Rationale and Objectives
Presurgical assessment of fatty degeneration is important in the management of patients with rotator cuff tears. The Goutallier classification is widely accepted as a qualitative scoring system, although it is highly observer-dependent and has poor reproducibility. The objective of this study was to quantify fatty degeneration of the supraspinatus muscle using a 2-point Dixon technique in patients with rotator cuff tears by multiple readers, and to evaluate the reproducibility compared to Goutallier classification.
Materials and Methods
Two hundred patients with rotator cuff tears who underwent magnetic resonance imaging (MRI), including 2-point Dixon sequence at 3.0-T, were selected retrospectively. Qualitative and quantitative analyses of fatty degeneration were performed by two radiologists and three orthopedic surgeons independently. The fat quantification was performed by measuring signal intensity values of in phase (S(In)) and fat image (S(Fat)), and calculating fat fraction as S(Fat)/S(In). The reproducibility of MR quantification was analyzed by the intra- and interclass correlation coefficients and Bland-Altman plots.
Results
The interobserver agreement of the Goutallier classification among five readers was moderate (k = 0.51), whereas the interclass correlation coefficient regarding fat fraction value quantified in 2-point Dixon sequence was excellent (0.893). The mean differences in fat fraction values from the individual segmentation results were from −0.072 to 0.081. Proposed fat fraction grading and Goutallier grading showed similar frequency and distribution in severity of rotator cuff tears.
Conclusions
Fat quantification in the rotator cuff muscles using a 2-point Dixon technique at 3.0-T MRI is highly reproducible and clinically feasible in comparison to the qualitative evaluation using Goutallier classification.
Introduction
The assessment of rotator cuff muscle abnormalities after tear is one of the main factors in clinical decision-making in the management of patients with rotator cuff tears . Severity of presurgical fatty degeneration is especially relevant to the higher frequency of retear and worse functional outcomes after treatment . An accurate determination of fatty degeneration in the rotator cuff muscle is therefore a crucial element in evaluating surgical indications and postoperative prognosis.
For the qualitative assessment of fatty degeneration, computed tomography and magnetic resonance imaging (MRI)-based classifications have been established. The Goutallier classification has become widely accepted as standard 5-grade scoring systems for muscle fatty degeneration in current practice . The Goutallier classification was initially created based on axial computed tomography images; however, recently it was adapted for the evaluation of fatty degeneration on sagittal MR images. Although the Goutallier classification has been widely used, it is shown to be highly observer-dependent, and inter- and intraobserver reliability is not high . This fact has been a critical problem for the preoperative evaluation of fatty degeneration and assessment of operative indication.
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Materials and Methods
Patients
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MRI Acquisition
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Evaluation of the Rotator Cuff
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Qualitative Analysis of Fatty Degeneration
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Quantitative Analysis of Fatty Degeneration
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S(Water)+S(Fat)=S(In) S
(
Water
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+
S
(
Fat
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=
S
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In
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Fat fraction=S(Fat)/(S(Water)+S(Fat))=S(Fat)/S(In) Fat fraction
=
S
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Fat
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/
(
S
(
Water
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+
S
(
Fat
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)
=
S
(
Fat
)
/
S
(
In
)
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Statistical Analysis
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Results
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TABLE 1
Patient’s Demographic Data
Group Partial Tear Small Tear Medium Tear Large Tear Massive Tear Combined No. of patients 100 9 39 21 31 200 Percentage of patients 50 4.5 19.5 10.5 15.5 100 Age, y, mean ± standard deviation 63.3 ± 11 56.6 ± 9.2 68.6 ± 8.5 68.8 ± 8.2 7.29 ± 10 66.1 ± 10.8 Sex, n (%) Male 48 (48.0) 4 (44.4) 16 (41.0) 8 (38.0) 10 (32.3) 86 (43.0) Female 52 (52.0) 5 (55.6) 23 (59.0) 13 (62.0) 21 (67.7) 114 (57.0)
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TABLE 2
Unweighted/Weighted Cohen’s Kappa Value of the Goutallier Classification Between Reader Pairs
Reader 1 Reader 2 Reader 3 Reader 4 Reader 5 Reader 1 0.47/0.73 0.44/0.80 0.65/0.86 0.53/0.78 Reader 2 0.16/0.64 0.54/0.78 0.50/0.76 Reader 3 0.36/0.76 0.34/0.68 Reader 4 0.52/0.79 Reader 5
TABLE 3
Bland-Altman Analysis of Interobserver Agreement of Measurement of Fat Fraction Value of Supraspinatus Muscles
Proportional Bias Fixed Bias Reader PMC \* 95% CI_P_ Value † Mean Difference SD 95% Limits of Agreement R1-R2 0.211 (−0.103, 0.437) 0.353 −0.011 0.05 (−0.109, 0.087) R1-R3 0.149 (−0.076, 0.459)0.048 −0.032 0.083 (−0.195, 0.131) R1-R40.001 (0.191, 0.644)<0.001 0.049 0.064 (−0.076, 0.174) R1-R5 0.863 (−0.256, 0.301)0.048 −0.023 0.059 (−0.139, 0.093) R2-R3 0.451 (−0.175, 0.376) 0.176 −0.021 0.072 (−0.162, 0.120) R2-R40.025 (0.042, 0.547)<0.001 0.06 0.061 (−0.060, 0.180) R2-R5 0.345 (−0.400, 0.148) 0.353 −0.012 0.055 (−0.120, 0.096) R3-R4 0.203 (−0.100, 0.439)<0.001 0.081 0.063 (−0.042, 0.204) R3-R5 0.205 (−0.439, 0.101) 0.444 0.009 0.086 (−0.160, 0.178) R4-R50.008 (−0.588, −0.103)<0.001 −0.072 0.073 (−0.215, 0.071)
CI, confidence interval; SD, standard deviation.
Bold: statistically significant difference at P < 0.05.
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TABLE 4
Bland-Altman Analysis of Intraobserver Agreement of Measurement of Fat Fraction Value of Supraspinatus Muscles
Proportional Bias Fixed Bias Reader PMC \* 95% CI_P_ Value † Mean Difference SD 95% Limits of Agreement R1(#1-#2)<0.001 (−0.668, −0.231) 0.27 0.008 0.05 (−0.090, 0.106) R2(#1-#2) 0.508 (−0.188, 0.364) 0.227 0.01 0.044 (−0.076, 0.096) R3(#1-#2) 0.51 (−0.188, 0.364)0.017 0.021 0.059 (−0.095, 0.137) R4(#1-#2) 0.275 (−0.127, 0.417) 0.189 −0.009 0.046 (−0.099, 0.081) R5(#1-#2) 0.149 (−0.075, 0.459)0.026 −0.022 0.066 (−0.151, 0.107)
CI, confidence interval; SD, standard deviation.
Bold: statistically significant difference at P < 0.05.
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Discussion
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Conclusion
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Acknowledgment
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