No. 42	                        October 3, 2013	197

               IN THE SUPREME COURT OF THE
                     STATE OF OREGON

                      Peggy N. TREES,
                    Petitioner on Review,
                              v.
                 Julio A. ORDONEZ, M.D.,
       and Greater Portland Neurosurgical Center, P.C.,
                   Respondents on Review,
                             and
                  Werner R. MEIER, M.D.;
                   W. R. Meier, M.D., P.C.;
                   David Jay Silver, M.D.;
               and David J. Silver, M.D., P.C.,
                         Defendants.
         (CC 060505489; CA A139893; SC S060752)


    On review from the Court of Appeals.*

    Argued and submitted May 2, 2013.

   Rick Pope, Kirklin Thompson & Pope LLP, Portland,
argued the cause and filed the briefs for petitioner on review.
With him on the briefs was George Kirklin.

   Larry Brisbee, Brisbee & Stockton LLC, Hillsboro, argued
the cause for respondents on review. Michael T. Stone filed
the brief for respondents on review.

  Travis Eiva filed a brief for amicus curiae Oregon Trial
Lawyers Association.

   Before Balmer, Chief Justice, and Kistler, Walters,
Linder, Landau, and Baldwin, Justices.**
______________
	**  Appeal from Multnomah County Circuit Court, Frank L. Bearden, Judge.
250 Or App 229, 279 P3d 337 (2012).
	   **  Brewer, J., did not participate in the consideration or decision of this case.
198	                                                        Trees v. Ordonez

    BALMER, C. J.
   The decision of the Court of Appeals is reversed. The
judgment of the circuit court is reversed, and the case is
remanded to the circuit court for further proceedings.

     Plaintiff brought a negligence action against defendants, alleging, among
other things, that defendant neurosurgeon had failed to properly place and secure
a titanium plate and its screws, resulting in damage to plaintiff’s esophagus
that led to other injuries. At trial, plaintiff presented expert testimony from
a biomechanical engineer, who was not a doctor, about the design, use, and
installation of the plate, but no medical doctor testified that defendant had
breached the standard of care. At the close of plaintiff’s evidence, the trial court
denied a directed verdict for defendants on the issue of causation, but granted a
directed verdict for defendants on the issue of negligence. The Court of Appeals
affirmed. Held: (1) Testimony from an expert who is not a medical doctor may
be sufficient to establish the standard of care, but on a motion for a directed
verdict, the trial court must make that determination in each case, based on
the particular expert’s testimony and the particular specifications of negligence
alleged by the plaintiff; (2) the trial court erred in granting defendants’ motion
for a directed verdict on the issue of negligence; (3) the trial court did not err in
denying defendants’ motion for a directed verdict on the issue of causation.
    The decision of the Court of Appeals is reversed. The judgment of the circuit
court is reversed, and the case is remanded to the circuit court for further
proceedings.
Cite as 354 Or 197 (2013)	199

	          BALMER, C. J.
	        In this medical malpractice case, we decide whether
a plaintiff is required to present expert testimony from a
medical doctor to establish the standard of care and breach
of the standard of care. Plaintiff presented expert testimony
from a biomechanical engineer familiar with use of the
medical device installed on plaintiff’s cervical spine by defen-
dant, a neurosurgeon. For the reasons set out below, we
conclude that plaintiff introduced sufficient evidence from
an expert witness who is not a medical doctor to present a
jury question on at least one aspect of her negligence claim.
	         Dr. Ordonez, a neurosurgeon, performed surgery on
plaintiff that involved installing a plate made by Synthes
(“Synthes plate”) on plaintiff’s cervical spine. Following the
surgery, plaintiff’s health deteriorated, and she ultimately
sustained permanent injuries. Plaintiff brought this neg-
ligence action against Dr. Ordonez and Greater Portland
Neurosurgical Center, P.C., alleging, among other things,
that Dr. Ordonez had failed to properly place and secure the
Synthes plate and its screws, resulting in damage to plain-
tiff’s esophagus that led to other injuries.1 At trial, plain-
tiff presented expert testimony from Dr. Tencer, a bio-
mechanical engineer who is not a medical doctor, about the
design, use, and installation of the Synthes plate; however,
no medical doctor testified that defendant had breached the
standard of care. At the close of plaintiff’s evidence, the court
granted defendant’s motion for a directed verdict on the
standard of care and breach because, although Dr. Tencer’s
testimony established the “ideal” placement of the Synthes
plate, the court determined that defendant’s conduct had to
be compared to that of other neurosurgeons. The Court of
Appeals affirmed, concluding that Dr. Tencer’s testimony
had “failed to bridge the gap * * * between the biomechanical
construct of the plate and the methods with which they were
intended to be installed and whether compliance with those
same methods as a medical matter set the standard of care

	1
       For ease of reference, we refer to Dr. Ordonez and Greater Portland Neuro-
surgical Center, P.C., collectively as “defendant.” Plaintiff also named other doctors
and their professional corporations as defendants in her initial complaint, but she
later voluntarily dismissed those defendants from the case.
200	                                                        Trees v. Ordonez

for [defendant.]” Trees v. Ordonez, 250 Or App 229, 238, 279
P3d 337 (2012). We conclude that Dr. Tencer’s testimony
was sufficient for plaintiff to survive a motion for a directed
verdict, and we reverse.
                  FACTUAL BACKGROUND AND
                     PROCEEDINGS BELOW
	        We begin with the facts relating to plaintiff’s claim
that the trial court erred in granting defendant a directed
verdict on the issue of negligence.2 We state the facts in the
light most favorable to plaintiff, drawing every reasonable
inference from the evidence in her favor. See Shockey v. City
of Portland, 313 Or 414, 422-23, 837 P2d 505 (1992), cert den,
507 US 1017 (1993) (stating standard for viewing evidence
after trial court’s grant of a motion for a directed verdict for
defendants).
	       Defendant performed an anterior cervical decom-
pression and fusion on plaintiff. To perform that surgery,
defendant retracted plaintiff’s esophagus away from the
anterior surface of her cervical spine and placed bone grafts
between the cervical vertebrae. He then installed a Synthes
plate on the anterior surface of plaintiff’s cervical spine to
provide stability.
	        The Synthes plate that defendant used is a titanium
plate designed to provide stability to allow for cervical fusion.
Synthes plates generally come from the manufacturer in
a kit, which includes different-sized plates, a tool to bend
the plate to the curvature of the patient’s spine, and screws
to secure the plate to the spine. To install the plate, the
surgeon inserts a set of two screws into each of the six
holes in the plate. The surgeon first inserts a “bone screw”
through each hole in the plate and into one of the vertebrae.
The bone screws have a thread down the middle so that a
“locking screw” can be inserted into the bone screw. After
the surgeon has inserted the bone screws, he or she tightens
the locking screws into the bone screws. As the surgeon
tightens the locking screw, it forces the edges of the head of

	2
       We later discuss additional facts relating to defendant’s cross-assignments of
error regarding the trial court’s denial of defendant’s motion for a directed verdict
on causation and the trial court’s rulings admitting certain evidence.
Cite as 354 Or 197 (2013)	201

the bone screw apart so that they come into contact with the
inner edges of the hole in the plate. The contact between the
sharp edges of the bone screw and the inner edge of the hole
locks the screws in place.

	         For plaintiff’s surgery, defendant used the smallest
available plate, and he secured the plate using the six sets
of bone screws and locking screws. Following the surgery,
plaintiff experienced pain, difficulty swallowing, and the
sensation of a plate in her throat. Plaintiff had additional
symptoms, including contamination of the surgical wound
with oral bacteria and amylase, which indicated that plain-
tiff’s esophagus may have been perforated. Over the course of
the month following the initial surgery, plaintiff’s symptoms
worsened, and she underwent six additional surgeries,
including a surgery to remove the screws, plate, and bone
grafts, and replace them with a halo to stabilize her spine.3
Although plaintiff’s condition has improved since her final
surgery, she continues to experience frequent pain, and she
has limited mobility in her left arm. As a result, plaintiff
can no longer perform her work as a dental hygienist.

	        Plaintiff brought this medical malpractice action
against defendant. Her complaint, as amended, included eight
specifications of negligence, as well as a general allegation
of negligence. Among other things, plaintiff alleged that
defendant was negligent because he had “failed to properly
place and secure the Synthes plate and its upper screws to
the anterior surface of the C4 [cervical disk four] vertebral
body in the May 25 surgery, allowing the plate and/or its
attachment screws to erode and/or perforate plaintiff’s esoph-
agus or hypopharynx.” Plaintiff made a similar allegation of
negligence regarding the plate’s lower screws.

	        At trial, plaintiff presented expert testimony from
Dr. Tencer, a biomechanical engineer who works as a pro-
fessor in the Department of Orthopedic Surgery at the med-
ical school at the University of Washington. Dr. Tencer has a
Ph.D. in mechanical engineering and is not a medical doctor.
	3
      A halo is a device that goes around the head and is secured with pins that are
screwed into the skull. The halo is connected to a brace that fits over the shoulders
and back to prevent movement of the head and neck.
202	                                         Trees v. Ordonez

He testified, however, that there is overlap between the two
disciplines because biomechanical engineering involves
“engineering devices for the human body,” and “surgeon[s]
put[ ] in mechanical devices to hold bones together.”

	        In his current position as a professor, Dr. Tencer
lectures medical residents who are learning to become ortho-
pedists on various topics, including “what types of things
to watch out for” when using implants, and he guides some
of those residents through research projects. He acts as a
scientific reviewer for a variety of academic journals, includ-
ing the journal Spine, and he has lectured to the National
Association of Orthopedic Surgeons. In addition, he con-
ducts his own research and has developed an implant
system for spinal surgeries. Dr. Tencer testified that in the
course of conducting research comparing the Synthes plate
to other similar devices, he had watched and participated
in the placement of a Synthes plate on a cadaver, but had
not participated in such a surgery involving a living person.
Earlier in his career, Dr. Tencer had worked on a daily
basis with medical doctors, including neurosurgeons, in a
trauma center, but he did not testify that he had watched
or participated in installation of Synthes plates in living
patients during that time. Outside the research and patient
care context, Dr. Tencer testified that he also had experience
with Synthes devices because he had done biomechanical
testing of some of those devices as part of the FDA approval
process, and he had helped Synthes come up with ways to
improve their products.

	        Dr. Tencer testified about the design of the Synthes
plate. He testified that the screw design, with the bone
screws and locking screws, “is a very critical design that’s
now found in some form or another in all of these types
of plates to make sure the screws stay in.” He explained
that the screws are designed to sit below the surface of the
plate because a partially seated screw has “no mechanical
function.” That is, the screws are designed with sharp edges
that must press against the inner edges of the plate’s holes to
create a mechanical lock. If the screws are elevated partially
above the hole, the edges of the screws will be distorted and
will not lock properly.
Cite as 354 Or 197 (2013)	203

	        Dr. Tencer explained some of the design features that
Synthes had implemented to prevent soft tissue erosion
related to use of the plate. Those features included the plate’s
rounded edges and polished surface, the thinness of the plate,
and screws that sit below the surface of the plate. He explained
that those design features “are essentially uniform throughout
orthopedic implant design” and are “commonplace.”
	        Dr. Tencer also testified about his biomechanical
assessment of defendant’s placement of the plate on plaintiff’s
cervical spine, and he identified two related concerns. His
first concern was that, unlike a correctly installed plate, the
plate had not been bent to follow the curvature of plaintiff’s
spine. As a result, the plate was not close enough to the
cervical spine to allow the screws to be fully seated in the
plate. His second concern was that some of the screw heads
protruded above the plate.
	         Dr. Tencer focused on the second concern, testifying
that the plate that defendant had selected was the incorrect
size. The plate was too short, and, as a result, the screws
used to secure the plate were “over angled,” and five of the
six screws did not sit flush with the plate. Dr. Tencer went on
to state that “it’s very well defined as a step that the screw
head must sit underneath down below the plates so it doesn’t
present any sharp edges” because “obviously [sharp edges]
can lead to damage to the tissue.” Specifically, he noted that
a protruding screw head could come into contact with the
esophagus. Given that risk, Dr. Tencer testified that, because
there were screws protruding above the plate used on
plaintiff, “it’s pretty clear it’s a go/no-go situation. In other
words, any protrusion above the plate is essentially no-go,
because it’s clear that it can cause damage of some type, and
it’s very well described in all the literature that there should
be no protrusion.” Dr. Tencer further emphasized that screw
heads should never protrude above the plate when he stated
that he did not agree with defense counsel’s statement that
having screw heads protruding above the plate “to some
degree, is acceptable.”
	       Following Dr. Tencer’s testimony, plaintiff did not
present expert testimony from a neurosurgeon establishing
that defendant had breached the standard of care. The only
204	                                                          Trees v. Ordonez

neurosurgeon who testified during plaintiff’s case was one
of defendant’s witnesses, who was called to testify out of
order. That witness, Dr. Silver, had performed the surgery
to remove the screws, plate, and bone grafts from plaintiff’s
cervical spine. He acknowledged that at least two of the
screws used to secure plaintiff’s plate were protruding above
the plate. He also stated, however, that a small protrusion
of the screw above the plate is not an unusual finding and
that it is within the realm of acceptability for neurosurgery.
Thus, the only neurosurgeon who testified during plaintiff’s
case indicated that defendant had not breached the standard
of care.
	        At the close of plaintiff’s evidence, defendant moved
for a directed verdict, arguing that the case could not go to
the jury in the absence of expert testimony that defendant
had failed to conform to the standard of care. Defendant
contended that Dr. Tencer’s testimony did not satisfy that
requirement. Alternatively, defendant argued that plaintiff
had not proven causation and that, even if plaintiff relied on
the doctrine of res ipsa loquitur, she would have to present
expert testimony that the kind of injury she had experienced
normally would not occur in the absence of negligence.
	        The trial court denied the motion as to causation, but
granted the motion as to negligence because the court agreed
that Dr. Tencer’s testimony did not establish that defendant’s
conduct failed to meet the standard of care. The court con-
cluded that, although Dr. Tencer’s testimony established the
“ideal” placement of the plate and screws, it was “unfair and
legally unsupported to compare Dr. Ordonez’s surgery to
the ideal. Dr. Ordonez’s actions must be compared to other
neurosurgeons.” Because plaintiff had not presented the nec-
essary expert testimony from a neurosurgeon, and because
the trial court determined that plaintiff’s res ipsa loquitur
argument failed, the court granted defendant’s motion for a
directed verdict.4
	4
       In making that ruling, the court stated that “[p]laintiff ha[d] failed to estab-
lish that it [was] more likely than not that Dr. Ordonez was negligent in the
placement of the plate or screws *  *.” (Emphasis added.) Although that ruling
                                       * 
addressed only two of the eight specifications of negligence, the court entered a
general judgment in favor of defendant. Plaintiff did not explicitly limit her appeal
to those two specifications of negligence, but plaintiff framed her appeal in terms
of the sufficiency of Dr. Tencer’s testimony to show that defendant’s installation of
Cite as 354 Or 197 (2013)	205

	        The Court of Appeals affirmed the trial court’s
ruling regarding the standard of care and breach, concluding
that Dr. Tencer’s testimony did not establish defendant’s
negligence. Trees, 250 Or App at 237-39. The court reasoned
that Dr. Tencer’s testimony had established that defendant’s
installation of the plate presented a biomechanical problem,
but the court went on to note that Dr. Tencer’s testimony had
“failed to bridge the gap, however, between the biomechanical
construct of the plate and the methods with which they were
intended to be installed and whether compliance with those
same methods as a medical matter set the standard of care
for [defendant].” Id. at 238. The court stated,
    “Tencer’s testimony established what the plate is designed
    to do and the biomechanical problems that are presented if
    the plate is not installed in the manner recommended by
    the manufacturer, but it does not establish, from a medical
    standpoint, that an ordinarily careful surgeon exercising the
    degree of care, skill, and diligence required when performing
    an anterior cervical decompression and fusion in the same
    or similar circumstances and community would install the
    plate in the manner that Tencer described.”

Id. at 238-39. The court went on to conclude that expert med-
ical testimony was required in this case to establish the
standard of care and breach of that standard, and the court
rejected plaintiff’s res ipsa loquitur argument. Id. at 242.
Because the Court of Appeals affirmed the trial court’s
grant of a directed verdict for defendant as to negligence, it
did not address defendant’s cross-assignments of error. Id.
at 231.
                    STANDARD OF CARE
	        Because the trial court granted defendant’s motion
for a directed verdict as to the standard of care and breach,
we must determine whether there was any evidence in the
record to support that element of plaintiff’s claim. See Bolt
the plate was improper. As we explain below, Dr. Tencer’s testimony was sufficient
to allow plaintiff to survive a motion for a directed verdict on the two specifications
of negligence that allege negligent installation of the Synthes plate. See Kirby v.
Sonville, 286 Or 339, 347, 594 P2d 818 (1979) (stating that a “judgment of nonsuit
must be reversed if there was sufficient evidence on any one charge of negligence,”
and noting that the court did not have to consider “which, if any, charges of neg-
ligence [we]re not actionable or unsupported by the evidence”).
206	                                                       Trees v. Ordonez

v. Influence, Inc., 333 Or 572, 578, 43 P3d 425 (2002) (“[T]he
jury must be permitted to consider every claim on which the
plaintiff has presented some evidence tending to establish
each element of that claim. In other words, only when
there is no evidence to support an element may the claim
be withdrawn from the jury’s consideration.” (Emphasis
omitted; internal quotation marks omitted; citations omitted;
brackets omitted.)); Vandermay v. Clayton, 328 Or 646,
655, 984 P2d 272 (1999) (“A directed verdict for defendant
was proper if plaintiff failed to present sufficient evidence
regarding whether defendant’s conduct fell below that
required by the standard of care.”). That is, if a reasonable
jury could have found, based on the evidence, that defendant
had breached the standard of care, the entry of a directed
verdict for defendant was improper. See T. R. v. Boy Scouts of
America, 344 Or 282, 296-97, 300, 181 P3d 758, cert den, 555
US 825 (2008) (concluding that the trial court did not err in
denying defendant’s motion for a directed verdict because,
although a reasonable jury could have reached a conclusion
in defendant’s favor, that was not the only conclusion that a
reasonable jury could have reached). On review, this court
will not weigh the evidence, and instead will view the evi-
dence in the light most favorable to plaintiff, the party who
opposed the motion. See Rathgeber v. James Hemenway, Inc.,
335 Or 404, 411, 69 P3d 710 (2003) (so stating).
	       The standard of care for physicians in Oregon has
been codified in ORS 677.095(1):
    	 “A physician *  * licensed to practice medicine *  * by
                        *                                    * 
    the Oregon Medical Board has the duty to use that degree
    of care, skill and diligence that is used by ordinarily careful
    physicians * * * in the same or similar circumstances in the
    community of the physician * * * or a similar community.”5

That statute essentially codified the common-law standard.
See, e.g., King v. Ditto, 142 Or 207, 213, 19 P2d 1100 (1933)
(noting that a physician must “exercise that degree of skill
and care usually possessed and exercised by those engaged
in the same line of practice in similar localities”). In this
	5
       The legislature amended ORS 677.095(1) in 2013, but those amendments are
not relevant to this case. See Or Laws 2013, ch 129, §§ 4, 8. We therefore cite the
2011 version of the statute.
Cite as 354 Or 197 (2013)	207

case, the issue is whether the testimony of an expert who is
not a medical doctor can establish “that degree of care, skill
and diligence that is used by ordinarily careful physicians
*  * in the same or similar circumstances” and a breach of
 * 
that standard.
	        Plaintiff argues that Dr. Tencer’s testimony was
sufficient to establish the standard of care and defendant’s
breach of that standard. As plaintiff frames that testimony,
Dr. Tencer testified that defendant’s installation of the plate
was inadequate because it was not proper under uniform
standards for installing the Synthes plate, it failed to meet
Synthes’ minimum recommendations for installing the plate,
and it constituted a “no-go” situation because the screws were
elevated above the plate. Plaintiff contends that the Court
of Appeals imposed a “medical testimony” requirement that
is not supported in this court’s case law, specifically State
v. Rogers, 330 Or 282, 4 P3d 1261 (2000), or the case law of
other jurisdictions.
	        Defendant responds that Dr. Tencer’s testimony did
not—and could not—establish the standard of care and
breach of that standard because Dr. Tencer is not a medical
doctor. That is, according to defendant, nothing Dr. Tencer
could have said would have been sufficient to establish the
standard of care because he is not a neurosurgeon who is
familiar with the standard of care for performing an anterior
cervical decompression and fusion. Moreover, defendant
argues, Rogers does not control because it was not a medical
malpractice case.
	         In most medical malpractice cases, expert testimony
is required to establish the standard of care. See Getchell v.
Mansfield, 260 Or 174, 179, 489 P2d 953 (1971) (“In most
charges of negligence against professional persons, expert
testimony is required to establish what the reasonable prac-
tice is in the community.”). The rationale behind that rule is
that a layperson typically would not know what an “ordinarily
careful” surgeon would do under the circumstances. See id.
(noting that the reason for the expert testimony requirement
is that “what is reasonable conduct for a professional is ordi-
narily not within the knowledge of the usual jury”). That
reasoning is consistent with the general rationale for allowing
208	                                         Trees v. Ordonez

expert testimony, described in OEC 702, which provides that
“a witness qualified as an expert by knowledge, skill, experi-
ence, training or education” may testify “[i]f scientific,
technical or other specialized knowledge will assist the trier
of fact to understand the evidence or to determine a fact in
issue.” (Emphasis added.)
	         Neither party points to an Oregon case where a non-
medical expert’s testimony has been held to be sufficient—or
insufficient—to establish a medical doctor’s standard of care
and the failure to meet that standard. Other jurisdictions
have split on the issue: some jurisdictions have required
expert testimony from a medical doctor to establish the
standard of care, and others have held that experts who are
not medical doctors may, in certain cases, provide testimony
sufficient to establish the standard of care for a medical
doctor. Compare Bell v. Hart, 516 So 2d 562, 570 (Ala 1987)
(finding pharmacist and psychologist could not testify to
standard of care in negligent prescription case against phy-
sician because “the standard of care must be established by
medical testimony,” meaning “testimony by physicians or
properly introduced medical treatises”), with Thompson v.
Carter, 518 So 2d 609, 614-15 (Miss 1987) (toxicologist and
pharmacologist should have been allowed to testify regard-
ing the standard of care for physician prescribing a drug
because an expert on the standard of care must possess
medical knowledge, but need not possess a medical degree).
Even in jurisdictions that require a medical doctor to estab-
lish the standard of care, the rationale for that rule is
grounded in the knowledge and experience of the expert.
See, e.g., Bell, 516 So 2d at 570 (reasoning that an expert who
is not a physician is not competent to testify to the standard
of care for a physician because such an expert lacks any
“practical experience or knowledge of what physicians do”
(internal quotation marks omitted)).
	        This court’s medical malpractice cases that do dis-
cuss expert testimony on the standard of care mostly address
whether a particular expert is qualified to testify, and those
cases focus on whether the expert has the necessary knowl-
edge to support his or her testimony, rather than whether
the expert has a particular degree or specialty. See, e.g.,
Cite as 354 Or 197 (2013)	209

Sheppard v. Firth, 215 Or 268, 270, 272, 334 P2d 190 (1959)
(finding that trial court erred in allowing orthopedic sur-
geon, who had no training in treatment using chiropractic
adjustments, to testify that chiropractor’s treatment was
improper). For example, unlike decisions from some other
jurisdictions, our cases have allowed experts from schools
of medicine different from the defendant’s to testify to the
standard of care, if they have the necessary knowledge.
Compare Wemett v. Mount, 134 Or 305, 313, 292 P 93 (1930)
(noting that “the testimony of physicians of other schools
or experts in other lines” should be admitted “when such
testimony bears on a point as to which the principles of the
schools do or should concur”), with Dolan v. Galluzzo, 77 Ill
2d 279, 285, 396 NE2d 13, 16 (1979)) (“[T]o testify as an
expert on the standard of care in a given school of medicine,
the witness must be licensed therein.”). In allowing experts
from other schools of medicine, our cases have recognized
that a plaintiff is not required to present testimony from
an expert who is better qualified than any other expert, as
long as the expert can assist the jury in understanding the
standard of care. Cf. Sandow v. Weyerhaeuser Co., 252 Or
377, 384, 449 P2d 426 (1969) (“The law does not require
that in order to qualify as an expert the witness be better
qualified than anyone else. It only requires that he have
sufficient expertise to make it probable that he will aid the
jury in its search for the truth.”).

	In Creasey v. Hogan, 292 Or 154, 157-58, 166-67,
637 P2d 114 (1981), for example, this court held that two
orthopedic surgeons could testify regarding the standard
of care for a podiatrist in performing a bunionectomy. The
court based its decision on evidence that orthopedic surgeons
as well as podiatrists perform bunionectomies, use similar
methods of treatment, rely on some of the same texts, and
attend the same medical conferences. Id. at 167. The court
also noted that at least one of the methods that the podi-
atrist had used in that case was commonly used by both
disciplines. Id. Thus, in determining the qualifications of
experts in medical malpractice cases, our cases have looked
to substance, rather than form, and have focused on the
knowledge of the expert, see id., rather than on an expert’s
particular medical degree or area of specialty.
210	                                          Trees v. Ordonez

	        Similarly, our cases have emphasized the knowledge
of the expert, rather than the expert’s particular medical
degree or specialty, when examining the qualifications of
medical experts outside the context of medical malpractice.
For example, in a workers’ compensation case, this court
determined that the Workers’ Compensation Board had
erred in not considering testimony from medical doctors
regarding diagnosis of the psychological component of the
claimant’s injury. Barrett v. Coast Range Plywood, 294 Or
641, 644-45, 649, 661 P2d 926 (1983). The court noted that,
in that context, expert testimony was required to prove the
causal connection between the accident and the injury and
between the injury and the disability. Id. at 645-46. The
issue, similar to the issue presented here, was what kind of
expert testimony was required, because the plaintiff had to
prove the causal connection between the injury and the psy-
chological components of the injury. Id. at 646. We concluded
that diagnosis of the psychological component of the injury
was within the medical doctors’ competency, even though they
were not psychotherapists. Id. at 649. That is, we rejected a
rule tying the expert testimony requirement to a particular
degree or discipline and instead held that the fact that the
doctors were not psychotherapists went to the weight of their
testimony. Id. We followed the same logic in Rogers, stating
that “[a] medical degree is not a necessary predicate to find-
ing an expert witness qualified to testify about medical knowl-
edge, assuming that witness otherwise is qualified to do so.”
330 Or at 316. In Rogers, we concluded that a neuropsy-
chologist was qualified to testify about the possible causes of
the defendant’s frontal lobe dysfunction during the penalty
phase of an aggravated murder case. Id. at 284-85, 308, 317.
	        We agree with defendant that cases like Barrett
and Rogers, which are not medical malpractice cases, are
not sufficient, in and of themselves, to resolve the issue
presented in this case. Courts in other jurisdictions have
declined to extend rulings on expert testimony from other
contexts to medical malpractice cases because of the unique
nature of the knowledge required to establish the standard
of care. See, e.g., Bell, 516 So 2d at 567 (declining, in medical
malpractice case, to extend reasoning from case where state
toxicologist was allowed to testify about cause of death
Cite as 354 Or 197 (2013)	211

because that case did not involve medical malpractice).
Moreover, Barrett and Rogers address the admissibility of
expert testimony, not the sufficiency of that testimony to
overcome a motion for a directed verdict. Nonetheless, cases
like Barrett and Rogers illustrate this court’s preference for
examining the knowledge of each expert witness regarding
the subject of his or her testimony, rather than adopting a
rigid rule tied to a particular degree or specialty. In addition,
our malpractice cases allowing expert testimony from prac-
titioners from schools of medicine different from that of a
particular defendant further illustrate that we traditionally
have rejected an expert testimony rule based solely on edu-
cation or professional license. That is, the central inquiry
in our cases on the qualification and admissibility of expert
testimony is whether the expert has sufficient knowledge of
the methods used by the practitioner in the circumstances
to testify regarding the standard of care.
	        Based on our cases, testimony from a qualified expert,
who has knowledge about the standard of care that is helpful
to the trier of fact, is admissible, and we see no principled
reason why such testimony is necessarily insufficient to
establish the standard of care in a medical malpractice case
merely because that testimony comes from an expert who is
not a medical doctor. Consistent with this court’s cases
involving expert qualification and the admissibility of expert
testimony, which consider the knowledge of each individual
expert, we reject a rule requiring expert testimony from a
medical doctor to survive a motion for a directed verdict on the
issue of negligence in a medical malpractice case. Defendant
has not demonstrated why this court should abandon its
approach of examining the knowledge of the expert, and the
expert’s testimony about that knowledge, and instead create
a requirement that only a medical doctor can establish the
standard of care.
	      In fact, requiring a medical doctor to establish the
standard of care would do little to advance defendant’s argu-
ment that the reason that Dr. Tencer cannot establish the
standard of care is that, as a nonphysician, he does not have
knowledge of the skill and care required of a neurosurgeon,
and he has never performed surgery on a living patient.
Requiring an expert to be a medical doctor would not ensure
212	                                         Trees v. Ordonez

that the expert had knowledge of the skill and care required
of a neurosurgeon in “plac[ing] and secur[ing] [a] Synthes
plate” and its screws or had performed surgery on a living
patient. Cf. Sheppard, 215 Or at 272 (concluding that it was
error to allow a medical practitioner to testify regarding the
value of using a particular instrument where the practi-
tioner had “no knowledge of the instrument or its uses”).
Conversely, an expert who is not a medical doctor, but who
has placed and secured a Synthes plate or a similar plate,
and who has extensive knowledge of the installation of such
devices, may have knowledge of the skill and care required
of a neurosurgeon in installing those devices. Cf. Monk v.
Doctors Hospital, 403 F2d 580, 583 (DC Cir 1968) (noting
that, in medical malpractice case arising out of alleged
negligent operation of a “Bovie machine,” expert testimony
was required only to explain to the jury the operation of that
machine).
	        Moreover, many of defendant’s concerns about allowing
a nonphysician to establish the standard of care can be
addressed through cross-examination of the nonphysician
experts and through a defendant doctor’s own testimony or
that of his or her experts. That is, a defendant can challenge
the weight that the trier of fact should afford to testimony
from an expert who is not a medical doctor, and then the
jury—not this court—ultimately must determine what
weight to afford that testimony. See W.R. Chamberlin & Co. v.
Northwestern Agencies, 289 Or 201, 207, 611 P2d 652 (1980)
(“[T]he weight of the opinion of an expert witness is a matter
particularly within the province of the jury.”).
	        We therefore reject defendant’s argument that expert
testimony from a medical doctor is necessarily required to
establish the standard of care in a medical malpractice case
to overcome a motion for a directed verdict. Testimony from
an expert who is not a medical doctor may be sufficient to
establish the standard of care, but on a motion for a directed
verdict, the trial court must make that determination in each
case, based on the particular expert’s testimony and the par-
ticular specifications of negligence alleged by the plaintiff.
	        Returning to the facts of this case, we begin by noting
that, on review, no party argues that Dr. Tencer’s testimony
Cite as 354 Or 197 (2013)	213

was admitted improperly, and we therefore presume that
that testimony was relevant and helpful to the trier of fact
in understanding at least some aspect of plaintiff’s mal-
practice claim.6 See Malila v. Meacham, 187 Or 330, 335,
211 P2d 747 (1949), abrogated on other grounds by Rogers v.
Meridian Park Hospital, 307 Or 612, 772 P2d 929 (1989) (“If
it is admissible it must be because it is pertinent to the issue
of malpractice; otherwise, it should be excluded.”). Plain-
tiff alleged that defendant was negligent because, among
other things, he “failed to properly place and secure the
Synthes plate and its upper [and lower] screws to the
anterior surface of the C4 [and C6] vertebral body in the
May 25 surgery, allowing the plate and/or its attachment
screws to erode and/or perforate plaintiff’s esophagus or
hypopharynx.” As defendant notes, Dr. Tencer is not a neuro-
surgeon, does not have a medical degree, and has never
“place[d] and secure[d]” the Synthes plate in a living patient.
In addition, the scope of Dr. Tencer’s admitted testimony was
limited to explanation and opinion from a biomechanical
perspective, because that is Dr. Tencer’s area of expertise.
Nonetheless, expertise in biomechanical engineering can
include expertise in placing and securing devices in the
body because, as Dr. Tencer explained it, that field involves
“engineering devices for the human body.” Moreover, as
noted, Dr. Tencer lectures medical residents about medical
implants, has lectured to and worked with physicians, has
developed an implant system for spinal surgeries, and has
done laboratory research comparing the Synthes plate to
other similar plates, which included both watching and par-
ticipating in the placement of a Synthes plate on a cadaver.
	        We turn to an examination of Dr. Tencer’s testimony
in this case to determine whether it provided evidence of the
standard of care—that is, we must determine whether that
testimony provided evidence from which a reasonable jury
could determine what an ordinarily careful surgeon would
	6
      Defendant argues that Dr. Tencer was not “qualified” to testify about the
propriety of defendant’s installation of the Synthes plate, but, as the Court of
Appeals noted, Dr. Tencer’s qualification as an expert witness is not at issue on
review. See Trees, 250 Or App at 237 (noting that “Tencer’s competency to testify
as an expert is not presented on appeal”). Although defendant made objections to
Dr. Tencer’s qualifications and to some of Dr. Tencer’s testimony at trial, defendant
did not renew those objections as cross-assignments of error.
214	                                         Trees v. Ordonez

have done under the circumstances faced by defendant. We
must examine the testimony given in this case because,
for the same reasons that we reject a rule requiring expert
testimony from a medical doctor, we also reject a rule that an
expert who is a biomechanical engineer or other specialist
without a medical degree always can establish the standard
of care in a medical malpractice case.
	        As noted, Dr. Tencer testified about both the general
design and installation of the Synthes plate and defendant’s
placement of the plate in this case. In explaining the design
of the plate, Dr. Tencer testified that there are two reasons
why, from a design perspective, the screws must sit below
the surface of the plate. First, he testified that if the screws
are not fully seated in the plate’s holes, the screws will not
have any mechanical function. Second, he noted that Synthes
had used several design features to eliminate snagging and
erosion damage to soft tissues, including that “the holes
[in the plate] are designed so that the screws fit down into
the holes. And then if you were to put, you know, a straight
edge, for example, across it, the screw head would be below.
It wouldn’t be protruding above.” He testified that the design
features Synthes used to eliminate snagging and erosion of
soft tissues “are essentially uniform throughout orthopedic
implant design” and are “commonplace.”
	        In discussing installation of the plate, Dr. Tencer
expressly disagreed with defense counsel’s statement that
leaving screw heads protruding above the plate is “acceptable.”
In contrast, Dr. Tencer stated that “any protrusion above the
plate is essentially no-go, because it’s clear that it can cause
damage of some type, and it’s very well described in all the
literature that there should be no protrusion.” (Emphasis
added.) Based on Dr. Tencer’s testimony, a reasonable jury
could infer that an “ordinarily careful” surgeon would not
leave screws protruding above the plate because that would
present a “no-go” situation, particularly when those screws
specifically are designed to sit below the surface of the plate
due to the risk of damage to the soft tissue. In other words,
a reasonable jury could infer that an ordinarily careful
surgeon “plac[ing] and secur[ing] the Synthes plate and its
*  * screws” would ensure that no screws were protruding
  * 
above the plate.
Cite as 354 Or 197 (2013)	215

	        In discussing how the plate in this case was placed
and secured, Dr. Tencer testified that at least five of the six
screws used in plaintiff’s surgery showed physical evidence
that they had been protruding above the plate. Moreover,
Dr. Tencer noted that an X-ray taken on the day of plaintiff’s
surgery showed screw heads protruding above the surface of
the plate. Dr. Silver, the neurosurgeon who removed the plate,
also testified that at least two of the screws were protruding
above the plate. Based on that testimony, a reasonable jury
could conclude that defendant breached the standard of care
for placing and securing the Synthes plate and its screws
by allowing some of the screw heads to protrude above the
plate. See Malila, 187 Or at 336 (stating that an expert need
not frame the standard of care and breach “in the words
of a particular formula” as long as the expert “testifies in
substance to what amounts to a failure *  * to conform to
                                              * 
the standard”).
	        We note that the nature of Dr. Tencer’s testimony
is important: Dr. Tencer essentially testified that it is never
reasonable, under any circumstances, to leave a screw head
protruding above the Synthes plate. In contrast, when dis-
cussing a different aspect of placing and securing the
plate, he described what would be “optimal,” but conceded
that some variation would be permissible. He repeatedly
emphasized, however, that the screws could not be angled to
protrude above the plate. Therefore, a jury reasonably could
infer that Dr. Tencer was not testifying to the “ideal” or
“optimal” placement of the Synthes plate and screws when he
said that the screws could not protrude above the plate, and
instead was testifying that no circumstances could justify
protrusion of screw heads above the plate. Based on that
testimony, the evidence that the screw heads in this case
were protruding above the plate could allow a jury to find
that defendant breached the standard of care, at least as to
two of the specifications of negligence. As noted, however,
Dr. Tencer’s testimony does not address every specification
of negligence, such as plaintiff’s allegation that defendant
negligently failed to repair the perforation in her esophagus.
Nonetheless, because Dr. Tencer’s testimony is sufficient for
plaintiff to survive a motion for a directed verdict on the
standard of care and breach of the standard of care for at
216	                                                        Trees v. Ordonez

least two of her specifications of negligence, we reverse the
directed verdict.7
                                CAUSATION
	        Because the trial court erred in granting defendant’s
motion for a directed verdict on the standard of care and
breach, we turn to defendant’s first cross-assignment of
error to determine whether the trial court erred in denying
defendant’s motion for a directed verdict on causation.
	        At trial, there was testimony from multiple experts
on the issue of causation. Dr. Tencer testified that at least
five of the six screws used in plaintiff’s surgery showed
physical evidence that the screws were protruding above the
plate, and he explained that a protruding screw head would
present the opportunity for contact with the esophagus.
He testified that “any protuberance, anything that’s above
the plate, is clearly going to be penetrating into that [soft]
tissue.”
	        Dr. Silver, a neurosurgeon, testified that, before the
initial surgery was performed, plaintiff’s esophagus would
have run just in front of cervical disks C3, C4, C5, C6, and
C7, and he stated that at least one of the screws at the C4
level and one of the screws at the C6 level was standing
out, away from the plate.8 Dr. Silver testified that when he
performed the operation to remove the plate, screws, and
bone grafts from plaintiff’s cervical spine, he did not inspect
the esophagus. He testified, however, that he believed that a
perforated esophagus was the most likely source of plaintiff’s
illness following her initial surgery:
    	 “Q  Because you already knew, by the time you saw
    [plaintiff], that she probably had, or undoubtedly did have,
    an esophageal perforation?

	7
      Because we conclude that the trial court erred in granting defendant’s
motion for a directed verdict, we do not address plaintiff ’s alternative argument
that the doctrine of res ipsa loquitur applied to her claim and negated the need for
expert testimony on the standard of care.
	8
      Dr. Silver did note that the esophagus would not necessarily have run in
front of the plate after surgery due to swelling of the tissue, but he did not rule
out the possibility that the esophagus could have come into contact with the plate
following the initial surgery.
Cite as 354 Or 197 (2013)	217

   	 “A Right.
   	 “Q  There was never any question, in your mind, that
   her esophagus had been torn in some manner as a result
   of the surgery that she had done on the 25th of May, [the
   initial surgery done by defendant,] was there?
   	 “A  No. I thought that was the most likely explanation
   for her problem.”
When asked about plaintiff’s condition after he removed the
plate, screws, and bone grafts, Dr. Silver testified that “she
was better, and, you know, her condition had improved. She
had regained some strength. She still had weakness, but
she had regained some strength in her left arm. She was
starting to have trouble with her right arm.”
	        Dr. Dierks, a doctor specializing in oral-maxillofacial
surgery and otolaryngology—head and neck surgery—also
testified about plaintiff’s alleged esophageal perforation.
Dr. Dierks had treated plaintiff about a week after her initial
surgery, and he also stated that he believed that plaintiff
had an esophageal perforation:
   	“Q      And you had no question that [plaintiff] had a perfor-
   ation of the esophagus, and your concern was it was being
   adequately drained?
   	   “A  That’s correct.”
Similarly to Dr. Silver, Dr. Dierks testified that he did not
attempt to find and repair the perforation because “the
tissue [of the esophagus] is not a very tough tissue” and, in
the circumstances presented, “sutures tend not to be mechan-
ically retained.” As it turned out, repair was unnecessary
because, as Dr. Dierks testified, after the surgery removing
the plate, screws, and bone grafts, there was evidence that
the esophageal perforation was beginning to close. Dr. Dierks’s
assessment was that the perforation closed within a few
weeks of that surgery.
	        At the close of plaintiff’s evidence, defendant moved
for a directed verdict on the issue of causation, arguing that
“there’s been no proof of causation in the sense of, yes, there
was a screw that was elevated, probably something between
a half and a millimeter above the surface of the plate. But
218	                                                       Trees v. Ordonez

there’s no indication about where the perforation occurred,
that this may have caused it.” As noted, the trial court
rejected that argument, stating that its ruling was “based
on testimony and other evidence that during the surgical
procedure the placement of one of the fixation screws either
did not seat perfectly flush or was not sufficiently secured so
that the screw worked its way out shortly after the closure of
the incision.” The court determined that the evidence taken
in the light most favorable to plaintiff established that “the
perforation of the esophagus caused a massive infection”
that required additional surgeries.
	        On review, defendant renews the argument that
this case involves a complex medical question that requires
expert testimony to establish that there is a reasonable medi-
cal probability that defendant’s negligence caused plaintiff’s
injuries. Defendant asserts that there is no evidence of actual
esophageal perforation and that there is no expert medical
testimony that defendant’s negligence caused plaintiff’s
alleged injuries. Thus, according to defendant, the jury would
have to engage in impermissible speculation regarding
whether defendant’s negligence caused the alleged esopha-
geal perforation.9
	        In negligence cases generally, “[t]he proof of the
material issue [of causation] must have the quality of rea-
sonable probability, and a mere possibility that the alleged
negligence of the defendant was the proximate cause of [the]
plaintiff’s injuries is not sufficient.” Sims v. Dixon, 224 Or
45, 48, 355 P2d 478 (1960). That is, “the causal connection
between [the] defendant’s acts or omissions and the plaintiff’s
injuries must not be left to surmise or conjecture.” Id. As
applied to this appeal, resulting from the denial of a motion
for a directed verdict, we review to determine whether there
was any evidence from which a reasonable jury could find
that it was more probable than not that defendant’s alleged
	9
      In a footnote in defendant’s reply brief on the cross-assignments of error
before the Court of Appeals, defendant appears to argue that, for the same reasons
that Dr. Tencer could not establish the standard of care, Dr. Tencer could not
establish causation. Just as Dr. Tencer’s lack of a medical degree does not prevent
him from establishing the standard of care, his lack of a medical degree does
not prevent him from establishing causation. We reject defendant’s argument
regarding Dr. Tencer’s testimony on causation without further discussion.
Cite as 354 Or 197 (2013)	219

negligence—as noted above, leaving screws protruding above
the plate—caused plaintiff’s injury.
	In Sims, this court considered the type of expert tes-
timony required to prove causation. Although it was not a
medical malpractice case, Sims involved testimony from a
doctor regarding whether the plaintiff’s near collision with
the defendant’s truck caused her later angina attack. Id. at
49. The doctor testified that it was “probable” that an indi-
vidual who was frightened badly “could” experience extreme
emotional stress, which “could” lead to an anginal syndrome.
Id. The court reasoned that the doctor’s testimony was an
insufficient “statement of possibility,” rather than a statement
of “reasonable certainty.” Id.; see also Joshi v. Providence
Health System, 342 Or 152, 155-56, 164, 149 P3d 1164 (2006)
(affirming a directed verdict for the defendants in wrongful
death action based on alleged medical malpractice where
expert testified that he could not state “to a reasonable
degree of medical probability” that administration of certain
medication would have changed the outcome and saved the
decedent’s life).
	Both Sims and Joshi are distinguishable. In Sims,
the doctor’s testimony was tentative and equivocal. Similarly,
in Joshi, the expert explicitly testified that he could not
state that there was a reasonable probability that defendant
caused the outcome. In contrast, here, experts testified
about the position and location of the screws in relation to
plaintiff’s esophagus, as well as the likelihood that those
screws could perforate the esophagus. Moreover, at least one
expert testified that “the most likely explanation” for plain-
tiff’s symptoms was a perforated esophagus, and her con-
dition improved and her esophagus healed after the screws
were removed.
	       Specifically, plaintiff presented testimony from
Dr. Tencer that screws protruding above the plate “clearly”
would penetrate into the soft tissue of the esophagus. In
addition, Dr. Silver testified that there were screws protrud-
ing above the plate in the area where plaintiff’s esophagus
was located before the surgery. He also stated that “the most
likely explanation for [plaintiff’s] problem” was that her
esophagus had been torn as a result of the surgery that
220	                                          Trees v. Ordonez

defendant performed, and he noted that plaintiff’s condition
improved after he removed the plate, screws, and bone grafts.
Dr. Dierks similarly testified that the perforation began to
close after Dr. Silver removed the plate, screws, and bone
grafts.
	         We agree with defendant that none of those experts
explicitly stated that it is more probable than not that defen-
dant’s alleged negligence in leaving screws protruding above
the plate caused plaintiff’s injuries. Nonetheless, the testi-
mony from various experts provided evidence from which
a reasonable jury could infer that it is more probable than
not that defendant’s alleged negligence caused plaintiff’s
injuries: sharp screws were protruding in the area where
plaintiff’s esophagus was before the surgery, the esophagus
is a soft tissue, multiple experts agreed that the esophagus
had been perforated, the perforation started to close after
the screws were removed, and plaintiff’s condition improved
after the screws were removed. See W. Page Keeton et al.,
Prosser and Keeton on the Law of Torts § 41, 269-70 (5th
ed 1984) (“The plaintiff need not negative entirely the pos-
sibility that the defendant’s conduct was not a cause, and
it is enough to introduce evidence from which reasonable
persons may conclude that it is more probable that the
event was caused by the defendant than that it was not.
* * * Circumstantial evidence, expert testimony, or common
knowledge may provide a basis from which the causal
sequence may be inferred.” (Footnotes omitted.)). The trial
court did not err in denying defendant’s motion for a directed
verdict on causation.
	         Defendant renewed two other cross-assignments of
error on review, challenging the trial court’s rulings allowing
plaintiff to introduce two Synthes product brochures and a
Synthes instructional video, all of which warned that screws
protruding above the plate could damage the esophagus.
Defendant requests that we address those rulings to provide
guidance for the trial court on remand. Although the evi-
dentiary issues raised by defendant may arise in later pro-
ceedings, those issues are likely to arise in a different posture
on remand. For that reason, we do not address defendant’s
additional cross-assignments of error regarding the admis-
sibility of the brochures and the video, nor do we address
Cite as 354 Or 197 (2013)	221

plaintiff’s arguments about the purposes for which that evi-
dence was or can be admitted.
	       The decision of the Court of Appeals is reversed.
The judgment of the circuit court is reversed, and the case
is remanded to the circuit court for further proceedings.
