First and second year — the floor first, then every step
On the lateral wrist film, follow the radius–lunate–capitate column: they must stack like cups. A capitate sitting off the lunate (perilunate) or a lunate tipped out of the radius (lunate dislocation) is missed in a large share of first presentations.
Orient first
Carpal instability progresses around the lunate: scapholunate ligament → capitolunate → lunotriquetral → lunate dislocation (Mayfield stages).
On a PA view the carpal rows form three smooth arcs (Gilula); a break in an arc is a dislocation or fracture.
Scapholunate widening can be dynamic — present only on a clenched-fist view.
Acquire the study
PA in neutral and a true lateral; a clenched-fist PA for dynamic scapholunate instability.
The manoeuvre
Lateral view: radius, lunate and capitate collinear; the lunate "cup" holds the capitate head.
PA view: Gilula's three arcs; overlap of carpal bones (a "pie-shaped" lunate suggests dislocation).
Scapholunate interval on PA (compare with the other wrist); cortical ring sign of a flexed scaphoid.
Scapholunate angle on the lateral view.
Greater-arc fractures: scaphoid waist, capitate, triquetrum, radial and ulnar styloids.
What confirms it
Loss of radius–lunate–capitate collinearity on the lateral view, or a broken Gilula arc.
What licenses you to exclude it
A normal static PA does not exclude dynamic scapholunate instability.
The classic misread
Reading only the PA film — the lateral is where a perilunate dislocation declares itself.
Scapholunate interval in mm (widening above about 3 mm is abnormal — verify against the other wrist); scapholunate angle (normal about 30–60°; above 60–70° suggests DISI — verify); capitolunate angle.
What to report
Alignment on the lateral view, Gilula arcs, scapholunate interval and angle, associated greater-arc fractures, median nerve compression signs on MRI.
How to report it
X-ray: "Dorsal perilunate dislocation with a displaced scaphoid waist fracture — trans-scaphoid perilunate fracture-dislocation. The lunate remains in the radial fossa."
What not to report
Do not report the scapholunate interval as normal without the contralateral comparison or the clenched-fist view when instability is suspected.
Associated injuries to look for
Scaphoid fracture, median nerve compression, radial styloid fracture.
What changes management
Perilunate or lunate dislocation → urgent reduction and usually surgical repair.
Complete scapholunate ligament tear → surgical repair or reconstruction.
Reference values
Each value carries the caveat that keeps it from being misused. Normal limits and diagnostic criteria are kept apart on purpose: a disease cut-off read as a normal range is the more dangerous mistake.
Normal limits
Radiolunate articulation · Radiolunate angle
the lunate sits aligned with the radius on a true lateral; published numeric ceilings cluster around the mid-teens of degrees, and the capitolunate / scapholunate angles already registered are the usual DISI–VISI pair
True lateral wrist (pisiform overlapping the distal pole of the scaphoid): the angle between the long axis of the radius and the mid-axis of the lunate.
A flexed lunate is VISI; an extended lunate is DISI. Do not quote a remembered radiolunate ceiling against a capitolunate threshold.
X-ray
Diagnostic criteria
Scapholunate articulation · Scapholunate angle
commonly taken as 30–60°; above 60° indicates DISI
True lateral wrist. The angle between the long axis of the scaphoid and the mid-axis of the lunate.
⚠️ THE UPPER BOUND IS THE WELL-SOURCED HALF. Radiopaedia states DISI above 60°; the lower bound of 30° is widely taught but was not confirmed at the same source, so treat it as unverified until checked in a hand-surgery text. Read with the scapholunate INTERVAL on the PA view, and with VISI as the mirror abnormality.
up to about 2 mm, and symmetrical with the other intercarpal spaces
PA wrist radiograph with the wrist neutral; a clenched-fist PA is added when instability is suspected because it stresses the interval.
Widening beyond roughly 3 mm suggests scapholunate dissociation. ⚠️ A NORMAL STATIC FILM DOES NOT EXCLUDE DYNAMIC INSTABILITY — the clenched-fist view exists for that reason. Read with the scapholunate ANGLE on the lateral, and compare with the opposite wrist.
X-ray
See it on real cases
Direct links to Radiopaedia — the reference article and worked cases with their images. Each opens on Radiopaedia.