Carpal Instability - Radsource (2023)

Medical history:A 45-year-old woman with a history of arthritis presents with progressive wrist pain. Fat-suppressed weighted axial proton density (1a), fat-suppressed T2-weighted coronal (1b), and sagittal proton density (1c, 1d) images are provided. What are the discoveries? What is your diagnosis?




1 day







Non-dissociative midcarpal instability, dorsal type.


Carpal instability remains a complex issue, in part related to many different patterns of instability and also to the existence of a myriad of intrinsic and extrinsic ligaments. This instability is related to biomechanical alterations of multiple causes that, if not promptly identified and treated, will lead to the gradual collapse of the joint. Knowledge of normal wrist anatomy is important for the proper diagnosis and treatment of carpal instability. (At the end of the text you will find a list of abbreviations used in this Web Clinic).


The wrist is not a single joint but is made up of many joints with the carpal bones arranged in two rows, proximal and distal. The proximal carpal row consists of the scaphoid, lunate, and triquetrum, which articulate with the distal ends of the radius and ulna. The distal row of the carpus consists of the trapezium, trapezium, capitate and hamate. An additional carpal bone, the pisiform, acts as a sesamoid and provides an attachment for the flexor carpi ulnaris tendon.1

The radiocarpal joint is formed, in part, by the distal articular surface of the radius and the convexities of the scaphoid and lunate bones. The distal articular surface of the radius is biconcave with a mean inclination of 10 degrees in the sagittal plane and an ulnar inclination of 24 degrees in the frontal plane.2The midcarpal joint is formed laterally by the scaphotrapeziotrapezoidal (STT) space and the scaphocapitate space, centrally by the lunocapitate space, and medially by the space conquered by the triquetrum.3

Most ligaments of the wrist are intracapsular, except for the transverse carpal ligament and two ligaments that attach to the pisiform (ie, the pisohamate and pisometacarpal ligaments). There are two categories of intracapsular ligaments, extrinsic and intrinsic. Extrinsic ligaments connect the bones of the forearm (i.e. radius and ulna) to the carpal bones, while the intrinsic ligaments connect two or more carpal bones (6a, 7a, 8a).




The intrinsic ligaments include the scapholunate interosseous ligament (SLIL), the lunotriquetral interosseous ligament (LTIL), the midcarpal ligaments, and the interosseous ligaments of the distal row of the carpus. Intrinsic ligaments demonstrate greater resistance to yielding than extrinsic ligaments and often fail by avulsion at their attachment sites.1The dorsal portion of the SLIL and the volar portion of the LTIL are the strongest. With regard to the midcarpal ligaments, the trichotrohamatecapitate (THC) and scaphocapitate (SC) ligaments are the most important and, together, fix the midcarpal joint as an arcuate ligament (9a). There is no distinct capsular ligament on the volar surface of the wrist connecting the lunate and capitate bones. This relatively faint region of the capsule is called the Poirier space. The interosseous ligaments of the distal carpal row are particularly important in protecting the contents of the carpal tunnel.4


The extrinsic ligaments can be divided into palmar and dorsal ligaments. There are several important extrinsic volar radiocarpal and ulnocarpal ligaments: radioscaphocapitate (RSC), radioscaphocapitate (LRL) or radiolunotriquetral, radioscaphoid (RS), short radiolunate (SRL), ulnocapitate (UC), ulnolunar (UL), and ulnotriquetral (UT). ligaments. The RSC and LRL ligaments can be identified on routine MRI scans (10a).


The UC and RSC ligaments form the deltoid ligament, which is superficial to the arcuate ligament (11a).


The dorsal radiocarpal ligaments are less important than the volar radiocarpal ligaments, although consideration should be given to the dorsal radiotriquetral ligament (DRT), which is a broad, fan-shaped ligament that connects the dorsal surfaces of the radius and triquetrum.5

Biomechanics and Pathomechanics

Wrist movement is produced either passively by an external force or actively by muscle contraction. Wrist kinematics (dynamic movement of carpal components) and kinetics (ability to withstand high physiological loads) are made possible by the interaction between tendons, ligaments and joint surfaces.1As the proximal carpal bones do not have direct tendon insertions, movement is generated by muscle contraction initiated in the distal carpal bones and the proximal carpal bones passively following, with most of the movement occurring in the proximal carpal bones. During radial and ulnar deviation, the proximal carpal bones move synergistically from a flexed position in radial deviation to an extended position in ulnar deviation. During flexion, the distal row synchronously rotates toward flexion, but with some degree of ulnar deviation; during extension, the distal row is extended with a slight radial deviation. These movements allow for the so-called “javelin throwing” movement, which combines radial and ulnar translocation of the proximal carpal row with flexion and extension of the radiocarpal joint.6This movement plays a vital role in daily activities and it is this mechanism that is affected in midcarpal instability, described below.

Wrist stability can be affected at any level, including the radiocarpal joint, midcarpal joint, distal carpal row, and proximal carpal row. Any injury or disease that alters bone geometry, joint slope, ligament integrity, or muscle function can alter carpal motion and lead to carpal instability.1The obliquity of the volar and dorsal radiocarpal ligaments helps protect against the inherent tendency of the carpus to translate ulnarly and volarly, thereby stabilizing the radiocarpal joint.7The especially important midcarpal stabilizers are the STT joint, the SC ligament laterally, and the THC ligament medially.8Failure of these ligaments results in a distinct pattern of carpal collapse characterized by abnormal unrestricted proximal row flexion and known as volar intercalated segment instability (VISI). In this pattern of sagittal misalignment, there is a volar tilt of the lunate and scaphoid and a dorsal tilt of the capitate, with the distal articular surface of the lunate facing the palm of the hand. An important stabilizer of the proximal row is the SLIL; When this ligament is torn, the scaphoid is no longer bounded by the remainder of the proximal row, resulting in dorsal intercalated segment instability (DISI).1On sagittal views, there is a volar tilt of the scaphoid and a dorsal tilt of the lunate. DISI and VISI are two of the most common misalignment patterns in carpal instability and are best identified in the lateral view (12a).



Patients who present with carpal instability may or may not have had a previous traumatic event. The first line of imaging is conventional radiography. The radiographs allow measurement of the SL and CL angles as described above, as well as the ulnar variance, radiolunar (RL) angle, and carpal height ratio. In some cases, further evaluation includes CT and MRI with or without arthrography. Magnetic resonance imaging demonstrates sensitivity and specificity of 63% and 86%, respectively, in diagnosing SLIL lesions.9Stress testing and physical examination remain valuable in diagnosing carpal instability, although imaging and arthroscopy also play important roles in accurate diagnosis.

Classification of carpal instability

The classification of carpal instability has evolved over the past 20 years. The Mayo classification (Table 1) divides carpal instability into four main categories:

Carpal Instability - Radsource (16)

table 1

Carpal instability - Mayo classification


Dissociative carpal instability (DIC) involves a disorder within or between bones in the same carpal row. This can affect the proximal carpal row, four examples of which are scapholunate dissociation (SLD), lunotriquetral dissociation, scaphoid fracture, and Kienbock's disease; or the distal row of the carpus, the so-called axial carpal dislocations. The most common pattern of instability in this group is SLD, which is usually caused by an injury that causes hyperextension and ulnar deviation of the wrist. This results in static collapse of the carpus with volar flexion of the scaphoid and dorsal tilt of the lunate.

dissociation of scapholunate

Scaphoid dissociation (SLD) refers to the rupture of the mechanical connection between the scaphoid and lunate.10SLD is the most common pattern of carpal instability and can appear as an isolated lesion or in association with distal radius fractures or displaced scaphoid fractures. Rotational scaphoid subluxation represents an advanced stage of this injury,11in which the ligaments that attach to both ends of the scaphoid have failed (13a) and the scaphoid bone has collapsed in flexion and pronation. If there is concomitant failure of the scaphoid stabilizers, the RSC and SC volar ligaments, and the anterolateral STT ligament, permanent carpal misalignment results.12A DISI deformity occurs when the scaphoid tilts volarly and the lunate tilts dorsally (14a).



Advanced scapholunate collapse (SLAC) is a clinical condition in which progressive degenerative changes resulting from chronic SLD occur. This distinct arthropathy is characterized by severe narrowing of the RS space followed by progressive proximal migration of the capitate (15a) migrating between the scaphoid and lunate.11


The clinical diagnosis of SLD is established by a positive scaphoid displacement test.13In this test, firm pressure is applied to the volar tuberosity of the scaphoid as the wrist is moved from ulnar to radial deviation. If the SLIL ruptures, the proximal pole of the scaphoid subluxates dorsally to the radius, producing pain on the dorsoradial aspect of the wrist. When the pressure is released, the scaphoid assumes a normal position and a typical pop is produced. The images reveal a larger SL space,14characterized by a widened and irregular SL interosseous space greater than 4.5 mm, non-parallelism of the scaphoid and lunate bones on coronal images, and accumulation of fluid adjacent to the torn or missing ligament. On sagittal images, the appearance of DISI should raise suspicion of SLD.10

lunotriquetral dissociation

The causes of lunotriquetral dissociation (LTD) include trauma or ulnocarpal pillar, with frequent association with injuries of the fibrocartilage triangular complex.15Most isolated LTIL injuries result from a backward fall onto an outstretched hand, with the arm externally rotated, the forearm supinated, and the wrist extended and radially deviated. With LTD, slight dorsal translation of the lunate is caused by flexion of the scaphoid, which is attached to the lunate through an intact SLIL, producing a VISI deformity.

The accuracy of MRI in diagnosing a ruptured LTIL is only about 50%. An indirect sign is the accumulation of fluid around the torn ligament.


CIND is defined as symptomatic carpal dysfunction between the radius and the proximal row or between the proximal and distal carpal rows, with no abnormality within or between the bones of the proximal or distal carpal row.sixteenCIND is subdivided into radiocarpal and mesocarpal patterns.17,18

Radiocarpal CIND is associated with insufficiency or rupture of the obliquely oriented extrinsic radiocarpal ligaments, allowing the proximal row to slide ulnarly along the sloped articular surface of the distal radius.7,19Radiocarpal CIND is seen in a variety of conditions such as rheumatoid arthritis or developmental abnormalities including Madelung deformity, after surgical excision of the distal ulna, or after injury.21The three most common forms of radiocarpal CIND are ulnar translocation, radial translocation, and pure radiocarpal dislocation.

ulnar translocation

With ulnar translocation, a portion or all of the proximal row of the carpus slides ulnar along the sloped distal articular surface of the radius. Hyperextension, pronation, and ulnar deviation of the wrist in a fixed hand at the time of injury can produce this pattern of instability.

Taleisnik reported two types of ulnar translocation.19In type I (16a), the entire carpus, including the scaphoid, is displaced ulnarly, typically related to failure of the RS and RSC ligaments, and the distance between the radial styloid process and the scaphoid is widened (17a). In type II ulnar translocation, the scaphoid and radius remain in their anatomical position, and the other carpal bones move ulnarly as a unit, causing a marked increase in the scapholunate gap (18a, 19a).17





Non-dissociative midcarpal instability (or midcarpal instability; MCI)

Midcarpal instability is associated with dysfunction of the radiocarpal and midcarpal joints (with a predominance of involvement of the midcarpal joint). Especially important stabilizers of this joint are the THC ligament, the dorsolateral STT ligament, and the RSC ligament, as these ligaments span the midcarpal joint.1There are four main types of midcarpal instability: palmar, dorsal, combined, and extrinsic (20a).


In volar ICM, the entire proximal row of the carpus is flexed palmarly, resulting in a VISI pattern, related to failure of the intrinsic ligaments that cross the midcarpal joint. The primary ligament injured in this pattern is the THC ligament, with additional insufficiency of the dorsal radiocarpal ligament. Dorsal mild cognitive impairment usually occurs in young patients with bilaterally hypermobile wrists.1It is characterized by dorsal subluxation of the capitate bone and dorsal tilting of the scaphoid and lunate, associated with additional insufficiency of the volar ligament of the RSC.

Combined mild cognitive impairment is characterized by exaggerated dorsal mild cognitive impairment with additional dorsal subluxation of the lunate, scaphoid, and capitate. Mild extrinsic cognitive impairment is due to a misunion fracture of the distal radius with consequent dorsal inclination of the articular surface with subsequent dorsal inclination similar to the lunate.


When the carpal disorder has altered the relationship (a) between bones within the same carpal row (CID features) and (b) between the proximal and distal carpal rows (CIND features), the dysfunction is classified as CIC. Five groups of CIC were identified.

  1. Dorsal Perilunate Dislocation (Less Lesser Arch)
  2. Dorsal perilunate fracture-dislocation (greater arch injury)
  3. Palmar perilunate dislocation (major or minor arch injury)
  4. axial displacement
  5. Isolated carpal bone dislocation

Purely ligamentous injuries of the wrist are classified as minor arch injuries, while transosseous variants are considered major arch injuries, in which one or more bones around the lunate fracture concomitantly.

The first two groups have in common a carpal disorder occurring around the lunate, the first group is characterized as a minor arch injury and the second group is considered a major arch injury. The third group, although perilunate, results from a different mechanism that produces palmar displacement of the distal row of the carpus in relation to the lunate. The fourth and fifth groups represent various non-perilunar dislocations, usually as a result of high-energy trauma.1

Dorsal Perilunate Dislocation (Less Lesser Arch)

There are different forms of carpal injury under the dorsal perilunate dislocation pattern, confined to a relatively vulnerable area around the lunate. Along with scapholunate injuries, dorsal perilunate dislocations are one of the most common injuries seen; the lunate remains within the semilunar fossa of the radius while the rest of the carpus is displaced dorsally. As part of a minor arch injury, this pattern is a pure dislocation with no associated fracture.

Mayfield et al reported four stages of progressive perilunate instability (21a-24a).20


Progressive perilunate instability. Schematic representation of the four stages of perilunate instability (21a-24a), seen from the ulnar side. The numbers on the diagrams correspond to the numbers used in the text descriptions of each step after each image. The red arrows represent the distracting forces that occur in the ligaments.

Internship I: As the distal carpal row is forced to hyperextend (blue arrow), the scaphotrapeziocapitate ligament [1] pulls the scaphoid towards extension, thus opening Poirier's space (red asterisk). The lunate cannot extend to the scaphoid because it is directly limited by the SRL [2]. When the SL torque reaches a certain level, the SLIL ligament can fail, usually in a palmar to dorsal direction. SLD is defined by changing the dorsal SLIL [3]. (21a)


Stage II: The scaphoid-capitate array complex may shift dorsally into the lunate as it dissociates from the lunate. The extent of this dorsal translation (blue arrow) is determined by the RSC ligament [4]. The entire distal row and the dissociated radial portion of the proximal row follow the capitate dorsally, further opening Poirier's space. (22a)


Stage III: If hyperextension persists (blue arrow), the ulnar branch (i.e. THC ligament) of the arcuate ligament [5] may pull the triquetrum to abnormal length. As the triquetrum extends, this torque is transmitted to the LTIL. A rupture of the LTIL or an avulsion fracture of the triquetrum may occur. With complete rupture of the LTIL [6], the ulnar expansions of the LRL ligament are also severed, leaving the SRL ligament [2] and the volar ligament of the UL as the only stabilizing forces in the lunate. (23a, 25a, 26a).


Stage IV: Finally, the dorsally displaced capitate can be pulled proximally and volarly (blue arrows) into the radiocarpal space by a still intact RSC ligament [4]. The capitate pushes the lunate volarly, causing it to rotate in the still-intact SRL [2] and fly through Poirier space rotationally. Therefore, a lunate dislocation is the final stage of a dorsal perilunate dislocation (24a, 25a, 26a).




Dorsal perilunate fracture-dislocation (greater arch injury)

Dorsal perilunate fracture-dislocations refer to perilunate dislocations with concomitant fracture of the scaphoid, great, hamate, or triquetrum bones. The only true greater arch injury is a transscaphoid, transcapitate, transtriquetral, and perilunate transhamata fracture-dislocation. All other perilunate fracture-dislocations involve ligament tears, bone avulsions, and additional fractures. The most common form of greater arch injury is the transscaphoid perilunate dislocation.


Carpal dysfunction is not always a consequence of intracarpal pathology, but can also result from extracarpal pathology.1A typical example of ASD is malunion of a distal radius fracture that induced postural adaptation of the proximal carpal row to accommodate abnormal radial inclination (28a). Another example could be the result of a Madelung deformity, where there is a volar inclination of the distal radius and a subluxated and dorsally elongated ulna, with adaptive alterations of the carpal bones of the proximal row.23When making the diagnosis of ASD, it is important to exclude significant intracarpal ligament injury, which helps to differentiate it from extrinsic CCL, in which there is usually significant injury to the ligaments that cross the midcarpal joint. However, these patterns are still very similar and it can be difficult to differentiate them, since extracarpal pathology is common to both. Treatment is aimed at correcting malunion.24,25


treatment principles

Describing the treatment of carpal instability is beyond the scope of this review and depends on the specific type of carpal instability. Basic determinants of treatment include the presence or absence of arthritic changes, the chronicity of the injury, the quality of the tissues to be repaired, and the reducibility of the deformity.26

In a relatively acute injury with good soft tissue quality and reducible deformity, treatment principles include restoration of normal anatomy whenever possible. This involves ligament repair, restoration of normal carpal angles, and anatomical reconstruction. In similar cases where tissue quality is poor, ligament reconstruction or salvage procedures are considered. The salvage procedure includes intercarpal arthrodesis or total wrist arthrodesis.


Carpal instability is often a confusing and challenging subject, the understanding of which requires basic knowledge of anatomy and pathophysiology. This knowledge can then be applied in the analysis of imaging studies, including magnetic resonance imaging, allowing a more complete and meaningful diagnosis in cases of wrist instability. Specifically, understanding the wrist instability classification system currently used by many hand surgeons will promote a more meaningful conversation between the radiologist and the referring physician.




1Garcia-Elias M, Geissler WB. carpal instability. In: Green DP, Hotchkiss RN, Pederson WC, et al, eds. Operative surgery of the hand. 5th edition. Philadelphia: Elsevier; 2005. pg. 465-520.

2Schuind FA, Linscheid RL, et al. A normal database of posteroanterior radiographic measurements of the wrist. J Bone Joint Surg Am 1992;74:1418-1429.

3Moritomo H, Apergis E, et al. Report of the IFSSH Committee on wrist biomechanics: biomechanics of the so-called javelin throwing movement of the wrist. J Hand Surg [Am] 2007;32:1447-1453.

4Garcia-Elías M, Dobyns JH, et al. Traumatic axial carpal dislocations. J Hand Surg [Am] 1989;14:446-457.

5Berger RA. The ligaments of the wrist: a current overview of anatomy with considerations of their potential functions. Hand Clin 1997;13:63-82.

6Toms A, Chojnowski, et al. Midcarpal instability: a radiological perspective. Radiol Esquelético 2011;40:533-541.

7Rayhack JM, Linscheid RL, et al. Post-traumatic ulnar translation of the carpus. J Hand Surg [Am] 1987;12:180-189.

8Lichtman DM, Written ES. Understanding midcarpal instability. J Hand Surg [Am] 2006;31:491-498.

9Morley J, Bidwell J, et al. A comparison of wrist arthroscopy and magnetic resonance imaging findings in the investigation of wrist pain. J Hand Surg [Br] 2001;26:544-546.

10Linscheid RL, Dobyns JH, Beabout JW, et al. Traumatic wrist instability: diagnosis, classification and pathomechanics. J Bone Joint Surg Am 1972;54:1612-1632.

11Watson HK, Weinzweig J, Zeppieri J. The natural progression of scaphoid instability. Hand Clin 1997;13:39-49.

12Short WH, Werner FW, Green JK, et al. Biomechanical evaluation of scaphoid and lunate ligament stabilizers: Part III. 32:297-309.

13Watson HK, Ashmead D IV, Makhlouf MV. Examination of the scaphoid. Hand Surgery (Am) 1988;13:657-660.

14Schimmerl-Metz SM, Metz VM, Totterman SMS, et al. Radiological measurement of the scapholunate joint: implications of biological variation in scapholunate joint morphology. J Hand Surg (Am) 1999;24:1237-1244.

15Shin AY, Weinstein LP, Berger RA, et al: Treatment of isolated lunotriquetral ligament injuries: comparison of arthrodesis, ligament reconstruction, and ligament repair. J Bone Joint Surg Br 2001;83:1023-1028.

sixteenWright TW, Dobyns JH, Linscheid RL et al. Non-dissociative carpal instability. J Hand Surg (Br) 1994;19:763-773.

17Resnick D, Heung KS, et al. Internal Articular Disorder, 2nd Edition. Philadelphia: WB Saunders; 2006.

18Dobyns JH, Linsheid RL, Chao EY, Weber ER, et al. Traumatic wrist instability. In Instructional Lectures Course, American Academy of Orthopedic Surgeons, Vol. 24. St. Louis: CV Mosby; 1975. pg. 182-199.

19Taleisnik J. The doll. New York: Churchill Livingstone; 1985.

20Mayfield JK, Johnson RP, Kilcoyne RK. Carpal dislocations: pathomechanics and progressive perilunate instability. 5:226-241.

21Cooney WP, Dobyns JH, Linscheid RL. Complications of Colles fractures. J Bone Joint Surg Am 1980;62(4):613-619.

22Cooney, W.P. External fixation of distal radius fractures. 180:44-49.

23Taleisnik J, Watson HK. Midcarpal instability caused by malunion fractures of the distal radius. 9A:350-357.

24Carlsen BT, Shin AY. Wrist instability. Scand J Surg 2008;97(4):324-32.


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