1 PROFESSIONAL NEGLIGENCE CAUSATION: MAKING SENSE OF ATHEY v. LEONATI ). These materials wer.e prepared by Brad Hunter, Pamela Kovacs and NicholasCaan of McKercher MCl(ercher&Whitmore lawfirm, Regina, Saskatchewan for the Saskatchewan Legal EducationSociety Inc. seminar,tort La.w Decisions Highlights,. June :2005..
3 TABLE OF CONTENTS I. Introduction 1 II. Athey: Facts and Judicial History, 2 A. Facts '.' 2 B. Judicial History Trial Division 2 2. Court of Appeal 3 3. Supreme Court of Canada III. Principles of Causation 4 N. Principles of Causation Meet Athey A. The Tests 5 1. But For Test 5 2. Material Contribution Test 6 3. Applying the Tests 6 (a) But For Test Suffices (i) Straightforward Cases.."... 7 (ii) Combined Force Cases 7 (iii) Tortious and Non-tortious Causes Cases 7 (b) Material Contribution Test Required (i) Multiple Sufficient Causes Cases (ii) Independent and Parallel Tortious Conduct Cases 9 4. Medical Malpractice Cases 10 B. Pre-Existing Conditions: The Thin Skull and Crumbling Skull Doctrines C. Standards of Proof: Past Events, Future Events, Hypothetical Events D. Contingencies E. Intervening Causes Non-tortious Intervening Causes Tortious Intervening Causes 16 v. Conclusion 17
5 CAUSATION: MAKING SENSE OF ATHEYV. LEONATI I. INTRODUCTION In an action for negligence, causation identifies the relationship that must be found in fact to exist between the tortious act ofa defendant and the injury suffered by the plaintifffor the plaintiffs claim to succeed. Within the tort system, defendants are liable for injuries caused or contributed to by negligence and plaintiffs are entitled to recover damages that place them into the same position they were pre-injury. Necessarily intertwined into discussions of causation are standards of proof, and pre-existing and intervening causes. Each bears upon whether causation is sufficiently proved and when a defendant will in fact be liable and a plaintiff entitled to damages. Unfortunately, damage assessment is sometimes confusingly dealt with at the liability assessment or causation stage, which has resulted in difficulty interpreting decisions. Athey v. Leonati  3 S.c.R. 458 (Athey) was thought by many to clarify existing principles of causation,l but some concern has also been expressed that the decision favours plaintiffs,2 does not adequately explain the basis of the material contribution test, 3 and in fact confused well-accepted remedial principles. 4 As of May 2005, the decision has been considered 521 times by Canadian courts, indicating its continued importance. The following comments will review principles of causation law, highlight what the Athey decision expressed, and identify cases and commentary that have interpreted and shed light on the Athey decision since Mitchell McInnes, "Causation in Tort Law: A Decade in the Supreme Court of Canada" (2000) 63 Sask. L. Rev. 445 [McInnes]. 2 Terence J. Collier, Susan E. Gunter, Deborah G. Neilson, Jennifer J. Earle, "Causation Sensation... An Updated Guide to Athey" Advocates' Soc. J.:. (Ontario) February 9, 2001 [Collier et al.]. 3 Gillian Demeyere, "The 'Material Contribution' Test: An hnmaterial Contribution to Tort Law: A Comment", Case Comment on Briglio v. Faulkner (2000) 34 U.B.C.L.Rev. 317 [Demeyere]. 4 Dennis Klimchuk & Vaughan Black, "Athey v. Leonati: Causation, Damages, and Thin Skulls" (1997) 31 U.B.C.L.Rev [Klimchuk & Black].
6 -2- II. ATHEY: FACTS AND JUDICIAL HISTORY A. FACTS Athey, a 43 year old man, had a history of minor back problems and worked as an autobody shop manager. In 1991, he was involved in two severe motor vehicle accidents within months of each other where he suffered back and neck injuries. He had pain in both, but responded well to physiotherapy and subsequently his doctor recommended that he return to an exercise program, which he subsequently did. During mild stretching, he suffered a herniated disc and required surgery. Post-surgery, he could not return to the same position he had prior to the accident and found lower paying employment. 5 B. JUDICIAL HISTORY 1. Trial Division (1994),44 A.C.W.S. (3d) 908 The trial judge held that although the accidents were not solely responsible for the disc herniation, they did playa minor causative role and thus awarded 25 percent ofassessed damages including past wage loss, future wage loss, non-pecuniary damages and special damages. There was a finding of fact that, on the balance of probabilities, the accidents contributed in some degree to the disc herniation. The judgment was problematic as the finding on a balance of probabilities that there was a causal link between the accidents and the herniated disc directly contradicted the ultimate finding that the causal link was established at 25 percent, which would not satisfy the burden ofproofrequired on an all or nothing balance of probabilities civil standard. 5 The defendants were represented by the same insurer, so all parties proceeded as though there was a single accident without apportioning fault as between the two accidents.
7 -3-2. Court of Appeal  B.C,J. No. 666 Mr. Athey appealed and claimed that 100 percent ofhis damages should be awarded, following the material contribution test of causation, based on the finding of fact that the negligence of the respondents was a cause ofthe herniation. The Appeal was dismissed outright. 3. Supreme Court of Canada The court ruled unanimously that Mr. Athey was entitled to full recovery based on the finding offact at the trial level that there was a causal link between the accidents and the disc herniation. The issues under consideration were whether the Court of Appeal erred in: (a) Failing to hold that the trial judge's apportionment of causation was a reversible error; and (b) Limiting the scope of judicial review by not considering a theory of liability advanced by the appellant (the material contribution test). These issues directly raised a further question for the court, namely whether the loss could be apportioned between tortious (the accidents) and non-tortious (prior backtrouble) causes where both were necessary to create the injury. The Supreme Court ofcanada ruled that the Court ofappeal and the Trial Judge had both erred and that the disc herniation was a single and indivisible injury - it could not be separated and apportioned. Necessarily, any defendant found to have negligently caused or contributed to the injury was in turn fully liable. This was not a break from traditional causation principles, but rather identified that once causation is established, liability is established and can only be reduced or increased at the assessment of damages stage. Previous conditions, post-negligence events, and future contingencies all influence this stage. This is especially important in the medical context as plaintiffs frequently have underlying conditions affecting future income earning potential and the status of their health.
8 -4- Nevertheless, Athey created discussion because, on its face, a man witha pre-existing back condition received 100% damages for a disc herniation. The decision was criticized as plaintiff-friendly, but several fact-specific findings led to this outcome and need to be placed in proper context. This will be discussed below as will some ofthe major challenges that courts have grappled with post-athey. III. PRINCIPLES OF CAUSATION First, it is useful to identify principles of causation that were expressly identified in Athey: (a) Causation is established when the plaintiff proves to the civil standard on a balance of probabilities that the defendant caused or contributed to the injury (para.13); (b) The general, but not conclusive, test for causation is the but for test, which requires the plaintiff to show that the injury would not have occurred but for the negligence of the defendant (para. 14); (c) The butfor test is unworkable in some circumstances, so the courts have recognized that causation is established where the defendant's negligence "materially contributed" to the occurrence ofthe injury and a contributing factor is material ifit falls outside the de minimus range (para. 15); (d) The causation test is not to be applied too rigidly. It need not be determined by scientific precision but is best determined by ordinary common sense. Although the burden ofproof remains with the plaintiff, in some circumstances an inference of causation may be drawn from the evidence without positive scientific proof (para. 16); (e) It is not necessary for the plaintiffto establish that the defendant's negligence was the sole cause ofthe injury. As long as the defendant is part ofthe cause ofthe injury, the defendant is liable, even though the act alone was not enough to create the injury (para. 17); (f) Apportionment between tortious causes is permitted (para. 22);
9 -5- (g) Apportionmentbetween non-tortious and tortious causes is notpermitted. A defendantdoes not escape liability merely because other causal factors for which he is not responsible also helped produce the harm (paras. 19 and 23); (h) Apportionment is not equivalent to separating distinct and divisible injuries (para. 24); (i) Hypothetical or future events need not be proven on the balance ofprobabilities but are given weight according to their relative likelihood and only if they are a real and substantial possibility and not mere speculation (para. 27); (j) Past events must be proven, and once proven are treated as certainties (para. 28); (k) Independent intervening events reduce damages on the basis that plaintiffs are to be returned to their original position but not one that is better (paras. 31 and 32); (1) Defendants must take victims as they are found (Thin Skull Doctrine) (para. 34); (m) Defendants are not responsible for injuries that would have occurred regardless of the tortious act or omission (Crumbling Skull Doctrine) (para. 35); (n) The Loss of Chance Doctrine is neither approved nor disapproved (para 38). IV. PRINCIPLES OF CAUSATION MEET ATHEY At its most basic, causation connects the tortious act in question and the loss or damage suffered. It requires an act or omission by the defendant that in turn causes the plaintiff's loss, entitling them to be put into the position they were pre-injury, but not one that is better. The principles ofcausation identified aboveworktoestablish whetherliabilitywill attach, buttheyare notwithoutcontroversy. A. THE TESTS 1. But For Test The general determinant of causation is the butfor test: but for the defendant's action, would the plaintiff have been injured? If the answer is yes, then causation is not established and the defendant's actions did not cause the harm suffered by the plaintiff as the damage would have occurred regardless. If the answer is no, then causation is established as the defendant's actions caused the harm suffered. This test first came to light in Newis v. Lark (1571),2 Plow. 403.
10 -6- The butfor test proceeds on the balance of probabilities, meaning that the plaintiff must establish that it is more probable than not that the defendant's tort was the cause of the injury. This is often referred to as the all or nothing standard, as the defendant is fully liable ifthe butfor test is met but escapes liability if it is not. 2. Material Contribution Test Defendants escaping liability under the butfortest caused courts pause and in turn they decided that the test does not work in all cases. An exception to its general application developed in response to cases where a butfor analysis unfairly relieved defendants from liability. The standard example is Cook v. Lewis  S.c.R. 830 where application of the but for test would have relieved two individual tortfeasors from liability after they simultaneously shot at the plaintiff. Using the standard test, it could not be proven who was the shooter as the plaintiffonly suffered one bullet wound. The court held that both defendants must be found liable as both contributed to the tort and allowing both to go free would create too large an injustice. This has also been referred to as alternative liability. 3. Applying the Tests In the Athey decision, it remains unclear which test was applied by the court in order to arrive at a conclusion of causation. Commentators have argued that the material contribution test is not well enough defined and that a simple butfor analysis would have sufficed under the Athey fact scenario without muddying the waters. 6 The butfor test remains the standard in negligence actions, butthere exists confusion over when it is appropriate to break away from the standard analysis. Athey has been criticized for not explicitly stating when a butfor analysis will not suffice: "the butfor test is unworkable in some circumstances, so the courts have recognized that causation is established where the defendants 'materially contributed' to the occurrence ofthe injury.,,7 Demeyere questions what 6 See Klimchuk & Black supra note 4 at para. 9 and Demeyere supra note 3 generally. 7Athey at para. 15.
11 -7- the circumstances are, what standard is set by the test, and how it differs from the but for test?8 Other commentators focus on the classification of one-cause tortious claims from multiple-cause tortious claims. 9 Commentators Klimchuk and Black offer five fact scenarios that identify when each test should be applied: (a) But For Test Suffices (i) Straightforward Cases: There is one defendant, one average skulled plaintiff, and no unusual background conditions. (ii) Combined Force Cases: There are two or more defendants, neither ofwhich individually could be a tortfeasor without the other. Each thus contributes to the state of affairs causing the plaintiffs suit. Klimchuk and Black offer Lambton v. Mellish  3 Ch.D. 163 as an illustrating case. Here two street vendors playing organs produced sufficient noise to base a suit in nuisance, but neither street vendor was the sole contributor. It was the combined effect that resulted in the claim and but for each vendor's playing, there would not have been a tort. A butfor analysis suffices in this type of situation. (iii) Tortiousand Non-tortious Causes Cases: There is an identifiable tortious cause as well as other non-tortious causes that may have contributed to the plaintiff's injury. So long as the defendant's act is a cause of the plaintiff's damage, it need not be proven that the defendant is the sole or predominant cause of the injury. Klimchuk and Black suggest Bonnington Castings  AC. 613 (H.L.) (Bonnington) is the appropriate example to illustrate this category and criticize the ruling in Athey that this type ofscenario makes 8Demeyere supra note 3 uses Briglio v. Fauklner (1999),69 B.c.L.R. (3d) 122 as a case in which application of the material contribution test was used incorrectly on the basis of the Athey decision. 9 See generally Collier et al. supra note 2,
12 -8- the butfor test unworkable. In Bonnington, the defendant inhaled particles from operating a hammer and from swing grinders operating near him while at work in a foundry. Under statutory duty, the dust from the swing grinders was to have been removed, but the dilemma was how to prove whether the plaintiff's resulting pneumoconiosis was a result ofthe hammers or the swing grinders? The ruling indicated that contribution by the tortious cause was beyond a de minimus range and thus materially contributed to the plaintiff's injury. Klimchuk and Black argue that a straightforward application of the butfor test would have resulted in the same finding. Put another way, but for the operation of the swing grinders, the plaintiff would not have had sufficient exposure to particles to contract the injury. (b) Material Contribution Test Required (i) Multiple Sufficient Causes Cases: Here it cannot be shown whether or not the act or omission was the butfor cause of the plaintiffs injury but there is evidence that the act or omission contributed to the injury. Klimchuk and Black offer McGhee v. National Coal Board  3 All E.R.1008 (H.L.) [McGhee] as the illustrating case. Here McGhee laid brick and contracted dermatitis following exposure to dust from kilns. The likelihood of injury increased the longer the skin was in contact with the dust and the defendant employer did not provide showering facilities, which was the basis for the action. It was impossible to prove, however, whether McGhee would have contracted the disease regardless of the availability of showering facilities. There was potential for the employer to escape liability as a butfor analysis revealed only that but for the lack of showering facilities, the risk of injury still would have existed. Essentially the test was silent in terms of assigning liability. The court held that the employer's omission did materially contribute to the risk that the injury would be suffered even ifit did not prove
13 -9- (ii) material contribution to the injury. This case was for a time held to mean that the burden of proof was reversed in such situations and the defendant was then required to prove that the negligence was not a cause ofthe loss. Snell v. Farrell  2 S.c.R. 311 (Snell) halted the reversal ofthe burden ofproof, but did allow for a more flexible approach to causation rules - a more pragmatic and common-sense approach. Snell also identified that when the facts lie particularly within the knowledge ofthe defendant, little affirmative evidence is required and without evidence contradicting the causation, an inference of causal connection is warranted. This was affirmed in Athey. Independent and Parallel Tortious Conduct Cases: Here, each defendant's contribution is individually sufficient in order for the tort to occur. Klimchuk and Black suggest the case of Corey v. Havener 65 N.B. 69 (Mass. S.J.c. 1902) applies. The plaintiff was injured when his horse bolted after the defendant's passed on either side of him while riding motorcycles. Each defendant could escape liability by claiming that his contribution was not necessary in order for the injury to have occurred - it would have occurred anyway due to the other rider. As in McGhee, the butfor test proved limited in its application and provided a defence that allowed escape from liability. Cook v. Lewis, supra also falls into this category. In summation, Klimchuk and Black would reserve material contribution causation cases "for circumstances where the but for test is frustrated by the facts, but the defendant's actions clearly played an important causal role in producing the plaintiff's injury." 10 They also argue thatathey falls underthe thirdcategorywhere the analysis is between non-tortious and tortious causal factors and thus need not be within thematerialcontributiontest at all. Theysuggestthatthenon-tortiousfactors 10 Supra note 4 at para. 18.
14 -10- were the pre-existing back condition and the stretching exercises even though the Athey decision characterizes the stretching as the effect or injury and not the cause. 4. Medical Malpractice Cases Medical malpractice cases are a unique area in causation and are identified below as possible exceptions to the Crumbling Skull Doctrine. It is outside the scope ofthis paper to address fully the standards and specific rules thathave been bought into medical malpractice cases (specificallyfailure to warn and informed consent cases), but there are some basic principles that have been identified and shed light on the causation area. In Snell, it was identified that there are difficulties in proving causation for the medical malpractice patient. The physician is usually in a better position to know the cause ofthe injury than the patient and there was historically an argument that the burden of proof should thus be allocated to the defendant. This was not subsequently ultimately applied by the courts, but there was a definite recognition that proof need not be established to a scientific precision and that common sense interpretation of the facts would yield better results. In Walker Estate v. York Finch General Hospital  1 S.C.R. 647 (Walker Estate) the plaintiffs contracted HIV from tainted blood supplied by the Canadian Red Cross Society. The Court maintained that the appropriate test was whether the defendant's conduct materially contributed to the plaintiff's injury. In cases of negligent donor screening, it is difficult to prove what the donor might have done if he or she had been properly screened, making the butfor test unworkable. As commentators Browne and Dawe mention: "this case clarifies (somewhat) the application of the 'material contribution' test. Defense counsel might use Walker Estate as authority for the position that the 'material contribution' test is not merely a stop-gap measure whenever the plaintiff can not make out causation using the but for test. Rather the application for the material contribution test should be limited to narrow situations where the butfor test
15 -11- is simply not workable on the facts. In Walker Estate, the courtstated: 'the unique difficulties in causation make this area ofnegligence [donor screening] atypical.",ii B. PRE-EXISTING CONDITIONS: THE THIN SKULL AND CRUMBLING SKULL DOCTRINES Athey clearly affirmed the understanding that a defendant is required to take the plaintiffas they are found. In this instance, Mr. Athey had a twenty year history ofback trouble (his thin skull) and his original position going into the accidents included this reality. Necessarily, the defendants were liable for the full loss even though the back condition pre-existed. His pre-injury position included his existing back trouble. Often thought of as the exception to the Thin Skull Doctrine, the Crumbling Skull Doctrine recognizes that a tortfeasor is liable only for the damages caused by their tort and not for pre-existing conditions that would have manifested themselves anyway. Essentially, defendants are not required to over-compensate for that which would have occurred regardless ofthe tort and is outside the realm of their liability for damages. On the facts, there was no evidence that Mr. Athey would have been subject to a disc herniation simply because ofhis prior back pain. The disc herniation resulted from his involvement in the motor vehicle accidents. If there was evidence that he was likely to have herniated a disc at some point in the future, then the Crumbling Skull Doctrine would apply and limit the damages to that which directly followed the tort. In medical malpractice cases, some have suggested that the Crumbling Skull Doctrine should not apply as the "negligent treatment complained ofis a failure to act - as opposed to a positive negligent act. The point of the medical treatment sought is to alleviate that very 'crumbling skull' and application of the doctrine works as an injustice to the plaintiff.,,12 11 Peter N. Browne & Curtis Dawe, Biennial Review ofkey Developments (Key Rulings & Developments on Damages, Limitations, Standard ofcare and Causation): Athey v. Leonati: How to Effectively Deal With Thin Skulls, Crumbling Skulls andnumbskulls [paper] at 5 [Browne & Dawe]. 12 See generally Collier et.al supra note 2 at para. 20.
16 -12- c. STANDARDS OF PROOF: PAST EVENTS, FUTURE EVENTS, HYPOTHETICAL EVENTS The Court in Athey held that hypothetical events (such as how the plaintiff's life might have proceeded without the tortious injury) or future events need not be proven on a balance of probabilities but that past events must be proven to the civil standard and are then treated as certainties. In Athey, the disc herniation occurred prior to trial and was a past event which could not be addressed in terms of probabilities. In Rosvold v. Dunlop  B.C.J. No.4 (C.A.) the court, applying Athey held: "the standard of proof to be applied when evaluating hypothetical events that may affect an award is simple probability, not the balance of probabilities. Possibilities and probabilities, chances, opportunities and risks must all be considered, so long as they are real and substantial possibility not mere speculation. These possibilities are to be given weight according to the percentage chance they would have happened or will happen.,,13 This discussion becomes important in the context ofincreasing or decreasing damage awards on the basis of relative likelihood and substantial possibility of occurrence for future and hypothetical events. As the Athey decision highlights: "had the trial judge concluded (which she did not) that there was some realistic chance that the disc herniation would have occurred at some point in the future without the accident, then a reduction of the overall damage award may have been considered... however, in the absence of such a finding, it remains speculative and need not be taken into consideration.,,14 As will be discussed below, many commentators question whether this was the appropriate finding on the facts. 13 Rosvold v. Dunlop supra at para Athey at para. 48.
17 -13- D. CONTINGENCIES Browne and Dawe point out that "determining tortious responsibility for the damage done, and assessing the ultimate responsibility for damages payable, although intertwined, often entail separate considerations ofcausal factors." 15 This is a requisite separation ofstages between assessing liability and assessing damages that courts sometimes overlap with confusing consequences for the jurisprudence. McInnes suggests that "if the evidence had established a 30% chance that Athey eventually would have suffered the same loss, even in the absence ofthe defendant's negligence, his damages would have been reduced accordingly" and cites Andrews v. Grand & Toy Alberts Ltd.,  2 S.c.R. 229 at 253 (Andrews) as authority. He further suggests that "if the evidence had established a 30% chance that Athey's disability, caused by the defendant, would worsen in the future, his damages would have been increased accordingly" and cites Schrump v. Koot (1977),82 D.L.R. (3d) 553 (Ont. c.a.) as authority.16 Klimchuk and Black argue that a downward adjustment in damages was required in Athey in order to comply with the Supreme Court's ruling in Andrews where it was held that lost or future earnings damages should alsotakeinto accountcontingencies thatmayhave affectedfuture earnings (such as a bad back). This would not have affected the 100% causal liability of the defendants, it merely would have recognized that Athey did not have a good back to begin with and the defendants should not be responsible for a condition that may have affected him into the future. This is not to be confused with the causal analysis of the plaintiff under the Thin and Crumbling Skull Doctrines. 15 Browne & Dawe supra note 11 at McInnes supra note 1at para. 18.
18 -14- The decision in Athey declined imposition of a contingency deduction explicitly on the basis that a finding offuture disc herniation was too speculative on the facts, but the ruling is very fact-specific and does not preclude considering pre-existing conditions at both the causation and the damages stages. In Gardnerv. John  O.J. No (Gen. Div.) the court required more extensive evidence that the subject injury materially contributed to the current injury given the pre-existing backinjury. In Athey, something more than "speculative" may have resulted in a decrease in damages and Andrews suggests that contingency deductions should consider future illness, not merely the chance that an identical injury would have been suffered by the plaintiff. "Although the principle that defendants must take victims as they find them benefits plaintiffs at the causation stage (by resulting in finding that the defendant caused a given injury, even though a plaintiffofaverage constitution might not have suffered any injury), at the damages assessment stage it benefits defendants.,,17 The Athey decision also mentions Graham v. Rourke (1990), 74 D.L.R. (4 th ) 1 (Ont. c.a.) (Graham) which identified that it is not appropriate to treat the plaintiff as thin skulled at the causation stage and then to not consider this same treatment at the damages stage as the result would be to treat the plaintiff as a normal healthy person when assessing future pecuniary loss. Klimchuk and Black argue that the Athey decision improperly applied this principal from Graham and also suggest that while the Athey decision was: "on firm ground in noting that on the question ofcausation, the causal status ofthe defendants' actions should be determined on an all or nothing (balance of probabilities) basis, that does not mean that once the causal hurdle is crossed and the damage assessment process begins, other causal candidates - here the pre-existing bad back and the health club incident - can no longer be relevant.,,18 They further go on to suggest that: 17 Klimchuk & Black supra note 4 at Klimchuk & Black supra note 4 at para. 29.
19 -15- "in Athey the defendants' actions were straightforward but for causes of the plaintiff's injury. The condition ofthe plaintiff's back, at the assessment ofliability stage, does not constitute a competing cause, but is instead one ofthe conditions that formed the context of the defendant's actions and shaped the contours of the consequences ofthose actions; this much is required by the Thin Skull Rule. On the other hand, as one of these conditions, the plaintiff's back is also an aspect of the original position to which the compensation principle requires the defendants to return the plaintiff. The plaintiff's literal or metaphorical thin skull gives no defence to liability, partial, or complete, but it can warrant a reduction in damages. The application of the but for causation test and adherence to well-accepted remedial principles would have resolved Athey more simply, more fairly and with a less confusing message for lower courts.,,19 A proper approach, in law, is evidenced by Chesherv. Monaghan (1999), Carswell Ont (April 12, 1999) (Ont. H.C.). Here the plaintiff suffered a knee injury while waterskiing and the physician at the hospital examined the leg, took x-rays and discharged the plaintiff. The following day, at a different hospital, surgery was ordered and the need for further vascular surgery was required due to a completely avulsed peroneal nerve and tear of the popliteal artery. Post surgery and after a long period ofhospitalization, the plaintiff's leg required amputation below the knee. A suit followed on the basis that negligence caused or contributed to the loss ofthe leg. It was held that damages were payable but they were reduced by 25 percent as this equated to the chance that the severity of the original trauma would have led to amputation anyway. E. INTERVENING CAUSES In Athey, it was held that the return to the exercise routine was not an intervening cause, but rather the product of the accidents and therefore not an independent intervening event. When the test for causation is met, then the loss must be compensated. The loss is the difference between the plaintiff's original position (including pre-existing conditions) and the position they are in following the tort. In between are intervening causes that may affect the plaintiff's final position, but once causation is established, and a defendant is found liable for the injury or contributed to the injury by 19 Ibid. at 30.
20 -16- negligence, then the defendant is 100% liable. Reduction ofthis liability only occurs outside ofthe causation analysis in remoteness or with contingency adjustments. This liability may also be spread among defendant's should they be non-severable. 1. Non-tortious Intervening Causes Even prior to Athey, it has always been understood that a subsequent non-tortious injury suffered by the plaintiff is a relevant fact and interrupts the chain of causation so as to end the defendant's liability for subsequent injuries occurring outside ofthe tortious act ofthe defendant. This follows basic tort principles that impose liability only for those acts actually caused by the defendant. 2. Tortious Intervening Causes Some confusion has followed the Athey decision on the basis of the holding that "the law does not excuse a defendant from liability merely because other factors for which he is not responsible also helped produce the harm... it is sufficient ifthe defendant's negligence was a cause ofthe harm.,,20 The principle applies when the injuries caused by a number offactors are indivisible as in the case of E.D.G. v. Hammer  2 S.C.R Alderson v. Alllaghan (1998),40 O.R. (3d) 136 (C.A.) interpreted Athey to mean that subsequent tortious events did not relieve the defendant from full responsibility. The case referred to the Negligence Act, but Collier et al. point out that the application ofthe Negligence Actis only appropriate where there are multiple tortfeasors, not where there are multiple tortious events. Non-apportionment between tortious and non-tortious causes is one of those confusing areas that have plagued Athey. As Browne and Dawe suggest "it is imperative for defence counsel to recognize the principle's narrow application and effectively distinguish between situations where the defendant 20 Athey at para. 19.