Bennett Fracture: Base of Thumb Injury, Surgery, and Recovery

A Bennett fracture is a break at the base of the thumb’s first metacarpal bone that extends into the joint where the thumb meets the wrist. What makes it distinct from a simple thumb break is that it splits the bone into two fragments and disrupts the carpometacarpal (CMC) joint, causing the thumb to partially dislocate under the pull of surrounding muscles and tendons. Because the thumb accounts for roughly 40 percent of overall hand function, getting this fracture treated properly matters far more than its small size might suggest.

How a Bennett Fracture Happens

The classic mechanism is a forceful blow directed along the length of the thumb, driving it into the wrist bones. Think of punching something with a partially closed fist, falling onto an outstretched thumb, or catching a ball awkwardly. A systematic review of treatment outcomes found that sports injuries are the most frequent cause, followed by occupational accidents, traffic collisions, falls, and fist injuries.¹ Contact sports like boxing, rugby, and football are particularly common culprits, as are cycling crashes where the handlebars jam into the base of the thumb.

When that axial force hits the thumb metacarpal, it drives the bone against the trapezium, the small wrist bone it sits on. The bone cracks in a characteristic pattern: a small triangular fragment stays anchored to the trapezium by a strong ligament called the volar beak ligament, while the larger shaft of the metacarpal slides upward and outward. This displacement happens because the muscles that move the thumb, particularly the one running along the back of the thumb toward the wrist, keep pulling the shaft out of position once the stabilizing joint surface is broken.²

What It Looks Like and How It Is Diagnosed

After the injury, the base of the thumb swells quickly. You’ll have pain when you try to grip or pinch anything, and the thumb may look slightly shortened or sit at an odd angle compared to the other hand. Moving the thumb, especially rotating it or pressing it toward the palm, will be painful. In some cases, you can feel a bony bump at the base of the thumb where the metacarpal has shifted out of place.

Standard X-rays of the thumb taken from at least two angles are usually enough to confirm the diagnosis. The images show the fracture line running obliquely through the base of the metacarpal into the joint, along with the displacement of the larger fragment. In cases where the fracture pattern is complicated or the fragment is very small, a CT scan gives a more detailed picture of how the joint surface is disrupted. This detail helps the surgeon plan the approach, especially when deciding between pinning the fragments percutaneously versus opening the joint surgically.

How a Bennett Fracture Differs from Related Thumb Injuries

Not every fracture at the base of the thumb is a Bennett. The term specifically refers to a two-part fracture-dislocation where one small fragment remains attached to the trapezium while the rest of the metacarpal shifts. A Rolando fracture involves three or more fragments at the same location, creating a Y-shaped or T-shaped break that is harder to reconstruct. Highly comminuted fractures shatter the base into many pieces and are the most challenging to manage.³ There are also extra-articular fractures, where the break stays outside the joint entirely. Those are generally simpler to treat because the joint surface is intact.

The distinction matters because Rolando and comminuted fractures often require more advanced surgical techniques like locking plates, external fixation devices, or arthroscopic assistance, while a straightforward Bennett fracture can frequently be handled with pins alone.⁴ In practice, the surgeon’s decision hinges on how well the joint surface can be restored to its normal alignment.

Why Surgery Is Almost Always Recommended

For decades, hand surgeons have debated how aggressively to treat Bennett fractures. That debate is largely settled. A long-term follow-up study tracked seventeen patients who had been treated with a cast alone for an average of 26 years. All of them had decreased range of motion and grip strength, twelve had a visible deformity at the base of the thumb, and X-rays showed persistent subluxation and marked degenerative arthritis. The authors concluded that conservative management should be avoided in favor of some form of surgery.⁵

A separate study reinforced the importance of achieving an accurate reduction. Among patients whose fractures healed in excellent position, the vast majority were symptom-free at a median follow-up of over seven years. But among those with residual displacement, less than half were free of symptoms, and arthritis appeared on X-rays at a much higher rate.⁶ The takeaway is clear: the closer the joint surface is restored to its original anatomy, the better the long-term outcome.

The rare exception where a cast may be considered is a fracture with almost no displacement and a stable joint, but even then, close monitoring with repeat X-rays is essential to catch any shift early. If the fragments move even a small amount during healing, surgery becomes necessary.

Surgical Options

The most common surgical approach is closed reduction with percutaneous pinning. The surgeon manipulates the thumb to push the fragments back into place without making a large incision, then drives thin metal wires (called K-wires or Kirschner wires) through the skin to hold the fragments while the bone heals. A systematic review and cohort analysis concluded that this method should be the first choice for surgical treatment, given its excellent long-term functional results and low complication rate.⁷

When closed reduction cannot achieve an acceptable alignment, open reduction and internal fixation (ORIF) becomes the fallback. This involves a small incision over the base of the thumb to directly visualize the fracture, reposition the fragments, and fix them with screws, a small plate, or wires. ORIF gives the surgeon better control over the reduction but comes with higher rates of reintervention (roughly 4 to 20 percent) and a notable risk of persistent numbness or tingling near the surgical scar (5 to 28 percent of patients in some series).⁸

One tricky scenario involves Bennett fractures where the avulsion fragment is tiny. These small pieces can be difficult to pin with standard-size wires. A study of patients with these small-fragment Bennett fractures found that using thinner K-wires to fix the fragment directly and stabilize the CMC joint achieved strong results. At final follow-up, grip strength returned to about 98 percent of the uninjured hand, and pinch strength to about 91 percent. None of the patients developed arthritis in the thumb joint during the follow-up period.⁹

Arthroscopic-Assisted Repair

A newer approach uses a tiny camera inserted into the CMC joint to guide the reduction. This arthroscopic-assisted technique lets the surgeon see the joint surface directly, clean out any debris or cartilage damage, and confirm that the fragments are perfectly aligned before pinning them in place. No study has yet shown that outcomes are better than those from standard percutaneous pinning or open surgery.¹⁰ However, the technique offers some practical advantages: smaller incisions, shorter operating time, fewer complications, and the ability to assess whether the cartilage inside the joint was damaged during the original injury.¹¹

Detecting cartilage damage at the time of surgery could prove important in the long run. The theory is that if surgeons can confirm a more precise joint surface reduction under direct visualization, the rate of late-onset arthritis may drop.¹² Right now, that remains plausible but unproven. Arthroscopic repair also requires specialized equipment and training, so it is not available at every surgical center.

Complications and Long-Term Outlook

The most significant long-term concern after a Bennett fracture is post-traumatic arthritis in the thumb CMC joint. Even with surgery, a systematic review found that about 9 percent of patients developed arthritis.¹³ Pain was reported in roughly 13 percent, while reoperation was needed in about 2 percent. Nonunion, where the bone simply fails to heal, was not observed in any of the studies included in that review, making it an extremely rare problem for this fracture type.

The quality of the initial reduction is the strongest predictor of whether arthritis develops. As the earlier-cited follow-up study showed, patients whose fractures healed with residual displacement developed arthritis on X-rays at roughly double the rate of those with excellent reductions.¹⁴ This is why surgeons emphasize restoring the joint surface as precisely as possible, even when it means converting from a percutaneous approach to an open one during the operation.

When arthritis does develop, it may not appear for years. Some patients remain symptom-free despite X-ray evidence of joint wear, while others develop aching pain during heavy gripping tasks. If the arthritis becomes disabling, later treatment options include cortisone injections, joint fusion, or joint replacement, but those are rarely needed when the fracture was well-managed initially.

Recovery and Rehabilitation

After percutaneous pinning, the thumb is typically immobilized in a cast or splint for four to six weeks while the bone heals. The K-wires are then removed in a clinic visit, which is usually quick and well-tolerated. After wire removal, hand therapy begins to restore motion, strength, and dexterity.

When stable internal fixation is achieved with screws or a plate during open surgery, early active rehabilitation may be started sooner. A study of patients treated with open reduction and stable fixation followed by an early active rehabilitation program found satisfactory functional and radiological results.¹⁵ Another study using an early rehabilitation protocol for articular base fractures found that patients recovered pinch strength to about 94 percent and grasp strength to about 98 percent of their uninjured side, with no measurable difference between the two hands.¹⁶

Most patients can expect to return to desk work within a few weeks of surgery, but jobs or sports involving heavy gripping, twisting, or impact typically require three to four months before full participation. In a cohort of patients treated with K-wire fixation, 85 percent returned to unrestricted movement during hand therapy, and at an average of over five years from injury, the group’s mean disability score was very low, indicating minimal lasting functional impairment.¹⁷

The Role of Ligaments in Fracture Behavior

Understanding why the fracture displaces the way it does helps explain the treatment rationale. A biomechanical study found that positioning the thumb in radial abduction and pronation reduced fracture displacement, while extending the CMC joint or tensioning the anterior oblique ligament did not help.¹⁸ This explains why, when surgeons perform a closed reduction, they typically push the thumb into abduction and pronation to seat the fracture fragments. It also clarifies why simply casting the thumb in extension, an older treatment approach, did not produce reliable results.

The volar beak ligament, which anchors the small fragment to the trapezium, is the reason the Bennett fracture forms its characteristic two-part pattern rather than the metacarpal simply dislocating outright. Without that ligament holding one piece in place, the entire metacarpal would shift, producing a pure dislocation rather than a fracture-dislocation. The ligament’s integrity also explains why the small fragment almost never needs to be reduced on its own; it stays where it belongs. The surgical challenge is getting the larger shaft fragment back down to meet it.

Bennett Fractures in Children and Adolescents

Children and teenagers can sustain an injury that looks and behaves like a Bennett fracture, but the anatomy is slightly different. In growing bones, the growth plate near the base of the first metacarpal has not yet fused. A Bennett-equivalent injury in a child involves the growth plate rather than the adult joint surface, producing what is classified as a Salter-Harris type III or IV fracture.¹⁹

When these fractures are displaced, the standard approach mirrors that for adults: closed or open reduction with pin fixation to restore both the joint surface and the growth plate alignment. The stakes are slightly different, though, because a growth plate disruption can affect future bone growth if not properly aligned. These injuries are rare enough that there is limited published data on long-term outcomes, and the optimal management strategy is still evolving. Surgeons generally err on the side of anatomic reduction, especially in younger patients whose hands still have years of growth and heavy use ahead.

Percutaneous Pinning Complications Worth Knowing About

K-wire fixation is the workhorse treatment for Bennett fractures, but it is not complication-free. Superficial wound infection around the pin sites occurs in roughly 4 to 8 percent of patients.²⁰ These infections are usually mild and resolve with a short course of oral antibiotics and wire removal once the bone has healed sufficiently. More serious deep infections are rare.

Pin migration, where the wire backs out or shifts before the bone is fully healed, can also occur. If this happens early, the fracture may lose its reduction, potentially requiring a second procedure. Stiffness in the thumb after wire removal is common initially but typically improves with consistent hand therapy over several weeks. The most reassuring finding across the literature is the absence of nonunion: Bennett fractures heal reliably once the fragments are held in an acceptable position.