one can expect of the average driver." (T. Vol. V., p. 49.)
The second condition Mr. Nagler considered was the fact that the tie rod was bent after the accident, even though he admitted that the final shape of the tie rod did not exist before the accident. (T. Vol. V., p. 46.) No explanation was given for this conclusion.
The most significant condition upon which he based his opinion was the observation of excessive uneven tire wear on the first set of front tires which indicated to him that something was wrong with the steering, suspension and front end alignment. (T. Vol. V., p. 45.) Yet the evidence adduced at trial was that the set of front tires on the Kridler automobile at the time of the accident were not wearing excessively.
In Knapp v. Willys-Ardmore, Inc., 174 Pa.Super. 90, 100 A.2d 105 , the purchaser of an automobile sought to recover the purchase price of his automobile because an alleged defective steering mechanism caused the new car to go out of control and strike a telephone pole. In the eight day period following delivery the plaintiff had driven the car for a total of 107 miles and prior to the accident had no indication of any defects. Plaintiff testified that the car was proceeding normally and suddenly veered to the right. A disinterested third-party corroborated this by testifying that the car suddenly wobbled and that the accident occurred immediately thereafter. On inspection of the car after the collision, a tie rod at the right end of the steering assembly was disconnected and bent and the connecting sleeve was broken. A mechanic testified that the bend in the rod was from a force from below and not from a head-on force. The Court found that the plaintiff had carried the burden of proof as to the inference that the car was defective when delivered and stated that the test of sufficiency of the plaintiff's evidence was whether or not the circumstances shown were such as would satisfy a reasonable mind that the defective condition existed when the automobile was delivered to plaintiff.
In the present case, even with the extenuating circumstances of the car being driven for over 12,000 miles, the fact that Mr. Kridler had struck a deer with the front portion of the car, and the fact that Mr. Nagler found no basic design fault with the tie rod of the Ford Fairlane series, we believe plaintiff under this state of the evidence would be entitled to have the jury determine whether or not the Kridler automobile was defective at the time of its delivery. See also Flavin v. Aldrich, 213 Pa.Super. 420, 250 A.2d 185 ; Topelski v. Universal South Side Autos, Inc., 407 Pa. 339, 180 A.2d 414 .
But having sufficient evidence to support an opinion of a defect in the tie rod does not satisfy all burdens which plaintiff must meet. Plaintiff still carries the burden of proof that the defect was the proximate cause of the accident. For this proof he relies entirely upon the opinion testimony of Mr. Nagler. Mr. Nagler testified in response to a hypothetical question that an appreciable and noticeable distortion of some of the pertinent steering parts was the "major contributing condition". (T. Vol. V., p. 64.) Our concern with this opinion is that it leaves open to the jury's speculation what the other conditions may have been, and whether the alleged defect was in actuality a proximate cause, or whether it was merely a "condition" upon which other and independent causes operated. A number of other possible causes were introduced by defendants, for which the present defendants would not be responsible, the quick application of the brakes by John Kridler, a wet road, a high crown in the road, the skidding and loss of control of the vehicle occurring after the application of the brakes by John Kridler. Basically, Mr. Nagler's opinion relates to a possibility rather than a reasonably certain probability. This is not sufficient.
Where an injury may be the result of one or more causes, for only one of which the other party is responsible, the burden is upon the party alleging such causal relationship to point out the one which was, in fact, the proximate cause of his damage. Therefore, when expert testimony is such as to leave one of two inconsistent inferences possible of adoption by the jury, its decision would be nothing more than a guess and the burden of proof is not met. Mudano v. P.R.T. Co., 289 Pa. 51, 137 A. 104 . In Clark v. Pennsylvania Power & Light Co., 336 Pa. 75, 6 A.2d 892 , it was held that the expert's opinion did not meet the burden of proof as to causation where plaintiff's expert could not testify that defendant's negligence, apart from a probable source of the fire within plaintiff's exclusive control, was the cause of the fire. "To prove a possibility only, or to leave the issue to surmise or conjecture, is never sufficient to sustain a verdict." Rennekamp v. Blair, 375 Pa. 620, p. 627, 101 A.2d 669 .
But, while the plaintiffs' expert's opinion would require the jury to guess as to the cause of the accident, we do not rest our decision on that ground alone because we find a more compelling reason for its exclusion.
An expert's opinion must be based upon facts established in the evidence. If it is not, or if it is based upon assumptions not supported by the evidence, it is worthless. Clark v. Pennsylvania Power & Light Co., supra. Unless the plaintiff produces either directly or inferentially some evidence to support the assumptions of the expert, his opinion must be excluded. In Moyer v. Ford Motor Company, 205 Pa.Super. 384, 209 A.2d 43 , where the expert had no other basis for an opinion than plaintiff's testimony that his brakes failed, the court held that the expert could not testify from this that the brakes had locked or frozen because of improper lubrication or wheel adjustment.
Mr. Nagler's opinion was very clearly based upon an assumption not only not established by the evidence, but in fact contrary to the testimony of plaintiff John Kridler. This involved the sequence of events prior to the accident and dealing specifically with the question of whether plaintiff's car went out of control before or after Mr. Kridler applied his brakes. This is illustrated by the following testimony:
(T. Vol. V., p. 74)