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.

Keywords: atrophy; cross-sectional area; multiplanar reconstruction; rotator cuff repair; rotator cuff tear.

Figure 1.

Measurement of the cross-sectional area of the supraspinatus in conventional Y-view.

Figure 2.

Reconstruction of oblique-sagittal T1-weighted magnetic resonance images perpendicular to the new scapular axis. Superior view of the left scapula. The cube in the lower right corner indicates the orientation: A, anterior side; L, lateral side; S, superior side. Point A is on the base of the scapular spine and point B on the spinoglenoid notch. Line AB forms a new scapular axis. The cross-sectional areas of the supraspinatus were measured in 3 sections perpendicular to the axis.

Figure 3.

Measurement of the angle between planes in conventional Y-view in preoperative and immediate postoperative magnetic resonance imaging (MRI) scans. The cube in the lower right corner indicates the orientation: L, lateral side; P, posterior side; S, superior side. The green plate represents the plane of the conventional Y-view for preoperative MRI and the red plate that for postoperative MRI. Two yellow lines are drawn perpendicular to each plate. The angle between the 2 yellow lines is equivalent to the angle between the planes in conventional Y-view in preoperative and postoperative MRI scans.

Figure 4.

The omohyoid muscle on a reconstructed oblique-sagittal magnetic resonance image. Consecutive sections from lateral to medial sides (from A to D) in reconstructed oblique-sagittal images, showing the omohyoid attachment to the superior border of the scapula. Asterisks indicate the omohyoid muscle. (D) is the most medial section that did not show omohyoid attachment to the scapula; in this section, supraspinatus cross-sectional area was measured as shown in Figure 1 (the section crossing the medial edge of the origin of the omohyoid).

Figure 5.

(A) Conventional Y-view, (B) reconstructed Y-view, and (C and D) 2 medial sections on reconstructed oblique-sagittal images of a preoperative magnetic resonance imaging (MRI) scan (left) and an immediate postoperative MRI scan (right).

Figure 6.

Preoperative to immediate postoperative differences between the cross-sectional areas (CSAs) of the supraspinatus (SS) measured in conventional Y-view and reconstructed Y-view. Delta CSA refers to CSA differences of the SS in preoperative and postoperative magnetic resonance images. A positive value means CSA increased postoperatively. Each line refers to a case. A positive or negative slope suggests that there may have been inconsistencies in the measurement of the conventional Y-view.