Quantitative MRI indicators and features for partial subscapularis tendon tears on conventional shoulder MRI

In this study, we enrolled a large sample to explore specific imaging features of the partial SSC tears by comparing the case group confirmed by arthroscopy with those of the normal group, verifying that several particular signs and quantitative indicators on conventional MRI can be used to improve the preoperative diagnostic efficacy of partial SSC tears. Compared with the previously proposed predictors, we defined these semi-quantitative MRI signs with more detailed methods of observing and evaluating, aiming to make them more operable and repeatable.

Our study indicated that the “fissure sign” on oblique sagittal MRI was the most specific sign for diagnosing partial SSC tears with high sensitivity (92%) and accuracy (81.3%). In our data, the incidence of the fissure sign was 75.3% (67/89). Small defects and fluid-like signal within the tendon have been reported as a high predictor of partial tears in previous studies [14, 17, 18, 22]. Our results supported this finding, furthermore, the detailed observation approach has been interpreted in this study to objectively evaluate this sign. Most of the partial SSC tears occur in facet 1 of the insertion of the SSC tendon into the lesser tuberosity [17], the width of facet 1 is about 13.8 mm, and has a certain angle of inclination at the tendon insertion [3]. Therefore, we defined the first three slices on oblique sagittal MRI (slice thickness 4.0 mm) counting from the lateral cortex of lesser tuberosity to the medial SSC footprint as the best observation planes, which were approximately equivalent to the width of facet 1 of SSC insertion, and the fluid-filled gap must be found on at least two continuous slices. In our clinical practice, the false-positive fissure sign is more common at the more medial slices to lesser tuberosity, because the tendon already departs the footprint area and joint effusion is easy to flow into the interspace between tendon and humerus head. Subsequently, we continued to define two subtypes of fissure sign according to the orientation of fluid-filled gap, parallel or vertical to the short axis of SSC tendon at footprint corresponding with the tendon detachment and split tear of SSC, respectively [4, 7, 22, 23].

We investigated the fluid collection under the CGA and proposed to establish quantitative measurement methods of them in the slices of the coraco-glenoid arch on oblique sagittal MRI. This area is equal to the part of the SSR which lies between the SSC muscle and the anterior surface of the scapula, extends above the superior margin of the SSC tendon, and communicates with the glenohumeral joint, but not with the subcoracoid bursa [18, 22, 23]. Given the adjacent relation between the SSR and the SSC tendon, partial SSC tears may result in effusions in the SSR due to reactive inflammation or as a result of impingement [27]. Our results showed the fluid collection had a high specificity of 80% and moderate sensitivity of 50.6%. Sugimori et al. [23] reported that SSR fluid had a sensitivity of 100% but a specificity of only 62.5% regarding the incomplete SCC tear detection. We think that our suggested quantification method and the cutoff value (> 3.55 mm) of the effusion may improve its specificity compared to previous studies.

However, no significant difference in quantitative measurement of fat accumulation under the CGA was found between the case group and the control group in our study. Previous studies have shown that muscle atrophy and fatty degeneration can be observed after rotator cuff tendon tears [24]. These are likely the consequence of decreased mechanical load and denervation changes, which results in the proliferation of adipocytes, and ultimately leads to fat accumulation [26]. Several studies evaluated the SSC atrophy or fatty degeneration in SSC lesions [17, 18, 23, 28, 29]. However, SSC atrophy is often seen in a full-thickness tear which frequently represents a significant longstanding of SSC tears. Animal models of SSC tears also showed that complete SSC tenotomy resulted in significant atrophy at 6 weeks, while the changes were not seen in partial SSC tenotomy models [18]. This supported our result that fat accumulation was of no special value to partial SSC tendon tears.

Based on our observations, thinning of the SSC tendon and combined SSP complete tears also showed a good predicting ability of partial SSC tears (specificity: 86% and 80%; accuracy: 55.4% and 59.7%, respectively). Tendon thinning may be due to a reduction of intratendon fibers or a localized defect of the tendon parenchyma [10]. Similar to muscle contraction and tendon lengthening caused by the partial tear of the SSP tendon [30, 31], this may also be the cause of tendon thinning in partial SSC tears. The isolated SSC tears are relatively uncommon. Most SSC tears occur in combination with tears of at least the anterior portion of the SSP [32,33,34]. Fibers from the SSC and SSP interlock and converge together as they course around and above the humeral head to their respective insertion sites [35], this anatomical structure makes SSC tendon tears usually combined with SSP lesions. Some studies have reported that there is a significant association between SSP full-thickness tear and the presence of SSC abnormality [28, 29], which was consistent with our findings.

The incidence of lesser tuberosity cysts in the partial SSC tears group was 48.3% (43/89) while only 20% (10/50) in the control group in our investigation. And this sign showed only moderate sensitivity (56.2%) and specificity (68%) for partial SSC tears. The relationship between LTC and SSC tears has been reported in several studies [17, 25, 36, 37]. Lee at el. found the lesser tuberosity bone marrow edema and cysts had a sensitivity of 97.8% and specificity of 17.9% in partial SSC tears [17]. As a potential reason for cyst formation, the intact SSC tendon can prevent the lesser tuberosity to contact with synovial fluid after microavulsions, therefore minimizing the fluid-filled cavity anterior to the lesser tuberosity and covering the footprint of the SSC tendon which stays no longer isolated from the synovial fluid after a tear [38]. Chronic impingement of the lesser tuberosity or fluid intrusion through cortical micro-trauma or necrosis may substantially contribute to the formation of the cysts with SSC tears [25, 36]. However, lesser tuberosity cysts are very common in clinical practice. Needell et al. [39] reported that humeral head cysts could also be seen in asymptomatic patients. In addition to be caused by tendon tears, cysts can also develop in other conditions secondary to elevated intra-articular pressure and degenerative changes associated with aging [25].

Finally, all of the MRI features in this study presented a relatively moderate and low sensitivity. We think it may be related to the following reasons: First, to improve the identification and repeatability of these subjective MR features, we gave them relatively clear and rigorous definitions and added some conditional restrictions, so that the positive detection rate of these signs in the case group may be lower than the actual occurrence. Second, although the positive rate of these signs was not very high in the case group, their occurrence was also significantly lower in the normal group, potentially making these signs highly specific in identifying the partial tear and non-partial tear groups.

There are some limitations in this study. First, this is a retrospective study. We only diagnosed the partial SSC tear by referring to arthroscopic records, without accurately matching the MRI features with the intraoperative findings. Second, we did not evaluate the grading and subsection of partial SSC tears due to the limited information of arthroscopic records, and this may potentially decrease the accuracy of these features in certain areas of partial SSC tears. Third, all shoulder arthroscopic surgeries were not performed by one single surgeon, which might result in bias of intraoperative diagnosis. But in our single-center, all the orthopedists were accepted by a standardized course and training, and all the procedures were maintained with the same approach and patient position. Future work is needed to make a prospective control study by comparing preoperative conventional MRI features to arthroscopic findings and develop new imaging techniques such as 3D high-resolution MRI or dynamic MRI sequences in different positions to explore more specific quantification methods for partial tears.

In conclusion, this study identified several specific MRI signs, such as fissure sign, thinning of SSC tendon, and fluid collection under the CGA, with the explicit definition of some quantitative indicators to improve the accuracy of preoperative diagnosis of partial SSC tears on conventional MRI alone.

留言 (0)

沒有登入
gif