Using Substantial Factor
Analysis in Closed Head Injury Cases
||by Judith F. Tartaglia and
Kevin F. Amatuzio
million closed head injuries occur in the United States each year,
and ninety percent of these involve mild to moderate injury.1 Medical
research has progressed rapidly in the past decade in both the
diagnosis of these injuries and in documenting outcome. It is therefore
expected that closed head injury claims will grow in number, in
the severity of the injury claimed, and in the amount of damages
In the typical closed head injury claim, the plaintiff describes
a post-traumatic syndrome following a mild to moderate head injury.
Such syndrome includes attention and memory deficits as well as
chronic headache, dizziness, and emotional reactions, such as anxiety
Defending the causation and damage aspects of a closed head injury
case is frequently a difficult and intimidating undertaking. The
defendant's negligence is often clear; the plaintiff's complaints
are usually severe and ominous, although vague and hard to quantify.
However, the authors believe these cases may nonetheless be vigorously
defended in the areas of proximate cause and apportionment of damages,
through substantial factor analysis. This approach applies, both
to the event itself and to the claimed resulting damages, the general
negligence principle that one's conduct must be a substantial factor
in producing the claimed harm. This article first discusses recent
medical studies that document favorable outcomes in closed head
injury cases and the significance of pre-existing conditions in
causing or contributing to symptoms identified with closed head
injuries, and then analyzes substantial factor analysis as a framework
for applying this information to rebut causation and to limit damages.
Bases of the Closed Head Injury
medical research indicates that no direct impact to the head is
required to sustain a closed head injury and the symptoms of closed
head injuries are frequently not associated with any lesion that
can be visualized on a computerized topography scan (CT scan) or
by magnetic resonance imaging (MRI). For example, swelling and
lesions, such as subdural hematomas, are typical symptoms of closed
head injuries and are demonstrable on CT scans and MRIs. However,
another typical head injury, caused by acceleration-deceleration
of the brain, such as that which occurs with whiplash injury or
severe infant shaking, is a brain stem injury frequently described
as a diffuse axonal injury.3
Diffuse axonal injuries are not demonstrable with MRIs and CT
scans (although they probably will be in the future since they
are now demonstrable on autopsy and on auditory brain stem testing).4 And
yet the consequences of a diffuse axonal injury can be severe as
such an injury is thought to disrupt neurological processes
that are necessary for attention and memory.5 Memory loss has been
found to occur despite the preservation of consciousness and it
is hypothesized that acceleration/deceleration accidents resulting
in brain stem injuries can ultimately cause more damage in the
memory centers of the temporal lobe than in other areas of the
A plausible neurophysiological basis is therefore possible for
symptoms resulting from certain kinds of head injuries even when
no objective findings of brain injury can be found on CT scan or
Effects of Mild and Moderate Head Injuries Disputed
goal in closed head injury litigation is to demonstrate that the
plaintiff's physical complaints may as well stem from conditions
that were not caused by the defendant's allegedly tortious behavior.
For example, even though the defendant's negligence may have caused
an automobile accident that hurt the plaintiff, that accident may
not have been even a substantial factor in causing the plaintiff's
current physical problems. Even if defendant's negligence was a
contributing factor, defense counsel should attempt to apportion
the damages among several causes, and thereby reduce his or her
Pre-existing conditions affecting brain functions, such as head
trauma, substance abuse, and psychiatric problems, are common.
The problem in closed head injury cases has not been in obtaining
recognition of pre-existing conditions, but rather in obtaining
an acknowledgment of their significance as elements contributing
to the plaintiff's present allegedly impaired condition.
Acknowledging the significance of the pre-existing conditions
is the key to apportionment of damages. While apportionment in
non-head trauma cases has increased with developments in medical
knowledge and technology, experts in closed head injury cases have
remained reluctant to attempt to apportion damages. The medical
literature now provides a basis for apportionment in some cases.
Use of substantial factor analysis, both in legal argument and
in presentation and cross examination of expert testimony, best
establishes the significance, and thus, apportionability of preexisting
Application of the substantial factor and apportionment analysis
requires familiarity with recent medical studies that describe
outcome after mild and moderate closed head injuries. Early studies
were not helpful.6 The frequently cited Rimel study indicated very
high rates of disability and unemployment in patients three months
after seemingly insignificant head injuries. The conclusion was
that many of these people may have suffered irreversible organic
brain damage. The Barth study had similar findings, showing high
rates of unemployment after minor head injuries.
More recent studies have produced strikingly different results
from the Rimal and Barth studies and are advantageous in the defense
of mild and moderate closed head injury cases. These studies have
emphasized the necessity to control for preexisting head injuries,
drug abuse, alcohol abuse, and psychiatric problems in order to
obtain valid data regarding the outcome of mild to moderate head
injuries.7 Gentilini made a significant contribution by studying
fifty mild head injured patients and fifty uninjured subjects using
a strict methodological approach and adequate control groups. Standard
neuropsychological testing was administered. After one month, no
conclusive evidence was found that mild head injury caused cognitive
impairment. He concluded that if there was structural damage after
a mild head injury, the patient generally recovered from a neuropsychological
standpoint within one month after trauma.
In 1986, Binder also challenged the argument that persisting,
measurable cognitive deficits typically occur after mild head injury.8 He found that findings of persistent cognitive impairment are attributable
to failure to control for the effects of previous injuries. Binder
described the "selective vulnerability" of certain populations
to the long term effects of mild head injuries. These populations
include those with prior head injuries and patients over forty
Another important study is that done by Dikmen.9 Dikmen studied
twenty subjects with minor
head injuries and compared them to an uninjured group at one and
twelve months after injury, using a battery of neuropsychological
and psychological measures. The results indicated that a single
minor head injury in persons with no prior compromising conditions
was associated with mild but probably clinically nonsignificant
difficulties at one month after injury. Dikmen concluded that prior
reports and literature may have overestimated head injury-related
losses; he criticized the earlier writings' failure to take into
account effects of pre-injury characteristics and injuries to other
parts of the body.
In 1987, a study noted that the majority of hospital admissions
for head trauma were due to minor injuries.10 Minor injuries
were described as those where the patient suffered no loss of consciousness
or only a transient loss of consciousness without major complications
and without requiring intracranial surgery. Levin acknowledged
the controversy surrounding the long-term effect of closed head
injuries. Therefore, he studied fifty-six patients with minor head
injury three months postinjury using quantified tests of memory,
attention and information processing speed.
The postconsussion symptoms that nearly all of the patients in
the Levin study initially reported, including cognitive problems,
physical complaints, and emotional malaise, had substantially subsided
by the three month follow-up examination. These data suggested
that a single uncomplicated minor head injury produces no permanent
disabling neurobehavioral impairment in the great majority of patients
who are free of pre-existing neuropsychiatric disorder and substance
abuse. The Gentilini, Binder, Dikmen, and Levin studies suggest
that closed head injuries are often associated with conditions
or damages which are the product of many contributing factors and
causes, potentially commencing before birth and continuing through
the time of the negligent act of the defendant and after.
Substantial Factor Approach to Causation
||The significance of the
above-referenced studies is as a tool in limiting and apportioning
damages claims. The task for the defense practitioner is to integrate
the above findings into a framework that can be used to argue causation
and damage apportionment issues. An overview of substantial
factor analysis as such a mechanism is therefore appropriate.
A principal test of legal cause is "but for" a test
of exclusion. The defendant's conduct is not a cause of the event
if the event would have occurred without it; or conversely, the
defendant's conduct is a cause of the event if the event would
not have occurred "but for" that conduct.11 The "but
for" test usually fairly and accurately expresses the requirement
of legal causation. However, when two or more causes concur to
bring about an event and any one of them operating alone would
have been sufficient to bring about the results, a "but
for" causation test fails. It is suggested that the standard
of proof for determining causation under these circumstances
should be a substantial factor test. Under this standard, the
defendant's conduct may be a "but for" cause of plaintiff's
harm, but defendant's conduct can be shown to have made such
an insubstantial contribution to the ultimate outcome that liability
should not be imposed.
A substantial factor analysis was applied in early cases where
two causes concurred to bring about an event, and either one
of them operating alone would have been sufficient to cause the
identical result, as when concurrent negligently set fires merge
and burn the plaintiffs property. 12 Historically, the substantial
factor test has been increasingly used not only when "but
for" analysis inappropriately relieved a defendant from
liability, but also when application of the "but for" rule
resulted in excessive liability for one defendant. The substantial
factor analysis was therefore deemed appropriate by many courts
when multiple potential causes complicated the causation analysis.
It gained increasing acceptance and refinement, culminating in
its inclusion in § 431(a) and § 433 of the Second Restatement
of Torts. Acceptance of the substantial factor test, and application
of it, varies by jurisdiction. 13 Some jurisdictions have rejected
the doctrine entirely. 14
The comments to Section 431 of the Second Restatement suggest
an important shift in application of the substantial factor rule.
While the rule originally addressed multiple concurrent causes,
the Second Restatement indicates that the rule also applies when
causes apart from the defendant's negligence may
not each be of sufficient significance independently to have
caused the claimed injury.15 The
focus under such an analysis is whether the actor's conduct was
of sufficient significance to attach liability for the claimed
damages.16"Substantial factor" has
been increasingly viewed not necessarily as an alternative to
the "but for" test
of causation, but rather an additional requirement.17
Prosser and Keeton note that the substantial factor formula
also applies to other "troublesome" situations:
... One is that where a similar, but not identical result would
have followed without the defendant's act; the other where
one defendant has made a clearly proved but quite insignificant
to the result, as where he throws a lighted match into a forest
The relevant considerations for determining whether a given
act or conduct constitutes a substantial factor are set forth
in Section 433 of the Second Restatement. These considerations
include the number of other factors which contribute in producing
the harm and the extent of the effect which they have in producing
Official Comment d to § 433(a) elaborates on the general
There are frequently a number of events each of which is not
only a necessary antecedent to the other's harm, but is also
recognizable as having an appreciable effect in bringing it about.
Of these the actor's conduct is only one. Some other event which
is a contributing factor in producing the harm may have such
a predominant effect in bringing it about as to make the effect
of the actor's negligence insignificant and, therefore, to prevent
it from being a substantial factor. So too, although no one of
the contributing factors may have such a predominant effect,
their combined effect may, as it were, so dilute the
effects of the actor's negligence as to prevent it from being
factor. (Emphasis added).
The concept of "dilution" in comment d to §433(a)
is intriguing, because it recognizes that actions or conduct
which, in a vacuum, could reasonably be held a "substantial
factor" in causing the plaintiffs damages may not be substantial or significant when
viewed in light of the totality of the plaintiffs circumstances.
In other words, events legally sufficient to constitute legal
cause standing alone, may not rise to that level considering
the other contributing factors in the case.
Based on medical studies that describe good outcomes for mild
and moderate head injuries and that suggest that those who do
not experience total recovery from mild and moderate head injuries
are probably demonstrating the result of cumulative injuries,
it can be argued that "but for" the prior insults to
the brain, the injury of which the plaintiff complains probably
would not have occurred or events unrelated to the defendant's
conduct were also substantial factors contributing to the plaintiff's
current condition. In such a case it would be patently unfair
to ascribe the plaintiffs cumulative brain injury to one defendant.
Substantial factor analysis provides the legal mechanism to attack
causation by requiring the fact finder to assess the totality
of causes or factors contributing to the plaintiff's condition.
Substantial Factor Approach to Damages
It is a general principle
that the extent or type of harm caused by one's negligence, or
the manner by which the harm was caused, need not be foreseeable
or expected before there can be a recovery.19 This principle
will be asserted by the plaintiff in head injury cases resulting
from minor trauma or where there was no direct impact to the head,
leaving defense counsel facing the proverbial "thin skulled" or "eggshell" plaintiff.
Defense of such damages is made more difficult in that even where
there is evidence of other prior insult or injury which would have
contributed to causing the plaintiffs condition, many jurisdictions
will hold the most recent tortfeasor responsible for the whole
of the damages, unless they can be apportioned with reasonable
Despite these legal principles, the two separate issues of legal
cause of the event causing injury and causation of resulting damages
are closely, if not inextricably, intertwined. While an actor may
properly be held responsible for unlikely or attenuated damage
caused by a negligent act, the plaintiff must nonetheless demonstrate
by his or her evidence that, to a reasonable degree of probability,
such damages did in fact flow from that negligent act. Further,
at some point the legal limit of cause-and-effect is reached, and
obscure or remote actual causes will not be recognized as actionable.21
Logically, a substantial factor analysis should be used to determine
recoverability of damages as well as to determine legal cause.
Whether it can be applied to damages is ambiguous under the law.
Section 431(a) of the Second Restatement speaks in terms of an
actor's conduct being a "substantial factor in bringing about
the harm.22 Section 433A states that damages for harm
are to be apportioned among two or more causes where there are
distinct harms, or where there is a reasonable basis for determining
the contribution of each cause to a single harm. Virtually all
types of "causes," whether innocent, tortious, pre-existing
or even acts of God, are subject to apportionment under Section
Use of the substantial factor approach to damages does have a
basis in the concept, often recognized, that at some point the
liability of an actor, even for negligent conduct, must be limited.
This need for some limitation upon consequences is sometimes stated
as one of foreseeability.z3
Alternatively, the limitation may be imposed by public policy,
thereby recognizing the "rule of law" exceptions to liability
stated in the Reporter's Notes to § 433, Restatement (Second)
of Torts Appx. (1966).24 Whatever
the rubric, courts, in giving credence to these policy considerations,
have reduced damages and
have refused to find liability, even in the face of admitted negligence
and a "cause-in-fact" relationship to the claimed damages.
Application of substantial factor analysis to damages, then, has
a foothold in existing law and a reasonable basis exists for urging
a further expansion of existing law to recognize it. In Lacy, supra,
the court held substantial factor analysis appropriate "whenever
there are concurring causes of a single injury, regardless of whether
the other causes are relatively passive or preexisting,
such as a physical condition; or relatively active and occur subsequently,
such as intervening negligent or
criminal acts.25 As we have seen, recent medical research indicates
that a failure to recover from mild to moderate head injuries is
seen in individuals with cumulative injuries. While an expert witness
such as a neuropsychologist or neurologist might not be able to
say that "but for" some specific prior insult (such as
a previous head injury), the subject accident would not have impaired
the plaintiff, the same expert might testify that it is reasonably
probable that the prior injury was a "substantial factor" contributing
to the overall reduction in function which the plaintiff now exhibits.
The expert than may be able to reasonably apportion the cumulative
harm suffered to the various contributing causes, depending
upon the amount of information available concerning the plaintiff's
pre- and post-accident level of function.
strategy that anticipates the use of the substantial factor test
of causation requires discovery which must be thorough and undertaken
early in the litigation process. The focus upon the pre-accident
plaintiff is at least as important as his post-accident condition.
Interrogatories should be designed to elicit information as to
plaintiff's medical, psychological, social, academic and employment
status pre-accident, and must seek information as to prior injuries
and prior accidents and significant medical history as well as
psychological or psychiatric intervention. Report cards, standardized
IQ test result, and counseling or disciplinary records even as
early as elementary school may be probative as to pre-existing
deficiencies or conditions. In cases involving children and even
young adults, prenatal, birth and pediatric histories could contain
facts indicative of an early brain injury. Complete records for
all post-accident care and treatment must be obtained, including
the underlying raw test data used or relied on by the plaintiffs
Any prior alcohol, drug or other substance abuse by the plaintiff
should be probed in detail, although this injury seems best suited
to a deposition environment. Substance abuse is relevant in a brain
damage case and any attempt by plaintiff to withhold such relevant
information by, for example, a Fifth Amendment privilege, requires
imposition of sanctions by the court, probably including dismissal.26
Experts should be hired as early as possible in the litigation.
They should be used not only for performing independent medical
examinations, but also in helping to formulate deposition questions
for the plaintiff and plaintiff's experts. Another important role
of the defense expert is to apprise defense counsel of the pertinent
medical research which will further guide discovery and development
of trial tactics. The successful use of a defense expert in this
regard is illustrated in Lima v. United States,27 a
case in which the issue was whether the swine flu immunization
cause of the plaintiff's Guillain Barre syndrome. The court emphasized
the importance of the medical and epidemiological evidence that
was presented. "Where, as here, the exact organic cause of
a disease cannot be scientifically isolated, epidemiologic data
becomes highly persuasive ."28 The
court ultimately held that, since the medical research did not
support the plaintiff's theory
of causation, the plaintiff had failed to sustain his burden of
proof. Some courts require such epidemiological evidence to establish
a prima facie case of causation when such evidence is obtainable.29
A primary goal of taking the plaintiff’s expert's deposition
is to obtain admissions that factors other than the current accident
were substantial factors in bringing about the plaintiffs symptoms'
and that by comparison, defendant's negligence was not a substantial
factor. Defense counsel should methodically point out and obtain
agreement that factors other than the defendant's conduct were
substantial in bringing about the plaintiff's harm. It is then
unlikely that the plaintiff's expert will be able to state within
a reasonable degree of medical or psychological probability that
the accident complained of was the cause of the plaintiffs symptoms.
All discovery should be undertaken with an eye toward filing successful
dispositive pre-trial motions. As discussed before, motions to
dismiss can be based on plaintiffs assertion of Fifth Amendment
privilege in regard to drug usage. A motion for summary judgment
or eventually one for directed verdict can be based on the plaintiff's
failure to establish causation. In addition, motions in limine should be filed regarding the scope of admissible psychological
While jurisdictions vary, most courts appear to give a "substantial
factor" jury instruction, when appropriate, in addition to
and not in lieu of a "but for" instruction. A separate
instruction should also be submitted articulating the "dilution
of the effect of negligence" concept of Section 433 of the
Second Restatement.31 Instructions defining each type of substantial
factor which the evidence supports (pre-existing conditions, concurrent
causes, intervening or subsequent causes) are necessary, together
with an enabling instruction providing the mechanism for the jury's
assessment of the contribution of each to the plaintiff’s
condition. Since legal determinations by the trial court as to
use of substantial factor evidence and law are the bases for its
instructions, proposed instructions must be carefully drafted and
submitted with supporting factual and legal authority.
Given the findings of
current medical research on closed head injuries, defense counsel
should not hesitate to advocate substantial factor analysis in
such cases as a way to fairly analyze the causal relationship of
the injury to the symptoms and to apportion damages. In so doing
defense counsel will not only impart a rule of reason to the awarding
of damages, he will also provide the defense a favorable theme
around which the case can be structured and presented to the judge
Tartaglia is Assistant General Counsel for the CIGNA Companies
in the Mountain States and Pacific Northwest regions. She is a
member of the Defense Research Institute. Ms. Tartaglia is also
a certified speech pathologist with experience in diagnosing and
treating head injuries.
Kevin F. Amatuzio is a partner with the Denver
law firm of Montgomery, Green, Jarvis, Kolodny & Markusson,
which specializes in personal injury and products liability defense,
disputes and bad faith defense. He is a member of the Defense
||1 See Long, Postconcussion
Symptoms After Head Trauma, 79 So. Med. J. 728-732 (1986).
2 Alves, Understanding Postraumatic Symptoms After Minor Head
Injury, l J. Head Trauma Rehab. (1986).
3 See Vowles, Diffuse Axonal Injury in Early Infancy, 40 J. Clinical
Pathology 185-189 (1987); and Gennarelli, Diffuse Axonal Injury
and Traumatic Coma in the Primate, 12 Annals of Neurology 564-574
4 See Elwany, Auditory Brain Stem Responses (ABR) in Patients
with Acute Severe Closed Head Injuries. The Use o f the Grading
System, 102 J. Laryngology & Otology 755-759 (1988).
5 See Gentilini, Neuropsychological Evaluation of Mild Head Injury,
J. Neurology, Neurosurgery, & Psychiatry 137-140 (1985).
6 See, e.g., Rimal, Disability Caused by Minor Head Injury, 9
Neurosurgery 221-228 (1981); Barth, Neuropsychological Sequelae
of Minor Head Injury, 13 Neurosurgery 529-533 (1983).
7 See, e.g., Gentilini, Neuropsychological Evaluation of Mild
Head Injury, 48 J. Neurology, Neurosurgery, & Psychiatry 137
8 See, Binder, Persisting Symptoms After Mild Head Injury: A Review
of the Postconcussive Syndrome, 8 J. Clinical & Experimental
Neuropsychology 323-346 (1986).
9 Neuropsychological and Psychosocial Consequences of Minor Head
Injury, 49 J. Neurology, Neurosurgery, & Psychiatry 1227-1233(1986).
10 Levin, Neurobehavioral Outcome Following Minor Head Injury:
A Three-Center Study, 66 J. Neurosurgery 234-243 (1987).
11 See Prosser & Keeton, The Law of Torts, §41, at 266
(5th ed. 1984); Rudeck v. Wright, 218 Mont. 41, 709 P.2d 621, 628
12 Prosser & Keeton, supra, at 266-267.
13 See generally, 57A Am. Jur. 2d, Negligence § 478.
14 See, e.g., Markiewicz v. Salt River Valley Water Users' Association,
118 Ariz. 329, 338 n. 6, 576 P.2d 517, 526 n. 6 (1978).
15 See Mahoney v. Beatman, 110 Conn. 184, 147 A. 762 (1929); Whitner
v. Von Hintz, 437 Pa. 448, 263 A.2d 889 (1970); Carney v. Goodman,
38 Tenn. App. 55, 270 S.W.2d 572 (1954); Milwaukee & Suburban
Transport Corp. v. Royal Transit Co., 29 Wis. 2d 620,139 N.W.2d
16 Spinks v. Chevron Oil Co., 507 F.2d 216 (5th Cir. 1975).
17 Restatement (Second) of Torts, § 431, comment a, Mitchell
v. Gonzales, 819 P.2d 872, 1 Ca1.Rptr. 2d 913 (1991); State of
Alaska v. Abbott, 498 P.2d 712 (Alaska 1972); Spinks v. Chevron
Oil Co., supra.
18 The Law of Torts, supra, at 267-268.
19 See Lafferty v. Wattle, 349 S.W.2d 519 (Mo. App. 1961); Crislip
v. Holland, 401 So.2d 1115 (Fla. App. 1981); Restatement (Second)
of Torts, § 435 (1).
20 Richman v. City of Berkley, 84 Mich. App. 258, 269 N.W.2d 555
(1978); Newbury v. Vogel, 151 Colo. 520, 379 P.2d 811 (1963); Walsh
v. Snyder, 295 Pa. Super. 94, 441 A.2d 365 (1982).
21 Doe v. Manheimer, 212 Conn. 748, 563 A.2d 699 (1989).
22 See Hook v. Lakeside Park Co., 142 Colo. 277, 351 P.2d 261
(1960); Galioto v. Lakeside Hospital, 123 App.Div.2d 421, 506 N.Y.S.
2d 725 (1986), Roberson v. Counselman, 235 Kan. 1006, 686 P.2d
23 Palsgraf v. Long Island R. Co., 248 N.Y. 339, 162 N.E. 99 (1928);
Alegria v. Payonk, 101 Idaho 617, 619 P.2d 135 (1980); Newton v.
Davis Transport & Rentals, Inc., 312 So.2d 200 (Fla. App. 1975).
24 See also Lacy v. District of Columbia, 424 A.2d 317 (D.C. App.
1980); Restatement (Second) of Torts § 435(2).
25 5424 A.2d at 322.
26 Bramble v. Kleindienst, 357 F. Supp. 1028 (D.Colo. 1973); Pavlinko
v. Yale-New Haven Hospital, 192 Conn. 138, 470 A.2d 246 (1984).
27 508 F. Supp. 897 (D.Colo. 1981), affd, 708 F.2d 502 (loth Cir.
28 508 F. Supp. at 907.
29 Brock v. Merrell Dow Pharmaceuticals, Inc., 874 F.2d 307 (5th
Cir. 1989) modified, 884 F.2d 166 (5th Cir. 1989), reh'g denied,
884 F.2d 167 (5th Cir. 1989); Renaud v. Martin Marietta Corp.,
749 F. Supp 1545 (D.Colo. 1990).
30 Executive Car & Truck Leasing, Inc. v. DeSerio, 468 So.2d
1027 (F1a.App. 1985); GIW Southern Valve Co. v. Smith, 471 So.2d
81 (F1a.App. 1985).
31 Smith v. State Compensation Insurance Fund, 749 P.2d 462 (Colo.App.