dissenting, with whom VOIGT, Chief Justice, joins.
[¶ 20] I respectfully dissent.
[¶ 21] Mr. Straube injured his right knee while at work. During surgery, paid for by workers' compensation, a loose fragment of bone or cartilage was removed from the knee joint. The surgeon's notes indicated that Mr. Straube had a "preexisting ... lesion that merely was knocked loose when the patient kneeled on it." Later, Mr. Straube's doctor recommended a second surgical procedure to repair cartilage in the knee. The basic issue before the Medical Commission was whether the second surgery was necessary because of the pre-existing condition, or whether the work-related injury had caused or materially aggravated the pre-existing condition. As the Medical Commission correctly set forth in its decision, pre-existing conditions are generally not compensable. Workers' compensation benefits are proper, however, if the "work effort contributed to a material degree to the precipitation, aggravation or acceleration of the existing condition of the employee." Haynes v. State ex rel. Wyoming Workers' Comp. Div., 962 P.2d 876, 878 (Wyo.1998).
[¶ 22] After a hearing, the Medical Commission found that the recommended surgery was attributable to the pre-existing condition, not the work-related injury. "We defer to an agency's findings of fact if supported by substantial evidence upon the record as a whole." Langberg v. State ex rel. Wyoming Workers' Safety & Comp. Div., 2009 WY 39, ¶ 10, 203 P.3d 1098, 1101 (Wyo.2009), citing Dale, ¶¶ 22-26, 188 P.3d at 561-62. The basic question before us on appeal, then, is whether there is substantial evidence in the record to support the Medical Commission's findings. There is.
[¶ 23] Reports from Drs. Davis and Whipp stated that the condition was preexisting, and indicated that it was not caused or materially aggravated by the work-related injury. The majority observes that these two doctors' opinions were based not "so much on medical information as their individual thoughts on the state of the law." Stripped to basics, however, Dr. Davis's report set forth his medical opinion that Mr. Straube's "follow up surgery is a result of a pre-existing condition and not of the acute episode that occurred at work." Dr. Whipp's report related his medical opinion that Mr. Straube's work-related injury "was not of a nature that we believe actually caused" the underlying condition, which was "a genetic predisposition that this patient had and that he probably already had." These opinions provided substantial evidence to support the Medical Commission's findings.
[¶ 24] Contrary evidence was provided by Dr. Dunn. He agreed that Mr. Straube had a pre-existing condition, but opined that further treatment would not have been necessary except for the work-related injury. The Medical Commission weighed the conflicting evidence, and made its position clear; "This Panel disagrees with Dr. Dunn's opinion, and finds that the respective opinions of Drs. Davis and Whipp are more persuasive." On that basis, the Medical Commission found that Mr. Straube's second surgery was nee-essary because of his pre-existing condition, and not because of his work-related injury.
[T 25] The majority seems to discount the opinions of Drs. Davis and Whipp because they reviewed Mr. Straube's medical records but did not examine the patient. This is common enough in workers' compensation cases, and does not render the evidence inadmissible or incompetent. It may affect the credibility or persuasiveness of the doctors' opinions, but it is up to the Medical Commission, not this Court, to determine the credibility of witnesses and the weight afforded to conflicting evidence. "[Wle defer to the experience and expertise of the ageney in its weighing of the evidence." Southwest Wyoming Rehabilitation Center v. Employment Sec. Comm'n of Wyoming, 781 P.2d 918, 921 (Wyo.1989). Deference is particularly appro*50priate here, as the Medical Commission was established specifically as "a means for par-tics to have difficult medically contested issues such as these resolved by a panel of the medical commission, which is comprised of health care providers with the professional expertise to make an informed decision." Snyder v. State ex rel. Wyoming Worker's Compensation Div., 957 P.2d 289, 294 n. 2 (Wyo.1998).
[¶ 26] I would defer to the Medical Commission's findings of fact, and affirm its decision.