Muscle volume imbalance may be associated with static posterior humeral head subluxation

Background The transverse force couple (TFC) of the rotator cuff (subscapularis vs. infraspinatus and teres minor muscle) is an important dynamic stabilizer of the shoulder joint in the anterior-posterior direction. In patients with posterior static subluxation of the humeral head (PSSH), decentration of the humeral head posteriorly occurs, which is associated with premature arthritis. We hypothesize that not only pathologic glenoid retroversion but also chronic muscle volume imbalance in the transverse force couple leads to PSSH. Methods A retrospective analysis of the TFC muscle volumes of 9 patients with symptomatic, atraumatic PSSH, within 8 were treated with glenoid correction osteotomy, was conducted. The imaging data (CT) of 9 patients/10 shoulders of the full scapula and shoulder were analyzed, and the muscle volumes of the subscapularis (SSC), infraspinatus (ISP) and teres minor muscles (TMM) were measured by manually marking the muscle contours on transverse slices and calculating the volume from software. Furthermore, the glenoid retroversion and glenohumeral distance were measured. Results The mean glenoid retroversion was − 16° (− 7° to − 31°). The observed mean glenohumeral distance was 4.0 mm (0 to 6.8 mm). Our study population showed a significant muscle volume imbalance between the subscapularis muscle and the infraspinatus and teres minor muscles (192 vs. 170 ml; p = 0.005). There was no significant correlation between the subscapularis muscle volume and the glenohumeral distance (r = 0.068), (p = 0.872). Conclusion The muscle volume of the SSC in patients with PSSH was significantly higher than the muscle volume of the posterior force couple (ISP and TMM). This novel finding, albeit in a small series of patients, may support the theory that transverse force couple imbalance is associated with PSSH. Level of evidence Level 4 – Case series with no comparison group.

A novel and simple technique for correcting localised rotations in the early alignment stage

Correcting severe tooth rotations can be challenging. There are many ways to de-rotate teeth with fixed or removable appliances. Mechanically, the best and most effective way is one that produces a two-force couple system to rotate a tooth around its centre of rotation (longitudinal axis). The aim of this article was to introduce a simple and efficient technique using a closed coil to correct localised tooth rotations in the early alignment stage, utilising a simple two-force couple system. Furthermore, some of the biomechanical principles concerning de-rotation will be revisited.

Multimodal Construal of Attitude in the Online City Guide of Guangzhou

This study conducts a social semiotic analysis of the online city guide of Guangzhou. Drawing on Martin’s Appraisal theory with a particular focus on the semantic systems of attitude and graduation, this paper investigates the attitudinal meanings adjusted by graduation in both modes of language and visual images. It is revealed that positive appreciation resources are dominant among the three subsystems of attitude, with the pervasive use of reaction and valuation resources to stimulate tourist desires and promote unique identity of the city. Graduation resources, especially force, couple with attitude resources to upscale the positivity of the attitude and strongly align the readers into the same value position. The language and images in most cases coordinate with each other, with the evaluative meanings of visual images elaborating or extending those of verbal texts, whereas complementary intermodal relation exists in some cases, with the evaluative meanings conveyed by visual images and the verbal texts merely offering factual information. The findings may help to better understand the way online city guides achieve the communicative purposes through multimodal evaluative devices.