Tiny Finger, Big Lesson: Ultrasound Reveals Hidden Toddler Fracture X-rays Missed

When an 18-month-old girl arrived at the hospital with a swollen left middle finger and a noticeably limited range of motion after a crush injury, her clinicians faced a diagnostic puzzle that pediatric radiologists know all too well. The bones of very young children are largely cartilage, and the growth centers, called epiphyses, that will eventually ossify into adult bone are often invisible on standard X-rays. A new case report published in Pediatric Radiology by Nicole Blattman, Peter J. Strouse, and Aparna Joshi of the University of Michigan Medical School and Michigan Medicine documents exactly how this invisibility can hide a serious injury, and how ultrasound can step in where radiography falls short. The case, published open access on 24 September 2026, describes a Salter-Harris type I fracture with dislocation of the distal phalangeal epiphysis, an injury so subtle on initial films that it could easily have been dismissed as simple soft tissue trauma.

The technical anatomy behind this case is worth unpacking. In toddlers, the distal phalanx, the small bone at the very tip of each finger, consists of a bony shaft, or metaphysis, and an epiphysis at its base that may not yet contain any calcified tissue. The growth plate, or physis, sits between the two. Salter-Harris fractures are injuries that cross this growth plate, and they are classified into types based on which components are involved. A type I injury passes cleanly through the physis itself, separating the epiphysis from the metaphysis without breaking either piece of bone. In an adult, such a separation would be obvious on an X-ray because the epiphysis is fully ossified and its displacement would be visible as a break in the normal contour of the joint. In an 18-month-old, however, the epiphysis may be entirely cartilaginous, rendering it radiolucent, meaning X-rays pass through it without producing an image.

That is precisely what happened in this case. The initial lateral radiograph of the injured finger demonstrated soft tissue swelling and a curvilinear calcification located dorsal to the head of the middle phalanx, the bone just proximal to the fingertip. What the radiograph did not show was any ossified distal phalangeal epiphysis in its expected normal location. To an untrained eye, or even to an experienced one working without the benefit of comparison, the absence of a visible structure is far harder to recognize than the presence of an abnormal one. The curvilinear calcification dorsal to the middle phalangeal head was the only clue, a faint whisper of displaced anatomy rather than a clear fracture line.

The clinical course added weight to the concern. A follow-up radiograph obtained four months later showed that the dorsal ovoid ossific density had increased in size. This progressive enlargement suggested that the calcified structure was not a static artifact or a simple avulsion fragment but living, growing skeletal tissue sitting in the wrong place. Still, neither the initial nor the follow-up radiograph demonstrated an ossified distal phalangeal epiphysis in a normal location, leaving the fundamental question unanswered: where was the growth center of the fingertip, and was it where it belonged?

The answer came from ultrasound, and this is where the case report carries its most broadly applicable lesson. Ultrasound imaging, which uses high-frequency sound waves rather than ionizing radiation, excels at visualizing cartilage precisely because cartilage reflects sound differently from surrounding soft tissue and fluid. When the team scanned the injured finger, they confirmed dorsal displacement of the distal phalangeal epiphysis relative to the middle phalangeal head. The displaced epiphysis sat deep to the extensor tendon, the structure on the back of the finger that straightens the tip, and away from the distal phalangeal metaphysis to which it should normally be attached. In other words, the entire growth center of the fingertip had been torn loose through the growth plate and shoved backward, out of joint.

Critical to the diagnostic confidence was a comparison study. Ultrasound of the contralateral right middle finger demonstrated the normal positioning of the distal phalanx epiphysis, giving the radiologists a direct internal control. Asymmetric comparison imaging is a cornerstone of pediatric musculoskeletal radiology, because children vary widely in skeletal maturity and because paired anatomy offers an ideal baseline. With both hands imaged in the same session, the abnormal dorsal displacement on the left and the normal alignment on the right made the diagnosis unambiguous: a Salter-Harris type I fracture with dislocation of the distal phalangeal epiphysis.

The mechanism of injury fits the imaging findings. Crush injuries to fingertips are among the most common hand traumas in toddlers, who habitually explore their world by grabbing and who frequently catch their fingers in doors, drawers, and heavy objects. The distal phalanx of a young child is mechanically weak relative to the forces such accidents generate, and the growth plate is biomechanically the weakest link in the developing bone chain, more vulnerable to shear and compression than the surrounding ligaments and tendons. A force that would sprain an adult finger can therefore shear through a toddler’s physis, separating cartilage from bone in a way that leaves no radiographic fracture line at all.

Why does this diagnostic subtlety matter beyond a single finger? Untreated displacement of the epiphysis can affect the growth plate’s future function and the alignment of the digit as the child grows. The dorsal position of the displaced epiphysis, deep to the extensor tendon, also has mechanical consequences for how the fingertip extends and flexes. The authors note that although the injury was subtle on initial radiographs, ultrasound provides an alternative, non-invasive method of confirmation in skeletally immature patients. That framing is deliberately practical: ultrasound is widely available, relatively inexpensive, free of radiation, and can be performed at the bedside, often by the same clinicians evaluating the child. In an 18-month-old, avoiding additional radiographic exposures, particularly repeat imaging over months of follow-up, is a meaningful benefit in itself.

The case also illustrates a broader principle in pediatric imaging that radiologists emphasize in training: absence of a visible structure can be a finding. Recognizing that a distal phalangeal epiphysis should be present, or at least inferring its expected position from the contralateral side, requires knowledge of the normal sequence of skeletal ossification. The distal phalangeal epiphyses of the fingers typically begin to ossify in the first years of life, but the timing varies, and in some toddlers the cartilaginous precursor remains entirely invisible on radiographs. When the epiphysis is cartilage-only, its displacement produces no direct radiographic sign; only indirect clues such as soft tissue swelling, unusual calcifications, and joint incongruity hint that something is wrong.

For clinicians evaluating fingertip injuries in the youngest patients, the practical takeaways are concrete. First, a crush injury with swelling and limited motion deserves careful consideration of a growth plate injury even when radiographs appear unrevealing. Second, comparison imaging of the uninjured side, whether by radiograph or ultrasound, dramatically improves diagnostic accuracy in children. Third, ultrasound should be considered early when radiographic findings are equivocal or discordant with the clinical examination, because it can directly visualize the cartilaginous epiphysis and its relationship to the metaphysis, the physis, and the extensor tendon. The University of Michigan team, whose study was completed in accordance with the HIPAA Privacy Rule with informed consent from the patient’s father, and who declared no competing interests, have offered the pediatric imaging community a compact but instructive demonstration: in the hands of a toddler, the most important structures are sometimes the ones the X-ray cannot show, and sound waves can find what light and X-rays cannot.

Subject of Research: Ultrasound diagnosis of a Salter-Harris type I fracture-dislocation of the distal phalangeal epiphysis in a toddler

Article Title: Fracture-dislocation of the distal phalangeal epiphysis in a toddler

Article References: Blattman, N., Strouse, P. J., & Joshi, A. (2026). Fracture-dislocation of the distal phalangeal epiphysis in a toddler. Pediatric Radiology. https://doi.org/10.1007/s00247-026-06791-z

Image Credits: AI Generated

DOI: 10.1007/s00247-026-06791-z

Keywords: pediatric radiology, Salter-Harris fracture, distal phalanx, epiphysis, ultrasound, fracture-dislocation, toddler, crush injury, growth plate, physis, radiography, musculoskeletal imaging