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Musculoskeletal Imaging |
1 From the Department of Radiology, University of California, San Diego, Veterans Affairs Medical Center, 3350 La Jolla Village Dr, San Diego, CA 92161 (O.H., C.B.C., N.L., D.T., R.D.B., D.R.), and the Division of Orthopaedic Surgery, Scripps Clinic and Research Foundation, La Jolla, Calif (M.J.B.). From the 1999 RSNA scientific assembly. Received August 25, 1999; revision requested September 29; revision received January 5, 2000; accepted January 17. Supported by Veterans Affairs grant SA-360. Address correspondence to D.R. (e-mail: dresnick@ucsd.edu).
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONMATERIALS AND METHODS RESULTS DISCUSSIONREFERENCES |
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MATERIALS AND METHODS: Three groups of cadaveric fingers underwent computed tomography (CT), magnetic resonance (MR) imaging, and ultrasonography (US). The normal anatomy of the pulley system was studied at extension and flexion without and with MR tenography. Pulley lengths were measured, and anatomic correlation was performed. Pulley lesions were created and studied at flexion, extension, and forced flexion. Two radiologists reviewed the studies in blinded fashion.
RESULTS: MR imaging demonstrated A2 (proximal phalanx) and A4 (middle phalanx) pulleys in 12 (100%) of 12 cases, without and with tenography. MR tenography showed the A3 (proximal interphalangeal) and A5 (distal interphalangeal) pulleys in 10 (83%) and nine (75%) cases, respectively. US showed the A2 pulley in all cases and the A4 pulley in eight (67%). CT did not allow direct pulley visualization. No significant differences in pulley lengths were measured at MR, US, or pathologic examination (P = .512). Direct lesion diagnosis was possible with MR imaging and US in 79%–100% of cases, depending on lesion type. Indirect diagnosis was successful with all methods with forced flexion.
CONCLUSION: MR imaging and US provide means of direct finger pulley system evaluation.
Index terms: Computed tomography (CT), comparative studies, 43.12111, 43.12112, 43.12115 • Fingers and toes, injuries, 43.489 • Hand, CT, 43.1211 • Hand, MR, 43.121411, 43.121412, 43.121413, 43.121415 • Hand, US, 43.1298 • Ultrasound (US), tissue characterization, 43.1298, 43.12988
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODS RESULTS DISCUSSIONREFERENCES |
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The diagnosis, location, and extent of pulley system lesions are of great importance in managing and predicting functional sequelae (6–10). Although several investigators (11–22) have studied ultrasonography (US), computed tomography (CT), and magnetic resonance (MR) imaging in the evaluation of flexor tendon abnormalities, diagnosis of lesions of the pulley system has been made only indirectly with the detection of a gap between the flexor tendon and the bone on sagittal CT scans and MR images, a finding referred to as the bowstring sign. This sign usually reflects an extensive abnormality of the pulley system that leaves limited or partial lesions of the system virtually undetected by means of indirect methods of visualization. In addition, these images must be obtained with the finger in flexion or forced flexion, which can prove challenging with regard to patient positioning and motion artifact.
The purpose of this study was twofold: to describe the normal anatomy of the pulley system with MR imaging, CT, and US by using gross anatomic correlation as a standard of reference and to define the diagnostic criteria used to identify abnormalities of the pulley system by using these imaging modalities.
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MATERIALS AND METHODS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODS RESULTS DISCUSSIONREFERENCES |
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The annular pulleys are of biomechanical importance in preventing tendon excursion during digital flexion, whereas the cruciate pulleys provide the necessary flexibility for approximation of the annular pulleys at flexion while maintaining the integrity of the flexor sheath. The primary function of the flexor pulley system in the fingers is to convert the available linear translation and force in the muscle-tendon unit into rotation and torque at the finger joints. Loss of all or part of the flexor tendon pulley system may have a significant effect on digital performance.
Study results have shown that the A2 pulley is the strongest, followed by the A1 and A4 pulleys (23–25). The pattern of injury follows a progressive and predictable pattern: Disruption begins at the distal part of the A2 pulley and progresses from partial to complete rupture, which is followed by involvement of the A3, A4, and, in rare situations, A1 pulleys.
Three groups of cadaveric hands were studied. The first and second groups had no known finger abnormalities and were used to depict the normal anatomy of the flexor tendon pulley system; the third group was composed of specimens with surgically created lesions of the pulley system. In all three groups, MR imaging, CT, and US were performed with the hands in a pronated position. Images were acquired with the fingers in extension and as close as possible to the following flexed position: metacarpophalangeal joint in full extension, with the proximal interphalangeal joint in 60° of flexion and with the distal interphalangeal joint in 10° of flexion. Only the second through fourth digits were investigated, since they were the most common sites of injury (6,10,25).
Anatomic Study
Eight hands were harvested from four fresh frozen cadavers (three men and one woman, 68–78 years of age at death [mean age at death, 73.5 years]). The specimens were divided into two groups of four hands each (12 fingers per group), which subsequently were evaluated with MR imaging, CT, and US without (group I) and with (group II) opacification of the tendon sheaths with contrast material (MR tenography).
MR Tenography
With fluoroscopic guidance, a 25-gauge needle was inserted into the volar surface of the finger and was advanced, 1 cm distal to the level of the metacarpophalangeal joint, into the flexor tendon sheath of the finger (group II). Subsequently, 0.8 mL of a solution of 1 mL gadopentetate dimeglumine (Magnevist; Schering, Berlin, Germany) diluted with 250 mL of normal saline and 1 mL of iodinated contrast material (iohexol, Omnipaque; Nycomed Amersham, Princeton, NJ) was injected into the tendon sheath to verify accurate needle positioning and distend the tendon sheath.
Imaging
MR imaging was performed with a 1.5-T clinical system (Signa; GE Medical Systems, Milwaukee, Wis) with a dedicated phased-array wrist coil. T1-weighted spin-echo (repetition time, 400 msec; echo time, 22 msec [400/22]) and fast spoiled gradient-recalled echo (400/12; flip angle, 20°) imaging in the transverse and sagittal planes were performed in group I (n = 12). Fat-suppressed T1-weighted spin-echo (400/12) imaging in the transverse and sagittal planes was performed in group II (n = 12) after opacification of the tendon sheaths (section thickness, 3 mm; field of view, 8 x 8 cm; matrix, 512 x 256; with two signals acquired).
Helical CT (PQ 5000; Picker International, Cleveland, Ohio) was performed in both groups (120 mAs; 150 kVp; section thickness, 2 mm; incremental table movement, 1 mm). Images were displayed by using soft-tissue windows.
Gray-scale US was performed by using a 12-MHz transducer (HDI 5000; Advanced Technical Laboratories, Bothell, Wash) in all specimens in both groups by an investigator (O.H.) who was experienced in performing musculoskeletal US. All specimens were studied in sagittal and transverse planes. The study of flexed fingers was limited to the transverse plane because the transducer was too wide for accurate analysis in the sagittal plane.
Imaging-Anatomic Correlation and Analysis
After imaging, all cadaveric specimens were frozen for 24 hours at -60° C, and 3-mm-thick sections were obtained with a band saw in the transverse (four hands, two in each group) and sagittal (four hands, two in each group) planes.
Two musculoskeletal radiologists (O.H., C.B.C.) randomly analyzed all specimen images, in accordance with imaging technique. First, all MR images in all fingers were evaluated in a random order and were followed by randomly selected CT and US images and anatomic sections of the fingers. Images and anatomic sections were reviewed with consensus. The Pearson correlation test was performed to evaluate any significant differences between the measurements obtained with each imaging technique, as compared with the gross anatomic sections. A P value of less than .05 was considered to indicate a significant difference.
Simulated Pulley Lesions
To evaluate the imaging of abnormalities in the pulley system, an additional 11 hands (group III) were harvested from six fresh frozen cadavers (four men and two women, 57–81 years of age at death [mean age at death, 71 years]). As before, only the second through fourth fingers (n = 33) in each hand were analyzed. Partial and complete lesions were created in various combinations to simulate well-documented mechanisms of injury with regard to technique and progression (6,25) (Table 1). Complete lesions constituted total longitudinal pulley transection, whereas partial lesions involved the transection of approximately 10 mm of the distal portion of the pulley. The latter were imposed on the A2 pulley alone. All lesions were created by an orthopedic surgeon (M.J.B.) who specialized in procedures in the hand.
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To simulate active tendon digital flexion, preparation was made to load each of the digital flexor tendons. At the proximal portion of each specimen, a volar incision was made at the level of the distal forearm and wrist to allow identification of the flexor digitorum profundus (FDP) and flexor digitorum superficialis tendons of each digit. The flexor tendons were sutured together with 3-0 vicryl suture in the distal forearm to produce a single common tendon to each digit, which could be loaded to produce digital flexion. A 2-mm nylon cord then was attached to the flexor tendon complex in each digit; this provided a means of loading the tendon with weight (to parallel active muscle contraction), which resulted in finger flexion. The volar forearm incision was closed with 4-0 nylon suture by using a running, locking suture pattern.
Imaging
In all cases, imaging was performed before and within 5 days after lesion creation. US, CT, and MR imaging of the fingers were performed with the same nonenhanced technique described previously. To simulate forced flexion of the fingers at CT and MR imaging, the fingers were taped in flexion, and traction was applied to the flexor tendons, with a 500-g weight attached to the common flexor tendon complex of each finger. No opacification of the tendon sheath was performed because lesion creation led to disruption of the sheath.
Because of the potentially interactive nature of US, an attempt was made to maximize forced flexion, which closely approximates the clinical situation. Pressure was applied to the common flexor tendon complex as described previously, with simultaneous counterpressure at the fingertip to extend the finger. During this time, the operator performed US with the transducer in the concavity of the finger, at the level of the distal third of the proximal phalanx.
Analysis
Images obtained before lesion creation with each of the three modalities were reviewed, with consensus of the two musculoskeletal radiologists to determine whether or not the pulleys could be visualized. Then the images in those fingers with lesions were reviewed separately by the same musculoskeletal radiologists, who knew that lesions had been created but did not know their number or location. The following parameters were chosen for evaluation on the basis of the results of the initial anatomic study: direct signs related to the appearance of the A2 and A4 pulley system (visualized and normal in appearance vs visualized and disrupted or nonvisualized), and evaluation of the pulley system by using indirect quantitative methods (measurements of the distance between the dorsal edge of the FDP tendon and the bone in the sagittal plane at the level of the distal two thirds of the proximal phalanx, with the fingers in extension, flexion, and forced flexion, ie, the bowstring sign).
Measurements were obtained electronically (Fig 2) by using calipers provided with the Windows Advantage version 2.0 software (GE Medical Systems) at the workstation. First, the Pearson correlation test was performed to evaluate any significant differences among the measurements obtained with the different modalities (MR imaging, CT, and US). Subsequently, the measurements obtained with each modality were assessed separately by performing analysis of variance and post-hoc Tukey tests to detect any significant differences among the positions (extension, flexion, and forced flexion) with regard to different lesions (A2 + A3 + A4, A2 + A3, total A2, and partial A2). Again, a P value of less than .05 was considered to indicate a significant difference.
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RESULTS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODS RESULTS DISCUSSIONREFERENCES |
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US depicted the A2 pulleys in the sagittal plane in 12 (100%) of 12 cases. The pulleys appeared as focal hyperechoic thickenings of the sheath that were in the proximal third of the proximal phalanx. Again, the distal end of the pulley was easily recognizable because of its abrupt transition in thickness compared with the normal sheath (Fig 5). The mean length of the A2 pulley at US was 16.3 mm. US depicted the A4 pulley, which appeared as subtle focal hyperechoic thickening of the sheath at the level of the midportion of the middle phalanx, in eight (67%) of 12 cases. The A4 pulley had a mean length of 5.8 mm. Transverse imaging did not allow further detection or characterization of the A4 pulleys. As with MR imaging, the A3 and A5 pulleys were not seen routinely.
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Simulated Pulley Lesions (group III): Imaging
Complete lesions.—Results are summarized in Tables 4–7. On MR images, the A2 and A4 pulleys were visualized in 33 (100%) and 30 (91%) of the 33 fingers, respectively, in the sagittal and/or the transverse plane with T1-weighted spin-echo imaging and gradient-recalled echo imaging. The A3 and A5 pulleys were never visualized. After the creation of complete lesions with total medial transection, diagnosis was possible with direct visualization of the disrupted sheath on the transverse images (Fig 7) and/or with nonvisualization of the involved pulleys on the sagittal images. Diagnosis with direct imaging signs was possible in all cases in which the A2 and/or A4 pulley was visualized before lesion creation.
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US initially allowed direct visualization of the A2 pulleys in all cases. After lesion creation, images obtained in the sagittal plane demonstrated the absence of the distal part of the A2 pulleys. Again, the measurements of the distance between the FDP tendon and the bone showed a minimal tendinous gap at forced flexion alone; such measurements had no significance.
Statistical Analysis
MR imaging and US proved equally matched for the detection of direct signs of partial and complete lesions of the finger pulley system. With regard to the detection of indirect signs of pulley lesions, each imaging modality offered accurate gap measurements between the FDP tendon and the bone in all finger positions, with no significant difference between measurements derived with the various techniques. For the detection of indirect signs of partial A2 lesions, no significant gap was present in any position. For the detection of indirect signs of all complete lesions, all provocative finger positions yielded a significant change in the gap between the FDP tendon and the bone; this suggested the diagnosis of a complete pulley lesion (the gap present with the finger in forced flexion (P < .05) was significantly greater than the gap with the finger in flexion (P < .05), which was significantly greater than the gap with the finger in extension).
Among lesion types, a comparison of the gap measurements in extension did not show any significant differences, except that the partial A2 lesion gap was significantly smaller than the complete A2 + A3 + A4 lesion gap (P < .05). In flexion, the gap observed in the partial A2 lesions was significantly smaller than that observed in the other three lesion types. At forced flexion, all differences between lesion types became significant (the A2 lesion gap in partial pulley lesions was smaller than that in the complete A2 lesions, and the gap in the complete A2 lesions was smaller than that in either a complete A2 + A3 or a complete A2 + A3 + A4 lesion). There were no significant differences between the measured gaps in the complete A2 + A3 lesions and those in the complete A2 + A3 + A4 lesions.
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DISCUSSION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODS RESULTS DISCUSSIONREFERENCES |
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Anatomic Study
Our results indicate that normal A2 and A4 pulleys can be identified and localized accurately by using conventional MR imaging. T1-weighted spin-echo imaging and fast spoiled gradient-recalled echo imaging were equally successful in depicting the normal pulleys. The transverse plane proved more reliable than the sagittal plane for pulley depiction and offered optimal visualization of the insertion of the pulley system into adjacent bone, thereby increasing the ease of identification of the pulleys.
Identification of the A3 and A5 pulleys also was possible but required a more elaborate technique such as MR imaging with contrast material distention of the tendon sheath (ie, MR tenography). Although MR tenography proved to be an elegant method of analysis of the pulley system, knowledge of both the pattern and clinical importance of injury to the pulley system suggests that information regarding the A2 and A4 pulleys, as opposed to the A3 and A5 pulleys, is critical.
With US, the A2 and A4 pulleys were identified readily in both imaging planes and appeared as focal hyperechoic thickenings of the tendon sheath. The distal end of the A2 pulley, the thicker part of the pulley (1), always was identified easily. The difficulty in the identification of the A4 pulley (compared with the A2 pulley) with US but also with MR imaging can be explained by the fact that the A4 pulley constantly is much smaller (6.4-mm length in our study) and thinner than the A2 pulley. Moreover, as specified previously, the length of the pulley is directly proportional to the length of the finger (1,2). This explains why the A4 pulley generally is difficult to identify in the index finger or a small hand. This also explains the impossibility of detection of the A3 and A5 pulleys with both US and conventional MR imaging, as these pulleys are thin (thinner than the A4 pulley) and do not have an osseous insertion site. At CT, only the gross morphology of the flexor tendons was depicted. These findings have significant implications with regard to the evaluation of abnormalities of the flexor tendon, which indicates that conventional imaging techniques allow accurate and reliable direct evaluation of the pulley system of the flexor tendons. In addition, such evaluation obviates secondary diagnostic maneuvers, which can prove difficult to perform, owing to patient motion and inconsistencies in patient positioning.
Simulated Pulley Lesion Study
The second purpose of this study was to define the diagnostic criteria related to the identification of abnormalities of the pulley system by using different imaging modalities. With conventional MR imaging, the direct diagnosis of abnormalities of the A2 pulley was possible in all cases (100%), with either direct visualization of the disrupted pulley in the transverse plane or nonvisualization of the pulley in the sagittal plane. In the A4 pulley, direct diagnosis of an abnormality was possible in 30 (91%) of the 33 cases. If the A4 pulley was not identified on initial MR images, lesion detection also was not possible. At the time of surgical inspection, these pulleys appeared to be thin and delicate.
With US, our results showed that direct diagnosis of abnormalities of the A2 and A4 pulleys was possible in 33 (100%) and 26 (79%) of the 33 cases, respectively, which corresponded again to the number of A4 pulleys identified before lesion creation. Thus, MR imaging appeared to be the most accurate in the detection of A4 lesions.
In contrast, all imaging proved successful in the evaluation of indirect signs of pulley system lesions, with no significant differences among modalities. With the three modalities used in our study, the resultant tendinous gap from total pulley lesions always was maximum and significantly greater at forced flexion than at flexion or extension. It was not unexpected that the tendinous gap at forced flexion increased significantly in proportion to the number of disrupted pulleys. This gap was 5–8 mm for complete combination lesions of multiple pulleys (A2 + A3 or A2 + A3 + A4), 2–5 mm for isolated complete lesions of the A2 pulley, and 0–3 mm for partial A2 lesions. These findings have definite implications for the evaluation of not only the presence but also the extent of the lesions. Moreover, by considering the data regarding the evaluation of direct and indirect findings, a distinction between partial and total A2 lesions is possible. With nonvisualization of the A2 pulley in the evaluation of direct signs of pulley lesions, a tendinous gap at forced flexion indicates a total lesion, whereas a minimal tendinous gap indicates a partial lesion.
Given our findings, MR imaging and US appear promising with regard to the detection of direct signs of complete or partial pulley lesions without provocative finger positioning. This might be helpful in current practice because it would reduce motion artifacts caused by forced flexion, which currently are one of the major limitations of MR imaging for the detection of pulley lesions. The diagnosis of pulley lesions at an early stage (partial A2 lesion) also is of clinical importance because treatment options for partial versus total lesions are different (ie, conservative therapy for partial lesions vs open surgery for total lesions). In addition, diagnosis and treatment at an early stage will prevent the progression of lesions and decrease the risk of long-term complications that are associated with fixed finger contracture.
This study had several limitations. First, it appears that the ideal method for complete identification of the A2, A3, A4, and A5 pulleys is MR imaging with tenography. This technique is not available routinely and would not appear to be valuable in cases of pulley disruption, owing to the inevitable associated disruption of the tendon sheath. This limitation, however, has little consequence because the functionally important A2 and A4 pulleys are seen well with routine MR imaging or US. Second, although we made every possible effort to re-create a physiologically and clinically accurate model of abnormalities of the tendons and tendon sheaths of the finger, the lesions were created surgically in cadaveric specimens. The choice of a cadaveric model allowed us to create a large number of lesions encountered in clinical practice and compare imaging findings in the various patterns of injury. The imaging appearance of long-term pulley disruption may differ between patients because of the development of scar or fibrous tissue. However, such fibrous tissue has already been described in the literature and has not been thought to create any diagnostic difficulty (21). In addition, the cadaveric specimens used in the study were harvested uniformly from an elderly population; this was necessitated by availability. Finally, the quality of the MR images obtained in this study may be difficult to reproduce routinely because, even at extension, some motion artifacts may occur. In these cases, transverse images are of particular interest because they allow visualization of the sites of bone insertion.
In summary, our results indicate that the A2 and A4 pulleys can be identified directly with conventional MR imaging and US, while depiction of the A3 and A5 pulleys requires additional techniques such as MR tenography for direct visualization. These findings represent means for the evaluation and direct diagnosis of complete and partial lesions of the pulley system of the flexor tendon system, which may have an effect on the clinical treatment of patients with these injuries.
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ACKNOWLEDGMENTS |
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FOOTNOTES |
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Author contributions: Guarantors of integrity of entire study, O.H., C.B.C., N.L., D.R.; study concepts, D.R.; study design, O.H., D.R.; definition of intellectual content, O.H., D.R.; literature research, O.H., R.D.B.; experimental studies, O.H., N.L., C.B.C., D.T.; data acquisition, O.H., N.L., M.J.B., C.B.C., D.T.; data analysis, O.H., C.B.C., D.R.; manuscript preparation, O.H., C.B.C.; manuscript editing and review, O.H., C.B.C., D.R.
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REFERENCES |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODS RESULTS DISCUSSIONREFERENCES |
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