The employee appeals from the compensation judge’s finding that the employee’s work injury is not a substantial contributing factor in any loss of earnings or earning capacity sustained by the employee from April 30, 2004, through the date of hearing and from the judge’s order allowing the employer to discontinue the employee’s temporary partial disability benefits.  We affirm.

For purposes of this appeal, the relevant facts are essentially undisputed.  Margaret McQuiston [the employee] has worked for Independent School District #77–Mankato [the employer] part time as a substitute clerical worker since the early 1980's.  As a substitute clerical worker, the employee fills in for the employer’s permanent clerical workers when they miss work.  The employer maintains a list of approved substitutes, and typically a permanent clerical worker who needs a substitute makes arrangements for his or her own substitute in advance of any absence.  Permanent clerical workers are free to call anyone on the approved substitute list to fill in while they are away.  Under this arrangement, the employee works on an as-needed basis, and her earnings have varied over the course of time.

On January 4, 2001, the employee slipped and fell on some ice in the parking lot at Mankato East High School, fracturing her right wrist.  Subsequently she underwent three surgeries–on December 3, 2001, March 15, 2002, and December 12, 2003–all admittedly related to this injury.  The employee was off work following the latter surgery until April 2004, by which date her wrist symptoms had improved significantly and her wrist had become stronger and less painful.  Subsequent to her work injury and over the course of her several surgeries, the employee had continued to work intermittently for the employer in her capacity as a substitute clerical worker.  It is undisputed that the employee has restrictions related to her injury and that she has been paid permanent partial disability benefits for a 9.35% whole-body impairment.  However, except for several periods of temporary total disability, the employee’s wrist condition has not prevented her from performing her job, and she has never turned down a substitute opportunity because of that condition.  Notwithstanding this continuing work, records of the employee’s post-injury earnings reflect that, with the exception of the year 2001, the employee’s post-injury earnings have steadily declined.^[1]  Since April 30, 2004, this decline in earnings is due primarily to the fact that the employee’s opportunities for substitute work have been limited.

On July 11, 2005, the employer filed a petition to discontinue the employee’s temporary partial disability benefits from and after April 30, 2004, on grounds that the employee’s work injury was not a substantial contributing factor in the employee’s wage loss.  The employer asserted that temporary partial disability benefits paid since April 30, 2004, had been paid under mistakes of fact and law.^[2]

The employer’s petition to discontinue came on for hearing before a compensation judge on September 13, 2005.  Evidence offered at trial included testimony from the employee, from the employer’s Health and Safety Coordinator, Joseph Meixl, and from Counseling Center Secretary Dorothy Norland.  The employee testified in part that her wrist injury does not prevent her from performing her substitute job and that she has never turned down a substitute opportunity because of her wrist condition.  Mr. Meixl testified in part that the employee’s opportunities to work for the employer have declined since April 30, 2004, primarily because the employer has been doing more “cross-training” or training full-time clerical workers to cover for absent co-workers, because budget cuts have reduced resources to pay substitutes, and because other substitutes are being called ahead of the employee.  Ms. Norland testified that the employee’s right wrist condition has never been a factor in her decision to call or not to call the employee for work.

In a Findings and Order issued September 26, 2005, the compensation judge concluded that the evidence failed to establish that physical limitations associated with the employee’s work injury were a substantial contributing factor in the reduction of the employee’s substitute work opportunities since April 30, 2004, adopting instead the explanations of Mr. Meixl.^[3]  On that basis, the judge concluded that the employee’s work injury was not a substantial contributing factor in any loss of earnings or earning capacity sustained by the employee from April 30, 2004, through the time of hearing.  Accordingly, the judge granted the employer’s petition to discontinue benefits as of April 30, 2004.  The employee appeals.

To demonstrate entitlement to temporary partial disability benefits, an employee must show a work-related physical disability, an ability to work subject to the disability, and an actual loss of earning capacity that is causally related to the disability.  See Dorn v. A.J. Chromy Constr. Co., 310 Minn. 42, 47, 245 N.W.2d 451, 454, 29 W.C.D. 86, 91 (1976).  In Roberts v. Motor Cargo, Inc., the supreme court held that an injured employee’s actual post-injury earnings are presumed to be an accurate measure of the employee’s ability to earn.  Roberts v. Motor Cargo, Inc., 258 Minn. 425, 431, 104 N.W.2d 546, 550, 21 W.C.D. 314, 319 (1960), citing 2 Larson, Workmen’s Compensation Law § 57.21; see also Owens v. Pako Corp., 386 N.W.2d 711, 714-15, 38 W.C.D. 627, 631 (Minn. 1986).  In appropriate circumstances, however, this presumption can be rebutted.  See Einberger v. 3M Co., 41 W.C.D. 727, 739 (W.C.C.A. 1989); Borchert v. American Spirits Graphics, 582 N.W.2d 214, 215, 58 W.C.D. 316, 318 (Minn. 1998).  The employee contends that there is no evidence in this case, even conceding the facts found by the judge, sufficient to overcome the presumption.  She contends, citing this court’s decision in Patterson v. Denny’s Restaurant, that, in order to rebut the presumption, the employer has the burden of proving that the employee has an earning capacity different from that reflected in her actual earnings and that this requires a showing of something more than a theoretical possibility of a different position or wage.  See Patterson v. Denny’s Restaurant, 42 W.C.D. 868, 875 (W.C.C.A. 1989).  We do not agree.

The presumption that an injured employee’s actual post-injury wage reflects his or her earning capacity maybe be rebutted either with evidence indicating that the employee’s ability to earn is something affirmatively different from that reflected in the post-injury wage, see Einberger, 41 W.C.D. at 739, or with other evidence affirmatively establishing that the reduction in the employee’s earning capacity is unrelated to the employee’s disability, see Borchert, 582 N.W.2d at 215, 58 W.C.D. at 318.  At the outset of the hearing, the compensation judge identified the issue for determination as whether or not the employee’s January 4, 2001, work injury has been a substantial contributing factor in any loss of earnings or earning capacity sustained by the employee from April 30, 2004, through the time of hearing.  In holding that the employee’s injury was not a substantial contributing factor in such a loss, the judge did not determine that the employee had no post-injury reduction in earning capacity, nor did she hold that the employee was or was not capable of earning more money at a job different from her post-injury job with the employer.  The judge held only that the employee’s post-injury reduction in earnings was due not to her injury but to other specific causes.  Pursuant to the supreme court’s decision in Borchert, such a conclusion, if supported by substantial evidence, is sufficient to rebut the actual wage earning capacity presumption.  Id.

In the end, contrary to the employee’s argument, the issue here is not whether the judge erred as a matter of law in her application of the presumption but whether substantial evidence supports the judge’s conclusion that the employee’s reduction in wages resulted from cost-saving measures implemented by the employer rather than from the employee’s disability.  Whether an employee’s reduction in earnings during a period of post-injury employment is due to the employee’s injury or to some nonwork-related cause is a question of fact for the compensation judge.  Borchert, 582 N.W.2d at 215, 58 W.C.D. at 318 (citation omitted).  In light of Mr. Meixl’s testimony at hearing, we conclude that the judge’s finding on this issue was not unreasonable and is therefore supported by substantial evidence; and therefore we affirm.  See Hengemuhle v. Long Prairie Jaycees, 358 N.W.2d 54, 59, 37 W.C.D. 235, 239 (Minn. 1984).