The thumb is formed by the metacarpal bone, the proximal and distal phalanges. A thumb fracture can occur in any of these three bones.
The distal end of the thumb metacarpal forms a joint with the proximal phalange, which is named the metacarpo-phalangeal (MCP) joint. The proximal end of the thumb metacarpal and the carpal bone (trapezium) form the carpo-metacarpal (CMC) joint. A thumb fracture can occur in any of these anatomical regions but is more frequent at the base of the metacarpal bone. The thumb metacarpal is the broadest tubular metacarpal bone of the hand. Anatomically it is slightly detached from the other bones of the hand to allow for grasping. Therefore, a thumb fracture can have serious functional implications.
Due to the unique anatomy, a fracture of the thumb metacarpal is quite different compared to other metacarpal bones. Metacarpal fractures can be isolated or combined with injury of the CMC joint and involve the trapezium. These fractures generate instability of the CMC joint producing chronic pain and weakness, commonly requiring surgical reconstruction of the joint surface. A fracture of the thumb metacarpal is also called skier’s thumb. In case of fractures to the metacarpal head, the knuckle seems to disappear and its movement triggers pain. When associated with damage to the tendon abductor pollicis longus (APL), it leads to instability of the CMC joint.
There are different types of thumb fractures that are named based either on their location relative to the joint and take the name of the specialist who first described them. These definitions are:
1. Intra-articular comminuted
2. Extra-articular transverse
3. Extra-articular oblique
4. Intra-articular or Bennett’s fracture
5. Intra-articular or Rolando’s fracture
Thumb fractures can be stable, non-displaced or minimally displaced, when the bone fragments maintain their anatomical position, or displaced when the bone fragments have moved from their original anatomy. They can also be transverse, oblique, spiral, or comminuted when multiple bone fragments are released.
A Bennett’s fracture of the thumb base is the most common type of fracture producing an oblique break of the metacarpal affecting the function of the underlying joint. This requires immediate medical attention.
A Rolando’s fracture is a 3-part fracture at the base of the thumb metacarpal generating a T- or Y-fracture pattern. It is located either in the frontal or in the sagittal plane. It is caused by an axial overload along the thumb metacarpal causing a compression fracture of the joint surface. This type of pathology is uncommon but has a worse prognosis than a Bennett's fracture.
According to the Habermeyer Classification the fractures to the proximal humerus are divided into:
Type 0 one fractured part without dislocation
Type A two-part fracture of the great tuberosity and lesser tuberosity avulsion
Type B involves the humerus “surgical” neck below the femoral head as two-part, three-part and four-part with one or both tuberosities
Type C involves the humerus anatomical neck (between the head and greater tuberosity) as two-part, three-part and four-part with one or both the greater and lesser tuberosities.
These are defined further as:
One-part fractures are non-displaced fractures or fractures with minimal displacement
Two-part fractures only involve a single segment
Three-part fractures involve two segments
Four-part fractures occur when all humeral segments are involved (see image in pathology section)
The injury severity is proportional to the increasing number of fractures.
A thumb fracture is the result of an impact and/or torsion energy and is mostly found in men. It is caused by a force pulling the thumb backwards in a flexed position at the metacarpal joint as it happens in:
Falls onto the hand
When catching a ball
The following sports and activities represent the main risk factors for a thumb fracture:
Contact sports (hockey, football, rugby)
The symptoms arising from thumb fractures are:
Knuckle asymmetry and/or depression
Instability of the carpo-metacarpal joint
During the medical examination the patient provides information including the history of previous hand injuries and mechanisms that have caused the current injury to the thumb. Clinical examination of the hand will determine:
Changes in the anatomy of the affected thumb against the healthy thumb
Presence of skin lacerations, bruises
Tenderness at touch
Pain triggered by movement
Reduced range of movement
If a thumb fracture is suspected X-rays are taken under the antero-posterior, lateral, and oblique view to confirm the presence of a fracture and assess its characteristics. CT and MRI scans may be required for a detailed definition of complex fractures.
Management of thumb fractures varies in relation to fracture site and its classification. In case of stable fractures surgery is not required and conservative treatment with a cast is usually sufficient. Sometimes a closed reduction by an orthopaedic/hand surgeon may be necessary to realign the fractured metacarpal. However, surgery is needed if displacement of the abductor pollicis longus (APL) muscle has occurred during the thumb reduction. A special cast named thumb spica cast or a splint are used to hold the bone fracture in place for 4-6 weeks and then replaced with a removable splint if there is sufficient stability with hand movement. Additional thumb fracture management includes:
Administration of NSAIDs
Physiotherapy with specific thumb exercises while the hand is in a cast or brace.
Surgery is required in significantly displaced thumb metacarpal fractures or those fractures that do not maintain alignment despite the immobilisation with a cast. Different methods are available for surgical fixation depending on the type of fracture:
Open reduction and internal fixation (ORIF) is used in displaced fractures. The procedure begins with a dorsal incision and the placement of screws, plates and k-wires. The pins are kept in place for 4-6 weeks.
External fixation is used in unstable complex thumb fractures. A closed reduction with percutaneous pinning using k-wires is also a frequent surgical option.
Traction of the fractured thumb with Chinese finger traps achieves fracture alignment and is used as a sort of traction device.
Complications after thumb fracture are rare and include:
Non-union of the thumb metacarpal may occur when a fracture is neglected, with delayed surgery, or in very unstable fractures. This results in bone misalignment causing improper thumb angulation and possibly surgery (or a second surgery)
Infection following surgery
Arthritis can develop if the joint and joint ligaments are affected
Chronic Regional Pain Syndrome (CRPS) leads to prolonged pain of the injured thumb area but is rare.
With or without surgery, the use of a cast or splint is recommended for 6-12 weeks following thumb metacarpal fracture. The prognosis depends on the severity of the fracture. Any physical activities that involve grasping, gripping, pulling and punching should be avoided until a complete fracture healing has been achieved. Once pain has resolved the patient can begin to move the wrist, hand and fingers to prevent stiffness of all joints. Intensive physical therapy usually commences approximately 6-8 weeks after surgery. A physical or occupational therapist will recommend exercises to restore flexibility and strength of the thumb (thumb opposition, extension flexion, etc). The therapist will also advice the patient methods to avoid recurrent injuries. Standard rehabilitative therapy includes:
Return to activity plan
Taping / bracing
Preventing thumb fractures is mostly achieved by reducing the risk of falls and protecting the thumb during sports and other professional activities. Common strategies are:
Use of devices to improve elderly patient stability and avoid falls
Wearing protective gear during sport training and carpentry work
Modification of physical activities
Exercise to improve muscle strength, flexibility and posture.