What does the wrist joint consist of?

The human wrist joint is a very complex joint. In daily life, we often use our hands, especially when exercising, the wrist needs to move constantly, so the wrist is easily injured. Some people will suffer wrist injuries due to work reasons. If not treated in time, it will affect people’s daily life and work, and may also cause the condition to worsen.

What does the wrist joint consist of?

The wrist joint is a complex joint composed of multiple joints, including the radiocarpal joint, intercarpal joint and carpometacarpal joint. These three joints are interrelated (except the carpometacarpal joint of the thumb) and are collectively referred to as the wrist joint. In a narrow sense, the wrist joint refers to the joint between the lower end of the radius and the first row of carpal bones (excluding the pisiform bone), that is, the radiocarpal joint; but from a functional perspective, the wrist joint should actually include the radiocarpal joint, the intercarpal joint and the distal radioulnar joint, which are unified in movement, and the wrist joint is located deep in the carpal tunnel.

The radiocarpal joint is composed of the triangular cartilage disc at the distal end of the radius and ulna and the scaphoid, lunate, and triquetrum bones in the proximal row of carpal bones. The intercarpal joint is formed by the proximal and distal row of carpal bones. The carpometacarpal joint is composed of the distal row of carpal bones and the bases of the 2nd to 5th metacarpal bones, while the carpometacarpal joint of the thumb, composed of the trapezium and the first metacarpal bone, is an independent joint. The distal end of the radius is enlarged, extending downward on the outside to form the radial styloid process, with a concave articular surface on the inside and the ulnar notch of the radius. The dorsal protrusion of the ulnar head is the ulnar styloid process. In normal people, the radial styloid process is 1 to 1.5 cm longer than the ulnar styloid process. The ulnar head is a completely extra-articular structure relative to the carpal bones, but its lateral semicircular articular surface forms the distal radioulnar joint with the radius, and its distal side articulates with the articular disc. The articular disc (triangular cartilage disc) is located between the distal ulna and radius, and separates the ulna from the wrist joint. It is attached to the ulnar styloid process, the medial surface of the radius and the wrist joint capsule. The articular disc is an important part of the distal ulna and has the function of maintaining the stability of the distal radioulnar joint.

Each carpal bone forms an inward-concave, nearly arched cavity on the palm side, called the carpal tunnel, which is covered by the palmar carpal ligament. The flexor tendons and median nerve pass through it, and the ulnar nerve passes through the superficial surface of the carpal tunnel. Normally, the pressure in the carpal tunnel is not high, but changes in the joint can cause compression of the nerve. The flexor tendons of the wrist are surrounded by a tendon sheath lined with synovium, and the extensor tendons are also surrounded by a tendon sheath.

The wrist capsule is attached to the edges of the wrist joint and is reinforced by ligaments on all sides. The main ligaments of the wrist are:

① Palmar carpal ligaments: The palmar carpal ligament is the strongest, originating from the radial styloid process and the anterior edge of the distal radius, and ending at the proximal row of carpal bones and the capitate bone.

② Dorsal carpal ligament: Not as strong as the palmar carpal ligament, mainly the dorsal radiocarpal ligament, which starts from the dorsal edge of the distal radius and ends at the proximal row of carpal bones (mainly the triangular bone).

③Radial carpal collateral ligament: from the radial styloid process to the tuberosity of the scaphoid and the trapezium.

④Ulnar collateral ligament of the wrist: from the styloid process of the ulna to the triangular bone and pisiform bone.

⑤ Transverse carpal ligament: from the tuberosity of the scaphoid bone and the trapezium to the pisiform bone and the hook of the hamate.

⑥ Intercarpal ligaments: There is a series of ligaments that tightly connect the carpal bones, and the blood supply enters the carpal bones at their attachment points.

Function: The wrist joint mainly has the functions of flexion and extension, and also has radial deviation and ulnar deviation functions. The carpometacarpal joint of the thumb is a saddle-shaped joint with two axial planes, so it has the functions of flexion, extension, adduction, abduction, rotation and various activities. The distal radioulnar joint and the proximal radioulnar joint work together to complete the pronation and supination functions of the forearm.