The employee appeals from the compensation judge’s decision that the employee’s need for bilateral knee surgery is not causally related to her work-related right knee injuries.  We affirm.

The employee began working as a certified nursing assistant [CNA] for Lakeview Methodist Healthcare Center [the employer] in early 1988.  During the course of her employment there, she sustained two work-related injuries to her right knee.

The first injury occurred on March 11, 1996, as the employee was helping a resident get ready for bed.  The employee testified that, as she was squatting to take the resident’s shoes and socks off, she lost her balance and struck her right knee on the floor.  The employee further testified that she experienced pain just below her right knee cap at the time of the incident and that she reported the injury immediately to her supervisor.  A few days later, on March 15, 1996, the employee sought treatment from Dr. M.B. Wolverton, who diagnosed a right knee strain and restricted the employee to light duty.

In late April of 1996, the employee returned to see Dr. Wolverton, who referred her to Dr. Corey Welchlin, an orthopedic surgeon, for further evaluation.  Dr. Welchlin suspected a tear in the posterior horn of the medial meniscus and ordered physical therapy.  When the employee continued to experience symptoms, Dr. Welchlin ordered an MRI scan, which was performed on June 6, 1996.  The report from the scan reads as follows:

During the summer of 1996, Dr. Welchlin suggested arthroscopic surgery as a treatment option, but the employee elected to pursue a second opinion.  Accordingly, the employee was seen by Dr. John Springer in August of 1996.  Dr. Springer’s assessment was “[a]nterior knee pain due to deconditioning,” and he referred the employee for additional physical therapy.  As of September 16, 1996, the employee was reporting 50% improvement in her symptoms.  A month later, improvement had reportedly increased to 60%.  As some point, Dr. Springer prescribed a “sleeve brace” for the employee to use on her right knee.

In December 1996, Dr. Springer wrote that the employee’s “improvement will be directly related to her effort in performing her outpatient physical therapy exercises,” further noting that he saw “no indication for further diagnostic studies [or arthroscopic intervention] at this time.”  The employee further testified that she subsequently continued to experience right knee symptoms, but she was able to perform her usual CNA work without additional formal medical care or restrictions.

On May 3, 1999, the employee sustained her second work-related injury to her right knee while employed by the employer.  She testified that this injury occurred when she was kicked, just below her right knee cap, while attempting to transfer a resident from bed to a wheelchair.  The employee testified that she experienced pain in the same location as before, but this time the pain was more severe.

The employee returned to see Dr. Springer on May 17, 1999, about two weeks after the second injury.  In his notes from that evaluation, Dr. Springer indicated that the employee had been experiencing increased right knee pain over the past six months and that she had also recently been kicked in the knee at work.  The employee was instructed to minimize squatting and to avoid lifting over 50 pounds.  An MRI scan performed on May 26, 1999, disclosed joint effusion with a small popliteal cyst and an abnormal-appearing anterior cruciate ligament [ACL], possibly a “high grade partial tear with intra substance hemorrhage.”  The employee was referred for physical therapy and advised to wear her brace at work.  On July 21, 1999, Dr. Springer indicated that the employee should continue exercising at home and should wear her knee brace for heavy lifting at work, noting that “resolution of her symptoms lies in obtaining acceptable quadriceps strength.”  Other than use of the brace, no restrictions were recommended.

Dr. Springer subsequently completed a report indicating that the employee had a 3% permanent partial disability of the whole body, due to an ACL partial tear, as a result of the May 3, 1999, injury.  The employee was paid benefits for a 3% whole body impairment in accordance with this report.^[1]

The employee left her job with the employer in the fall of 1999 to provide daycare in her home.  In about February of 2000, she returned to CNA work for a different employer.

On February 16, 2001, the employee sought treatment again for right knee symptoms, reporting that she had slipped on ice the previous evening at home, jarring her knee.  An MRI was recommended but apparently not performed at that time.

On May 14, 2003, the employee was seen by a physician’s assistant with complaints of both left and right knee pain.  Because the symptoms had been worsening, the employee was advised to consult an orthopedist for further evaluation, and, two days later, she was seen by Dr. Gordon Welke.  Dr. Welke noted the employee’s history of right knee symptoms and treatment, and, after reviewing “the old MRI,” concluded that the employee had “definitely” had an ACL injury in the past.  Right knee x-rays taken by Dr. Welke on that date showed two “very early osteophytes” but were otherwise normal.

In June of 2003, the employee came under the care of Dr. Jeffrey Garske, complaining of bilateral knee pain, the right side much worse than the left.  Dr. Garske suspected that most of the employee’s complaints were related to the patellofemoral joint and indicated that, if this were the case, the employee would be a candidate for arthroscopic debridement.  His diagnosis was bilateral advanced chondromalacia patellae and a torn meniscus.

On July 21, 2003, the employee underwent an MRI scan of both knees.  Following the scan, Dr. Garske’s office notified the employee that she had a high grade tear of the ACL in her right knee as well as chondromalacia.  In an office note of August 12, 2003, Dr. Garske indicated that there was “some concern about possible bilateral partial ACL tears, although clinically this does not fit the bill nor has she any injury in the past that would indicate this.”  Dr. Garske also indicated that the employee had evidence of patella malalignment and chronic advanced chondromalacia.  The possibility of arthroscopic surgery and chondroplasty of the patella was raised again; however, the employee testified that, at that time, she was still unwilling to consider surgery.

In November of 2003, the employee was evaluated by independent examiner Dr. K. Stephen Kazi.  According to Dr. Kazi’s report, the employee “thought that the right knee was twisted sometime in the 1980's, and the left knee was injured at [the employer] in 1999.”  Dr. Kazi concluded that,

The employee returned to Dr. Garske’s clinic again in August of 2004, reporting a significant increase in knee pain over the previous several months.  In a report from a follow-up evaluation on September 7, 2004, Dr. Garske again recommended debridement surgery.  Also, noting the employee’s history of work-related knee injuries, Dr. Garske indicated that, if the employee had had multiple falls on the anterior part of the knee, “this would be a contributing factor for the chondromalacia.”

In June of 2005, the employee was seen again by Dr. Welchlin.^[2]  Dr. Welchlin’s impression was bilateral knee pain, right worse than left, secondary to work injuries in 1996 and 1999, and he wrote that it was “obvious” that the employee’s right knee was a “work comp situation” and that “the left knee is obviously aggravated following the excessive duties and activities she has had to do to support the right.”  For treatment of the employee’s condition, Dr. Welchlin recommended arthroscopies with chondroplasties, debridement, shaving, and lateral release if necessary.  Dr. Welchlin subsequently issued reports reiterating that the employee’s work injuries had substantially contributed to the employee’s bilateral knee condition and need for surgery.

The employee was also evaluated by independent examiner Dr. Gary Wyard.  In a July 21, 2005, report, Dr. Wyard wrote that, in his opinion, the employee’s 1996 work injury was a sprain/strain, which had resolved, and that the employee’s 1999 work injury was a contusion, which had also resolved.  With regard to the employee’s increased bilateral knee symptoms, Dr. Wyard concluded that the employee had mild chondromalacia of the patellofemoral joint, which he found to be the result of the employee’s pregnancies, her obesity, smoking, and her natural body configuration.  Dr. Wyard later expanded on his opinions in deposition testimony.  In that testimony, he explained again that the employee’s current knee symptoms were the result of a natural progressive condition unrelated to the employee’s admitted work injuries.  He also testified that the ACL tear shown on the employee’s MRI scans was not causing instability in the employee’s right knee and was not the cause of her ongoing pain.

The matter came on for hearing before a compensation judge on October 4, 2005, for resolution of the employee’s claim that the proposed bilateral knee surgery was reasonable, necessary, and causally related to either or both of her admitted right knee injuries.  The claim with respect to the left knee was based on the theory that the employee had over-used her left knee while compensating for her right knee condition.  At hearing, the employee testified that she could not remember exactly when her left knee symptoms had begun.

In a decision issued on October 27, 2005, the compensation judge concluded that the proposed surgery was not causally related to either of the admitted work injuries.  Accordingly, the judge denied the employee’s claim.  The employee 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 (2004).  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 the 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).

The compensation judge’s decision is relatively brief.  In relevant findings, the judge determined that:

On appeal, the employee does not contend that Dr. Wyard and Dr. Kazi lacked foundation for their opinions or that either physician had assumed facts that were not supported by the record.  Rather, the employee appears to be arguing that the judge erred in focusing entirely on the expert opinions, to the apparent exclusion of the employee’s medical history and the employee’s testimony as to the ongoing nature of her right knee symptoms following the 1996 injury.  As such, the employee contends, the judge’s decision is not adequately supported by the “entire record.”  We are not persuaded by this argument.

It may be true, as the employee alleges, that the compensation judge did not make any specific finding concerning the credibility of the employee’s testimony about her knee symptoms.  However, a compensation judge need not comment on every piece of evidence introduced at hearing.  See, e.g., Engels v. City of Delano, 65 W.C.D. 497 (W.C.C.A. 2005); Winkel v. Jacobson Transp., slip op. (W.C.C.A. Oct. 12, 2004); see also LaValley v. Erie Mining, slip op. (W.C.C.A. Oct. 24, 2003) (a compensation judge’s failure to make a specific finding as to credibility provides no grounds for reversal).  More importantly, the critical issue before the compensation judge was medical causation, an issue almost always resolved by a judge’s choice between conflicting expert opinions.  As the Minnesota Supreme Court has explained,

The employee also contends that there is simply no evidence in the medical records of “any other source of causation for the employee’s knee difficulties.”  However, according to Dr. Wyard, chondromalacia is a very common progressive degenerative condition, affecting ten times as many women as men; as he phrased it, “[a] female with chondromalacia is a ubiquitous diagnosis.”  Dr. Kazi agreed that the employee was suffering from a developmental condition, which was due in part to the employee’s excess body weight^[3] and not related to any work injury.  As such, the record clearly contains an alternative explanation for the employee’s current condition.

The record establishes that the proposed surgery is intended to treat the employee’s chondromalacia,^[4] and the opinions of Dr. Wyard and Dr. Kazi amply support the judge’s determination that the employee’s chondromalacia is not causally related to the employee’s admitted right knee injuries.  We therefore affirm the judge’s decision in its entirety.  See Nord v. City of Cook, 360 N.W.2d 337, 37 W.C.D. 364 (Minn. 1985).