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Imaging Finger Joint Instability with Ultrasound Carlo Martinoli, MD1 Maribel Miguel Perez, MD2 Bianca Bignotti, MD1 Sonia Airaldi, MD1 Luigi Molfetta, MD3 Andrea Klauser, MD4 Xavier Demondion, MD5 Anne Cotten, MD5 Alberto Tagliafico, MD6

Italy 2 Unit of Human Anatomy and Embryology, Department of Pathology and Experimental Therapy, Faculty of Medicine (C Bellvitge), University of Barcelona, Barcelona, Spain 3 Department of Orthopaedic Surgery, DINOGMI, Università di Genova, Genova, Italy 4 Department of Diagnostic Radiology, Medical University Innsbruck, Innsbruck, Austria 5 Department of Skeletal Radiology, Roger Salengro Hospital, Lille, France 6 Department of Experimental Medicine, DIMES, Università di Genova, Genova, Italy

Address for correspondence Carlo Martinoli, MD, Department of Radiologia, DISSAL, Università di Genova, Largo Rosanna Benzi 8, I-16132 Genova, Italy (e-mail: [email protected]).

Semin Musculoskelet Radiol 2013;17:466–476.

Abstract Keywords

► finger instability ► metacarpophalangeal joint ► proximal interphalangeal joint ► radial collateral ligament ► ulnar collateral ligament ► palmar plate ► gamekeeper’s thumb ► Stener lesion ► finger sprains ► ligament injuries ► ultrasound

Closed injuries affecting the metacarpophalangeal and interphalangeal joints and their stabilizers in the thumb and fingers occur very commonly in athletes, possibly leading to finger joint instability and long-standing or permanent disability. This article reviews the spectrum of joint injuries of the thumb and fingers that are common in the athletic population with a main focus on the ultrasound features of collateral ligament tears, palmar plate injuries, and thumb sesamoid fractures. A thorough understanding of the complex anatomy, mechanism of injury, soft tissue abnormalities, and imaging findings is critical in the diagnostic work-up of closed finger joint trauma and may help improve outcomes.

Hand injuries are very common in athletes accounting for up to 9% of all sports injuries.1,2 In the hand, digits are particularly vulnerable, especially in the context of sporting activities that involve catching and contact (e.g., rugby, American football, baseball, soccer) or have a high risk for falling (e.g., skiing, biking, inline skating, gymnastics).2 Sports-related injuries that occur in the fingers and thumb usually result from accidents and are

Issue Theme Sport Injuries of the Elbow and Fingers; Guest Editor, Mario Padrón, MD

therefore difficult to prevent. Many are minor trauma and respond favorably to a conservative regimen based on rest, ice, and splinting. On the contrary, severe sprains or contusions may lead to residual deformities or loss of joint movement. They can be debilitating if not recognized early on and may even have a lasting effect on long-term function, keeping athletes of both recreational and competition levels sidelined for a considerable

Copyright © 2013 by Thieme Medical Publishers, Inc., 333 Seventh Avenue, New York, NY 10001, USA. Tel: +1(212) 584-4662.

DOI http://dx.doi.org/ 10.1055/s-0033-1360667. ISSN 1089-7860.

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1 Department of Radiology, DISSAL, Università di Genova, Genova,

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time. Although diagnosis is often made clinically, imaging can be very useful in equivocal cases to assess the severity of the injury and determine the appropriate treatment plan. In the recent literature, much attention has been given to MR imaging and MR imaging arthrography as reference methods for evaluating acute and chronic lesions of the stabilizing articular elements of the fingers and thumbs, particularly in the most commonly affected metacarpophalangeal joint (MCPJ) and proximate interphalangeal joint (PIPJ).1,3,4 However, ultrasound (US) can provide excellent depiction of articular surface abnormalities and juxta-articular soft tissue injuries, possibly leading to finger instability problems. This article reviews the spectrum of closed injuries of the thumb and fingers occurring at the MCPJ and PIPJ levels. The pertinent anatomy, biomechanics, clinical presentation, and imaging findings of abnormalities affecting collateral ligaments, palmar plate, thumb sesamoids, and other joint stabilizers are discussed, placing emphasis on the value of dynamic US.

Thumb The first MCPJ is a diarthrodial hinge joint allowing motion in the sagittal (extension/flexion) and coronal (adduction/abduction) planes.5 Different from other fingers, the extent of flexion is less in the thumb, and higher stability is required to resist radial and ulnar deviation during powerful pinching and grasping.6 The amount of joint laxity is  6% in full extension and increases to 14% when the joint is 15% flexed. The first MPCJ is stabilized by static and dynamic structures. Static stabilizers are mainly four: the volar plate, the dorsal capsule, and the ulnar and radial collateral ligaments. Dynamic stabilizers include some extrinsic tendons, that is, the extensor pollicis longus (EPL), extensor pollicis brevis (EPB), and flexor pollicis longus (FPL), and intrinsic aponeurotic expansions, that is, the abductor pollicis brevis (APB), flexor pollicis brevis (FPB), and adductor pollicis (ADP).7

MCPJ: Ulnar Collateral Ligament Injuries The ulnar collateral ligament (UCL) of the thumb may be considered the most important stabilizer of the first MCPJ.5 The UCL is a thick band (4–8 mm wide and 12–14 mm long) arising from the dorsal ulnar aspect (dorsal condyle) of the metacarpal head and inserting distally into the medial tubercle of the proximal phalanx (PPh).8 Similar to other collateral ligaments of the finger joints, it consists of proper (pCL) and accessory (aCL) bundles4 (►Fig. 1a). In MCPJ flexion, the pCL and the dorsal joint capsule are taut and help to resist radially directed forces and palmar subluxation of the PPh. In MCPJ extension, there is opposite tensioning of ligaments with the aCL and the palmar plate (PPl) becoming taut and concomitant laxity of the pCL. Among dynamic stabilizers, the ADP plays an important role. This muscle inserts into the extensor hood with a broad expansion that lies just superficial to the UCL and ulnar to the EPL (►Fig. 1b). On the radial side, the APB has a similar aponeurosis attaching to the extensor hood. On either side, the two aponeuroses of ADP and APB contribute to maintain the EPL aligned in the midline axis of the phalanx.9 Their situa-

Fig. 1 Anatomy of the ulnar collateral ligament (UCL) of the first metacarpophalangeal joint (MCPJ). Cadaveric specimens demonstrate (a) the location of the UCL complex that is composed of the proper collateral ligament (1) and accessory collateral ligament (2); (b) the adductor pollicis aponeurosis as a wide flattened band (dashed lines) bridging the medial aspect of the MCPJ and joining the extensor pollicis longus (EPL) tendon dorsally. Note the extensor pollicis brevis (EPB) running in a more radial position relative to the longus.

tion is different, however: The ADP lies palmar on the ulnar side of the joint, whereas the APB runs more dorsally. Based on the palmar-situated position of the ADP, a torn UCL may retract and displace proximal and dorsal to it10 (►Fig. 2a). First described in Scottish gamekeepers as a result of chronic repetitive valgus strains11 produced while strangling rabbits by stretching and hyperextending their neck between the thumb and the index finger, the UCL tear is most likely encountered today in skiers with some causative role played by the ski poles while impacting the ground, whether designed with or without a strap at the pole handle.12 UCL injury rates in skiers account for  2.3 to 4.4 cases/103 per skiing day and represent the second most prevalent skiing injury after medial collateral ligament tears in the knee.7,12 Other contact sports such as rugby and football are also implicated in this injury.13 Biomechanically, the UCL tear occurs when a sudden forced valgus (abduction) stress is applied to the thumb MCPJ.7 In the acute setting, patients typically complain of pain and swelling over the ulnar side of the MCPJ. When the injury is chronic, they usually experience weakness while holding a pen, grasping an object, and turning a key.14 Three types of UCL injuries can occur: (1) midsubstance UCL rupture including incomplete and nondisplaced complete tears, (2) avulsion fracture of the ulnar palmar base of the PPh (displaced or not), and (3) the so-called Stener lesion. In the Stener lesion, the UCL detaches from the footprint at the PPh base and retracts proximally displacing superficial to the ADP aponeurosis.15 Under these circumstances, there is surgical Seminars in Musculoskeletal Radiology

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Imaging Finger Joint Instability with Ultrasound

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Fig. 2 Thumb ulnar collateral ligament (UCL) tears. (a) Schematic drawing of the dorsal aspect of the first metacarpophalangeal joint (MCPJ). The aponeuroses of the abductor pollicis brevis (1) and adductor pollicis (2) are shown fusing dorsally to reinforce the extensor hood formed by extensor pollicis longus (EPL) and extensor pollicis brevis (EPB) fibers. An intact radial collateral ligament (RCL) and a torn and displaced UCL are also depicted. (b) Nondisplaced full-thickness tear of the UCL. Coronal 17–5 MHz ultrasound (US) image obtained over the ulnar aspect of the first middle interphalangeal joint shows a vertical cleft (arrow) in an abnormally swollen ligament indicating a complete UCL tear. The adductor pollicis (ADP) aponeurosis (arrowheads) overlies the torn ligament without dislocation of the UCL proximal stump. (c) Stener lesion. Coronal 17–5 MHz US image over the ulnar aspect of the first MCPJ reveals a swollen and retracted UCL presenting as a hypoechoic pseudomass (asterisk) located proximally and in a more superficial position (dashed line) relative to the ADP aponeurosis (arrowheads). Note the small distal stump (arrow) of the UCL. PPh, proximal phalanx.

indication for repair because spontaneous healing is unfeasible given the interposition of the ADP aponeurosis between the torn ligament and the PPh insertion site.15–17 Physical examination is helpful in the general assessment for UCL injuries but is inaccurate to determine its severity.17 Plain films can be used as the initial imaging modality to determine the presence of an avulsion fracture at the distal ligament insertion but cannot assess the ligament status.18 On radiographic stress views, 30-degree valgus instability at the MCPJ indicates collateral injury disruption.19 High-resolution US can image the UCL by sinking the probe into the first interosseous space while pushing the metacarpal head dorsally. With this technique, the probe is aligned in a coronal plane relative to the first metacarpal and the long axis of the UCL. Bone landmarks for correct transducer positioning include a shallow metacarpal groove between the lateral tubercle and the articular surface of the first metacarpal and a smaller concavity in the ulnar aspect of the PPh, adjacent to the phalangeal collateral tubercle.17,20,21 The UCL may look slightly hypoechoic, especially at the metacarpal footprint, due to anisotropy related to the oblique course of its fibers.8,17,22 In nondisplaced UCL sprains, the ligament becomes diffusely swollen and hypoechoic with loss of the fibrillar echotexture8,17 (►Fig. 2b). In these cases, static scans are often inconclusive to distinguish incomplete from complete UCL tears because the ligament ends may be close together in the absence of a definite gap. Dynamic imaging with valgus stress applied to the MCPJ may be helpful by causing fluid to extend into the ligament tear and spacing out the ligament Seminars in Musculoskeletal Radiology

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ends.17 This manoeuver should be performed carefully and under US control, involving minimal stress on the joint to avoid conversion of a nondisplaced to a displaced tear. In the Stener lesion, typical US findings include absence of UCL fibers spanning the MCPJ and detection of a soft tissue hypoechoic mass that represents the retracted proximal stump of the UCL located, at least in part, cranial to the apex of the metacarpal lateral tubercle.8,17 The distal stump is usually negligible. Using high-frequency probes, the diagnostic confidence in distinguishing nondisplaced from displaced UCL tears may be increased by depicting the position of the ADP aponeurosis (►Fig. 2b, c). This structure looks like a very thin hypoechoic band (< 0.2 mm thick) spanning the MCPJ space.8,17,23 If the UCL is torn and retracted but the ADP aponeurosis remains to cover it, the lesion is nondisplaced. In displaced tears, in contrast, the aponeurosis points directly to the bulk of the retracted proximal ligament and does not overlie it more (sonographic “yo-yo on a string” sign). The exact position of the normal ADP aponeurosis covering the UCL is difficult to define on static scans. On the contrary, its visibility can be improved during passive flexion and extension movements of the interphalangeal joint of the thumb. With this manoeuver, the examiner induces passive gliding of the EPL tendon and subsequent proximal/distal sliding of the ADP aponeurosis that is attached to the extensor hood (►Fig. 3a). The movement is minimal but greatly contributes to increase the ADP conspicuity and the examiner’s confidence in diagnosing a Stener lesion. In most cases, dynamic scans may demonstrate the aponeurosis clashing with the retracted ligament stump or infolding within its deep fibers (►Fig. 3b, c).

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Fig. 3 Dynamic ultrasound (US) assessment of a Stener lesion. (a) Schematic drawings of the dorsomedial aspect of the first metacarpophalangeal joint (MCPJ) during (top) extension and (bottom) flexion of the interphalangeal joint. During thumb flexion, the adductor pollicis (ADP) aponeurosis glides cranially impacting with its proximal edge on the retracted ulnar collateral ligament (UCL) stump. Part of the ligament is displaced superficial to the aponeurosis. (b, c) Coronal 17–5 MHz US images obtained over the ulnar aspect of the first MCPJ during (b) extension and (c) flexion of the interphalangeal joint demonstrate changes in the position of the ADP aponeurosis (arrows) relative to the retracted and hypoechoic UCL. The tip of the aponeurosis (arrowhead) is seen clashing with the ligament at a higher extent in flexion. PPh, proximal phalanx; M, metacarpal.

Overall, the performance of diagnostic US to differentiate nondisplaced from displaced tears has proved to be excellent with 100% sensitivity, specificity, positive predictive value, negative predictive value, and accuracy.13 MR imaging and MR arthrography of the MCPJ can be also used to confirm the injury and assess its severity, but there is general consensus that there is no significant difference between MR imaging and US to diagnose thumb UCL lesions.

MCPJ: Radial Collateral Ligament Injuries On the radial side of the MCPJ, the main stabilizer is the proper band of the radial collateral ligament (RCL), which arises dorsally from the lateral condyle of the metacarpal head and extends distally and palmarly to insert into the proximal third of the PPh, merging with the aCL.5 Other stabilizers around the radial aspect of the MCPJ include (1) the tendons of the two heads of the FPB, one (superficial)

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inserting into the palmar aspect of the PPh and the dorsal capsule, the other (deep) attaching to the palmar plate and the lateral sesamoid; (2) the APB tendon, which runs superficial to the FPB to insert into the PPh, and (3) the EPB tendon.9 The APB consists of a wide aponeurotic attachment that extends dorsally to join the ADP aponeurosis in the midline to form a dorsal sheath and stabilize the EPL. The EPB may exhibit variable insertion. In most cases, it attaches into the PPh, but it may send distal slips to the distal phalanx without attaching to the proximal or it may reach the dorsal capsule of the PIPJ without attaching to the PPh.24 RCL injuries cause loss of dorsal capsular support. Different from the ulnar side, the APB overlies the RCL completely, precluding any proximal displacement and dorsal migration of the ligament stump superficial to the aponeurosis. In other terms, the formation of a “radial-sided Stener lesion” is unfeasible. With lateral instability of the thumb, the palmar traction exerted from the ulnar side by the intact ADP aponeurosis becomes prevalent and causes volar and ulnar subluxation of the PPh relative to the axis of the metacarpal head, leading to subsequent joint incongruity and secondary degenerative arthritis.9 An excessive dorsoradial prominence of the metacarpal head (radial metacarpal condyle) can be often noted at physical examination. The RCL injury is often sports related (48.8%), especially in handball and soccer, but it may be also secondary to a fall (24%) or door entrapment (6.6%).25 From the clinical point of view, a RCL tear may present with pain, swelling, and stiffness of the MCPJ. It can lead to weakness in activities such as grasping an object, handwriting, or turning a key. Contrary to UCL tears (distal tears accounting for  90% of cases), a higher prevalence of proximal injuries is expected in the thumb RCL because the distal attachment of this ligament is equal to or wider than the proximal one. Based on location, proximal RCL tears account for  55% of cases, distal tears for 29%, and midsubstance tears for 16%.26 A EPB tendon tear may be associated, especially in cases of tendon insertion into the dorsal MCPJ capsule.27 In chronic tears, lateral plain films can demonstrate volar subluxation of the PPh relative to the metacarpal axis. MCPJ subluxation > 3 mm has been encountered in 68 to 86% of chronic RCL injuries.26,28 Stress radiography may help to assess whether instability is > 30%, thus indicating complete ligament rupture.9 In the case of bone avulsion, fragment displacement > 2 mm or rotation > 30 to 45 degrees may warrant surgery (►Fig. 4a). US may be contributory to depict the torn ligament, bone misalignment, and any bone avulsion at the injury site. In midsubstance tears, distinguishing partial from complete tears may not be straightforward. The ulnar stress test can be used to better visualize the ligament ends and assess the width MCPJ space between the injured and uninjured sides (►Fig. 4b, c). With this manoeuver, an increased gap and volar subluxation of the PPh is indicative of thumb RCL rupture.

MCPJ: Sesamoids The thumb MCPJ is the most frequent location of sesamoid bones in the hand with a prevalence of  100%. The dorsal Seminars in Musculoskeletal Radiology

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Imaging Finger Joint Instability with Ultrasound

Imaging Finger Joint Instability with Ultrasound

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Fig. 4 Thumb radial collateral ligament (RCL) tears (different cases). (a) Anteroposterior radiograph of the first metacarpophalangeal joint (MCPJ) shows marked ulnar deviation compatible with a complete tear of the RCL. A small bony fragment (arrowhead) is seen detached from the proximal origin of the RCL. (b, c) Coronal 17–5 MHz ultrasound (US) images obtained over the radial aspect of the first MCPJ (b) in neutral position and (c) during ulnar deviation. Significant MCPJ widening (distance between the vertical dashed bars) is demonstrated while in ulnar deviation. The RCL (open arrowheads) appears as a hypoechoic band bridging the joint space. With ulnar deviation, it assumes a wavy course with proximal discontinuity (white arrowheads). This can be considered a sign of a complete ligament tear. PPh, proximal phalanx.

aspects of the radial and ulnar thumb sesamoids are invested with hyaline cartilage to slide over the respective condyles of the metacarpal head.30 Relevant local structures include the PPl of the MCPJ with transverse fibers connecting the sesamoids with each other, the proximal and distal palmar ligaments, and the aCLs that insert on either side onto the lateral margins of the sesamoids. The proximal palmar ligaments connect sesamoids and the PPl to the head of the first metacarpal, whereas the distal palmar ligaments attach sesamoids to the PPh. In addition, the ulnar sesamoid is housed within the ADP tendon and the radial sesamoid within the FPB tendon. Overall, these structures act as stabilizers of the thumb MCPJ. Ulnar sesamoid fractures account for  60% of cases.31 Most are related to an avulsion mechanism during a fall on an outstretched hand with forced thumb hyperextension.32 Sesamoid injuries are classified in two types depending on whether the PPl is intact (type 1) or disrupted (type 2).32 In type 1, there is no associated PPl disruption. The ability to flex the MCPJ and the interphalangeal joint is preserved with normal flexion posture. In the type 2 injury, the PPl is disrupted and the patient cannot flex the MCPJ. Some MCPJ instability in hyperextension may occur.32 It is not uncommon that thumb sesamoid injuries go unnoticed on initial radiographic examination. US is then performed to assess local soft tissue problems and incidentally identifies either a cleft in the sesamoid splitting the bone into two parts or an avulsed bony fragment (►Fig. 5a). In these instances, the US diagnosis should be always confirmed on additional oblique views or computed tomography scan (►Fig. 5b). Sonographically, a bipartite sesamoid Seminars in Musculoskeletal Radiology

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Fig. 5 Sesamoid fracture. (a) Transverse 17–5 MHz ultrasound (US) image obtained over the volar aspect of the first metacarpophalangeal joint (MCPJ) demonstrates the flexor pollicis longus (FPL) surrounded by the hypoechoic halo of the A1 pulley. At the base of the flexor tendon complex, the ulnar (1) and radial (2) sesamoids appear as bright echogenic structures. A closer look at the radial sesamoid reveals an irregular cortical break (arrow) in its midsubstance splitting the ossicle into two parts (2a and 2b). This indicates a fracture. Note edematous changes in the deep fibers of the flexor pollicis brevis (FPB). (b) Correlative computed tomography scan.

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Fig. 6 Anatomy of finger metacarpophalangeal joint (MCPJ). (a) Cadaveric slice and (b) corresponding schematic drawing illustrate the transverse view of the relevant structures of the MCPJ at the level of the metacarpal head including (1) palmar plate, (2) flexor digitorum superficialis tendon, (3) flexor digitorum profundus tendon, (4) proper collateral ligaments, (5) accessory collateral ligaments, (6) extensor tendon, (7) interosseous muscles, (8) lumbrical muscles (white arrows), sagittal bands, and (black arrows) deep transverse metacarpal ligaments.

should not be confused with a fracture. It has a smooth rounded contour, and the two pieces of bone do not appear to “fit together.”31 After bone assessment, careful scanning using transverse and sagittal planes with different degrees of MCPJ flexion should be performed to disclose PPl injuries. Conventional arthrography and MR arthrography can help diagnose PPl rupture by depicting contrast leakage from the volar aspect of the joint (Bianchi et al. 1993).

Fingers The MCPJs of the fingers are condyloid (knuckle-like) types of synovial joints characterized by great mobility in flexion and extension and some degree of adduction, abduction, and circumduction. Rotation is very limited and cannot take place alone; however, it may accompany flexion and extension. The MCPJ is stabilized by static and dynamic structures. Static stabilizers are the UCL and RCL complexes, the palmar plate, the deep transverse metacarpal ligaments (DTMLs), the sagittal band, and the A1 pulley. Dynamic stabilizers include some intrinsic muscles (i.e., interosseous and lumbrical) and tendons (i.e., flexors and extensors).33 The PIPJs of the fingers are uniaxial hinged joints with a bicondylar anatomy that allows movements in flexion and extension only. Their movement ranges from full extension up to 110 degrees of flexion. PIPJs exhibits greater lateral stability than MCPJs due to the peculiar shape of the bony surfaces allowing resistance to lateral (sideways) and rotational stress.34 Static stabilizers of the PIPJ are the PPl, the RCL and UCL complexes, the A3 pulley, the central and lateral slips of the extensor tendon, and the distal aponeurotic attachment (transverse fibers) of the interosseous and lumbrical muscles.34

MCPJ: Radial and Ulnar Collateral Ligament Injuries In the fingers, the MCPJ capsule is relatively loose. It is reinforced on each side by the collateral ligaments each

consisting of the pCL and aCL (►Fig. 6). The pCLs arise in depressions on the radial and ulnar side of the metacarpal head and extend distally to reach the base of the PPh. The aCLs have a common origin from the same depression as the pCLs but run in a more ventral position. The RCL and UCL thickness tends to slightly decrease in size between the second and fifth digit.33 The PPl is a thick fibrocartilaginous structure in the palmar aspect of the joint forming part of the articular surface for the metacarpal head between the two aCLs to which it is connected. It tapers proximally into a membranous capsule forming a groove for the flexor tendons that are here stabilized by the A1 pulley. At the volar aspect of the metacarpal heads, the DTMLs are short, wide transverse bands connecting the PPLs of the second to fifth MCPJ. With respect to them, the lumbrical muscles and neurovascular bundle lie palmarly; the interosseous muscles and tendons are located dorsally (►Fig. 6). On the dorsal aspect of the MCPJ, the sagittal bands (radial and

Fig. 7 Metacarpophalangeal joint collateral ligament injury of the third finger. Transverse 17–5 MHz ultrasound image over the dorsal aspect of the metacarpal head reveals markedly increased thickness (distance between the vertical dashed bars) and hypoechoic appearance of the ulnar-sided proper collateral ligament (on the right) compared with the radial one (on the left). The extensor tendon and sagittal bands look normal.

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Imaging Finger Joint Instability with Ultrasound

Imaging Finger Joint Instability with Ultrasound

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Fig. 8 Metacarpophalangeal joint (MCPJ) collateral ligament injury of the second finger (different cases). Coronal 17–5 MHz ultrasound images of (a) partial-thickness and (b) complete tears of the radial collateral ligament (RCL) complex. In (a), the thickened ligament (white arrowheads) is characterized by interstitial hypoechoic defects (void arrowheads). In (b), the RCL (white arrowheads) is completely disrupted. Only a few strands of residual tissue are observed in the ligament bed. PPh, proximal phalanx; M, metacarpal.

ulnar) pass between the interosseous tendons and the pCL, extending from the extensor tendon (middorsal plane) to the junction of the PPl with the DTMLs and the root of the A1 pulley. The interosseous muscle and tendons are dorsal to the DTMLs and insert into the PPh with fibers continuing into the extensor hood. The lumbrical muscles are ventral to the DTMLs and pass alongside the radial aspect of the MCPJ to insert into the digital extensor mechanism.

MCPJ collateral ligament injuries are less common in the fingers (39% of cases considering digits as a whole from the second to the fifth) than in the thumb (60% of cases).35 The likelihood that the injury occurs in the RCL is higher in the ring and little fingers. In the index, the UCL is most often involved, whereas no side predominance exists for RCL and UCL lesions in the middle finger.35 The trauma mechanism is typically based on application of a palmar to dorsal force directed radially or ulnarly. It has been hypothesized that RCL injuries occur less frequently in the index finger due to the protective action against ulnar stresses that the middle through the little fingers exert.36 Conversely, the higher incidence of these injuries in the little finger could be explained by the lack of buttress given by the other digits. The DTML ruptures infrequently. The tear is typically located between the fourth and the fifth digits and causes painful ulnar deviation of the little finger. Patients with MCPJ collateral ligament injuries complain of local pain and instability while grasping objects. US is able only to depict the RCL of the second MCPJ and the UCL of the fifth MCPJ in full extent.37 Collateral ligaments appear as thick fibrillar bands that originate from cortical bone depressions of the metacarpal heads and direct distally toward the base of the proximal phalanx. Coronal planes obtained in extension and full flexion can show ligaments in their long axis under different degrees of tensioning. The differentiation of the two bands (pCL and aCL) is unfeasible even using specific MCPJ positions. For the other joints with problems of access for the US beam, the use of a small linear array probe, such as a “hockeystick” type, can improve visualization of the ligaments by pressing the edges of the transducer into the intermetacarpal groove. Despite this, ligaments remain partially hypoechoic due to an unfavorable incidence angle of the US beam. Injured MCPJ collateral ligaments typically appear thickened and hypoechoic with blurred external boundaries. For the RCL

Fig. 9 Anatomy of finger metacarpophalangeal joint. (a) Cadaveric slice and (b) corresponding schematic drawing illustrate the transverse view of the relevant structures of the proximate interphalangeal joint at the level of the head of the proximal phalanx including (1) palmar plate, (2) flexor digitorum superficialis tendon, (3) flexor digitorum profundus tendon, (4) central band of the extensor tendon, (5) lateral slips of the extensor tendon, (6) proper collateral ligaments, (7) accessory collateral ligaments (arrow) dorsal joint recess (arrowheads) A3 pulley. Seminars in Musculoskeletal Radiology

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Fig. 10 Anatomy of the palmar plate (PPl) at the proximate interphalangeal joint (PIPJ) level. (a) Sagittal cadaveric slice of the index finger shows the PPl (large arrow) as a curved triangular structure attached to the base of the middle phalanx (MPh) (asterisk) reinforcing the capsule on the volar aspect of the PIPJ. Note the close relationship of the PPl with the overlying flexor digitorum superficialis (void arrowhead) and flexor digitorum profundus (FDP). One of the checkrein ligaments (narrow arrow) is seen proximally, lying superficial to the ventral joint recess (curved arrow). White arrowhead indicates dorsal joint recess. (b) Schematic drawing illustrates the intra-articular view of an hemisection of the PIPJ with the respective position of the proper collateral ligament (1), accessory collateral ligament (aCl) (2), PPl (asterisk), and central band of the extensor tendon (3). The PPl is attached distally to the volar lip of the base and the metaphysis of the MPh. On each side, it receives fibers from the aCL, whereas its proximal end is U-shaped due to the presence of the checkrein ligaments (3) (modified from Bowers WH et al. The proximal interphalangeal joint volar plate. I. An anatomical and biomechanical study. J Hand Surg 1980;5:84). (c) Midsagittal 17–5 MHz ultrasound image over the ventral aspect of the PIPJ demonstrates the normal PPl (arrows) as an echogenic triangle of fibrocartilage attached to the base (asterisk) of the MPh. Note the position of the ventral joint recess (arrowheads). PPh, proximal phalanx; MPh, middle phalanx.

of the second MCPJ and the UCL of the fifth MCPJ, dynamic scanning during finger adduction may help to assess whether the ligament is discontinuous showing joint space widening and improved visualization of the gap between the ligament ends. For the other MCPJ ligaments, transverse planes may enable size comparison of the RCL and UCL, but the overall evaluation with US results less informative (►Fig. 7). MR imaging has reported a sensitivity of 66.7% and a specificity of 90.9% for detection of RCL and UCL of the lesser MCPJ.38 Both sensitivity and specificity have proven to increase after injection of intra-articular contrast agent to 75% and 97.7%, respectively.38 In acute injuries, the main US and MR imaging signs of collateral ligament disruptions include frank discontinuity or detachment, ligament thickening with intrasubstance fissurations or hyperintensity in fluid-sensitive sequences and extracapsular leakage of joint fluid into adjacent superficial soft tissues (►Fig. 8).3 In chronic lesions, the ligament may appear thickened and fibrotic.3,4 Although most lesions are treated conservatively, severe MCPJ instability or intraarticular migration of the torn ligament end may require surgery.39 Following rupture, the UCL of the fifth finger may incidentally displace over the intact sagittal band, a condition somewhat similar to the Stener lesion.38

PIPJ: Palmar Plate and Collateral Ligament Injuries The main stabilizers of the PIPJ are the PPl and the collateral ligaments (►Fig. 9). The PPl is made of fibrocartilage and constitutes the palmar aspect of the joint capsule (►Fig. 10a).

Its superficial aspect provides a smooth gliding surface for the flexor tendons, whereas the deep surface is invested by the synovium of the ventral recess. Distally, the PPl is attached to the volar lip of the base and metaphysis of the middle phalanx (MPh). On each side of its distal attachment, the PPl is thicker and fuses with aCL fibers. Proximally, the PPl is more elastic and consists of two lateral bands, the so-called checkrein ligaments, forming a reversed U-shape complex to insert into the PPh (►Fig. 10b).40,41 From the biomechanical point of view, the PPl limits finger hyperextension, playing a major role in dynamic stability, whereas the collateral ligaments reinforce and thicken the fibrous capsule at both sides of the joint. On sagittal planes, US demonstrates PPls as meniscal-like triangular structures of homogeneous medium-level echogenicity lying over the articular cartilage that covers the head of the phalanx (►Fig. 10c). On transverse planes, PPls assume a more rectangular shape filling the gap between articular cartilage and flexor tendons. US has been used to investigate the normal motion of the plantar plate during PIPJ flexion.42 PPl dynamics include a first “sliding phase,” in which the PPl slides horizontally along the condylar slope, a second “elevation phase,” in which it moves volarward attracted by the A3 pulley, and a third “rolling phase,” in which the lip of the MPh rolls dorsalward in the recess.42 On MR imaging, PPls exhibit the typical signal of fibrocartilaginous structures, being strongly hypointense on fluid-sensitive sequences. Damage of the PIPJ is frequently secondary to a hyperextension trauma causing a shift of the MPh backward beyond Seminars in Musculoskeletal Radiology

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Imaging Finger Joint Instability with Ultrasound

Imaging Finger Joint Instability with Ultrasound

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Fig. 11 Complete palmar plate (PPl) avulsion injury at the proximate interphalangeal joint (PIPJ) level. (a) Photograph of the affected ring finger shows abnormal PIPJ hyperextension. (b) Midsagittal 17–5 MHz ultrasound (US) image over the ventral aspect of the PIPJ reveals avulsion and proximal migration of the PPl (arrows) at the level of the neck of the proximal phalanx (PPh). This has resulted in a decreased distance between the undersurface of the flexor digitorum profundus (fdp) and the head of the PPh; MPh, middle phalanx.

neutral in respect to the PPh.43 This may occur in sporting activities and especially in ball sports, when the ball or a hard object strikes the end of the finger.44 Many injuries are incomplete with partial disruption of periarticular soft tissues and some degree of disruption of the ligament complex. In these cases, patients may present with local pain, swelling, and limited range of movement, but joint stability is maintained.45 In more severe injuries, bony avulsion fractures and a complete tear of PIPJ supporting structures can occur resulting in joint instability.46 PIPJ injuries are generally classified into three types based on increasing severity: type I (hyperextension injury), type II (dorsal dislocation), and type III (fracture-dislocation). In PIPJ traumas, the base of the MPh is driven against the head of the PPh with the brunt of the force absorbed by the volar lip of the MPh.44,46 Three types of PPl injuries have also been described. In type I injury, forced hyperextension results in avulsion of the PPl from the base of the MPh or, less frequently, from the proximal insertion of the checkrein bands on the PPh (►Fig. 11). Experimental biomechanical data indicate that the rate of application of the force may influence nature and site of injury: Rapid rates cause distal attachment rupture, whereas slow rates tend to involve the proximal checkrein ligaments. Imaging can contribute to an early diagnosis and may help planning an appropriate treatment to prevent secondary flexion contracture of the PIPJ, the so-called pseudoboutonnière, that occurs with an intact extensor mechanism as a result of adhesions.47 On midsagittal planes, US can demonstrate (1) avulsion and proximal migration of the PPl at the neck of the PPh; (2) decreased tendon-to-bone distance between flexor tendons and the head of the PPh, and (3) joint effusion filling the PIPJ recesses in the acute phase. Midsubstance tears of the plate occur less commonly.

Fig. 12 Palmar plate (PPl) injury at the proximate interphalangeal joint (PIPJ) level (different cases). (a) Lateral plain film reveals a small fleck of bone (arrowhead) avulsed from the base of the middle phalanx. (b, c) Type III injury. (b) Midsagittal 17–5 MHz ultrasound (US) image over the ventral aspect of the PIPJ shows a small bright echo (arrowhead) reflecting the avulsed fleck of bone in continuity with the PPl (arrows). (c) Lateral sagittal 17–5 MHz US image demonstrates concomitant injury of the accessory collateral ligament that appears swollen and hypoechoic (arrows). PPh, proximal phalanx; MPh, middle phalanx. Seminars in Musculoskeletal Radiology

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13 Smith RJ. Post-traumatic instability of the metacarpophalangeal

joint of the thumb. J Bone Joint Surg Am 1977;59(1):14–21 14 Catalano LW III, Cardon L, Patenaude N, Barron OA, Glickel SZ.

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In a type II injury, the involvement of periarticular soft tissues is more extensive, with PPl avulsion and a split in the collateral ligament complex. The PIPJ shows more severe instability than in type I lesions because dorsal subluxation or dislocation of the MPh may take place following extensor hood traction. US is able to identify the concurrent injury of the aCL on coronal planes. Basically, there is no side predominance in the ligament involvement. Lateral plain film may detect some degree of dorsal articular displacement. A type III injury is typified by fracture-dislocation of the volar base of the MPh. Careful attention to cortical details should be given radiographically if a PPl fracture is suspected. The lateral view is able to show avulsion of a small fleck of bone from the base of the phalanx and some degree of dorsal displacement of the PPh (►Fig. 12a). For this purpose, the Xray beam should be perfectly aligned to the phalangeal base. Even slight obliquity needs to be avoided not to miss the fragment. US can confirm the continuity of the avulsed piece of bone with the PPl and can assess the size of the fragment relative to the volar surface of the phalangeal base, a factor influencing PIPJ stability (►Fig. 12b, c).48 A stable injury usually involves < 40% of the articular surface while leaving the collateral ligaments attached to the MPh. Lesions that are unstable extend > 40% of the articular surface showing volar plate and collateral ligaments attached to the avulsed fragment. In trigger finger, the PPl may be thickened in association with the A1 pulley, possibly causing exacerbation of the disease and worsening of flexor tendon gliding.49

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interphalangeal joint volar plate. I. An anatomical and biomechanical study. J Hand Surg Am 1980;5(1):79–88 Saito S, Suzuki Y. Biomechanics of the volar plate of the proximal interphalangeal joint: a dynamic ultrasonographic study. J Hand Surg Am 2011;36(2):265–271 Sprague BL. Proximal interphalangeal joint injuries and their initial treatment. J Trauma 1975;15:380–385 Palmer RE. Joint injuries of the hand in athletes. Clin Sports Med 1998;17(3):513–531 Bowers WH. Sprains and joint injuries in the hand. Hand Clin 1986; 2(1):93–98 Nance EP Jr, Kaye JJ, Milek MA. Volar plate fractures. Radiology 1979;133(1):61–64 Kahler DM, McCue FC III. Metacarpophalangeal and proximal interphalangeal joint injuries of the hand, including the thumb. Clin Sports Med 1992;11(1):57–76 Glickel SZ, Alton Barron O, Catalano LW III. Dislocations and ligament injuries of the digit. . In: Green DP, Hotchkiss RN, Pederson WC, Wolfe SW, eds. Green’s Operative Hand Surgery. 5th ed. Vol 1. Philadelphia, PA: Churchill Livingstone; 2005:343–388 Sato J, Ishii Y, Noguchi H, Takeda M. Sonographic appearance of the flexor tendon, volar plate, and A1 pulley with respect to the severity of trigger finger. J Hand Surg Am 2012;37(10):2012–2020

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Copyright of Seminars in Musculoskeletal Radiology is the property of Thieme Medical Publishing Inc. and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use.