The differences of the acromiohumeral interval between supine and upright radiographs of the shoulder

www.nature.com/scientificreports OPEN The differences of the acromiohumeral interval between supine and upright radiographs of the shoulder Prakasit Sanguanjit, Adinun Apivatgaroon*, Phanuwat Boonsun, Surasak Srimongkolpitak & Bancha Chernchujit The acromiohumeral interval (AHI) is a measurement used to determine the superior migration of the humeral head in rotator cuff (RC) tear patients. The purpose of this study was to compare the AHI of; supine, upright shoulder radiographs, and magnetic resonance imaging (MRI) of the shoulder. The 86 shoulders were divided into 3 groups that included; (1) non-full thickness tear (50%), (2) full thickness (FT) tear ≤3 cm (33.7%), and (3) FT tear > 3 cm (16.3%). The mean difference of AHI noted was significantly lower in the supine radiographs and MRIs than with the upright (1.34–1.37 mm, 1.62– 1.87 mm, respectively). Upright AHI ≤ 7.0 mm had 27.9% sensitivity and 100% specificity in diagnosing FT tears with 64% accuracy (p < 0.001). The supine AHI ≤ 6.5 mm had 32.6% sensitivity, 100.0% specificity, and 66.3% accuracy (p < 0.01). The results revealed the AHI in supine radiographs were significantly lower than upright shoulder radiographs. For AHI ≤ 7 mm in upright shoulder radiographs, this remains as an appropriate diagnostic test for ruling in shoulders with full thickness rotator cuff tears. This value was not relevant for use as the cut point in the supine radiographs and MRIs. Rotator cuff (RC) tears are one of the common shoulder problems seen in orthopaedic practice and while plain shoulder radiographs are the standard, initial investigation tools for rotator cuff tear patients, the acromion morphologies, os acromiale and the congruence of the glenohumeral articulation, are radiographic features used to evaluate the possibility of underlying pathologies. The superior migration of the humeral head (SMHH) is a phenomenon noted in late-stage rotator cuff tears. The pathology of an upward displacement of the humeral head is not clearly defined. Osseous structures and the capsulolabral complex are the main static stabilizers of the glenohumeral articulation while the rotator cuff, conjoint tendon and long head of the biceps play important roles in the dynamic glenohumeral stabilization1. The rotator cuff works in conjunction with deltoid muscle to create the force that couples around the glenohumeral joint2. Subscapularis (anterior) and infraspinatus/teres minor (posterior) create a balanced couple-force in the horizontal plane for centralizing the center of rotation of the humeral head during shoulder elevation. Increased deltoid pulls, lack of rotator cuff stabilization and the absence of the spacer by tendon structures may be the pathophysiologic causes of the S MHH3,4. The acromiohumeral interval (AHI) is one of the measurement methods used to calculate the SMHH. The mean AHI in shoulders with an intact rotator cuff is approximately 10 mm (7–14 mm)5,6. While the AHI ≤ 7 mm measured on an anteroposterior radiograph suggests subacromial space narrowing and is indicative of large rotator cuff tears. In these cases, the likelihood of successful outcomes after the repair are r educed4–6. A seated or standing AHI less than 6 mm is indicative of a longstanding, total infraspinatus tear7. The AHI value may be influenced by gravity during upright arm position and this has the possibility of obtaining false negative results in detecting rotator cuff tears. Measurement of the AHI from supine MRIs is lower than measurements seen in upright shoulder r adiographs8 but plain radiographs are still the best initial investigation for rotator cuff-related patients. Supine shoulder radiographs may have less of a chance of confounding the AHI measurement by gravity and may reduce false negative detection of rotator cuff tears. The purpose of this study was to compare the AHI of supine shoulder radiographs, upright shoulder radiographs, and magnetic resonance imaging (MRI) of shoulders with the MRI findings of the rotator cuff pathologies/tears. The sensitivity, specificity, and accuracy of the measured AHI in detecting full thickness RC tears by MRI were evaluated. Department of Orthopaedics, Faculty of Medicine, Thammasat University, Pathum Thani, Thailand. *email: adino_ Scientific Reports | (2022) 12:9404 | https://doi.org/10.1038/s41598-022-13632-0 1 Vol.:(0123456789) www.nature.com/scientificreports/ Materials and methods The study population consisted of 86 patients (34 men, 52 women; mean age, 61.06 years). All shoulder radiographs and MRIs were performed at Thammasat University Hospital, from the period of July 2020 to May 2021, were compared. The inclusion criteria were patients more than 18 years of age and patients with suspected rotator cuff related shoulder pain who underwent an MRI of the affected shoulder. The exclusion criteria were patients who had a fracture around the shoulder, a history of shoulder surgery, severe osteoarthritis, rotator cuff tear arthropathy, and/or a history of septic or inflammatory arthritis in the shoulder. Imaging protocol. Shoulder radiograph (Grashey view): Radiographs were performed with a Simens X-ray vacuum technology (Simens Healthcare, Jiangsu China). Assessment included true anteroposterior radiographs with the arm in a neutral position. The patients’ scapula parallel to the image receptor (rotating the body 35°- 45° forward). The beam was angled 20° craniocaudally. All radiographs were prospectively acquired with the patient in the upright and supine positions. MRI shoulder: The MRI examinations of the shoulders were performed in a supine position with a MAGNETOM Skyra is 3 T MRI, Siemens Healthcare Headquarters (Siemens Healthcare GmbH Henkestr, Erlangen Germany). The same units and the same protocols were used on all shoulder MRIs during the study period. The imaging planes were as follows; transverse, coronal oblique (perpendicular to the glenoid) and sagittal oblique (parallel to the glenoid). The Picture Archiving and Communication System (PACs), Synapse program (Fujifilm Medical Systems Inc., Hanover Park, Illinois) were used to make all measurements, on both radiographs and MRIs. Measurement of acromiohumeral interval. Two blinded orthopaedic surgeons, separately measured the AHI on shoulder radiographs (Grashey view) and on the sagittal oblique MRI. The process of reviewing the images required the Picture Archiving and Communication System (PACS) work station. The AHI was measured in millimeters. The interpretations by both reviewers consisted of the assessment of inter-observer and intra-observer reliability, the interval period of measurement was 2 weeks. The AHI of the shoulder radiographs was measured by using the distance between the dense cortical bone at the inferior aspect of the acromion and the subchondral lamina of the humeral head3. The shortest distance was measured. The same measurement was performed by reviewers on sagittal oblique T1-weighted MRI. The AHI (...truncated)