Thumb UCL Tear: MRI, Ultrasound, and Stener Lesion

How the Injury Happens

The mechanism is a forced sideways bend of the thumb away from the palm. The classic description comes from skiing, where a pole strap catches the thumb during a fall and levers it outward, which is why the injury is still widely called skier's thumb. The same lever appears when a ball strikes the end of an outstretched thumb, when a hand is caught in a jersey or a harness, or when a fall onto an open palm pushes the thumb wide.

A slower version exists too. Repeated low-grade stress — years of a gripping trade or racquet sport — can stretch the ligament gradually rather than rupture it in one event. That chronic pattern has historically been called gamekeeper's thumb. It matters for imaging because a long-standing stretch looks different from a fresh tear: the band is thinned and lax rather than torn and swollen, and the surrounding tissue shows little of the acute fluid signal that a recent injury produces.

What MRI and Ultrasound Look For

• Partial versus complete UCL tear
• Displaced ligament stump suggesting Stener lesion
• Avulsion fragment at the ulnar base of the proximal phalanx
• MCP joint subluxation, edema, or associated volar plate injury

What Each Modality Shows and What It Misses

X-ray is almost always first. It answers one question well: is there a fragment of bone pulled off the ulnar base of the proximal phalanx, and if so, how large is it and how far has it moved? A stress view may be added, though many hands are too painful to tolerate one early. What X-ray cannot show is the ligament itself, so a film reported as normal leaves the soft-tissue question completely open.

MRI shows the whole ligament along its length and can place a retracted stump relative to the adductor aponeurosis, which is the finding a surgeon most wants described. It also picks up bone marrow oedema, an occult fracture, volar plate damage, and joint surface injury in the same acquisition. Its limits are practical rather than anatomical: the ligament is only a few millimetres across, so thin slices, a small field of view and a dedicated coil matter more than raw field strength, and the study is a static image of a thumb lying still.

Ultrasound adds the one thing the other two cannot: movement. A sonographer can apply a gentle sideways stress while watching the ligament in real time and see whether the stump stays in place or rolls up above the aponeurosis. It is quick, uses no ionising radiation, and costs less. The trade-off is that it depends heavily on the operator, it can mistake swollen scar tissue for an intact ligament, and it gives a narrow window that may overlook injuries elsewhere in the joint.

How the Injury Is Graded

Thumb UCL injuries follow the familiar three-grade sprain scale. Grade I is a stretched but continuous ligament with tenderness and no abnormal sideways opening. Grade II is a partial tear with some opening that still comes to a firm endpoint. Grade III is a complete rupture where the joint opens without a firm stop. The grade is assigned from the clinical stress examination; imaging is used to support it and to add the detail the examination cannot reach.

For a complete tear, the decisive extra detail is displacement rather than severity. Reports usually state where along the ligament the tear sits — most are at the phalangeal end — whether the stump has retracted, and whether it lies deep or superficial to the adductor aponeurosis. When a bone fragment is involved, its size and the gap between it and its bed are measured, because a fragment that is still seated is described very differently from one that has rotated away.

Report Phrases and What They Mean

• "Yo-yo on a string" or "balled-up retracted stump" — a descriptive shorthand for a torn ligament end bunched above the adductor aponeurosis
• "Ligament remains deep to the adductor aponeurosis" — a torn ligament that is still in contact with its footprint, which is the opposite of a Stener lesion
• "Non-displaced avulsion at the ulnar base of the proximal phalanx" — the ligament pulled bone away but the fragment has not moved from its bed
• "Attenuated ligament without surrounding oedema" — wording that suggests a long-standing stretch rather than a recent tear
• "Volar subluxation of the proximal phalanx" — the joint is no longer centred, which often accompanies a higher-grade injury

What Usually Happens Next

Lower-grade injuries with a continuous ligament are generally managed without surgery, with immobilisation of the thumb column followed by a graded return to loading pinch. The decision point is the stress examination rather than the scan, and a hand therapist usually guides the progression. Because the thumb is involved in almost every grip, work and sport modifications are planned around pinch demands rather than around pain alone.

A complete tear with a displaced stump is handled differently, because the interposed aponeurosis prevents the two ends from reaching one another. Surgeons therefore want the imaging question answered clearly before planning. Where a bone fragment has displaced, the same logic applies to the fragment. None of this is decided from images in isolation; a hand specialist combines the report with the examination, your hand dominance, and what you need the thumb to do.

Repeat imaging is not routine. It is most often considered when pinch strength does not recover as expected after a course of immobilisation and therapy, when the joint remains painful or feels unstable on the ulnar side months later, or when a first study was done through so much acute swelling that the ligament could not be traced with confidence. A second look at the original images is sometimes more useful than a new scan, which is why having your own copy of the study is worth keeping.

Key Takeaways

• X-ray checks for avulsion fracture and alignment
• MRI gives a broad view of ligament, marrow, and joint injuries
• Dynamic ultrasound can be excellent when local expertise is strong
• The Stener lesion is defined by position, not severity: the torn stump sits above the adductor aponeurosis, which blocks contact with its bony footprint
• Grades are assigned from the sideways stress examination; imaging adds tear location, retraction, and fragment displacement
• A thinned ligament with little surrounding fluid points to chronic stretching rather than a fresh rupture