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1
Department of Radiology, Warren Grant Magnuson Clinical Center, National
Institutes of Health, Bldg. 10, Rm. 1C660, 10 Center Dr., MSC 1182, Bethesda,
MD 20892-1182.
2
Department of Rehabilitation Medicine, Warren Grant Magnuson Clinical Center,
National Institutes of Health, Bethesda, MD 20892-1182.
3
Division of Biostatistics, National Cancer Institute, National Institutes of
Health, Bethesda, MD 20892-1182.
Received June 14, 2001;
accepted after revision August 6, 2001.
Presented at the annual meeting of the American Roentgen Ray Society, New
Orleans, May 1999.
Abstract
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SUBJECTS AND METHODS. Fifteen healthy volunteers and 31 patients (44 tendons) who were clinically suspected of having posterior tibial tendinopathy were prospectively evaluated with MR imaging and sonography.
RESULTS. On MR imaging, the normal tendon was elliptic on cross section and showed low signal intensity on all sequences. Minimal peritendinous enhancement and fluid were seen. On sonography, the tendon showed homogeneous longitudinal echogenic fibers. No flow was seen in or around the tendon. Tendinopathy was characterized by enhancement of the tendon on MR imaging (19/44 tendons); intratendinous flow on color Doppler sonography (16/44 tendons); increase in the anteroposterior diameter causing a rounding of the tendon (18/44 tendons); and inhomogeneity of the tendon (16/44 tendons on MR imaging and 21/44 tendons on sonography). Peritendinosis was characterized by peritendinous enhancement on MR imaging (29/44 tendons); flow on color Doppler sonography (20/44 tendons); and increased soft tissue (20/44 tendons on MR imaging and 27/44 tendons on sonography). When compared with MR imaging, the sensitivity and specificity of sonography for diagnosing tendinopathy were 80% and 90%, respectively, and for diagnosing peritendinosis were 90% and 80%. Addition of abnormal size to the structural abnormality criteria did not improve diagnostic ability.
CONCLUSION. Sonography can be useful as the initial imaging study in evaluating abnormalities caused by posterior tibial tendinopathy.
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Our study was designed to evaluate the appearance of the normal and abnormal posterior tibial tendon on MR imaging and high-resolution sonography with color and power Doppler imaging, and to determine if sonography is as accurate as MR imaging in diagnosing posterior tibial tendinopathy.
MR imaging cannot further categorize tendon abnormalities once they are recognized. When inhomogeneity of the tendon is seen on MR imaging, it could be due to tendinitis, partial tear, degeneration, or other tendinopathy. All these entities fall into a spectrum of disorders, and it is difficult to determine when one ends and the second begins [8,9,10]. Hence, all these entities should be considered in the differential diagnosis. One can speculate that inhomogeneity alone without enhancement is indicative of partial tear or a chronic tendinopathy, but those are not diagnosable on MR imaging. Therefore, we did not attempt to classify these entities but rather labeled all intratendinous abnormalities "tendinopathy."
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Thirty-one consecutive patients (44 tendons) who were clinically suspected of having posterior tibial tendinopathy (by the same criteria used for the healthy volunteers), and who consented to participate in this protocol, were then evaluated. The patients, 25 women and six men, ranged in age from 20 to 73 years (mean, 43 years). Nineteen patients had inflammatory arthritis, 11 had idiopathic tendinitis, and one had connective tissue disease. Of those with inflammatory arthritis, seven had rheumatoid arthritis and 12 had other forms of inflammatory arthritis such as psoriasis or Reiter or other seronegative forms of arthritis. MR imaging and real-time sonography were performed using the same parameters and techniques used for the healthy volunteers.
Imaging
MR imaging was performed on a 1.5-T scanner (General Electric Medical
Systems, Milwaukee, WI). The ankle was placed in a neutral position in a knee
coil. Sagittal images along the plane of the posterior tibial tendon and axial
images perpendicular to that plane were obtained of both ankles using the
following protocol: T1-weighted spin-echo images (TR/TE, 400/10; 3-mm section
thickness; 192 x 256 matrix, 1 signal acquired) and fat-suppressed fast
spin-echo T2-weighted images (TR/effective TE, 4000/105; section thickness, 3
mm; echo-train length, 4; matrix, 192 x 256; signals acquired, 2). After
the IV injection of gadolinium (0.1 mmol/kg), spoiled gradient-echo MR images
with fat suppression (150/6; flip angle, 90°; matrix, 192 x 256;
signals acquired, 2) were obtained in the axial and sagittal planes.
Sonography was performed using a small-parts 10-MHz transducer (Advanced Technology Laboratory, Bothell, WA). The patient was in a prone oblique position and the ankle was slightly elevated on a rolled towel so that the posterior tibial tendon and flexor digitorum longus tendon could be optimally evaluated. The posterior tibial tendon was first identified just posterior to the medial malleolus. The tendon was followed along its entire length to the insertion into the navicular tuberosity. The anteroposterior diameter was measured on the longitudinal view of the posterior tibial tendon at approximately 1 cm distal to the tip of the medial malleolus. The transducer was then turned 90°, and transverse scans and measurements of the transverse diameter of the posterior tibial tendon were obtained. The flexor digitorum longus tendon (which lies slightly posterior to the posterior tibial tendon) was then evaluated in a similar manner. Anteroposterior and transverse diameters of the posterior tibial tendon and the flexor digitorum longus tendon were measured 1 cm distal to the medial malleolus. Color and power Doppler sonography were then used to evaluate both tendons and the peritendon area. The Doppler gain was set so that there was no flow in the cortical bone.
The MR images and sonograms were interpreted by two experienced radiologists who agreed on the findings. They were unaware of the results of the other imaging study and of the clinical findings.
On MR imaging, recorded measurements and observations included the diameters of the posterior tibial and flexor digitorum longus tendons; the signal intensities of the tendons; the presence of enhancement of the tendons on contrast-enhanced images; the presence of peritendinous fluid or soft tissue; and the presence of enhancement of the peritendon area on contrast-enhanced images.
On sonography, evaluation included the diameters of the posterior tibial and flexor digitorum longus tendons; echogenicity of the tendons; presence of flow within the tendons on color and power Doppler imaging; the presence of fluid and hypoechoic tissue in the peritendon area; and the presence of flow in the peritendon area on color and power Doppler imaging.
Statistical Methods
Correlations were made between structural abnormalities seen on MR imaging
and those seen on sonography. Comparisons between MR imaging and sonography
were made using individual as well as a combination of structural abnormality
criteria. Correlations using structural and size criteria were also
obtained.
The mean ± a standard deviation of 1.960 of the normal tendon diameters was used as the upper limit of normal to distinguish normal from affected tendons. Deviations between sonography and MR imaging measurements of the same tendons were assessed using the Wilcoxon's rank sum test. Confidence intervals were calculated using the standard Clopper-Pearson method [11].
All analyses were repeated using the generalized estimating equation method to adjust for the correlation between the two ankles of bilaterally affected patients. The p values based on the empiric standard error estimates were in all cases smaller than those reported. Confidence intervals also differed by no more than 2% from the standard results. The SAS version 8 statistical package (SAS Institute, Cary, NC) was used for all analyses.
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The Abnormal Posterior Tibial Tendon
MR imaging.—We studied 31 patients with clinically suspected
tendinosis. Because 13 patients had bilateral clinical findings, a total of 44
affected tendons were studied. Because partial tear cannot be distinguished
from degeneration or tendinitis using imaging criteria
[12], we did not identify
these entities separately but simply labeled them "tendinopathy."
No cases of complete tear were seen.
Contrast enhancement of the tendon (seen in 19/44 [43%] tendons) was the most common finding (Fig. 3A,3B,3C). Inhomogeneity and an increase in signal intensity in the tendon on T1- and T2-weighted images were seen in 16 (36%) of 44 tendons (Fig. 4A,4B). An increase in the anteroposterior dimension of the tendon was seen causing a rounding of the tendon (Table 2). Enhancement of the peritendinous tissue (29/44 [66%] tendons) was characteristic of peritendinosis (Fig. 5A,5B,5C,5D,5E). An increase in soft tissue, which was of low signal intensity on T1-weighted images, was also seen around the tendon (20/44 [45%] tendons). An interesting finding in 11 (25%) of 44 patients was an area of low signal intensity seen in the immediate peritendon area on the T1- and T2-weighted sequences. This area did not enhance on the contrast-enhanced images, although the surrounding peritendon area showed enhancement (Fig. 5A,5B,5C,5D,5E).
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Sonography.—The findings in tendinosis were flow within the tendon on power Doppler sonography and inhomogeneity of the tendon. Flow in the tendon was seen in 16 (36%) of 44 tendons (Fig. 3A,3B,3C). Inhomogeneity with mixed echogenicity and disruption of echogenic fibers was seen in 21 (48%) of 44 tendons. The tendon was also enlarged more prominently in the anteroposterior than the transverse dimension (Fig. 4A,4B,Table 2).
The findings in peritendinosis were increased flow in the peritendon area on power Doppler sonography (20/44 [45%] tendons) and hypoechoic tissue around the tendon (16/44 [36%] tendons) (Fig. 5A,5B,5C,5D,5E).
Statistical Analysis
The affected tendons showed a significant increase in the anteroposterior
dimension when compared with the normal tendons on both MR imaging (p
< 0.00001) and sonography (p < 0.0001) by Wilcoxon's rank sum
test. Likewise, the anteroposterior-to-transverse ratio was increased in the
affected tendons when compared with the normal (p < 0.00001 for MR
imaging and p < 0.0001 for sonography).
Correlation between MR imaging and sonography for structural abnormalities.—For the diagnosis of tendinosis, the two criteria, other than size, used for MR imaging were contrast enhancement and abnormal signal intensity of the tendon. These criteria were compared with sonographic findings of flow in the tendon seen on color Doppler imaging and inhomogeneity of the tendon. For the diagnosis of peritendinosis, the criteria used for MR imaging were contrast enhancement of the peritendinous tissues and an increase in the amount of soft tissue and fluid in the peritendon area. The corresponding criteria used for sonography were flow in the peritendon area on color Doppler imaging and an increase in the amount of soft tissue and fluid in the peritendon area. Table 3 shows the correlation of sonographic and MR imaging findings.
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Analysis using single criteria.—Using MR imaging as the gold standard, the specificities of sonographic findings of flow in and inhomogeneity of the tendon for diagnosing tendinosis were 96% (95% confidence interval [CI], 79-99.9%) and 71% (CI, 50-86%), respectively. The sensitivities were 79% (CI, 54-94%) and 81% (CI, 54-96%), respectively.
The specificities of sonographic findings of increased flow on color Doppler imaging and increased tissue and fluid in the peritendon area for diagnosis of peritendinosis were 100% (CI, 77-100%) and 67% (CI, 45-84%), respectively; and the sensitivities were 69% (CI, 49-85%) and 95% (CI, 75-99.9%), respectively.
Combination of criteria for correlation of MR imaging and sonography of structural abnormalities.—Table 4 shows the number of patients with tendinosis and peritendinosis seen on MR imaging compared with sonography using a combination of criteria. The presence of either enhancement or inhomogeneity of the tendon was used to diagnose tendinosis. The presence of either enhancement or increased soft tissue in the peritendon area was used to diagnose peritendinosis.
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On the basis of MR imaging, 7% of patients had tendinosis alone, 20% had peritendinosis alone, 45% had both, and 27% had neither. Thus, the presence of tendinosis was positively correlated with the presence of peritendinosis (p < 0.01); tendinosis was seen in 69% of patients with peritendinosis but in only 20% of patients without peritendinosis; conversely, peritendinosis was seen in 87% of patients with tendinosis and in 43% of patients without tendinosis.
Tables 5 and 6 compare separately the MR imaging and sonographic findings for tendinosis and peritendinosis.
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The prevalence of tendinosis as seen on MR imaging was 52%. The sensitivity of sonography for diagnosing tendinosis was 83%, the specificity was 90%, the positive predictive value was 90%, and the negative predictive value was 83%.
The prevalence of peritendinosis as seen on MR imaging was 66%. Sensitivity of sonography for diagnosing peritendinosis was 86%, specificity was 80%, positive predictive value was 89%, and negative predictive value was 75%.
Correlation of tendon size and structural abnormalities.—Using 0.43 (mean ± 1.960 SD) as the upper limit of normal for tendon diameter ratios, an abnormal tendon size was found to be strongly associated with tendon structural abnormalities (i.e., flow or inhomogeneity) (p = 0.0018 by Fisher's exact test) on sonography. Seventy-eight percent of tendons enlarged on sonography showed inhomogeneity or flow on Doppler imaging, whereas only 27% of normal-sized tendons showed inhomogeneity or flow.
The added diagnostic value of combining tendon size and structural features into the sonographic diagnostic criteria was assessed by comparing the sensitivities and specificities based on size and structural features alone with those based on size and structural features in combination (when abnormal size and abnormal structure were both present and when either abnormal size or abnormal structure was present). As seen in Table 7, criteria based on size and structural features combined showed only slight improvement in diagnostic performance over criteria based on structural features alone, but combined criteria had greater sensitivity and specificity than criteria based on size alone.
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Evaluation of the flexor digitorum longus tendon.—Because the posterior tibial tendon is in close proximity to the flexor digitorum longus tendon, it was difficult to clinically distinguish posterior tibial tendon abnormalities from those involving the flexor digitorum longus tendon. However, imaging could distinguish these structures (Table 8).
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Using the analogous combination of criteria as for the posterior tibial tendon, no evidence of tendinosis of the flexor digitorum longus was seen on MR imaging in any patient.
On sonography, flow in the tendon was seen in eight of 44 tendons, and seven of 44 tendons showed inhomogeneity, giving a specificity of 82% (CI, 67-92%) and 84% (CI, 70-93%), respectively, assuming that the findings on sonography are false-positive.
Using the analogous combination of criteria as for the posterior tibial tendon, peritendinosis of the flexor digitorum longus was seen on both MR imaging (25/44 tendons) and sonography (21/44 tendons). The specificity of sonography was 95% (CI, 76-99.9%) for enhancement of the peritendon area and 88% (CI, 68-97%) for peritendinous soft tissue. The sensitivities were 74% (CI, 5-90%) and 85% (CI, 62-97%), respectively.
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MR imaging, with its superior soft-tissue contrast resolution and multiplanar capabilities, is the imaging procedure of choice for evaluating the musculoskeletal system [8,9,10, 17,18,19,20,21,22]. Sonography is becoming an increasingly important imaging modality for evaluating musculoskeletal disorders because of its easy availability, noninvasiveness, lack of ionizing radiation, multiplanar and real-time capabilities, and low cost. Higher resolution transducers and the dynamic real-time capability of sonography make it attractive for evaluating muscles and tendons. Because of its superficial location, the posterior tibial tendon is particularly amenable to evaluation with sonography [23,24,25,26,27].
Enhancement of the tendon and peritendon area on MR imaging and increased flow on color-flow Doppler sonography were the most useful features for diagnosing tendinosis and peritendinosis. Other criteria that are useful, but with lower specificity and sensitivity, are, for tendinosis, a change in signal intensity of the tendon on MR imaging and inhomogeneity of the tendon on sonography; and for peritendinosis, increased soft tissue and fluid in the peritendon area. Using the combination criteria of flow or inhomogeneity of the tendon for diagnosing tendinosis yielded the best positive predictive value (90%) and negative predictive value (83%) for sonography compared with MR imaging. The addition of abnormal size of the tendon as a criterion did not improve the sensitivity, specificity, or predictive values for the diagnosis of tendinosis. Likewise, the combination criteria of flow or increased soft tissue in the peritendon area for diagnosing peritendinosis yielded the best positive predictive value (89%) and negative predictive value (75%) for sonography.
We accepted the MR imaging findings in tendinosis and peritendinosis as the gold standard. Positive findings seen on sonography and not seen on MR imaging were therefore labeled false-positive. However, it is possible that such findings are in fact true-positive findings. This possibility would be difficult to verify because such a possibility would require a gold standard other than MR imaging.
Both MR imaging and sonography could distinguish tendinosis from peritendinosis. This distinction is important because a more rigorous treatment is needed if the tendon is involved because it might lead to partial and complete tear. Imaging also provides an insight into the pathophysiology of the disease process. Tendinosis and peritendinosis were often seen together (45% of cases), which is readily explained by a common causal mechanism of injury to the two sites. It was more common to see peritendinosis by itself without tendinosis (20% of cases) than tendinosis alone without peritendinosis (7%), possibly because the tendon is stronger than the peritendinous tissue and more resistant to injury.
Another area in which the imaging studies helped was in distinguishing flexor digitorum longus tendon abnormalities from posterior tibial tendon abnormalities. In this series, no patient had abnormalities of the flexor digitorum longus tendon seen on MR imaging, although peritendinous abnormalities around the flexor digitorum longus were seen. Often, when diffuse swelling of the ankle is present, separating the two entities clinically is difficult because of the close proximity of the posterior tibial and the flexor digitorum longus tendons.
An abnormally low-signal-intensity area was seen in patients with peritendinosis on the T1- and T2-weighted images. This area did not enhance on the contrast-enhanced images. It is unclear what the exact cause of this low-signal-intensity area is because we have not yet obtained a biopsy of this area. Some possibilities are thickening of the synovium, fibrosis, or calcification in the peritendon region, because patients with posterior tibial tendinosis often have arthritis and chronic synovitis with superimposition of acute episodes of tendonitis.
An inherent drawback of both these imaging modalities is an inability to further categorize tendon abnormalities. Inhomogeneity of the tendon on MR imaging could be due to tendinitis, partial tear, degeneration, or other tendinopathy. All these entities fall into a spectrum of pathologic disorders, and it is difficult to determine when one ends and the second begins [8,9,10]. One can speculate that inhomogeneity alone without enhancement is indicative of partial tear or chronic tendinopathy, but those disorders cannot be diagnosed on MR imaging, and sonography does not help in resolving this problem.
In summary, MR imaging findings in clinically suspected tendinosis and peritendinosis correlated closely with findings on sonography. Although abnormality in the size of the tendon was a useful feature to diagnose tendinosis, evaluations of structural abnormalities of the tendon were more useful. We recommend that sonography be used as an initial imaging modality for the diagnosis of posterior tibial tendinopathy.
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