Patient selection
This study was approved by our hospital’s Institutional Review Board. From July 2015 to May 2020, we reviewed 534 patients under the diagnosis of unilateral frozen shoulder and received intra-articular injection of triamcinolone acetonide. We defined frozen shoulder based on previous studies as forward flexion less than 100° (maximal 150°; forward flexion is glenohumeral motion without scapulohumeral rhythm), external rotation under 45° (maximal 90°) in 0° of horizontal abduction, or internal rotation at a level lower than the third lumbar spine (L3) (maximal T7 level).(6, 7)
For enrollment, we selected patients who underwent both plain radiograph and magnetic resonance imaging to detect reliable imaging indicators of frozen shoulder such as thickening of the capsule in the rotator interval, thickening of the coracohumeral ligament and obliteration of the fat triangle under the coracoid process.(8) Also, detection of combined shoulder lesions that could cause restriction in shoulder motion or decreased ROM was made. Patients with concomitant shoulder lesions, including rotator cuff tear, labral tear, or arthritis, and those with a history of previous shoulder surgery or fracture were not included in the analysis.
In order to avoid including patients with inflammatory stage, of which the limitation is primarily caused by the subjective pain without actual pathological change of the intra-articular capsule itself, we have confined the cohort to the patients with at least 3 months of symptom duration before the injection. Also, patients with previous shoulder injection history were not included on the analysis. However, patients with other attempts including oral medications or physiotherapy prior to the injection were not excluded.
To reduce the risk of complications following an increase in blood glucose level after the injection of triamcinolone acetonide, injections were allowed in diabetic patients with controlled diabetes (HbA1c < 7) under the same medication for the past three months. Other underlying systemic conditions known to affect shoulder ROM or be associated with etiology of frozen shoulder such as thyroid diseases, hyperlipidemia, and hypertension were not considered as contraindications for intra-articular injection of triamcinolone acetonide. These conditions were considered to be underlying conditions when the patient was under treatment or management after diagnostic confirmation. After excluding 229 patients, 305 patients with primary frozen shoulder were enrolled and evaluated.
Injection technique
All injections were performed after sterilization of the injection site. A high-resolution transducer (12 MHz linear array) was utilized for needle guidance. A 21-gauge needle on syringe containing 40 mg of triamcinolone acetonide mixed with 1 mL of lidocaine (2%) was prepared. The procedure was performed with the patients sitting on a chair with a neutral position of the shoulder and elbow flexed 90°. The needle was inserted anteriorly at the level of coracoid process aiming medially to the humeral head. As soon as the needle made contact with the humeral head, the needle was tilted away from the head and advanced into the articular cavity. The location of the needle within the joint was confirmed by ultrasound.
Post-injection rehabilitation
The same standardized rehabilitation protocols were applied to every patient from the day after injection. The patients were required to follow the home-based instruction daily without additional clinic-based physiotherapy. Pendulum circumduction and self-stretching passive motion exercise in every plane were recommended for six weeks after injection. Pulley exercise was recommended for advanced forward flexion; isometric exercise was also recommended. No limit was imposed on use of the shoulder to the extent tolerated. Periodic supervision for compliance of rehabilitation was made every two weeks.
Assessment
The passive ROM was checked twice before and after the injection. For the measurement, forward flexion and external rotation were evaluated with a goniometer when patients were in a supine position, excluding scapulohumeral motion. Internal rotation, which was measured in the sedentary position, was evaluated by the vertebral level reached by the tip of the thumb; internal rotation up to the level of the sacrum was designated as a zero point, and one point was added for each additional level upward. At six weeks post-injection, ROM was evaluated in the same manner.
Then, we also sought to determine what factors were correlated with improvement or unresponsiveness to the intra-articular injection for the treatment of frozen shoulder. The analyzed factors were as follows: age, sex, body mass index (BMI), initial ROM before injection, symptom duration, hand dominance, smoking history, and the existence of underlying disease including diabetes mellitus, hypertension, coronary disase, thyroid disease and hypercholesterolemia. All data were collected and evaluated by a clinical researcher who was blinded to the study assignments.
Statistical Methods
The primary outcome variable of interest was the range of changes in each aspect of ROM at six weeks after injection. A paired t test was used to compare the differences in ROM before and after injection for enrolled patients. Pearson’s correlation coefficient (ρ) was performed to determine the relationship between ROM improvement and evaluated factors. Multivariate analysis using logistic regression analysis was performed to identify significant factors related to responsiveness and irresponsiveness of ROM to injection of triamcinolone acetonide. The amount of ROM improvement at six weeks post-injection was determined using dependent variables and independent variables, including the other factors mentioned above. The level of significance was set at p<0.05. Statistical analysis was performed using the SPSS software version 18.0 (SPSS Inc., Chicago, IL, USA).