12.30 Instabilities of the carpus

Carpal instabilities can seem unduly complicated and unapproachable. With a better understanding of the anatomy and ligamentous support of the wrist, the instabilities seen become more logical, and the clinical assessments for instabilities makes more sense. Treatments of carpal instabilities, both acutely and established, are emerging with the growing appreciation of the kinematics and carpal kinetics of this complex of articulations.

The wrist represents a complex of articulations between the forearm bones, the carpal bones, which are arranged into two rows, and the bases of the metacarpals. The carpal bones are arranged into a proximal and a distal row This gives rise to a confluent joint between the radius/ulna (covered by the triangular fibrocartilage) and the proximal carpal row, called the radiocarpal joint (RCJ), and a second confluent joint between the proximal and distal carpal rows, called the midcarpal joint (MCJ). The bones of the distal carpal row articulate with the metacarpal bases.

The bones are connected by the intrinsic ligaments, and by ligaments within the capsule that pass from the forearm bones to the carpal bones, collectively called the extrinsic ligaments.

The bones of the distal carpal row are held tightly together by the intrinsic ligaments and so can be considered to act as a monoblock. The intrinsic ligaments of the proximal carpal row allow a greater degree of intercarpal motion. Both the scapholunate (SL) and the lunotriquetral (LTq) ligaments have weak membranous proximal portions (which can be seen arthroscopically from the radiocarpal joint) and stronger palmar and dorsal portions; the SL is stronger dorsally, and the LTq stronger on the palmar side. Fibres of the dorsal and palmar portions of these ligaments connect to form the scaphotriquetral ligaments at the MCJ. As long as the membranous portions of the ligaments are intact, there is no communication between the RCJ and the MCJ; communication through this portion of the ligaments occurs via traumatic or degenerate perforations, which are not necessarily clinically important. The MCJ is supported by intrinsic ligaments on the dorsum by the dorsal intercarpal ligament (DIC) which passes from the triquetrum to the scaphoid, trapezoid and trapezium, blending with the dorsal scaphotriquetral ligament, and on the palmar surface by the triquetrohamatecapitate ligament complex on the ulnar side, and by the scaphocapitate and scaphotrapezial ligaments on the radial side (the latter passing around to the dorsoradial aspect of the MCJ). These ligaments tend to fail by avulsion.

The extrinsic ligaments arise from the palmar and dorsal surfaces of the radius, and on the palmar side, the ligaments broadly form the shape of two inverted Vs running proximal to distal, one with its apex on the lunate (short and long radiolunate and ulnolunate ligaments) and the other with its apex on the capitate (the radioscaphocapitate ligament complex, and the ulnocapitate ligament). There is a sulcus between these two Vs on the radial side, connecting into the space of Poirier.

The palmar ulnocarpal ligaments and the palmar and dorsal radioulnar ligaments, along with the triangular fibrocartilage between them, form the triangular fibrocartilaginous complex, which is considered in more detail in Chapter 6.4. On the dorsum, the dorsal radiocarpal ligament forms the proximal limb of a radially-based V (the distal limb being the DIC intrinsic ligament) running transversely with its apex on the triquetrum. The extrinsic ligaments tend to fail by midsubstance rupture.

The carpal bones are connected by other ligaments outside the wrist capsule, notably the transverse carpal ligament (TCL) from the hook of the hamate and the pisiform to the distal scaphoid and the trapezium, forming the roof of the carpal tunnel, and the pisohamate ligament (which makes the floor of Guyon’s canal). The TCL helps to maintain the convex-dorsal arch to the carpus in the transverse plane, and its division increases the width and volume of the carpal tunnel.

As no tendons insert into the proximal row of carpal bones (excepting the sesamoid pisiform bone), the position of the bones is determined by the shape of the joint surfaces, the integrity of ligaments connecting the bones and the forces applied across the carpus by the tendons passing from the forearm to the hand and distal carpal row, making it act as an intercalated segment. There has been an evolution in thinking regarding how the wrist moves, from the ‘row theory’ (proximal and distal carpal rows acting as functional units) through the ‘column theories’ (with combinations of bones from the two rows acting as functional units for load transfer and positioning), to the ‘oval ring theory’ (with the distal carpal row, the scaphoid, the lunate and the triquetrum acting as linked elements in a ring, with failure of any element or the binding ligaments altering wrist motion and load transfer).

In summary, current thinking is that the helicoid shape of the triquetrohamate articulation and the alignment and ligament attachments of the triquetrum and scaphoid cause them to tend to extend and flex respectively. As long as the SL and LTq ligaments are intact, the lunate remains in a state of dynamic balance within the proximal carpal row; if the linkages within the proximal row fail, the lunate falls under the unopposed influence of the bone to which it remains attached, rotating into dorsi- or palmar flexion respectively.

Motion of the wrist starts with movement of the distal carpal row at the MCJ, with palmar flexion coupled to a degree of ulnar deviation and dorsiflexion to a degree of radial deviation. Palmar and dorsiflexion produces motion in the same direction of the proximal row bones, but with the scaphoid showing greater motion than the other proximal row bones, acting as the ‘crank’ in the three-bar linkage mechanism between the proximal and distal rows. When considering radial and ulnar deviation, wrists lie on a spectrum between ‘row’ wrists (where the proximal row slides towards the ulna during radial deviation, with rotation occurring in the coronal plane) and ‘column’ wrists, (where deviation in the proximal row is achieved by scaphoid flexion during radial deviation and by the triquetrum extending in ulnar deviation, the rotation occurring in the sagittal plane).

Normal range of wrist motion is 70 degrees each of palmar and dorsiflexion, 20 degrees radial and 40 degrees ulnar deviation and minimal intracarpal rotation (most occurring a the radioulnar joints); a range of 5 degrees palmar flexion, 30 degrees dorsiflexion, 10 degrees radial deviation, and 15 degrees ulnar deviation is said to be functional.

While load distribution in the wrist is mainly dependent on hand and wrist positioning, most load transfer at the MCJ occurs through the capitoscapholunate articulation. In the main, about half the load will be transferred through the radioscaphoid articulation, about a third through the radiolunate articulation, and the remaineder through the ulnocarpal joint, although load transfer at the RCJ is affected by ulnar variance (relative lengthening of the ulna increasing transfer through the ulnocarpal articulation) and by radioulnar deviation (ulnar deviation increasing load transfer through the lunate).

The Mayo classification considers carpal instabilities (CI) to be dissociative (CID), non-dissociative (CIND), combined/complex (CIC) or adaptive (to forearm pathology, CIA); this is outlined in Table 12.30.1.

Most examples of CID reflect injuries to the intrinsic ligaments of the proximal carpal row, which can progress to perilunate dislocations with failure of other structures; as this happens, the instability moves into the CIC (complex) group.

The pathoanatomy of perilunate injuries was examined by Mayfield, who described a sequential failure of the structures around the lunate that gives rise to carpal instabilities and perilunate dislocations. In the usual pattern of soft tissue injury (so-called lesser arc injuries), the distal carpal row is subject to extreme extension and carpal supination from an indirect force, which is transmitted to the lunate via the scaphocapitate and scaphotrapezoid ligaments, the scaphoid and SL ligament; the extrinsic ligaments constrain lunate motion, causing tearing of the SL ligament (stage 1). If the force continues to be applied, the distal carpal row dislocates dorsally, tearing the capsule between the palmar extrinsic ligament Vs (stage 2). As the capitate translates dorsally, tension in the triquetrocapitate ligament pulls the triquetrum dorsally and into extension, tearing the LTq ligament (stage 3). At this point, the lunate remains attached to the radius by the short and long radiolunate ligaments and the dorsal capsule, the latter being vulnerable to rupture when the lunate is translated in a palmar direction by the displaced capitate, producing a palmar dislocation of the lunate (stage 4).

This normal Mayfield sequence may be associated with fractures of the radius or the carpal bones, in particular the scaphoid and the triquetrum. These injuries are termed greater arc injuries, and named by the pre-fix ‘trans- (name of fractured bone)’, perilunate injuries. If force is applied to the ulnar side of the carpus, a so-called reverse Mayfield sequence of structural failure may uncommonly occur.

Damage to the ligaments crossing the MCJ can give rise to CIND instability patterns. This is most commonly seen in constitutionally lax individuals in whom a comparatively minor injury gives rise to on-going symptoms from the resultant manifest midcarpal instability. This often presents with ulnar-sided dorsal wrist pain and an associated sensation of clunking; this occurs as the laxity allows the proximal carpal row to remain flexed for a larger arc as the wrist moves from radial to ulnar deviation, with the flexed proximal row ‘snapping’ into extension with the perception of a clunk (often termed a catch-up clunk). This is the principle underlying the midcarpal pivot shift test.

CIND is also seen at the radiocarpal joint, either due to acute trauma (with extrinsic ligament avulsions), or in rheumatoid arthritis (with ulnar translation of the carpus).

CIA generally reflects carpal malalignments seen after distal radial malunions. Under these circumstances, abnormal inclination of the distal radial articular surface causes the proximal row to adopt an unusual position (e.g. dorsiflexed positioning following a dorsally-tilted malunion after a Colles pattern of fracture), with compensatory instability at the midcarpal joint (palmarflexed in the example given).

Following an acute wrist injury, there should be a high index of suspicion for any underlying carpal bone fracture, ligament injury or dislocation. These injuries should be actively sought and excluded.

The mechanism of injury determines the magnitude of the forces that have been applied to the wrist and consequently the likely type of injury that must be excluded.

The injury can range from a high-energy road traffic collision (particularly involvig a motorcycle) to other high-velocity injuries such as a fall fronm a height, or during sport, that may cause perilunate dislocations and fracture–dislocations. Lower velocity falls on the outstretched hand/wrist may cause hyperextension and more isolated carpal fractures or ligament injuries. The patient often underestimates the injury severity, assuming that it is a trivial ‘wrist sprain’. Other subtle or apparently trivial injuries that communicate significant extension, flexion or rotational forces to the wrist, such as when a power drill jams while drilling, should also raise suspicions.

Patients with perilunate dislocation injuries present with wrist deformity, limited motion, pain, and swelling. Single carpal bone dislocations may cause a subcutaneous prominence or a hollow over the dislocated bone. More subtle carpal instabilities will present with complaints of pain, swelling, and possibly clicking of the wrist.

Severe pain and swelling may make a careful complete wrist examination difficult in the early stages. However, the wrist should be inspected for haematoma, swelling, and altered shape. Subtle changes are best visualized by comparing the involved and uninvolved wrists.

Wrist palpation is performed following the bony anatomy, the distal wrist flexion crease is proximal to the carpus. There may be global wrist tenderness, but areas of maximum tenderness, and the structures that lie under them, should be identified and prioritized

The active and passive ranges of motion are assessed, noting any ‘clicks’ or ‘clunks’ indicating possible abnormal kinematics. A detailed neurovascular examination is performed.

Standard posteroanterior (PA) and lateral radiographs are obtained, with a radiographic wrist motion series, if wrist instability is suspected (see later).

Acute SL dissociation is generally suspected clinically but confirmed radiographically. However, most patients present with chronic SL dissociation (>6 months after injury). There may be an uncertain mechanism of injury, chronic dorsal or global wrist pain, swelling aggravated by lifting or gripping, and possibly wrist ‘clunking’.

Physical examination may demonstrate, dorsal tenderness over the SL interval, a ballottable proximal scaphoid with pain and crepitus, and occasionally a ‘click’ demonstrable on ulnar to radial deviation, as the scaphoid subluxes or rotates out of the scaphoid fossa in radial deviation and relocates in ulnar deviation.

Watson’s scaphoid shift test (Box 12.30.3) is performed as the examiner (seated opposite the patient) holds the patient’s hand with the examiner’s thumb overlying the distal pole of the scaphoid; the examiner’s finger palpates the proximal pole of the scaphoid on the dorsum, and the patient’s elbow is stabilized on the examination table. Starting with the patient’s hand in ulnar deviation, the wrist is passively moved into radial deviation. Dorsally directed pressure, applied on the scaphoid tuberosity by the examining thumb, will cause the unstable scaphoid to ‘back out’ or sublux dorsally from the radial fossa. It is important to compare tenderness, pain, mobility, crepitus, and ‘clicks’ with the contralateral side. SL instability is likely when the test demonstrates an objective difference in stability of the two sides, or a palpable ‘clunk’ is elicited as the scaphoid proximal pole exits or returns to the scaphoid fossa.

LTq instability is a subtle clinical diagnosis. With an acute injury, there may be a history of a fall onto the ulnar side of the hand and ulnar sided wrist pain and swelling. LTq instability often presents as a chronic problem with ulnar-sided wrist pain and swelling aggravated by power grip, and popping or ‘clunking’ on radial/ulnar deviation. There is tenderness directly over the LTq interval, and increased pain, crepitus, and excessive motion compared with the other side, when performing a LTq ballottement test. During this test the examiner stabilizes the patient’s triquetrum with their index finger volarly and the thumb dorsally. The patient’s lunate is similarly stabilized with the examiner’s other hand. The examiner attempts to ‘shuck’ the triquetrum back and forth on the stabilized lunate.

CIND conditions present following repeated stress or trauma with a history of underlying congenital ligamentous laxity in approximately 50% and poorly localized chronic wrist pain and tenderness (aggravated by activities). A ‘catch-up clunk’ of the proximal carpal row may be demonstrated (by either the patient or the examiner moving the wrist from radial to ulnar deviation or vice versa, or through a circumduction arc, possibly under axial compression).

Normally the helicoid articulation between the triquetrum and the hamate, causes a tendency for the triquetrum to dorsiflex (with the tendency of entire proximal row to follow being balanced by the flexion moment from the scaphoid). In a traumatized or congenitally lax wrist, the laxity of the carpus permits exaggerated or prolonged flexion of the proximal carpal row in radial deviation. With ulnar deviation there is a delay before the proximal carpal row ‘snaps’ back into place and congruent articulation is restored.

Perilunate dislocations often occur in the context of high-energy trauma and a multiply injured patient and can cause characteristic wrist deformities. When the carpus is dislocated dorsally the radius is prominent in the carpal tunnel, on the palmar surface of the wrist as is the lunate in a pure lunate dislocation. Despite this up to 25% of these injuries are diagnosed late.

In dorsal perilunate dislocation the palmar skin and median nerve must be examined carefully. Median nerve damage is the most common associated injury and laceration of the palmar skin may indicate an open dislocation or fracture–dislocation. Palmar skin ischaemia may also be caused by pressure from the radius. Both arterial and compartment problems may occur and must be excluded. Bones or their fragments may be significantly displaced or even extruded.

Radiographic evaluation of wrist pain should include standard PA and lateral radiographs of the carpus. The PA film is centred over the radiocarpal articulation to assess accurately the SL interval, scaphoid position, LTq articulation, ulnar styloid, distal radius articular surface, and distal radioulnar joint.

The PA film is taken with the shoulder abducted 90 degrees, the elbow flexed at 90 degrees, neutral forearm rotation, an overhead x-ray beam, and the wrist placed flat on the x-ray plate, and 10 degrees x-ray beam radial angulation will enhance visualization of the SL interval. As discussed in Chapter 12.31, pronation causes relative shortening of the radius and will be apparent if the PA radiograph is incorrectly taken in this position.

Axial loading of the wrist, achieved with a ‘clenched-fist’ PA view, will accentuate any SL diastasis.

The lateral wrist film must also be taken in neutral forearm rotation, with the patient adjacent to a radiography table, the shoulder adducted, the thumb positioned toward the ceiling, and the wrist resting on the x-ray plate. A good lateral radiograph of the wrist should display: complete superimposition of the lunate, proximal scaphoid pole and triquetrum, the scaphoid tubercle overlies the pisiform, the radial styloid is in the ‘centre’ of the radius, and metacarpal shaft superimposition. If the lateral radiograph is incorrectly taken in ulnar deviation, then proximal carpal row dorsiflexion will produce an apparent DISI pattern.

Scaphoid views are obtained if there is tenderness in the anatomic snuffbox or if the PA and lateral radiographs suggest scaphoid pathology. The conned scaphoid waste view is obtained with the wrist in maximal ulnar deviation and 10-degree distal x-ray beam angulation. This produces an elongated, enlarged, detailed image of the scaphoid waste accentuating the trabecular pattern.

A wrist motion series includes flexion lateral, extension lateral, PA radial deviation, and PA ulnar deviation radiographs of both wrists. In ulnar deviation the scaphoid extends and appears elongated, while in radial deviation it should flex and appear shortened. SL diastasis usually accentuates in ulnar deviation and closes in radial deviation.

A so-called ‘six shot’ wrist series includes: PA, PA radial deviation, PA ulnar deviation, PA clenched fist, lateral, and lateral clenched fist views.

The normal SL interval on a PA radiograph measures 3mm or less. Diastasis beyond this indicates a possible SL dissociation. In SL dissociation, the scaphoid typically rotates out of the radial fossa into increased flexion. When viewed on the PA radiograph, this ‘scaphoid rotatory subluxation’ produces an ‘end on’ image of the scaphoid with overlapping cortical edges, known as the ‘scaphoid cortical ring sign’.

Gilula described three smooth arcs, assessed on PA radiographs which can be traced along the proximal radiocarpal surface of the scaphoid, lunate, and triquetrum; the distal midcarpal surface of these same bones; and the proximal midcarpal surface of the capitate and hamate. An assessment of Gilula’s lines provides a quick screen for fracture, dislocation, or instability of the carpus.

A PA distraction view (20–25-kg finger-trap traction) helps to define carpal fractures and dislocations in complex acute injuries such as perilunate dislocations. It can alert the physician to other injuries, e.g. palmar avulsion fracture of the triquetrum indicating a significant ulnar-sided ligament injury.

The normal lateral SL angle (formed by the intersection of the longitudinal axes of the lunate and the scaphoid) measures 30–60 degrees. An angle greater than 70 degrees is diagnostic for DISI pattern, while an angle less than 30 degrees represents a VISI pattern. A ‘double check’ for this diagnosis is the evaluation of the capitolunate angle (measured as the angle bisecting the longitudinal axis of the lunate and the capitate, normally 0 degrees) measuring greater than 15 degrees in a DISI deformity and less than 0 degrees in a VISI deformity. An apparently increased SL angle will appear with displaced scaphoid fractures and displaced/malunited Colles type distal radius fractures.

Standard arthrography has traditionally been used as an aid to the diagnosis of carpal ligament injuries. However as discussed in Chapter 12.31 (injuries to DURJ) false positive results can occur, particularly if, for example, there is a small perforation in an otherwise functionally competent SL ligament, which still allows contrast to pass from the radiocarpal to the MCJ. Arthroscopy remains the gold standard in the diagnosis of intraosseous ligament tears. Cadaveric studies have shown a high incidence of asymptomatic communications. Bilateral wrist arthrography has demonstrated similar communications in the contralateral asymptomatic wrists of patients evaluated for wrist pain.

Magnetic resonance imaging (MRI) or computed tomography (CT) scanning is now commonly performed as adjunct to plain arthrography, further improving its diagnostic accuracy, and providing extremely useful diagnostic information that helps to inform the patient and physician in the decision-making process prior to embarking on more invasive procedures.

CT scanning is now widely available and is extremely useful, particularly in the context of acute injuries, for identifying suspected carpal bones fractures that remain ‘occult’ on plain radiographs, and for assessing preoperatively the true nature and full extent of complex wrist injuries. Unless it is combined with arthrography, it does not demonstrate wrist ligament injuries well.

Where high field strength magnets and dedicated wrist coils are employed, high-resolution MRI scans offer increasing accuracy in the diagnosis of carpal ligament injuries, particularly if combined with magnetic resonance arthrography (MRA).

MRI can demonstrate bone oedema, injury, and circulation, and intraosseous ligament damage, and increasingly also evidence of extrinsic or capsular ligament injuries. Gadolinium-enhanced MRI scans provide additional information about the vascularity and viability of carpal bones that is helpful in the context of scaphoid or lunate fractures, presenting with delayed or non-union.

Wrist arthroscopy remains the gold standard in the diagnosis of intra-articular wrist disorders and ligament injuries.

If non-invasive investigations have failed to identify a cause for a patient’s wrist pain, particularly if follows a significant injury, then an examination under anaesthetic and diagnostic wrist arthroscopy should be considered.

Despite some limitations, which result from the necessity to place the wrist in traction, wrist arthroscopy provides a dynamic evaluation of the wrist including the status of: cartilage surfaces; synovium; most portions of the ligaments (intrinsic and extrinsic); the relative stability/motion between carpal bones; any anomalous structures, entrapped tissues, cartilage or bone debris, and tethering scar tissue.

Classifications of arthroscopic findings have been devised to facilitate accurate descriptions and to grade their significance as part of the decision-making process for treatment. For example, the classification of SL instability described by Geissler based on arthroscopic findings (Table 12.30.2).

CID is when instability arises due to injury between two bones in the same carpal row. Most commonly this occurs between the scaphoid and lunate or the lunate and triquetrum.

Following a ligament injury, the normal forces that act on the carpal bones can lead to the development of a progressive DISI carpal malalignment. This may be prevented if following an acute injury an anatomical reduction is achieved and maintained for long enough to allow the soft tissues to heal correctly.

Acute SL injuries without carpal malalignment may be treated with percutaneous K-wire fixation under image intensifier control. Temporary K-wires are inserted from the dorsum and used to ‘joystick’ the scaphoid and lunate to ensure anatomical reduction. Ideally two K-wires (mechanically more stable than one wire) are then passed from the scaphoid into the lunate to maintain position while the SL ligament heals. The wires are maintained for 8–10 weeks, so must be left buried under the skin to reduce the risk of infection. To reduce the risk of wire breakage, the wrist is immobilized in a below-elbow cast, until the wires are removed. Following which, intensive physiotherapy is commenced.

Some authors have reported good results with arthroscopically assisted K-wire fixation, allowing improved accuracy of reduction and wire placement. Arthroscopy also facilitates the debridement of any prominent ligament remains.

Complete disruption of the SL ligament may result in dynamic SL dissociation, where DISI malalignment of the carpal bones occurs only when forces are applied across the wrist. Following an acute injury of this magnitude, it is desirable to restore the anatomical position of the carpus and to formally repair the ligaments. The SL ligament can rupture through its midsubstance or be avulsed from (usually the scaphoid) with or without bone.

Although volar and dorsal approaches have been described, studies have suggested that a dorsal repair may be adequate. The wrist joint is approached between the third and fourth dorsal compartments. Anatomical reduction of the carpal alignment is achieved and maintained with buried K-wire fixation (as described earlier). A direct suture repair of midsubstance tears may be possible, but augmentation with bone anchors is often required. Small avulsion fractures are also reattached with bone anchors. The repair may also be augmented with a Blatt’s dorsal capsulodesis, tightening the capsule between the radius and the distal scaphoid and preventing excessive scaphoid flexion. Postoperatively the patient is treated as previously described.

If the presentation is delayed and the SL dissociation has not been treated in the acute phase, then the remains of the SL ligament retract and a primary repair is no longer possible. If the secondary restraint of the external ligaments fails progressively a permanent DISI carpal malalignment may develop. In symptomatic patients where carpal subluxation is still reducible and no degenerative changes have developed, a soft tissue reconstruction is possible.

Several ligament reconstruction techniques are described using tendon grafts, to maintain the normal carpal alignment. Perhaps the most popular tendon reconstruction currently is that described by Brunelli, who described using a distally based strip of FCR which is passed through a drill hole in the distal scaphoid. The remaining FCR tendon is then sutured across the SL interval to the remains of the SL ligament and attached to the distal radius. This was later modified to avoid crossing the radio carpal joint and instead the FCR tendon is (attached with a bone anchors to the dorsal lunate) and passed under the dorsal radiotriquetral ligament and then sutured back on its self. The long-term benefits of this procedure are not yet known.

Long standing SL dissociation may eventually lead to the characteristic progressive secondary degenerative changes described as a Scapholunate advanced collapse (SLAC) wrist. Many patients who reach this stage will respond to non-operative treatment. If this fails to control their symptoms then surgical intervention with one of the following salvage procedures may be considered.

The early stages of SLAC wrist involve the development of painful isolated radioscaphoid degenerative changes, which can be successfully treated with a radial styloidectomy. This pain relieving procedure does not correct the underlying pathological process, and degenerative changes may continue to progress across the midcarpal joint.

Proximal row carpectomy with excision of the scaphoid, lunate and triquetrum, creates a new articulation between the capitate head and the lunate fossa of the radius. This procedure does not rely on successful bone healing at an arthrodesis site and so allows early mobilization. However, it requires healthy articular cartilage on both the capitate head and the lunate fossa, so is contraindicated when degenerative changes have already spread across the MCJ. Patients report good pain relief and a functional range of movement and grip strength. If symptomatic degenerative changes subsequently develop between the capitate head and radius a wrist arthrodesis can be performed.

Scaphoid excision and four-corner arthrodesis (capitate, lunate, triquetrum and hamate) is a successful procedure for an intermediate stage SLAC wrist. Various fixation techniques have been used to stabilize the arthrodesis site including K-wires, staples, screws, and more recently low profile circular plates. A supplementary circular bone graft can also be placed at the junction of the four bones. Healthy cartilage in the radiolunate joint is a prerequisite for this procedure, but it is successful at relieving pain even in the presence of degenerative change in the MCJ, between the capitate head and lunate.

In all the chronic wrist instabilities with associated degenerative change, pan-carpal wrist arthrodesis remains a salvage option. In order to obtain a successful outcome, solid fusion of the radioscaphoid, radiolunate, SL, capitolunate, scaphocapitate and capitate–third metacarpal joints needs to be achieved. Various fixation techniques have been described, including K-wires, interosseous pins, and dynamic compression plates. Dedicated AO wrist arthrodesis plates benefit from built in wrist extension, smaller 2.7-mm screws for the metacarpal shaft, 3.5-mm screws for the radius, and achieve high rates of successful fusion.

These injuries were previously treated non-operatively in a moulded cast. However this does not prevent the subsequent development of a chronic VISI deformity. The development of wrist arthroscopy has enabled the early diagnosis and treatment of LTq dissociation. It is desirable to reduce and fix these acute injuries with percutaneous K-wires, or to perform a repair by open or arthroscopically assisted means, in a manner similar to that for the treatment of acute SL dissociation.

As with the management of a delayed SL dissociation, the remains of the LTq ligament can be debrided arthroscopically. If the deformity is still reducible, tendon reconstruction may be attempted using a strip of ECU between the lunate and triquetrum, as described by Shin and Bishop. LTq arthrodesis has also been attempted, but with a relatively high rate of failure to achieve bony fusion.

Late ligament reconstruction is not possible, and if LTq arthrodesis does not adequately control the deformity, then a midcarpal or pancarpal arthrodesis should be considered.

CIND occurs when the instability is due to dysfunction between the proximal and distal rows. The relationship between individual bones within a row however remains unaffected.

Pure dislocation of the radiocarpal joint is rare. It is more usually associated with an avulsion fracture of the radial styloid and urgent reduction is required. Neurovascular injury is commonly associated with these injuries. Following reduction, the radiocarpal joint is often unstable and open ligament reattachment may be required. Any associated radial styloid fracture is reduced and fixed restoring joint congruence and ligament stability.

Acute midcarpal fracture dislocation is rare and should be treated in a similar manner to an acute perilunate dislocation. Chronic instability and malalignment of the MCJ represents a complex spectrum of conditions. When it presents as a dynamic problem, in the context of a congenital increase in ligamentous laxity, the initial treatment should be non-operative with splintage, activity modification and physiotherapy. Several soft tissue reconstructions and fusions have been described for patients with persistent symptoms, but these are all small studies.

CIC covers a group of injuries in which there is disruption between bones of the same row and between separate rows.

Dislocation of the carpus around the lunate can be treated with an initial closed manipulation. If there are symptoms of median nerve compression then urgent carpal tunnel decompression is performed.

The extreme instability that results from these severe, often high-energy injuries, means that it is unusual for a true anatomical reduction to be achieved by closed manipulation alone. Therefore, early percutaneous K-wire fixation should be considered. Reduction of the lunate and scaphoid can be achieved using ‘joystick’ K-wires. Buried K-wires are then placed, in a similar manner to that described earlier for SL and LTq dissociations, to maintain the carpal alignment.

Severe injuries with gross instability, or those that are not fully reducible by percutaneous means, require open reduction via a dorsal approach which allows precise anatomical carpal alignment. The reduction is restored and maintained with the placement of transfixing K-wires. The dorsal approach facilitates the repair of the dorsal intrinsic and extrinsic ligaments. An additional palmar approach, via an extended carpal tunnel decompression, may also facilitate the reduction (especially of palmar dislocations) and a repair of the palmar wrist capsule.

The treatment of trans-scaphoid perilunate dislocations follows similar principles to pure perilunate dislocations. Urgent reduction and probable carpal tunnel decompression are required. It is important to achieve an anatomical reduction and stable fixation of the scaphoid fracture.

Open reduction and internal compression screw fixation of the scaphoid fracture and repair of the dorsal ligaments is best achieved via a dorsal approach. Arthroscopically assisted percutaneous scaphoid fixation may also be considered. The perilunate dislocation component of the injury is then stabilized with percutaneous K-wires as described earlier.

The wrist is initially immobilized for 8 weeks until the K-wires immobilizing the LT and MCJs are removed. Further immobilization may then be required if there is delayed healing of the scaphoid fracture. Ultimately, if a scaphoid fracture non-union develops it may require reconstruction with a bone graft and repeat fixation.

Patients should always be advised to avoid cigarette smoking to ensure the optimum bone-healing environment is maintained.

This variation of a perilunate dislocation involves fractures through the carpal bones adjacent to the lunate and is distinguished from the lesser arc injury in which there are purely ligamentous disruptions between the lunate and its neighbouring carpal bones. The classic injury involves fractures of the scaphoid, capitate, hamate, and triquetrum, but other fracture patterns or combinations of fractures and ligamentous injuries can occur. These severe injuries usually require open reduction via a dorsal approach, anatomical fracture reduction and internal compression screw fixation. Postoperative treatment is similar to that which is required following the lesser arc perilunate dislocation.

This rare injury involves a scaphoid waist fracture and a transverse fracture of the capitate proximal pole, which then rotates through 180 degrees. The injury represents an incomplete greater-arc injury, propagated from the radial side of the carpus. Treatment includes open reduction and internal fixation and good results have been reported.

Early reconstruction of SL dissociation has been show to have better outcomes compared with delayed treatment. In a study of 21 patients who underwent direct repair of the SL ligament with or with out capsulodesis, 19 patients had and improvement in their pain and grip strength. In addition a normal SL angle was maintained at 3-year follow-up.

There are few reports of the long-term results of delayed tendon reconstruction. Seventy-nine percent of patients undergoing a Brunelli reconstruction have satisfactory results. These results are promising, but the longer-term results are not yet known.

Radiocarpal arthrodesis is often avoided due to the potential for a reduced range of movement. However radiolunate fusion has been used with success in carpal instability. Pain relief was excellent and the preoperative range of motion was maintained. Radiocarpal fusion still allows movement at the MCJ, in particularly the functional ‘dart throwing’ movement (radial-extension toward ulnar-flexion).

Advanced degenerative changes (SLAC wrist) are best treated with either an excision of scaphoid and four-corner arthrodesis, or a proximal row carpectomy. A prospective study comparing these two procedures in 30 cases found no difference in pain or functional improvement. However, there were more complications in the four-corner arthrodesis group.

Proximal row carpectomy results in a high degree of patient satisfaction, a functional range of wrist motion and good pain relief but requires healthy articular cartilage on capitate head and lunate fossa.

If the degenerative SLAC wrist changes have extended to involve the capitate head then an excision of scaphoid and four-corner arthrodesis should give the best results. However, as with any midcarpal arthrodesis, it will result in the loss of approximately 50% flexion and extension and some radial deviation at the wrist.

In cases with advanced SLAC degenerative changes that require a pan carpal wrist arthrodesis as a salvage procedure, the AO wrist arthrodesis plate has been demonstrated as a reliable implant and technique.

Perilunate dislocations of the wrist are devastating injuries with poor results if left untreated. Despite treatment more than 50% of patients will go on to develop degenerative changes. However the incidence of carpal instability is reduced with open reduction and SL repair. If these injuries are treated appropriately at the time of injury, reasonable results can be achieved. In 14 patients with trans-scaphoid perilunate fracture dislocations whom underwent open reduction and internal fixation, all the scaphoid fractures healed and more than two thirds reported good functional recovery (Box 12.30.6).

The best reported results of radiocarpal dislocation have been with percutaneous K-wiring with or without open ligamentous repair.

Acute fractures of the lunate are relatively rare. They usually occur following a fall on a hyperextended wrist. Patients complain of pain and tenderness over the dorsum of the wrist. Standard poster anterior and lateral radiographs should be performed. If these appear normal, but a fracture is suspected, a CT scan should be obtained. Most small or undisplaced fractures can be treated non-operatively in a forearm cast. Displaced fractures require open reduction and internal fixation with cannulated screws (or K-wires). Wrist arthroscopy may be used to aid fracture reduction.

Perhaps the most common cause of lunate fractures is fragmentation secondary to the osteonecrosis seen in Kienböck’s disease. The diagnosis of Kienböck’s is usually based on the changes on plain radiographs. In the very early stages of the disease when radiographs remain normal, an MRI may be diagnostic. A more detailed discussion of Kienböck’s disease is given in Chapter 6.3.

As with all carpal bone fractures, there may be a somewhat tenuous blood supply to the fracture site, and a harsh mechanical environment. Biological and mechanical factors should be addressed to ensure an optimal bone-healing environment is maintained and patients should always be advised to avoid cigarette smoke.

Fractures of the triquetrum are the second most common carpal bone fracture. Tenderness over the ulnar side of the wrist raises the possibility of a triquetral fracture. Triquetral fractures may be associated with other carpal bone fractures or perilunate dislocations.

Small dorsal cortical triquetral fractures are common and may be due to impaction against the ulnar styloid or avulsion. These fractures can usually be treated with immobilization in a cast or splint. If they fail to unite and become symptomatic, then the fragment can be excised. Triquetral body fractures are usually identified on routine poster anterior radiographs of the wrist while dorsal chip fractures are generally identified on the lateral radiograph.

Triquetral body fractures can occur with perilunate injuries so these patients should be carefully examined for wrist instability. Open reduction and internal fixation should be considered for displaced triquetral body fractures.

Palmar ligamentous avulsion fractures are often not demonstrated on plain radiographs, but may be identified on CT scanning. These fractures may indicate a ligamentous injury with carpal instability. These injuries are managed as a LTq instability.

Fractures of the trapezium should be suspected in patients with pain at the base of the thumb after a direct blow. The fracture may be evident on plain radiographs or on a CT scan with sagittal reconstruction.

Trapezial ridge fractures may be identified on a carpal tunnel view. These usually represent an avulsion injury of the flexor retinaculum. These and nondisplaced trapezial body fractures may be treated by thumb spica cast immobilization for 4 weeks followed by mobilization if the fracture has healed clinically. Displaced trapezial body fractures with intra-articular extension require open reduction to restore the joint surface. Fixation is achieved with screws or K-wires. Subsequent symptomatic degenerative changes may later require arthrodesis or excision arthroplasty.

Fractures of the trapezoid are extremely rare, most are detected on plain PA and lateral radiographs, but CT scanning will demonstrate fracture anatomy more precisely. Non-displaced fractures or small fragments should be treated conservatively in a short arm cast for 4 weeks followed by mobilization. Displaced fractures may require open reduction and pin or screw fixation.

Capitate fractures can occur in isolation or in association with other carpal bone fractures and wrist ligament disruptions. Isolated non-displaced capitate fractures may be treated with cast and immobilization for 6 weeks followed by mobilization, provided clinical union is present. Isolated displaced capitate fractures require open (or arthroscopic assisted) reduction and internal fixation. Capitate fractures are prone to non-union and secondary post-traumatic osteoarthrosis. Capitate fracture non-unions should be treated with open reduction and internal fixation with bone grafting, possibly incorporating a partial arthrodesis.

Hamate fractures either involve the body or more commonly the hook. Since hamate body fractures generally occur as a result of high-impact injury, a careful neurological examination is required. Standard PA, lateral, and oblique radiographs are obtained initially although a CT scan may be to determine the orientation of the fracture. Undisplaced, isolated body fractures can usually be treated conservatively with immobilization. If the fracture is displaced and involving the CMC joint, or if there is CMC joint instability, then reduction and fixation is required.

Fractures of the hook of the hamate typically present with hypothenar pain and tenderness. The diagnosis can often be difficult. A carpal tunnel view can be helpful, while CT scanning will usually confirm the diagnosis. Patients complain of pain in the hypothenar region which is worse on gripping. If diagnosed early, hamate hook fractures may be treated with a short arm cast for 4 weeks. However, painful hamate hook non-union is not unusual and can cause secondary flexor tendon attrition ruptures. Excision for hamate hook non-union through a carpal tunnel approach generally produces excellent results.

Pisiform fractures are uncommon, difficult to diagnose on radiographs, and are consequently often missed. As the Pisiform lies close to Guyon’s canal, the ulnar nerve must be carefully examined. Pisiform fractures are treated with 4 weeks of short arm cast immobilization. If the fracture is comminuted, non-union occurs, or post-traumatic osteoarthrosis of the pisotriquetral joint develops, excision of the pisiform may be performed via a short longitudinal incision at the base of the hypothenar eminence (just distal to the distal wrist flexion crease). There is no significant loss of grip strength following pisiform excision.

Carpal instabilities represent a continuum of injuries, including subluxations, dislocations, unstable fractures, and fracture–dislocations, that are propagated from the radial or ulnar side of the wrist as a force is applied across a wrist (usually in hyperextension but occasionally in flexion). The force applied, site of application, force direction, and wrist position all determine the type of injury.

A detailed history and clinical examination with high-quality radiographs and if indicated a radiographic motion series remain the principle initial diagnostic tools. Additional imaging with standard arthrography, plain CT or MRI scans, or CT or MR arthrography are now providing increasingly accurate additional diagnostic information that can help the patient and physician to make informed decisions about treatment. Although more invasive, arthroscopy remains the gold standard investigation for diagnosing wrist ligament injuries.

The ‘intercalated segment’ concept helps to relate injuries to structure and function, to classify injuries, and to develop a logical approach to their diagnosis and treatment. Carpal instabilities can be classified as CID, CIND, or CIC, along with the simulated instabilities of ‘CIA’. These injuries can then be further modified descriptively as DISI or VISI. Improved understanding of the complex anatomy and kinematics of the wrist is helping to further the development of rational surgical treatments for these problems, with earlier and more anatomic repair/reconstruction, and rehabilitation.

The carpal bones and their associated ligaments form an anatomically compact unit that functions by sharing forces throughout the carpus. Consequently, isolated carpal bone fractures are unusual but do occur. Because they are rare, they are often overlooked or passed off as insignificant.

Fractures of the proximal scaphoid, lunate, and capitate have a precarious interosseous blood supply and an increased risk for osteonecrosis. Symptomatic non-union of hamate hook fractures or pisiform fractures may be successfully treated with excision. Instability is often the ‘common ingredient’ in carpal injuries and its improved understanding and management remains central to the treatment of wrist injuries.