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Increased or altered carpal motion may occur as a result of:

1. Ligament tears.

2. Bony abnormality.

3. Ligamentous laxity.

If this altered motion causes symptoms, the wrist is said to be ‘unstable’ and treatment may be indicated.

Carpal instability can occur:

1. Between the bones of the same carpal row, e.g.

scapholunate dissociation, lunotriquetral dissociation.

2. Between the proximal and distal rows (mid-carpal instability).

3. Between the radius and proximal carpal row (radiocarpal instability). This is often associated with rheumatoid disease (ulnar translocation of the carpus) or developmental Madelung’s deformity.

Most midcarpal instabilities have involvement of both the radiocarpal and midcarpal ligaments.

1. Scapholunate dissociation

Scapholunate ligament injuries are a common cause of wrist pain and the diagnosis is frequently missed (Fig. 12.33). Untreated scapholunate dis-sociation will result in wrist osteoarthritis due to abnormal loading of articular surfaces, i.e. scapho-lunate advanced collapse deformity (the SLAC wrist).

Figure 12.33. This 55-year-old man has a

long-standing scapholunate injury. Note the increased scapholunate gap (‘Terry Thomas’ sign) and

foreshortened appearance of the scaphoid giving a

‘signet ring’ appearance as a result of scaphoid flexion. Note also the early loss of joint space in the radioscaphoid joint. Arthritis begins here before involving the midcarpal joint. The radiolunate joint is usually spared (SLAC pattern).

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Patient presentation

The patient presents with wrist pain and weakness, sometimes associated with a click or a feeling of

‘giving way’. There may or may not be a history of trauma (usually a hyperextension injury). Instabil-ity may be associated with a dorsal wrist ganglion.

Generalized ligamentous laxity is sometimes a predisposing factor. Patients with hypermobile joints are usually able to demonstrate the following:

1. Passive extension of the little finger MCP joint beyond 90 degrees.

2. Passive opposition of the thumb to the flexor aspect of the forearm.

3. Elbow hyperextension beyond 10 degrees.

4. Knee hyperextension beyond 10 degrees.

5. Forward flexion of the trunk with straight knees so that the palms of the hand rest easily on the floor.

Clinical assessment

There is periscaphoid tenderness, particularly dor-sally over the scapholunate joint. Wrist motion may be normal although there is pain on full extension. Grip strength is often reduced compared with the opposite side. Generalized ligamentous laxity should be looked for.

The Watson scaphoid shift test (Fig. 12.34)

The Watson scaphoid shift test may be positive.

This test can be difficult to perform and may be positive in normal wrists. Place the examining thumb on the tubercle of the scaphoid and the index finger adjacent to the proximal pole dorsally.

As the wrist moves from ulnar to radial deviation, the examiner feels the scaphoid flex. Dorsal pressure is applied with the thumb on the scaphoid tubercle. If the S-L ligament is lax or torn, the scaphoid may sublux dorsally. This can be felt and may be associated with a painful click. Always compare with the opposite side.

Radiological examination

A thorough history and clinical examination will usually suggest the diagnosis which is best con-firmed by arthroscopy. Plain X-rays are frequently normal, even if appropriate views are taken. These are: PA in radial and ulnar deviation, PA and lateral

views in neutral. A clenched fist view may be helpful. The opposite wrist should be X-rayed for comparison.

X-ray signs that are consistent with scapho-lunate ligament instability include:

1. Increased scapholunate gap (‘Terry Thomas’

sign).

2. Increased scapholunate angle on lateral view (greater than 60 degrees); compare with the opposite side (Fig. 12.35).

3. DISI pattern (dorsal intercalated segment disa-bility), i.e. the lunate is extended and the scaphoid is flexed (Fig. 12.36).

4. Foreshortened appearance of the scaphoid in the PA view due to increased scaphoid flexion;

the scaphoid may resemble a signet ring.

The radiological features of scapholunate insta-bility are frequently discussed but it is important to remember that instability, by definition, is a dynamic condition. Radiographs, even if ‘motion’

or ‘stress’ views are taken, are merely a static record of the wrist position at the time the picture was taken. Imaging studies frequently record fixed deformity, not instability. The instability grading system suggested by Herbert (1991) acknowledges the importance of clinical assessment.

Figure 12.34. The Watson scaphoid shift test.

(Reproduced from Garcia-Elias, M. Carpal instabilities and dislocations. 1999. In Green’s Operative Hand Surgery (D. P. Green, R. N. Hotchkiss and W. C.

Pederson, eds) p. 884, Churchill Livingstone, with permission.)

Lunate

Scaphoid 30 – 60

(a) NORMAL

(b) DORSIFLEXIONINSTABILITY(DISI)

< 60

< 30

(c) PALMARFLEXIONINSTABILITY(VISI)

Instability grading

1. Symptomatic wrist with no demonstrable clin-ical instability.

2. Clinically subluxable scaphoid.

3. Subluxed scaphoid, reducible.

4. Subluxed scaphoid, irreducible.

5. Secondary osteoarthritis.

Diagnostic assessment

An MRI scan can demonstrate partial or complete scapholunate tears. Dynamic ultrasound can show abnormal scapholunate motion when compared with the opposite wrist and will demonstrate an associated ganglion when present.

Figure 12.35. (a) When the normal wrist is viewed in neutral extension on a lateral X-ray, the normal scapholunate angle is from 30 to 60 degrees. Note how the long axis of the distal radius, lunate, capitate and metacarpal bones are collinear. Note also how the articular surfaces of the distal radius, lunate and capitate fit together like multiple Cs facing in the same direction. (b) When the lunate faces dorsally, the scapholunate angle is greater than 60 degrees (usually about 100 degrees). This angle indicates a dorsal intercalated segment instability (DISI). The capitate is displaced dorsally in relation to the radius. (c) When the lunate faces palmarly and the scapholunate angle is less than 30 degrees, this demonstrates a volar intercalated segment disability (VISI). (Reproduced from Frykman, G. K. and Kropp, W. E. Fractures and traumatic conditions of the wrist. 1995. In

Rehabilitation of the Hand: Surgery and Therapy (J. M. Hunter, E. J. Mackin and A. D. Callahan, eds) p. 329, Mosby, with permission.)

Figure 12.36. (a) This is the lateral view of the normal right wrist of a 22-year-old professional footballer. (b) Note the DISI (dorsal intercalated segmental instability) pattern on the injured left side where the lunate is extended and the scaphoid is flexed.

(a)

(b)

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Bone scan is unreliable in diagnosing scapho-lunate dissociation.

Arthroscopy is the most accurate way to confirm the diagnosis. The ligament tear and abnormal motion are clearly visible.

Conservative treatment

Conservative treatment can be trialled with Grades 1 and 2. If the symptoms are mild or the ligament tear is partial, non-operative treatment is appro-priate. A resting wrist splint is applied and resisted activities are avoided until symptoms settle. Gentle isometric wrist strengthening exercises are then gradually increased as comfortable. When the patient returns to heavy activities and/or sport, protective strapping or a splint is applied.

Surgical treatment and aftercare

For complete ligament tears, surgical repair is indicated. The malrotated scaphoid and lunate bones are reduced via a dorsal approach and the ligament is repaired with transosseous sutures. The reduction and ligament repair are protected with temporary K-wires (Fig. 12.37).

The wrist is immobilized in 10 to 15 degrees of extension for a period of 6 to 8 weeks. The K-wires are then removed and active wrist movements are commenced. A removable wrist splint is applied for a further month. Heavy physical activities are avoided for 3 months postoperatively.

Maximum wrist motion may not be achieved for at least a year. Wrist flexion range will be restricted to about 60 per cent of its former range.

Other surgical options include:

(i) Partial wrist fusion, e.g. scapho-trapezial-trapezoid (STT).

(ii) Ligament reconstruction using tendon or reti-nacular grafts.

As yet, no single technique has been universally successful in treating this difficult clinical problem.

Late presentation with established arthritis

Untreated scapholunate dissociation leads to arthritis resulting from the abnormal loading of articular surfaces. Cartilage wear begins in the

Figure 12.37. (a) Acute scapholunate ligament disruption. Note the widening of the S-L interval. (b) Ligament repair and reduction of malrotation. The reduction and repair are protected with temporary K-wire fixation (6 to 8 weeks).

(a) (b)

radioscaphoid joint and goes on to involve the midcarpus. The radiolunate joint is almost always spared.

Non-operative treatment involves activity mod-ification and intermittent splinting.

Surgical options include:

(i) Radial styloidectomy.

(ii) Proximal row carpectomy.

(iii) Partial fusion (four-corner fusion, i.e. fusion of the capitate, hamate, lunate and trique-trum with excision of the scaphoid).

(iv) Total fusion.

2. Lunotriquetral dissociation

As with scapholunate instability, there may be a history of trauma (hyperextension). This diagnosis can often be confused with TFCC injury or ulnocarpal impaction.

Patient presentation

The patient presents with ulnar-sided wrist pain, sometimes associated with a click or clunk that accompanies active ulnar deviation of the wrist and forearm supination. There is local tenderness over the lunotriquetral joint. The distal ulna may be prominent.

Diagnosis

The ‘shear’ (or ballottement) test

Stability can be assessed by ballotting the joint.

Stabilize the lunate with one thumb; grasp the triquetrum and pisiform between the index finger and thumb of the opposite hand. Applying shear to the joint may cause abnormal motion, pain or crepitus. Comparison should be made with the other wrist.

Investigations

Lateral X-rays may show a volar intercalated segment instability (VISI), i.e. the unrestrained lunate assumes a flexed posture and the triquetrum is distal in relation to the hamate. Note should be taken of the ulnar variance as this instability may be difficult to distinguish from ulnar carpal impingement due to a long ulna.

A bone scan is locally hot. Abnormal luno-triquetral motion may be confirmed by arthroscopy.

Conservative treatment

Mild symptoms may be managed with splinting, non-steroidal medication, injections and activity modification.

Prosser (1995) has described a programme for ulnar carpal instability that involves the following:

1. Eccentric ECU exercises.

2. A soft splint which attempts to ‘relocate’ the subluxed carpus from its supinated position.

3. Grip strengthening exercises which provide the isometric component of the programme.

The ECU exercises are carried out 3 times a day with 10 repetitions using a 500 g weight and progressing to 1 kg in weight. Grip strengthening exercises are performed with the forearm in the supinated, pronated and neutral positions.

The splint is comprised of a snugly fitting elastic wrist brace which has a strap sewn into the ulnar aspect of the midpalmar area. The section of the strap which passes beneath the ulna is firm while the section over the ulnar aspect of the wrist is elasticized. As the strap is drawn around the ulnar carpus and onto the dorsum of the hand, the subluxed carpus is elevated (or ‘relocated’). This correction gives most patients significant relief of pain (Fig. 12.38).

The splinting/exercise programme is maintained for a minimum of 6 weeks. Grip strength is re-examined. If there has been improvement, the splint is gradually withdrawn.

Figure 12.38. Soft splint used in the early manage-ment of ulnar carpal instability.

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Surgery

If non-operative measures fail, the most reliable surgical treatment is a four-corner fusion (trique-trum, hamate, capitate and lunate). Various liga-ment reconstructions have been tried with limited success.

3. Midcarpal instability

Midcarpal instability includes a diverse group of conditions. Most midcarpal instabilities involve both the radiocarpal and midcarpal joints, the latter of these predominating. Congenital ligamentous laxity is frequently associated with these condi-tions. Ulna minus variance or an increased slope of the distal radius may also be present.

(i) The capitate-lunate instability pattern (CLIP)

This appears to result from attenuation of the radiocapitate ligament which allows dorsal sub-luxation of the capitate during movement of the wrist into ulnar deviation.

(ii) Triquetro-hamate-capitate ligament laxity

This will result in a VISI deformity. The ligaments supporting these bones prevent midcarpal collapse and ensure a smooth transition of the proximal carpal row from flexion to extension as the wrist ulnar deviates. Where this restraint is lacking, the proximal row stays flexed for too long, this resulting in a catch-up clunk when the wrist reaches the end range of ulnar deviation.

Patient presentation

The patient is frequently a young female present-ing with a painful click that is associated with ulnar deviation and pronation of the wrist. There may be a supination deformity of the distal carpal row relative to the forearm bones. Symptoms are often precipitated by minor trauma or repetitive activity.

Wrist movement is sometimes restricted and grip strength is often reduced.

Conservative treatment

Conservative management includes splinting and strengthening of extensor carpi ulnaris (see ‘Luno-triquetral dissociation’), non-steroidal medication and modification of work and leisure activities.

Surgery

Where conservative measures prove ineffective, the following surgical options can be considered:

soft tissue reconstruction (e.g. tenodesis using a slip of ECRB), a triquetro-hamate or four-corner fusion, or levelling of the DRUJ where there is ulna minus variance.