- Joints of the proximal carpal row, that connect the adjacent surfaces of the scaphoid, lunate and triquetrum bones. The pisiform joint, an articulation between the pisiform and triquetrum, is described as a separate joint but it belongs to the proximal carpal joints.
- Joints of the distal carpal row, via which the adjacent surfaces of the trapezium, trapezoid, capitate, and hamate bones articulate
- Midcarpal joint, by which the carpal rows articulate with each other.
The joints of the proximal and distal carpal rows are supported and fixed by many ligaments, so there is minimal movement within them. Their function is to coordinate the movements of the wrist (radiocarpal) and midcarpal joints. The midcarpal joint, however, is able to produce a noticeable range of motion organized into two degrees of freedom; flexion-extension and abduction-adduction.
|Type||Synovial plane joints; biaxial|
|Articular surfaces||Joints of the proximal carpal row: Adjacent articular surfaces of scaphoid, lunate, and triquetrum bones
Joints of the distal carpal row: Adjacent articular surfaces of trapezium, trapezoid, capitate and hamate bones
Midcarpal joint: distal articular surfaces of proximal carpal bones, proximal articular surfaces of distal carpal bones
|Ligaments||Interosseous ligaments of proximal and distal carpal rows, palmar intercarpal, dorsal intercarpal ligaments|
|Innervation||Articular branches of anterior interosseous nerve, posterior interosseous nerve, deep and dorsal branches of ulnar nerve|
|Blood supply||Palmar and dorsal carpal arches|
|Movements||Flexion-extension, abduction-adduction, circumduction|
This article will discuss the anatomy and function of the intercarpal joints.
- Articular surfaces
- Ligaments and joint capsule
- Blood supply
- Muscles acting on the intercarpal joints
Intercarpal joints are all classified as synovial plane joints, meaning that the articular surfaces are functionally considered as nearly flat and lined with fibrocartilage. The joints are enclosed by the thin fibrous capsules whose internal surfaces are lined by the synovial membranes.
The joints of the proximal carpal row connect the relatively flat/planar adjacent surfaces of the scaphoid and lunate, and triquetral bones, forming the scapholunate and lunotriquetral joints. The pisiform bone, which lies within the tendon of the flexor carpi ulnaris muscle, articulates with the palmar surface of triquetrum bone, forming the pisiform joint. The pisiform bone is also connected to the hook of hamate bone and fifth metacarpal bones via pisohamate and pisometacarpal ligaments, respectively.
The joints of the distal carpal row connect the adjacent surfaces of the trapezium, trapezoid, capitate and hamate bones. These articulations form the trapeziotrapezoid, trapezoideocapitate and capitohamate joints which are substantially less mobile than those of the proximal carpal row.
The midcarpal joint is the compound articulation between the distal surfaces of the proximal carpal bones and the proximal surfaces of the distal carpal bones. More specifically, it is a joint formed collectively by the:
- Scaphoid, lunate and triquetral bones proximally
- Trapezium, trapezoid, capitate and hamate bones distally
The midcarpal joint is divided into medial and lateral compartments. The medial compartment presents two articular regions. The first is that formed by the convex surface of the head of capitate bone which is received by the collective concave distal surfaces of the scaphoid and lunate bones. The second part, the triquetrohamate component, is more complex, presenting both distally convex and concave surfaces. The lateral compartment consists of the plane surfaces of trapezium and trapezoid bones, which articulate with the distally convex surface of the scaphoid bone. Thus, this is a planosellar compound joint, slightly convex distally.
Ligaments and joint capsule
The intercarpal and midcarpal joints are enclosed by an irregular two layered, joint capsule. The outer layer of the capsule is composed of fibrous connective tissue which provides structural support to the joint, while the inner layer is composed of a synovial membrane responsible for the secretion of synovial fluid, keeping the joint lubricated. It spans the distal surfaces of the proximal carpus to the proximal surfaces of the distal carpus. It also interdigitates between the bones, showing proximal projections over the scapholunate and lunotriquetral joints. In the same manner, the capsule projects between the bones of the distal carpal row. The distal projection between the trapezium and trapezoid bones often communicates with the joint space of the corresponding carpometacarpal joint. The joint between the pisiform and triquetrum bones is usually isolated, having its own thin fibrous capsule lined by a synovial membrane.
The joints of the carpal bones are supported by an array of ligaments, namely the interosseous intercarpal ligaments, dorsal intercarpal ligaments, and palmar intercarpal ligaments. It’s worth noting that these ligaments are variably described in the literature, which has led to a degree of confusion in regards to their anatomy. The dorsal and palmar intercarpal ligaments are bound within the joint capsule of the carpal joints, with the palmar ligaments being much more numerous than those found on the dorsum. The interosseous intercarpal ligaments are conversely intracapsular. Additionally, the stability of the carpus is also supported by the flexor retinaculum.
Interosseous intercarpal ligaments
The interosseous ligaments of the proximal carpal row are named according to the bones that they connect; namely the scapholunate and lunotriquetral ligaments. These structures span between the adjacent sides of the relevant carpal bones, thus separating the joint spaces of the midcarpal and radiocarpal joints.
The interosseous ligaments of the distal row connect the trapezium, trapezoid, capitate and hamate bones. They have superficial and deep components.
Dorsal intercarpal ligament
The dorsal intercarpal ligament is a horizontal strap that arises from the dorsal tubercle of the triquetrum bone to the dorsal groove of the scaphoid bone, and may pass additional fibres to the trapezoid and capitate bones. It forms the floor of the fourth and fifth dorsal (extensor) compartments of the wrist. The thickened proximal part of the dorsal intercarpal ligament ligament, extending between the dorsal aspects of the scaphoid and triquetrum bones, is sometimes specifically referred to as the dorsal scaphotriquetral ligament.
Palmar intercarpal ligaments
The palmar midcarpal ligaments are a collection of fan-shaped ligaments, named according to the bones that they connect. Following radial to ulnar, they are:
- The scaphotrapeziotrapezoidal ligament, which connects the distal pole of the scaphoid bone to the trapezium and trapezoid bones
- The scaphocapitate ligament, that courses from the scaphoid to the capitate bone\
- The triquetrocapitate ligament, attaching between the distal margin of triquetrum and body of capitate bone.
- The triquetrohamate ligament,connecting the triquetrum and hamate bones
The flexor retinaculum (transverse carpal ligament) is a fibrous band that spans the anterior surface of the carpus. In this way, the retinaculum encloses the anterior/palmar concavity of the carpus into the carpal tunnel; a passageway for the median nerve and the tendons of the digital flexors.
The medial attachment of flexor retinaculum is on the pisiform and the hook of the hamate bone, while the lateral one is split into the superficial and deep laminae. The superficial lamina inserts to the tubercles of the scaphoid and trapezium bones, while the deep lamina attaches to the medial lip of the groove on the medial aspect of the trapezium. This groove and the two laminae bound a tunnel that the tendon of the flexor carpi radialis traverses. The ulnar artery and ulnar nerve pass across the superficial surface of the retinaculum. A slip of superficial fibers of retinaculum crosses over the ulnar neurovasculature and attaches to the lateral aspect of pisiform bone, enclosing them in a tunnel called Guyon’s canal.
The intercarpal joints are innervated by the anterior interosseous and posterior interosseous nerves, which are the branches of the median and radial nerves, respectively. The deep and dorsal branches of the ulnar nerve also contribute to the innervation of these joints.
The movements of the intercarpal and midcarpal joints follow the movements of the radiocarpal joints and are usually described together with them. Concerning that the ligamentous apparatus of the carpus strongly binds the bones together, there isn’t much movement at the proximal and distal intercarpal joints. The proximal intercarpal joints allow noticeable flexion and extension, while the distal joints move significantly less. Instead, these movements are important for adjusting the shape of the hand while the movements on the radiocarpal and midcarpal joints occur.
Recall that the radiocarpal joint is a biaxial joint which moves into two degrees of freedom;
- Flexion (range of motion 35°) - extension (RoM 50°)
- Abduction (RoM 8°) - adduction (RoM 15°).
Circumduction is also possible, as a combination of the above movements.
The slight movements on the midcarpal joint follow these occurring on the radiocarpal joint. They happen around transverse and sagittal axes that pass through the head of capitate bone. The movements are as follows;
- During flexion and extension of the wrist, the head of capitate rotates against the adjacent surfaces of the scaphoid and lunate, while the hamate rotates against the triquetrum.
- In wrist adduction (ulnar deviation), the proximal end of the capitate rotates laterally. The hamate rotates in the same manner, approaching the lunate and separating it from triquetrum bone.
- In abduction (radial deviation), the proximal part of the hamate rotates towards the triquetrum, thus separating the hamate from the lunate.
Abduction and adduction are followed by the slight torsion movements between the carpal rows. In abduction, the distal row twists in the direction of supination and extension, while the proximal row rotates in the opposite direction (pronation and flexion). In adduction, the opposite occurs; the proximal row rotates in the direction of supination and extension, while the distal twists in the direction of pronation and flexion.
The joint takes a close packed position when the hand is extended. The open (resting) position occurs when the hand is in a neutral position or slightly flexed. The capsular pattern hasn’t been described in the intercarpal joints, while for the midcarpal joint it’s equal limitation of flexion and extension. The proximal and distal intercarpal joints permit accessory movements of anteroposterior gliding of any two adjacent bones. This is also possible on the midcarpal joint, producing anteroposterior gliding between the proximal and distal rows of carpus.
Muscles acting on the intercarpal joints
Muscles that produce the movements on the intercarpal joints are the same that act on the radiocarpal (wrist) joint.
- Flexion is produced chiefly by the flexor carpi radialis, flexor carpi ulnaris and palmaris longus. It is assisted by the flexor digitorum superficialis, flexor digitorum profundus and flexor pollicis longus.
- Primary extensors are the extensors carpi radialis longus, brevis and ulnaris, while the extensors digitorum, digiti minimi, indicis, and pollicis longus muscles assist.
- The adductors are the flexor and extensor carpi ulnaris.
- The primary abductors are the flexor carpi radialis, extensor carpi radialis longus and extensor carpi radialis brevis. The accessory muscles for this movement are the abductor pollicis longus and extensor pollicis brevis.