Wrist Joint
On this page
Direct answer
Radius plus its triangular fibrocartilaginous articular disc — never the ulna itself — faces the proximal carpal row (scaphoid, lunate, triquetral) to form the radiocarpal or wrist joint, an ellipsoid synovial joint allowing flexion and extension of about 80 degrees each, radial deviation (abduction) of 15–20 degrees and ulnar deviation (adduction) of 30–45 degrees. The pisiform sits outside the joint, and the ulna is kept out of it by the disc that grips its styloid. Strong palmar radiocarpal ligaments and weaker dorsal ones stabilise the ellipsoid, the anterior interosseous nerve (median) and posterior interosseous nerve (radial) supply it, and a fall on the outstretched hand tests every structure in turn — producing Colles and Smith fractures, scaphoid fractures and lunate dislocations in predictable sequence.
What you must remember
- Articulating surfaces: inferior surface of the distal radius and the articular disc (attached to the ulnar styloid) above; scaphoid, lunate and triquetral below — during abduction the scaphoid meets the radius, during adduction the triquetral rotates onto the disc.
- Ulna excluded: the ulnar styloid is gripped by the triangular fibrocartilage complex, so ulnocarpal force passes through the disc — which tears in triangular fibrocartilage injuries of racket and stick players.
- Movement sharing: flexion is fairly evenly shared with the midcarpal joint; adduction occurs mainly at the radiocarpal and abduction mainly at the midcarpal joint — a distribution examiners rarely forgive forgetting.
- Ligaments: palmar radiocarpal (strongest, from radius to capitate-triquetral), dorsal radiocarpal, and radial and ulnar collateral ligaments; the capsule is lax anteriorly to permit flexion.
- Nerve supply: anterior interosseous branch of the median nerve and posterior interosseous branch of the radial nerve — wrist disease can present as diffuse wrist pain along either.
- Scaphoid rules: the largest bone of the proximal row; blood vessels enter its distal half (mainly through its dorsal ridge and tubercle), so the proximal pole is last to be perfused — a waist fracture risks avascular necrosis and non-union of the proximal fragment.
- Clinical quartet of the fall: Colles (dorsally angulated distal radius, dinner-fork deformity), Smith's (volar, reverse), scaphoid fracture (anatomical snuffbox tenderness), lunate dislocation (median nerve compression in the carpal tunnel).
Sorting a fall on the outstretched hand
The FOOSH pathway — every Indian casualty night contains several — sorts itself by age and point of impact. In a young adult, the load drives the scaphoid waist; the patient presents with a "sprained wrist", tender in the anatomical snuffbox between the extensor pollicis longus and brevis tendons. A normal initial X-ray does not exclude the fracture, because the line is hairline: the safe protocol repeats films at two weeks (or proceeds to MRI), and the hand goes into a cast including the thumb. Miss it, and the retrograde blood supply fails the proximal pole — avascular necrosis, then painful non-union and early wrist arthritis in a twenty-year-old. In the elderly with osteoporotic bone, the same fall shears the distal radius metaphysis: a Colles fracture with its dinner-fork deformity (dorsal and radial displacement of the distal fragment). Between these ages, the lunate can be forced out of the row, and its dislocated body presses on the median nerve in the carpal tunnel — a wrist injury presenting with paraesthesia of the thumb and fingers, which demands reduction as an emergency.
Where students slip
The recurring examination error is including the ulna or pisiform among the articulating bones — the ulna is separated by the articular disc, and the pisiform is a sesamoid-like bone in the flexor carpi ulnaris tendon, articulating only with the triquetral. The second slip is the direction of movement predominance: adduction is chiefly radiocarpal, abduction chiefly midcarpal — stating the reverse is marked wrong because it reflects the shape of the radius's slope (its styloid is long and stops radial deviation early). Third, candidates call the wrist "a ball-and-socket joint": it is ellipsoid (condyloid), biaxial, with circumduction only as a composite movement.
Frequently asked questions
Which bones articulate at the radiocarpal joint?
The distal end of the radius and the triangular articular disc above, with the scaphoid, lunate and triquetral below; the ulna and pisiform take no part.
Why does the proximal fragment of a fractured scaphoid undergo avascular necrosis?
Blood vessels enter the scaphoid mainly distally on its dorsal ridge and tubercle, so a fracture through the waist cuts off the proximal pole's retrograde supply.
What is the dinner-fork deformity and which fracture produces it?
A dorsal concavity of the wrist from dorsal displacement and angulation of the distal radial fragment in a Colles fracture after a fall on the outstretched hand.
Which movements occur mainly at the midcarpal rather than the radiocarpal joint?
Abduction (radial deviation) occurs mostly at the midcarpal joint, because the long radial styloid limits the radiocarpal side; adduction is mostly radiocarpal.
How can a lunate dislocation present with nerve symptoms?
The dislocated lunate lies in the floor of the carpal tunnel and compresses the median nerve, producing thenar-side paraesthesia with the wrist injury.