The employee appeals from the compensation judge’s determination that the employee’s August 1999 knee injury was temporary in nature and had resolved by November 18, 1999, along with the compensation judge’s subsequent determinations that the employee did not sustain a consequential psychological injury and that the employee was not entitled to any additional benefits after November 18, 1999.  We affirm.

This case has a long, complicated procedural history.  The employee, Ms. Julie Small, was employed as a certified nursing assistant for the employer, St. Louis Park Plaza Healthcare Center, on August 17, 1999, which is the date of injury herein.

Before her injury in August 1999, the employee had an extensive history of prior right knee problems.  In November 1977, the employee sustained an injury to her right knee while trying out for a broomball team.  She was eventually diagnosed with a probable medial meniscal injury, and she underwent a right knee arthroscopic surgery in March 1978.  During surgery, Dr. Donald Madsen found a loose posterior medial meniscus with a small tear and peripheral tearing.  Doctor Madsen removed what he believed to be the entire medial meniscus.

The employee returned for additional right knee treatment in July 1984, reporting some chronic discomfort and swelling in the right knee over several months, along with some instability.  Doctor Patrick Kraft, of North Memorial Medical Center, performed a partial meniscectomy in July 1984, removing the remaining remnants of the posterior horn of the medial meniscus in the employee’s right knee.  Doctor Kraft also debrided some softened cartilage from the tibial plateau on the medial side of the right knee.  Doctor Kraft viewed the employee’s anterior cruciate ligament (ACL) during the 1984 surgery and noted that it was non-functional.  After surgery, Dr. Kraft diagnosed the employee with grade III chondromalacia of the tibial plateau medial compartment and a torn ACL.

Doctor Kraft took the employee back to the operating room on July 17, 1989 because of increasing pain and swelling in the medial compartment of the right knee.  He noted that there was complete loss of articular cartilage on the weight-bearing area of the tibial plateau, and significant deterioration (grade III changes) of the articular surface of the medial portion of the femur bone at the knee.

The employee also had a significant history of mental health issues before the August 1999 injury.  The compensation judge noted, in an unappealed finding, that the employee had a tragic childhood and was subjected to horrible abusive episodes.  The employee received mental health treatment leading up to the injury on 1999, and the compensation judge found that:

The original injury that is the subject of the current litigation occurred on August 17, 1999.  The employee testified that as she was assisting a patient that had fallen from a wheelchair, she felt discomfort and a tearing sensation in her right knee.  The employer and its workers’ compensation insurer initially admitted liability for the employee’s work injury of August 17, 1999.

The employee left work to obtain medical care for her right knee on the date of injury, and she continued treating thereafter.  An MRI of the right knee was taken in early September 1999, which was reportedly consistent with the prior medial meniscectomy, and the employee’s ACL was not visualized.  One of the employee’s initial treating physicians, Dr. Klock, noted that the ACL must have atrophied from the prior injury.  A small tear in the posterior cruciate ligament (PCL) and a strain of the fibular collateral ligament (FCL) were noted as well, along with fluid in the joint.

The employee was referred to an orthopedic surgeon at Park Nicollet, Dr. Allen Hunt.  Doctor Hunt noted that the employee had instability in the right knee, degenerative joint disease, and a definite varus (bow-legged) deformity in the right knee compared to the left.^[1]  On September 23, 1999, Dr. Hunt took the employee to the operating room for an arthroscopic debridement of the medial right knee compartment due to mechanical catching and locking in the knee.  In his notes, Dr. Hunt indicated that the employee had severe medial degenerative disease and an ACL deficient right knee.

The records from October and early November 1999 show that the employee was reportedly doing better following the September 1999 surgery.  Therefore, on November 16, 1999, Dr. Hunt released the employee to return to work with restrictions on lifting, bending, twisting, and reaching below the knee.  The employee was not able to return to work at the employer because there was no work available within her restrictions.  The employer and insurer continued to pay both wage loss and medical benefits, and they did not seek an independent medical examiner’s opinion, initially.

When he released the employee to return to work with restrictions, Dr. Hunt also recommended that the employee have an opening wedge proximal tibial osteotomy surgery to unload the diseased medial compartment of the right knee.  The employee underwent this procedure with Dr. Hunt on April 10, 2000.  The employee developed problems with the hardware in the right knee after a fall in June 2000.  The hardware was removed on September 7, 2000.  After the September 2000 surgery, the wound was healing, initially.  However, the edges of the wound pulled apart, and the employee began what was to become a very long period of wound treatment.  The employee went on to have, as the compensation judge described, “dozens of wound care surgical procedures from 2000 through 2012,” some of which were outpatient and some inpatient.  The compensation judge found the following:

The parties entered into two stipulations for settlement regarding the employee’s August 1999 right knee injury.  The first of these settlements was filed in 2002, and it resolved disputed benefits through May 8, 2002.  The second settlement was filed in 2003.  In the 2003 stipulation, the parties agreed that the employee was permanently and totally disabled for an indefinite period of time as of September 27, 2002.  The compensation judge made the following unappealed finding regarding the settlement agreements between the parties:

The case eventually came on for hearing before Compensation Judge Penny Johnson on December 28, 2012, and December 31, 2012.  The parties introduced voluminous medical evidence, including expert opinions regarding the employee’s physical and mental health claims.

The employee’s primary physician, Dr. Hunt, testified by deposition.  He acknowledged that he did not review the employee’s medical records before the work injury, but he was aware of the prior treatment by hypothetical, including the surgeries.  Doctor Hunt indicated that the employee’s ACL deficient knee and instability in 1999 was acute because the employee had indicated that these were new symptoms.  As such, Dr. Hunt felt that the work injury caused the degenerative knee to flare up and be permanently symptomatic.  Doctor Hunt opined that the 1999 right knee injury at work substantially contributed to the employee’s need for the post-injury surgeries, including the employee’s issues related to her non-healing wound.  Doctor Hunt opined that the left knee condition in 2009 was a consequential injury due to the overuse of the left knee as well.  Doctor Hunt indicated that a meniscal tear may be either related to a specific trauma or may develop over time.

The employer and insurer presented medical opinions from Dr. D’Amato, an orthopedic surgeon.  Doctor D’Amato conducted an independent medical examination (IME) of the employee on January 8, 2010, he issued reports on January 6, 2010, January 21, 2010, and February 16, 2010, and he gave a deposition.  Ultimately, Dr. D’Amato opined that the employee had severe arthritis in the medial compartment of the right knee by 1989.  Doctor D’Amato opined that most of the findings after the employee’s 1999 work injury were chronic findings.  He noted that there were acute findings of edema in the FCL, consistent with a very minor strain of the ligament and a temporary aggravation of the pre-existing severe medial compartment arthritis.  The ACL and PCL findings and severe loss of cartilage in the bones of the knee were chronic conditions, in Dr. D’Amato’s opinion.  There was swelling and inflammation in the knee related to the 1999 injury, but Dr. D’Amato opined that there was no progression of underlying and pre-existing arthritis or any progression of the ACL or PCL damage.

Doctor D’Amato opined that the employee sustained a strain-type injury to her right knee that would have resolved by November 18, 1999.  Although Dr. D’Amato noted that these types of injuries usually resolve in about six weeks, he felt that the employee’s injury resolved in November 1999, when her knee was functioning better and her increased pain had resolved.  Doctor D’Amato opined that the first arthroscopic surgery was not warranted because the employee did not have mechanical symptoms such as catching and locking, but she had symptoms of severe arthritis that the arthroscopy could not change, and the knee was still unstable after the first surgery because the employee continued to have an ACL deficient knee.  Doctor D’Amato further opined that the employee’s ongoing treatment was meant to treat the underlying arthritis, including the osteotomy in 2000, which was meant to shift weight from the diseased medial compartment to the lateral non-diseased compartment.  Doctor D’Amato concluded that all of the subsequent knee surgeries were meant to treat chronic arthritis and not the strain-type work injury.

The employee presented reports and testimony from Dr. Marie-Clair Buckley, who worked closely with the employee regarding her right calf wound care from June 2007 to the date of hearing.  Doctor Buckley opined that the employee was doing a remarkable job in caring for the wound despite pain.  Other than being unable to quit smoking permanently, Dr. Buckley was very satisfied with the employee’s care for the wound.  She did not think the employee was doing anything to harm the healing process.

Doctor Ronald Vessey performed an IME at the employer and insurer’s request on April 19, 2010.  He issued a report dated May 12, 2010.  He felt that the employee’s long history of smoking impacted her wound healing, and he wondered if the employee would ever achieve wound healing without smoking cessation and weaning from opiate medications.  He also noted that the employee had some behavior inconsistent with healing, such as home incision and drainage of an infected osteotomy incision, and non-compliance with treatment, including detaching a VAC machine while on bed rest and smoking in her hospital bathroom.  Doctor Vessey felt there was not much question that the wound directly related to the work injury, but he did not explain how he reached that conclusion, according to the compensation judge, and she noted that Dr. Vessey “was probably assuming the osteotomy surgeries were definitely causally related to the injury.”

The employee also claimed to have sustained a consequential psychological injury.  The employer and insurer paid for psychological treatment that the employee started in April 2001 and continued through 2003.  The employee treated in January 2003, contemplating suicide.  The employee had tried to cut one wrist.  She was also hospitalized on multiple occasions for intoxication.  The employee subsequently began psychotherapy sessions with Susan Langston, a licensed clinical social worker, in August 2007.  These sessions continued through the December 2012 dates of hearing.^[2]  Ms. Langston ultimately diagnosed the employee with depression due to chronic pain that was caused by her right knee injury, stress related to chronic pain and psychosocial stressors, alcohol and narcotic addiction in full and sustained remission, panic disorder, and some symptoms of post-traumatic stress disorder.  Ms. Langston testified that the work injury was a substantial contributing factor in the employee’s psychological condition and need for the mental health treatment that she had provided.

Doctor Thomas Gratzer, a psychiatrist, conducted an IME at the employer and insurer’s request in April 2010, and he gave a deposition before hearing.  Doctor Gratzer had a colleague administer an MMPI psychological test, but the results were determined to be invalid.  Therefore, Dr. Gratzer reviewed three prior MMPI tests.  Doctor Gratzer diagnosed the employee with mixed personality features, chemical dependency, depression, and anxiety.  He opined that these were all pre-existing conditions that were not changed by the work injury.

After reviewing the evidence presented, including the employee’s testimony from hearing, the compensation judge determined that the employee’s work injury had resolved by November 18, 1999, when Dr. Hunt released her to return to work with restrictions after the first surgery.  In her memorandum of law, the compensation judge indicated that the employer and insurer had made payments pursuant to the 2002 and 2003 injuries, and they had admitted the injury, but they had reserved their defenses.  She concluded that they “had never admitted” to owing permanent total disability benefits, that Dr. D’Amato’s opinions provided a basis for the discontinuance of benefits pursuant to the stipulations, and that the employer and insurer appropriately discontinued benefits after Dr. D’Amato’s report.  Ultimately, the compensation judge found that Dr. D’Amato’s causation opinion was more persuasive than the causation opinion of Dr. Hunt.  The compensation judge stated, “it is tempting in this case to find the employee’s treatment and disability compensable as a result of a work-related injury because the insurer admitted there was a work injury and paid very large sums of money for wage loss benefits, and for five orthopedic surgeries and dozens of wound surgeries.”  However, based on Dr. D’Amato’s conclusion that the effects of the injury were merely a temporary strain, the compensation judge denied the ongoing benefits sought beyond November 1999.^[3]

“A settlement agreement is a contract.”  Hampton v. Spectro Alloys Corp., 65 W.C.D. 541, 545 (W.C.C.A. 2005).  In Hampton, this court went on to explain that:

The employee argues that the language in the 2002 and 2003 stipulations is unambiguous and that in those stipulations, the employer and insurer accepted primary liability for a permanent injury resulting in the payment of permanent total disability benefits.  The employee also argues that there can be no dispute that the parties’ mutual understanding was that the injury or injuries that would give rise to the employee’s entitlement to benefits, and even governmental benefits when considering a permanent total disability offset, were related to the right knee and the post-surgical condition, including the chronic wound on the right calf.  Ultimately, the employee is arguing that the compensation judge, as a matter of law, erred in considering a defense at hearing regarding the nature and extent of the employee’s injury, including the claimed consequential injuries, given the language of the stipulations and the other extrinsic evidence at the time the parties entered into the 2002 and 2003 stipulations.

In the 2002 stipulation, the employer and insurer denied that the employee was entitled to temporary total disability benefits from August 2001 to the present and continuing, and they denied that the employee was permanently and totally disabled.  However, they agreed to pay “total disability” benefits for nine months.

In the 2003 stipulation, the employer and insurer again denied that the employee was entitled to temporary total disability benefits from August 2001 to the present and continuing, and they denied that the employee was permanently and totally disabled indefinitely.  However, they agreed that the employee was permanently and totally disabled as of September 27, 2002.  They agreed to continue paying PTD benefits to the employee “for so long as her condition shall warrant,” subject to certain conditions laid out in the 2003 stipulation.  The parties then agreed that the employer and insurer could terminate payment of PTD benefits, without the necessity of filing a Notice of Intention to Discontinue Benefits or any other procedural requirements, upon the occurrence of certain qualifying events.  The qualifying events included “any of the factors set forth in Minn. Stat. § 176.101, subd. 1” and “the employee being released to return to work by her treating physicians or an independent medical evaluator.”  The stipulation further provided that that if the parties agreed the employee was not permanently totally disabled, or there was a judicial determination as such, that the agreement of the parties would be void.  Furthermore, in both stipulations, the employer and insurer “expressly reserve and maintain any and all rights and defenses that they may have to any future claims that the Employee may make.”

After reviewing the language of the stipulation, we agree with the compensation judge’s determination that the employer and insurer never admitted to a permanent injury such that they owed ongoing permanent total disability and other benefits.  All payments made pursuant to stipulation were made under a reservation of defenses.  Although Dr. D’Amato’s IME was conducted several years after the injury itself, his opinion that the injury had resolved and that the employee no longer required restrictions as a result of the work injury as of November 1999 did provide a basis for discontinuance pursuant to the stipulation, and it was not a legal error for the compensation judge to consider the arguments raised at hearing regarding the nature and extent of the employee’s injury.^[4]

The employee goes on to argue that because the employer and insurer acquiesced to the fact that the employee would be entitled to a future flow of benefits, even in order to recoup overpayments, the employer and insurer admitted that any potential ongoing disability would be a direct result of the August 1999 injury.  In other words, the employee argues that by choosing to pay benefits over the years, the employer and insurer clearly relied upon their own reasonable evaluation of the employee’s ongoing condition, they concluded that the work injury was a substantial contributing factor in the employee’s ongoing right knee condition, and they were contractually bound to concede the nature and extent of the employee’s injury.

We disagree.  Similar arguments have been rejected in a number of cases, and a voluntary payment of benefits does not preclude a later denial of liability for those benefits paid.  See, e.g., Getman v. Carlson Holdings, slip op. (W.C.C.A. June 5, 2009) (noting that although the employee repeatedly argued that the employer and insurer initially accepted and paid medical expenses for low back treatment for several years after her initial low back treatments and implied that this is a factor supporting her causation claim, “it is settled law that an employer may deny primary liability for an injury, in the absence of prejudice to the employee, after making a voluntary payment of benefits”) (citing Zontelli v. Smead Mfg. Co., 343 N.W.2d 639, 36 W.C.D. 453 (Minn. 1984); Hoch v. Duluth Clinic, slip op. (W.C.C.A. August 3, 2007); Minn. Stat. § 176.179).  See also Minn Stat § 176.221, subd. 1.

The employer and insurer’s payment of benefits did not amount to an admission of liability for a permanent injury as the employee argues, and there was no allegation of prejudice to the employee in this case such that the employer and insurer would be prevented from later denying liability.  Given the circumstances of this case and the language of the stipulations at issue, it was not legal error for the compensation judge to conclude that the employer and insurer never admitted to a permanent injury such that they continued to owe ongoing permanent total disability and other benefits.

The employee also argues that the compensation judge’s finding that the employee did not sustain a consequential psychological injury is not supported by substantial evidence in the record.  She argues that while it was well documented that she had a difficult personal history that affected her mental status, chemical dependency and its associated diagnoses are separate from a diagnosis of depression resulting from chronic pain.  The employee argues that the chronic pain diagnosis offered by Ms. Langston was not contested, and it was unique from the diagnosis of chemical dependency relied upon by Dr. Gratzer in his analysis.  The compensation judge found that Ms. Langston assisted the employee with stress reduction and coping strategies to help manage her pain and mental health concerns.  As such, the employee argues that these were reasonable and necessary treatment expenses, and the compensation judge’s findings that the treatment provided by Ms. Langston was helpful and necessary while also concluding that the employee did not suffer from a consequential injury were inconsistent and should be reversed.

Questions of medical causation fall within the province of the compensation judge.  Felton v. Anton Chevrolet, 513 N.W.2d 457, 50 W.C.D. 181 (Minn. 1994).  It is the function of the compensation judge to resolve conflicts in expert medical testimony, and the choice of expert opinion is usually upheld unless the facts assumed by the expert in rendering the opinion are not supported by the evidence.  Nord v. City of Cook, 360 N.W.2d 337, 37 W.C.D. 364 (Minn. 1985).  Where evidence is conflicting or more than one inference may reasonably be drawn from the evidence, the findings of the compensation judge are to be upheld.  Redgate v. Sroga’s Standard Serv., 421 N.W.2d 729, 734, 40 W.C.D. 948, 957 (Minn. 1988).

The compensation judge did not find Ms. Langston’s opinions persuasive.  Although Ms. Langston worked with the employee for many years, the compensation judge noted that Ms. Langston

The compensation judge addressed the chronic pain issue in her memorandum of law and further explained the basis for her conclusion.  She stated that “[t]he employee’s psychological injury claim is premised on having chronic pain and depression as a result of the work injury.”  However, the compensation judge determined that the employee’s chronic pain was caused by the pre-existing and underlying knee condition and treatment.  Furthermore, the compensation judge determined that “[e]ven if a finding was made” that the work injury contributed to the employee’s chronic pain, her “psychological issues are primarily driven by chemical dependency, personality traits, and psychosocial stressors.”  We do not find these conclusions to be inconsistent as the employee purports.

The compensation judge based her determinations regarding the employee’s physical condition, in part, on Dr. D’Amato’s opinion, and she based her determinations regarding the employee’s mental health condition, in part, on Dr. Gratzer’s opinion.  The employee does not challenge the foundation for either of these opinions, and these opinions provide sufficient support for the compensation judge’s conclusions.  Therefore, we affirm the compensation judge’s denial of the employee’s consequential psychological injury claim.^[5]