Last Updated on April 3, 2024
Carpal bone fractures are fractures of the bones that make the carpus or wrist, also called carpal bones.
Carpal fractures account for about about 5% of all fractures. A scaphoid fracture is the most common of carpal bone fractures accounting for almost about 70 percent of carpal fractures. It is followed by triquetrum (about 20%) and trapezium (about 5%). The rest of the carpal bones contribute 5-7% of carpal bone fractures.
The missed injuries are common in the case of carpal bones due to their complex shapes and articulations.
Relevant Anatomy of Carpal Bones and Wrist
Carpal bones are a major constituent of the wrist. The wrist is an arrangement between the forearm and carpal bones, stabilized by ligaments. The wrist is quite a mobile joint and has 80 degrees of flexion, 70 degrees of extension, and 30 degrees of ulnar deviation.
There are 8 carpal bones arranged in 2 rows
- Proximal row- the scaphoid, lunate, triquetrum, and pisiform
- Distal row- the trapezium, trapezoid, capitate, and hamate.
The scaphoid bone is the boat-shaped bone that is the lateralmost bone of the proximal row. It is involved with most wrist movements, especially flexion. It is covered in cartilage about 80 percent and articulates with 4 other bones. It has a very important role in writ movements and is the most common carpal bone to get fractured.
The scaphoid bone is unique as its vascular supply of this bone travels from the distal region of the scaphoid back proximally.
The lunate is half-moon-shaped and is positioned between the scaphoid and the triquetrum. It is another important bone responsible for wrist motion esp flexion/extension. It is also involved radial/ulnar deviation at the radiocarpal and midcarpal movements.
The triquetrum is located on the ulnar side of the proximal row. It is pyramid-shaped with an oval-shaped facet on its volar side that articulates with pisiform. On the lateral side, it articulates with the lunate and proximally with the triangular fibrocartilage complex.
The pisiform is a pea-shaped bone medial to the triquetrum that is enclosed in the sheath of flexor carpi ulnaris and lies close to the ulnar nerve.
The trapezium is a quadrangular-shaped bone located on the radial side of the distal row. It articulates with the 1st metacarpal and participates in movements of flexion/extension, abduction/adduction, circumduction, and opposition at the joint.
The trapezoid is positioned medial to the trapezium and lateral to the capitate bone.
The capitate is medial to the trapezoid and articulates with the proximal row’s scaphoid, lunate, and hamate, and 2nd, 3rd, and 4th metacarpals distally. It is the largest carpal bone.
The hamate is a wedge-shaped bone on the ulnar side of the distal carpal row. Distally on the volar surface, a hook protrudes out from the ulnar side, known as the hook of the hamate. It acts as a pulley for the flexor tendons of the 4th and 5th fingers.
Various intracarpal and intercarpal ligaments act as stabilizers of the wrist. Several hand muscles originate primarily in the forearm and pass over the wrist with the flexor carpi ulnaris being the only one that inserts into the wrist (pisiform bone) into the pisiform bone. a
The ulnar nerve runs deep to the flexor carpus ulnaris tendon through the canal of Guyon. The median nerve lies between the flexor carpus radialis and the palmaris longus tendon in the carpal tunnel.
Branches of radial and ulnar arteries supply the blood to the carpal bones.
The carpal bones are involved in the formation of the following joints
- Radiocarpal joint
- Distal radioulnar joint
- Midcarpal joint
- Carpometacarpal joints
Causes and Mechanism of Injury To Carpal Bones
Most of carpal bone fractures occur due to falling on the outstretched hand concentrating the body weight and external forces on the wrist. Trauma, and sports injuries are frequent causes. Repetitive injuries can also injure the carpus.
Axial compression force applied with the wrist in hyperextension places palmar ligaments under tension and the dorsal joint surfaces put under compression and shear stresses.
High-energy forces result in carpal bone fractures or ligamentous disruptions whereas low-energy forces result in sprains.
The following article discusses carpal bone fractures other than scaphoid.
Fractures of Individul Carpal Bones
Fractures of Triquetrum
The triquetrum is the second most common of the carpal bone fractures, the first being the scaphoid. Most of these fractures are avulsion injuries and the most common cause is impingement of the ulnar styloid [Occurs with the wrist in extension and ulnar deviation] or hamate.
The triquetral fracture occurs when the wrist is forced into extreme extension and ulnar deviation causing the proximal hamate and distal radius to impinge on the triquetrum and sheer it.
Fractures of Trapezium
The trapezium is the third most common fractured carpal bone and often results from high-energy trauma. There are two main types
- Ridge fractures- Ridge fractures are mostly avulsion fractures caused by the capsular ligaments and can occur during forceful deviation, traction, or rotation.
- Body fractures- Most of these fractures are vertical body split fractures.
Fracture through the articular surface of the trapezium is produced by the base of the first metacarpal being driven into the articular surface of the trapezium by the adducted thumb.
The stability of the joint is evaluated before carrying out the treatment. Rupture of the surrounding ligaments and the dorsal joint capsule may result in instability and they need to be repaired.
Fractures of Lunate
Acute fractures of the lunate are classified into five types-
- Frontal fractures of the palmar pole
- Frontal fractures of the dorsal pole.
- Osteochondral fractures of the proximal articular surface
- Transverse fractures of the body.
- Transarticular frontal fractures of the body of the lunate.
There is a history of fall on outstretched hand. There is a pain on a radio-dorsal aspect of the wrist. There may be associated swelling and there is tenderness on the radiocarpal joint.
Most lunate fractures can be treated by immobilization in the cast for four weeks. Osteonecrosis is a known complication and needs to be followed up for that.
Fractures of Trapezoid
The trapezoid, being located between the first and second ray may be exposed to fewer forces
Injury to the trapezoid generally occurs when force is applied through the second metacarpal. The fracture typically occurs due to pressure from the second metacarpal when the finger and wrist are hyper-extended. The tenderness is a line of the index finger near the wrist.
Fractures of Capitate
The capitate is the largest carpal bone and capitate fractures are being reported increasingly. Capitate may get fractured due to a direct blow or fall on the outstretched hand.
Pain and swelling is in the line of the third and fourth metacarpals. Tenderness may be present. A ligament injury should be suspected and ruled out when this diagnosis is made (or considered).
Fractures of Hamate
Hamate fractures are thus classified as type I fractures involving the hook (more common) and type II fractures involving the body. Hamate body fractures are typically seen in injuries where an axial force was applied to a closed fist.
There is ulnar-sided pain and swelling.
Most of hamate hook fractures are seen in individuals who participate in sports involving a racquet, bat, or club or in individuals who have a history of falling on an outstretched hand.
Hamate body fractures are commonly associated with dislocation of the fourth and fifth fingers.
The usual complaint is of pain in the wrist in the line of the fourth and fifth metacarpal. The pain is aggravated by grasp, and pain with dorso-ulnar deviation.
Physical examination reveals tenderness on palpation over the hook of the hamate. There would be a decrease in grip strength. Sometimes, the ulnar nerve may get involved [Compression in Guyon’s canal], and paresthesia may be present in the fourth and fifth fingers.
Clinical Presentation of Carpal Bone Fractures
There is a history of injury either a fall on the outstretched hand or motor vehicle injury. A direct blow to the wrist may also cause a fracture. The patient presents with wrist pain and swelling. On examination, the convolved area would be tender on palpation. There would be tenderness and swelling at the base of the thumb and pain on pinching.Because the bones have ill-defined boundaries on palpation and are stacked quite close together, the exact fractured bone may not be very apparent.
Triquetral fractures present with tenderness on the ulnar side whereas scaphoid and lunate have tenderness on the radial side of the wrist. For palpating the triquetrum, the hand may be placed in radial deviation.
Hamate fractures also have pain on the ulnar side, pain in the hypothenar region, and decreased grip strength. The examination may reveal an ulnar nerve deficit as the ulnar nerve lies in the vicinity. It can be suggested by paresthesias in the ring and small fingers and weakness of intrinsic muscles supplied by ulnar nerve.
The chief complaint is ulnar-sided wrist pain and the physical exam is notable for point tenderness over the pisiform.
many carpal bone fractures may have diffuse pain and lead to missed diagnosis of arthritis or tendinitis.
Imaging of Carpal Bone Fractures
X-rays
Routine views for detecting injury are standard PA, lateral and oblique views of the wrist. Special views include Bett’s View- and carpal tunnel view.
A scaphoid series of X-rays may help to find the triquetral fracture not visible on routine x-rays.
Lunate fractures are difficult to visualize early due to superimposed structures. .Fractures of the capitate can usually be identified on standard scaphoid views.
Hamate fractures are difficult to detect on routine imaging. Oblique, lateral, or modified lateral views may be needed.
CT
CT scan may help to detect missed fractures and associated injuries.
A CT scan would show the fracture clearly. Osteonecrotic changes are also more easily seen on CT. A computed tomography scan with 3-D reconstruction may help in confirmation of diagnosis where the diagnosis cannot be made on routine imaging.
MRI
MRI not only shows a fracture but also can assess the blood supply. It can pick osteonecrosis in the early stage and in the healing stage can help to asses revascularization.
Routine wrist views including oblique views are done. Loss of the normal relationship between the second metacarpal base and the trapezoid may indicate injury to the trapezoid.
Treatment
The treatment of carpal bone fractures depends on the bone injured, displacement of fracture, and associated bony or ligamentous injuries.
Nonoperative Treatment of Carpal Bone Fractures
For most of undisplaced isolated carpal bone fractures, a forearm plaster cast for 4-6 weeks is sufficient. Displaced fractures are treated by closed reduction and immobilization after reduction is successful. If closed reduction cannot be achieved, open reduction and internal fixation is done.
Operative Treatment
Dsiplaced fractures and fractures involving an articular surface require accurate reduction. Therefore open reduction and internal fixation are recommended. The internal fixation can be done using K-wires, Herbert screws with or without bone grafting.
The excision of very small proximal fragments has also been described.
Complications
- Carpal tunnel syndrome
- Ulnar artery compromise
- Partial or complete flexor tendon ruptures involving the fourth, and fifth fingers.
- Entrapment of the ulnar nerve
