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Sonography of a Rupture of the Tendon of the Extensor Pollicis Longus Muscle: Initial Clinical Experience and Correlation with Findings at Cadaveric Dissection

¹ Department of Radiology, Vrije Universiteit Brussel, Laarbeeklaan 101, Brussels 1090, Belgium.
² Department of Radiology, Sint-Andries, Tielt, Belgium.
³ Department of Experimental Anatomy, Vrije Universiteit Brussel, Brussels, Belgium.
⁴ Present address: Aalsters Stedelijk Zienkenhuis, Alast, Belgium.
⁵ Department of Radiology, Parc Leopold, Brussels, Belgium.

Received December 12, 2003; accepted after revision June 7, 2004.

 
Supported by the A. L. Baert Prize, Katholieke Universiteit Leuven, 2001; the Department of Experimental Anatomy, Vrije Universiteit Brussel, Brussels, Belgium.

Address correspondence to M. De Maeseneer (michel.demaeseneer{at}az.vub.ac.be).

Abstract

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OBJECTIVE. The objectives of our study were to report our initial clinical experience with sonography of the wrist for diagnosing a proximal rupture of the tendon of the extensor pollicis longus (EPL) muscle and to perform sonographic-anatomic correlation of the EPL tendon.

MATERIALS AND METHODS. Clinical and imaging files of five patients who underwent sonography and subsequent open wrist surgery were reviewed retrospectively. Imaging was performed by four radiologists experienced in musculoskeletal sonography. Tendon retraction was evaluated on sonography and at surgery. In cadavers, sonography was performed in concert by two musculoskeletal radiologists during progressive stages of dissection of four embalmed specimens. One specimen was sliced in the transverse plane.

RESULTS. In cadavers, the EPL tendon was located on or adjacent to Lister's tubercle and extended to the base of the thumb. The EPL tendon crossed over the extensor carpi radialis tendons where it exhibited a flattened aspect. In the five patients in the study, a tubular-shaped hypoechoic area was evident at the position of the ruptured EPL tendon on sonograms. At surgery, this area corresponded to fluid, hemorrhage, and scar tissue in the EPL tendon sheath. The assessment of tendon retraction on sonography correlated with findings at surgery.

CONCLUSION. Sonography may aid in diagnosing a rupture of the EPL tendon and in the preoperative assessment of gap size and position of the retracted tendon ends. A characteristic tubular hypoechoic area may be seen crossing over the extensor carpi radialis tendons.

Introduction

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Various conditions have been implicated in the proximal rupture of the tendon of the extensor pollicis longus (EPL) muscle at the wrist. Spontaneous ruptures of the EPL tendon include wrist fractures, callus formation, and rheumatoid arthritis [1-5]; performing push-ups [1-5], prominent orthopedic fixation screws [1-5], and spontaneous ruptures of the EPL tendon also have been reported [6, 7]. Often accurate diagnosis is delayed. In addition, it is not possible to assess the size of the tear on the basis of clinical findings or to determine the precise position of the retracted ends of the tendon. Accurate diagnosis and assessment of the size of the tear are essential because these findings may show that a direct suture of the tendon is possible, thus avoiding a tendon graft procedure [8]. In addition, the position of the retracted ends determines the site of the surgical incision, which should be as small as possible for cosmetic concerns.

The aims of our study were to diagnose the EPL tendon rupture on sonography, evaluate associated lesions, and determine the degree of tendon retraction. Hence, we studied the EPL tendon using sonographic-anatomic correlation during dissection of cadaveric specimens and report our initial clinical experience with sonography.

Materials and Methods

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Cadaveric Study
Five embalmed hand specimens were obtained from the department of anatomy (Vrije Universiteit Brussel). Embalming was performed immediately after death of the individuals (age range, 62-74 years; mean age, 68 years). Before dissection, sonography was performed on an ATL HDI 5000 system (Philips) with a 12-MHz transducer in concert by two experienced musculoskeletal radiologists. Compound imaging was used liberally. The EPL tendon was investigated in a transverse and longitudinal imaging plane from Lister's tubercle to the base of the thumb. We assessed the obliquity, thickness, and sonographic pattern of the tendon.

The second phase of the investigation consisted of a progressive dissection of four specimens: first, removal of skin; second, removal of subcutaneous fat; and third, removal of the extensor retinaculum. Dissections were performed in concert by a musculoskeletal radiologist and an anatomist. We assumed that if a structure was removed and then no longer seen on sonograms, its absence on sonography was proof that this structure corresponded to that present on sonography before removal. One specimen was frozen at -40°C and sliced in the transverse plane using a band saw.

Clinical Study
Sonography of the wrist was performed by musculoskeletal radiologists from four institutions, each of whom had at least 10 years of experience in musculoskeletal sonography. Informed consent was obtained to search patients' records retrospectively. Five consecutive patients were identified during a 6-month period by searching the databases of the four institutions. The radiologists were given each patient's clinical history of pain, difficulty extending the thumb, or both. Different clinical systems were used (Prosound 5500, Aloka; ATL HDI 5000, Philips; Technos, Esaote; Elegra, Siemens) with 12-MHz transducers. A standoff pad was not used by any of the radiologists; instead, transmission gel was used liberally.

For each sonographic evaluation, the patient sat on a chair in front of the examinator and placed the pronated wrist on the examination table. First, Lister's tubercle was identified as a bony protrusion on the dorsoradial aspect of the radius by placing the probe in the transverse plane. This tubercle was used as a landmark to identify the EPL tendon. When the transducer is placed in an oblique plane extending from Lister's tubercle to the base of the first metacarpus, the normal course of the EPL tendon can be identified. We continued with an assessment of the presence of the extensor indicis proprius tendon. In addition, the extensor carpi radialis brevis and longus tendons were imaged in the transverse and longitudinal plane.

On sonography the diagnosis of EPL tendon rupture was made when a defect was noted in the normal fibrillar tendon structure. A dynamic examination was performed to confirm the absence of tendon continuity. The distance between the reappearance of fibrillar structures proximally and distally was assessed and indicated the degree of tendon retraction. A diagnosis of extensor carpi radialis brevis and longus tenosynovitis was made when these tendons were thickened and heterogeneous and fluid was present in the synovial sheath.

Results

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Anatomic Study
After the skin and subcutaneous connective and fatty tissues were removed, the extensor retinaculum was exposed. On further dissection at the level of the first carpal row, the EPL tendon crossed over the extensor carpi radialis brevis and longus tendons (Fig. 1). Anatomic slices showed the thin and flattened aspect of the extensor pollicis longus tendon (Fig. 2). When reaching the base of the first metacarpal bone, the EPL tendon joined the extensor pollicis brevis tendon. At this position, the EPL tendon was covered by fibrous dorsal reinforcements (Fig. 3). The oblique position of the EPL tendon relative to the extensor carpi radialis brevis and longus tendons also was shown. The EPL tendon was located on top of Lister's tubercle in two of the five specimens and on the ulnar side of Lister's tubercle in the remaining three specimens.

View larger version (124K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 1. —Photograph of specimen 1 after partial removal of extensor retinaculum during dissection shows extensor pollicis longus tendon (P) at intersection with extensor carpi radialis brevis (B) and longus (L) tendons. Tendon of extensor indicis proprius (i) is seen. On more radial aspect of wrist, extensor pollicis brevis and abductor pollicis longus tendons (arrowheads) are shown.

View larger version (135K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 2. —Photograph of transverse slice of specimen 3 at level of distal radius shows that extensor pollicis longus (EPL) tendon (P) is situated on ulnar aspect of extensor carpi radialis brevis (B) and longus (white L) tendons. EPL tendon is seen on top of Lister's tubercle (black L). Also note extensor digitorum tendon group (D).

View larger version (143K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 3. —Photograph of dissection in specimen 4 shows proximally (curved arrow) that extensor pollicis longus (EPL) crosses over extensor carpi radialis tendons. More distally (small black arrows), EPL reaches base of metacarpal head where it joins extensor pollicis brevis tendon (arrowheads) and is covered by dorsal reinforcements (r). EPL tendon (large black arrow) continues distally.

Sonography of Cadaveric Specimens
The EPL tendon was located either on the top of Lister's tubercle or on the ulnar side of the latter (Figs. 4A and 4B). From this position, the EPL tendon showed a 50° oblique course toward the base of the first metacarpal bone. In the longitudinal plane, a 2-mm-thick structure with a fibrillar pattern was recognized [8]. On sonography, the EPL tendon was visualized in a transverse plane by rotating the probe 90° from the previously described position. When the described position of the ultrasound probe is used along the transverse aspect of the tendon, the EPL tendon appears either hypoechoic or hyperechoic depending on the obliquity of the ultrasound beam. The extensor tendons of the second digit also were depicted clearly [9]. Before and during all phases of dissection, the EPL tendon was clearly identifiable in the longitudinal and transverse planes.

View larger version (115K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 4A. —Sonograms of specimen 3. Transverse sonogram of dorsal aspect of radius at level of Lister's tubercle (Li) shows that extensor pollicis longus tendon (calipers) is located on top of Lister's tubercle.

View larger version (76K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 4B. —Sonograms of specimen 3. Sonogram obtained before dissection in oblique imaging plane extending from Lister's tubercle (L) to base of first metacarpal shows fibrillar structures of extensor pollicis longus tendon (arrowheads). Left side of image is caudal; right side, cranial.

Clinical Study
The clinical and sonographic findings (Figs. 5A, 5B, and 6) for five patients who underwent sonography and open wrist surgery are shown in Table 1. At surgery, the patients were placed in the dorsal decubitus position with the involved arm on the hand table. Surgery was performed by one of four surgeons experienced in wrist and tendon surgery. The surgeons were aware of the findings in the sonography report.

View larger version (95K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 5A. —Sonograms of 36-year-old woman with extension deficit of thumb (patient 2 in Table 1). Left side of images is proximal; right side, distal. In longitudinal plane, hypoechoic area with fusiform (R) aspect (between stars) is seen at normal position of extensor pollicis longus (EPL) tendon.

View larger version (90K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 5B. —Sonograms of 36-year-old woman with extension deficit of thumb (patient 2 in Table 1). Left side of images is proximal; right side, distal. In longitudinal plane, transition zone (asterisk) between rupture (R) and normal fibers (arrows) is shown at base of first metacarpal bone.

View larger version (74K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 6. —Sonogram in 37-year-old man with extension deficit of thumb (patient 3 in Table 1). Longitudinal view of extensor pollicis longus (EPL) shows empty tendon sheath of EPL (r). Area of rupture (between stars) is indicated. Deep in relation to ruptured EPL tendon, extensor carpi radialis tendon (e) is shown. Left side is proximal; right side, distal.

A ruptured EPL tendon was identified in all patients. All patients underwent a tendon transfer procedure. The hypoechoic tubular area seen on sonography corresponded to an empty tendon sheath filled with fluid, hemorrhage, or scar tissue at surgery. Retraction was measured and correlated with findings on sonography.

Discussion

Top Abstract Introduction Materials and Methods Results Discussion References

 
Clinical findings of proximal ruptures of the EPL tendon usually include pain and the inability to extend the thumb. The latter finding, however, may be difficult to elicit because of associated conditions, such as wrist fracture and arthritis. When Lister's tubercle is used as a bony landmark, the normal position of the tendon can be identified easily.

Although MRI has been used in the evaluation of wrist tendons, in our experience this technique is not suited for the diagnosis of EPL tendon abnormalities. This is related to the finding that the EPL tendon at the level of the wrist has a 50° oblique orientation relative to the routine MRI planes that results in significant magic angle effect artifact. This limitation renders accurate MRI evaluation of the tendon difficult even with the use of dedicated surface coils. In addition, the EPL tendon, in contradistinction to the adjacent tendons, is flat at its crossing point over the extensor carpi radialis brevis and longus tendons; even in a normal setting, the EPL tendon may be difficult to depict on MRI. In our experience, the use of surface coils and special imaging planes may yield good results on MRI but is more time-consuming.

We explored the use of sonography to assist in the diagnosis of proximal rupture of the tendon of the EPL. In contradistinction to proximal ruptures, the EPL tendon also may be avulsed from the distal phalanx, a situation similar to mallet finger. Our results indicate that sonography of the wrist can be used to show proximal rupture of the EPL tendon and can aid in the assessment of the amount of retraction of the tendon ends. Accurate diagnosis of a tear of the EPL tendon is important, so proper surgical treatment may be prescribed. In addition, sonography may depict additional findings in the adjacent tendons [9].

Sonography results in this study were similar in all patients. We found in five consecutive cases of rupture of the EPL tendon the normal tendon was replaced by a tubular hypoechoic or slightly heterogeneous area at the level of the proximal carpal row. As shown intraoperatively, the hypoechoic area corresponded to a synovial sheath distended by fluid, hemorrhage, or scar tissue. The tendon ends were retracted proximally and distally. Tenosynovitis of the extensor carpi radialis brevis and longus tendons was an additional finding in three cases. On the basis of anatomic descriptions, this finding may be expected given the fact that at the intersection there is a communication between the synovial sheets of the EPL tendon and the extensor carpi radialis tendons [10, 11].

Sonography aided in assessing the amount of retraction of the tendon ends, as shown by the findings at surgical exploration. When the diagnosis of an EPL tear is confirmed, surgical therapy is mandatory to restore thumb and hand function. If retraction of the tendon ends is limited, a direct suture is performed. However, if retraction is significant, a graft procedure is unavoidable. Hence, most typically the extensor indicis proprius tendon is sectioned and is reattached to the distal stump of the EPL tendon [2, 8].

Limitations of this study include the small number of clinical cases. This limitation is related primarily to the fact that the use of sonography for the preoperative assessment of EPL tendon tears has not been addressed previously, to our knowledge, in the surgical or radiology literature. Additional studies are required to confirm our findings in a larger number of patients. The number of anatomic specimens also was limited, and the specimens used for our study may not represent all possible anatomic variations. In addition, neither intra- nor interobserver variability was calculated because of the limited number of patients. All radiologists, however, were experienced in musculoskeletal sonography. The use of embalmed specimens yielded good results. This is in contradistinction to the situation with MRI-anatomic correlation for which fresh specimens are better [12, 13].

In conclusion, sonography may be used to diagnose EPL tears and assess the amount of tendon retraction. In addition, the status of the tendons that may be used as a graft, such as the extensor indicis proprius tendon, may be evaluated. A characteristic hypoechoic or slightly heterogeneous tubular area was observed at the normal position of the torn EPL tendon. Tenosynovitis of the extensor carpi radialis tendons, related to communication with the sheath of the EPL tendon, also may be present.

References

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