A Cast Alone Matched Surgery for a Common Unstable Ankle Fracture

CATEGORY: MOBILITY, BONES & JOINTS

When a broken ankle fails a stability test, the next stop is usually an operating room. Finnish surgeons asked whether it has to be. They followed 126 adults with one common type of unstable ankle fracture for two years, half treated with a metal plate and screws, half with nothing but a cast.¹ The cast group ended up averaging 89 out of 100 on a standard questionnaire covering ankle pain and everyday function. The surgery group averaged 87. That gap of 1.3 points sat well inside the eight-point margin the trial had set in advance for calling the two treatments equal, and nearly every complication landed on the surgical side.

A Twist Under a Live X-Ray Decided Who Qualified

The fracture in question is a single break of the fibula, the thin bone on the outer side of the ankle, with the joint itself still sitting in line on ordinary X-rays. Surgeons call it a Weber B fracture, and it’s everyday work in a trauma clinic. The hard question is what to do when the pictures look reassuring but the joint might wobble. To find out who truly was unstable, the team at Oulu University Hospital screened 840 adults and gave the candidates a stress test: a clinician gently turned the injured foot outward while a live X-ray watched whether the inner side of the joint gaped open. Most ankles held firm. The 126 that gaped while still aligned went into the trial. A sealed envelope opened at the hospital then settled each person’s treatment at random: six weeks in a cast, or open reduction and internal fixation, an operation that lines the bone up and holds it with a plate, followed by the same six weeks in a cast.

Two Points Apart, With the Complications on One Side

Two years on, 121 of the 126 were still reporting in. The questionnaire behind the main result, the Olerud-Molander Ankle Score, asks about pain, swelling, stair climbing, running and work. Cast patients averaged 89, surgical patients 87, and the margin of error around that 1.3-point difference ran from 4.8 points in surgery’s favor to 7.3 in the cast’s, never approaching the eight-point line the trial counted as a meaningful loss. Pain, quality of life, ankle motion and the X-ray picture told the same story. One bone in each group failed to knit, and the cast patient’s never caused symptoms. That was the cast group’s whole complication list. The surgery group’s was longer: one wound infection, one slow-healing wound, and nine people back in the operating room to have hardware removed, with two infections following those procedures. Roughly one in four surgical patients had some treatment-related problem. The trial was publicly funded by the hospital and Finland’s state research financing.

A Narrow Gate, On Purpose

The result travels exactly as far as the fracture it tested. Everyone enrolled had a single outer-ankle break with the joint surfaces still matching; fractures that had shifted, dislocated or broken in more places never entered. The trial was also modest in size, 126 people at one hospital, though 96% stayed the full two years. Other evidence points the same way. A British trial of 620 adults over 60 with unstable ankle fractures found a closely molded cast matched surgery on the same questionnaire at six months, though casting left more crookedly healed bones on X-rays there, and about one in five of its cast patients went on to have an operation.² For the carefully defined slice of fractures the Finnish trial enrolled, the plate added risk without adding function.

Key Takeaways

• Nearly all the complications fell on the surgery side: nine hardware-removal operations, two of them followed by infection, plus wound problems. The cast group’s only event was one painless non-union.
• Two years after an unstable outer-ankle fracture, people treated in a cast scored 89 out of 100 for ankle function; the surgery group scored 87, inside the trial’s margin for calling the treatments equal.
• The verdict covers a single, well-aligned fibula fracture that fails a stress test. Shifted or dislocated fractures were excluded, and the trial ran at one hospital with 126 patients.

References

1. Kortekangas T, Lehtola R, Leskelä HV, et al. Cast immobilisation versus surgery for unstable lateral malleolus fractures (SUPER-FIN): randomised non-inferiority clinical trial. The BMJ. 2026;392:e085295. link
2. Willett K, Keene DJ, Mistry D, et al. Close contact casting vs surgery for initial treatment of unstable ankle fractures in older adults: a randomized clinical trial. JAMA. 2016;316(14):1455–1463. link