An, Kai‐Nan

Concavity-compression is an important mechanism for keeping a joint centered despite a large range of motion. The purpose of this study was to explain how the results of a test measuring the joint intrinsic stability can be interpreted and related to joint architecture. As an example, the method was demonstrated for the glenohumeral joint although the versatility allows any articulating joint, whether natural or prosthetic, to be analyzed. The initial slope from the central point was relatively steep, indicating a large resistance to translation. The peak translation force occurred within the first 5 mm of displacement for the glenohumeral joint, indicating a high congruence between the humerus and glenoid surfaces. Stability ratio, calculated as the maximum translation force divided by the applied joint compressive force, makes it possible to compare the stabilizing effect under different compressive loads for different anatomical directions. In hanging arm position, the joint stability ratio ranged from 30.5% to 60.1%. Finally, the effective depth of the concavity and the maximum range of joint translation can be measured by completely dislocating the joint. For the glenohumeral specimen, the smallest glenoid concavity depth, 3.8 mm, occurred in the anterior direction. The joint translation limit was smallest in the anterior-posterior direction (28.0 mm). The methodology presented in this study will allow consistent testing parameters between different trials, easily allowing parametric studies to gain a more complete understanding of articular joints.

The purpose of this study is to develop an electromechanical system for dynamic simulation of the stance phase of a human gait using cadaveric foot specimens. The system can be used for quantification of foot and ankle pathomechanics and design of foot and ankle reconstructive surgeries. Servo-pneumatic systems were used for application of the tibial weight loading and muscle loadings. A four-bar mechanism was constructed to provide the progressive motion of a tibia during the simulation while the external loadings were simultaneously applied. Muscle loadings were estimated based on the physiological cross-sectional area and normal electromyography (EMG) data with the assumption of the linear EMG–force relationship. Ad hoc tuning of the unknown muscle gains was conducted until a reasonable match with the normal vertical ground reaction force profile, center of pressure advancement, and characteristic foot motion events (heel strike, foot flat, heel rise and toe-off) could be made. Three cadaver feet and an artificial foot were tested with five repeated trials. The simulator reproduced the stance phase of a human gait in the sagittal plane with reasonable accuracy and consistency without compromising either kinematics or kinetics of the foot and ankle complex.

The supraspinatus tendon is frequently involved in rotator cuff tears. It has been suggested that joint position affects the structural mechanics of the tendon–bone complex. The purpose of this study was to determine regional variations in structural properties of the supraspinatus tendon in two glenohumeral positions. Supraspinatus tendons from 17 fresh frozen cadavers were divided into three strips of equal width and tested with a material-testing machine. The arm orientation was either in hanging position or 60 degrees glenohumeral abduction corresponding to 90 degrees arm abduction assuming 30 degrees scapular rotation. Tensile force, tendon elongation and failure mode were recorded. Overall, there was no significant difference in structural properties between hanging arm position and 60 degrees of glenohumeral abduction (p>0.05). However, the mean ultimate load (385 N, SD 56 N) and mean ultimate stress (14 MPa, SD 3 MPa) of the anterior tendon section with the arm in glenohumeral abduction were lower in 60 degrees abduction than in the hanging arm position (611 N, SD 276 N; 24 MPa, SD 10 MPa). In hanging arm position, the anterior tendon portion had a significantly greater ultimate load and stiffness than the middle and posterior portions (p<0.05). The regional variation in structural properties substantiates the clinical finding that rotator cuff ruptures easily extend posteriorly. Our study suggests that glenohumeral abduction reduces the failure strength of the supraspinatus tendon, specifically of its anterior portion. In our study, the maximum load of the anterior portion was substantially higher than predicted maximum loads transmitted physiologically through the entire tendon.

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.