Introduction
Bennett fracture is the most common fracture involving the thumb's base. This fracture usually refers to an intraarticular fracture that separates the palmar ulnar aspect of the first metacarpal base from the remaining first metacarpal. These fractures are unstable. The radiographs are necessary for the evaluation of these injuries and also to help in planning surgical approaches for reduction. The surgical treatment differs for these fractures. The surgical treatments include closed reduction with percutaneous pinning or open reduction with either pin or inter-fragment pinning. The clinical results are good when there is good alignment of the fracture fragments at post-surgical fixation.
What Is the Etiology of Bennett Fracture?
The cause of Bennett fracture is the axial load that occurs on the partially flexed metacarpal along with the fractures that involve adjacent carpal bone, and ulnar collateral ligament injuries of the thumb metacarpophalangeal joint.
What Is the Epidemiology of Bennett Fracture?
Thumb fractures are most commonly found in children and older people. Bennett fracture is a subtype of fracture that involves the thumb. Tubular bone fractures are observed in children between infancy and 16 years, and in older patients, 20% of hand fractures occur in the thumb. The thumb is the most common tubular bone fracture with oblique and intra-articular bone fractures.
What Is the Pathophysiology of Bennett Fracture?
The fracture pattern is distinct. The base of the first metacarpal is fractured with the intraarticular extension because of the palmar ulnar fragment of the first metacarpal, which is held in place by the ligamentous attachment to the trapezium during the axial loading. The rest of the metacarpal moves in the opposite direction, and the main fracture line occurs along the point of weakness. Because of this, the first metacarpal shaft subluxated proximally, dorsally, and radially due to the pull of the extensor pollicis longus, abductor pollicis longus, and extensor pollicis brevis, which remains attached to the fracture fragment.
The physical signs of Bennett fractures include pain and localized swelling to the base of the thumb.
How Is Bennett Fracture Diagnosed?
The diagnosis of Bennett fracture is made using radiographs that include lateral, oblique, and anteroposterior views. If necessary, additional views of the thumb can be obtained to evaluate the injury. The accurate AP (anterior to posterior) view of the first carpometacarpal joint with hyper pronation of the forearm by an X-ray beam directed 90 degrees to the plate and by placing the dorsal aspect of the thumb against the radiographic plate. The second view is called Bett's, which is obtained by a beam directed 15 degrees proximal to the distal with the palm overpronated 20 degrees from flat against the radiographic plate. Finally, by pressing the radial aspect of the thumbs together on AP view stress, radiographs can be performed, demonstrating subluxation of the metacarpal base radially in relation to the trapezium on the symptomatic side. Based on radiographic appearance, Gredda classified Bennett fractures into three types, that is:
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Type 1 - Fracture with single ulnar fragment and subluxation of the metacarpal base.
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Type 2 - Impaction fracture without subluxation of the first metacarpal.
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Type 3 - Injury with the small ulnar avulsion fragment concerning metacarpal dislocation.
What Is the Management of Bennett Fracture?
Avoiding thumb extension is recommended as it has been shown to cause displacement of the fracture in cases of Bennett fracture. In the 1970s, Bennett described the splinting and closed reduction as the preferred treatment method, which has shown good outcomes, although some studies have shown poor results.
The surgical treatment of Bennett fracture includes closed reduction with percutaneous pinning or open reduction using pins or interfragmentary screws. In addition, the methods of fixation have been proven effective. Treatment with closed reduction with intermetacarpal fixation from the first to the second metacarpal to the trapezium is often effective in reducing the first metacarpal shaft subluxation. Treating a fracture with open reduction is usually performed through a Wagner incision.
The way these fractures must be treated with either open or closed reduction is still a matter of debate. Some authors have found no correlation between the radiographic outcome and the quality of articular reduction. Still, biomechanical studies have found that two millimeters of articular surface step-off does not affect the contact pressure at the step-off location. So it has been concluded that bony apposition of the fragments within two millimeters and the correction of the joint subluxation can be tolerated without the increased risk of posttraumatic arthritis. Many studies have preferred anatomic reduction.
What Are the Differential Diagnoses of Bennett Fracture?
The differential diagnosis of Bennett fracture includes the following:
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Rolando Fracture: This is a more severe form of Bennett fracture that involves the same area of the thumb. It is a comminuted fracture, which means that the bone is broken into multiple pieces.
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Scaphoid Fracture: This is a fracture of one of the small bones in the wrist. The symptoms of a scaphoid fracture can be similar to those of a Bennett fracture, and it may be difficult to distinguish between the two without an X-ray.
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Metacarpal Fracture: A fracture of the metacarpal bone, which is the bone that connects the wrist to the fingers, can also cause symptoms similar to those of a Bennett fracture.
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Ligament Injury: A sprain or tear in the ligaments of the thumb can also cause pain, swelling, and difficulty moving the thumb.
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Arthritis: Arthritis can cause pain, stiffness, and swelling in the thumb joint. It may be difficult to distinguish between arthritis and a Bennett fracture without an X-ray.
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Tendinitis: Inflammation of the tendons in the thumb can cause pain and difficulty moving the thumb.
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De Quervain's Tenosynovitis: This is a condition that causes pain and swelling in the tendons that run along the thumb side of the wrist. It can be caused by overuse or repetitive motions.
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Trigger Finger: This is a condition that causes one of the fingers to become stuck in a bent position. It can also affect the thumb and cause pain and difficulty moving the thumb.
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Nerve Injury: Injuries to the nerves in the hand or wrist can cause pain, numbness, or weakness in the thumb and hand.
What Is the Prognosis of Bennett Fracture?
About 86% of the patients with Bennett fracture had no residual symptoms with anatomic reduction, and 46% with sound reduction were asymptomatic. Different range of motion exercises may begin five to ten days after the screw fixation and four weeks after pinning. The long-term outcomes were based on the quality of fracture reduction. Unfortunately, definitive treatments are lacking due to a small number of patients, lack of randomized prospective data and lack of long-term imaging follow-up definitive therapies are lacking.
Conclusion
The management of Bennett fracture is complex, and it is best done with the help of an interprofessional team that includes a physical therapist, orthopedic surgeon, nurse, and surgeon.
