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The Gap Between Your Thumb and Index Finger Is Worth Fighting For.
A C-bar splint (first web space splint) holds your thumb stretched away from your index finger so the web between them can’t shrink. It’s used after burns, crush injuries, web space surgery, trapeziectomy, nerve palsy and stroke.
Most people wear it at night and during rest periods for 6 weeks to 6 months. After a burn, it’s worn for as long as the scar is still active, often 12 to 18 months.
A web that shrinks by even a small amount makes it hard to grip a bottle, a steering wheel or a cup.
Here’s how it usually goes. After an injury the hand rests with the thumb pulled in against the index finger…it’s the comfortable position. Swollen, sore, guarded. Nobody notices the web quietly tightening.
Then at week 8 you reach for a 1-liter bottle and the hand won’t open around it. The skin, scar and muscle in the web have shortened to fit the position you rested in. Opening it back up takes months of stretching, serial splints, and sometimes another operation.
Prevention is FAR easier than correction. That’s the whole job of this splint.
You don’t notice the web until it’s tight. Then you notice it every time you pick something up.
What is the first web space and why does it tighten?
The first web space is the fold of skin and muscle between your thumb and index finger. Two muscles live there: adductor pollicis, which pulls the thumb in, and the first dorsal interosseous, the fleshy bump that pops up when you pinch. Over the top sits a fold of skin that has to stretch every time you open your hand wide.
That web is what gives the hand its span. Open, the thumb swings wide and sits opposite the fingers to wrap around a jar, a bottle or a racket handle. Shortened, the thumb gets stuck beside the index finger. You can still pinch small things, but anything bigger than a cup slips.
- Resting position. A hurt hand rests with the thumb pulled in. Hours in that position become weeks.
- Swelling. Fluid that sits in the web for weeks thickens and stiffens, and scar tissue forms around it. See crush injuries and hand swelling.
- Scar. Burn scar and surgical scar contract as they mature. A scar that crosses the web pulls the thumb in with it.
- Muscle imbalance. If the muscles that swing the thumb out are paralyzed (median nerve injury) or the muscles that pull it in are overactive (spasticity after stroke), the thumb sits in and the web shortens to match.
The web runs on a closing window. While scar is young and still remodeling, a splint and daily stretches can shape it. Once the scar has matured, it’s set…and a splint does far less.
Who needs a C-bar splint?
- Burns to the web, the back of the hand or the palm, often alongside silicone gel and pressure garments.
- Crush injuries with heavy swelling in the thumb and web.
- After web space contracture release or skin grafting, to hold the new length while the scar matures.
- After trapeziectomy. Some surgeons and therapists add a C-bar or soft web spacer at night once the thumb spica comes off, if the web is starting to tighten. The point of that operation was a thumb that opens without pain. A tight web undoes half of it.
- Median nerve injury, or long-standing carpal tunnel with wasting at the base of the thumb, where the thumb can’t lift away from the palm. Also before or after tendon transfers to restore that movement.
- Stroke, brain injury and cerebral palsy, where spasticity pulls the thumb tight into the palm. Often the C-bar is built into a resting splint for stroke.
What does a C-bar splint look like?
- Hand-based C-bar: a curved piece of thermoplastic shaped into the web, strapped around the hand. The wrist stays free.
- Forearm-based thumb abduction splint: when the wrist also needs support, or early after surgery.
- Soft web spacers: foam, neoprene or silicone, for night use and for burns where rigid pressure isn’t tolerated.
- Serial splints: remolded wider every week or two as the web gains length. See static progressive splints and serial casting.
A C-bar is the Gandalf of splints. It stands in the web and says one thing: you shall not close.
How should a C-bar splint fit?
- Seated deep in the web. The curve sits right in the crease, in contact with the thumb’s long bone (the first metacarpal) on one side and the index finger’s on the other.
- The push goes through the long bone, not the thumb tip. Push on the tip and you bend the thumb’s knuckle backwards and stretch its ligament instead of the web. The thumb knuckle should sit straight or slightly bent, never bent backwards.
- Wide, but not at the edge of pain. You want a firm stretch you can sleep in. A gentle stretch held for hours does more than a hard stretch you rip off after 20 minutes.
- Thumb tip and fingers free to move.
- Smooth, rolled edges and wide straps. No strap should dig into swollen skin or sit across a fresh graft.
(If your splint was made more than a month ago and the web has been improving, it probably no longer reaches the new end of range. That’s a good problem. Get it remolded.)
How long do you wear a C-bar splint?
Your surgeon’s or therapist’s schedule wins. These are the typical ranges.
- After burns: at night, and often between daytime sessions, for as long as the scar is active. Burn scar can keep tightening for 12 to 18 months.
- After a crush injury: mainly at night for the first 4 to 6 weeks, while swelling settles.
- After contracture release or grafting: close to full time early, off only for exercises and washing once your surgeon allows. Then nights, usually for 3 to 6 months.
- After trapeziectomy: usually nights only, for a few weeks to a few months after the spica comes off, and only if the web is tightening.
- Nerve injury: nights and rest periods until the nerve recovers or a tendon transfer takes over. That can be many months.
- Stroke or brain injury: nights and rest periods, often long term, reviewed as muscle tone changes.
Breaking a new splint in
- First 1 to 2 days: wear it for 1 to 2 hours in the evening. Check the skin after the first 30 minutes.
- From day 3: wear it to bed if the skin stays clear.
- Every time it comes off: look at the skin. Red marks should fade within about 30 minutes. If they don’t, it’s pressing too hard.
What stretches go with a C-bar splint?
The splint holds the length. The exercises earn it. Do these 3 to 5 times a day unless your therapist has set something different.
- Web stretch. Rest your forearm on a table, little finger side down. With your other hand, push the base of the thumb (not the tip) forward and away from the index finger. Hold 30 to 60 seconds, 3 to 5 times.
- Flat-hand slide. Hand flat on the table, slide the thumb out sideways as far as it goes. Hold 30 seconds, 5 times.
- Cup wrap. Wrap your hand around the largest cup or bottle you can hold comfortably. Hold 30 seconds. Go up a size when it gets easy.
- Thumb circles and opposition. Touch the thumb tip to each fingertip, then make big slow circles with the thumb. 10 of each.
- Scar massage once the wound has fully healed: firm circles across the web scar for a few minutes, several times a day. Moisturize burn scar first. See scar management after hand surgery.
The rule: a stretch should ease off within minutes of letting go. Pain that’s still there an hour later means you pushed too hard.
Is the C-bar splint working?
Measure it, don’t guess it. Once a week, at the same time of day, put your hand flat on a sheet of paper, spread the thumb as wide as it goes, and trace around it. Date the sheet. Compare.
Signs it’s working:
- The span on your tracing widens, or at least holds steady while the scar is still active.
- The splint starts to feel loose in the web. It needs remolding.
- You can wrap around bigger things: a mug, then a bottle, then a jar.
- The scar is getting softer, flatter and paler.
Signs it isn’t:
- The tracing narrows over 2 to 3 weeks.
- The web feels tighter despite wearing it every night.
- The thumb knuckle is starting to bend backwards. The splint is stretching the wrong joint.
- You’ve quietly stopped wearing it because it hurts. Be honest. That’s a fit problem, and it’s fixable.
Common C-bar splint problems
- Pressure on fragile grafts or new scar.
- Stretching the wrong joint. The force should open the web, not bend the thumb knuckle backwards.
- Sweat and blistering in the web crease. Dry the web properly before it goes on, and ask about a thin cotton or silicone liner.
- A splint that no longer reaches the new end of range.
- Straps too tight over a swollen hand, especially overnight.
This is one of dozens of splints a hand therapist makes. See what a hand therapist does for the full list.
Take it off and get it checked today if
- The thumb or fingers turn white, blue or dusky, or go cold, and don’t pink up within a few minutes of taking the splint off. If the color doesn’t come back, go to the ER.
- New numbness or pins and needles in the thumb or fingers that doesn’t settle within 30 minutes of taking the splint off.
- A red, white or dark mark still there 30 minutes after removal, a blister, or broken skin. That’s a pressure sore starting. On grafted or numb skin it matters double, cos you won’t feel it coming.
- A graft or wound that’s weeping, smells, has spreading redness, or comes with a fever.
Get it checked if
- The web is getting tighter despite wearing the splint.
- The thumb knuckle is starting to bend backwards.
- The splint no longer fits snugly in the web.
- Stretches leave pain that lasts for hours.
Keep the web open while it heals, because reopening it later is much harder.
Written by Nigel Chua, hand occupational therapist in practice since 2005. Thousands of hands, wrists and elbows assessed and treated. My credentials are here. This article explains; it doesn’t examine. A web that’s tightening while you wear the splint deserves a therapist’s eyes this week.
Part of: Hand, wrist and elbow splints: which one, why and how long
Every article on this site is written using the Closing Window Method: name the window your condition runs on, find where you are in it, and act while it’s still open.