Appeal from the United States District Court for the District of Columbia (No. 1:23-cv-03381)

Governor E. Jackson III argued the cause for appellant. On the briefs was Kim Parker .

Peter R. Naugle argued the cause for appellees. With him on the brief was Derek M. Stikeleather . Donna Sturtz entered an appearance.

Before: MILLETT, WILKINS and KATSAS, Circuit Judges .

Opinion for the Court filed by Circuit Judge WILKINS.

Page 2WILKINS, Circuit Judge : This appeal arises from a medical malpractice action brought on behalf of Kevin Welch against MedStar Washington Hospital Center, Dr. Stephen Luczycki, Dr. Maxwell Hockstein, and Dr. Kaitlyn Dunphy (collectively, 'the Hospital'). The Complaint alleged that Intensive Care Unit ('ICU') providers failed to implement timely stroke-mitigation measures following Mr. Welch's emergency Type A aortic dissection repair, resulting in permanent neurological injury. The District Court excluded the causation testimony of Mr. Welch’s experts under Federal Rule of Evidence 702 and Federal Rules of Civil Procedure 26(a)(2) and 37(c)(1). Since medical malpractice suits brought in the District of Columbia require expert testimony to establish causation and the only proffered causation experts’ testimony was deemed inadmissible, the District Court granted summary judgment in favor of the Hospital. Mr. Welch's appeal challenges the exclusion of the testimony and the grant of summary judgment.

On June 14, 2022, 42-year-old Kevin Welch presented with severe chest pain and was diagnosed with an ascending aortic dissection requiring emergency surgery. App.012-14. The operation included six different procedures, with the primary procedure being a Type A aortic dissection (“TAAD”) repair. App.014. The procedures were completed “without any complication[s].' Id. Mr. Welch was intubated and transferred to the ICU in “critical but stable condition” under the care and supervision of ICU attending physician Dr. Hockstein, critical care physician Dr. Luczycki, as well as surgical ICU rotating resident Dr. Dunphy. Id.

Page 3On June 15, Mr. Welch woke up confused and disoriented—not fully understanding where he was or why he was in the hospital. Id. By June 16, his physicians expressed concern about possible changes in brain activity. Id. ; see also App.041. The next day, after Mr. Welch began 'exhibiting severe bi-lateral lower extremity weakness,' he underwent a neurology consultation. App.015. Following the examination, and due to a “concern for spinal cord infarct” (i.e., a stroke that occurs in the spinal cord), neurology recommended performing magnetic resonance imaging ('MRI') and a head computed tomography ('CT'); however, the MRI was not performed because Mr. Welch was showing improvement and because of 'safety reasons.' Id. ; see also App.041. According to the Hospital, the MRI was deferred because the procedure required transport outside the ICU, reduced monitoring, and removal of epicardial lead wires needed for blood-pressure management— all of which were not considered safe unless Mr. Welch was at a certain level of stability. Appellees’ Br. 4; App.160. Over the next few days, the MRI was deferred again for safety reasons and because Mr. Welch’s blood pressure was “under better control.” App.016.

The MRI performed on June 22 indicated that Mr. Welch had suffered a stroke. App.016–17. Mr. Welch alleges that, prior to June 21, no actions were taken “to increase [his] blood pressure to mitigate the risk of neurological insult,” nor did the Hospital consider “the placement of a lumbar drain to mitigate the risk of neurological insult' prior to June 22. App.041 (citing App.017).

A little over two weeks later, Mr. Welch was transferred to MedStar National Rehabilitation Hospital for treatment of residual functional impairments and was discharged in September with instructions to obtain occupational, physical, and speech therapy. App.017.

Page 4Throughout the litigation, Mr. Welch maintained that he “continues to struggle with executive functioning, apathy, and visual-spatial issues.' App.042; see also Appellant's Br. 5 (quoting a letter stating that Mr. Welch is 'permanently disabled'). The Hospital responds that the record reflects substantial improvement in Mr. Welch's physical condition, including examinations showing 'full range of motion and strength in all extremities,” no focal deficits, and an ability to 'independently perform all of his activities of mobility and daily living.” Appellees’ Br. 5. Further, the Hospital contends that the reference to “permanent[] disab[ility]” concerns “ cognitive issues,' rather than the lower-extremity weakness on which Mr. Welch principally bases his medical-malpractice claims. Id. at 5–6 (emphasis in original). In support of this contention, the Hospital notes that, in an examination note by one of Mr. Welch's physicians, Mr. Welch exhibited 'full range of motion and strength in all extremities.' Id. at 5.

Ms. Shana Hargrove, as power of attorney for Mr. Welch, filed suit in District Court in November 2023, alleging that the Hospital negligently failed to recognize, diagnose, and treat Mr. Welch’s strokes. See, e.g. , App.001, 009–27. Mr. Welch specifically asserts that the Hospital “prolonged the performance of [an MRI],' 'fail[ed] to take steps to control [his] blood pressure,” and “fail[ed] to document and/or otherwise place a lumbar drain,” all of which exacerbated the consequences of his stroke. App.019–21.

At the close of discovery, the Hospital filed two motions in limine to exclude the testimony of two of Mr. Welch's experts, Dr. Ahmad Elakil and Dr. Peter Schulman, addressed to proximate causation and damages. Mr. Welch opposed both motions. Following responses from Mr. Welch, the Hospital Page 5moved for summary judgment on the grounds that if Dr. Elakil and Dr. Schulman's testimony were excluded, Mr. Welch would be unable to successfully prove his medical malpractice claims. On August 7, 2025, the District Court granted the Hospital's motions in limine, excluding Dr. Elakil and Dr. Schulman’s testimony under Federal Rule of Evidence 702 as well as Federal Rules of Civil Procedure 26(a)(2) and 37(c)(1), respectively, and granted the Hospital’s motion for summary judgment. See, e.g. , App.040–59. Mr. Welch filed this timely appeal on September 5, 2025.

We have jurisdiction to review this case under 28 U.S.C. § 1291.¹ And we begin our review with Mr. Welch's contention that the District Court improperly excluded Dr. Elakil’s expert testimony under Federal Rule of Evidence 702. We disagree and sustain the District Court's decision to exclude Dr. Elakil’s testimony.

Page 6We review a district court’s decision to admit or exclude expert testimony under Daubert v. Merrell Dow Pharms., Inc. , 509 U.S. 579, 597 (1993), for abuse of discretion. Kumho Tire Co., Ltd. v. Carmichael , 526 U.S. 137, 142 (1999). We “must … afford trial judges great discretion” in admitting or excluding expert testimony. United States v. Morgan , 45 F.4th 192, 200 (D.C. Cir. 2022) (quoting United States v. Day , 524 F.3d 1361, 1367 (D.C. Cir. 2008)).

Federal Rule of Evidence 702 vests district courts with a “gatekeeping role” to “ensur[e] that an expert’s testimony both rests on a reliable foundation and is relevant.” Daubert , 509 U.S. at 597. Under Rule 702, a witness may be qualified as an expert based on 'knowledge, skill, experience, training, or education.” FED. R. EVID. 702. Before admitting Dr. Elakil’s expert testimony, the District Court was required to determine that the proponent had demonstrated, by a preponderance of the evidence, that the testimony would be (a) “help[ful] [to] the trier of fact to understand the evidence or to determine a fact in issue,” (b) “based on sufficient facts or data,” (c) “the product of reliable principles and methods,” and (d) “reflect[] a reliable application of the principles and methods to the facts of the case.' Id. ; FED. R. EVID. 702 advisory committee's note to 2023 amendment 2 (citing Bourjaily v. United States , 483 U.S.

Page 7171, 175 (1987)). The Supreme Court in Daubert explained that the requirements of relevance and reliability must be 'established by a preponderance of proof' pursuant to Rule 104(a). 509 U.S. at 592 n.10. We likewise applied that standard before the 2023 amendment made it explicit. Meister v. Med. Eng’g Corp. , 267 F.3d 1123, 1127 n.9 (D.C. Cir. 2001) (quoting Daubert , 509 U.S. at 592 n.10). The amendment therefore confirmed, rather than altered, our existing burdenof-proof rule.

In assessing the admissibility of expert testimony, courts may consider a myriad of factors 'includ[ing] whether the expert’s theory or technique (i) can be (and has been) tested, (ii) has been subjected to peer review and publication, (iii) has a high known or potential rate of error, and (iv) enjoys general acceptance within a relevant scientific community.” Morgan , 45 F.4th at 200. District courts have “considerable leeway” both in determining how to assess reliability, the final prong of Rule 702, and in reaching their “ultimate conclusion[s]” on that question. Kumho Tire , 526 U.S. at 152.

The District Court held that the grounds underlying Dr. Elakil’s causation opinions did not reflect the “level of intellectual rigor” required under Federal Rule of Evidence 702Page 8 and therefore excluded the testimony. App.051 (citation modified). Though the District Court appears to have placed undue emphasis on Dr. Elakil’s clinical experience, the District Court’s analysis as a whole falls well within the scope of its discretion. Accordingly, we affirm.

First, the District Court held that the threshold causation question in the case was whether “stroke mitigation procedures following the TAAD repair would have improved plaintiff's outcomes” because “plaintiff’s recovery from the TAAD repair is inseparable from the causation analysis.' App.047-48 (emphasis in original). The District Court then explained it would evaluate whether Dr. Elakil had “good grounds” to opine on this question. Id. (quoting Daubert , 509 U.S. at 590). While Mr. Welch takes issue with the District Court’s characterization of his theory of the case, neither party challenges the District Court’s framing of the causation issue. Appellant’s Br. 15–16; Appellees’ Br. 20. Finding no issues, we will uphold this framing and continue with our analysis.

Dr. Elakil, a board-certified neurosurgeon, opined that delays in responding to Mr. Welch’s post-operative neurological symptoms caused or exacerbated his lowerextremity weakness as well as bowel and bladder dysfunction such that his weakness is “now permanent … instead of likely temporary.” App.345, 351–52, 459. In particular, he testified that better blood pressure management and placing a lumbar drain after the onset of symptoms might have resulted in a “complete resolution” of those symptoms or, at least, greater improvement than what Mr. Welch ultimately experienced. App.449, 454, 460.

Page 9Dr. Elakil based that opinion principally on medical records from Mr. Welch’s 2022 hospitalization and the period immediately following his surgery, App.345, 437, his professional training and experience, App.345, and four medical articles, only one of which concerned a TAAD repair and post-operative spinal cord injuries. See, e.g. , App. 050–51, 439 (explaining which articles were relied on for which components of his testimony). Dr. Elakil also testified that he recalled placing lumbar drains in patients who had undergone TAAD repairs “a few” times during his residency and once at a hospital where he was previously employed prior to his deposition, but he could not recall any patient who experienced complete resolution of symptoms. App.450–52. Finally, Dr. Elakil admitted that he failed to examine Mr. Welch or review his medical records after 2022, including subsequent rehabilitation or neurological reports. App.437, 440. He even acknowledged during his deposition that, without performing a medical examination himself, he could not determine the extent of Mr. Welch's current lower-extremity weakness, including whether it was permanent or resolved. App.458–59.

The District Court carefully considered the three foundations Dr. Elakil identified as the basis for his causation opinions: (i) his clinical experience, (ii) his review of some medical records and the deposition transcripts in this case, and (iii) select medical literature. App.048. Although the District Court placed undue emphasis on Dr. Elakil's role as a neurosurgeon, it permissibly considered the extent to which his clinical experience related to the specific causation question. Ultimately, we find no error in the District Court’s determination that Dr. Elakil's limited medical experience, deficient review of the medical records, and narrow set of Page 10literature failed to provide an adequate basis for his causation opinions. App.051–52.

First, the District Court found Dr. Elakil's clinical experience deficient based on the limited number of TAAD repairs he had performed and patients he cared for following such repairs, as well as his role as a neurosurgeon rather than a cardiothoracic surgeon. App.048-49. The District Court acknowledged that expert witnesses do not need to be specialists in a specific field to testify. However, in this case, the District Court felt the issues were more specifically related to cardiothoracic surgery and vascular neurology, and thus Dr. Elakil’s specialty paired with his lack of experience “[did] not align with the medical expertise needed to opine on the nuanced causation questions” regarding TAAD repairs. App.049.

We agree only in part with this aspect of the District Court’s reasoning. We have long held that physicians are “not incompetent to testify as an expert merely because [they are] not [] specialist[s] in the particular field [in] which” they seek to testify. Baerman v. Reisinger , 363 F.2d 309, 310 (D.C. Cir. 1966) (citation modified). It is entirely possible for physicians to have sufficient experience with the surgery at issue without practicing in a field that routinely performs that surgery, or without having performed the surgery a great number of times. Nevertheless, the District Court did not abuse its discretion in considering Dr. Elakil’s lack of familiarity with a complicated medical procedure as a relevant consideration, because it was considered alongside the weightier problems of Dr. Elakil's deficient review of Mr. Welch's medical records and the substantial gaps in the medical literature on which he relies. See Meister , 267 F.3d at 1126-32 (affirming exclusion of expert medical testimony after considering multiple Page 11deficiencies in the experts' methodologies and supporting evidence).

Second, we find no error in the District Court’s determination that Dr. Elakil’s conclusion—that the Hospital’s alleged negligence caused Mr. Welch's deficits to become permanent-was not 'based on sufficient facts or data.' App.050 (quoting FED. R. EVID. 702(b)). As the District Court explained, Dr. Elakil admitted he had neither examined Mr. Welch himself nor reviewed Mr. Welch’s medical records after 2022, even though such records were available. App.049–50. This is particularly significant because Dr. Elakil testified that, “without a medical . . . examination” it would be “really hard to say' 'how much improvement [Mr. Welch] had after all these years.' App.459. We do not hold that a medical examination is always required before an expert may offer a causation opinion in a medical-malpractice case. But here, where Dr. Elakil opines specifically that Mr. Welch’s deficits were permanent in 2024, the District Court reasonably concluded that the opinion did not rest on “sufficient facts or data” because Dr. Elakil had not reviewed any medical records after 2022 and instead relied primarily on those dated records and Mr. Welch’s own assessment of his condition to form his opinion. App.049–50.

Finally, the District Court reasonably concluded that the articles “do not establish that [Dr. Elakil’s] theories have been tested, subject to peer review, or generally accepted.” App.050 (citing Morgan , 45 F.4th at 200 (explaining factors that can inform the reliability analysis under Rule 702)). Three of the four articles were 'facially irrelevant.' App.050. And the article with the most relevant factual parallels (i.e., a discussion of a 77-year-old patient who underwent a TAAD repair and suffered post-operative spinal cord injuries) did not support, and in some respects contradicted, Dr. Elakil's proffered Page 12conclusions. App.051. In the article, the treating physicians “rejected” blood-pressure management as a means of addressing the patient’s post-surgery complications, contrary to Dr. Elakil's testimony. App.050-51, 054. The article characterized the blood pressure management interventions that Dr. Elakil said were warranted as “unnecessary.” See App.651. Dr. Elakil testified that 'many articles in the literature . . . say[] that the patient[s] have complete resolution [of symptoms] day one after placement of a lumbar drain.' App.449. However, the article he relied on stated that the lumbar drain placed at the “onset of symptoms” provided only “partial benefit[s]” to the patient. App.651. It is also unclear what “benefits” the patient experienced. Ultimately, Dr. Elakil failed to provide any articles that supported the methodologies underlying his testimony.

Accordingly, the District Court did not abuse its discretion in deeming Dr. Elakil’s testimony on what caused the permanency of Mr. Welch’s injuries to be unreliable within the meaning of Federal Rule of Evidence 702 and our precedents. We affirm the District Court’s exclusion of Dr. Elakil’s causation testimony.

We now turn to Mr. Welch’s contention that the District Court erred in precluding Dr. Schulman’s causation testimony. Mr. Welch argues that the District Court abused its discretion by excluding Dr. Schulman’s testimony because he disclosed him as a causation expert and the Hospital was prepared to question him about causation during his deposition. We find no merit in Mr. Welch’s arguments.

Page 13We review the District Court’s evidentiary rulings under an abuse of discretion standard. Carey Canada, Inc. v. Columbia Cas. Co. , 940 F.2d 1548, 1559 (D.C. Cir. 1991).

Under Federal Rule of Civil Procedure 26(a)(2), a party must disclose its expert witnesses to the opposing parties, and each expert must provide a written report that includes 'a complete statement of all opinions the witness will express and the basis and reasons for them,” along with “the facts or data considered by the witness in forming them.” FED. R. CIV. P. 26(a)(2) (emphasis added). When a party fails to make the required expert disclosure, that party “is not allowed to use that . . . witness to supply evidence on a motion, at a hearing, or at a trial, unless the failure was substantially justified or is harmless.” FED. R. CIV. P. 37(c)(1).

The District Court excluded Dr. Schulman's causation testimony because he was only disclosed as an expert on the standard of care elements of Mr. Welch's claims. App.053; see also App.294–99. The District Court found that, contrary to the requirements of Federal Rule of Civil Procedure 26(a)(2)(B), neither Mr. Welch's expert disclosures nor Dr. Schulman's expert report indicate that he planned to testify about proximate causation. App.052-53, 294-99. As the District Court noted, it is especially telling that, during his deposition, Dr. Schulman confirmed opposing counsel’s characterization that he would “testify about [the] standard of care only” and, as to “causation opinions, [he would] defer to an expert in other areas such as neurology[.]” App.053, 074. Since Mr. Welch offered no argument that his failure to disclose was substantially justified or harmless, and the Hospital explained why it was both surprised and unprepared to examine Dr. Schulman as a potential causation expert, the Page 14District Court excluded the expert testimony under Rule 37(c)(1). App.053. Because Mr. Welch did not attempt to explain to the District Court why the failure to disclose Dr. Schulman as a causation expert was either substantially justified or harmless, App.053, it was not an abuse of discretion for the District Court to conclude that Mr. Welch failed to meet his burden under Rule 37(c)(1).

Pivoting, Mr. Welch now argues that the District Court’s initial finding that he did not disclose Dr. Schulman as a causation expert was incorrect. Appellant’s Br. 29–30. In Mr. Welch's view, Dr. Schulman's expert disclosure includes references to causation testimony such that the Hospital was 'able to predict the scope of Dr. Schulman's causation testimony.” Id. at 29 . Specifically, Dr. Schulman's witness designation states that Dr. Schulman would opine that a finding of a hospital radiologist who read Mr. Welch’s MRI was “more likely than not, the explanation for Mr. Welch’s ongoing lower extremity weakness.' Id. (emphasis omitted). As further support for his contention that the disclosure encompasses causation opinions, Mr. Welch argues the Hospital’s deposition questions demonstrated that it was “apprised” of his “causation opinions.” Id .

Mr. Welch’s arguments find insufficient support in the record or governing law and therefore fall short of demonstrating that the District Court abused its discretion. Based on Dr. Schulman’s own understanding of his role as an expert witness, he was not providing a causation opinion. See App.074. As the District Court found, there were no references to causation in Mr. Welch’s expert designation, nor does Dr. Schulman provide causation opinions in his expert report. App.052; see also App.294-99. At best, Dr. Schulman's disclosure describes what he believed to be an implied opinion on causation held by someone else—a hospital radiologist. The Page 15record citations on which Mr. Welch relies do not contradict the District Court’s finding. Further, Mr. Welch’s contention that opposing counsel’s ability to ask causation related questions during Dr. Schulman’s deposition demonstrates that his disclosure was adequate is unpersuasive. First, he cites no authority supporting that proposition. Second, comments made by Dr. Schulman for the first time in his deposition regarding causation do not provide fair notice such that the Hospital had “a reasonable opportunity to prepare.” See FED. R. CIV. P. 26 advisory committee’s note to 1993 amendment.³

For the reasons stated above, the District Court did not abuse its discretion in excluding Dr. Schulman as an expert witness on the issue of causation.

Finally, we review “ de novo orders granting motions to dismiss under Rule 12(b)(6) or granting summary judgment under Rule 56.” Goodrich v. Bank of Am., N.A. , 136 F.4th 347, 353 (D.C. Cir. 2025). Summary judgment is appropriate 'against a party who fails to make a showing sufficient to establish the existence of an element essential to that party’s case, and on which that party will bear the burden of proof at trial.” Celotex Corp. v. Catrett , 477 U.S. 317, 322 (1986).

Under District of Columbia law, '[t]he plaintiff in a negligence action bears the burden of proof on three issues: ‘the applicable standard of care, a deviation from that standard by Page 16the defendant, and a causal relationship between that deviation and the plaintiff's injury.'' Butera v. District of Columbia , 235 F.3d 637, 659 (D.C. Cir. 2001) (quoting Toy v. District of Columbia , 549 A.2d 1, 6 (D.C. 1988)). District of Columbia medical malpractice law requires expert testimony on each element of a medical malpractice claim “except where proof is so obvious as to lie within the ken of the average lay juror.” Snyder v. George Washington Univ. , 890 A.2d 237, 244 (D.C. 2006) (quoting Derzavis v. Bepko , 766 A.2d 514, 519 (D.C. 2000)). Mr. Welch does not dispute that an expert was required to testify to causation in this case.⁴ See Appellant’s Br. 30.

Dr. Elakil and Dr. Schulman are the only expert witnesses offered by Mr. Welch to support the causal element of his medical negligence claims. Without their testimony, there is no path forward for Mr. Welch to prove the highly technical causation element. Accordingly, Mr. Welch’s “failure to offer” essential testimony “justif[ies] the grant of summary judgment against him.' Burke v. Air Serv. Int'l, Inc. , 685 F.3d 1102, 1106 (D.C. Cir. 2012).

Page 17Since the District Court properly excluded Dr. Elakil’s testimony under Federal Rule of Evidence 702 and Dr. Schulman’s testimony under Federal Rules of Civil Procedure 26 and 37, Mr. Welch lacked the required expert testimony on causation. Therefore, the District Court properly granted summary judgment in favor of the Hospital. We affirm.

So ordered .