In the Matter of the Worker's Compensation Claim of: Phylis Stevens , 338 P.3d 921 ( 2014 )


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  •                 IN THE SUPREME COURT, STATE OF WYOMING
    
    2014 WY 153
    OCTOBER TERM, A.D. 2014
    December 2, 2014
    IN THE MATTER OF THE WORKER’S
    COMPENSATION CLAIM OF:
    PHYLIS STEVENS,
    Appellant
    (Petitioner),
    v.                                                   S-14-0076
    STATE OF WYOMING, ex rel.,
    DEPARTMENT OF WORKFORCE
    SERVICES, WORKERS’ SAFETY AND
    COMPENSATION DIVISION,
    Appellee
    (Respondent).
    Appeal from the District Court of Sublette County
    The Honorable Marvin L. Tyler, Judge
    Representing Appellant:
    F. Gaston Gosar of F. Gaston Gosar, P.C., Pinedale, Wyoming.
    Representing Appellee:
    Peter K. Michael, Wyoming Attorney General; John D. Rossetti, Deputy Attorney
    General; Michael J. Finn, Senior Assistant Attorney General; Samantha Caselli,
    Assistant Attorney General.
    Before BURKE, C.J., and HILL, KITE, DAVIS, and FOX, JJ.
    NOTICE: This opinion is subject to formal revision before publication in Pacific Reporter Third.
    Readers are requested to notify the Clerk of the Supreme Court, Supreme Court Building,
    Cheyenne, Wyoming 82002, of any typographical or other formal errors so that correction may be
    made before final publication in the permanent volume.
    FOX, Justice.
    [¶1] The Wyoming Department of Workforce Services, Workers’ Safety and
    Compensation Division (Division) determined that Phylis Stevens’ avascular necrosis
    (AVN) in her right hip was not caused by her October 2010 slip and fall at work, and
    denied her claim for medical treatment of the AVN. After a contested case hearing, the
    hearing examiner for the Office of Administrative Hearings (OAH) agreed with the
    Division that Mrs. Stevens’ right hip AVN was not caused by her fall at work. The
    district court affirmed the decision, and Mrs. Stevens appealed. We affirm.
    ISSUES
    [¶2] 1. Was there substantial evidence to support the hearing examiner’s
    determination that Mrs. Stevens’ fall did not cause the avascular necrosis in her right hip?
    2. The hearing examiner concluded that the absence of evidence of disease prior
    to the work-related injury and the presence of the disease afterwards was not sufficient to
    establish a causal link. Was that conclusion in accordance with the law?
    FACTS
    [¶3] On October 25, 2010, Phylis Stevens slipped and fell down a flight of stairs
    outside of her workplace, the Pinedale Aquatic Center (PAC). Mrs. Stevens crawled
    back into the PAC where she was assisted by several of her co-workers.
    [¶4] Shortly thereafter, her husband transported her to the Pinedale Medical Clinic. At
    the clinic, Mrs. Stevens was seen by a physician’s assistant who diagnosed fractures to
    her fourth finger and fifth metacarpal in her left hand. According to Mrs. Stevens’ intake
    form, she was ambulatory on arrival, her “chief complaint” was pain in her left hand, and
    she denied any other injuries from the fall. She was referred to Teton Orthopedics for
    surgery on her hand.
    [¶5] The following day, Dr. Peter Rork of Teton Orthopedics saw Mrs. Stevens, took
    x-rays, and performed surgery to repair her fractured hand. Her pain assessment chart
    indicated pain in her left hand and arm only. She was discharged with pain medication,
    and over the next several months, Mrs. Stevens returned to Dr. Rork to monitor the
    recovery of her hand.
    [¶6] Julie Huntley, PAC Director, met with Mrs. Stevens two days after the fall to fill
    out a Wyoming Report of Injury. The report contains no indication that Mrs. Stevens
    injured her hip in the fall or was suffering from any hip pain at the time of the report.
    1
    [¶7] On October 29, 2010, Mrs. Stevens returned to work for the PAC Halloween
    festivities. At that time she felt soreness in her right hip, but she thought it would go
    away.
    [¶8] On November 2, 2010, Mrs. Stevens followed up with Dr. Rork. Dr. Rork’s notes
    from that visit indicate that her hand was healing well, and he would follow up with her
    in three weeks. There is no mention of any other medical problems in Dr. Rork’s notes.
    [¶9] On November 10, 2010, the Division issued its Final Determination of
    Compensability, in which it found Mrs. Stevens’ hand injury compensable.
    [¶10] On November 29, 2010, Mrs. Stevens again followed up with Dr. Rork at Teton
    Orthopedics, who determined her hand was healing well. At the conclusion of the visit
    with Dr. Rork, Mrs. Stevens mentioned for the first time the soreness in her right hip. Dr.
    Rork thought she had developed bursitis in her right hip and prescribed an anti-
    inflammatory for relief.
    [¶11] Mrs. Stevens’ next visit with Dr. Rork was on December 23, 2010. At that time,
    Dr. Rork noted her hand wounds were clear, she was nontender, with increasing range of
    motion, and he would follow up in one month. There is no mention of Mrs. Stevens’ hip
    in Dr. Rork’s record of the visit.
    [¶12] On January 13, 2011, approximately two and one-half months after her fall, Mrs.
    Stevens visited the Pinedale Medical Clinic, complaining of pain in her right hip. During
    the visit, x-rays were taken of both her hips, and no abnormal findings were detected.
    She was diagnosed with a possible tendon tear or bursitis in the right hip and scheduled
    for an MRI.
    [¶13] On January 17, 2011, Mrs. Stevens obtained an MRI of her hips. The radiologist’s
    interpretation of the MRI was as follows:
    1. Bilateral degenerative changes of the hips, right greater
    than left.
    2. Heterogeneous signal noted within femoral head and
    femoral neck. This most likely represents reactive stress
    edema; however, this could be a very atypical appearance
    of avascular necrosis.
    3. Edema within the obturator femoris muscle with probable
    tear of the superior fibers at the pubic ramus origin.
    4. Joint effusion.
    That day, interpreting the results of the MRI, Dr. Rork diagnosed Mrs. Stevens with AVN
    in the femoral head of her right hip. (AVN is the death of a bone due to lack of blood
    2
    supply.) Dr. Rork noted, “This is probably a posttraumatic event related to the slip and
    fall accident of 10/26/10 [sic]. I am going to put her on crutches. We will see her back
    for follow up in 6 weeks[.]”
    [¶14] At her February 28, 2011, follow-up, Dr. Rork’s notes indicate, “[Mrs. Stevens]
    was complaining of hip pain that occurred at the time of the initial injury, this was
    probably overshadowed by the pain in her left hand. What has occurred is that she has
    gone on to an AVN which may or may not require surgical intervention.”
    [¶15] On April 25, 2011, another MRI was taken of Mrs. Stevens’ hips.                               The
    radiologist’s report from this MRI provided the following interpretation:
    1. The extent of marrow signal alteration on the right side is
    similar to the prior study although a more characteristic
    zone of signal alteration contained within a broader area
    of marrow edema in the right femoral head is more
    apparent.     These findings suggest the presence of
    avascular necrosis of the right femoral head. There is
    evidence for arthritic change about the right hip joint and
    a hip effusion.
    2. On the left hip, there is evidence for degenerative arthritic
    changes and evidence for a left hip effusion. Signal
    alternations in the femoral head have progressed . . . since
    the prior study. . . . Some component of avascular
    necrosis is possible although . . . signal changes of the
    avascular necrosis are more apparent on the right side than
    the left. Again, however, signal alterations diffusely in
    the left femoral head have progressed since the prior
    exam.
    [¶16] Dr. Rork’s April 25 notes indicate, “[Mrs. Stevens] states that her hip is feeling
    better.” However, regarding the MRI, Dr. Rork noted, “shows fracture of the femoral
    head [on right hip] with some mild degenerative changes in the left hip.” Dr. Rork
    decided to take her off the crutches and start her on water therapy. Eventually, the
    femoral head on her right hip collapsed due to the AVN progression, and on December
    14, 2011, Mrs. Stevens received a total right hip replacement.
    [¶17] On February 18 and March 1, 2011, the Division issued its Final Determinations,
    denying all payments for Mrs. Stevens’ hip-related treatment based on the conclusion that
    “the right hip is not related to the original work injury to the left hand[.]” Mrs. Stevens
    timely requested a contested case hearing, which was held December 7, 2012.1
    1
    While an important function of the Medical Commission is to evaluate conflicting expert medical
    evidence, the record does not indicate that either the OAH or Mrs. Stevens sought to transfer the case to
    3
    [¶18] At the hearing, three of Mrs. Stevens’ colleagues from the PAC testified on her
    behalf: Charlotte Keyser, Ellen Ramsey, and Julie Huntley. There were no eyewitnesses
    to Mrs. Stevens’ fall and she could not remember exactly how she fell down the concrete
    stairs, other than she slipped, twisted or turned in the fall, and ended up with her left hand
    tangled up on the railing and her lower body straddling the last few steps. She crawled
    up the stairs, pushed the handicap button to open the doors, and crawled into the foyer of
    the PAC. Once inside, she began screaming for help, and the evening custodian,
    Charlotte Keyser, responded.
    [¶19] Ms. Keyser found Mrs. Stevens lying in the fetal position in the PAC foyer crying
    for help. On direct examination at the contested case hearing, Ms. Keyser was asked to
    testify as to what Mrs. Stevens reported to her about the fall, to which she responded “Oh
    gosh, I don’t remember.” Later in her testimony, Ms. Keyser reported that Mrs. Stevens
    was clutching her wrist and also indicated that she hurt her right hip in the fall. Ms.
    Keyser further testified, “I was more concerned about her wrist, because that’s what
    looked -- visually, that’s where the problem was.” After assisting Mrs. Stevens into a
    seated position inside the main area of the PAC, fellow PAC employees Sue Phlughoft2
    and Ellen Ramsey took over her care.
    [¶20] Ellen Ramsey testified that she first saw Mrs. Stevens at a table in the PAC lobby
    shortly after she fell and she approached to see if she could help. Ms. Ramsey testified
    that she remembered Mrs. Stevens sitting on a table by the lobby doors, and “she was
    screaming in pain.” In response to Ms. Phlughoft’s question if she was hurt elsewhere,
    Ms. Ramsey remembered Mrs. Stevens telling Ms. Phlughoft that her hip was hurting and
    then making a head gesture toward her right side. On cross examination, Ms. Ramsey
    indicated that in a conversation two weeks after the fall, Mrs. Stevens talked about her
    wrist injury, did not talk about any hip pain, and was not limping. Ms. Ramsey did
    testify that approximately four weeks later Mrs. Stevens was limping and mentioned her
    hip pain to Ms. Ramsey in conversation.
    [¶21] Julie Huntley recounted her interactions with Mrs. Stevens after the fall,
    specifically, meeting her two days later to fill out the Wyoming Report of Injury: “Oh, I
    just remember she said how sore she was, generally speaking, and that her hand was --
    she definitely had a hand injury, and that she was sore everywhere. And beyond that, you
    know, I wouldn’t be able to tell you.” Ms. Huntley did testify that “somewhere in there
    within a couple of weeks” after Mrs. Stevens’ fall, she observed her limping and told her
    the Medical Commission. See Russell v. State ex rel. Wyo. Workers’ Safety & Comp. Div., 
    944 P.2d 1151
    , 1156 (Wyo. 1997); see also 
    Wyo. Stat. Ann. § 27-14-616
    (e) (LexisNexis 2013) (“Upon agreement
    of all parties to a case, the hearing examiner in a contested case . . . may transfer a medically contested
    case to a medical hearing panel or may seek the advice of the medical commission on specific medical
    issues in the contested case.”).
    2
    Ms. Phlughoft did not testify at the contested case hearing.
    4
    to go get it checked out. The Wyoming Report of Injury contained no indication that
    Mrs. Stevens hurt her hip in the fall.
    [¶22] Although the hearing examiner found each of these women credible, she stated in
    her Findings of Fact, Conclusions of Law, and Order, “suffice it to say that the Office
    finds and concludes that any statements or implications that Stevens had significant pain
    in the hip immediately after the fall are not supported.”
    [¶23] Mrs. Stevens testified about her fall and treatment to her wrist and hip. She
    indicated that her hip started to hurt immediately following the fall. However, the
    documentation of her fall and subsequent care did not indicate any hip pain until her first
    mention of hip pain to Dr. Rork on November 29, and her hip did not become the focus
    of her care until January 2011. From Mrs. Stevens’ testimony, the hearing examiner
    found and concluded:
    46. It is undisputed that Stevens denied any other
    injuries at the emergency room of the Pinedale Clinic. . . .
    The report does indicate obvious swelling, deformity and
    significant pain in Stevens’ left hand. . . . On cross
    examination, when asked about the emergency room report,
    Stevens testified that she doesn’t remember giving a history at
    the clinic but she gave an accurate history. She testified that
    she has worked in the medical field so she tries to remember
    her medical history so that she can help them and herself.
    Stevens again stated that she doesn’t remember much about
    that night.
    ....
    73. Overall Stevens’ testimony was found to be
    credible. The evidence was undisputed that she had a fall and
    a significant injury to the hand that was her primary focus. . . .
    Her description of the impact to the hip or actual injury to her
    hip and the pain following the injury is somewhat suspect
    however given her lack of complaint at the emergency room
    and her lack of memory as to many of the other events
    occurring at the time. . . . The weight of the evidence also
    showed that at a minimum Stevens probably did suffer some
    injury to her hip at that time, but the Office was not
    convinced that there was in fact any subluxation of the hip
    as later suggested in the [medical expert] deposition
    testimony. . . . While the Office was persuaded that
    Stevens[’] focus in the first few weeks was on her hand, the
    5
    Office also concludes that any injury to the hip that occurred
    during the fall was not significant enough at that time to draw
    anything other than a passing acknowledgement. Indeed
    Stevens herself later reported that she thought it was simply a
    bruise or strain and would go away. . . . Stevens[’] testimony
    of a progressively worsening pain and the history reported in
    Dr. Rork’s records, i.e., that it was tolerable and then became
    intolerable appears to be more accurate. As is set forth in
    more detail below this conclusion is used in weighing and
    evaluating the opinions of the medical experts.
    [¶24] Mrs. Stevens offered the deposition of her treating physician, Dr. Rork, at the
    hearing. Summarizing the manifestation of her hip injury, he explained:
    She didn’t even mention it the first time she came in.
    And then about a month later she started mentioning it. And
    then as the pain didn’t resolve, as a matter of fact worsened
    over time. And the natural history for something like an
    AVN is about three months after the incident, these patients
    are starting to develop significant discomfort. . . . And once I
    saw the AVN, I thought it was one of an acute nature, hadn’t
    been there a long time.
    When asked whether her slip and fall caused or aggravated some preexisting condition
    that caused AVN, Dr. Rork insisted: “I think this is a posttraumatic event. I think that her
    avascular necrosis occurred -- began with that fall.” Explaining the basis for his opinion,
    Dr. Rork, testified:
    She probably had a subluxation of her hip at the same time
    when she fell and broke her hand. She had an insidious onset
    of the avascular necrosis that resulted and went on to a
    collapse of the femoral head as a result of this. So -- and I
    draw that index event to be the slip and fall injury from
    October 2010.
    [¶25] On cross examination, it was noted that Mrs. Stevens was seen at the Pinedale
    Clinic after the fall and denied any pain in the pelvic area. Dr. Rork agreed that this
    would be inconsistent with a person who had twisted the hip or had a trauma to their hip
    sufficient to cause AVN.
    [¶26] Also under cross examination, Dr. Rork was asked about the presence of bilateral
    AVN and how that affected his opinion.
    6
    Yeah. You know, it does throw a wrench into the
    works and raises a question, but [Dr. Newton is] looking at
    the radiologist’s report. And, of course, you know, our joke
    in medicine is that the national flower for the radiologist is
    the hedge, that they always, you know, hedge their bets with
    their -- with their reading and they tend to be cautious in that
    respect. From my recollection of looking at the MRI, I don’t
    think the left hip had anything going on at all, and -- but all
    the -- all the issues were in the right.
    [¶27] The Division presented the medical report and deposition of Dr. Bruce Newton.
    At the Division’s request, Dr. Newton performed an independent medical evaluation of
    Mrs. Stevens on September 27, 2011. Dr. Newton’s report was comprehensive in scope
    and detail, including a review of Mrs. Stevens’ medical history, a review of all records
    including x-rays and MRIs taken in the course of Mrs. Stevens’ hand and hip treatment,
    as well as a physical examination of Mrs. Stevens. In his report, Dr. Newton concluded:
    I believe it is very unlikely that her right hip pathology is the
    direct result of the industrial injury of 10-25-10. Let me give
    the following rationale.
    A. There is no documented injury to the right hip from the
    fall of 4-25-10 [sic]. Retrospectively, Phylis reported hip
    pain ever since the injury. This was neither serious nor
    concerning until sometime between 12-22-10 and 1-13-
    11, so in other words, we do not have a reliable history of
    direct right hip injury.
    B. The onset for post-traumatic AVN was too early. Post-
    traumatic AVN typically develops at earliest six months
    after trauma, more likely 18 months. The development of
    symptomatic AVN within three months of a trauma is
    highly unlikely.
    C. Post-traumatic AVN does not follow a hip contusion.
    AVN of the hip can occur following serious trauma. The
    type of trauma that develops into AVN is femoral neck
    fracture or dislocation. Phylis’s trauma to the hip, if any,
    (nothing was documented) would have been simply a hip
    contusion and certainly not the type of force that leads to
    avascular necrosis.
    7
    D. The presence of bilateral avascular necrosis on MRI, i.e.,
    stage one AVN on the left hand side essentially rules out
    the possibility of post-traumatic avascular necrosis to the
    right hip.
    [¶28] In her final decision denying Mrs. Stevens’ benefits for her hip, the hearing
    examiner concluded:
    109. Stevens argues that this case is similar to
    Murray vs. State ex rel. Wyoming Workers’ Compensation
    Division, 
    1999 WY 184
    , 
    993 P.2d 327
     (Wyo. 1999) in that
    the lack of prior symptoms and then the presence of
    symptoms after a work related incident establishes the causal
    connection. The Office finds and concludes that Murray is
    distinguishable in that the injury in the Murray case occurred
    within 15 or 20 minutes of the work related incident. The
    onset of Stevens[’] hip injury, and specifically her AVN is not
    so clear cut. Moreover, the Office finds and concludes that
    this case is more akin to Langberg [] vs. State ex rel.
    Wyoming Workers’ Compensation Division, 
    2009 WY 39
    ,
    
    203 P.3d 1098
     (Wyo. 2009) which involved a work related
    injury and a diagnosis of Kienbock’s disease which also
    involves necrosis of the bone. In that case the mere absence
    of evidence of disease prior to the work related injury and
    presence of the disease afterwards was not sufficient to
    establish the causal connection.
    110. Having reviewed the evidence and testimony in
    this case, the Office finds and concludes that while Stevens
    did suffer some injury to her hip as a result of the slip and
    fall, the Office was not persuaded that the injury suffered in
    the fall was anything more that [sic] a muscular injury or
    contusion. More particularly the Office was not persuaded
    that Stevens suffered a subluxation or any other injury that
    caused her to then develop AVN. . . . [H]er description of the
    actual injury to her hip and the pain immediately following
    the injury is somewhat suspect given her lack of complaint at
    that time and lack of memory as to many of the other events
    occurring at that time and in any event was not sufficient to
    establish the trauma necessary to cause AVN.
    ....
    8
    112. [I]n weighing the opinions of the experts, this
    Hearing Officer found that the opinions expressed by Dr.
    Newton were entitled to more weight. Dr. Newton and Dr.
    Rork have similar credentials. . . . Their credentials were not
    however the deciding factor. . . . Rather, Dr. Newton’s
    opinions were stronger and reasons given for it appeared
    more logical.
    113. The testimony of Dr. Rork appeared weaker and
    somewhat speculative. He appeared to make assumptions
    that there was a subluxation or a twisting type injury when
    asked whether the injuries were related to the fall. He did not
    address the direction of force needed for subluxation or the
    signs and symptoms of subluxation.
    114. Dr. Newton on the other hand rendered a
    definitive opinion that addressed the direction of the force,
    the lack of signs or symptoms of subluxation, ie. [sic]
    immediate and extreme pain and inability to bear weight. Dr.
    Newton’s opinion was based more on the evidence as
    opposed to Dr. Rork’s opinion which was based upon
    assumptions.
    115. As to the timing of onset of symptoms or
    diagnosis of AVN, even if the Office accepted Dr. Rork’s
    opinion that the onset can occur in a shorter time frame, . . .
    the absence of symptoms at the time of injury would not
    necessarily indicate the absence of the disease process.
    116. Finally with respect to the difference of
    opinions as to the presence of bilateral AVN, . . . Dr.
    Newton’s opinion was deemed stronger and more persuasive.
    Dr. Rork just seemed to dismiss the finding out of hand, but
    did acknowledge that it “would throw a wrench in” his
    opinion if there was bilateral AVN.
    117. Overall, the Office found that Dr. Newton’s
    opinion was more thorough and had a stronger basis and that
    Dr. Rork’s opinion was based upon assumptions. Therefore
    this Hearing Officer finds that Stevens has not proven by a
    preponderance of the evidence that she suffered an injury to
    her hip that led to the development of AVN while in the
    course and scope of her employment.
    9
    [¶29] Mrs. Stevens timely petitioned the Ninth Judicial District Court for review of the
    OAH decision to deny benefits. On November 26, 2013, the district court issued its
    decision affirming the OAH decision. This appeal followed.
    DISCUSSION
    I.   Was there substantial evidence to support the hearing examiner’s determination
    that Mrs. Stevens’ fall did not cause the avascular necrosis in her right hip?
    [¶30] On appeal from a district court’s review of an administrative decision, we review
    the case as if it came directly from the administrative agency. Hirsch v. State ex rel.
    Wyo. Workers’ Safety & Comp. Div., 
    2014 WY 61
    , ¶ 33, 
    323 P.3d 1107
    , 1115 (Wyo.
    2014) (citing Birch v. State ex rel. Wyo. Workers’ Safety & Comp. Div., 
    2014 WY 31
    ,
    ¶ 12, 
    319 P.3d 901
    , 906 (Wyo. 2014)). Our review is governed by 
    Wyo. Stat. Ann. § 16
    -
    3-114(c) (LexisNexis 2013); we examine agency findings of fact by applying the
    substantial evidence standard. Birch, 
    2014 WY 31
    , ¶ 12, 319 P.3d at 906.
    [¶31] Substantial evidence “means relevant evidence that a reasonable mind might
    accept as adequate to support a conclusion.” Green v. State ex rel. Dep’t of Workforce
    Servs., Workers’ Safety & Comp. Div., 
    2013 WY 81
    , ¶ 13, 
    304 P.3d 941
    , 946 (Wyo.
    2013) (citing Jacobs v. State ex rel. Wyo. Workers’ Safety & Comp. Div., 
    2013 WY 62
    ,
    ¶ 8, 
    301 P.3d 137
    , 141 (Wyo. 2013)). “‘Findings of fact are supported by substantial
    evidence if, from the evidence preserved in the record, we can discern a rational premise
    for those findings.’” 
    Id.
     (quoting Kenyon v. State ex rel. Wyo. Workers’ Safety & Comp.
    Div., 
    2011 WY 14
    , ¶ 11, 
    247 P.3d 845
    , 849 (Wyo. 2011)). Whether we might reach the
    same result or not, we will not reweigh the evidence, but instead defer to the OAH’s
    decision if it is based upon relevant evidence that a reasonable mind might accept. See
    Torres v. State ex rel. Wyo. Workers’ Safety & Comp. Div., 
    2011 WY 93
    , ¶ 24, 
    253 P.3d 175
    , 181 (Wyo. 2011).
    [¶32] If an agency’s decision determines that the claimant failed to meet her burden of
    proof, under our substantial evidence standard, “‘this Court must decide whether [the]
    determination was contrary to the overwhelming weight of the evidence.’” Hirsch, 
    2014 WY 61
    , ¶ 34, 323 P.3d at 1115 (quoting Leavitt v. State ex rel. Wyo. Workers’ Safety &
    Comp. Div., 
    2013 WY 95
    , ¶ 18, 
    307 P.3d 835
    , 840 (Wyo. 2013)). On review, the
    appellant has the burden of demonstrating that the findings of fact were not supported by
    substantial evidence. Watkins v. State ex rel. Wyo. Med. Comm’n, 
    2011 WY 49
    , ¶ 16,
    
    250 P.3d 1082
    , 1086 (Wyo. 2011) (citing Anaya v. Holly Sugar Corp., 
    928 P.2d 473
    , 475
    (Wyo. 1996)).
    [¶33] Mrs. Stevens argues that the hearing examiner’s determination that her fall did not
    cause her AVN is contrary to the overwhelming weight of the evidence. She challenges
    10
    the hearing examiner’s conclusion that the opinion of the Division’s physician, Dr.
    Newton, was stronger and more persuasive than the opinion of her expert and treating
    physician, Dr. Rork. She argues that Dr. Newton’s opinion that subluxation of her right
    hip did not occur is based on a misunderstanding of her fall; his opinion regarding the
    force and direction necessary for a subluxation of the hip was contradictory; and his
    opinion that Mrs. Stevens suffered bilateral AVN was not supported by substantial
    evidence.
    [¶34] The Division asserts that Mrs. Stevens’ and her co-workers’ retrospective
    testimony indicating she immediately had pain in her hip following the fall is inconsistent
    with the medical documentation describing her injuries following the fall. In light of this
    inconsistency, the Division contends it was appropriate to weigh the conflicting opinions
    of the medical experts in this case in order to determine causation. On this front, the
    Division argues that Mrs. Stevens’ medical expert presented speculative testimony which
    relied on assumption more than on the actual evidence. The Division supports the
    finding of the hearing examiner that Dr. Newton
    rendered a definitive opinion that addressed the direction of
    the force, the lack of signs or symptoms of subluxation, ie.
    [sic] immediate and extreme pain and the inability to bear
    weight. Dr. Newton’s opinion was based more on the
    evidence as opposed to Dr. Rork’s opinion which was based
    upon assumptions.
    [¶35] A compensable injury is one “arising out of and in the course of employment[.]”
    
    Wyo. Stat. Ann. § 27-14-102
    (a)(xi) (LexisNexis 2013). In order to show that the
    compensable injury arises out of or in the course of employment, the workers’
    compensation claimant has the burden of proving each of the essential elements of the
    claim by a preponderance of the evidence, including a causal connection between the
    work-related incident and the injury. Delacastro v. State ex rel. Wyo. Workers’ Safety &
    Comp. Div., 
    2014 WY 40
    , ¶ 22, 
    321 P.3d 327
    , 333 (Wyo. 2014).
    [¶36] The OAH hearing examiner was tasked with determining whether Mrs. Stevens’
    AVN, which ultimately resulted in replacement of her right hip, was caused by her
    October 2010 fall outside of the PAC. 3 To resolve the issue of causation, the hearing
    3
    “Although pre-existing conditions are excluded from the definition of compensable injury by 
    Wyo. Stat. Ann. § 27-14-102
    (a)(xi)(F) (LexisNexis 2013), an employee may recover if his employment has
    ‘aggravated, accelerated, or combined with the disease or infirmity’ to produce the condition for which
    compensation is sought.” Hayes v. State ex rel. Wyo. Workers’ Safety & Comp. Div., 
    2013 WY 96
    , ¶ 14,
    
    307 P.3d 843
    , 847 (Wyo. 2013) (citing Dutcher v. State ex rel. Wyo. Workers’ Safety & Comp. Div., 
    2010 WY 10
    , ¶ 14, 
    223 P.3d 559
    , 562 (Wyo. 2010)). Mrs. Stevens did not advance this preexisting causation
    theory, and the hearing examiner made note of this in her conclusions, “Neither medical expert provided
    an opinion that her AVN was preexisting . . . . Dr. Newton was not asked whether or not the work injury
    11
    examiner looked to the expert medical testimony presented by Mrs. Stevens and the
    Division. When presented with conflicting expert medical testimony, the hearing
    examiner determines the credibility and weight of the experts’ opinions.
    The finder of fact is not necessarily bound by the expert
    medical testimony . . . . It is the hearing examiner’s
    responsibility, as the trier of fact, to determine the relevancy,
    assign probative value and ascribe the relevant weight given
    to medical testimony. The hearing examiner is also in the
    best position to judge the weight to be given to the medical
    evidence. The trier of fact may disregard an expert opinion if
    he finds the opinion unreasonable or not adequately supported
    by the facts upon which the opinion is based.
    Little v. State ex rel. Dep’t of Workforce Servs., 
    2013 WY 100
    , ¶ 37, 
    308 P.3d 832
    , 843
    (Wyo. 2013) (citations omitted).
    [¶37] Mrs. Stevens’ claim that the hearing examiner’s decision was not supported by
    substantial evidence is based on the assertion that the hearing examiner did not properly
    weigh the expert testimony presented at the contested case hearing. She argues that Dr.
    Newton’s determination that her hip did not sublux4 was improperly based on his
    misunderstanding of Mrs. Stevens’ fall.
    [¶38] We agree that Dr. Newton’s testimony on the mechanism of the fall was
    equivocal. However, regardless of disagreement over whether a posterior- or anterior-
    forced subluxation is sufficient to cause AVN, Dr. Newton’s testimony did indicate that
    trauma-induced AVN is usually caused by a significant injury such as a femoral neck
    fracture or dislocation of the hip joint. He concluded that in the absence of any
    immediately documented reports of such a significant injury, or imaging data indicating a
    femoral neck fracture or dislocation to Mrs. Stevens’ right hip from the fall, she did not
    sustain the force sufficient for trauma-induced AVN.
    [¶39] Mrs. Stevens argues that Dr. Newton’s misunderstanding of the fall and his
    opinion drawn therefrom contradicts the overwhelming weight of evidence presented at
    the hearing. She argues that her testimony at the hearing “clearly showed” that she had
    not simply fallen on her buttocks, but fell down a flight of concrete steps, “going forward
    caused a ‘material or substantial aggravation’ of Stevens’ AVN. Nor did Dr. Rork testify to any
    aggravation as in his opinion the fall was the cause of the AVN.” Accordingly, we will not address
    whether Mrs. Stevens’ AVN was a pre-existing condition aggravated by her work injury.
    4
    Mrs. Stevens also argues that Dr. Newton did not understand the term “subluxation” due to his recanting
    a previous position statement that “the hip does not sublux.” This appeared to be more a question of
    semantics than a misunderstanding of what a subluxation is. Both parties seemed to agree that
    subluxation is a temporary, partial dislocation of the hip joint.
    12
    and down the stairs, twisting and turning as she fell, eventually landing on her right hip
    with her right knee jammed into the bottom steps.” She argues that her physician, Dr.
    Rork, had a clear understanding of how she fell, and that his understanding fits his theory
    that she subluxed her hip.
    [¶40] Having reviewed the record, we cannot find any evidence that Mrs. Stevens fell
    forward in her fall down the steps. At the hearing, Mrs. Stevens testified:
    I lifted my left foot, and as I lifted my left foot, my
    body just went. And the next thing I knew, twisting or
    turning, I landed down here with my hand -- it seemed like
    my hand was up here on this bar, and my legs were down
    here [referencing photo exhibit of stairs].
    [¶41] Mrs. Stevens’ own treating physician appeared not entirely clear on the
    mechanism of Mrs. Stevens’ fall: “You know, I don’t recall the mechanism of action.”
    Instead, Dr. Rork used the case of pro athlete Bo Jackson to analogize Mrs. Stevens’ hip
    injury. Dr. Rork stated, “they theorize” that he “probably had a transient subluxation of
    the hip” that caused him to develop AVN. Dr. Rork indicated that the deep bruise on
    Mrs. Stevens’ right hip and the initial findings on the MRI were “consistent with a mild
    subluxation such as Bo Jackson.” Regarding Dr. Rork’s use of Bo Jackson’s injury, the
    hearing examiner found, “this . . . seemed to then become the focus of the case. Indeed it
    appeared to be the only mechanism of injury that would provide the causal connection to
    the work related injury.” The hearing examiner concluded:
    113. The testimony of Dr. Rork appeared weaker and
    somewhat speculative. He appeared to make assumptions
    that there was a subluxation or a twisting type of injury when
    asked whether the injuries were related to the fall.
    “If, in the course of its decision making process, the agency disregards certain evidence
    and explains its reasons for doing so based upon determinations of credibility or other
    factors contained in the record, its decision will be sustainable under the substantial
    evidence test.” Dale v. S & S Builders, LLC, 
    2008 WY 84
    , ¶ 22, 
    188 P.3d 554
    , 561
    (Wyo. 2008).
    [¶42] Mrs. Stevens’ lack of clarity and Dr. Rork’s conjecture hardly paint a clear picture
    of the type of fall suffered by Mrs. Stevens. While Dr. Newton’s understanding of Mrs.
    Stevens’ fall may not be complete, his explanation of the significant amount of force
    necessary to cause AVN is compelling regardless of how Mrs. Stevens fell. Dr. Newton
    reiterated several times in his deposition testimony that trauma-induced AVN would
    require a significant force, which in turn would likely register as a serious, immediately
    reportable, injury to the patient. The hearing examiner’s determination that the facts did
    13
    not support a finding of the severe hip injury required to cause trauma-induced AVN is
    supported by substantial evidence.
    [¶43] Dr. Newton provided two additional reasons5 why the fall did not cause Mrs.
    Stevens’ AVN. He opined that the time of onset of Mrs. Stevens’ AVN was not
    consistent with trauma-induced AVN. Mrs. Stevens’ medical records indicate that her
    hip pain did not reach a reportable level until one month after her fall, and she was
    diagnosed with AVN three months after the fall, which Dr. Newton testified, “is
    exceptionally fast for the development of AVN following trauma.” Dr. Newton relied on
    a peer-reviewed article which examined the onset of symptoms and diagnoses of 146
    patients who actually fractured or dislocated their hip, “a population where you’re
    actually looking for [trauma-induced AVN].” Dr. Newton reported that even in this
    population, the range of onset of symptoms of AVN ranged from 3 to 47 months, and the
    average time of diagnosis was 18.8 months. Mrs. Stevens’ onset of symptoms, as well as
    her AVN diagnosis within three months of the fall, are statistically inconsistent with the
    data presented by Dr. Newton.
    [¶44] Finally, Dr. Newton considered the fact that Mrs. Stevens’ April MRI revealed
    bilateral AVN, “which would not occur with an injury to -- to a right hip. You wouldn’t
    have AVN on the left side as a result of that.” In other words, trauma-induced AVN to
    the right hip would not explain AVN in the left hip.
    [¶45] On this final point, Mrs. Stevens argues that “for over two years after the original
    fall, Mrs. Stevens did not have any problems with her left hip up to the date of hearing
    date [sic] on December 7, 2012; ruling out AVN was a systemic condition.” While the
    hearing examiner did not address this in her final determination, Dr. Newton testified:
    A: AVN can stay quiescent for a long time. If it were
    degenerative change, we’d expect the same thing. We’d
    expect her to have increasing symptoms. So in either case,
    either arthritis or AVN, it would be unusual for her not to
    develop eventual symptoms in that left side.
    Q: All right. But if onset is 18 months, looking at it, I
    mean, it’s kind of unusual not to have two years symptom
    free if it’s a systemic event?
    5
    Dr. Newton enumerated four bases supporting his conclusion that Mrs. Stevens’ AVN was not trauma
    induced: 1) no immediate, documented pain; 2) the AVN developed too quickly for traumatic AVN; 3)
    she did not suffer from a fracture or dislocation typical of AVN; and 4) a traumatic injury to one hip
    causing bilateral systemic AVN is improbable. Through the course of his testimony, he tended to lump
    bases one and three together, explaining that trauma-induced AVN usually results from a fracture or
    dislocation, which in turn would be immediately reportable.
    14
    A: Oh, no. It’s very, very common. But
    that’s because this would not be considered traumatic AVN.
    So in -- in patients that have idiopathic AVN, it can stay
    quiescent for a long time.
    Dr. Newton’s explanation of Mrs. Stevens’ bilateral AVN is well-reasoned and fits within
    the earlier explanations he gave regarding the onset of trauma-induced AVN. On the
    other hand, Dr. Rork simply dismissed the fact that Mrs. Stevens’ April MRI revealed
    bilateral AVN, but did acknowledge that it “would throw a wrench in” his opinion if
    there was bilateral AVN.
    [¶46] Mrs. Stevens has failed to establish that the hearing examiner’s deference to Dr.
    Newton’s expert opinion was contrary to the overwhelming weight of evidence. While
    Mrs. Stevens’ expert medical testimony was speculative in nature, Dr. Newton provided
    articulate explanations for his opinion based on a comprehensive review of Mrs. Stevens’
    complete medical history as well as a physical exam of Mrs. Stevens. The hearing
    examiner considered both expert opinions, explained the weaknesses in Dr. Rork’s
    speculative testimony, and ultimately found the weight of Dr. Newton’s opinion most
    persuasive. We conclude that the hearing examiner, as trier of fact, could reasonably
    conclude as she did, based on all the evidence before her. Accordingly, there was
    substantial evidence to support the hearing examiner’s final determinations.
    II. The hearing examiner concluded that the absence of evidence of disease prior to
    the work-related injury and the presence of the disease afterwards was not
    sufficient to establish a causal link. Was that conclusion in accordance with the
    law?
    [¶47] We review an agency’s conclusions of law de novo, and will affirm only if the
    agency’s conclusions are in accordance with the law. 
    Wyo. Stat. Ann. § 16-3-114
    (c);
    Kenyon, 
    2011 WY 14
    , ¶ 13, 247 P.3d at 849. When reviewing a mixed question of law
    and fact, we separate the factual and legal aspects of the hearing examiner’s decision to
    determine whether the correct rule of law has been properly applied to the facts. City of
    Casper v. Haines, 
    886 P.2d 585
    , 587 (Wyo. 1994) (citing Aanenson v. State ex rel. Wyo.
    Workers’ Comp. Div., 
    842 P.2d 1077
    , 1079-80 (Wyo. 1992)).
    [¶48] Mrs. Stevens argues that the hearing examiner erred as a matter of law by failing
    to apply the holding of Murray v. State ex rel. Wyo. Workers’ Safety & Comp. Div., 
    993 P.2d 327
     (Wyo. 1999) to the facts of her case. She contends that, under Murray, her
    good health prior to the fall and the changes afterward are sufficient to find a causal
    connection between the fall and her right hip AVN, even when there is conflicting expert
    medical testimony regarding causation.
    15
    [¶49] In Murray, the claimant was working as a plant operator at a gas processing plant.
    993 P.2d at 328. Murray drew a routine sample of raw gas and approximately 15 to 20
    minutes later, he suffered an outbreak of a severe rash on his wrists. Id. Murray was
    eventually diagnosed with urticaria, but when his doctor attempted more allergy tests to
    determine the specific cause, Murray suffered severe, life-threatening allergic reactions.
    Id. at 329. The severity of these reactions prevented further testing, and left the
    determination of the cause of his urticaria inconclusive. Id. The Division denied his
    claim for benefits. Id.
    [¶50] At the contested case hearing, Murray’s treating physician opined that exposure to
    chemicals in his gloves at work likely caused his rash. Id. at 331. The Division’s doctor
    “did not disagree, but stated that he could not offer the same opinion to a reasonable
    degree of medical certainty due to the limitations of the present science in identifying a
    specific cause.” Id. at 332.6 Both doctors agreed that “something happened,” but that the
    tests for causation were inconclusive. Id. Lacking proof of causation, the hearing officer
    denied benefits to Murray.
    [¶51] On appeal, we held that “proof of prior good health and change immediately
    following and continuing after an injury may establish that an impaired condition was
    due to the injury.” Id. (citing Waldorf Corp. v. Industrial Comm’n, 
    708 N.E.2d 476
    , 480
    (Ill. App. Ct. 1999)). We further stated:
    [E]vidence of the timing of symptoms has been specifically
    recognized as a competent way of studying causation; the
    manner in which the disease developed, with reference to the
    claimant’s medical and work history is entirely appropriate
    for the court to consider. Indeed, we have recognized that
    when a single incident injury is so [immediate] and directly or
    naturally and probably the result of an accident, . . . medical
    evidence is not essential to find a causal connection.
    
    Id.
     (internal citations and quotation marks omitted).
    6
    We have clarified that the standard to establish causation in workers’ compensation cases is a reasonable
    degree of medical probability:
    [T]he causal connection between an accident or condition at the
    workplace is satisfied if the medical expert testifies that it is more
    probable than not that the work contributed in a material fashion to the
    precipitation, aggravation or acceleration of the injury. We do not invoke
    a standard of reasonable medical certainty with respect to such causal
    connection.
    Trump v. State ex rel. Wyo. Workers’ Safety & Comp. Div., 
    2013 WY 140
    , ¶ 22, 
    312 P.3d 802
    , 809 (Wyo.
    2013) (quoting Anastos v. Gen. Chem. Soda Ash, 
    2005 WY 122
    , ¶ 20, 
    120 P.3d 658
    , 666 (Wyo. 2005)).
    16
    [¶52] Murray presented uncontradicted evidence that his injury occurred while he was at
    work, and that it was triggered when he collected the sample of raw gas. Murray’s
    treating physician and the Division’s expert agreed that “something happened” at work,
    the onset of his symptoms was immediate, the causation tests were inconclusive, and
    further testing would be dangerous to Murray. While Murray’s treating physician
    testified that the urticaria was caused by something in Murray’s gloves, the Division’s
    expert did not disagree but refused to offer a similar opinion to a reasonable degree of
    medical certainty due to the limitations of science in identifying specific causes to
    urticaria. Id. at 333. Considering the uncontradicted evidence, the immediacy of the
    onset of symptoms, and the limitations of science, we reversed in favor of Murray.
    [¶53] We recognized in Murray that, in certain circumstances, the temporal connection
    between a work-related incident and an adverse change in health can be “a competent
    way of studying causation.” Id. at 332. We did not hold that such a temporal relationship
    will necessarily be sufficient to establish causation. In fact, in Murray we cautioned,
    “where a medical question is complex, and the fact finding must be done in a realm that
    appropriately relies upon technical medical knowledge and expertise, medical testimony
    should not be ignored.” Id. (quoting Forni v. Pathfinder Mines, 
    834 P.2d 688
    , 693 (Wyo.
    1992)).
    [¶54] Here, the circumstances are more complex than in Murray. The two experts
    disagreed regarding the cause of Mrs. Stevens’ AVN. Mrs. Stevens made no documented
    report of her hip problems for over a month after her fall, and did not seek treatment for
    more than two months after the fall. While her co-workers testified that Mrs. Stevens
    immediately indicated pain in her hip following the injury, this testimony conflicted with
    the absence of documentation of any hip pain. Thus, the hearing examiner gave little
    weight to their testimony regarding the immediate onset of hip pain following Mrs.
    Stevens’ fall. “‘Credibility determinations are the unique province of the hearing
    examiner, and we eschew re-weighing those conclusions.’” Willey v. State ex rel. Wyo.
    Workers’ Safety & Comp. Div., 
    2012 WY 144
    , ¶ 20, 
    288 P.3d 418
    , 427 (Wyo. 2012)
    (quoting Beall v. Sky Blue Enters., Inc., 
    2012 WY 38
    , ¶ 28, 
    271 P.3d 1022
    , 1034 (Wyo.
    2012)). Considering the conflicting expert opinions regarding causation and the
    equivocal evidence of immediate onset of pain, we find Mrs. Stevens’ case is materially
    different than Murray.
    [¶55] The hearing examiner was not persuaded that Murray should apply to Mrs.
    Stevens’ case, concluding “that Murray is distinguishable in that the injury in the Murray
    case occurred within 15 or 20 minutes of the work related incident. The onset of
    Stevens[’] hip injury, and specifically her AVN is not so clear cut.” We agree with the
    hearing examiner that Mrs. Stevens’ fall and the onset of her AVN are “not so clear cut.”
    17
    [¶56] Because of the complexity of the onset of Mrs. Stevens’ AVN, we find Langberg
    v. State ex rel. Wyoming Workers’ Safety & Compensation Division, 
    2009 WY 39
    , 
    203 P.3d 1098
     (Wyo. 2009) is more applicable. In that case, the claimant injured his left
    wrist while at work. Id. at ¶ 3, 203 P.3d at 1100. Four months later, he re-injured the
    same wrist. Id. at ¶ 4, 203 P.3d at 1100. He was diagnosed with Kienbock’s disease, and
    eventually underwent surgery because he was developing avascular necrosis due to the
    Kienbock’s disease. Id. at ¶ 7, 203 P.3d at 1100. Langberg’s claim was denied by the
    Division based on lack of proof of causation. He contested this determination, asserting
    that his Kienbock’s disease was caused by a “single traumatic injury,” Id. at ¶ 11, 203
    P.3d at 1101, and that proof of lack of medical problems before a work injury and change
    immediately following the injury was sufficient to prove causation. Id. at ¶ 12, 203 P.3d
    at 1101. However, Langberg’s treating physician’s deposition testimony “explained the
    cause of Kienbock’s disease is unknown,” and that he “found no significance in the fact
    that Langberg had no wrist problems prior to his work injuries.” Id. at ¶¶ 13-14, 203 P.3d
    at 1101-02.
    [¶57] On appeal we concluded that “[t]he flaw in Langberg’s reasoning is that [his own
    treating physician], an expert in the field and intimately familiar with Langberg’s medical
    condition, effectively testified that Langberg’s theory is pure speculation.” Id. at ¶ 16,
    203 P.3d at 1102.
    [¶58] Langberg establishes that a claimant’s lack of symptoms, followed by a work
    incident, followed sometime later by symptoms, does not always meet a claimant’s
    causation burden. See Hayes v. State ex rel. Wyo. Workers’ Safety & Comp. Div., 
    2013 WY 96
    , ¶ 21, 
    307 P.3d 843
    , 850 (Wyo. 2013) (citing Jacobs, 
    2013 WY 62
    , ¶¶ 19-25, 
    301 P.3d at 145-48
    ) (“[T]he temporal relationship between [claimant’s] pain and the
    workplace injury, i.e., his pain started when antibiotics were used to treat the infection
    from his work injury, was insufficient to establish a causal link.”).
    [¶59] Langberg also stands for the proposition that a hearing examiner may rely on
    expert medical testimony regarding causation to negate a claimant’s speculative theory of
    causation. Id. at ¶ 21, 307 P.3d at 850. In Mrs. Stevens’ case, the hearing examiner
    relied on Dr. Newton’s expert medical testimony rather than the speculative post-
    traumatic theory provided by Mrs. Stevens and her own expert, Dr. Rork. The hearing
    examiner relied on Dr. Newton’s four bases for concluding Mrs. Stevens’ AVN was not
    caused by her fall at work: 1) no immediate, documented pain; 2) the AVN developed too
    quickly for traumatic AVN; 3) she did not suffer from a fracture or dislocation typical of
    AVN; and 4) a traumatic injury to one hip causing bilateral systemic AVN is improbable.
    Dr. Rork only speculated that Stevens had suffered some sort of subluxation resulting in
    AVN while Dr. Newton provided comprehensive evidence to a reasonable degree of
    medical probability that Mrs. Stevens’ fall did not cause her AVN. “[S]peculative
    medical testimony is insufficient to satisfy a claimant’s burden of proof.” Anastos v.
    Gen. Chem. Soda Ash, 
    2005 WY 122
    , ¶ 21, 
    120 P.3d 658
    , 666 (Wyo. 2005) (citing
    18
    Frazier v. State ex rel. Wyo. Workers’ Safety & Comp. Div., 
    997 P.2d 487
    , 490 (Wyo.
    2000)); see also Corman v. State ex rel. Wyo. Workers’ Comp. Div., 
    909 P.2d 966
    , 972
    (Wyo. 1996) (“A claimant cannot prevail if factors necessary to prove his claim are left to
    conjecture.”).
    [¶60] Our conclusion in Langberg that the mere absence of evidence of disease prior to
    the work-related injury and the presence of the disease afterwards was not sufficient to
    establish the causal link, is equally applicable to Mrs. Stevens’ case, and we find no error
    in the hearing officer’s conclusions of law. See Langberg, 
    2009 WY 39
    , ¶ 12, 
    203 P.3d at 1101
    .
    CONCLUSION
    [¶61] The OAH’s findings of fact and conclusions of law are supported by substantial
    evidence and are in accordance with the law. Therefore, we affirm the district court’s
    order which affirmed the OAH’s findings and conclusions.
    19