Citations

Wheelchair propulsion is a man-machine interaction in which chair design and fit affect the relative positions and orientations of the upper extremity relative to the handrim and wheel axle. To understand these relationships better, experimental data were collected in five hand positions from five subjects exerting maximal effort to propel an instrumented wheelchair with its wheel in a locked position. The results of experiments revealed that the progression moment was greater at both initial and terminal propulsion positions and smaller in the mid-propulsion position. The vertical and horizontal force components were directed radially away from the wheel axle posterior to the dead centre position and radially towards the wheel axle anterior to top dead centre. Subsequently, a subject-specific quasi-static model of the upper extremity which maximized wheel progression moment was developed to augment our understanding of experimental measures. Model-predicted trends in progression moments and hand force direction were similar to experiment. Model predictions revealed that the optimal progression moment generation could potentially be affected by an individual's anthropometric parameters, joint strengths and also the direction of force applied by the hand on the handrim. Through wheelchair fitting and training of wheelchair users, it may be possible to improve propulsion technique.

Three-dimensional kinematics of the ulnohumeral joint under simulated active elbow joint flexion-extension was obtained by using an electromagnetic tacking device. The joint motion was analyzed based on Eulerian angle description. In order to minimize the effect of "downstream cross-talk" on calculation of the three Eulerian angles, an optimal axis to best represent flexion-extension of the elbow joint was established. This axis, on average, is close to the line joining the centers of the capitellum and the trochlear groove. Furthermore, joint laxity under valgus-varus stress was also examined. With the weight of the forearm as the stress, maximums of 7.6° valgus-varus laxity and 5.3° axial rotation laxity were observed within a range of elbow flexion. The results of this study provide useful baseline information on joint laxity for the evaluation of elbow joints with implant replacements and other surgical treatment modalities.

The goal of this study was to visualize the supraspinatus tendon three-dimensionally using fast spin-echo (FSE) MRI and validate the accuracy of measuring the dimensions of the supraspinatus tendon based on 3D reconstructed images. Nine cadaver shoulders (51–84 y/o, mean 70.0 y/o) were imaged at conventional T2-weighted spin-echo (CSE), gradient echo (GRE), and 3D T2-weighted FSE sequences. Each "object" of the supraspinatus muscle, tendon and scapula was three-dimensionally reconstructed using ANALYZE™ image data processing software. The FSE images revealed significantly higher contrast of the tendon and contrast-to-noise ratios of the fat-to-tendon and fat-to-muscle. The length of the anterior, middle, and posterior portions of the tendon were measured in two ways: (1) from the three-dimensional reconstructed images, and (2) directly from the cadaver specimen using calipers. No statistically significant differences were found between the ANALYZE™ and caliper measurements using a paired t-test for the anterior (p = 0.55), middle (p = 0.57) and posterior (p = 0.44) portions of the supraspinatus. The 3D FSE sequence exhibits higher spatial resolution, spends shorter acquisition time, and constructs a voxel data set. These advantages can prevent blurring artifacts when imaging the supraspinatus tendon of a human body. Tendon length measurements derived from three-dimensional reconstructions using ANALYZE™ were found to be good estimates of actual tendon length. Therefore, the combination of FSE sequence and 3D image data processing provides a method for noninvasive quantitative analysis of supraspinatus tendon morphology. The results lay the groundwork for future quantitative studies of cuff pathology.

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.

Reduced shoulder endurance in rotator cuff tear patients has been observed clinically. A simple and inexpensive shoulder endurance test protocol was developed. This study reports the test-retest reliability of the protocol. Twenty healthy volunteers without a history of shoulder pathology participated in the study. Each subject was tested twice, each on a separate day. Test-retest correlation coefficients of the arm endurance times were 0.59 and 0.60 for the dominant and nondominant sides, respectively. The protocol appears promising for assessing shoulder function.

Thumb motion and stability were examined after sequential division of support ligaments of the trapeziometacarpal (TMC) to simulate the pathologic condition of ligament laxity. The motion obtained with passive circumduction was measured with a magnetic tracking system. The lengths of the TMC joint ligaments were approximated by measuring the distance between origin and insertion of each ligament. The change in this apparent interorigin distance of the ligaments was measured before and after ligament sectioning. The anterior oblique ligament (AOL) and the ulnar collateral ligament (UCL) had the greatest effect on TMC joint stability during circumduction of the thumb. Division of the first intermetacarpal ligament (IML) did not produce a change in apparent length of other ligaments. We conclude that small changes in ligament length affect thumb stability and alter the path of circumduction. Neither the IML or posterior oblique ligaments were major stabilizers of the TMC joint during circumduction, prehensile grasp, or tip pinch. Reconstruction of the AOL and UCL ligaments should be considered for treatment of the initial stages of TMC instability.

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.