[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Anatomy](https://durgical.com/en/anatomy/) › [Upper limb](https://durgical.com/en/anatomy/region/upper-limb/) › Scapholunate ligament [Joints and ligaments](https://durgical.com/en/anatomy/system/joints-and-ligaments/) · [Upper limb](https://durgical.com/en/anatomy/region/upper-limb/) # Scapholunate ligament The scapholunate ligament joins the scaphoid and lunate, two key wrist bones; when it tears they drift apart, the most common wrist instability. Official name: Scapholunate interosseous ligament [See in 3D →](https://durgical.app/?from=durgipedia&lang=en#region=upper_limb&select=scapholunate_lig&side=r) Opens in the Durgical app, no sign-up needed. ## What it is A C-shaped ligament joining the scaphoid and the lunate. ## What it does Keeps the two key wrist bones moving together; when it tears they drift apart. ## Key points - Scapholunate dissociation is the commonest form of carpal instability; the dorsal part of the ligament is the thickest and matters most - When it fails, the scaphoid flexes while the lunate and [triquetrum](https://durgical.com/en/anatomy/triquetrum/) extend: dorsal intercalated segment instability (DISI) - Untreated, it progresses to SLAC wrist: arthritis first at the radial styloid and scaphoid, then the whole radioscaphoid joint, then the capitolunate joint; the radiolunate joint is spared ## Key facts **Attaches** Scaphoid to lunate (dorsal, proximal membranous and palmar parts; dorsal strongest) **Function** Keeps the scaphoid and lunate moving as a unit **Tight in** Extension + ulnar deviation with grip ## Relations **Above** [Scaphoid](https://durgical.com/en/anatomy/scaphoid/) and [lunate](https://durgical.com/en/anatomy/lunate/) fossae of the distal [radius](https://durgical.com/en/anatomy/radius/); the radioscapholunate ligament (ligament of Testut) reaches the interval from the palmar side, carrying its vessels **Below** Head of the [capitate](https://durgical.com/en/anatomy/capitate/), which sits in the cup formed by the scaphoid and lunate **In front** [Palmar wrist ligaments](https://durgical.com/en/anatomy/palmar-radiocarpal-ligaments/): radioscaphocapitate and long radiolunate ligaments **Behind** [Dorsal intercarpal ligament](https://durgical.com/en/anatomy/dorsal-intercarpal-ligament/) and [dorsal radiocarpal ligament](https://durgical.com/en/anatomy/dorsal-radiocarpal-ligament/), which merge with its dorsal part; over them the [extensor tendons](https://durgical.com/en/anatomy/extensor-digitorum-tendons/) of the third and fourth compartments ## How to find it The scapholunate interval is felt on the back of the wrist about a finger's breadth distal to Lister's tubercle, in line with the [3rd metacarpal](https://durgical.com/en/anatomy/3rd-metacarpal/); slight wrist flexion makes it easier to find. The 3–4 arthroscopy portal is placed here. ## Examination - Watson scaphoid shift test: the examiner's thumb presses on the scaphoid tubercle as the wrist moves from ulnar to radial deviation; a painful clunk when the pressure is released (the scaphoid slips over the dorsal rim of the radius and back) suggests scapholunate instability. Lax, uninjured wrists can clunk too, so both sides are compared - Scapholunate ballottement: the scaphoid and lunate are held between the examiner's fingers and moved against each other; pain or excess play suggests a tear ## On imaging PA view: a gap of 3 mm or more between scaphoid and lunate (Terry Thomas sign), best shown on a clenched-fist view and compared with the other wrist; a flexed, foreshortened scaphoid gives a cortical ring sign. Lateral view: an extended lunate and a scapholunate angle above about 60° (normal roughly 30–60°) mean DISI. MR arthrography or arthroscopy grades the tear. ## Common problems - Tear from a fall on an outstretched hand; often missed as a 'sprained wrist'. - The scaphoid and lunate drift apart, the wrist clunks and weakens. - Years later this pattern wears out the wrist (SLAC wrist). ## How it is diagnosed Pain on the back of the wrist and the scaphoid shift (Watson) test. X-rays may show a gap between the bones, sometimes only on a clenched-fist view; MRI or arthroscopy confirms. ## Treatment - Splint for partial sprains. - Repair or reconstruction of the ligament for complete tears. - Salvage surgery (partial fusion or removing the first row of wrist bones) when arthritis has set in. ## Clinical notes - Perilunate injuries (Mayfield) begin here: stage I scapholunate tear, II capitolunate disruption, III lunotriquetral tear, IV palmar dislocation of the lunate - Dorsal wrist ganglia, the most common lump of the hand, usually arise from the dorsal part of this ligament - Often accompanies distal radius and scaphoid fractures, where the bony injury can draw attention away from the ligament - Salvage options for SLAC wrist (scaphoid excision with four-corner fusion, proximal row carpectomy) depend on which joints are still preserved ## Memory aid Terry Thomas sign: the English comedian's gap-toothed smile is the scapholunate gap on a PA view (some call it the David Letterman sign). ## Related conditions - [Ganglion cyst](https://durgical.com/en/conditions/ganglion-cyst/) ## Test yourself Think of the answer, then tap the question to see it. ## Which part of the scapholunate ligament is the strongest and most important? The dorsal part, the thickest of its three parts (dorsal, proximal membranous and palmar). ## What carpal deformity follows a scapholunate ligament tear? Dorsal intercalated segment instability (DISI): the scaphoid flexes while the lunate and triquetrum extend. ## What is the Watson scaphoid shift test? The thumb presses on the scaphoid tubercle as the wrist moves from ulnar to radial deviation; a painful clunk suggests scapholunate ligament instability. ## In SLAC wrist after a scapholunate ligament tear, which joint is spared? The radiolunate joint; arthritis starts at the radial styloid and scaphoid, then the radioscaphoid and capitolunate joints. ## What common hand lump usually arises from the scapholunate ligament? The dorsal wrist ganglion, from the dorsal part of the scapholunate ligament. [Add to my cards (5)](https://durgical.app/estudiar/?add=/en/anatomy/scapholunate-interosseous-ligament/) Educational information, not medical advice. For any symptom, see a health professional. ## Its names **Official Latin (TA2)** ligamentum scapholunatum interosseum TA2 1819 **Official Spanish (DeCS)** Ligamento escafosemilunar interóseo **English (TA2)** Scapholunate interosseous ligament **Also called** SL ligament ## Related - [Dorsal intercarpal ligament](https://durgical.com/en/anatomy/dorsal-intercarpal-ligament/) - [Palmar wrist ligaments](https://durgical.com/en/anatomy/palmar-radiocarpal-ligaments/) - [Lunotriquetral ligament](https://durgical.com/en/anatomy/lunotriquetral-ligament/) - [Wrist cartilage (radius)](https://durgical.com/en/anatomy/articular-cartilage-of-the-distal-radius/) - [Capitate](https://durgical.com/en/anatomy/capitate/) - [Lunate](https://durgical.com/en/anatomy/lunate/) - [Scaphoid](https://durgical.com/en/anatomy/scaphoid/) Sources: Terminologia Anatomica (TA2); [Anatomy, Shoulder and Upper Limb, Hand Carpal Bones](https://www.ncbi.nlm.nih.gov/books/NBK535382/); [Anatomy, Shoulder and Upper Limb, Wrist Joint](https://www.ncbi.nlm.nih.gov/books/NBK534779/). ## **Spotted a mistake?** We are always improving for the community. Tell us what is wrong and our team will review it. Report a mistake Representative model, for educational purposes only. --- Source: https://durgical.com/en/anatomy/scapholunate-interosseous-ligament/ License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/anatomy/scapholunate-interosseous-ligament/