372-73 (Minn. 1985).  While acknowledging that the employee may have been more susceptible to a meniscal tear because of her obesity, the judge, citing Schlichting v. Holm Bros., properly noted that “an employer takes the employee as it finds him [or her] with all of his [or her] inherent weaknesses.”  Schlichting v. Holm Brothers, 30 W.C.D. 289, 291 (W.C.C.A. 1978).  Further, a work injury need not be the sole cause of an employee’s condition, only a substantial contributing cause, to support a finding of liability.  See Salmon v. Wheelabrator Frye, 409 N.W.2d 495, 497-98, 40 W.C.D. 117, 122 (Minn. 1987).

No one comprehensive definition can be fashioned to fit all cases addressing whether an injury arises out of and in the course of employment.  To a great extent, each case stands on its own facts.  See Gibberd v. Control Data Corp., 424 N.W.2d 776, 780, 40 W.C.D. 1040, 1047 (Minn. 1988); Novack v. Montgomery Ward & Co., 158 Minn. 495, 498, 198 N.W. 290, 292, 2 W.C.D. 156, 159 (1924).  In Bohlin v. St. Louis County/Nopeming Nursing Home, this court stated as follows: