Citations

Scientifically, it has been questioned if the coracoacromial ligament has a significant role of serving as a pulley for the supraspinatus tendon. The purpose of this study was to examine the changes of abduction moment arms of the rotator cuff and deltoid muscle after anterior acromioplasty. In normal condition and after sectioning of the coracoacromial ligament and acromioplasty, abduction moment arms of four cuff tendons and three portions of the deltoid were obtained with four cadaver shoulders by computing the slope of the tendon excursion versus the glenohumeral abduction angle curve using a magnetic tracking device. In intact joints, the abduction moment arms of the supraspinatus increased from 20 mm to 27 mm with the arm abducted from 0° to 30°, which showed a better condition of the glenohumeral abduction. Then, they decreased to 23 mm with arm in 60° abduction. After sectioning of the coracoacromial ligament and acromioplasty less than 4 mm thick, the abduction moment arms of supraspinatus did not increase. This finding suggested that the coracoacromial ligament and acromion, anatomically, did not serve as pulleys for the supraspinatus tendon. However, the abduction moment arm of the middle deltoid decreased after an acromioplasty.

Abstract Purpose: The purpose of this study was to investigate the difference in contact geometry at the undersurface of acromion in shoulders with and without a rotator cuff (RC) tear. Type of Study: Case‐control study. Methods: Forty fresh cadaveric shoulders (average age at death, 61 years) without gross osteoarthritic changes were divided into the intact RC group (n = 20) and the RC tear group (n = 20). Clinical impingement was simulated by compressing the humeral head and the intact portion of the RC against the coracoacromial arch with an axial compressive force of 25 kg while the humerus was held abducted 20° in the scapular plane. The contact pattern between the acromion and the RC was measured with Fuji Prescale super low‐pressure–sensitive film (Fuji Photo Film Co, Ltd, Tokyo, Japan). The imprint image was analyzed using Global Lab image software (Automatix, Marlboro, MA). Results: The percentage of the maximum anteroposterior dimension of the imprint on Fuji film to the anteroposterior diameter of the acromial undersurface was 29% ± 9% in intact RC shoulders, and 39% ± 13% in shoulders with an RC tear ( P >.05). The percentage of the maximum mediolateral dimension of the imprint to the mediolateral diameter of the corresponding part of the acromial undersurface was 27% ± 12% in intact RC shoulders, and 48% ± 11% in shoulders with an RC tear. This difference was statistically significant ( P <.005). Conclusions: The contact geometry of the acromial undersurface with the underlying RC in the anteroposterior dimension, which might be related to the appearance in supraspinatus outlet view, was not significantly different between shoulders with and without an RC tear. These findings suggest that factors other than acromial shape play a significant role in the pathogenesis of RC tears. The implication regarding the role of acromioplasty remains to be clarified.

The technique of surgical repair for zone two flexor tendon injuries has been debated extensively throughout the years, yet adhesion formation, suture rupture, and suture locking on the pulley edge remain possible consequences of a poor repair. The partially lacerated tendon is especially challenging to treat since there can be justification for not intervening surgically. In a partial laceration canine model we measured failure load and suture gap formation for tendons repaired with the Lee, modified four-strand Savage, Kessler, modified Kessler, and Augmented Becker core suture techniques and with a simple running peripheral suture. The modified Kessler (106.3 N, SD 18.8 N) and modified Savage (108.2 N, SD 19.9 N) repair techniques had a significantly higher failure load than the Lee (85.0 N, SD 20.6 N) suture method p<0.05, while there were no differences among the other techniques. There were no significant differences in resistance to gap formation among the repair techniques, with the mean values ranging from 38.9 N/mm (SD 15.7 N/mm) using the simple running suture to 53.2 N/mm (SD 25.8 N/mm) with the Kessler repair. The mean load to produce a 1.5 mm repair site gap ranged from 71.1 N (SD 21.5 N) in the Lee repair to 91.3 N (SD 22.2 N) in the Augmented Becker repair although there were no significant differences among repair methods. All repair methods were much weaker than tendons left unrepaired (184.7 N, SD 41.3 N). [S0148-0731(00)00706-8]

A methodology was developed for determining the compressive properties of the supraspinatus tendon, based on finite element principles. Simplified three-dimensional models were created based on anatomical thickness measurements of unloaded supraspinatus tendons over 15 points. The tendon material was characterized as a composite structure of longitudinally arranged collagen fibers within an extrafibrillar matrix. The matrix was formulated as a hyperelastic material described by the Ogden form of the strain energy potential. The hyperelastic material parameters were parametrically manipulated until the analytical load-displacement results were similar to the results obtained from indentation testing. In the geometrically averaged tendon, the average ratio of experimental to theoretical maximum indentation displacement was 1.00 (SD: 0.01). The average normalization of residuals was 2.1g (SD: 0.9g). Therefore, the compressive material properties of the supraspinatus tendon extrafibrillar matrix were adequately derived with a first-order hyperelastic formulation. The initial compressive elastic modulus ranged from 0.024 to 0.090 MPa over the tendon surface and increased nonlinearly with additional compression. Using these material properties, the stresses induced during acromional impingement can be analyzed.

An optical spin micromotor operated by optical tweezers, described in the present study, converts radiant energy directly to mechanical energy. This conversion is of great practical and fundamental interest. The optical spin micromotor consists of a two-bead linkage. The large bead (2.0 μm in diameter) is trapped by the optical tweezers and rotates around the laser beam axis. The small bead (0.94 μm in diameter) is partially coated with gold/palladium for generating the spin torque through the change of momentum from gradient radiation pressure of the same laser applied on the coated small bead. With a laser power of 29 mW at the sample plane, the spin speed averaged 158.8±155.5 rpm (mean±standard deviation) and the torque was estimated as 101.9±99.8 pN nm. This optical spin micromotor will be useful in (1) providing a fundamental step toward developing optical-operated mechanical devices, (2) twisting macromolecules, and (3) generating vortex and shear force in medium at nanoscale.