STUDY GROUP
The institutional review board of the CHRU of Nancy, FRANCE, approved this study, and all patients gave written informed consent. All experiments were performed in accordance with relevant guidelines and regulations. From October 10, 2013, and October 16, 2017, 170 patients over 18 years of age were enrolled prospectively and consecutively. These patients had been diagnosed with AC by orthopedic surgeons or rheumatologists and underwent shoulder radiographs and MRI.
Patients with MRI contraindications, prior shoulder surgery, shoulder osteoarthritis, calcific tendinosis, shoulder bursitis, and fractures on MRI were excluded. One patient withdrew from the study; four were excluded because of missing clinical data, 33 because of rotator cuff pathology (at least one full-thickness tendon tear). Thus, the final study population consisted of 132 patients with a mean age 54.1±9.3 (22-78) years. There were 55 men and 77 women (0.63 M/F sex ratio). Two patients had bilateral AC, yielding 134 shoulder MRI studies.
SHOULDER FUNCTION ASSESSMENT
A modified CMS was applied to all patients by a senior radiologist just prior to the MRI examination 19. Two subjective variables for a maximum score of 35 were evaluated: daily living pain (varying from 0 – severe pain to 15 points – no pain) and daily living activity limitation (varying from 0 – maximal limitation to 20 points – no limitation). The patients answered a questionnaire assessing the degree of pain (no pain, slight, moderate or severe pain), activity level (pain during work, sports, and recreation, sleep) and arm range of motion (ROM) (arm elevation up to the waist, xiphoid process, neck, top of the head, above the head). The examiner received prior training in performing the CMS. ROM was also quantitatively assessed with a goniometer, in external and internal rotation, forward and lateral elevation, and scored in each position by the examiner (varying 0°-30° = 0 to 151°-180°= 10 points for each movement). Thus, the ROM scored varied from 0 – minimal mobility to 40 – maximal mobility). The final CMS, therefore, ranged from 0, (highly impaired shoulder) to 75 points (normal shoulder) (supplementary material 1). Shoulder strength, which was part of the original CMS, was not evaluated in this study, because there was no reliable measurement device available.
Pain duration was graded from 1-5 as follows: less than 6 weeks; between 6 weeks and 3 months; between 3 and 6 months; between 6 months and 1 year and over 1 year. The presence of diurnal pain, nocturnal pain, and nocturnal pain predominance were also evaluated.
CLINICAL FOLLOW-UP
A clinical follow-up was available in 49 patients with a mean age of 54±8.8 (37-74) years treated by physical therapy. There were 17 men and 32 women (0.53 M/F sex ratio). Based on medical record data (pain, activities, and ROM), the symptoms at 9 to 13 months after the MRI examination were classified as improved, stable, or worsened. None of these patients had been treated by intra-articular corticosteroid injection.
MRI EXAMINATION
MRI examinations were performed with either a 1.5T (105 patients) or a 3.0T scanner (27 patients) (Signa HDxt, GE Healthcare, Milwaukee, WI, USA) using a dedicated eight-channel shoulder coil and similar protocols. The patients were in a supine position with the arm placed in external rotation by the side of the body.
All MRI examinations consisted of an axial and oblique sagittal fast spin-echo (FSE) T1-weighted acquisitions; axial, oblique sagittal and oblique coronal FSE T2-weighted fat-saturated images. MRI protocols are summarized in table 1.
IMAGE ANALYSIS
The images were retrospectively reviewed by two musculoskeletal radiologists with three (FZ) and seven years (PP) of clinical experience with MRI blinded to clinical and demographic data using a PACS station (Synapse®, v4.1.600, Fujifilm, Montigny, France). A third radiologist (P.A.G.T.) with 11 years of clinical experience with MRI performed a training session with the two readers with 20 MRI studies of patients with AC, not included in the study population prior to the readouts.
The signal intensity of the IGHL on oblique coronal T2-weighted fat-saturated images was graded from 1-4 as follows (Figure 1): normal homogenous low signal intensity; partial or foci of signal hyperintensity; global signal hyperintensity; linear hyperintensity of the peri-articular soft tissues.
The patients with IGHL scores of 1 and 2 were considered to have a low IGHL signal intensity, and those with grades 3 and 4 were considered to have high IGHL signal intensity. The thickness of the IGHL was measured at the glenoidal and humeral insertions on oblique coronal T2-weighted fat-saturated images 9 and classified as <4 mm, between 4 and <6 mm and ≥6 mm (Figure 2)27. The thickest portion of the coracohumeral ligament (CHL) was measured on the sagittal T2-weighted fat-saturated images 9 (Figure 3).
STATISTICAL ANALYSIS
The R Development Core Team software (version 3.0.12013, R Foundation for Statistical Computing, Vienna, Austria) was used to perform statistical analysis. Statistical significance was defined as P<0.05. Quantitative data are presented as mean ± standard deviation (range).
Linear regression analysis with the Pearson test was used to evaluate the correlation between the signs of AC studied on MRI and pain, mobility, activity scores, and pain duration. The association between MRI findings, global modified CMS score, diurnal pain, night pain, and predominance of night pain was assessed with the Fisher exact test. The association between MRI findings and clinical follow-up was assessed with the Wilcoxon test. For each MRI measurement, intraclass correlation coefficients (ICC) were calculated to assess interobserver variability. ICC values below 0.5 were considered poor, between 0.5 and 0.75 moderate, between 0.75 and 0.90 good and above 0.9 excellent28.