What is Bennett Fracture?
A Bennett fracture is the most frequent type of break involving the base of the thumb. When this happens, the lower inside part of the first bone in the thumb separates from the rest of it. This injury usually happens from a heavy force applied on a slightly bent thumb and might be linked with other wrist bone fractures or ligament injuries. X-rays are crucial for diagnosing these injuries and for putting together a surgery plan, as these fractures are generally unstable. Surgery for these breaks can involve a few different methods. This could be setting the bone back into place and then securing it with pins through the skin or using pins during an open surgical procedure. If the pieces of broken bone are properly aligned after surgery, patients typically recover well.
What Causes Bennett Fracture?
This type of break happens when a force is applied to a bent metacarpal, which is a bone in the hand. This injury might also be linked to breaks in the nearby wrist bone, known as the trapezium, or damage to the ligament on the side of the thumb joint.
Risk Factors and Frequency for Bennett Fracture
A Bennett fracture is a specific kind of fracture that involves the thumb. Thumb fractures most frequently occur in children and the elderly. For children aged from infancy up to 16 years, 22% of all long bone (tube-shaped bone) fractures involve the thumb. In people over 65 years old, thumb fractures account for 20% of all hand fractures. In older adults, the thumb is the most frequently fractured long bone, and the fracture is usually at an angle and affects the joint.
Signs and Symptoms of Bennett Fracture
If you have pain and swelling at the base of your thumb, these could be signs of a medical issue that needs to be addressed.
Testing for Bennett Fracture
When looking at hand injuries, there are several types of X-rays that can be taken for a detailed view. The three primary views are from the front (anteroposterior or AP), the side (lateral), and diagonally (oblique). For specific injuries, doctors may order additional views of the thumb, like the Robert’s view. This specialized AP view focuses on the joint at the base of the thumb and is taken by turning the arm and thumb in a certain way before directing the X-ray beam at a 90-degree angle to the thumb.
Another specialized view, known as the Bett’s view, is taken by slightly turning the palm further than normal and angling the X-ray beam 15 degrees from the base to the tip of the thumb. Stress X-rays are also helpful in certain situations. They are done by pushing the thumbs together during the front view X-ray. This can highlight potential misalignments or displacements at the base of the thumb on the affected side.
With the help of these X-rays, doctors can classify thumb injuries per the Gredda classification. There are three types under this system. Type 1 involves a single bone fragment and displacement of the thumb base. Type 2 describes an injury where the bone is compacted but the thumb base is normally positioned. Lastly, Type 3 refers to a small bone chip coupled with a dislocation of the thumb at the base.
Treatment Options for Bennett Fracture
The process of repairing a Bennett fracture requires applying a steady pull along with moving the hand toward the body and slowly rotating the hand while applying pressure over the base of the thumb. However, straightening the thumb into a hitchhiker position can actually make the fracture worse, and should be avoided.
Historically, these fractures were treated by moving the broken parts back into place and then splinting the thumb. This approach was popular until the 1970s and showed favorable results. But, more recent studies have shown that this treatment approach has unsatisfactory outcomes when done alone. The current strategies for treating Bennett fractures involve either minimally invasive surgery to realign the bones and hold them together with pins, or open surgery to repair the fracture using pins or screws. Both methods have been effective in treating this type of fracture.
Once successful reduction is performed, the thumb is usually fixed in position with pins from the first to the second finger bone, or towards a small bone in the wrist called the trapezium. This is usually successful in re-positioning the fractured part of the thumb. If open surgery is chosen to treat the fracture, a popular incision known as the Wagner incision is usually performed. Deciding between the two types of surgery remains a topic of discussion among healthcare providers.
There’s also debate over the acceptable amount of misalignment at the fracture site in non-athletes. Some studies didn’t find a link between how perfectly the bone surfaces are realigned and the outcomes of the treatment, while others have shown that even a slight misalignment doesn’t alter the pressures at the location of it. Therefore, it’s accepted that a small misalignment of up to 2mm, and adjusting any displacement of the joint, won’t increase the risk of developing arthritis due to injury. However, despite these findings, several other studies suggest perfect realignment is preferred.
What else can Bennett Fracture be?
A Rolando fracture is a type of complex injury that occurs at the bottom of the first bone in the thumb. The break results in several small bone pieces. However, a ligament (a band of strong tissue) at the palm side of the wrist remains intact, keeping a portion of the bone from moving out of place.
What to expect with Bennett Fracture
Patients may be able to start range of motion exercises about 5 to 10 days after their screw fixation operation, and four weeks after pinning (once the pins have been removed). A study that reviewed 41 cases of Bennett fractures found interesting long-term outcomes. Eighty-six percent of patients who had a near-perfect fracture reduction (less than 1 mm step off) had no remaining symptoms, while only 46% of patients with average or subpar reduction (greater than 1 mm step off) were symptom-free.
However, defining a strict treatment plan is challenging due to the rarity of these fractures, insufficient long-term imaging follow-ups, and the absence of random testing with prospective data.