MRI Web Clinic — February 2016

Ulnar Collateral Ligament Tears of the Thumb
Michael E. Stadnick, M.D.

 

Clinical History:  A 16 year-old male presents with pain and laxity at the thumb metacarpophalangeal joint after a fall onto his right hand 12 days prior to the MRI examination. What are the findings? What is your diagnosis?

1a
1b
1c
Figure 1:

STIR coronal images through the volar (1a) and dorsal (1b) aspect of the first metacarpophalangeal joint and STIR axial images at the metacarpal head (1c) are provided.

 

Findings

2a
2b
2c
Figure 2:

(2a) The STIR coronal image at the volar aspect of the 1st metacarpophalangeal joint demonstrates a fluid-filled defect at the insertion of the proper ulnar collateral ligament at the base of the proximal phalanx (red arrow) with mild cortical irregularity. A portion of the inserting adductor pollicis tendon (blue arrow) is seen distal to this abnormality. (2b) The STIR coronal image at the dorsal aspect of the joint demonstrates mild radial subluxation of the proximal phalanx. The ulnar collateral ligament (red arrowhead) remains attached at its origin at the metacarpal head, but the ligament projects away from the joint at the proximal margin of the adductor aponeurosis (blue arrowhead). (2c) The displaced ligamentous tissue is also demonstrated on the STIR axial image through the distal metacarpal head (blue arrowhead). A bone bruise (asterisks) is evident within the metacarpal head on all images.

 

Diagnosis

Ulnar collateral ligament tear at the thumb metacarpophalangeal joint with a Stener lesion.

 

Introduction

Tears of the ulnar collateral ligament (UCL) of the thumb metacarpophalangeal joint (MCP) are among the most common injuries of the hand. Gamekeeper’s thumb was originally described by Campbell as a chronic repetitive injury of the UCL of the thumb MCP seen in 24 Scottish gamekeepers as a result of repetitive valgus stresses across the thumb MCP from their method of breaking the necks of rabbits.1 Thus gamekeeper’s thumb is commonly used to describe chronic UCL tears associated with repetitive stresses.  An alternative term, Skier’s thumb, indicates an acute injury of the UCL from valgus stress of the thumb at the MCP and was originally used to describe the injury sustained in a fall onto the outstretched hand with the thumb abducted while holding a ski pole. Failure to diagnose and effectively treat UCL tears can lead to loss of pinching function between the index finger and thumb and may lead to arthritis at the MCP. Physical examination and stress testing are the mainstays in the diagnosis of an UCL tear; however advanced imaging, especially MRI, is increasingly relied upon for diagnosis and treatment planning.   While MRI has proven to be an excellent tool for evaluating UCL tears, recognition and accurate description of UCL tears depend on careful attention to technical considerations as well as familiarity with the varied MRI appearances that can be encountered.

 

Anatomy and Function

The thumb MCP is a diarthrodial ginglymoid joint that allows motion primarily in flexion and extension.  The ulnar collateral ligament (UCL) and radial collateral ligament (RCL) are the primary static stabilizers of the MCP with additional stability provided by articular surface congruity, the dorsal capsule, and the volar plate. The adductor pollicis muscle is the primary dynamic stabilizer resisting valgus stress and inserts onto the ulnar tubercle of the proximal phalanx, volar plate, ulnar sesamoid, and the adductor aponeurosis, the latter blending with the extensor hood and inserting on the extensor pollicis longus tendon.  Additional dynamic stabilizers include intrinsic hand muscles (abductor pollicis brevis and flexor pollicis brevis) and extrinsic muscles (extensor pollicis longus, extensor pollicis brevis, and flexor pollicis longus).2

Both the UCL and RCL are composed of two bundles (Fig. 3).  The proper ulnar collateral ligament is cord-like measuring 4 to 8 mm wide and 12 to 14 mm long.3 The ligament arises at the dorsal ulnar aspect of the metacarpal head with the center of the origin volar to the dorsal cortex by approximately a third of the AP dimension of the metacarpal head and 3 to 5 mm proximal to the articular surface.4 The origin is slightly volar and distal to the posterior tubercle of the metacarpal.4  The ligament extends in a distal volar fashion to insert just beyond the base of the proximal phalanx dorsal to the volar cortex by approximately a quarter of the AP dimension of the phalangeal base.4 The center of the phalangeal insertion is approximately 3 mm distal to the articular surface and lies just volar and proximal to the ulnar tubercle at the base of the proximal phalanx.4 The accessory UCL is contiguous with and just volar to the proper UCL appearing slightly more superficial. The accessory UCL inserts into the volar plate and the ulnar sesamoid.5 The RCL complex demonstrates a comparable origin and insertion.4

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3
Figure 3:

The proper UCL (pUCL) arises at the dorsal ulnar aspect of the metacarpal head and inserts on the proximal phalanx near the volar cortex. The accessory UCL (aUCL) is contiguous with the pUCL and inserts onto the volar plate and ulnar sesamoid (asterisk).

The UCL provides primary support against valgus stress and volar subluxation of the proximal phalanx.2 Based on the degree of flexion of the MCP, the accessory and proper UCL provide selective stability.2  In flexion, the volar plate moves proximally relaxing the accessory UCL, while tightening the proper UCL and dorsal capsule. Thus, the proper UCL provides primary resistance to valgus stress when the MCP is flexed by more than 20 degrees. In extension, the accessory UCL is taut and the proper UCL is mildly lax, and the primary resistance to valgus stress arises from an intact accessory UCL and volar plate.6,7 This understanding of functional ligament stability provides the basis for approaches to stress testing.7 Untreated UCL insufficiency leads to weakness of both key and tip pinch, and may progress to further laxity, pain, and arthritis.8,9,7

Mechanism of Injury

Acute injuries of the UCL result from forced valgus stress at the thumb MCP, such as the classic injury of falling while holding an object such as a ski pole.10 Injuries are common in sports that place the thumb in a vulnerable position such as catching a ball or from a fall onto an outstretched hand with the thumb abducted. Acute injuries of the ulnar aspect of the MCP are considered to occur in a sequence that begins with abduction and rotatory force at the MCP initially stretching and eventually rupturing the proper UCL and joint capsule.10 With additional force, the volar plate and embedded sesamoids rotate radially and finally there is disruption of the accessory UCL.10  This disruption allows radial subluxation of the proximal phalanx, which if severe enough slides the adductor aponeurosis distal to and/or beneath portions of the disrupted UCL . The Stener lesion, originally described by Bertil Stener10, occurs when the UCL is distally torn and is retracted with the UCL folded proximal to the proximal edge of the adductor aponeurosis (Fig 4).6 Chronic injuries of the UCL can occur from neglected acute UCL tears or as the result of repetitive valgus stress across the MCP.

4
Figure 4:

Dorsal renderings of the thumb MCP demonstrating the (left) normal UCL (arrow) deep to the adductor aponeurosis (asterisk), (middle) torn UCL (arrow) resulting from valgus stress at the MCP with the ligament deep to the adductor aponeurosis (asterisk), and (right) a torn UCL (arrow) displaced proximal to the proximal margin of the adductor aponeurosis (asterisk) resulting in a Stener lesion.

Clinical Presentation and Physical Examination

Acute UCL tears typically present with swelling, tenderness, and ecchymosis over the UCL with weakness and pain in pinch and key grip. Frank instability can be present, but often stress exams are limited by patient pain.  Palpable nodularity along the ulnar aspect of the MCP suggests the presence of a Stener lesion.

Patients with chronic UCL tears present without the accompanying soft tissues changes of an acute injury.  These patients commonly describe weakness of pincer grip, holding a key, grasping objects, unscrewing jar lids, or turning a key or door knob. Chronic tears can result in scarring and thickening of the UCL, the adductor aponeurosis, and the surrounding soft tissues and can mimic a Stener lesion.

Ulnar collateral ligament stability at the MCP is assessed by evaluating angulation of the joint with valgus forces applied at the proximal phalanx.  Local anesthesia with intra-articular lidocaine is frequently used to relieve discomfort and increase the accuracy of the examination.11  While there is no clear consensus on methodology, evaluation of UCL stability is typically performed with the MCP in extension as well as flexion to assess the integrity of the accessory and proper UCL, respectively.  Visual examination combined with goniometry measurements have several shortcomings, including relying on surface anatomy to approximate the location and angle of the metacarpal and proximal phalanx.12 There is also a lack of consensus regarding what constitutes an abnormal valgus stress angle.13 Various studies indicate that valgus angulation ranging from 20–45 degrees is diagnostic of a complete UCL tear. Comparing the injured to the non-injured side has also been advocated with a 10-45 degree difference being indicative of a complete UCL tear.7,3,9,14,15 Malik et al. demonstrated significant variability in the degree of UCL laxity between the right and left thumb in normal individuals, suggesting that a lack of a firm endpoint on stress testing in 30 degrees of flexion can, in fact, represent a more reliable finding for a complete UCL tear.13

Imaging

X-ray

Plain films are routinely used after an appropriate history of trauma to diagnose avulsion fractures and to identify evidence for instability at the MCP.  Avulsion fractures have reportedly been seen at the ulnar aspect of the base of the proximal phalanx in up to 40% of acute UCL ruptures, though in Radsource’s experience the frequency of fractures is much lower.  Significantly displaced avulsed fracture fragments are generally associated with a displaced ligament tear or Stener lesion.  However, non-displaced or minimally displaced fractures do not necessarily correspond to the amount of ligament displacement. With valgus stress injuries, fractures can occur at the base of the proximal phalanx and mimic a nondisplaced or minimally displaced avulsion at the UCL attachment, leading to conservative management.  Multiple cases have been reported of misleading minimally or nondisplaced fracture fragments in the presence of severely displaced UCL ligament tears or Stener lesions (Fig. 5).15,16,17 Additional indicators of UCL disruption include radiographic evidence of dislocation of the ulnar sesamoid bone either laterally or longitudinally, which is associated with a complete rupture of the accessory and proper UCL.18 Volar subluxation of the proximal phalanx can be seen due to loss of stability from the UCL and dorsal capsule.  An exostosis along the dorsal radial or dorsal ulnar aspect of the metacarpal head is a specific but not very sensitive sign of chronic UCL tear.19

5
Figure 5:

An AP radiograph of the thumb demonstrates a nondisplaced avulsion fracture at the ulnar aspect of the base of the proximal phalanx (arrow). Fractures in this position cannot be safely assumed to represent the location of the distal end of the UCL. This finding does not exclude the presence of a displaced complete UCL tear or Stener lesion.

Stress views are routinely performed with X-ray or fluoroscopic assistance.  In addition to the normal variability that can be encountered as discussed above, the accuracy of results can be adversely affected by incorrect positioning.  Slight rotation of the flexed MCP  will artifactually increase or decrease the appearance of radial deviation.15

 

Ultrasound

Ultrasound has been used successfully to evaluate UCL tears and Stener lesions.20,21 However, ultrasound is very dependent on an experienced musculoskeletal ultrasonographer and is less accurate than MRI.2,20

MRI

MRI is the advanced imaging modality that has met with the most success in evaluating UCL tears.22,23,24 Careful attention to proper positioning is vital to diagnosing and characterizing UCL tears (Fig. 6). Coronal images are most helpful in evaluating the UCL.  Axial images are most useful in identifying or confirming Stener lesions. Small deviations in alignment, especially on coronal series, can lead to false negative examinations.

6
Figure 6:

The proper coronal plane for evaluating the thumb metacarpophalangeal joint should parallel the dorsal cortex of the metacarpal head (left)(green line). At this level the metacarpal head is rectangular or trapezoidal in contour. The next distal cut typically includes the sesamoids(right), which can be used as a landmark for planning with the coronal plane parallel to the plane of the 2 sesamoids. Sagittal images are perpendicular to the coronal image plane.

 

Normal MRI anatomy

The ulnar collateral ligament is made up of proper and accessory ulnar collateral ligament components. The ligament components blend on MRI and are not clearly separable.  Their distinction is based on an understanding of their normal course. The proper UCL extends in an oblique manner from the dorsal ulnar aspect of the metacarpal head to the volar portion of the proximal phalanx inserting just proximal to the adductor pollicis attachment at the ulnar tubercle of the proximal phalanx.  The proper UCL is best seen on coronal and axial images (Figure 7).

7a
7b
Figure 7:

Consecutive proton density-weighted coronal images from dorsal to volar (above) and consecutive axial T1-weighted images from proximal to distal (below) demonstrate normal thumb MPJ anatomy. The proper UCL (red arrows)arises at the dorsal ulnar aspect of the metacarpal head and extends distally and volarly to insert at the base of the proximal phalanx just proximal to the adductor pollicis(AdP) attachement at the ulnar tubercle. The accessory UCL (red arrowheads) is contiguous with the proper UCL and is best seen on the axial images located just proximal and volar to the proper UCL extending from the metacarpal head to the ulnar sesamoid (red asterisk) and volar plate (yellow asterisk). The adductor aponeurosis (red dots) arises from the adductor pollicis muscle and tendon and covers the UCL, extending dorsally to blend with the extensor hood. Comparable anatomy is found at the radial aspect of the joint with the proper UCL (blue arrows) and accessory UCL (blue arrowheads), the abductor pollicis brevis (AbP), aponeurosis of the abductor pollicis brevis(blue dots), and radial sesamoid (blue asterisk) representing analogous structures. The extensor pollicis longus tendon (EPL), extensor pollicis brevis tendon (EPB), and flexor pollicis longus tendon (FPL) are indicated.

 

MRI of thumb MPJ UCL injury

Diagnosis of UCL injuries is made by detecting abnormalities in size, contour, and signal. Caution should be exercised in relying on signal abnormality alone as Hirschman et al. found that the proper UCL and adductor aponeruosis commonly had a striated appearance on fat-suppressed intermediate-weighted images, while the radial collateral ligament was mainly low in signal, and the accessory collateral ligaments showed variable signal intensity.25 On fluid-sensitive sequences, partial tears of the UCL demonstrate focal attenuation of the ligament with hyperintense signal partially traversing the ligament (Fig. 8).

8
Figure 8:

Consecutive fat-suppressed coronal T2-weighted images in a 16 year-old male following an injury to the thumb during football practice. Edema is demonstrated within the adductor pollicis muscle (asterisk) adjacent to the site of attachment at the volar aspect of the proximal phalanx (left). The middle image is one slice dorsal and demonstrates fibers of the UCL that are attached at the proximal phalanx (arrowhead). One slice further dorsal (right) demonstrates a tear of the dorsal fibers of the UCL insertion (arrow) compatible with a partial tear.

 

Complete tears are identified by hyperintense signal fully traversing the ligament or at the site of bony attachment on fluid-sensitive sequences (Fig. 9). The amount of displacement can be evaluated based on the size of the fluid signal filled ligament gap (Fig.15).

9
Figure 9:

A 17 year-old male injured his thumb playing basketball 4 days prior to the MRI scan. Consecutive STIR coronals along the volar 1/3 of the MPJ demonstrate a minimally displaced complete tear of the UCL.

 

Tears of the UCL are most common at the proximal phalangeal attachment but can occur proximally at the metacarapal origin (Fig. 10) or as a tear of the ligament substance.

10
Figure 10:

Consecutive coronal STIR images in a 49 year-old female with recent thumb injury from a fall and physical exam findings suspicious for a Stener lesion demonstrate a minimally displaced complete tear of the UCL at the metacarpal origin (arrow).

 

The Stener lesion is a common complication of UCL tears and occurs in 64-88% of complete UCL tears.26,6 When the proper UCL is completely torn from the proximal phalanx and there is disruption of the accessory UCL, the ligament becomes retracted and folded proximal to the adductor aponeurosis.  Because the torn end of the ligament is blocked from reapproximating the proximal phalangeal insertion, normal healing and stability cannot be achieved and surgery is required to repair the UCL (Fig. 11).

11
Figure 11:

This intraoperative photograph demonstrates a Stener lesion. The proximal margin of the adductor aponeurosis (arrowheads), arising from the adductor pollicis muscle (asterisk), blocks the displaced UCL (arrow) from reapproximating the proximal phalangeal insertion (blue asterisk) which lies beneath the adductor aponeurosis. Operative photo courtesy of Sunil Thirkannad, MD, Kleinert Kutz Hand Care Center.

 

Stener lesions are typically well seen on coronal images.  The displaced ligament remains attached at the dorsal ulnar aspect of the metacarpal head but demonstrates striking alteration of the ligament contour at the metacarpal origin with the torn end of the ligament projecting ulnarly (Fig 12). The proximal edge of the adductor aponeurosis is frequently identified distal to and abutting the displaced UCL.

12
Figure 12:

Coronal proton density-weighted (left and middle) and STIR (right) images through the dorsal aspect of the metacarpal head. The normal orientation of the UCL is vertical (green dotted line) and lies deep to the adductor aponeurosis (blue dotted line) which can be imperceptible. Stener lesions demonstrate a dramatic change in ligament orientation (red dotted lines) and the adductor aponeurosis is often seen just distal to and abutting the displaced ligament (arrowheads).

 

Occasionally the adductor aponeurosis is not identified as a discrete structure because of edema or slice selection.  In these instances, axial images are indispensable in identifying a Stener lesion. The adductor aponeurosis fuses with the extensor hood, and these structures are readily identified on axial images through the distal metacarpal head as a well-defined linear low signal structure extending between the extensor pollicis tendon dorsally and the adductor pollicis muscle and tendon. Simply following the adductor aponeurosis proximally on the axial images provides a useful landmark for identifying displaced ligamentous tissue, which is readily seen protruding beyond the plane of the aponeurosis (Fig. 13).

13
Figure 13:

A T1-weighted axial image (left) demonstrates the normal UCL (green arrow) deep to the adductor aponeurosis as it continues dorsally to fuse with the dorsal hood (arrowheads). Consecutive STIR axial images are obtained at the distal metacarpal head at the level of the sesamoids (middle) and one cut more proximal (right) in a patient with a Stener lesion. Note the well-defined adductor aponeurosis (arrowheads) highlighted by surrounding edema with no ligament tissue deep to the aponeurosis. A low signal focus is identified ulnar to the aponeurosis (arrow) and represents distally projecting fibers from the displaced UCL which is more completely seen on the next more proximal image (dotted outline).

 

Complex tears (Fig. 14) or displaced tears (Fig. 15) can be encountered and axial images often provide helpful information in characterizing the underlying ligament injury.

14
Figure 14:

STIR coronal and axial images in a 43 year-old male with a machinery injury 1 day prior demonstrate displaced ligament tissue (arrows) folded proximal to the adductor aponeurosis (arrowheads) compatible with a Stener lesion. On the more distal axial image on the right, substantial ligament tissue remains deep to the adductor aponeurosis (short arrows) attaching to the ulnar sesamoid (asterisk) and represents residual accessory UCL . At surgery the proper UCL and accessory UCL were torn from each other forming separate flaps with the proper UCL torn from the proximal phalanx forming the Stener lesion, and the accessory UCL ruptured at the metacarpal head.

15
Figure 15:

STIR coronal and axial images in a 40 year-old female who suffered a fall down steps 2 weeks before with a complete UCL tear. (Left) Increased signal intensity and loss of ligament tissue indicate the site of UCL rupture (asterisk) at the volar aspect of the proximal phalanx, just proximal to the adductor tendon insertion (blue arrow). (Middle) At the level of the UCL origin at the dorsal aspect of the metacarpal head, displaced UCL fibers are demonstrated (arrow) and appear to remain deep to the adductor aponeurosis (arrowheads). (Right) The axial image confirms that the torn UCL (arrow) remains deep to the adductor aponeurosis (arrowheads). Although the ligament is significantly displaced, this does not represent a Stener lesion.

 

Chronic UCL tears often lack surrounding edema, which can hinder the localization of the UCL defect.  Ligament laxity is commonly observed but in chronic tears scarring may obscure a ligamentous gap.27 Scar appears as an irregular area of decreased signal intensity on MR images (Fig. 16).27

16
Figure 16:

Coronal STIR images through the volar (left) and dorsal (right) aspects of the MPJ in a 48 year-old male injured 4 months prior to the MRI demonstrate a thickened, irregular, and lax UCL (arrows) consistent with a chronic tear with scarring and probable MCJ instability.

 

Stener-like lesions

The mechanism and anatomical factors which result in Stener lesions are not exclusive to the thumb MCP. A similar injury pattern can occur at other joints of the hand and even the knee.28,29,30,31,32 These type injuries have been termed “Stener-like” lesions.  In our practice, injury of the radial collateral ligament of the 5th MCP is the most common site of a “Stener-like” lesion in the hand (Fig. 17), but any of the metacarpophalangeal  joints can be affected.29 “Stener-like” lesions can involve the radial collateral ligament of the thumb MCP and have also been described at interphalangeal joints.30,31 Like the Stener lesion, surgical repair of “Stener-like” lesions is indicated, because interposed tissue prevents the torn ligament from healing to its normal site of attachment.

17
Figure 17:

A 39 year-old male presented 2 months after injury his little finger playing basketball. STIR coronal (top) and axial (bottom) images at the metacarpophalangeal joint of the little finger demonstrate a normal appearing ulnar collateral ligament (white asterisk) with absence of the radial collateral ligament at the radial aspect of the metacarpal head (red asterisk). Slightly more dorsal (top right) and proximal (bottom right) images identify the displaced radial collateral ligament folded proximal to the radial sagittal band (arrowheads) resulting in a Stener-like lesion.

 

Treatment

The generally accepted algorithm for treatment of acute UCL tears includes immobilization for sprains and partial tears. Surgery has traditionally been recommended for all complete UCL tears, regardless of the severity of ligament retraction.  Acute repairs are recommended within 3-6 weeks.9,33 Even within this time frame, decisions on repair or reconstruction are dependent on surgical findings including the quality of the ligament and the ability to mobilize the remnant  so that it can reach its anatomic insertion.  Augmentation with local tissue is often performed even if a primary repair can be achieved. Delays beyond this time frame often result in more complicated primary repair due to retraction and scarring of the ligament (Fig. 18).

18
Figure 18:

This patient presented 8 weeks after injuring her thumb. Coronal T1-weighted (left) and STIR coronal (middle) and axial (right) images reveal a Stener lesion, but the displaced ligament (arrow) demonstrates surrounding soft tissue that is slightly hyperintense to muscle on the T1-weighted image (left) and only mildly increased in signal on the fluid-sensitive STIR series (middle and right), representing granulation tissue and early fibrosis. At surgery, the Stener lesion was identified but the scarred ligament could not be sufficiently unfurled to allow a direct repair and reconstruction was required.

In contrast to the traditional approach, some authors have suggested that not all complete UCL tears require surgery.34,35 Recent strategies include utilization of MRI to help guide treatment for patients with complete UCL tears.36 Milner et al. describe successful outcomes for patients treated by immobilization with less than 3 mm of ligament displacement as determined by MRI examination.36 Tears with 3 mm or greater displacement required surgery because spontaneous, stable healing did not occur with 6-8 weeks of immobilization.36

Both pull-out suture through a bone tunnel and suture anchor fixation have been used with success for repairing distal UCL rupture.  Today suture anchor fixation techniques are more popular.  Suture anchors allow for  earlier mobilization resulting in greater range of motion and pinch strength.33 Chronic UCL tears typically require reconstruction because ligament attenuation, contraction, and scar prevent mobilization of the ligament to its anatomical osseous insertion.8 Various methods have been employed including dynamic repairs (tendon transfers) and static repair (UCL reconstruction).2 Arthrodesis is reserved for those patients with chronic instability, pain, and arthritis.37,8

 

Conclusion

Ulnar collateral ligament tears of the thumb metacarpophalangeal joint are common.  MRI is the imaging modality of choice for assessing patients with equivocal findings and in identifying ligament injuries which require surgical repair, such as the commonly occurring Stener lesion.  Although repair of complete UCL tears is the most common approach, some hand surgeons now rely on MRI to triage patients with complete tears into surgical and non-surgical groups, further emphasizing the importance of MRI in the management of these patients.

 

References

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