Inconsistencies in the MRI Evaluation of Supraspinatus Volume After Repair

Abstract

Background: Reversibility of rotator cuff atrophy after surgical repair is controversial. Traditionally, the cross-sectional area (CSA) of the rotator cuff was measured in conventional Y-view (CYV) via magnetic resonance imaging (MRI) to evaluate reversibility. However, it has been suggested that scanning axis inconsistency in CYV was overlooked and that the CSA in CYV reflects not only atrophy but also rotator cuff retraction. Hypothesis: Discrepancies between scanning axes in CYV cause significant errors when one is evaluating changes in the CSA of the supraspinatus (SS) using preoperative and postoperative MRI scans. A more medial section than the Y-view is not influenced as much by retraction recovery after repair. Study Design: Cohort study (diagnosis); Level of evidence, 3. Methods: The study included 36 patients with full-thickness SS tear and retraction who underwent arthroscopic complete repair with preoperative MRI and immediate postoperative MRI (within 5 days after rotator cuff repair). Angles between CYV planes in the preoperative and immediate postoperative MRI scans were measured. MRI scans were reconstructed perpendicular to the scapular axes by multiplanar reconstruction. Differences between the CSAs of the SS in preoperative and postoperative Y-view on the original and reconstructed MRI scans were compared, and changes in CSAs of the SS muscles after repair in 2 sections medial to the reconstructed Y-view (RYV) were compared. Results: The mean angle between CYV planes in preoperative and postoperative MRI scans was 13.1° ± 7.1°. Mean pre- to postoperative increase in the CSA of the SS was greater in CYV than in RYV (95 ± 72 vs 75 ± 62 mm2; P = .024). Furthermore, pre- to postoperative CSA differences in the 2 medial sections were less than in RYV. For the most medial section, crossing the omohyoid origin, the CSA differences were not significant (434 ± 98 vs 448 ± 98 mm2; P = .061). Conclusion: Scanning axes inconsistencies in CYV cause unacceptable errors in CSA measurements of the SS after repair. We recommend reconstruction along a consistent axis by multiplanar reconstruction when evaluating postoperative changes in SS atrophy and the use of sections more medial than the scapular Y-view to reduce errors caused by tendon retraction.

Longitudinal Changes in Overall 3D Supraspinatus Muscle Volume and Intramuscular Fatty Infiltration After Arthroscopic Rotator Cuff Repair

“…However, these reports of reversibility are currently attracting more scrutiny. The primary controversy involves the lateralization of the myotendinous unit after repair, which can immediately result in an immediate increase in the supraspinatus occupation ratio, even though the muscle volume is unchanged, by altering the assessment plane 3,18,19,33 . Some authors have used images made immediately after surgery as a baseline to overcome this drawback, but these studies have still reported contradictory results 3,6,34 .…”

“…the Y-view plane for radiographic measurements could be one of the main explanations, as data from a single slice fail to represent the actual 3D volume 9,33 .…”

Association Between Supraspinatus Tendon Retraction, Histologic Myofiber Size, and Supraspinatus Muscle Atrophy on MRI

“…Additionally, using the scapular Y view of MRI to evaluate supraspinatus CSA and occupation ratio has its own unique limitations with regard to inconsistencies in scanning axis of the reconstructed image. 10 Furthermore, there is an inability to perform volumetric analysis of muscle atrophy on standard shoulder MRI owing to the limited field of view, which does not include the entire muscle belly of the supraspinatus. Despite this, the methodology used in our study, including occupation ratio, supraspinatus CSA, and tangent sign, is consistent with the current standard for evaluating atrophy in the clinical setting.…”

“…3,[18][19][20]22 However, there is concern that 2-dimensional assessment of the supraspinatus muscle on cross-sectional imaging may not be an accurate representation of the true atrophy of the muscle fibers of the rotator cuff. 4,10,21 Specifically, rotator cuff tendon retraction has been shown to falsely overestimate muscle atrophy appreciated on MRI, 4,21 which can have clinically significant implications for determining the repairability and functional prognosis after rotator cuff repair. Although MRI is a clinically useful noninvasive method of assessing muscle atrophy, muscle biopsy has been performed to directly measure myofiber cross-sectional area (CSA) histologically.…”

“…3,18-20,22 However, there is concern that 2-dimensional assessment of the supraspinatus muscle on cross-sectional imaging may not be an accurate representation of the true atrophy of the muscle fibers of the rotator cuff. 4,10,21…”