The employee appeals from the compensation judge’s determination that the employee failed to prove that surgery for a trigger finger condition was causally related to the employee’s 1992 low back injury, and from the compensation judge’s ruling which excluded certain evidence offered by the employee. We affirm the compensation judge’s evidentiary ruling but vacate and remand the issue of causation for reconsideration.

The employee, Dennis Henchal, sustained an admitted work injury to his low back on May 14, 1992, while working for the employer, Federal Express Corporation. Despite low back surgery in October 1994 and again in 1995, the employee has continued to have chronic back pain and prolonged additional treatment. The employee began using a cane for support in 1994 or 1995.

The employee no longer works, and the parties reached a stipulated settlement in which the employee was determined to be permanently totally disabled. He testified that his typical routine consists of “putzing around the house,” going shopping with his wife, and playing guitar for about an hour each day.

He began to develop a painful “catching” in his right middle finger some time in 2005, and the finger joint would sometimes “lock.” He initially ignored these symptoms, but eventually mentioned them to Dr. Leonard Warren, his treating physician. Dr. Warren referred him to Dr. Owen O’Neill at Minnesota Orthopaedic Specialists, who saw the employee on September 12, 2005.

Dr. O’Neill diagnosed a right middle finger trigger finger condition. The condition was treated by a cortisone injection, which initially alleviated the employee’s pain. Subsequently, however, the employee’s finger symptoms returned. Additional injections provided only a few weeks of relief, after which triggering symptoms returned. Dr. O’Neill referred the employee to Dr. Laurie Koch for consideration of surgery. Dr. Koch evaluated the employee on May 8, 2006, and recommended that the employee undergo trigger release surgery.

The employee underwent a right long finger trigger release on June 13, 2006. The surgery resulted in a complete alleviation of symptoms other than some residual stiffness in the finger.

In a letter dated August 29, 2006, Dr. Koch provided her opinion that the employee’s trigger finger symptoms and need for the June 13, 2006, surgery had developed as a result of his long term cane use due to his work-related back injury. Dr. Koch further wrote that “[t]his likely would not have occurred in the absence of cane use.” In his hearing testimony, the employee described the manner in which he customarily gripped and used his cane, which he associated with the development of his trigger finger symptoms. The employee filed a claim petition seeking payment of his medical expenses for the trigger finger condition on the basis that the trigger finger condition was caused in substantial part by the effects of his 1992 work injury.

The employee was evaluated on behalf of the self-insured employer on February 27, 2007, by Dr. Jeffrey B. Husband. Dr. Husband agreed with the diagnosis of trigger finger of the right middle finger, but offered the opinion that the employee’s trigger finger condition was neither directly nor indirectly related to the 1992 work injury. In Dr. Husband’s view, “[t]rigger finger is an idiopathic disorder which occurs very frequently in middle-age individuals with no identifiable cause [and] . . . has not been shown to be associated with hand use, and, in particular, with use of a cane.”

At the hearing, the employee offered an exhibit consisting of some pages printed from various internet sites stating that repetitive and routine firm gripping and grasping may cause the onset of a trigger finger condition. The employer objected to the proposed exhibit on the basis that it was hearsay evidence for which no foundation had been established, and did not qualify as a “learned treatise” because it was not taken from peer-reviewed medical journal articles. The compensation judge ruled against admitting the exhibit.

In her findings and order of July 26, 2007, the compensation judge decided that Dr. Koch’s causation opinion was “insufficient” as a matter of law in that it failed to “set out the factual basis for [the] opinion.” Finding 16. The judge accordingly held that the employee had failed to carry his burden of proving a consequential injury to his finger. The employee appeals.

Generally, a compensation judge has broad discretion regarding the admissibility of evidence. Ziehl v. Vreeman Constr. Co., slip op. (W.C.C.A. Oct. 15, 1991). It is well settled that “[a] compensation judge is given broad latitude in conducting a hearing and in the admission of evidence in order to assure that justice and fairness prevail.” Murphy v. Keebler Co., 45 W.C.D. 356, 358 (1991). Minn. Stat. § 176.411, subd. 1, provides, in relevant part, that:

The employee contends on appeal that the compensation judge was required to admit a proposed exhibit which consisted of several pages printed from medical information sites on the internet. The employee cites Minn. R. 1420.2900, subp. 6A, which provides that “[t]he judge will accept only relevant and material evidence that is not repetitive or cumulative.” The employee argues that this rule compels the admission of relevant and material evidence that is not repetitive or cumulative. We disagree. The rule simply precludes the acceptance of repetitive and cumulative evidence, and does not mandate admission of all other evidence.

This court has previously emphasized the importance of proper foundation to qualify a medical journal article as an accepted medical authority or treatise.^[1] Here, what was offered were pages printed from short informational articles on several web sites, most of which were not attributed to a specific author. We conclude that the compensation judge did not abuse her discretion in failing to admit into evidence the employee’s proposed exhibit.

The employee alleged that his trigger finger condition had arisen as a consequence of his 1992 low back injury, in that his use of a cane because of the work injury was a direct cause of the development of the trigger finger condition. The employee’s claim relied primarily upon his own testimony and the medical opinion of his treating physician, Dr. Koch. Dr. Koch’s opinion was embodied in a letter which stated that she believed that “the symptoms and need for surgery developed as a result of long term cane use from a back injury [and] . . . likely would not have occurred in the absence of cane use. I believe there is a causal relationship between back [the] back injury and [the] development of triggering.”

In Finding 16, the compensation judge found that Dr. Koch’s letter was legally insufficient to support a finding of causation, in that it “. . . does not set out the factual basis for Dr. Koch’s opinion.” The finding cites Welton v. Fireside Foster Inn, 426 N.W.2d 883, 41 W.C.D. 109 (Minn. 1988), for the proposition that “[a] medical causation opinion set out without explanation is insufficient.” The compensation judge’s memorandum notes her further reasoning that Dr. Koch’s opinion could support a finding of medical causation, but that it would not support “a finding of legal causation,” quoting language from Klapperich v. Agape Halfway House, 281 N.W.2d 675, 31 W.C.D. 641 (Minn. 1979) to the effect that proof of medical causation, in and of itself, does not establish legal causation.

The employee argues on appeal that the compensation judge misconstrued Welton and Klapperich and applied an improper standard of proof. We agree.

As we recently noted in Gardner v. Elbow Lake Coop Grain, No. WC07-180 (W.C.C.A. Jan. 10, 2008), our case law has long held that a doctor’s failure to explain the mechanism of an injury or the underlying reasons for the doctor’s opinion respecting causation does not render that opinion without foundation, although the lack of an explanation may affect the opinion’s weight or persuasiveness. We further concluded in Gardner that the Welton case did not support the proposition that a medical expert must provide an explanation for his or her opinion. Rather, the Welton court simply affirmed a compensation judge’s rejection of an expert medical opinion as based on an inadequate foundation, where the opinion was based on facts unsupported by the record.

In the present case, Dr. Koch took the employee’s history, examined and treated his trigger finger condition, and performed the surgery. This information provides adequate foundation for the doctor’s opinion. See Grunst v. Immanuel-St. Joseph Hosp., 424 N.W.2d 66, 40 W.C.D. 1130 (Minn. 1988). While the weighing of Dr. Koch’s opinion was a matter for the compensation judge, the language of the finding indicates that she failed even to consider Dr. Koch’s opinion in weighing the evidence.

The compensation judge’s reliance on Klapperich, and her statements about the insufficiency of Dr. Koch’s opinion to establish legal causation, are also troubling. Klapperich is a case dealing with causation in the context of a stress-related heart condition. In such cases, a claimant must not only establish medical causation between the work-related stress and the heart condition, but must also show, by way of legal causation, that the stress to which the employee was exposed was unusual or extreme. Id. This standard of legal causation is stricter than that normally required to establish a causal link between an employee’s work injury and resulting disability, in which “legal cause” has been defined simply as “an appreciable or substantial contributing cause.” Salmon v. Wheelabrator Frye, 409 N.W.2d 495, 497-498, 40 W.C.D. 117, 122 (Minn. 1987).

This case, however, is one in which the underlying personal injury is admitted, and the issue presented was simply whether the low back injury caused a compensable consequential condition. In such cases, a different causation standard is applied, in which “the rules that come into play are essentially based upon the concepts of ‘direct and natural results,’ and of the claimant’s own conduct as an independent intervening cause.” Jackson v. Red Owl Stores, Inc., 375 N.W.2d 13, 18, 38 W.C.D. 170, 177 (Minn. 1985). The compensation judge’s memorandum, however, suggests that she may have applied an inappropriate causation standard applicable to cases asserting work stress as the cause of a heart attack.

On appeal, the self-insured employer argues that there is substantial evidence in the record which could support the compensation judge’s finding denying causation, including the opinion of Dr. Husband. However, we are reluctant to affirm where it appears that the compensation judge failed to even consider Dr. Koch’s opinion, and by the possibility that an improper burden of proof may have been applied. We conclude that it is necessary to remand the causation issue for reconsideration.