A Novel MRI Measurement for Analysing Coracoacromial Morphology

Kadosa Bodo, Mustafa Abbas, David Temperley, Adrian Midgley, Puneet Monga

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AIMS: Extrinsic factors of subacromial impingement of the shoulder can be potentially characterised by the angle between the acromion and coracoacromial ligament. A retrospective study was designed to test a novel angle measurement method for a potential new diagnostic tool. PATIENTS AND METHODS: The landmarks and outcome measures were determined on sagittal cuts of default 1.5 T MRI scans. Two independent observers made the measurements on 50 annotated images of a cohort of healthy and young individuals. RESULTS: The mean acromial-coracoacromial ligament (ACAL) angle was 129.8 degrees, (SD 10.0). The two independent measurements and a repeated one were compared for testing inter- and intra-observer reliability. Measurement of ACAL showed high internal consistency and strong measurement agreement between observers (Cronbach’s alpha values: 0.88, 0.86 and 0.94; Intraclass correlation coefficient values: 0.78, 0.75, 0.88). However, a statistically significant difference (p=0.035) was found on the retest measurement (1st to 2nd) of the same observer, despite the little difference (1st to 3rd p = 0.78; 2nd to 3rd p = 0.75) in inter-observer relation on paired sample t-test. CONCLUSIONS: The measuring error came from poor definition of the landmarks on standard 3 mm slice thickness MRI scans. Altered scanning sequences with thinner slices might provide more details of the structures, improve reliability, and prove to be a clinically useful measure in a future prospective study. KEY MESSAGES: ACAL measurement was not sufficiently reliable when performed on a default plane MRI scan; however, an altered scanning method might provide better visualisation and higher definition of the structures and could improve intra-observer reliability in further studies.
Original languageEnglish
Pages (from-to)883-890
JournalInternational Journal of Orthopaedics
Issue number1
Early online date28 Feb 2018
Publication statusE-pub ahead of print - 28 Feb 2018


  • Arch
  • coracoacromial
  • Ligament
  • Angle
  • Subacromial
  • Impingement


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