*77(Emphasis omitted.) Sherman v. Ronco , 294 Conn. 548, 554 n.10, 985 A.2d 1042 (2010).
**207"The relation back doctrine has been well established by this court." Alswanger v. Smego , 257 Conn. 58, 64, 776 A.2d 444 (2001). There is a " 'well settled' body of case law holding that 'a party properly may amplify or expand what has already been alleged in support of a cause of action, provided the identity of the cause of action remains substantially the same. ... If a new cause of action is alleged in an amended complaint ... it will [speak] as of the date when it was filed. ... A cause of action is that single group of facts which is claimed to have brought about an unlawful injury to the plaintiff and which entitles the plaintiff to relief. ... A change in, or an addition to, a ground of negligence or an act of negligence arising out of the single group of facts which was originally claimed to have brought about the unlawful injury to the plaintiff does not change the cause of action .... It is proper to amplify or expand what has already been alleged in support of a cause of action, provided the identity of the cause of action remains substantially the same, but [when] an entirely new and different factual situation is presented, a new and different cause of action is stated.' ... DiLieto v. County Obstetrics & Gynecology Group, P.C. , 297 Conn. 105, 140, 998 A.2d 730 (2010)." (Emphasis in original; footnote omitted.) Finkle v. Carroll , 315 Conn. 821, 837-38, 110 A.3d 387 (2015).
"Our relation back doctrine provides that an amendment relates back when the original complaint has given the party fair notice that a claim is being asserted stemming from a particular transaction or occurrence, thereby serving the objectives of our statute of limitations, namely, to protect parties from having to defend against stale claims .... Barrett v. Danbury Hospital , 232 Conn. 242, 263-64, 654 A.2d 748 (1995)." (Internal quotation marks omitted.) Alswanger v. Smego , supra, 257 Conn. at 65, 776 A.2d 444. "[I]n the cases in which we have **208determined that an amendment does not relate back to an earlier pleading, the amendment presented different issues or depended on different factual circumstances rather than merely amplifying or expanding upon previous allegations." Grenier v. Commissioner of Transportation , 306 Conn. 523, 560, 51 A.3d 367 (2012).
More specifically, where the proposed allegations promote a change in or an addition to a ground of negligence arising out of a single group of facts we have allowed use of the relation back doctrine. Gurliacci v. Mayer , 218 Conn. 531, 549, 590 A.2d 914 (1991) ("new allegations did not inject two different sets of circumstances and depend on different facts ... but rather amplified and expanded upon the previous allegations by setting forth alternative theories of liability" [citation omitted; internal quotation marks omitted] ); see DiLieto v. County Obstetrics & Gynecology Group, P.C. , supra, 297 Conn. at 139-43, 998 A.2d 730 (allegation that defendant physician failed to ensure that specific surgeon participated in surgery related back to allegation that defendant physician failed to communicate pathology results to that surgeon prior to surgery); Wagner v. Clark Equipment Co. , 259 Conn. 114, 119, 788 A.2d 83 (2002) (allegation that forklift was defective because backup alarm failed to sound when forklift was engaged in reverse did relate back to allegations that forklift was defective because it lacked, inter alia, backup alarm that sounded sufficiently distinct to warn plaintiff);
*78Barnicoat v. Edwards , 1 Conn.App. 652, 654, 474 A.2d 808 (1984) (allegations of different defects in house construction related back to other claims of defect in house construction in breach of contract claim); Miller v. Fishman , 102 Conn.App. 286, 299-300, 925 A.2d 441 (2007) (allegations describing specific manner in which defendant obstetrician delivered minor plaintiff and precise injuries minor plaintiff sustained related back to allegations that defendant negligently managed delivery **209of minor plaintiff), cert. denied, 285 Conn. 905, 942 A.2d 414 (2008). On the other hand, where new allegations directly contradict those in the operative complaint we have held that they do not relate back to those in the operative complaint. Dimmock v. Lawrence & Memorial Hospital, Inc. , 286 Conn. 789, 806-808, 945 A.2d 955 (2008) (allegation that defendant surgeons used incorrect spinal fusion material during surgery contradicted, and therefore did not relate back to, allegation that surgeons should not have performed surgery at all on plaintiff); see also Alswanger v. Smego , supra, 257 Conn. at 61, 776 A.2d 444 (allegation of lack of informed consent regarding surgical resident's participation in surgery did not relate back to allegation that defendant physician and defendant hospital had failed to disclose all material risks in connection with plaintiff's surgery, care and treatment); Keenan v. Yale New Haven Hospital , 167 Conn. 284, 285-86, 355 A.2d 253 (1974) (allegation of lack of informed consent to surgery did not relate back to allegation of negligence in performing surgery).
"When comparing [the original and proposed amended] pleadings, we are mindful that, '[i]n Connecticut, we have long eschewed the notion that pleadings should be read in a hypertechnical manner. Rather, [t]he modern trend, which is followed in Connecticut, is to construe pleadings broadly and realistically, rather than narrowly and technically. ... [T]he complaint must be read in its entirety in such a way as to give effect to the pleading with reference to the general theory upon which it proceeded, and do substantial justice between the parties. ... Our reading of pleadings in a manner that advances substantial justice means that a pleading must be construed reasonably, to contain all that it fairly means, but carries with it the related proposition that it must not be contorted in such a way so as to strain the bounds of rational comprehension.' ... Deming v. Nationwide Mutual Ins. Co. , [279 Conn. 745, 778, 905 A.2d 623 (2006) ]."
**210Dimmock v. Lawrence & Memorial Hospital, Inc. , supra, 286 Conn. at 802, 945 A.2d 955.
We acknowledge that in our prior cases applying the relation back doctrine we perhaps have not provided as much clarity as necessary for the trial court to apply the doctrine consistently. After a careful review of our case law, it is apparent that in order to provide fair notice to the opposing party,9 the proposed *79new or changed allegation of negligence must fall within the scope of the original cause of action, which is the transaction or occurrence underpinning the plaintiff's legal claim against the defendant. Determination of what the original cause of action is requires a case-by-case inquiry by the trial court. In making such a determination, the trial court must not view the allegations so narrowly that any amendment changing or enhancing the original allegations would be deemed to constitute a different cause of action. But the trial court also must not generalize so far from the specific allegations that the cause of action ceases to pertain to a specific transaction or occurrence between the parties that was identified in the original complaint. While these guidelines are still broad, a bright line rule would not serve the purpose of promoting substantial justice for the parties.10 **211If new allegations state a set of facts that contradict the original cause of action, which is the transaction or occurrence underpinning the plaintiff's legal claim against the defendant, then it is clear that the new allegations do not fall within the scope of the original cause of action and, therefore, do not relate back to the original pleading. But an absence of a direct contradiction must not end the trial court's inquiry. The trial court must still determine whether the new allegations support and amplify the original cause of action or state a new cause of action entirely. Relevant factors for this inquiry include, but are not limited to, whether the original and the new allegations involve the same actor or actors, allege events that occurred during the same period of time, occurred at the same location, resulted in the same injury, allege substantially similar types of behavior, and require the same types of evidence and experts.
In the present case, the plaintiff alleged in paragraph 36 of count one of the original complaint that Kruger was negligent in one or more of the following ways:
"A. [He] failed to plan a safe and effective operation.
"B. [He] failed to perform a safe and effective operation.
"C. [He] failed to position [the plaintiff] safely and securely on the operating table; and/or
"D. [He] failed to make sure the skull clamp was safely and securely applied to [the plaintiff's] skull; and/or
"E. [He] failed to make sure the locking device connecting the skull clamp to the [operating room] table was safely and securely applied; and/or **212"F. [He] failed to make sure that [the plaintiff's] positioning [in the surgical table apparatus] was safe and secure; and/or
"G. [He] failed to make sure that [the plaintiff] would not move during the surgery."
In support of his res ipsa locquitor claim, the plaintiff additionally alleged in paragraph 36 of count three of the original complaint that his injury could be presumed to be due to the defendants' negligence because:
"A. The damage to [the plaintiff's] spinal cord at [C3 through C5] is ordinarily *80not seen in the course of surgery at [C6 through C7] in the absence of someone's negligence.11
"B. The injuries were caused by an instrumentality solely within the defendants' control;
"C. The injury was not due to any voluntary action or contribution by [the plaintiff]; and
"D. The explanation of the event is more accessible to the defendants than to [the plaintiff]." (Footnote added.)
In his proposed amended complaint, the plaintiff replaced the allegations of negligence in count one of the original complaint with the following allegations found in paragraph 45 of count one of the amended complaint:
"A. [Kruger] failed to plan a safe and effective operation, and/or
"B. [He] failed to perform a safe and effective operation, and/or
"C. [He] failed to apply the retractor at [C3 through C4] properly, and/or **213"D. [He] failed to apply the retractor at [C3 through C4] properly so that the blades would not shift when the retractor was opened.
"E. The operative note is not a reasonably complete and accurate account of what happened during surgery.
"F. The discharge summary is not a reasonably complete and accurate account of what happened during [the plaintiff's] hospitalization."
The relevant allegations in the res ipsa locquitor claim contained in count three of the amended complaint remained the same as the allegations from the original complaint.
In construing the original complaint, we hold that the plaintiff's cause of action is that Kruger negligently performed spinal surgery on the plaintiff, resulting in the plaintiff's injuries. While count one of the original complaint does focus on improper use of the skull clamp, read as a whole it includes more general allegations that Kruger failed to properly perform the surgery.12 Further, looking to the original complaint as a whole, the plaintiff provided additional notice of the nature of his cause of action to the defendants through his allegations in the res ipsa locquitor count that his injuries were caused by an instrumentality solely in Kruger's control when he performed the surgery on the plaintiff's spine. At the very least, this additional count put the defendants on notice that the plaintiff's claim was not limited to the skull clamp allegations. Reading the two counts together, the transaction or occurrence **214that formed the basis of the plaintiff's claim was that Kruger improperly used medical instruments during the plaintiff's spinal surgery, resulting in his injury. Therefore, the plaintiff adequately put the defendants on notice that his claim related to Kruger's conduct during the surgery and, more specifically, his use of medical instruments during the surgery.
The plaintiff's amended complaint added new allegations that Kruger improperly used the retractor blade during surgery *81and removed the allegations related to the skull clamp. The retractor blade allegations do not contradict the theory that Kruger improperly used medical instruments during surgery. Instead, they constitute a change in and addition to an act of negligence, which is permitted under the relation back doctrine. Specifically, the single transaction or occurrence that constituted the cause of action was the negligent use of medical instruments during the plaintiff's spinal surgery in the operating room by Kruger, and this negligence caused the plaintiff to suffer quadriparesis.13
For the foregoing reasons, we conclude that the Appellate Court properly held that the amended complaint related back to the original complaint and that the trial court's denial of the plaintiff's request to amend and its subsequent granting of the defendants' motion for summary judgment should be reversed.
**215The judgment of the Appellate Court is affirmed.
In this opinion PALMER, EVELEIGH, McDONALD and ESPINOSA, Js., concurred.