Abstract
In this chapter on scapholunate ligament injury, we first describe wrist anatomy and biomechanics so that the reader can then have an understanding of the pathomechanics of scapholunate dissociation and its classification. We then take the reader through the diagnosis of scapholunate ligament injury including clinical assessment, imaging and other useful investigations. We then explain our algorithmic approach to aid decision-making but emphasise the need to tailor treatment to the individual as these cases are complex and often difficult to manage.
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Scapholunate ligament injury is the most common cause of carpal instability.
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A fall on the outstretched hand with the wrist extended and ulnarly inclined and associated with midcarpal supination can lead to a wide spectrum of injuries.
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Scapholunate dissociation is part of a recognised four-stage process called “progressive perilunar destabilisation”.
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Permanent carpal misalignment only occurs if there is also rupture of the secondary scaphoid stabilisers.
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Diagnosis is difficult, and scapholunate ligament injury is often missed at presentation.
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Common findings are pain aggravated by heavy use, weak grip strength, reduced mobility, dorsoradial swelling and point tenderness over the dorsal aspect of the SL interval.
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There are several key features to look for in plain radiographic examination.
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Patients should be carefully selected and treatment tailored to the individual based on an algorithmic approach to management.
Introduction
The wrist is a complex composite joint playing a fundamental role in the function of the upper limb, enabling optimal positioning of the hand to perform a multitude of complex tasks efficiently. An unstable, stiff or painful wrist compromises function with impaired activities of daily living as well as occupational tasks and sporting pursuits. Wrist injuries correctly diagnosed and treated tend to heal with low complication rates, but if not, outcomes are unpredictable, and there may be carpal collapse and articular cartilage degeneration. In this chapter, we discuss the aetiology, diagnosis and management of the most common cause of carpal instability, scapholunate ligament injury.
Wrist Anatomy and Biomechanics
To correctly diagnose scapholunate ligament injuries, one needs a thorough understanding of anatomy and biomechanics and what is normal and abnormal in a symptomatic wrist. The 20 interdependent articulations of the wrist connect 15 bones: the radius, ulna, 8 carpal bones and 5 metacarpal bases. The carpus has two rows: distal , consisting of four tightly bound bones (trapezium, trapezoid, capitate and hamate) with little mobility between and proximal, with three bones (scaphoid, lunate and triquetrum) with significant mobility between. The scapholunate (SL) and lunotriquetral (LTq) joints interconnect these three bones. This proximal row is an intercalated segment between the radius and distal row . The pisiform is not a carpal bone but a sesamoid increasing the leverage of flexor carpi ulnaris (FCU) .
The radiocarpal joint connects the carpal condyle (proximal scaphoid, lunate and triquetrum) with the antebrachial glenoid [distal radius and triangular fibrocartilage complex (TFCC)]. The scaphoid’s proximal joint surface is more curved than that of the lunate. The radius has two articular facets (the scaphoid and lunate fossae), separated by a cartilaginous sagittal ridge (the interfacet prominence).
The midcarpal joint has three columns of articulation: radial, or the scapho-trapezio-trapezoid (STT) joint ; ulnar, or the triquetrohamate (TqH) joint ; and, central, or the scaphocapitate (SC) and lunocapitate (LC) joints . There are two types of lunate: type 1, with one distal facet articulating with the capitate, and type 2, with two distal facets, one articulating with the capitate and one with the proximal pole of the hamate [1]. In the sagittal plane, the central column bones are collinear in 30% of people, but the lunate is slightly flexed in 30% and slightly extended in 40% [2]. The scaphoid , which is obliquely orientated in approximately 45° flexion in relation to the radius (range 30–60°), supports the thumb metacarpal which is anterior to the plane of the capitate [3].
A complex arrangement of ligaments interconnects these bones, some of which are important mechanically (tightly packed collagen fibres) and others sensorially (rich in Ruffini, Pacini or Golgi corpuscles) supplying the sensorimotor system with proprioceptive feedback for wrist stability [4]. All of these ligaments are intracapsular (Fig. 11.1) except for three extracapsular ligaments : the transverse carpal ligament and the two ligaments connecting the pisiform to the hook of the hamate and base of the fifth metacarpal.
The intracapsular ligaments are either extrinsic (connecting the forearm with the carpus) or intrinsic (originate and insert within the carpus) [5]. The extrinsic ligaments are more elastic with a lower yield strength sustaining mid-substance ruptures, whereas the intrinsic ligaments are more frequently avulsed. Arthroscopy best assesses the intracapsular ligaments, and most extrinsic ligaments can be seen under a thin synovial sheath [6]. The extrinsic ligaments consist of four palmar radiocarpal ligaments [radioscaphoid (RS), radio-scapho-capitate (RSC), long radiolunate and short radiolunate ligaments (long RL and short RL)], three palmar ulnocarpal ligaments (ulnocapitate, ulnotriquetral and ulnolunate) and one dorsal ligament binding the radius to the carpus (dorsal radiotriquetral ligament or dorsal radiocarpal ligament) [4]. There are no dorsal ligaments between the ulna and carpus. There are no collateral ligaments between the radial and ulnar styloid processes and the medial and lateral corners of the carpal condyle. These are substituted for by the dynamic actions of extensor carpi ulnaris (ECU) and abductor pollicis longus (APL) [7]. The radioscapholunate ligament of Testut-Kuentz is not a true ligament but loose connective tissue containing vessels supplying the proximal pole of the scaphoid [4].
The intrinsic ligaments are either transverse intercarpal, interconnecting bones of the same row, or midcarpal, linking bones across the midcarpal joint [4]. The SL joint is stabilised by two distinct transverse intercarpal ligaments (palmar and dorsal) and the proximal fibrocartilaginous membrane uniting both of them (Fig. 11.2).
The latter follows the arc of the proximal edges of the two bones from dorsal to palmar, separating the radiocarpal and midcarpal joint spaces. This membrane is often perforated in older individuals. The dorsal SL ligament is located in the depth of the dorsal capsule and connects the dorsal-distal corners of the scaphoid and lunate bones. It is formed by a thick collection of fibres, slightly obliquely oriented, with a key role in scaphoid stability. Its anterior counterpart, the palmar SL ligament, has longer, more obliquely oriented fibres, allowing substantial flexion and extension of the scaphoid relative to the lunate. The dorsal SL ligament has the greatest yield strength [260 newtons (N) on average], followed by the palmar SL ligament (118 N) and the proximal membrane (63 N) [4]. The LTq joint also has two transverse intercarpal ligaments (palmar and dorsal) and a fibrocartilaginous membrane closing the joint proximally. In contrast, the palmar LTq ligament is thicker and stronger than the dorsal [8]. The LTq ligaments are under greater tension through all ranges of motion than the SL ligaments. The most distal fibres of palmar and dorsal LTq ligaments are often connected to the distal fibres of the SL ligaments, forming the palmar and dorsal scaphotriquetral ligaments [9]. These structures contribute to the stability of the LC joint by increasing the depth of the midcarpal fossa [10].
The distal row bones are strongly bound by short, thick transverse intercarpal ligaments (dorsal, palmar and intra-articular) ensuring transverse carpal arch rigidity and protecting the carpal tunnel [11]. The midcarpal joint is crossed by three palmar ligaments [triquetrohamate (TqH), triquetrocapitate (TqC) and scaphocapitate (SC)], one dorsolateral STT ligament and one dorsal intercarpal ligament [5]. The TqH and TqC ligaments are substantial and important in midcarpal joint stabilisation [10]. Laterally, the scaphoid tuberosity is linked to the distal row by the anteromedial SC ligament and dorsolateral STT ligament, which behave as collateral ligaments for the STT joint [12]. The dorsal intercarpal ligament is the only ligament crossing the dorsum of the midcarpal joint, and there are no ligaments, palmar or dorsal, between the lunate and capitate [13].
Kinematics: How the Wrist Moves
The wrist moves actively by muscle contraction acting upon tendons crossing the joint, but none of these tendons insert onto the proximal row, and so the distal row is the first to move [14]. When the midcarpal ligaments become taut, the proximal row is pulled into motion. Thus, around neutral, the midcarpal joint is the only one to move [15] with centre of wrist rotation within the capitate head [14]. The proximal and distal rows move synchronously, with different amounts of rotation among the proximal row bones themselves [15].
The most common plane of wrist motion is the “dart-thrower’s motion ”, mediated by the wrist extensors ECRL and ECRB and main flexor FCU, going from extension and radial inclination to flexion and ulnar inclination [12] (Fig. 11.3).
The frontal (radial-ulnar inclination) and sagittal (flexion-extension) planes of motion are seldom used in activities of daily living. When in radial inclination , the scaphoid and lunate are flexed. If the wrist is then brought into extension, the lunate recovers its initial alignment, as when the wrist was in neutral. When the wrist goes into ulnar inclination, the scaphoid and lunate extend, but they regain that neutral position if the wrist is also flexed [16]. In other words, when the wrist moves along the oblique plane of the dart-thrower’s motion , the scaphoid and lunate remain in a neutral position. All wrist mobility takes place at the midcarpal joint [16]. The reversed dart-thrower’s motion (extension-ulnar inclination to flexion-radial inclination) is in contrast, mediated by FCR palmarly and ECU dorsally, and only the radiocarpal joint is mobilised with minimal contribution from the midcarpal joint.
In the sagittal plane of motion , or flexion-extension, the scaphoid rotates more than the lunate, due to differential radii of curvature. It is easier for the scaphoid to flex than to extend because it is obliquely oriented relative to the longitudinal axis of the forearm. In contrast, the lunate tends to extend as it is narrower dorsally than palmarly. Therefore, in the central column, most wrist motion in flexion-extension takes place in the midcarpal joint (55%), whereas in the radial column most takes place at the radioscaphoid joint (70%).
In the frontal plane of motion , or radial-ulnar inclination, both proximal and distal rows go into radial and ulnar inclination, but the proximal row also flexes and extends. In radial inclination, the trapezium and trapezoid approximate to the radius, and, therefore, the scaphoid has to flex because the space is reduced. The lunate and triquetrum also flex but to a lesser degree. In ulnar inclination the scaphoid extends, pulled by the trapezium and trapezoid, and the lunate and triquetrum also extend , again to a lesser degree.
The wrist is thus a universal (cardan) type of articulation with two axes of rotation : one through the capitate head for midcarpal dart-throwing and the other through the lunate for radiocarpal reversed dart-throwing (Fig. 11.4). These axes are separated by an intercalated segment, the proximal row, which transmits pronosupination torques from distal to proximal or vice versa, in all wrist positions, without losing stability.
Most axial rotation of the hand takes place in the forearm; however, some pronation and supination also take place in the wrist, mainly at the midcarpal joint. Passive intracarpal pronation and supination are greater than active rotation. Active pronosupination occurs due to the oblique path taken by most wrist motor tendons to their distal insertion, changing direction distal to the extensor retinaculum. In neutral, isolated isometric contraction of any of these muscles will generate a pronation or supination moment to the distal row [7].
Kinetics: How the Wrist Withstands Loads Without Yielding
At the distal row , loads are distributed among the midcarpal joints: 50% to the SC and LC joints, 30% to the STT joint and 20% to the TqH joint [1]. The SL interval is particularly overloaded, and as such most synovial cysts arise here with ganglions appearing on chronically strained ligaments. At the proximal row , the load is distributed: 50% to the RS joint (scaphoid fossa), 35% to the RL joint (lunate fossa) and 15% to the TFCC and into the ulna [1].
When axially loaded, the carpal bones displace following specific patterns dependent upon the shape of the articular surfaces, load direction and point of application and soft-tissue integrity. A kinetically stable wrist does not sublux under physiological loads throughout the entire range of motion. To achieve this, the articular surfaces must be normally oriented and congruous, all ligaments must be present and functional, and the muscles must generate forces on the carpal bones in a balanced way [17].
Carpal Stabilisation
The proximal carpal row bones are inherently unstable, and without the capsule, ligaments and muscles would collapse in different directions when compressed by the distal row against the radius. The obliquely oriented scaphoid would rotate into flexion and pronation and the wedge-shaped (thinner dorsally than palmarly) lunate and triquetrum into extension and supination [2]. If the SL ligaments were strong enough, the flexion tendency of the scaphoid would be counteracted by the opposite tendency of the loaded lunate and triquetrum to rotate into extension, and stability would be achieved. In fact they are not particularly strong [4], and the tensile forces generated in normal hand function are far too high for these ligaments to be the only wrist stabilisers. To achieve stability, the ligaments need muscle protection, and a timely protective muscle response is achieved via mechanoreceptors within the ligaments themselves providing proprioceptive information for the sensorimotor system. Thus the ligaments are the first line of defence ensuring the muscles are able to ultimately stabilise the wrist [18].
Instability was previously assumed to be a ligament insufficiency problem exacerbated by muscle contraction. In fact, the muscles ultimately stabilise the carpus [18]. ECRL and APL supinate the distal row, and the trapezium displaces dorsally, tightening the STT ligament. A taut STT ligament prevents the scaphoid collapsing into flexion and pronation. ECU pronates the distal row, tightening the TqH ligament and preventing the proximal row collapsing into flexion [19]. Hence in treatment, the supinators are useful in scaphoid instabilities and are “SL-friendly”, while the pronators are useful in most ulnar-sided instabilities and are “SL-unfriendly” [18].
Pathomechanics of Scapholunate Dissociation (SLD)
A fall on the outstretched hand with the wrist extended and ulnarly inclined and associated with midcarpal supination can lead to a wide spectrum of injuries, from minor SL sprains to complete perilunar dislocations (Fig. 11.5).
These are stages of a recognised four-stage process called “progressive perilunar destabilisation ” (Fig. 11.6) [21]. In stage I, the scaphoid extends and supinates, dragged by the trapezium. The lunate stays behind, constrained by the long and short RL ligaments. An increasing SL torque is created leading to progressive tearing of the SL membrane and ligaments, usually from palmar to dorsal. If this process occurs with the wrist radially inclined, the proximal pole of the scaphoid is strongly constrained by the RSC ligament, and instead of SLD, a scaphoid fracture is likely. Rarely, there may be a coronal fracture of the lunate [22]. Stage II is perilunate dislocation—the capitate leaves the lunate concavity, leading to a dorsal perilunate dislocation . Stage III is LTq disruption or triquetrum fracture and stage IV lunate dislocation. A reverse perilunate destabilisation pattern can occur, with the carpal derangement starting at the ulnar side and proceeding radially around the lunate, usually due to a backwards fall on an outstretched hand with the upper limb externally rotated. Stage I is then complete LTq ligament rupture, stage II is ulnocarpal ligament rupture plus lunocapitate dislocation, and stage III is SLD [23].
Cadaveric division of the palmar SL ligament and proximal membrane leads to only minor kinematic changes, and the SL joint does not show a detectable gap, even under stress (predynamic instability). When painful, this is due to joint synovitis and needs medical treatment [24]. Complete SL ligament division results in significant kinematic changes and force transmission parameters, but not carpal misalignment. Permanent misalignment only occurs if there is also rupture of the secondary scaphoid stabilisers, i.e. the palmar RSC, palmar SC and anterolateral STT ligament [25]. These ruptures may be acute, as a result of a hyperextension injury, or chronic, secondary to progressive stretching. The proximal row adopts a typical deformity: the loaded lunate and triquetrum go into extension, while the scaphoid moves away from the lunate with flexion around the RSC ligament, pronation and ulnar inclination [26]. The distal row is forced to pronate due to collapse of the scaphoid into flexion and triquetrum into extension. The proximal pole of the scaphoid is subluxed dorsoradially, and there are increased compressive and shear stresses on the dorsolateral aspect of the radioscaphoid fossa , which may explain the degenerative changes often seen here. The lunate extends but remains stable with the radius because both opposing articular surfaces have the same radius of curvature. This explains why the RL joint seldom shows degeneration. Watson et al. proposed scapholunate advanced collapse (SLAC) , defining three stages of progressive degenerative changes secondary to SLD [27]. Lluch later modified this into five: stage I, radial styloid and proximal scaphoid; stage II, scaphocapitate; stage III, lunocapitate; stage IV, triquetrohamate; and stage V, radiolunate.
Wrist Instability and Classification of SLD
SLD is the most frequent cause of carpal instability. In general, ligament-related instabilities may be subclassified into carpal instability dissociative (CID) , carpal instability non-dissociative (CIND) and carpal instability complex (CIC) . A dissociative instability involves rupture or elongation of the ligaments binding bones of the same row [26]. SLD is an example of a proximal row CID. CIND is when there is functional disconnection between the radius and the proximal row (radiocarpal CIND) and/or between the proximal and distal rows (midcarpal CIND) [28]. When an unstable wrist presents with features of both CID and CIND , this is termed CIC (Fig. 11.7).
Analysis of Wrist Instability
Larsen et al. [20] proposed a scheme analysing multiple parameters to aid decision-making (Fig. 11.8).
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Chronicity: The healing potential of a disrupted ligament is proportional to the time since injury due to retraction or devascularisation of ligament remnants. After 6 weeks, primary ligament healing is unlikely. The only exception is when the ligament has avulsed from the bone.
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Severity: Instability due to a partial ligament tear with no radiographic evidence of a gap under stress is termed predynamic. Instability due to a complete rupture with the dissociation observed only under certain loading conditions is called dynamic. A static instability is when there is permanent carpal misalignment [27].
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Aetiology: Most instabilities are secondary to trauma, and the ligaments may unite if repaired. However, when instability is due to disease, normal healing is unlikely. As well as trauma, SLD may occur following dorsal ganglion excision and capsular over resection. Rheumatoid, metabolic or septic arthritis may attenuate the ligament.
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Location: Identification of the site or sites of major dysfunction usually requires dynamic examination using fluoroscopy.
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Direction: The direction of carpal misalignment, if present, gives clues as to which structures are ruptured. Patterns include:
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DISI (dorsal intercalated segment instability): The lunate, understood as an intercalated link between the radius and capitate, is abnormally extended relative to the radius and capitate.
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VISI (volar intercalated segment instability): The lunate is abnormally flexed.
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Ulnar translocation: The proximal row, or a portion of it, is displaced ulnarly beyond normal boundaries .
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Radial translocation: When the proximal row can be passively displaced radially beyond normal, usually in the setting of a radially malunited distal radial fracture.
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Dorsal translocation: A dorsally tilted radial fracture forces the carpal condyle into an abnormal dorsal translocation.
In SLD, the scaphoid tends to sublux into flexion and pronation, while the lunate may remain still in its normally aligned posture or translocate ulnarly and palmarly.
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Pattern: The three patterns of instability (CID, CIND and CIC) each have their own peculiarities determining both prognosis and treatment.
Classification of Scapholunate Instability
There are three additional parameters that may influence SLD management:
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Extent of SL ligament disruption: Geissler et al. [29] used arthroscopy to grade SL ligament injury based on the amount of passive joint displaceability:
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Grade 1: minimal attenuation of the proximal membrane, sometimes with haemorrhagic points within the ligament substance, as seen from the radiocarpal joint. No step-off in the SL joint can be seen from the midcarpal space.
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Grade 2: substantial attenuation of the proximal membrane with a narrow SL gap, less than the width of a 2 mm probe, visible through the midcarpal portal.
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Grade 3: ligament disruption sufficient to allow the arthroscopic probe to enter the SL joint space, both from the radiocarpal and midcarpal joint spaces.
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Grade 4: complete ligament rupture, and the widened joint space may be easily entered by a 2.7 mm arthroscope.
A recent modification , which we recommend, has further divided grade 3 injuries into [30]:
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3a: affecting mostly the palmar ligament
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3b: affecting only the dorsal ligament
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3c: affecting both
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Amount of SL space widening (as seen from the midcarpal joint) [31]: A 1-mm-diameter probe is used as a reference, and there is correlation with the amount of ligament injury:
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Grade 1: It is not possible to enter the joint with the probe—the SL ligament is only slightly distended.
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Grade 2: <1 mm SL gap and SL step-off <2 mm; the SL ligaments are probably intact, and only the proximal membrane is partially ruptured.
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Grade 3: 1–2 mm SL gap and SL step-off <2 mm; the SL membrane plus one of the two SL ligaments are completely ruptured.
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Grade 4: >2 mm gap and SL step-off >2 mm; all SL ligaments are completely ruptured.
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Mode of dorsal SL ligament rupture [32]:
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Type 1: lateral avulsion from the scaphoid (40% of all dorsal SL ligament injuries)
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Type 2: medial avulsion fracture from the lunate (20%)
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Type 3: mid-substance rupture (20%)
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Type 4: partial rupture plus elongation (20%, particularly among chronic dissociations)
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Diagnosis
SLD is often missed, and the clinician needs a high index of suspicion when there is a history of a fall on the outstretched hand. In isolated partial lesions (such as in predynamic instabilities ), the radiographs are usually normal. Also, associated injuries may mask SLD and make diagnosis especially difficult [33]. It may be associated with other injuries such as distal radial fractures (almost a third are thought to be associated with some form of carpal ligament disruption) or displaced scaphoid fractures [34]. SLD is more readily diagnosed when static or resulting from a perilunate dislocation. Diagnosis in children is difficult given the immature skeleton and problems performing a thorough clinical examination. Thankfully, SLD is rare in this age group.
More commonly, SLD is diagnosed in the subacute or chronic phase, when the derangement is evident on plain radiographs. This occurs because progressive instability has led to the deterioration of the secondary stabilisers, particularly the STT ligament, and is now a complex multilevel ligament injury.
History and Examination
The history should include the mechanism of injury and the characteristics of any pain including location, duration and aggravating and relieving factors. Take note of any previous treatment. Chronic problems should be explored further taking particular note of sport- and occupation -related repetitive stress.
On examination , swelling may be moderate even acutely. SL joint palpation with the wrist flexed and pressure over the capsule distal to Lister’s tubercle may elicit sharp pain signifying a high probability of recent injury or chronic localised synovitis. Other areas to palpate include the anatomical snuffbox and the palmar scaphoid tuberosity. Acutely, pain usually limits range of motion, but this may be normal in chronic cases.
Common findings are pain aggravated by heavy use, weak grip strength, reduced mobility, dorsoradial swelling and point tenderness over the dorsal aspect of the SL interval [33]. They may complain of a clunking sensation during wrist motion due to dislocation or reduction of a dorsally subluxed proximal scaphoid. However, there is great variation in symptoms influenced by the time since injury , extent of ligament rupture and associated injuries.
There are three provocative tests of use here. A positive scaphoid shift test, i.e. when painful subluxation is elicited, is said to be diagnostic of SLD (Fig. 11.9) [35].
Four fingers are placed behind the radius with the thumb on the scaphoid tuberosity. The wrist is moved passively from ulnar to radial inclination with the other hand. In ulnar inclination, the scaphoid is extended and assumes a position more in line with the forearm. In radial inclination, the scaphoid is flexed. Pressure on the tuberosity while the wrist is moved from ulnar to radial inclination prevents the scaphoid from flexing. If the SL ligaments are completely ruptured or attenuated, the proximal pole subluxes dorsally, inducing dorsoradial pain. When pressure is released, a typical clunking may occur, indicating self-reduction of the scaphoid over the dorsal rim of the radius. However, this test is of low specificity. The SL ligaments may be intact, but other local problems such as synovitis (due to occult ganglion or dorsal RS impingement) may also provoke sharp pain, and it is difficult to discern whether there is an abnormally subluxable proximal scaphoid. Alternatively, patients with generalised laxity may exhibit painless “clunks” during this test, most likely arising from the midcarpal joint. Comparing both sides is important though sometimes the opposite “asymptomatic” side has a painful test as well [36]. Therefore, experience is necessary before this test can be interpreted with confidence.
In the resisted finger extension test , the patient is asked to extend the index and middle fingers fully against resistance with the wrist partially flexed [35]. In the presence of an injury or insufficiency of the dorsal SL ligament, sharp pain is elicited in the SL area, probably due to synovitis at the RS joint. This test is very sensitive but not specific for SL injury. Finally, the SL ballottement test involves stabilising the lunate with the thumb and index of one hand, while displacing the scaphoid dorsally and palmarly with the other, the thumb on the palmar tuberosity and index on the dorsal proximal pole. This is positive when there are pain, crepitus and excessive scaphoid mobility.
Imaging
Plain Radiographs
In a suspected carpal injury, four initial views of the wrist should be taken [37]. Initially a postero-anterior (PA) (palm down) view is recommended. In a normal wrist, the proximal and distal outlines of the proximal row, as well as the proximal outline of the distal row (“Gilula’s lines”), are smooth, without breaks in their continuity, and any step-off indicates an abnormality [37]. Normally articulating bones have parallel opposing surfaces separated by 2 mm or less. Any overlap between well-profiled carpal bones strongly suggests an intercarpal abnormality. Joint diastases are a sign of joint disruption if they are not present on the uninjured side. The normal lunate has a trapezoidal configuration, and a flexed or an extended lunate can be differentiated based on the shape of the lunate contour. When abnormally extended, the lunate is triangular in shape due to the distal displacement of the anterior horn. When the lunate is flexed, it has a half-moon configuration with its concavity facing towards the scaphoid [2]. The remaining initial views are a lateral view, scaphoid projection (a PA view centred on the scaphoid with the wrist in ulnar inclination and the fingers fully flexed) and a semipronated (45°) projection profiling the anterolateral and posteromedial corners of the carpus that is useful when investigating the presence of fractures of the dorsal ridge of the triquetrum and of the scaphoid tuberosity.
Additional views are recommended if the initial series is unhelpful: AP (palm up) view with a clenched fist or a longitudinal compression force applied to the wrist by an assistant that may accentuate the gap in SLD (it is best in neutral); PA (palm down) view with 10°of tube angulation from the ulna towards the radius which is ideal to assess the SL interval with measurement of the SL gap at the mid-portion of the joint where its anatomy is more consistent in comparison with the opposite side and surrounding articulations; oblique view at 20° of pronation from the lateral position; oblique view at 30° of supination from the lateral position; lateral view with the wrist radially inclined; carpal tunnel view; and static “motion” views in suspected instability that include PA and AP views in radial and ulnar inclination and lateral views in extension and flexion.
Determining carpal misalignment involves measuring specific distances and angles on PA or lateral radiographs [38]. However, the normal ranges for these parameters are quite diverse, and reproducibility is low with small errors in rotational positioning of the hand at the time of X-ray exposure resulting in substantial variations. The most relevant here is the SL angle, formed by a line tangential to the proximal and distal convexities of the scaphoid’s palmar aspect and that of the lunate and quoted as one of the major determinants of SLD. Normal values range from 30° to 60° (average 47°) [38]. Although angles greater than 80° indicate SL ligament disruption, smaller readings do not rule out this pathology, and values less than 30° are not unusual in patients with STT joint osteoarthritis. Other measurements used in misalignment include the LC angle (helpful in quantifying midcarpal misalignment), RL angle, ulnar variance, carpal height ratio and ulnar translocation ratio.
Distraction views : In patients with acute fracture dislocations, the four routine views described earlier may be difficult to interpret because of overlapping of the displaced carpal bones. In such cases, anteroposterior and lateral radiographs with the hand suspended in finger traps are recommended. Distraction views may reveal intra-articular fracture fragments or joint dissociations in the form of step-off that cannot be seen on routine films.
Stress views: In some instances, obtaining X-rays while stressing the joints in different directions may help visualise the abnormality [37]. A commonly used technique consists of taking PA projections of the wrist while forcing it into maximal radial or ulnar inclination. Lateral views while applying a dorsal or palmar force to the distal carpal row (“drawer test”) are also helpful to identify midcarpal instabilities. Lateral X-rays while extending a fully flexed wrist against resistance (“resisted extension test”) may reveal dynamic dorsal subluxation of the proximal scaphoid. In this case, if the SL ligaments are disrupted, the lunate will remain in a neutral or extended posture, substantially increasing the previously measured SL angle.
SLD is suspected in the presence of one or more of the following features. Dynamic instabilities require special projections or loading conditions for these features to be observed:
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Increased SL Joint Space: A positive “Terry Thomas sign” [39] is when the SL gap appears abnormally wide compared with the contralateral (Fig. 11.10). This is measured in the middle of the flat ulnar facet of the scaphoid [37]. Greater than 5 mm is diagnostic. If there is no history of a specific traumatic episode, and yet there is an obvious SL diastasis , one must consider a constitutionally increased SL gap, usually bilateral, with or without hyperlax ligaments. Other less common causes include rheumatoid arthritis, gout and calcium pyrophosphate deposition disease [33]. Comparative radiographic examination is recommended to rule out an occult asymptomatic SL ligament injury.
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Scaphoid Ring Sign: When the scaphoid has collapsed into flexion, it has a foreshortened appearance in the anteroposterior view [40]. Postero-anterior views show the scaphoid tuberosity projected as a radiodense circle or ring over the distal two-thirds of the scaphoid. This “ring sign” does not always indicate SLD as both scaphoid and lunate can be abnormally flexed with the SL ligaments intact (Fig. 11.11).
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Increased SL Angle: If in the lateral view , the scaphoid lies more perpendicular to the long axis of the radius and the lunate appears normally aligned or abnormally extended, SLD should be suspected. In such circumstances, the SL angle is greater than the normal 45–60°. This angle will progressively increase as the lunate extends to accommodate the loss of height of the radial column, causing a dorsal subluxation of the capitate.
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Palmar “V” Sign : In normal lateral views, a wide “C”-shaped line can be drawn joining the palmar margins of the scaphoid and radius. When the scaphoid is abnormally flexed, a “V”-shape is seen as the palmar outline of the scaphoid intersects the palmar margin of the radial styloid at an acute angle [41].
Cineradiography
Dynamic cineradiography provides considerable information in patients with altered kinematics (“clunking” wrists) [16]. Active motion is observed from radial to ulnar inclination in PA and lateral views and flexion and extension in lateral views. Provocative stress manoeuvres may help identify the location of maximal dysfunction. Cineradiography has a sensitivity of 90%, specificity of 97% and diagnostic accuracy of 0.93 in detecting SLD [42].
MRI
To be able to adequately assess the wrist ligaments, including the scapholunate ligament, high-resolution techniques with a dedicated wrist coil and slices of no more than 1 mm are required [24]. Arthro-MRI , where intravenous contrast medium is injected, is increasingly being used [43]. MRI remains attractive due to its superior soft-tissue contrast, direct multiplanar acquisition and lack of ionising radiation.
Ultrasound
Ultrasound is gaining ground as a useful adjunct in wrist assessment [44]. It is relatively inexpensive, radiation-free and without the need for contrast and can be performed in a clinic setting. Real-time dynamic evaluation of kinematic instabilities is possible. Colour Doppler provides additional information such as the presence of synovitis and soft-tissue inflammation.
Arthrography
Scans made after injecting dye sequentially into the midcarpal and radiocarpal joints may be useful delineating partial SL ligament tears and discovering other local problems such as osteochondral defects or capsular ligament ruptures [16]. Care must be taken not to confuse degenerative SL membrane perforations with true ligament ruptures. Asymptomatic degenerative tears of the proximal SL or LTq membranes are not unusual, especially in older adults, and flow of dye from the radiocarpal to the midcarpal space or vice versa is not necessarily pathological. Be wary that the incidence of bilateral SLD is very high in patients treated for symptomatic SLD [36]. Arthroscan, where arthrography is combined with high-resolution CT, can be used to assess cartilage defects and ligament injuries.
Arthroscopy
Due to the limitations of arthrography, arthroscopy has become the gold standard in the diagnosis of intracarpal derangements and in assessing the degree of injury to the intercarpal ligaments [6]. It enables the examination and treatment of intra-articular abnormalities without an extensive arthrotomy. Articular surfaces, synovial tissue and intercarpal ligaments can be directly visualised.
Treatment
Treatment of SLD is difficult and sometimes unpredictable [41]. It is often missed at presentation, and even if diagnosed early, the ligament remnants are short and difficult to repair. Also, it is not unusual for successful repairs to deteriorate with time as they encounter considerable tension and torque. As discussed previously, diagnosis is more common in the subacute or chronic phase, and the presence of retracted or attenuated ligament remnants and possibly also degenerative arthritis makes a successful outcome even more unlikely [45]. Careful patient selection is essential, taking into consideration age, occupational and recreational demands and symptom severity [24].
We use the following algorithm to aid decision-making [26]. Treatment must always be individually tailored based on the following general and local factors. General factors include age, co-morbidities, functional demands in the workplace and/or recreational activities, workers’ compensation and psychological features.
Local factors are:
-
1.
Dorsal SL ligament integrity: Most dynamic instabilities are caused by rupture of the palmar and proximal components of the SL interosseous ligament (SLIL) . If the dorsal SL ligament remains intact, only minor changes in carpal kinematics are likely. There will however be wrist discomfort, if not pain and weakness. Partial injury like this is almost exclusively diagnosed arthroscopically.
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2.
Dorsal SL ligament healing potential: Mid-substance ruptures heal poorly; however, the majority are avulsed off the scaphoid or lunate and heal well if properly secured with bone anchors.
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3.
Secondary scaphoid stabiliser status: When insufficient or torn, the scaphoid shows the “ring” sign on PA views, and the radioscaphoid angle on lateral X-rays is greater than 60°.
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4.
Lunate uncovering index : In SLD, regardless of the amount of scaphoid subluxation, the lunate may remain normally aligned relative to the radius or may appear abnormally extended and translocated palmarly and ulnarly. For DISI to appear, the lunate needs to have detached or attenuated its connections with the dorsal intercarpal ligament. For ulnar translocation to occur, both the long and short RL ligaments are detached or attenuated. The “lunate uncovering index” [46] reflects this and is the percentage of radiolunate contact relative to the transverse dimension of the lunate. When SLD is associated with lunate translocation , there are features of CID and CIND, so it can be categorised as CIC.
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5.
Carpal misalignment reducibility: If the scaphoid and lunate can be mutually realigned with minimal force, they are reducible. If they cannot be reduced without bending two 1.2 mm K-wire joysticks, then they are considered irreducible. Fluoroscopy can be used to assess this.
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6.
Cartilage status: Arthro-MRIs or arthroscopy is able to assess cartilage status. Treatment needs to take account of cartilage defects or joint degeneration.
After investigating these six local factors , six questions can be answered enabling categorisation of each case into one of seven stages (Table 11.1). The number of negative answers increases from left to right, indicating progression from a minor problem (stage I) to a global dysfunction (stage VII). In theory, all SLD sharing similar features are treated in the same way; however, in practice it is wise to tailor treatment to the specific peculiarities of each individual case.
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Stage I. Partial SLIL injury . The wrist tends to show normal carpal alignment, angles and height ratio, and the SL gap may be only slightly widened. Any pain is caused by synovitis due to increased joint shear stress. Arthroscopy is the only effective diagnostic tool. If acute and symptomatic, 3 weeks of cast immobilisation may be enough. If too unstable for conservative treatment, percutaneous K-wire fixation may be appropriate. If chronic and symptomatic, open fixation plus some sort of capsulodesis may be a good option. Once the wrist is stabilised, a proprioception re-education programme of the extensor carpi radialis longus (ECRL) , abductor pollicis longus (APB) and flexor carpi radialis (FCR) muscles should be initiated [7].
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Stage II. Complete repairable SLIL injury with good healing potential and normal alignment. Acutely, we recommend open or arthroscopic ligament repair or reattachment of avulsions.
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Stage III. Complete non-repairable SLIL injury with normal wrist alignment. A bone-ligament-bone graft replacing the dorsal SL ligament is an option here.
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Stage IV. Complete non-repairable SLIL injury , reducible rotary subluxation of the scaphoid, normal lunate alignment and normal cartilage. The radioscaphoid angle is greater than 45°, and the carpal height ratio reduced. This is an ideal indication for a ligamentoplasty using local tendons (three-ligament tenodesis technique or similar, Fig. 11.12) [10]. Results of the three-ligament tenodesis in professional athletes have shown 80% return to competition within 4 months and two-thirds reach their pre-injury level [47].
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Stage V. Complete non-repairable SLIL injury , reducible rotary subluxation of the scaphoid, reducible ulnar translocation of the lunate (lunate uncovering index abnormal but reducible) and normal cartilage. The anti-pronation spiral tenodesis technique is an option here [48].
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Stage VI. Complete non-repairable SLIL injury , irreducible misalignment and normal cartilage. Chronic scaphoid and lunate subluxation becomes stiff due to capsular retraction and fibrosis. The capsule should be released and fibrosis excised prior to any soft-tissue procedures. Different partial arthrodeses have been proposed to stabilise the scaphoid and lunate properly aligned relative to the radius. Commonly recommended treatments are radioscapholunate fusion, with or without distal scaphoid excision, or complete scaphoidectomy plus midcarpal fusion.
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Stage VII. Complete non-repairable SLIL injury , irreducible misalignment and cartilage degeneration. Chronic scaphoid and lunate subluxation may evolve into SLAC. The aim here is to relieve pain with minimal loss of function. The most common operations are proximal row carpectomy or four-corner fusion (complete scaphoidectomy plus midcarpal arthrodesis).
Summary
In summary, the diagnosis and management of scapholunate ligament injury requires a thorough understanding of wrist anatomy, biomechanics and assessment so that an analysis of the individual features of each case can be made. We present a staging system to aid decision-making in the further management of these difficult cases.
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Questions and Answers
Questions and Answers
Questions
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1.
Which is the correct answer? Place the following structures in order of decreasing yield strength:
-
(a)
Proximal SL ligament, proximal SL membrane, dorsal SL ligament
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(b)
Proximal SL membrane, proximal SL ligament, dorsal SL ligament
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(c)
Dorsal SL ligament, proximal SL membrane, proximal SL ligament
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(d)
Dorsal SL ligament , proximal SL ligament, proximal SL membrane
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(e)
Proximal SL ligament, dorsal SL ligament, proximal SL membrane
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(a)
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2.
Which is the most common plane of wrist motion?
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3.
What ultimately stabilises the wrist?
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4.
True or false? SLD is most likely to be diagnosed in the acute phase.
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5.
What is a positive scaphoid shift test?
Answers
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1.
(d)
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2.
The dart-thrower’s plane of wrist motion is the most commonly used in daily activities, going from extension and radial inclination to flexion and ulnar inclination.
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3.
The muscles are the ultimate stabilisers of the wrist with the ligaments the first line of defence providing proprioceptive feedback .
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4.
False. More commonly, SLD is diagnosed in the subacute or chronic phase, when the derangement is evident on plain radiographs. This occurs because progressive instability has led to the deterioration of the secondary stabilisers, particularly the STT ligament, and is now a complex multilevel ligament injury.
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5.
A positive scaphoid shift test is when painful subluxation of the proximal pole of the scaphoid is elicited when the wrist is moved passively from ulnar to radial inclination with four fingers placed behind the radius and the thumb placed on the scaphoid tuberosity.
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Adamthwaite, J., Babazadeh, S., Garcia-Elias, M. (2019). Scapholunate Ligament Injury. In: Hayton, M., Ng, C., Funk, L., Watts, A., Walton, M. (eds) Sports Injuries of the Hand and Wrist. In Clinical Practice. Springer, Cham. https://doi.org/10.1007/978-3-030-02134-4_11
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