Osseous anatomy.

In the coronal plane, the carpus is arranged into two rows: proximal and distal. The distal carpal row consists of four tightly bound bones (trapezium, trapezoid, capitate, and hamate) with little mobility between them. The proximal carpal row, by contrast, exhibits considerable intercarpal mobility. It consists of three bones (scaphoid, lunate, and triquetrum), interconnected by two intercarpal joints: scapholunate (SL) and lunotriquetral (LTq). The pisiform is a sesamoid bone that increases the lever arm of the flexor carpi ulnaris (FCU) tendon.

The radiocarpal joint is a glenoid articulation connecting the proximal convexities of the scaphoid, lunate, and triquetrum with the shallow concavities of the distal radius and triangular fibrocartilage complex (TFCC). The proximal joint surface of the scaphoid is more curved than that of the lunate. To ensure articular congruency, the radius has two articular facets (the scaphoid and lunate fossae), separated by a cartilaginous sagittal ridge (the interfacet prominence).

The midcarpal joint is a combination of three types of articulation. On the radial side, the convex distal surface of the scaphoid articulates with the concavity formed by the trapezium and the trapezoid: the scapho-trapezio-trapezoid (STT) joint. This structure is also known as the radial column. The central portion of the midcarpal joint is concave proximally and convex distally, and it has two sectors: the scaphocapitate (SC) and lunocapitate (LC) joints. The column formed by the lunate and capitate is also known as the central column. The lunate may have only one distal facet articulating with the capitate (lunate type I) or two distal facets to articulate with the capitate and proximal pole of the hamate (lunate type II). On the ulnar side, the triquetrum articulates with the hamate through the helicoidally shaped triquetrohamate (TqH) joint. This is known as the ulnar column.

Ligamentous anatomy.

A complex arrangement of ligaments interconnects the wrist bones ^, ( Fig. 10.1 ). Based on their histology, there are two types: mechanical (formed by tightly packed collagen fibers with a minimal number of sensory corpuscles) and sensorial (with a rich population of Ruffini, Paccini, or Golgi corpuscles embedded within a less dense structure of collagen fibers). ^, The former are static structures designed to hold the bones together. The latter provides proprioceptive information to the central nervous system to ensure joint stability.

Cadaveric dissection of a human wrist. Numbers indicate ligaments, letters indicate bones. (A) Palmar view: (1) radioscaphocapitate; (2) long radiolunate; (3) short radiolunate; (4) palmar lunotriquetral; (5) triquetral-hamate-capitate; (6) scaphocapitate. The white dotted line indicates the space of Poirier. It is a relatively weak interligamentous sulcus through which most perilunate dislocations occur. (B) Dorsal view: (7) radiotriquetral; (8) dorsal scapholunate; (9) scaphoid-trapezio-trapezoid; (10) remnant of dorsal intercarpal ligament. Asterisk , Hook of the hamate; C, capitate; H, hamate; L, lunate; S, scaphoid; Tq, triquetrum; Tr, trapezium; Tzd, trapezoid.

(Courtesy Marc Garcia-Elias).

The vast majority of ligaments involved in carpal stability are intracapsular. These are categorized into extrinsic and intrinsic. Extrinsic ligaments connect the forearm with the carpus, whereas intrinsic ligaments originate and insert within the carpus. Extrinsic ligaments are inserted mostly onto bone, whereas intrinsic ligaments insert mostly onto cartilage. The extrinsic ligaments are more elastic and less resistant to traction than most intrinsic ligaments. Hence, extrinsic ligaments tend to sustain midsubstance ruptures, whereas the intrinsic ligaments are more frequently avulsed than ruptured.

Extrinsic ligaments: There are four palmar radiocarpal ligaments: radioscaphoid (RS), radioscaphocapitate (RSC), long radiolunate, and short radiolunate (long RL and short RL). The RSC ligament courses from the radial styloid to the capitate, along the palmar concavity of the scaphoid, forming a sling over which the scaphoid rotates. Between the two diverging RSC and long RL ligaments lies the interligamentous sulcus (space of Poirier), which represents a weak zone through which perilunate dislocations can occur.

There are three palmar ulnocarpal ligaments: one superficial (ulnocapitate) and two deep (ulnotriquetral and ulnolunate). The ulnotriquetral and ulnolunate ligaments are deep fascicles that form part of the TFCC.

There is only one dorsal extrinsic ligament binding the radius to the carpus, the dorsal radiotriquetral ligament, also known as the dorsal radiocarpal ligament. It originates from the dorsal edge of the distal radius and travels obliquely toward the dorsal aspect of the triquetrum. ^, Some of its fibers spread out and insert onto the lunate, but rarely onto the scaphoid.

There are no longitudinal ligaments between the radial and ulnar styloid processes and their respective radial and ulnar corners of the carpus. This absence of collateral ligaments is replaced by the dynamic action of the extensor carpi ulnaris (ECU) ulnarly and the abductor pollicis longus (APL) radially.

Intrinsic ligaments: These fall into two categories: transverse intercarpal and midcarpal. The former interconnect bones from the same carpal row, whereas the latter link bones across the midcarpal joint. ^,

The SL joint is stabilized by two distinct transverse intercarpal ligaments (palmar and dorsal) and the proximal fibrocartilaginous membrane uniting both of them. This structure follows the arc of the proximal edges of the two bones from dorsal to palmar in a “C” configuration. It acts as a barrier between the radiocarpal and midcarpal joint spaces. The dorsal SL ligament is the strongest component made of thick fibers. It plays a key role in scaphoid and carpal stability. The palmar SL ligament has longer, more obliquely oriented fibers, allowing substantial flexion and extension of the scaphoid relative to the lunate. The dorsal SL ligament has the greatest yield strength (260 N), followed by the palmar SL ligament (118 N) and the proximal membrane (63 N).

The LTq joint also has two transverse intercarpal ligaments (palmar and dorsal) and a fibrocartilaginous membrane. In contrast to the SL ligaments, the palmar LTq ligament is thicker and stronger than its dorsal counterpart (average yield strengths: 300 N and 120 N) with the proximal portion being the weakest (64 N). The proximal membrane also prevents communication between the radiocarpal and midcarpal joint spaces.

The distal carpal row bones are strongly bound to each other by stout transverse intercarpal ligaments (dorsal, palmar, and intraarticular). They are essential to ensure the rigidity of the transverse carpal arch and to protect the carpal tunnel contents.

The midcarpal joint is crossed by three palmar ligaments (triquetrohamate [TqH], triquetrocapitate [TqC], and scaphocapitate [SC] ligaments), one dorsolateral STT ligament, and one dorsal intercarpal [DIC] ligament. The TqH and TqC ligaments play an important role in the stabilization of the midcarpal joint. Laterally, the scaphoid tuberosity is linked to the distal row by the SC ligament and the dorsolateral STT ligament.

The dorsal intercarpal ligament originates from the dorsal surface of the triquetrum and courses transversely along the dorsal edges of the proximal row bones to later fan out and insert onto the dorsal rim of the scaphoid, the trapezium, and the trapezoid.

History.

Pain during forceful activities, giving way of the wrist, and weakness are the main symptoms of carpal instabilities. The instability can happen in any adult ages, often having trauma history in young or middle-aged patients, or having longstanding degenerative changes of the carpus in elderly. The causal conditions may have their own clinical presentations.

Carpal dissociations are often missed at presentation, especially when they are associated with other more obvious injuries (scaphoid or distal radius fractures). A patient with a history of a high-energy injury to the wrist (extreme sports, fall from a height, fall while running, or motor vehicle accidents) should alert the clinician to the possibility of carpal pathology (bony and ligamentous).

The array of pathologies that can arise from such an injury is vast. Important injuries not to be missed include scaphoid fractures, SL ligament ruptures, and perilunate dislocations ( Boxes 10.1 and 10.2 ) .

In the acute setting, the examiner should ask about median nerve symptoms as this could point toward a diagnosis of a perilunate dislocation compressing the median nerve within the carpal tunnel, which is an emergency. Equally, the absence of median nerve symptoms does not exclude the presence of this severe condition. Perilunate dislocations follow the same pattern of disruption. Rupture of the SL ligaments (stage I) occurs first, followed by lunate-capitate (LC) dislocation (stage II) and, finally, rupture of the LTq ligaments (stage III).

In the chronic patient, the most common signs of carpal instability are pain that limits movement and a sensation of giving way under normal physiologic loads (inability to incorporate from a chair while leaning on the wrist or inability to perform pushups are common complaints). In other words, the patient cannot perform their usual work duties or hobbies. Painful or painless clunks are also commonly reported by patients. Examples of chronic carpal instability include scaphoid nonunion, SL chronic dissociation, or lunotriquetral ligament pathology. For instance, the LTq joint may become progressively disrupted as the result of a longstanding ulnocarpal abutment.

Lunotriquetral ligament ruptures are much less common but should be suspected when the patient has sustained a backwards fall onto the outstretched hand, with the arm externally rotated, the forearm supinated, and the wrist extended and radially inclined. Some patients describe painful crepitus as they incline the hand ulnarly. Pain is usually aggravated with ulnar inclination of the wrist and supination of the forearm.

In a patient with symptoms of carpal instability and no history of trauma, the approach is different. In this setting, carpal instability rarely results from injury to a specific ligament. These patients suffer from congenital laxity with poor neuromuscular control. Symptoms are triggered by some form of repetitive stress. These patients are difficult to treat, and realistic expectations should be set in the initial consultation. Admittedly, there is a large proportion of patients who cannot recall any trauma to the wrist, but their imaging clearly demonstrates the sequelae of old injuries.

Examination.

Physical examination should be performed with the patient’s elbow rested on a table. One of the examiner’s hands palpates and assesses while the other one stabilizes the limb. It is important to observe the patient’s facial reactions to the different stimuli. The contralateral wrist should also be examined.

General wrist range of motion (flexion, extension, radial/ulnar inclination, and prono/supination) should be recorded before any palpation or special maneuvers.

By flexing the wrist and palpating the dorsal capsule, just distal to Lister’s tubercle, we can obtain important information about the SL joint. Sharp pain suggests a recent injury or chronic synovitis, depending on the history.

Tenderness in the anatomical snuffbox and on the scaphoid tubercle are suggestive of scaphoid pathology. Lunotriquetral injuries exhibit point tenderness directly over the dorsal aspect of the joint.

Multiple special maneuvers can aid the clinician in the diagnosis as listed below. They should be selectively performed based on the history and location of symptoms (radial vs central vs ulnar wrist pain).

Special maneuvers.

A few physical examinations may help evaluate the degree of instability. However, there are false negative cases of these tests. Therefore, the examiners should combine the findings from these tests with radiographic findings.

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  Scaphoid shift test: A positive scaphoid shift test, as described by Watson and colleagues, is said to be diagnostic of SL dissociation ( Fig. 10.4 ). A negative result, however, does not rule out the presence of a SL injury. The examiner places four fingers on the dorsum of the radius and the thumb on the scaphoid tuberosity. To identify this structure, we recommend shifting the wrist between radial and ulnar inclination repetitively until the examiner notices the prominent tuberosity (more obvious during radial inclination, when the scaphoid is in a flexed position). The examiner uses their other hand to move the patient’s wrist passively from ulnar to radial inclination. Under normal anatomical circumstances, the scaphoid extends during ulnar inclination. As the wrist goes into radial inclination, the scaphoid will flex and the tuberosity will become more prominent and push onto the examiner’s thumb. Pressure on the tuberosity while the wrist is moved from ulnar to radial inclination prevents the scaphoid from flexing. If the SL ligaments are completely ruptured or elongated, the proximal pole will sublux dorsally out of the radius fossa from pressure elicited by the examiner’s thumb. This subluxation will induce pain in the dorsoradial aspect of the wrist. When pressure is released, a typical clunking may occur, indicating self-reduction of the scaphoid over the dorsal rim of the radius.

  
  
  
  
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    When performing the scaphoid shift test, one should be aware of its low specificity. If the SL ligaments are intact but there are other local problems, inducing local synovitis (occult ganglion or dorsal RS impingement), this test may also provoke sharp pain, and it is difficult to discern whether there is an abnormally subluxable proximal scaphoid. Patients with generalized laxity may exhibit painless “clunks” during this maneuver, which most likely originates from the midcarpal joint. Comparison of both wrists is important, although sometimes the opposite “asymptomatic” wrist has a painful scaphoid shift test as well. This test is not easily reproduced, and experience with it is necessary before it can be interpreted with confidence.

  
  

  
  

  
  

  

  
  

  
  

  Watson’s scaphoid shift test. In a normal wrist, the scaphoid cannot flex because of the external pressure exerted by the examiner’s thumb on the tuberosity. A positive test is seen in the presence of scapholunate ligament incompetence when the scaphoid is no longer constrained proximally and subluxes dorsally out of its fossa (straight arrow) . When pressure on the scaphoid is removed, the scaphoid goes back into its anatomical position with an audible clunk.

  
  

  (Courtesy Marc Garcia-Elias).

  
  
  
  
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  Scapholunate ballottement test: The lunate is stabilized with the thumb and index finger of one hand, while the scaphoid, held with the other hand (thumb on the scaphoid tuberosity and index on the dorsal proximal pole) is displaced dorsally and palmarly. The test is positive when there is pain, crepitus, and/or excessive mobility of the scaphoid.

  
  
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  Lunotriquetral ballotment test: Described by Reagan and coworkers to assess LTq instability. The lunate is firmly stabilized with thumb and index finger of one hand, while the triquetrum and pisiform are displaced dorsally and palmarly with the other hand. Pain, crepitus, and excessive displacement of the joint will become evident in the presence of LTq ligament pathology. The test is negative in nondissociative instabilities and induces pain and a typical grinding sensation when there is LTq dissociation.

  
  
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  The Derby test: This test is useful in diagnose LTq dissociation when there is a VISI deformity. In this test, the VISI misalignment is reduced by applying volar to dorsal pressure onto the pisiform aiming for extension and radial inclination of the triquetrum. This maneuver reduces the subluxed LTq joint, the feeling of instability disappears immediately, and grip strength increases as long as pressure over the pisiform is maintained.

  
  
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  Midcarpal shift test: This maneuver described by Lichtman et al helps determine the presence of midcarpal joint laxity. It consists of reproducing a painful clunk by passive palmar translation and ulnar inclination of the wrist in pronation ( Video 10.1 ). Based on how much force is necessary to maintain the wrist palmarly subluxed in ulnar inclination, wrists are classified into five grades. In grade I, the palmar midcarpal ligaments are so tight that the distal row can hardly be displaced palmarly. Grade II, III and IV midcarpal instability respectively indicates minimal, moderate, maximal palmar midcarpal translocation under pressure of the examiner. Grade V instability (i.e., self-induced instability) occurs when the patient can actively reproduce and maintain the palmar sag in ulnar inclination without assistance from the examiner.

  
  
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  Posterior drawer test : This test is used to assess for suspected carpal instability nondissociative with dorsal intercalated segment instability (CIND-DISI), as discussed later in the chapter. If the capitate can be passively translocated beyond the dorsal edge of the lunate with manual dorsal translation of the hand while stabilizing the radius, the dorsal intercarpal ligament is probably lax or absent. In ulnar inclination, slight subluxation of the capitate may occur. In a normal wrist, the alignment returns back to normal after the dorsally directed force is removed. When minimal force is necessary to dislocate the capitate in neutral position, a posterior midcarpal instability is likely. The posterior drawer test is also useful to assess radiocarpal instability.

Radiographs.

Signs of SL ligament incompetence include increased SL gap (Terry Thomas sign) , scaphoid ring sign, and increased SL angle, but these appear only once SL incompetence has reached a static stage (this will be discussed later in the chapter). An increased SL gap may be constitutional; if in doubt, the contralateral hand should also be imaged. A scaphoid ring sign appears when the scaphoid has collapsed into flexion and the scaphoid tuberosity appears in the posteroanterior (PA) projection as a radiodense circle or ring ( Fig. 10.5 ). It is important to ensure that the radiograph has not been taken in radial inclination as this will cause the scaphoid to flex regardless. The SL angle is assessed in the lateral view ( Fig. 10.6 ). If the axis of the scaphoid lies close to a perpendicular line to the long axis of the radius and the lunate appears normally aligned or abnormally extended, SL dissociation should be suspected. In such circumstances, the SL angle is greater than the usual 45 to 60 degrees.

Posteroanterior view of a wrist with signs of scapholunate ligament injury: widened scapholunate gap and a ring sign. The dotted oval indicates the area to look for the ring sign. It represents the frontal projection of the flexed scaphoid tuberosity.

(Courtesy Marc Garcia-Elias).

Lateral view of a wrist with an increased scapholunate angle as a result of an abnormally flexed scaphoid and an extended lunate. These are the typical positions that these two carpal bones adopt in the presence of a scapholunate ligament disruption.

(Courtesy Marc Garcia-Elias).

Radiographically, DISI is diagnosed when the scapholunate angle is greater than 80 degrees and the capitolunate angle greater than 30 degrees on a lateral view (pathologic extension of the radiolunate joint accompanied by pathologic flexion of the lunocapitate joint while the wrist remains in neutral position). Its counterpart, VISI, is diagnosed when the scapholunate angle is less than 30 degrees and the capitolunate angle is greater than 30 degrees (pathologic flexion of the radiolunate joint accompanied by pathologic extension of the lunocapitate joint while the wrist remains in neutral position). The lateral view of the wrist should be obtained with the elbow flexed 90 degrees and adducted against the trunk.

Clenched fist stress views are also useful to reveal an underlying dynamic carpal instability, but they may not provide all the necessary information to achieve a diagnosis. In view of this, Puig de la Bellacasa et al described the bilateral ulnar deviation supination (BUDS) test that uses a bilateral forearm-holding device to assess the SL gap during resisted isometric contraction of the ECU muscle while the forearm remains in full supination ( Fig. 10.7 A and B ).

(A and B) Bilateral ulnar deviation supination (BUDS) test. The arrow points at a scapholunate gap revealed during this stress test.

(Courtesy Marc Garcia-Elias).

A perilunate dislocation is an emergency, and it is extremely important not to miss this diagnosis on a radiograph ( Fig. 10.8 ). They can be easily missed by the untrained eye, particularly on PA views. The lateral view is the most important for diagnosis. As a general rule, if something does not look quite right in the carpus on a radiograph, a CT scan should be requested.

Perilunate dislocation. The posteroanterior view does not look as dramatic as the lateral view, which can cause missed diagnosis and catastrophic results for the patient. Multiple views are always recommended, followed by a CT scan if the clinician remains in doubt about the diagnosis.

(Courtesy Marc Garcia-Elias).

When the radiographs of a clunking wrist reveal abnormal flexion of the proximal row (VISI), the differential diagnosis must include LTq instability. Radiographically, the SL and LTq angles are normal in nondissociative instabilities, whereas they may be altered in wrists with dissociative instability. When the LTq ligaments are completely torn, the triquetrum appears proximally migrated relative to the lunate in the ulnar inclination stress test; this does not occur in a wrist with nondissociative instability. LT insufficiency may present with a static VISI pattern of misalignment or a disruption of the normal convex arc of the proximal carpal row (Gilula’s line).

CT scans.

CT scans are more useful than radiographs to assess carpal alignment, dislocations, and fractures. With this technique, pathologic dorsal translation and pronation of the scaphoid can become more easily recognizable. CT scans are usually taken at 1 mm intervals along the axial, sagittal, and coronal planes. Some scanners can take slices as thin as 0.25 mm, which can give great trabecular detail. This is particularly useful in evaluating the union of scaphoid fractures or wrist arthrodeses, although in many instances the image can be distorted by the presence of hardware. CT also allows for computer manipulation to obtain 3D images of the carpal bones, which helps visualize the structure to be analyzed. When surgery is planned on a malunited scaphoid or a complex carpal dislocation, a 3D reconstruction provides excellent visual information about the amount and direction of the displacement.

Indeed, a CT scan should be routinely requested for preoperative planning when dealing with carpal pathology.

Technological advances now allow the capture of a sequence of 3D representations of the wrist, allowing visualization of the wrist in motion ( Video 10.2 ). This is called “dynamic 3D,” also known as “four-dimensional CT” (4D-CT). Although promising, this technology needs to be used with caution owing to the high dose of radiation involved.

Cineradiography.

Cineradiographic examination of the wrist with an image intensifier provides dynamic information in the evaluation of patients with altered kinematics (“clunking” wrists). It is a useful tool, but it may not be easily accessible in all centers. Cineradiography includes observation of active motion from radial to ulnar inclination in PA views; flexion and extension in lateral views; and radial and ulnar inclination in lateral views. If the patient has a painful clunk, the true nature of the subluxation may be identified by observing the moving wrist under an image intensifier. Provocative stress maneuvers as described earlier may be of help to document the location of maximal dysfunction. Cineradiography has been found to have a sensitivity of 90%, a specificity of 97%, and a diagnostic accuracy of 0.93 in detecting SL dissociation.

Dynamic stress views under fluoroscopy are useful for assessing radiocarpal CIND. When the dorsal radiocarpal ligament is incompetent, the axial load of the carpus induces abnormal ulnar translation of the lunate beyond the sigmoid notch of the radius.

CIND-VISI can also be diagnosed with this method. The carpus is translated from radial to ulnar inclination under a lateral view of the wrist. The proximal row remains flexed (VISI) until near the end of ulnar inclination, where it suddenly clicks into extension. This phenomenon has been termed the catch-up clunk.

In addition, suspected LT dissociation can also be assessed with this technique: as the wrist is moved from radial to ulnar inclination, the triquetrohamate joint remains engaged while the SL complex stays in a flexed position in ulnar inclination.

MRI.

Traditional MRI without dedicated wrist coils shows poor sensitivity and specificity when compared to wrist arthroscopy (63% and 86%, respectively) in the diagnosis of SL ligament injury. However, because of its superior soft-tissue contrast, direct multiplanar acquisition, and lack of ionizing radiation, MRI with dedicated wrist coils is an effective tool to evaluate the ligaments of the wrist. Technical improvements and advanced wrist imaging algorithms may enable accurate measurement of the articular cartilage thickness and length of specific ligaments. High-resolution noncontrast techniques have proven useful in the evaluation of intrinsic ligaments but require a dedicated wrist coil and slice thickness of no more than 1 mm.

Ultrasonography.

Ultrasonography is gaining a well-deserved reputation in the assessment of both intrinsic and extrinsic wrist ligaments. High-frequency linear transducers exhibit some benefits over other imaging techniques. Ultrasonography is considerably cheaper than MRI, measures in real-time (permitting dynamic evaluation of kinematic instabilities) and does not require intraarticular injection of contrast medium or the of use ionizing radiation. It is, however, user dependent and should be considered an adjunct and not a replacement for CT scanning when assessing carpal pathology. The surgeon may choose to undergo further training in this technique.

Arthroscopy.

Arthroscopy provides the technical capability to examine and treat intracarpal abnormalities without an extensive arthrotomy. ^, Allowing direct visualization of the articular surfaces, synovial tissue, and intercarpal ligaments, arthroscopy has become one of the most important tools in wrist surgery at present. It can be valuable in determining the status of the radial and capitate articular cartilages, particularly in the decision-making process between a four-corner fusion or a proximal row carpectomy.