CHAPTER 39 Chronic Volar-Flexed Intercalated Segment Instability

The definition of instability of the wrist has been described by the International Wrist Investigators’ Workshop as “the inability of the carpus to maintain its normal anatomical relationships under physiological loading.” Dobyns and colleagues,¹ and more recently the International Wrist Investigators’ Workshop, have suggested a number of terms that describe the patterns of instability:

It is now accepted that the stability of the carpus is wholly dependent on the integrity of the interosseous and capsular ligaments of the wrist joint and not on any inherent stability conferred by bone shape or position.²

One might look at the effects of failure of these ligaments by using an analogy of the coiled spring. This concept, proposed by Garcia-Elias, identifies that the scaphoid, the lunate, and the triquetrum are intimately connected and, as Kapandji has described,³ there is a variable geometry of the proximal row of the carpus as the loaded wrist is moved. Thus, the scaphoid flexes, extends, pronates, supinates, and translates. The lunate flexes, extends, and translates but does not pronate or supinate. Finally, the triquetrum flexes and extends much less than the lunate but does not pronate or supinate and although it does translate, it does not articulate with the distal radius and barely articulates with the triangular fibrocartilage complex (TFCC). The scaphoid has a long lever arm by comparison to the lunate and triquetrum and therefore has a profound effect on the biomechanics of the wrist. Using the coiled spring analogy, axial loading of the intact wrist requires the rotational moment of the scaphoid to be balanced by the opposite rotational moment of the triquetrum, with the lunate acting as the torque converter in its position as the intercalated segment of the proximal row. Failure of the scapholunate ligament gives rise to the potential for the scaphoid to flex under the axial loading but, of course, the triquetral/lunate complex rotational moment is unopposed and the lunate and triquetrum extend, giving rise to the radiographic appearance of dorsiflexed intercalated segment instability (DISI). If, however, the lunate is separated from the triquetrum, the rotational moment of the scaphoid takes the lunate into flexion, thus creating the radiographic appearances of volar-flexed intercalated segment instability (VISI) (Fig. 39-1).^4–7

FIGURE 39-1 A, The spring theory. The proximal row of the carpus can be represented as a spring indicating the relationship between the three bones. B, The spring theory in DISI. When the scaphoid and lunate are disconnected, the scaphoid falls into flexion because of its long lever arm. The lunate and triquetrum fall into extension, giving rise to the appearance of DISI on the lateral radiograph. C, The spring theory in VISI. When the proximal and distal rows are disconnected, the longer lever arm of the scaphoid prevails. If there is lunotriquetral dissociation, the lunate goes with the scaphoid into flexion, giving rise to the VISI appearance on the lateral radiograph.

The work of Mayfield and Johnson⁸ has shown us that there are patterns of ligamentous injury, through a radial-sided applied force, in which, with the wrist loaded in extension and ulnar deviation, axial loading resulted in sequential ligament disruption. In effect, these injuries occurred as a result of applying what might be described as a proximal row supination force to the cadaver specimens. This is translated into the in vivo injury when, as a result of falling on the outstretched hand, the thenar eminence (Fig. 39-2) contacts the ground first and thereafter the protective pronation reflex of the forearm forces the hand, and therefore the carpus, into supination, resulting in either a pronator quadratus fracture in the child, a Colles’ type fracture in the elderly, a scaphoid fracture in the young male, and a scapholunate, perilunate lesser arc, type of soft tissue injury in most adults. The sequence of ligament failure in this pattern of injury is well recognized and described elsewhere.

FIGURE 39-2 The Mayfield sequence. A, The first stage of the sequence is disruption of the scapholunate joint progressing from anterior to posterior. B, The second stage is progressive disruption of the dorsal attachments to the lunate. C, The third stage progresses through the triquetrolunate joint from posterior to anterior. D, The fourth and final stage is dislocation of the lunate.

The so-called reverse Mayfield sequence, or the proximal row pronation injury, occurs as a result of the forces acting on the hand as the hypothenar eminence strikes the ground first (Fig. 39-3). The patterns of injury are complex in that there are many more ligament attachments to the triquetrum than to the scaphoid. The act of falling on the outstretched hand when the heel of the hand strikes the ground concentrates the forces that now act on the ulnar side of the carpus and therefore through the pisiform to the triquetrum. The position of the pisiform on the volar aspect of the triquetrum results in this pair of bones decelerating rapidly, but the momentum of the individual suffering the injury drives the ulna toward the ground, which results in the forces being transmitted to the structures on the ulnar side of the wrist. There is a tendency to thus force the hand into a pronation attitude with reference to the distal radius and ulna. The ulnar head continues to approach the ground, which leads to a dorsal shearing force that may detach the posterior aspect of the TFCC from the dorsal ulnar carpal ligaments, giving rise to a separation of these two structures. This does not involve a true tear of the TFCC.

FIGURE 39-3 Operative sequence of ECU reconstruction. A, The incision along the fifth compartment. B, The triquetrum is exposed, and two bur holes are created. C, One third of the ECU is detached proximally and left attached distally. Then this is taken through the triquetrum and the dorsal aspect of the TFCC.

Any disruption of connections between the scaphoid and the lunate or the lunate and triquetrum can prevent the wrist from supporting physiological loading without collapsing.⁵ The proximal row variable geometry system becomes dyskinetic, that is, it is not in the appropriate configuration in most positions of the loaded wrist. It is accepted from anatomical studies that the most important part of the scapholunate interosseous ligament lies dorsally and the most important part of the triquetrolunate interosseous ligament lies anteriorly.⁷ This allows each of the bones to have its own axis or rotation different from the others and also for each bone to move within its limits set down by these two ligaments.

Ulnar midcarpal instability is traumatic, degenerative, or idiopathic.^9–12 The traumatic version is acute or chronic; the degenerative version is chronic and usually defined as part of the ulnar abutment syndrome; and the idiopathic version is related to hyperlaxity and pathological hyperlaxity, as exhibited in Ehlers-Danlos syndrome.

The clinical features of ulnar midcarpal instability are ulnar-sided pain and a sagging carpus. The posterior sag is a very characteristic one and is related to the detachment of the posterior part of the posterior TFCC from the ulnar carpal ligaments, a greater feel of the dorsal tubercle of the triquetrum as this bone flexes, the clunking wrist, tenderness over the lunotriquetral interval, a positive Regan shuck test, and, often, a positive Lichtman pivot shift test.¹³

The arthroscopic features can be defined as a significant step-off between the lunate and the triquetrum when viewed on midcarpal arthroscopy (Fig. 39-4).

FIGURE 39-4 The lunotriquetral joint. This arthroscopic view of the left wrist demonstrates disruption of the lunotriquetral joint and a large facet on the lunate—the hamate facet.

A possible sequence of events is proposed arbitrarily divided into discrete steps based on the known patterns of injury seen (Fig. 39-5):

FIGURE 39-5 Proposed mechanism of ulnar midcarpal instability. A, Stage 1: Detachment of ulnar carpal ligaments from the posterior aspect of the TFCC. B, Stage 2: Lunotriquetral ligament disruption. C, Stage 3a: Peritriquetral instability. D, Stage 3b: Disruption of the volar ulnar carpal ligaments. E, Stage 4a: Progressive damage to the scapholunate ligaments (the reverse Mayfield). F, Stage 4b: The complete disruption of the proximal and midcarpal joint system.

Treatment Options for Specific Patterns of Instability

Ulnar Midcarpal Instability (Carpal Instability Dissociative)

The treatment options for the management of chronic lunotriquetral instability are limited.¹⁴ An alternative to ligament reconstruction or augmentation is intercarpal fusion, which can give rise to a significant loss of wrist motion.⁹ At all levels of the problem the treating physician should respond to the patient’s symptoms and, as in any other nonprogressive musculoskeletal problem, the starting point is reassurance and lifestyle modification supported by orthoses and physical therapy in the acute phase or in the acute exacerbation of a chronic injury. Posterior ligament surgery in the form of an extensor carpi ulnaris reconstruction; anterior ligament surgery, which has been described both by Lichtman and by Garcia-Elias; and intercarpal fusions can be performed in cases unresponsive to conservative management. Limited wrist arthrodeses can significantly distort carpal motion, and the results can be disappointing.

Triquetrohamate fusion is ideal for patients with a peritriquetral instability, but this affects a very small number of patients.¹⁵

Capitolunate fusion will cure the midcarpal instability part of the problem but does not address the persistent detachment of the posterior part of the TFCC and, therefore, only partially solves the problem.

Four-corner fusion serves much the same purpose but is more reliable than capitolunate fusion in terms of achieving fusion.

Total wrist fusion is an extreme management of ulnar midcarpal instability, but the presence of degenerative changes and unremitting pain despite conservative measures would lead to the consideration of a full wrist fusion.

Extensor Carpi Ulnaris Tenodesis for Lunotriquetral Instability

We have described a technique for a ligament augmentation of the dorsal aspects of the ulnar carpal ligament complex, the ECU tenodesis.¹⁶ The operation is shown in Figure 39-6.

FIGURE 39-6 Ulnar midcarpal instability. Note the volar “sag” of the carpus on the ulnar side secondary to disruption of the dorsal ligament TFCC relationship.

The skin incision is over the line of the fifth extensor compartment; through the fifth compartment the extensor digiti minimi is exposed and retracted. The extensor retinaculum is reflected from the dorsal aspect of the triquetrum, revealing the ECU and its inner sheath, which is opened. Two holes are drilled through the dorsal cortex of the triquetrum using a rose bur to prevent perforation of the volar cortex (the pisotriquetral joint). The ECU tendon is exposed proximally, and a strip of the first third of the tendon is detached proximally and stripped toward the hand as far as the insertion, leaving it attached distally. The harvested tendon having been passed through the two holes in the triquetrum, distal to proximal, is then tunneled through the posterior aspect of the TFCC and then through the dorsal capsule of the distal radioulnar joint; it is then reattached to itself in the groove of the ulnar head. This ECU loop stabilizes the ulnar carpal complex. Pulling on the ECU, which in the normal course of events because of its position would tend to displace the wrist forward, now tends to reduce the wrist, bringing the triquetrum back toward the TFCC. This is probably not a dynamic tendon transfer because attachment to the dorsal ligaments prevents any active glide and in effect there has been a reconstruction of the dorsal ulnar carpal ligaments.

We have reviewed 46 of these procedures. In the review group there was no gender bias, the average age was 30, the dominant wrist was treated in 33% of patients, and significant trauma was recalled by the patients in 43 cases.¹⁶

Using the Mayo Wrist Score, in 72% recovery was excellent or good; in 15% it was satisfactory, which meant that although there was sufficient improvement for the patient to believe that the operation was worthwhile, these patients were still left with residual symptoms; and in 13% the patients had no improvement.

The patient dissatisfaction was 13%; that is, 87% of the patients were satisfied but those who failed to improve at all were disappointed with the surgery. The remainder stated that they would happily proceed to have the operation done on their other wrist if necessary or would recommend it to a friend.

Patient selection is crucial, and arthroscopy best identifies the problem and excludes other intra-articular pathological processes. The selection criteria for inclusion were ulnar-sided wrist pain after a fall on the outstretched hand with prominence of the triquetrum to palpation, tenderness over the triquetrolunate joint, a positive Regan shuck test, and evidence of lunotriquetral instability on arthroscopy. Contraindications were full midcarpal instability, previous surgery, and the presence of a full reverse Mayfield injury.

Lunotriquetral instability as a result of proximal row pronation injuries can be effectively treated with soft tissue reconstruction. Stage 2, 3a, and 3b pronation injuries are suitable for this procedure. This grading is done at the time of arthroscopy. The procedure is less effective in injuries to the triquetrolunate joint as a result of a supination pattern of injury of the carpus. Tensioning of the repair must be performed with the wrist in neutral, not in ulnar, deviation; the surgery is simple, the operating room time is short, and, more importantly, the procedure is reversible. The cosmetic appearance of the scar is very acceptable.

Ligament augmentation has a success rate that will improve with better patient selection. The best results of the series were seen in patients with a stage 2, 3a, or 3b proximal row pronation injury. Modest results were seen in those patients with a Mayfield stage 3 injury with a residual lunotriquetral instability; that is, they had a radial-sided injury. Those with significant full midcarpal instability of stage 4a and 4b also failed the procedure. The failures in the study have also been related to overtensioning of the repair and overambitious expectations of both the surgeon and the patient.

There is an alternative method of repairing the lunotriquetral interval, using a complex reconstruction described from the Mayo Clinic. Garcia-Elias and others have recommended the volar and dorsal approach, repairing both the anterior part of the lunotriquetral internal and the triquetrohamate ligament. This basically is the pisohamate ligament, which runs deep from the pisotriquetral joint to the hook of the hamate at its base. The triquetrocapitate ligament also is reconstructed. Future developments in arthroscopic-assisted surgery may allow earlier diagnosis and intervention, and the techniques of arthroscopic capsular shrinkage may be sufficient to reduce the symptom level to acceptable levels in the milder cases.¹⁷

True Midcarpal Instability Nondissociative

True midcarpal instability does not involve any injury to the intrinsic scapholunate or triquetrolunate interosseous ligaments; and because there is no such injury there is no dissociation between the individual bones of either the proximal or the distal rows of the carpus. The instability arises between the proximal and distal rows, and therefore the term “carpal instability nondissociative” is applied. This is related to problems where the extrinsic capsular ligament system fails to adequately maintain the relationship of the proximal row to the distal row and thus allows the distal row to fall into its default position, which forces the proximal row into flexion. This gives rise to the so-called tilting teacup or VISI pattern (Fig. 39-7). Ligament reconstruction (or more accurately augmentation or substitution) is unreliable in these circumstances, and one of the limited fusions may be required.

FIGURE 39-7 Lateral radiograph of wrist demonstrates the volar tilt of the lunate that occurs in midcarpal instability.

Limited wrist arthrodesis can be in the form of lunotriquetral fusion,¹⁸ triquetrohamate fusion, capitolunate fusion, lunotriquetral-capitohamate fusion (LTCH or so-called four-corner fusion), and radiolunate fusion (the Chamay fusion).

The future for ligament reconstruction in the ulnar midcarpal dissociative type of injury is for better identification of the injury pattern and earlier intervention in a repair and reconstruction mode rather than salvage in the chronic injury. Primary repair of the identifiable injured ligaments, in particular the detachment of the posterior TFCC from the dorsal ulnocarpal ligaments and the repair of the anterior ulnocapitate and radioscaphocapitate ligaments, can give satisfactory results in appropriate cases, but limited wrist arthrodesis may be necessary in the severe or recalcitrant case.

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