A Muscle Pulls the Bone Out of Place, Which Is Why These Kind Of Injuries CANT Be Cast
A break at the very base of the thumb, where the thumb’s long bone meets the wrist, is a different problem from a break anywhere else in the thumb.
Two reasons.
- It runs into the joint surface.
- And there’s a muscle attached just above it, constantly pulling the broken piece away.
That combination means most of these need fixing surgically, and the ones that get treated in a cast alone frequently slip.
It matters because that joint is the one you use for every pinch, key turn and jar lid, and a joint surface left uneven becomes thumb base arthritis earlier than it otherwise would.
Two names, one location
A Bennett’s fracture is the two-piece version.
- A small triangular fragment stays behind at the base, anchored by a strong ligament that doesn’t let go. The rest of the thumb bone gets pulled away from it: upwards, backwards, and out towards the side.
- What does the pulling is the muscle that hauls your thumb out and back. It doesn’t stop pulling because you’ve broken something, so the gap tends to open rather than close.
A Rolando fracture is the shattered version, broken into three or more pieces in a Y or T pattern. Same location, harder to rebuild, and generally a worse outcome even in good hands.
Both usually come from a punch, a fall onto a thumb, or a sporting impact driving the thumb backwards.
Recognizing it
- Pain and swelling right at the base of the thumb, in the fleshy web where it meets the wrist, rather than up the thumb itself.
- Bruising across the base and into the palm.
- Pinching anything is impossible or agonising.
- The thumb may look shortened or sit in an odd position.
If you injured your thumb and the pain is at the very base, say so specifically. This is one where the location of the tenderness is the difference between a straightforward thumb fracture and a joint injury.
Definitely need to separate from a skier’s thumb, which hurts on the inner side of the joint one level up, at the knuckle rather than the base.
Treatment
Genuinely undisplaced fractures can be treated in a thumb spica cast, with repeat X-rays at about a week and two weeks specifically to catch it if it drifts. That follow-up is not optional.
Most are treated surgically:
- Closed reduction and pinning. The bone is manipulated into position without opening the skin, then held with wires passed through the skin into the bone. Wires stay for around 4 to 6 weeks and come out in clinic.
- Open reduction with a screw or plate. The joint surface is rebuilt directly under vision, usually when the fragment is large enough to take a screw, or when the joint surface needs precision.
- External fixation or bridging for badly shattered Rolando patterns.
The aim isn’t a healed bone. Bone will heal almost regardless. The aim is a smooth joint surface, because that’s what decides how the thumb feels in fifteen years.
Recovery
- Weeks 0 to 4: thumb spica cast or splint. The thumb is out of action, but the fingers, wrist and shoulder should all be moving fully from day one. Elevation for the first week.
- Weeks 4 to 6: wires typically removed. Splint continues between exercise sessions. Gentle movement of the thumb starts, and this is where hand therapy takes over.
- Weeks 6 to 12: range of motion work in earnest, then pinch and grip strengthening. Web space stretching, because the space between thumb and index finger tightens after weeks of immobilisation and a tight web costs you function directly.
- Months 3 to 6: heavy use, sport, manual work. Pinch strength is the slowest thing to return and usually the last to normalise.
Honest expectations: Some stiffness at the base of the thumb is common. Aching with heavy or cold work can persist for a year. And there’s an increased chance of arthritis at that joint later in life even with a good result, because the joint surface has been injured. Good treatment reduces that risk substantially rather than removing it.
The short version
A break at the base of the thumb is a joint injury with a muscle actively pulling it apart, so it usually needs fixing rather than casting.
If it is being treated in a cast, make sure repeat X-rays are booked, because these slip quietly in the first two weeks.
And when the cast comes off, chase the web space and the pinch. Those are the two things that decide whether the thumb works, and neither returns on its own.
Written by Nigel Chua, hand occupational therapist in practice since 2005. Tens of thousands of hands, wrists and elbows assessed and treated. My credentials are here. This article explains; it doesn’t examine. Follow your own surgeon’s protocol where it differs from anything here.