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Musculoskeletal Imaging |
1 From the Department of Radiology, University of Michigan Medical Center, Taubman Center 2910G, 1500 E Medical Center Dr, Ann Arbor, MI 48109-0326 (D.P.F., J.A.J.); and Department of Radiology, Henry Ford Hospital, Detroit, Mich (P.H., M.T.v.H.). Received August 28, 2000; revision requested October 5; final revision received March 6, 2001; accepted March 9. Address correspondence to D.P.F. (e-mail: fessell@umich.edu).
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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MATERIALS AND METHODS: In part A of this study, sonographic findings (based on reports) in 26 consecutive cases of tears of the Achilles tendon were compared with surgical findings. In part B, the sonograms were blindly and retrospectively evaluated with respect to six sonographic characteristics possibly related to pathologic findings in the tendon, and the characteristics were correlated with surgical findings.
RESULTS: In part A, statistical data regarding the use of sonographic findings to distinguish full- from partial-thickness tears were as follows: sensitivity, 100%; specificity, 83%; accuracy, 92%; positive predictive value, 88%; and negative predictive value, 100%. In part B, tendon thickness (P < .001), posterior acoustic shadowing (P = .007), and tendon retraction (P < .001) were correlated with full-thickness tears. Visualization of fat herniation (P = .051) and of the plantaris tendon (P = .098) demonstrated marginal correlation with full-thickness tears. Echogenicity at the site of the pathologic finding in the tendon showed no significant correlation.
CONCLUSION: Sonography can be used to differentiate full- from partial-thickness tears or tendinosis of the Achilles tendon with 92% accuracy. Undetectable tendon at the site of injury, tendon retraction, and posterior acoustic shadowing demonstrate statistically significant correlation with full-thickness tears.
Index terms: Athletic injuries, 46.489, 46.491 • Tendons, injuries, 46.489, 46.491 • Tendons, US, 46.1298
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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The pathophysiologic characteristics of tendon tears likely represent a spectrum of disease, with tendinosis predisposing to partial tearing and, barring effective treatment, ultimately to complete tendon rupture (4–8). To date, the use of neither sonography nor magnetic resonance (MR) imaging has demonstrated a high degree of differentiation in helping to distinguish partial-thickness tears from tendinosis (8–10). However, this distinction may not be of great clinical importance since a partial-thickness tear or tendinosis, in the absence of a full-thickness tear, is usually initially treated with nonsurgical means (4,11,12).
Although controversial, investigators in several recent articles (1,7,13–17) favor surgical repair of full-thickness tears. Researchers (2–4,18) have reported that more than 20% of full-thickness tears can be missed clinically at initial presentation. Thus, there is a need for a rapid and reliable means of diagnosing full-thickness tears and of differentiating them from less severe pathologic conditions that are usually treated successfully with conservative means. The differentiation of a partial-thickness tear or tendinosis from a full-thickness tear represents a clear dichotomy in the treatment algorithm and provides information that directly affects patient care.
With use of surgical findings as the standard of reference, the purpose of this study was to evaluate the accuracy of sonography for use in differentiating full-thickness tears from partial-thickness tears or tendinosis of the Achilles tendon and to identify sonographic characteristics that could be used to differentiate the two tears and to aid in the diagnosis. To our knowledge, accuracy in the detection of full-thickness tears previously has not been reported for any imaging modality.
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MATERIALS AND METHODS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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From April 1995 through February 1998, the cases of 1,234 consecutive patients who underwent musculoskeletal sonography of the lower extremity (below the knee) were retrospectively evaluated to determine if the patients underwent subsequent surgery involving the Achilles tendon. Thirty-two cases were identified. Cases were excluded according to the following criteria: unavailability of the sonograms (two cases), unavailability of the surgical report (one case), and avulsion at the site of the insertion of the Achilles tendon on the calcaneus (two cases). One case of a normal sonogram with a normal Achilles tendon at surgery was identified. Statistical analysis was not possible with a single normal case. Therefore, this case was also excluded.
Twenty-six cases in 26 patients (17 male and nine female patients) were identified in which sonography was performed for examination of the Achilles tendon, and at subsequent surgery, the tendon was visualized. Mean age at the time of sonography was 40 years, with an SD of 9 years (age range, 14–61 years). The mean time between sonography and surgery was 6.6 days (SD, 9 days) for full-thickness tears and 216 days (SD, 197 days) for a partial-thickness tear or tendinosis.
Part A: Accuracy of Sonography Based on Report Findings in Distinguishing Full- from Partial-Thickness Tears or Tendinosis
The sonographic report findings were used by one author (D.P.F.) to assign cases to two categories: (a) full-thickness tendon ruptures and (b) partial-thickness tears or tendinosis. Full-thickness tears were diagnosed when complete rupture of the Achilles tendon was noted. A partial-thickness tear or tendinosis was diagnosed when increased anteroposterior diameter of the tendon was noted with or without defects in the tendon and when there was evidence of at least some intact tendon fibers. The findings from the surgical reports were also categorized by the same author into one of these two groups, and the sonographic findings were compared with the surgical findings.
A true-positive finding was defined as a full-thickness tear at both sonography and surgery. A true-negative finding was defined as a partial-thickness tear or tendinosis at both sonography and surgery. A false-positive finding was defined as a full-thickness tear at sonography with a partial-thickness tear or tendinosis at surgery. A false-negative finding was defined as a partial-thickness tear or tendinosis at sonography with a full-thickness tear at surgery. Sensitivity, specificity, accuracy, positive predictive value, and negative predictive value for distinguishing a full-thickness tear from a partial-thickness tear or tendinosis were calculated.
Part B: Blinded Retrospective Review of Sonographic Characteristics
To identify sonographic characteristics that may be used to better help in distinguishing partial-thickness tears or tendinosis from full-thickness tears, a musculoskeletal radiologist (J.A.J.), who was experienced in musculoskeletal US and who was blinded to the surgical findings, evaluated the sonograms for the following characteristics: (a) anteroposterior diameter of the tendon in the zone of abnormality, (b) amount of tendon retraction, (c) echogenicity of the tendon in the abnormal area, (d) pre-Achilles tendon (Kager) fat herniation into an area of tendon abnormality, (e) posterior acoustic shadowing from an area of tendon abnormality, and (f) visualization of the plantaris tendon. This musculoskeletal radiologist was the sonographer in five of 26 cases in this study. All cases in which he performed scanning were evaluated at least 1 year prior to the blinded review. The characteristics mentioned before were chosen for evaluation on the basis of our previous experience with musculoskeletal sonography.
Each characteristic was then separately evaluated for statistical correlation with a full-thickness tear, as one category, or a partial-thickness tear or tendinosis, as a second category. A nonparametric exact Wilcoxon rank sum test was used for comparison of the anteroposterior diameter and retraction of the tendon. The 
2 or Fisher exact test was used for all other calculations of probability. Values for the following characteristics were correlated with the presence of a full- or a partial-thickness tear or tendinosis at surgery: anteroposterior diameter of the tendon in the zone of abnormality, amount of tendon retraction, and echogenicity of the tendon in the abnormal area.
The presence of the following characteristics was correlated with the presence of a full- versus a partial-thickness tear or tendinosis at surgery: pre-Achilles tendon (Kager) fat herniation into an area of tendon abnormality, posterior acoustic shadowing from an area of tendon abnormality, and visualization of the plantaris tendon. Logistic regression was also applied to determine if a multivariate model of the characteristics produced an acceptable fit for predicting the type of tear. Odds ratios, estimated with univariate logistic regression, were used to summarize the association of partial- or full-thickness tears for each variable.
Echogenicity was categorized as predominantly anechoic or predominantly isoechoic or hypoechoic relative to the echogenicity of normal muscle. Three patients had posterior acoustic shadowing owing to calcification (identified at sonography). Shadowing from calcification could obscure shadowing from the ends of the torn tendon. Calculations regarding shadowing were performed with both inclusion and exclusion of these three patients.
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RESULTS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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Part A: Accuracy of Sonography Based on Report Findings in Distinguishing Full- from Partial-Thickness Tears or Tendinosis
With the use of sonography, sensitivity was 100% (95% CI: 81%, 100%), specificity was 83% (CI: 52%, 98%), accuracy was 92% (CI: 75%, 99%), positive predictive value was 88% (CI: 62%, 98%), and negative predictive value was 100% (CI: 74%, 100%) in distinguishing full- from partial-thickness tears or tendinosis (Figs 1, 2) (Table 1). There were two false-positive findings (full-thickness tear at sonography with a partial-thickness tear or tendinosis at surgery) and no false-negative findings.
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There were two false-positive findings for which full-thickness tears were diagnosed at sonography, with high-grade partial-thickness tears found at surgery (Fig 4). One patient had a 2 x 4-mm bundle of intact tendon fibers noted anteriorly at surgery. A second patient had a small bundle of intact but elongated fibers noted at surgery. In these cases, one of the authors, who interpreted the sonograms and who was blinded to the surgical findings, noted tendon retraction of 19 and 20 mm, Kager fat herniation, and posterior acoustic shadowing at the retrospective review, and these findings suggested full-thickness tears. Retrospective review of all available static sonograms in these two cases demonstrated no apparent intact tendon fibers. The time between sonography and surgery in these cases was 4 and 368 days.
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DISCUSSION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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Few prior investigators have used the findings at sonography and MR imaging to accurately classify and distinguish partial-thickness tears from tendinosis of the Achilles tendon with surgical and histologic findings as the standard of reference. Findings in studies (8,9,19) in which this standard of reference has been used have been reported in qualitative terms, that is, that more severe pathologic findings in the tendon suggest a partial-thickness tear. Åström et al (9) report that a tendon thickness greater than 10 mm suggests a partial-thickness tear. When Paavola et al (10) compared sonographic findings before surgery with surgical findings in the Achilles tendon, they found that sonographic findings were used to correctly predict partial ruptures in eight of 11 cases and to correctly predict tendinosis in three of seven cases. Åström et al (9) also note that findings at neither sonography nor MR imaging could be used to accurately distinguish partial-thickness tears from tendinosis. Kalebo et al (19) reported an accuracy of 95% in the use of sonography in the detection of partial-thickness tears of the Achilles tendon. However, details of the surgical findings were not included in their article, and the role of tendinosis was not addressed.
In this study, we did not attempt to distinguish partial-thickness tears from tendinosis but rather chose to focus on the more clinically relevant differentiation between full-thickness tears and other pathologic findings in the tendon.
Prior investigations with the use of MR imaging or sonography to examine the Achilles tendon have included few cases of complete rupture, and still fewer have included cases with correlation to surgical findings. To our knowledge, none have included data about sensitivity, specificity, or accuracy for the use of either imaging modality (6,8,9,12,20–33). Our results are similar to those of Paavola et al (10), who noted that before surgery sonography correctly depicted full-thickness tears in examination of the Achilles tendon in 25 of 26 cases. However, their methods did not allow calculations of sensitivity, specificity, or accuracy. We have shown that sonographic evaluation can be effective in the differentiation of full- versus partial-thickness tears or tendinosis, with a sensitivity and specificity of 100% and 83%, respectively, and an accuracy of 92%.
In our study, there were two cases of false-positive findings at sonography. In these two cases, full-thickness tears were diagnosed at sonography, with high-grade partial-thickness tears found at surgery (Fig 4). The false-positive findings in the two cases likely relate to incomplete sonographic evaluation once a tendon gap and retraction were identified. Complete medial-to-lateral and superior-to-inferior scanning is required to fully evaluate for any intact fibers. The long delay (368 days) between sonography and surgery in one of these two cases may also have allowed partial healing of a full-thickness tear.
A number of sonographic characteristics were evaluated and were correlated with full- versus partial-thickness tears or tendinosis. Median tendon thickness at the site of the tendon abnormality was 0 mm for full-thickness tears, as expected, and 9 mm for partial-thickness tears or tendinosis (P < .001). Normal Achilles tendons are typically 5–7 mm in anteroposterior dimension on a transverse scan (21, 22).
Posterior acoustic shadowing at the site of a tendon tear, which is thought to relate to sound-beam refraction at the frayed tendon ends (21,34), was correlated significantly with a full-thickness tear (P = .007). This P value was calculated by using data that did not include the three cases with posterior acoustic shadowing due to calcification. The P value, calculated by counting these three cases as refractive shadowing from the ends of the torn tendon, was .038 and remained statistically significant. Shadowing from calcification can be distinguished from refractive shadowing from the end of a torn tendon. Shadowing from calcification originates from a linear or round echogenic structure (the calcification), whereas refractive shadowing originates from a fibrillar-appearing tendon stump.
Median tendon retraction also was correlated significantly (P < .001) with a full-thickness tear. In our two cases with false-positive findings, tendon retraction, however, was present and measured 19 and 20 mm, which underscores the need to completely evaluate the site of the tendon abnormality even when retraction is noted. The precise position of the ankle (neutral, dorsiflexion, plantar flexion) cannot be determined with certainty in this retrospective study. This limits the value of our results for tendon retraction. Tendon retraction may be increased with dorsiflexion and decreased with plantar flexion.
There was a tendency to see fat herniation into the region of the tendon abnormality (P = .051) and a tendency toward visualization of the plantaris tendon with a full-thickness tear (P = .098). In cases of full-thickness tears, Kager fat and the plantaris tendon can move posteriorly into the tendon gap and become more visible at sonography. The plantaris tendon can be noted as a small but separate and distinct tendon at the medial aspect of the Achilles tendon. An intact plantaris tendon can mimic intact fibers in the Achilles tendon and cause a full-thickness tear of the Achilles tendon to be mistakenly interpreted as a partial-thickness tear. Awareness of this potential pitfall, as well as of the additional sonographic characteristics of full-thickness tears, helps increase diagnostic accuracy.
The relative echogenicity of the abnormal tendon was not statistically significant for predicting a full- versus a partial-thickness tear or tendinosis. Typically, with acute, retracted full-thickness tears, there are blood products of variable echogenicity, herniated fat, or debris noted at the site of the tendon gap. Hypoechoic or isoechoic scar tissue fills the tendon gap in long-standing cases. The echogenicity in these cases is not distinguishable from the hypoechoic or isoechoic tendon seen in cases of partial-thickness tears or tendinosis. Our sonographic results in cases of a partial-thickness tear or tendinosis are in agreement with those of Åström et al (9), who also noted tendon thickening that averaged 8–9 mm and statistically insignificant changes in tendon echogenicity in such cases.
Odds ratios listed in Table 2 provide an indication of the association between sonographic characteristics and tear type. Caution must be used when interpreting odds ratios. By definition, odds ratios give the change in odds for a single unit of change in each predictor. In our study, the odds ratio for tendon retraction was calculated for a 1-cm change and that for the other characteristics was calculated for a change between presence and absence. Therefore, the odds ratio for tendon retraction is not directly comparable with the odds ratios for the other characteristics.
Limitations of this study include the fact that acquisition and interpretation of the sonographic images were performed by six musculoskeletal radiologists in part A of the study. No doubt, there was variability in the scanning technique and interpretation among these six musculoskeletal radiologists. Given the fact that the radiologist who performs the study has more information than is on the static images, statistical analysis of interobserver variability in this retrospective study could not be performed. Given the advantages of using the real-time observations of the scanning radiologist, findings in the sonography reports were chosen for comparison with the surgical findings for calculations of sensitivity, specificity, and accuracy rather than a retrospective review of the sonographic images. Conversely, the interpretation from the reports did not always include comments on the sonographic characteristic assessed in part B of the study. Therefore, a retrospective evaluation was performed to assess these characteristics. Part B of the study is, thus, limited by the available static images. As with the use of sonography to examine any structure, it is possible that certain findings were present and not depicted on the image. Part B of this study is also limited in that one radiologist evaluated the sonographic characteristics.
No full-thickness tears were missed with sonography. In cases of a partial-thickness tear or tendinosis, the interval between sonography and surgery averaged 216 days, with an SD of 197 days. This reflects the standard treatment of a partial-thickness tear or tendinosis of the Achilles tendon in which conservative therapy is used prior to considering surgery (4,35). During such a long interval, changes, including healing or further tearing, can occur. In our study, findings in all cases of a partial-thickness tear or tendinosis at sonography were confirmed by findings at surgery. The degree of these changes, however, could have changed in the interval between sonography and surgery.
The study is biased by the inclusion of only those cases that have surgical correlation. Correlation with surgical findings as the standard of reference also obviates the inclusion of normal cases, since normal Achilles tendons rarely, if ever, undergo surgery. Given the shortcomings of clinical tests and clinical examination findings in some cases, correlation with surgical findings is the strongest standard of reference (1,4,7,18). In addition, patients who were receiving care from eight different orthopedic surgeons were included in this retrospective study. It is not possible to quantify or to control for differences in the clinical findings and examination techniques among these eight surgeons. However, determining if a full-thickness tear is present at surgery is straightforward. As with any retrospective study, caution must be used in applying our results to prospective practice.
In this study, the Achilles tendon was not systematically evaluated during dorsiflexion and plantar flexion. Dynamic imaging of full-thickness tears of the Achilles tendon can be used to assess approximation of the ends of the torn tendon during plantar flexion. If the ends of the tendon approximate during plantar flexion, some physicians advocate casting with the ankle in the talipes equinus position rather than surgery (7). A prospective, randomized study is needed to evaluate the effectiveness of this treatment.
In conclusion, the optimal treatment of full-thickness tears of the Achilles tendon is controversial, though many physicians favor surgical treatment. The accuracy of imaging must be firmly established before it can be expected to have an effect on determining optimal treatment. We have demonstrated that sonography can be used to differentiate a full-thickness tear from a partial-thickness tear or tendinosis of the Achilles tendon with 92% accuracy. Undetectable tendon at the site of injury, tendon retraction, and posterior acoustic shadowing at the ends of the torn tendon are characteristics that can be used to aid in the sonographic diagnosis of a full-thickness tear of the Achilles tendon.
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ACKNOWLEDGMENTS |
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FOOTNOTES |
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REFERENCES |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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This article has been cited by other articles:
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  R Syha, M Peters, H Birnesser, A Niess, A Hirschmueller, H-H Dickhuth, and M Sandrock Computer-based quantification of the mean Achilles tendon thickness in ultrasound images: effect of tendinosis Br. J. Sports Med., December 1, 2007; 41(12): 897 - 902. [Abstract] [Full Text] [PDF]
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 T. H. Grant, A. S. Kelikian, S. E. Jereb, and R. J. McCarthy Ultrasound Diagnosis of Peroneal Tendon Tears. A Surgical Correlation J. Bone Joint Surg. Am., August 1, 2005; 87(8): 1788 - 1794. [Abstract] [Full Text] [PDF]
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 M. Zanetti, A. Metzdorf, H.-P. Kundert, H. Zollinger, P. Vienne, B. Seifert, and J. Hodler Achilles Tendons: Clinical Relevance of Neovascularization Diagnosed with Power Doppler US Radiology, May 1, 2003; 227(2): 556 - 560. [Abstract] [Full Text] [PDF]
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 M. Shetty, D. P. Fessell, J. E. Femino, J. A. Jacobson, J. Lin, and D. Jamadar Sonography of Ankle Tendon Impingement with Surgical Correlation Am. J. Roentgenol., October 1, 2002; 179(4): 949 - 953. [Abstract] [Full Text] [PDF]
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D. A. Jamadar, J. A. Jacobson, S. E. Theisen, D. R. Marcantonio, D. P. Fessell, S. V. Patel, and C. W. Hayes Sonography of the Painful Calf: Differential Considerations Am. J. Roentgenol., September 1, 2002; 179(3): 709 - 716. [Full Text] [PDF]
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S. Patel, D. P. Fessell, J. A. Jacobson, C. W. Hayes, and M. T. van Holsbeeck Artifacts, Anatomic Variants, and Pitfalls in Sonography of the Foot and Ankle Am. J. Roentgenol., May 1, 2002; 178(5): 1247 - 1254. [Full Text] [PDF]
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