Medical Expert Testimony in Massachusetts Criminal Cases: The Hsu Decision on Abusive Head Trauma

Medical experts can help a Massachusetts jury understand how an injury occurred and whether the medical findings support the prosecution’s account. The judge must first decide whether the opinion is reliable and whether its wording risks unfairly influencing the jury’s decision about guilt. On September 9, 2026, the Supreme Judicial Court addressed both questions in Commonwealth v. Shu Feng Hsu, affirming an involuntary manslaughter conviction involving testimony about abusive head trauma.

The court upheld the admission of testimony that the child’s injuries were “consistent with” abusive head trauma. It also approved the trial judge’s decision to prohibit experts from stating that abusive head trauma caused those injuries. The distinction explains why a defense challenge can address both the scientific basis of an opinion and the precise conclusion the expert proposes to give.

The decision concerns a child’s fatal head injuries. Its discussion of reliability, alternative explanations, and limits on expert testimony also offers guidance for counsel preparing domestic violence cases, assault and battery cases, and other criminal trials involving disputed medical evidence. Applying that guidance requires attention to the particular injury and opinion, rather than assuming that every case requires the restrictions approved in Hsu.

The Decision and the Disputed Medical Evidence

In Commonwealth v. Shu Feng Hsu, No. SJC 13855 (September 9, 2026), the defendant challenged the admission of expert testimony concerning abusive head trauma. The appeal required the Supreme Judicial Court to consider the medical acceptance of the diagnosis, the risk associated with the word “abusive,” and testimony about whether a short fall could explain the child’s injuries.

Abusive head trauma describes a medical diagnosis encompassing several possible mechanisms, including blunt impact, shaking, or a combination. The court considered evidence that national and international medical organizations recognize the diagnosis and that physicians evaluate it through clinical history, examination, laboratory findings, and imaging.

The defense disputed the reliability of the diagnosis and relied on contrary scientific materials. The court concluded that scientific unanimity was unnecessary and that the trial judge had acted within the judge’s discretion on the record presented. The Supreme Judicial Court affirmed the conviction.

General Acceptance and the Particular Opinion

Under the Daubert-Lanigan standard discussed in Hsu, a judge examines the reliability of proposed expert testimony before allowing the jury to consider it. General acceptance in the relevant scientific community can establish reliability. A disagreement among scientists does not, by itself, require exclusion.

That conclusion requires counsel to identify precisely what the expert claims. Acceptance of a medical diagnosis and the explanation for a particular patient’s injuries are related but distinct questions. A defense review should examine the medical history, the images and other findings, the proposed mechanism of injury, and the reasons the expert accepts or rejects alternative explanations.

The distinction also affects the assignment given to a defense consulting or testifying expert. Reviewing whether the prosecution’s opinion has adequate support is different from offering an affirmative opinion about what caused the injury. Counsel should determine which work the evidence requires before deciding who should testify.

The Limits on the Word “Abusive”

The trial judge recognized that the word “abusive” could influence the jury beyond the medical information the experts were qualified to explain. The judge allowed testimony that the injuries were consistent with abusive head trauma but prohibited testimony that abusive head trauma was their cause.

The Supreme Judicial Court approved those limits as a way to reduce unfair prejudice and preserve the jury’s responsibility to determine guilt. A medical expert could explain the injuries and the possible mechanism without deciding the defendant’s legal culpability.

The court upheld that exercise of discretion. It did not require every judge to use the same wording in every injury case. Nor does adding “consistent with” establish reliability by itself. Counsel still needs to examine what the opinion means, what supports it, and what the witness can reliably conclude from the findings.

Short Falls and Alternative Explanations

The trial judge prohibited a categorical statement that short falls cannot cause abusive head trauma. The experts nevertheless testified that the particular child’s injuries were inconsistent with the short falls described in the case.

The Supreme Judicial Court found no violation of the order. A general assertion about all short falls differs from an opinion based on a particular child’s injuries and a particular proposed fall.

For the defense, that distinction requires a specific medical inquiry. Counsel should identify the proposed fall, the surface, the height, the position of the body, and the findings the expert relies on to reject that explanation. A general statement that falls can cause injuries does not answer whether the proposed fall explains the findings in the case.

The same preparation supports cross-examination of a medical expert. Counsel can ask which findings support the opinion, which alternatives the expert considered, and which assumptions would change the conclusion.

The Question About Shaking Without Impact

The court did not resolve the scientific reliability of shaking alone, without blunt impact, as the explanation for the injuries associated with abusive head trauma. The case involved blunt impact, and the court distinguished that record from the disputed shaking-only theory.

A future case alleging shaking without impact therefore requires examination of that specific mechanism and the evidence offered to support it. Hsu should not be cited as a decision resolving a question the court left unanswered.

Medical Evidence in Assault and Domestic Violence Trials

Injury evidence can affect several disputed questions in an assault prosecution: what contact occurred, how much force was involved, when the injury occurred, and whether the prosecution’s account fits the medical findings. Counsel should separate those questions rather than treat the presence of an injury as proof of the entire accusation.

In a prosecution for assault and battery by means of a dangerous weapon, for example, a dispute may concern the alleged mechanism or the extent of an injury. In a domestic violence case, counsel may need to compare medical findings with photographs, recordings, and the sequence described by the witnesses. These are applications of the evidentiary questions discussed in Hsu, not additional holdings about those offenses.

The medical testimony must remain tied to what the witness can explain reliably. Counsel should distinguish the physical findings from assumptions about the event and from the elements the Commonwealth must prove.

Pretrial Motions in the Superior Court

In a Superior Court prosecution involving disputed injury evidence, counsel should address the proposed expert testimony before trial. A motion in limine can identify the opinion, explain the objection, and request either exclusion or specific limits on the testimony.

Hsu illustrates why counsel should state alternative requests. If the judge admits the diagnosis, counsel can still seek limits on causal conclusions, emotionally charged terminology, or categorical assertions that exceed the supporting science. The requested order should identify the particular statements the witness may and may not make.

After the judge rules, counsel should compare the testimony with the order and raise an objection when the expert exceeds the permitted testimony. The broader rules for evidence, examination of witnesses, and courtroom procedure appear in the firm’s Massachusetts criminal court practice guide.

Reviewing a Case Involving Medical Testimony

A useful review identifies the complete medical record, the expert’s precise opinion, the scientific basis for that opinion, and the explanations the expert considered and rejected. Counsel then determines what to challenge before trial and what to address through cross-examination.

Hsu permits the testimony the judge admitted on that record. It also demonstrates that the wording and scope of a medical opinion remain subjects for a specific defense motion. Both parts of the decision belong in the preparation of a case involving disputed injury evidence.

Attorney Joe Serpa has practiced Massachusetts criminal defense since 1995 and represents defendants in the District Court, Boston Municipal Court, and Superior Court. Serpa Law Office can be reached at 617.936.0201.

This article provides general information based on a published court decision. It is not legal advice and does not create an attorney-client relationship. It may constitute attorney advertising.