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(ii) Carpal instability
Current Orthopaedics (1999) 13, 268-274 © 1999 Harcourt Publishers Ltd
Mini-symposium: The painful wrist
(ii) Carpal instability
D.A. Campbell
INTRODUCTION
relative positions constantly in response to movements of the adjacent bones and the constraints of their attached ligaments. As a unit, therefore, the proximal carpal row is a mobile adaptive structure whose overall configuration changes as a result of forces applied fi'om the more rigid structures either side of it. • The proximal carpal row therefore acts as a 'link' mechanism between forearm and hand. This row (the middle segment of a three-segment system) has no muscles attached to it and is inherently unstable in compression without its ligamentous attachments. 1.2
The mechanics of the wrist joint are difficult to describe without first understanding the anatomy and relationships of the structures involved. The wrist is a complex joint, which allows motion in three planes by a combination of movements at several areas simultaneously. These movements are interdependent and disruption of any part of this motion cycle has effects on the whole carpus. Carpal instability is therefore nothing more than carpal dysfunction, Before attempting to comprehend carpal instability, it is, however, necessary to describe and gain some understanding of carpal stability.
Stability of any synovial joint, or series of joints, relies on both bony and soft tissue components. Freely mobile joints (such as the gleno-humeral joint) have little contribution to stability from skeletal geometry and achieve their stability from strong soft tissue constraints. Conversely, synovial joints with a limited range of motion (such as the ankle joint) rely heavily on skeletal factors for stability. Disruption of these results in joint subluxation and abnormal movements (instability).
THE CARPUS
Whilst many of the finer points of carpal kinetics and kinematics remain the source of controversy, some fundamental biomechanical issues are widely agreed (Fig. 1): • The surface of the distal radius, the triangular fibrocartilage complex (TFCC) and the distal ulna form a stable base for radio-carpal motion. • The distal carpal row, comprising trapezium, trapezoid, capitate and hamate are bound together by strong interosseous ligaments and move together as a single unit. • The set of bones between these two relatively rigid structures - the proximal carpal row - (comprising scaphoid, lunate and triquetrum) change their
D.A. Campbell FRCS(orth), Consultant Hand Surgeon, Department of Orthopaedic Surgery, St James's University Hospital, Beckett Street, Leeds LS9 7TF, UK Tel: +44 (0)113 2065578; Fax" +44 (0) 113 2065156
Fig. 1 The anatomy of the carpus
268
Carpal instability The proximal carpal row is a highly mobile set of bones which depends on the integrity of the surrounding soft tissue constraints in order to maintain stability. These consist of short, strong interosseous ligaments, longer extrinsic intracapsular ligaments and extraarticular stabilizing factors. It is perhaps easier to understand the function of these structures if they are considered as preventing certain movements, rather than allowingthem.
Intrinsic ligaments These have their origin and insertion within the same carpal row. The ligaments controlling the proximal carpal row from within are the scapho-lunate ligament (SLL) and the luno-triquetral ligament (LTL). These prevent excessive separation of the bones in the proximal row during movement, and transmit forces along the row to ensure adaptive motion.
Extrinsic ligaments These are found on both dorsal and volar sides of the carpus. The volar ligaments are stronger and arranged in two distinct 'V' shaped ligament complexes (Fig. 2A). The proximal ligament is centred on the lunate with limbs attached to the ulna and radius, so stabilizing the lunate. The distal ligament centres on the capitare and extends to the triquetrum and the radius (via the scaphoid). This structure 'controls' the triquetrum and scaphoid. The dorsal extrinsic ligaments are also arranged in a 'V' shape (Fig. 2B) centred on the triquetrum and containing a radio-luno-triquetral
(RLT) segment and a trapezium, trapezoid and scaphoid segment.
Extraarticular structures Other structures, mainly centred on the ulnar side of the wrist, also contribute to stability but are insufficient on their own to prevent the changes of instability. The flexor and extensor retinaculae together with the ulnar wrist flexor and extensor combine to provide a degree of ulnar stability when tightened.
CARPAL M O V E M E N T S
Wrist flexion and extension The tightly bound bones of the distal carpal row move together as one unit and migrate proximally when the wrist is loaded axially. This causes a compressive load on the proximal row resulting in adaptive rotation of these bones. The scaphoid will rotate into flexion because of the attachments of the distal palmar extrinsic ligaments. This force is transmitted by the SLL to the lunate, which then also flexes. The capitate tends to slide in a palmar direction in the capitolunate articulation (by virtue of the scapho-capitate ligament, which will be taut) so causing further lunate flexion (Fig. 3). The triquetrum, however, is now under two opposing forces. The LTL will transmit torque from the flexed lunate to try and flex the triquetrum (Fig. 4) (force x). However, the arrangement of the joints made with the triquetrum by both capitate and hamate tends to force the triquetrum into extension (force y). This is the weaker of these two
A
5
Fig. 3 Capitate extensioncauses lunate flexion
B
Y
X Fig. 2 (A) The volar extrinsicligaments; (B) The dorsal extrinsic ligaments.
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Fig. 4 Opposingflexion(x) and extension (y) forcesfight to control the triquetrum.
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Current Orthopaedics
opposing forces, and axial load therefore tends to rotate the proximal carpal row into flexion. Should any of these 'links' fail, however, the triquetrum will move into extension. This process of midcarpal movement involves flexion of the proximal row as an adaptation to extension of the distal row and depends upon intrinsic and extrinsic ligamentous integrity. The loss of integrity of the scapho-lunate or luno-triquetral ligaments results in an imbalance between the flexion and extension forces around the triquetrum. The location of the ligament disruption determines whether the lunate will follow the scaphoid (into flexion) or the triquetrum (into extension). Scapho-lunate ligament insufficiency therefore results in excessive scaphoid flexion, whilst the lunate and triquetrum are unopposed in their attempts to extend. Conversely, luno-triquetral ligament insufficiency allows the lunate to join the scaphoid in flexion whilst the triquetrum can extend unopposed. The position of the lunate can therefore be used as a guide to presumed integrity (or otherwise) of the intrinsic proximal row ligaments.
Radial and ulnar deviation of the wrist When the wrist moves into ulnar deviation, the head of the capitate translates dorsally causing the lunate (and, therefore, scaphoid) to extend. Further ulnar deviation results in contact between the hamate and triquetrum, which produces triquetral extension as it slides up the hamate. The intact LTL transmits this to the lunate resulting in further lunate extension. The increased distance between the trapezium/ trapezoid complex and the distal radius allows the scaphoid to 'stretch out' (i.e. extend) into the space, under the influence of torque transmitted by the SLL. Conversely, radial deviation narrows the space between the trapezium/trapezoid and distal radius. This forces the scaphoid into flexion so that it can 'get out of the way'. This, in combination with a volar translation of the capitate on the lunate, results in lunate flexion. It can be seen from these descriptions that the proximal carpal row is the mobile and obedient row. Changes in bony architecture or ligamentous competence will result in abnormal patterns of motion - or 'instability' - of the carpus. Excessive extension of the lunate relative to the scaphoid (where the scapholunate angle is greater than 80 °) has been termed dorsal intercalated segment instability (DISI) since the lunate (the 'intercalated' segment) now faces more dorsal than is normal. Conversely, excessive flexion of the lunate (scapho-lunate angle lower than 30 °) has been termed volar intercalated segment instability (VISI).
CLASSIFICATION The existence of nnmerous classification systems3-6 is sufficient evidence that the perfect system does not
Fig. 5 Navarro's columnartheory of carpal stability.
exist. The theory of the columnar carpus proposed by Navarro in 1919 formed the basis for Taleisnik's first classification of carpal instability in 1985. 6 Navarro had suggested that the carpus was composed of three vertical columns: a central (flexion-extension) column; a lateral (mobile) column; and a medial (rotation) column (Fig. 5). Taleisnik described injury patterns based on the columnar carpus although he went on himself to later modify Navarro's theory by eliminating the pisiform and including the trapezium and trapezoid in the central column. This reinforced the role of the scaphoid as the midcarpal stabilizing link and the triquetrum as the pivotal centre of motion for carpal rotation.
TERMINOLOGY The terminology associated with many classification systems is complex but crucial to the understanding of each system. The current popular system of the Mayo Clinic 7 (Table 1) employs many acronyms, explained below.
Carpal instability dissociative (CID) CID refers to instability between (or through) carpal bones within the same row (either proximal or distal row). 'Dissociative' refers to the separation seen between adjacent elements within a carpal row.
Carpal instability non-dissociative (CIND) CIND occurs between separate carpal rows or transverse osseous 'segments'. It can occur after disruption of bony or ligamentous structures or a combination of both.
Axial instability Axial instability involves a longitudinal force of disruption resulting in dislocation or fracture-dislocation. If the pathway of the force is through a bone, it is referred to as trans-. If it is around a bone it is peri-. Axial instability can be seen on the radial
C a r p a l instability
Table1
271
Mayo classification system
Type, site and name Radiographic pattern I.
I1.
III.
IV
CID 1.1 Proximal carpal row CID a. Unstable scaphold fracture b. Scapho-lunate dissociation c. Luno-triquetral dissociation 1.2 Distal carpal row CID a. AR disruption b. AU disruption CIND 2.1 Radlocarpal CIND a. Palmar ligament rupture b. Dorsal ligament rupture c. Radial or scaphoid malunion, Madelung's 2.2 Midcarpal CIND a. Ulnar MCI from palmar disruption b. Radial MC! from dorsal disruption c. Combined UMCI/RMCI d. MCI from dorsal ligament injury 2.3 Combined radiocarpal-mldcarpaiCIND a. CLIP b. Radial & central ligament damage CIC a. Perilunate with radiocarpal instability b. Perilunate with axial instability c. Radiocarpal with axial instabihty d. Scapho-lunate dissociation with UT 'Adaptive carpus' Malposition of carpus with; a. Distal radial malunion b. Scaphoid malunion c. Lunate malunion d. Madelung's delbrmity
DISI DISI VISI RT, PT UT, PT
DISI, UT (of proximal row or with increased SL space) VISI, DT VISI VISI VISI DISI VISL DISI alternating UT +~ VIS[ or DISI DISI & UT AxUI & UT AxRI & UT DISI & UT
DISI or DT DISI DISI or VISI UT, DISI, PT
Abbreviations: AR, axial radial: AU, axial ulnar; AxRI, axial radial instabihty; AxUI, axial ulnar instability; CIC, carpal instability
complex: CID, carpal instability dissociative; CIND, carpal instability non-dissociative; CLIP, capito-lunate instability pattern; DISI. dorsal intercalated segment instability; DT, dorsal translation: MCI, midcarpal instability, PT, proximal translation; RMCI, radial mldcarpal instability; RT, radial translation; SL, scapho-lunate: UMCI, ulnar midcarpal instability: UT, ulnar translation; VISI, volar intercalated segment instability.
(axial r a d i a l ( A R ) ) or the u l n a r ( a x i a l - u l n a r (AU)) side o f the carpus.
Midcarpal instability (MCI)/radio-carpal instability (RCI) M C I occurs as a result o f d i s r u p t i o n at the m i d c a r p a l level, in c o n t r a s t to RCI, which occurs at the r a d i o c a r p a l level.
Carpal instability adaptive (CIA) S o m e a u t h o r i t i e s d o n o t r e g a r d changes in c a r p a l a l i g n m e n t in response to wrist b o n e architecture as being true c a r p a l instability. This ' s e c o n d a r y ' change in p o s i t i o n o f the c a r p u s (e.g. in response to m a l u n i o n o f the s c a p h o i d o r distal radius) is therefore t e r m e d ' a d a p t i v e ' o r p s e u d o - c a r p a l instability (PsCI).
DIAGNOSIS
Carpal instability complex (CIC) Several p a t t e r n s o f instability exist which are a c o m b i n a t i o n o f C I D a n d C I N D lesions. These are referred to as c a r p a l instability c o m p l e x (CIC). It is helpful to describe the C I D a n d C I N D c o m p o n e n t s o f each C I C injury, since this will guide treatment.
Capito-lunate instability pattern (CLIP) This occurs when the distal o f the two involved rows o r segments is d i s p l a c e d m o r e d o r s a l l y t h a n n o r m a l (i.e. the distal c a r p a l row is d i s p l a c e d m o r e d o r s a l l y relative to the p r o x i m a l row, o r the p r o x i m a l row relative to the radius).
History T h e p a t i e n t m a y o r m a y n o t recall a specific injury to the wrist. T h o s e w h o can recall a n injury will often present for m e d i c a l a t t e n t i o n after a delay since they perceive their injury as a wrist ' s p r a i n ' which has failed to resolve. U n d e r these circumstances, a careful h i s t o r y o f exact m e c h a n i s m o f injury, swelling, loss o f f u n c t i o n a n d site o f p a i n will help diagnosis. S o m e patients w h o have been treated b y non-specialists m a y be referred after a p e r i o d (or several s e p a r a t e p e r i o d s ) o f splintage where their s y m p t o m s only r e t u r n e d on cast removal. M a n y o f the a c u t e signs in these cases will have resolved.
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It is helpful initially to describe wrist pain as central, radial, ulnar or global. Add to this either dorsal or palmar, and the likely injured structures can be focussed upon. it is also important to enquire about grip strength, as this will often be reduced. Complaints of clicking or snapping within the wrist should be noted and recorded whether or not they are painful. Examination
Areas of swelling or bruising should be noted in the acute injury. Careful and accurate palpation of each landmark is critical in reaching a diagnosis. Once this is recorded, each specific structure is examined more closely with a series of provocative tests. The SLL is examined by palpating for tenderness directly over the dorsum of the ligament. The scaphoid is then firmly grasped between the examiner's index finger and thumb of one hand, and the lunate grasped between the other index finger and thumb. Scapho-lunate ballottement is then performed where passive dorsal-palmar mobility is assessed. Increased mobility is rarely felt, but the patient may experience discomfort. Watson's test involves the examiner sitting facing the patient, both placing their flexed elbows on the table as if about to arm-wrestle. The test hinges on whether or not the examiner's thumb can prevent normal scaphoid flexion on radial deviation of the wrist. The examiner places his thumb firmly on the patient's scaphoid tubercle. The index finger rests gently on the dorsum of the SLL to appreciate any 'clunks'. Normally, the scaphoid flexes as the wrist moves into radial deviation. This will be felt by the examiner's thumb. The intrinsic ligaments are responsible for initiation of scaphoid flexion, but it is completed by pressure from surrounding bones as radial deviation increases. If the SLL is incompetent, pressure from the examiner's thumb on the scaphoid tubercle will prevent initiation of scaphoid flexion and the scaphoid will remain extended as the wrist moves into radial deviation. If the SLL is competent (and stronger than the examiner's thumb) then the scaphoid tubercle will push the examiner's thumb away as it flexes. An incompetent SLL cannot do this and the scaphoid must wait for the configuration of the surrounding bones to change as radial deviation progresses, before it will be forced into flexion. This sudden movement may be experienced as a 'clunk' by patient, examiner or both but more often the patient will complain of pain and withdraw his hand before the (inevitable) 'clunk ~ appears. This 'apprehension test' occurs as the proximal pole of the scaphoid rides dorsally in the scaphoid fossa of the distal radius. Although this is an elegant and logical clinical test, up to 20% of normal subjects will exhibit a positive test. The LTL can also be examined by palpation for tenderness and ballottement by holding the lunate and triquetrum in two index/thumb grasps. The ulnar
of these two grasps places the index finger on the pisiform and the thumb on the dorsum of the triquetrum. Prior to this, a piso-triquetral grind test is performed to ensure that the test is not 'positive' because of pisotriquetral degeneration. Luno-triquetral ballottement (Reagan test) is positive if it elicits pain. The LTL can also be assessed using Kleinman's shear test. Sitting opposite the patient, the examiner places his contralateral thumb over the dorsum of the lunate, and his index finger over the pisiform. An attempt is then made to 'squeeze' the thumb and index together to see if this causes pain. Kleinman claims that this is a more sensitive clinical test than the Reagan test. Radiological examination s
Radiology of the painful wrist is covered in detail elsewhere in this symposium. Standard PA and lateral radiographs including clenched fist and radial and ulnar deviation views are regarded by many as the standard views. Radiological 'clues' of carpal instability include the ring sign of a flexed scaphoid, scapholunate diastasis, disrupted Gilula's arcs, abnormal scapho-lunate angle and excessive dorsal or palmar inclination of the lunate on a lateral view. Carpal collapse can also be measured by either the standard or modified carpal height ratio. The use of CT, arthrography, MRI and dynamic video-fluoroscopy may be appropriate under certain conditions. It is important to recall the results of a study performing bilateral wrist arthrography for patients with unilateral symptoms. 9 'Pathological' lesions were frequently found in asymptomatic wrists. Arthroscopy of the wrist
Arthroscopy will allow direct visualization of both surfaces of radio-carpal and midcarpal joints 1° (i.e. it can see the proximal row from both sides). It is normally performed under slight distraction so that the carpal bones will not be subjected to the (compressive) physiological loads which may provoke the abnormal movements. There is therefore some dispute as to whether or not you can actually 'see' carpal instability with an arthroscope. In the chronic situation, however, it allows inspection of joint surfaces, adjacent fibrillation and synovitis and is believed by some to have certain pathognomonic features in proximal row CID. Midcarpal inspection showing a step (Fig. 6) or edge fibrillation at either scapho-lunate or luno-triquetral junctions are felt to be the results of abnormaI motion at these joints. Furthermore, when the arthroscope can be passed from radio-carpal to midcarpal joints through the scapho-lunate gap, the SLL is clearly incompetent. What is not known° is the arthroscopic appearance of the other wrist, and it may be that some of these 'abnormalities' are present in the contralateral (asymptomatic) side, which questions their relevance.
Carpal instability 273
w
Fig. 6 MidcarpaIarthroscopyshowinga step betweenlunate and triquetrum. Arthroscopy in the acute situation is more valuable, since it will reveal blood-staining and torn edges of ligament as well as acute chondral injury. Arthroscopy of the wrist may offer another piece of evidence towards a diagnosis already suspected by history, examination and other investigations. It should rarely be used as the only decisive method of investigation.
TREATMENT The scope of this article is not to comprehensively cover the details of treatment of every type of carpal instability. The interested reader is directed to more detailed texts for further information.
Carpal instability dissociative (CID) The commonest causes of CID are found in the proximal row and consist of scaphoid non-union, scapholunate ligament injury and luno-triquetral ligament injury. Unstable scaphoid non-union results in separate movements of the proximal and distal poles. The distal pole flexes (as an intact scaphoid would), but the proximal pole extends by virtue of its attachment to the lunate (and therefore triquetrum). This results in the extended lunate/flexed scaphoid DISI deformity. Treatment is aimed at healing the non-union and correcting the 'wedge' deformity of the scaphoid by the insertion of an appropriately shaped graft on the palmar surface. Rotation of the scaphoid must also be corrected. It is now recognized that acute scapho-hmate ligament injury should be treated by early repair through a dorsal approach, supplemented by scapho-lunate and scapho-capitate Kirschner wires. However, not every injury presents early and the opportunity for definitive treatment may be missed. Untreated cases may adapt to their loss of function and pain by altering their
lifestyle and occupational demands, but fi'equently these patients present with end-stage degenerative change or SLAC wrist (scapho-lunate advanced collapse)J 1 This condition affects the radio-scaphoid joint first, then the scapho-capitate joint, before later carpal collapse ensues. When patients present before the onset of obvious degeneration, but too late for primary treatment, the options for treatment are controversial. Surgical procedures may be classified as either bony or soft tissue. Bony procedures in the form of limited wrist fusion such as scapho-trapezio-trapezoid fusion (STT) are vigorously recommended by proponents such as Kirk Watson and have shown good long-term results in some series. The procedure is technically demanding and failure to adhere to the strict surgical details can itself lead to complications. Soft tissue procedures have been employed for many years. Dorsal capsulodesis has fallen out of favour in some centres, and double FCR tenodesis is currently undergoing long-term evaluation. Treatment of symptomatic established SLAC wrist is less controversial. Most agree that excision of the scaphoid accompanied by four corner fusion (lunate, triquetrum, capitate and hamate) will preserve some motion in the wrist. Proximal row carpectomy produces similar results but demands normal articular surfaces on the capitate and lunate fossae. Symptoms can often be temporarily ameliorated by arthroscopic radial styloidectomy and wrist denervation, but patients must be made aware that this approach is only to 'buy time'. Injury of the luno-triquetral ligament is rarely recognized acutely. When it is, it should be treated by primary open repair. Chronic symptomatic luno-triquetral instability should be treated by luno-triquetral fusion, when patients should be warned that this may remove some of their range of wrist movement.
Carpal instability non-dissociative (CIND) Dissociation between separate carpal rows often implies injury to the extrinsic ligaments. They are easier to repair than the intrinsic ligaments and direct repair is recommended.
Carpal instability complex (CIC) injuries involving elements of both CID and CIND are most frequently represented by perilunate injury. This was classified by Mayfield and Johnson into four stages: ] II III IV
Scapho-lunate ligament injury; Capito-lunate ligament injury; Luno-triquetral ligament injury; Dislocation of the lunate.
The original radial force, which frequently occurs through the SL ligament, can also create a scaphoid fracture (trans-scaphoid perilunate dislocation) or a
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SUMMARY The concepts associated with a diagnosis of carpal instability remain confusing for many people. A basic and thorough knowledge of simple carpal biomechanics allows many of these instability patterns to be understood. It must always be remembered that the proximal carpal row is the adaptive and subservient row. It changes in response to forces placed upon it. Once an abnormal alignment has been detected clinically and radiologically, a search must be made for the precipitating factor and, therefore, underlying cause. REFERENCES
Fig. 7 Midcarpal arthroscopy showing a step between the lunate and triquetrum.
fracture of the radial styloid (trans-styloid perilunate dislocation). These injuries should be treated by fixation/repair of the radially damaged structure, lunate reduction and supplementary Kirschner wires if appropriate. Median nerve decompression may also be required.
Carpal instability adaptive (CIA) Most frequently, CIA is seen in the presence of malunion following distal radial fracture. Extension malunion of the radius results in a dorsally inclined articular surface. The lunate becomes flexed in order to place the capitate axis parallel to that of the radial shaft. Corrective osteotomy allows normal force transmission to occur and the adaptive carpal instability to resolve (Fig. 7).
1. Taleisnik J. The ligaments of the wrist. J Hand Surg 1976:1:110 118. 2, Berger RA, Landsmeer JM. The palmar radlocarpal ligaments" a study of adult and fetal human wrist joints. J Hand Surg 1990;15A:847 854 3 Lmscheid RL, Dobyns JH, Beabout et al. Traumatic instability of the wrist, diagnosis, classification and pathomechanics. J Bone Joint Surg 1972;54A: l 61 ~1632. 4. Mayfield JK, Johnson RP, Kilcoyne RK. Carpal dislocations: pathomechanics and progressive perilunar instability. J Hand Surg 1980:5:226 241. 5. Linscheid RL, Dobyns JH, Beckenbaugh RD et al. Instability patterns of the wrist. J Hand Surg 1983;8A:682 686. 6. Taleisnik J. Current concepts review: carpal instability. J Bone Joint Surg. 1988;70A:1262-1268. 7. Dobyns JH, Cooney WR Classification of carpal instability. The wrist: diagnosis and operative treatment. Cooney WR Linscheid RL and Dobyns JH (eds). Mosby, Philadelphia:CV, 1998: 490. 8 Gilula LA, Destouet JM, Weeks PM et al. Roentgenographic diagnosis of the painful wrist. Clin Orthop 1984:187:52-64. 9. Herbert TJ, Faithfull RG, McCann DJ et al. Bilateral arthrography of the wrist. J Hand Surg 1990;15A:233-235. 10. Weiss AP, Akelman E, Lambiase R. Comparison of the findings of triple injection cmearthrography of the wrist with those of arthroscopy. J Bone Joint Surg. 1996;78A'348 356. 11. Watson HK, Ballet FL. The SLAC wrist: scapholunate advanced collapse pattern of degenerative arthritis. J Hand Surg 1984;9A:358-365.
Mini-symposium: The painful wrist
(ii) Carpal instability
D.A. Campbell
INTRODUCTION
relative positions constantly in response to movements of the adjacent bones and the constraints of their attached ligaments. As a unit, therefore, the proximal carpal row is a mobile adaptive structure whose overall configuration changes as a result of forces applied fi'om the more rigid structures either side of it. • The proximal carpal row therefore acts as a 'link' mechanism between forearm and hand. This row (the middle segment of a three-segment system) has no muscles attached to it and is inherently unstable in compression without its ligamentous attachments. 1.2
The mechanics of the wrist joint are difficult to describe without first understanding the anatomy and relationships of the structures involved. The wrist is a complex joint, which allows motion in three planes by a combination of movements at several areas simultaneously. These movements are interdependent and disruption of any part of this motion cycle has effects on the whole carpus. Carpal instability is therefore nothing more than carpal dysfunction, Before attempting to comprehend carpal instability, it is, however, necessary to describe and gain some understanding of carpal stability.
Stability of any synovial joint, or series of joints, relies on both bony and soft tissue components. Freely mobile joints (such as the gleno-humeral joint) have little contribution to stability from skeletal geometry and achieve their stability from strong soft tissue constraints. Conversely, synovial joints with a limited range of motion (such as the ankle joint) rely heavily on skeletal factors for stability. Disruption of these results in joint subluxation and abnormal movements (instability).
THE CARPUS
Whilst many of the finer points of carpal kinetics and kinematics remain the source of controversy, some fundamental biomechanical issues are widely agreed (Fig. 1): • The surface of the distal radius, the triangular fibrocartilage complex (TFCC) and the distal ulna form a stable base for radio-carpal motion. • The distal carpal row, comprising trapezium, trapezoid, capitate and hamate are bound together by strong interosseous ligaments and move together as a single unit. • The set of bones between these two relatively rigid structures - the proximal carpal row - (comprising scaphoid, lunate and triquetrum) change their
D.A. Campbell FRCS(orth), Consultant Hand Surgeon, Department of Orthopaedic Surgery, St James's University Hospital, Beckett Street, Leeds LS9 7TF, UK Tel: +44 (0)113 2065578; Fax" +44 (0) 113 2065156
Fig. 1 The anatomy of the carpus
268
Carpal instability The proximal carpal row is a highly mobile set of bones which depends on the integrity of the surrounding soft tissue constraints in order to maintain stability. These consist of short, strong interosseous ligaments, longer extrinsic intracapsular ligaments and extraarticular stabilizing factors. It is perhaps easier to understand the function of these structures if they are considered as preventing certain movements, rather than allowingthem.
Intrinsic ligaments These have their origin and insertion within the same carpal row. The ligaments controlling the proximal carpal row from within are the scapho-lunate ligament (SLL) and the luno-triquetral ligament (LTL). These prevent excessive separation of the bones in the proximal row during movement, and transmit forces along the row to ensure adaptive motion.
Extrinsic ligaments These are found on both dorsal and volar sides of the carpus. The volar ligaments are stronger and arranged in two distinct 'V' shaped ligament complexes (Fig. 2A). The proximal ligament is centred on the lunate with limbs attached to the ulna and radius, so stabilizing the lunate. The distal ligament centres on the capitare and extends to the triquetrum and the radius (via the scaphoid). This structure 'controls' the triquetrum and scaphoid. The dorsal extrinsic ligaments are also arranged in a 'V' shape (Fig. 2B) centred on the triquetrum and containing a radio-luno-triquetral
(RLT) segment and a trapezium, trapezoid and scaphoid segment.
Extraarticular structures Other structures, mainly centred on the ulnar side of the wrist, also contribute to stability but are insufficient on their own to prevent the changes of instability. The flexor and extensor retinaculae together with the ulnar wrist flexor and extensor combine to provide a degree of ulnar stability when tightened.
CARPAL M O V E M E N T S
Wrist flexion and extension The tightly bound bones of the distal carpal row move together as one unit and migrate proximally when the wrist is loaded axially. This causes a compressive load on the proximal row resulting in adaptive rotation of these bones. The scaphoid will rotate into flexion because of the attachments of the distal palmar extrinsic ligaments. This force is transmitted by the SLL to the lunate, which then also flexes. The capitate tends to slide in a palmar direction in the capitolunate articulation (by virtue of the scapho-capitate ligament, which will be taut) so causing further lunate flexion (Fig. 3). The triquetrum, however, is now under two opposing forces. The LTL will transmit torque from the flexed lunate to try and flex the triquetrum (Fig. 4) (force x). However, the arrangement of the joints made with the triquetrum by both capitate and hamate tends to force the triquetrum into extension (force y). This is the weaker of these two
A
5
Fig. 3 Capitate extensioncauses lunate flexion
B
Y
X Fig. 2 (A) The volar extrinsicligaments; (B) The dorsal extrinsic ligaments.
269
Fig. 4 Opposingflexion(x) and extension (y) forcesfight to control the triquetrum.
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opposing forces, and axial load therefore tends to rotate the proximal carpal row into flexion. Should any of these 'links' fail, however, the triquetrum will move into extension. This process of midcarpal movement involves flexion of the proximal row as an adaptation to extension of the distal row and depends upon intrinsic and extrinsic ligamentous integrity. The loss of integrity of the scapho-lunate or luno-triquetral ligaments results in an imbalance between the flexion and extension forces around the triquetrum. The location of the ligament disruption determines whether the lunate will follow the scaphoid (into flexion) or the triquetrum (into extension). Scapho-lunate ligament insufficiency therefore results in excessive scaphoid flexion, whilst the lunate and triquetrum are unopposed in their attempts to extend. Conversely, luno-triquetral ligament insufficiency allows the lunate to join the scaphoid in flexion whilst the triquetrum can extend unopposed. The position of the lunate can therefore be used as a guide to presumed integrity (or otherwise) of the intrinsic proximal row ligaments.
Radial and ulnar deviation of the wrist When the wrist moves into ulnar deviation, the head of the capitate translates dorsally causing the lunate (and, therefore, scaphoid) to extend. Further ulnar deviation results in contact between the hamate and triquetrum, which produces triquetral extension as it slides up the hamate. The intact LTL transmits this to the lunate resulting in further lunate extension. The increased distance between the trapezium/ trapezoid complex and the distal radius allows the scaphoid to 'stretch out' (i.e. extend) into the space, under the influence of torque transmitted by the SLL. Conversely, radial deviation narrows the space between the trapezium/trapezoid and distal radius. This forces the scaphoid into flexion so that it can 'get out of the way'. This, in combination with a volar translation of the capitate on the lunate, results in lunate flexion. It can be seen from these descriptions that the proximal carpal row is the mobile and obedient row. Changes in bony architecture or ligamentous competence will result in abnormal patterns of motion - or 'instability' - of the carpus. Excessive extension of the lunate relative to the scaphoid (where the scapholunate angle is greater than 80 °) has been termed dorsal intercalated segment instability (DISI) since the lunate (the 'intercalated' segment) now faces more dorsal than is normal. Conversely, excessive flexion of the lunate (scapho-lunate angle lower than 30 °) has been termed volar intercalated segment instability (VISI).
CLASSIFICATION The existence of nnmerous classification systems3-6 is sufficient evidence that the perfect system does not
Fig. 5 Navarro's columnartheory of carpal stability.
exist. The theory of the columnar carpus proposed by Navarro in 1919 formed the basis for Taleisnik's first classification of carpal instability in 1985. 6 Navarro had suggested that the carpus was composed of three vertical columns: a central (flexion-extension) column; a lateral (mobile) column; and a medial (rotation) column (Fig. 5). Taleisnik described injury patterns based on the columnar carpus although he went on himself to later modify Navarro's theory by eliminating the pisiform and including the trapezium and trapezoid in the central column. This reinforced the role of the scaphoid as the midcarpal stabilizing link and the triquetrum as the pivotal centre of motion for carpal rotation.
TERMINOLOGY The terminology associated with many classification systems is complex but crucial to the understanding of each system. The current popular system of the Mayo Clinic 7 (Table 1) employs many acronyms, explained below.
Carpal instability dissociative (CID) CID refers to instability between (or through) carpal bones within the same row (either proximal or distal row). 'Dissociative' refers to the separation seen between adjacent elements within a carpal row.
Carpal instability non-dissociative (CIND) CIND occurs between separate carpal rows or transverse osseous 'segments'. It can occur after disruption of bony or ligamentous structures or a combination of both.
Axial instability Axial instability involves a longitudinal force of disruption resulting in dislocation or fracture-dislocation. If the pathway of the force is through a bone, it is referred to as trans-. If it is around a bone it is peri-. Axial instability can be seen on the radial
C a r p a l instability
Table1
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Mayo classification system
Type, site and name Radiographic pattern I.
I1.
III.
IV
CID 1.1 Proximal carpal row CID a. Unstable scaphold fracture b. Scapho-lunate dissociation c. Luno-triquetral dissociation 1.2 Distal carpal row CID a. AR disruption b. AU disruption CIND 2.1 Radlocarpal CIND a. Palmar ligament rupture b. Dorsal ligament rupture c. Radial or scaphoid malunion, Madelung's 2.2 Midcarpal CIND a. Ulnar MCI from palmar disruption b. Radial MC! from dorsal disruption c. Combined UMCI/RMCI d. MCI from dorsal ligament injury 2.3 Combined radiocarpal-mldcarpaiCIND a. CLIP b. Radial & central ligament damage CIC a. Perilunate with radiocarpal instability b. Perilunate with axial instability c. Radiocarpal with axial instabihty d. Scapho-lunate dissociation with UT 'Adaptive carpus' Malposition of carpus with; a. Distal radial malunion b. Scaphoid malunion c. Lunate malunion d. Madelung's delbrmity
DISI DISI VISI RT, PT UT, PT
DISI, UT (of proximal row or with increased SL space) VISI, DT VISI VISI VISI DISI VISL DISI alternating UT +~ VIS[ or DISI DISI & UT AxUI & UT AxRI & UT DISI & UT
DISI or DT DISI DISI or VISI UT, DISI, PT
Abbreviations: AR, axial radial: AU, axial ulnar; AxRI, axial radial instabihty; AxUI, axial ulnar instability; CIC, carpal instability
complex: CID, carpal instability dissociative; CIND, carpal instability non-dissociative; CLIP, capito-lunate instability pattern; DISI. dorsal intercalated segment instability; DT, dorsal translation: MCI, midcarpal instability, PT, proximal translation; RMCI, radial mldcarpal instability; RT, radial translation; SL, scapho-lunate: UMCI, ulnar midcarpal instability: UT, ulnar translation; VISI, volar intercalated segment instability.
(axial r a d i a l ( A R ) ) or the u l n a r ( a x i a l - u l n a r (AU)) side o f the carpus.
Midcarpal instability (MCI)/radio-carpal instability (RCI) M C I occurs as a result o f d i s r u p t i o n at the m i d c a r p a l level, in c o n t r a s t to RCI, which occurs at the r a d i o c a r p a l level.
Carpal instability adaptive (CIA) S o m e a u t h o r i t i e s d o n o t r e g a r d changes in c a r p a l a l i g n m e n t in response to wrist b o n e architecture as being true c a r p a l instability. This ' s e c o n d a r y ' change in p o s i t i o n o f the c a r p u s (e.g. in response to m a l u n i o n o f the s c a p h o i d o r distal radius) is therefore t e r m e d ' a d a p t i v e ' o r p s e u d o - c a r p a l instability (PsCI).
DIAGNOSIS
Carpal instability complex (CIC) Several p a t t e r n s o f instability exist which are a c o m b i n a t i o n o f C I D a n d C I N D lesions. These are referred to as c a r p a l instability c o m p l e x (CIC). It is helpful to describe the C I D a n d C I N D c o m p o n e n t s o f each C I C injury, since this will guide treatment.
Capito-lunate instability pattern (CLIP) This occurs when the distal o f the two involved rows o r segments is d i s p l a c e d m o r e d o r s a l l y t h a n n o r m a l (i.e. the distal c a r p a l row is d i s p l a c e d m o r e d o r s a l l y relative to the p r o x i m a l row, o r the p r o x i m a l row relative to the radius).
History T h e p a t i e n t m a y o r m a y n o t recall a specific injury to the wrist. T h o s e w h o can recall a n injury will often present for m e d i c a l a t t e n t i o n after a delay since they perceive their injury as a wrist ' s p r a i n ' which has failed to resolve. U n d e r these circumstances, a careful h i s t o r y o f exact m e c h a n i s m o f injury, swelling, loss o f f u n c t i o n a n d site o f p a i n will help diagnosis. S o m e patients w h o have been treated b y non-specialists m a y be referred after a p e r i o d (or several s e p a r a t e p e r i o d s ) o f splintage where their s y m p t o m s only r e t u r n e d on cast removal. M a n y o f the a c u t e signs in these cases will have resolved.
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It is helpful initially to describe wrist pain as central, radial, ulnar or global. Add to this either dorsal or palmar, and the likely injured structures can be focussed upon. it is also important to enquire about grip strength, as this will often be reduced. Complaints of clicking or snapping within the wrist should be noted and recorded whether or not they are painful. Examination
Areas of swelling or bruising should be noted in the acute injury. Careful and accurate palpation of each landmark is critical in reaching a diagnosis. Once this is recorded, each specific structure is examined more closely with a series of provocative tests. The SLL is examined by palpating for tenderness directly over the dorsum of the ligament. The scaphoid is then firmly grasped between the examiner's index finger and thumb of one hand, and the lunate grasped between the other index finger and thumb. Scapho-lunate ballottement is then performed where passive dorsal-palmar mobility is assessed. Increased mobility is rarely felt, but the patient may experience discomfort. Watson's test involves the examiner sitting facing the patient, both placing their flexed elbows on the table as if about to arm-wrestle. The test hinges on whether or not the examiner's thumb can prevent normal scaphoid flexion on radial deviation of the wrist. The examiner places his thumb firmly on the patient's scaphoid tubercle. The index finger rests gently on the dorsum of the SLL to appreciate any 'clunks'. Normally, the scaphoid flexes as the wrist moves into radial deviation. This will be felt by the examiner's thumb. The intrinsic ligaments are responsible for initiation of scaphoid flexion, but it is completed by pressure from surrounding bones as radial deviation increases. If the SLL is incompetent, pressure from the examiner's thumb on the scaphoid tubercle will prevent initiation of scaphoid flexion and the scaphoid will remain extended as the wrist moves into radial deviation. If the SLL is competent (and stronger than the examiner's thumb) then the scaphoid tubercle will push the examiner's thumb away as it flexes. An incompetent SLL cannot do this and the scaphoid must wait for the configuration of the surrounding bones to change as radial deviation progresses, before it will be forced into flexion. This sudden movement may be experienced as a 'clunk' by patient, examiner or both but more often the patient will complain of pain and withdraw his hand before the (inevitable) 'clunk ~ appears. This 'apprehension test' occurs as the proximal pole of the scaphoid rides dorsally in the scaphoid fossa of the distal radius. Although this is an elegant and logical clinical test, up to 20% of normal subjects will exhibit a positive test. The LTL can also be examined by palpation for tenderness and ballottement by holding the lunate and triquetrum in two index/thumb grasps. The ulnar
of these two grasps places the index finger on the pisiform and the thumb on the dorsum of the triquetrum. Prior to this, a piso-triquetral grind test is performed to ensure that the test is not 'positive' because of pisotriquetral degeneration. Luno-triquetral ballottement (Reagan test) is positive if it elicits pain. The LTL can also be assessed using Kleinman's shear test. Sitting opposite the patient, the examiner places his contralateral thumb over the dorsum of the lunate, and his index finger over the pisiform. An attempt is then made to 'squeeze' the thumb and index together to see if this causes pain. Kleinman claims that this is a more sensitive clinical test than the Reagan test. Radiological examination s
Radiology of the painful wrist is covered in detail elsewhere in this symposium. Standard PA and lateral radiographs including clenched fist and radial and ulnar deviation views are regarded by many as the standard views. Radiological 'clues' of carpal instability include the ring sign of a flexed scaphoid, scapholunate diastasis, disrupted Gilula's arcs, abnormal scapho-lunate angle and excessive dorsal or palmar inclination of the lunate on a lateral view. Carpal collapse can also be measured by either the standard or modified carpal height ratio. The use of CT, arthrography, MRI and dynamic video-fluoroscopy may be appropriate under certain conditions. It is important to recall the results of a study performing bilateral wrist arthrography for patients with unilateral symptoms. 9 'Pathological' lesions were frequently found in asymptomatic wrists. Arthroscopy of the wrist
Arthroscopy will allow direct visualization of both surfaces of radio-carpal and midcarpal joints 1° (i.e. it can see the proximal row from both sides). It is normally performed under slight distraction so that the carpal bones will not be subjected to the (compressive) physiological loads which may provoke the abnormal movements. There is therefore some dispute as to whether or not you can actually 'see' carpal instability with an arthroscope. In the chronic situation, however, it allows inspection of joint surfaces, adjacent fibrillation and synovitis and is believed by some to have certain pathognomonic features in proximal row CID. Midcarpal inspection showing a step (Fig. 6) or edge fibrillation at either scapho-lunate or luno-triquetral junctions are felt to be the results of abnormaI motion at these joints. Furthermore, when the arthroscope can be passed from radio-carpal to midcarpal joints through the scapho-lunate gap, the SLL is clearly incompetent. What is not known° is the arthroscopic appearance of the other wrist, and it may be that some of these 'abnormalities' are present in the contralateral (asymptomatic) side, which questions their relevance.
Carpal instability 273
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Fig. 6 MidcarpaIarthroscopyshowinga step betweenlunate and triquetrum. Arthroscopy in the acute situation is more valuable, since it will reveal blood-staining and torn edges of ligament as well as acute chondral injury. Arthroscopy of the wrist may offer another piece of evidence towards a diagnosis already suspected by history, examination and other investigations. It should rarely be used as the only decisive method of investigation.
TREATMENT The scope of this article is not to comprehensively cover the details of treatment of every type of carpal instability. The interested reader is directed to more detailed texts for further information.
Carpal instability dissociative (CID) The commonest causes of CID are found in the proximal row and consist of scaphoid non-union, scapholunate ligament injury and luno-triquetral ligament injury. Unstable scaphoid non-union results in separate movements of the proximal and distal poles. The distal pole flexes (as an intact scaphoid would), but the proximal pole extends by virtue of its attachment to the lunate (and therefore triquetrum). This results in the extended lunate/flexed scaphoid DISI deformity. Treatment is aimed at healing the non-union and correcting the 'wedge' deformity of the scaphoid by the insertion of an appropriately shaped graft on the palmar surface. Rotation of the scaphoid must also be corrected. It is now recognized that acute scapho-hmate ligament injury should be treated by early repair through a dorsal approach, supplemented by scapho-lunate and scapho-capitate Kirschner wires. However, not every injury presents early and the opportunity for definitive treatment may be missed. Untreated cases may adapt to their loss of function and pain by altering their
lifestyle and occupational demands, but fi'equently these patients present with end-stage degenerative change or SLAC wrist (scapho-lunate advanced collapse)J 1 This condition affects the radio-scaphoid joint first, then the scapho-capitate joint, before later carpal collapse ensues. When patients present before the onset of obvious degeneration, but too late for primary treatment, the options for treatment are controversial. Surgical procedures may be classified as either bony or soft tissue. Bony procedures in the form of limited wrist fusion such as scapho-trapezio-trapezoid fusion (STT) are vigorously recommended by proponents such as Kirk Watson and have shown good long-term results in some series. The procedure is technically demanding and failure to adhere to the strict surgical details can itself lead to complications. Soft tissue procedures have been employed for many years. Dorsal capsulodesis has fallen out of favour in some centres, and double FCR tenodesis is currently undergoing long-term evaluation. Treatment of symptomatic established SLAC wrist is less controversial. Most agree that excision of the scaphoid accompanied by four corner fusion (lunate, triquetrum, capitate and hamate) will preserve some motion in the wrist. Proximal row carpectomy produces similar results but demands normal articular surfaces on the capitate and lunate fossae. Symptoms can often be temporarily ameliorated by arthroscopic radial styloidectomy and wrist denervation, but patients must be made aware that this approach is only to 'buy time'. Injury of the luno-triquetral ligament is rarely recognized acutely. When it is, it should be treated by primary open repair. Chronic symptomatic luno-triquetral instability should be treated by luno-triquetral fusion, when patients should be warned that this may remove some of their range of wrist movement.
Carpal instability non-dissociative (CIND) Dissociation between separate carpal rows often implies injury to the extrinsic ligaments. They are easier to repair than the intrinsic ligaments and direct repair is recommended.
Carpal instability complex (CIC) injuries involving elements of both CID and CIND are most frequently represented by perilunate injury. This was classified by Mayfield and Johnson into four stages: ] II III IV
Scapho-lunate ligament injury; Capito-lunate ligament injury; Luno-triquetral ligament injury; Dislocation of the lunate.
The original radial force, which frequently occurs through the SL ligament, can also create a scaphoid fracture (trans-scaphoid perilunate dislocation) or a
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SUMMARY The concepts associated with a diagnosis of carpal instability remain confusing for many people. A basic and thorough knowledge of simple carpal biomechanics allows many of these instability patterns to be understood. It must always be remembered that the proximal carpal row is the adaptive and subservient row. It changes in response to forces placed upon it. Once an abnormal alignment has been detected clinically and radiologically, a search must be made for the precipitating factor and, therefore, underlying cause. REFERENCES
Fig. 7 Midcarpal arthroscopy showing a step between the lunate and triquetrum.
fracture of the radial styloid (trans-styloid perilunate dislocation). These injuries should be treated by fixation/repair of the radially damaged structure, lunate reduction and supplementary Kirschner wires if appropriate. Median nerve decompression may also be required.
Carpal instability adaptive (CIA) Most frequently, CIA is seen in the presence of malunion following distal radial fracture. Extension malunion of the radius results in a dorsally inclined articular surface. The lunate becomes flexed in order to place the capitate axis parallel to that of the radial shaft. Corrective osteotomy allows normal force transmission to occur and the adaptive carpal instability to resolve (Fig. 7).
1. Taleisnik J. The ligaments of the wrist. J Hand Surg 1976:1:110 118. 2, Berger RA, Landsmeer JM. The palmar radlocarpal ligaments" a study of adult and fetal human wrist joints. J Hand Surg 1990;15A:847 854 3 Lmscheid RL, Dobyns JH, Beabout et al. Traumatic instability of the wrist, diagnosis, classification and pathomechanics. J Bone Joint Surg 1972;54A: l 61 ~1632. 4. Mayfield JK, Johnson RP, Kilcoyne RK. Carpal dislocations: pathomechanics and progressive perilunar instability. J Hand Surg 1980:5:226 241. 5. Linscheid RL, Dobyns JH, Beckenbaugh RD et al. Instability patterns of the wrist. J Hand Surg 1983;8A:682 686. 6. Taleisnik J. Current concepts review: carpal instability. J Bone Joint Surg. 1988;70A:1262-1268. 7. Dobyns JH, Cooney WR Classification of carpal instability. The wrist: diagnosis and operative treatment. Cooney WR Linscheid RL and Dobyns JH (eds). Mosby, Philadelphia:CV, 1998: 490. 8 Gilula LA, Destouet JM, Weeks PM et al. Roentgenographic diagnosis of the painful wrist. Clin Orthop 1984:187:52-64. 9. Herbert TJ, Faithfull RG, McCann DJ et al. Bilateral arthrography of the wrist. J Hand Surg 1990;15A:233-235. 10. Weiss AP, Akelman E, Lambiase R. Comparison of the findings of triple injection cmearthrography of the wrist with those of arthroscopy. J Bone Joint Surg. 1996;78A'348 356. 11. Watson HK, Ballet FL. The SLAC wrist: scapholunate advanced collapse pattern of degenerative arthritis. J Hand Surg 1984;9A:358-365.