Full can test: Mechanisms of a positive test in patients with shoulder pain.

BACKGROUND: The full can test is theorized to produce compressive loads on the supraspinatus tendon within the subacromial space. Characterizing the width of the subacromial outlet, scapular orientation, and shoulder pain during the full can test will improve the mechanistic understanding of the positive full can test. METHODS: Cross-sectional repeated measures design. Participants with subacromial pain syndrome (n=30) were compared to a matched control group (n=30) during 2 conditions: passive support, and the full can test. The full can test was performed with the arm elevated to 90° in the scapular plane. In both conditions, measurements were taken of acromiohumeral distance with ultrasonography, scapular position using electromagnetic tracking, shoulder strength using a dynamometer, and shoulder pain with the 11-point rating scale. FINDINGS: During the full can test, both groups had a decreased acromial humeral distance, scapular upward rotation, posterior tilt, external rotation and clavicular protraction as compared to passive support (p<0.05). The subacromial pain group as compared to the control group reported greater shoulder pain (p<0.001), reduced strength (p=0.002) and greater scapular anterior tilt (p<0.05) during the full can test. INTERPRETATION: This study indicates the mechanisms of a full can test are a reduction in the acromial humeral distance, accompanied by scapular kinematic changes. A positive test of increased pain and reduced strength in those with subacromial pain syndrome can be explained additionally by an increase in scapular anterior tilt. These mechanistic changes may lead to tendon compression, but this cannot be verified as direct tendon compression was not measured.

Empty can exercise provokes more pain and has undesirable biomechanics compared with the full can exercise.

BACKGROUND: The purpose of this investigation was to characterize the scapular position and scapular muscle activation during the empty can (EC) and full can (FC) exercises. The EC exercise has been shown to produce scapular kinematics associated with the mechanism leading to subacromial impingement syndrome (SAIS) but has not been investigated in patients with (SAIS). This investigation will help improve the treatment of patients with SAIS. METHODS: Participants with SAIS (n = 28) performed 5 consecutive repetitions of FC and EC exercises. Scapular and clavicular 3-dimensional positions and scapular muscle activity were measured during each exercise. Pain was measured with the numeric pain rating 11-point scale. RESULTS: Participants reported greater pain during the EC exercise vs the FC exercise (difference, 1; P = .003). During the EC exercise, participants were in greater scapular upward rotation (difference, 3°; P < .001), internal rotation (mean difference, 2°; P = .017), and clavicular elevation (difference, 3°, P < .001) and in less scapular posterior tilt (difference, 2°; P < .001). There was greater activity of upper trapezius (difference, 4%, P = .002), middle trapezius (difference, 3%; P < .001), and serratus anterior (difference, 0.5%; P = .035) during ascent, and during the descent of greater upper trapezius (difference, 2%, P = .005), and middle trapezius (difference, 1%; P = .003), but less activity of the lower trapezius (difference, 1%; P = .039). CONCLUSIONS: The EC exercise was associated with more pain and scapular positions that have been reported to decrease the subacromial space. Scapular muscle activity was generally higher with the EC, which may be an attempt to control the impingement-related scapular motion. The FC exercise of elevation is preferred over the EC exercise.

Supraspinatus tendon and subacromial space parameters measured on ultrasonographic imaging in subacromial impingement syndrome.

PURPOSE: To characterize the supraspinatus tendon thickness, subacromial space, and the relationship between tendon thickness and subacromial space to further elucidate the mechanisms of subacromial impingement syndrome. METHODS: In a single-blind cross-sectional study, subjects were recruited with subacromial impingement syndrome (n = 20) and asymptomatic controls (n = 20) matched for age, gender, and hand dominance. Ultrasound images were collected using a 4-12-MHz linear transducer in B-mode of the supraspinatus tendon in the transverse (short axis) and the anterior aspect of the subacromial space outlet. Using image callipers, measurements of tendon thickness were taken at 3 points along the tendon and averaged for a single thickness measure. The subacromial space outlet was measured via the acromiohumeral distance (AHD) defined by the inferior acromion and superior humeral head. The occupation ratio was calculated as the tendon thickness as a percentage of AHD. RESULTS: The subacromial impingement syndrome group had a significantly thicker tendon (mean difference = 0.6 mm, p = 0.048) and a greater tendon occupation ratio (mean difference = 7.5 %, p = 0.014) compared to matched controls. There were no AHD group differences. CONCLUSIONS: The supraspinatus tendon was thicker and occupied a greater percentage of AHD, supporting an intrinsic mechanism. An extrinsic mechanism of tendon compression is theoretically supported, but future imaging studies need to confirm direct compression with elevation. Treatment to reduce tendon thickness may reduce symptoms, and surgical intervention to increase subacromial space may be considered if tendon compression can be verified.