De Smet A A, Norris M A, Yandow D R, Graf B K, Keene J S
Department of Diagnostic Radiology, University of Wisconsin Hospital, Madison 53792-3252.
AJR Am J Roentgenol. 1993 Mar;160(3):555-9. doi: 10.2214/ajr.160.3.8430552.
A wide range in the efficacy of MR imaging for the diagnosis of meniscal tears of the knee has been reported. To evaluate two possible causes for this variation, we studied how sensitivity and specificity are affected when different observers and sample sizes are used.
Two hundred MR examinations of the knee in patients for whom the results of arthroscopy were available were used for the study. One hundred eight medial meniscal tears and 58 lateral meniscal tears were found at arthroscopy. The sensitivity and specificity for detection of meniscal tears were determined for the original interpretations and retrospective evaluations by three observers. Comparisons were also made between sample sizes of 25 and 100. chi 2 analysis was used for unmatched data sets and McNemar's statistic was used for matched sets.
For the 200 examinations, the sensitivity was 0.89-0.93 for medial meniscal tears and 0.79-0.83 for lateral meniscal tears. The specificity was 0.86 for medial meniscal tears and 0.90-0.92 for lateral meniscal tears. Sensitivity and specificity varied widely among different observers and different sample sizes. However, we found no significant difference between any of the comparisons at the p < .05 level. The largest interobserver variation occurred in the detection of lateral meniscal tears, with a sensitivity of 0.71 for one observer and 0.88 for another observer (p = .16). The largest variation between sets of 100 examinations was a change in sensitivity for detection of lateral meniscal tears from 0.74 to 0.88 for the original interpretations (p = .10). For the sample sets of 25 cases, the variation was even larger, with the sensitivity for detection of lateral meniscal tears varying from 0.5 for one set to 1.0 for another.
We conclude that chance variation related to sample size can cause large but not statistically significant variations in sensitivity and specificity in this setting. These variations are of sufficient magnitude to explain many of the differences in reported sensitivity and specificity for MR imaging in the diagnosis of meniscal tears. We found no significant difference in observer performance.
已有报道称磁共振成像（MR）诊断膝关节半月板撕裂的效能存在很大差异。为评估造成这种差异的两个可能原因，我们研究了使用不同观察者和样本量时，敏感度和特异度是如何受到影响的。
本研究使用了200例膝关节MR检查，这些患者同时接受了关节镜检查。关节镜检查发现108例内侧半月板撕裂和58例外侧半月板撕裂。由三名观察者对半月板撕裂检测的原始解读和回顾性评估确定敏感度和特异度。还对样本量为25和100的情况进行了比较。对于不匹配的数据集使用卡方分析，对于匹配的数据集使用麦克尼马尔统计量。
在这200例检查中，内侧半月板撕裂的敏感度为0.89 - 0.93，外侧半月板撕裂的敏感度为0.79 - 0.83。内侧半月板撕裂的特异度为0.86，外侧半月板撕裂的特异度为0.90 - 0.92。敏感度和特异度在不同观察者和不同样本量之间差异很大。然而，在p < 0.05水平下，我们发现任何比较之间均无显著差异。观察者间差异最大的是外侧半月板撕裂的检测，一名观察者的敏感度为0.71，另一名观察者为0.88（p = 0.16）。100例检查组之间最大的差异是原始解读中外侧半月板撕裂检测敏感度从0.74变为0.88（p = 0.10）。对于25例样本组，差异甚至更大，外侧半月板撕裂检测敏感度在一组中为0.5，在另一组中为1.0。
我们得出结论，在这种情况下，与样本量相关的随机变异可导致敏感度和特异度出现较大但无统计学意义的差异。这些差异幅度足以解释报道的MR成像诊断半月板撕裂时敏感度和特异度的许多差异。我们未发现观察者表现存在显著差异。
