Korean J Radiol.  2019 Jun;20(6):931-938. 10.3348/kjr.2018.0541.

Evaluation of Inferior Capsular Laxity in Patients with Atraumatic Multidirectional Shoulder Instability with Magnetic Resonance Arthrography

• Park KJ
• Jeong HS
• Park JK
• Cha JK
• Kang SW

• KMID: 2447071
• DOI: http://doi.org/10.3348/kjr.2018.0541

Abstract

OBJECTIVE
To compare inferior capsular redundancy by using magnetic resonance arthrography (MRA) images in patients with multidirectional instability (MDI) of the shoulder and control subjects without instability and thereby develop a screening method to identify the presence of shoulder MDI.
MATERIALS AND METHODS
The MRA images of patients with MDI of the shoulder (n = 65, 57 men, 8 women; mean age, 24.5 years; age range, 18-42 years) treated over an eight-year period were retrospectively reviewed; a control group (n = 65, 57 men, 8 women; mean age, 27.4 years; age range, 18-45 years) without instability was also selected. The inferior capsular redundancy was measured using a new method we named the glenocapsular (GC) ratio method. MRA images of both groups were randomly mixed together, and two orthopedic surgeon reviewers measured the cross-sectional areas (CSAs) and sagittal capsule-head ratios on oblique sagittal images, as well as the axial capsule-head ratios on axial images and GC ratios on oblique coronal images.
RESULTS
The CSAs and GC ratios were significantly higher in patients than in controls (both, p < 0.001); however, the sagittal capsule-head ratios and axial capsule-head ratios were not significantly different (p = 0.317, p = 0.053, respectively). In addition, GC ratios determined the presence of MDI more sensitively and specifically than did CSAs. A GC ratio of > 1.42 was found to be most suggestive of MDI of the shoulder, owing to its high sensitivity (92.3%) and specificity (89.2%).
CONCLUSION
GC ratio can be easily measured and used to accurately screen for MDI of the shoulder.

Keyword

Multidirectional shoulder instability; MDI; Magnetic resonance arthrography; MRA; Capsular redundancy; Inferior instability

MeSH Terms

Arthrography*
Female
Humans
Male
Mass Screening
Methods
Orthopedics
Retrospective Studies
Sensitivity and Specificity
Shoulder*

Figure

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  Fig. 1 Flow chart of study groups.CSAs = cross-sectional areas, GC = glenocapsular, MDI = multidirectional instability, MRA = magnetic resonance arthrography

• 

  Fig. 2 GC ratios were obtained on oblique coronal images showing largest glenoid cut and insertion of biceps long head.Line A was drawn from top of glenoid to bottom of inferior capsule. Line B was drawn from top of glenoid to bottom of glenoid parallel to line A. GC ratio was calculated by dividing length of A by that of B.

• 

  Fig. 3 Axial capsule-head ratios were obtained using axial images showing largest posterior capsular area and glenoid.Line A was drawn from anterior aspect of lesser tuberosity to most posterior aspect of posterior capsule. Line B was drawn from anterior aspect of lesser tuberosity to posterior aspect of humeral head parallel to line A. Axial capsule-head ratio was calculated by dividing length of line A by that of B.

• 

  Fig. 4 Sagittal capsule-head ratios were obtained using sagittal-oblique images showing largest posterior fluid pocket.Line A was drawn from posterior aspect of coracoid to most posterior aspect of capsule, and line B from posterior aspect of coracoid to posterior aspect of humeral head parallel to line A. Sagittal capsule-head ratio was calculated by dividing length of line A by that of line B.

• 

  Fig. 5 Measurement of sagittal CSA.To measure sagittal CSA, sagittal-oblique cut with largest area of capsular pooling at or lateral to glenoid rim was selected, and total area of capsule was recorded A. On same cut, total area of humerus was recorded B. CSA was calculated by subtracting total area of humerus from total capsule area on same cut.

• 

  Fig. 6 ROC curves for GC ratio and CSA.Threshold values and diagnostic sensitivities and specificities were calculated using ROC curves. Mean GC ratio and CSA were significantly different in multidirectional shoulder instability group and control group. ROC = receiver operating characteristic

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