Acromiohumeral distance measurement in rotator cuff tendinopathy: is there a reliable, clinically applicable method?

Background: Narrowing of the subacromial space has been noted as a common feature of rotator cuff (RC) tendinopathy, and has been implicated in the development of symptoms, and forms the basis for some surgical and rehabilitation approaches. Various radiological methods have been used to measure the subacromial space, which is represented by a two-dimensional measurement of acromio-humeral distance (AHD). A reliable method of measurement could be used to assess the impact of rehabilitation or surgical interventions for RC tendinopathy, however there are no published reviews assessing the reliability of AHD measurement. Objectives: The aim of this review was to systematically assess the evidence for the intra- and inter-rater reliability of radiological methods of measuring AHD, in order to identify the most reliable method for use in rotator cuff tendinopathy. Study appraisal and synthesis: An electronic literature search was carried out and studies describing the reliability of any radiological method of measuring AHD in either healthy or RC tendinopathy groups were included. Eighteen studies met the inclusion criteria, and were appraised by two reviewers using the Quality Appraisal for reliability Studies (QAREL) checklist. Results: Eight studies were deemed to be of high methodological quality. Study weaknesses included lack of tester blinding, inadequate description of tester experience, lack of inclusion of symptomatic populations, poor reporting of statistical methods and unclear diagnosis. There was a strong evidence for the reliability of ultrasound for measuring AHD, with moderate evidence for Magnetic Resonance Imaging (MRI) and Computed Tomography (CT) measures, and conflicting evidence for radiographic methods. Overall there was a lack of research in rotator cuff tendinopathy populations, with only 6 studies including participants with shoulder pain. Conclusion: The results support the reliability of ultrasound and CT or MRI for the measurement of AHD, however more studies in symptomatic populations are required. The reliability of AHD measurement using radiographs has not been supported by the studies reviewed.