Explore the vast range of titles available.

Fractures of the acromion are a common complication following surgical procedures of the shoulder due to changes in joint biomechanics. To improve understanding of acromial stresses and evaluate surgical procedures, image-based finite element models (FEMs) may be used. Image-based FEMs are dependent on accurate volumetric bone mineral density (vBMD), as this relates to mechanical properties in FEMs. Image reconstruction kernel alters vBMD; however, the effect on FEM output during simulated loading of the acromion has not been reported. The objective of this study was to compare predicted forces from FEMs derived from two common kernels and four density-modulus relationships to experimental forces in cadaveric scapulae (n = 10). Scapular FEMs were generated from CT scans reconstructed using bone sharpening (BONE) and standard (STD) kernels using four density-modulus relationships. Displacements were applied corresponding to experimental data collected on cadaveric specimens and forces were compared for each FEM. Specimen-specific percentage errors were as low as 1 % when using BONE kernel vBMD as input. Across all FEMs, the most accurate density-modulus relationship had a lower mean absolute percentage error (40 %) compared to the other three relationships compared (275 %, 281 %, 547 %), which greatly overestimated experimental forces. Across all models, those derived with STD kernel vBMD (40 %) had lower mean absolute percentage error relative to BONE kernel vBMD (42 %). This study highlights the relative accuracy of current density-modulus relationships using vBMD from two common reconstruction kernels. More accurate density-modulus relationships that account for variations in kernel parameters are required for FEM estimates of acromial forces and fracture predictions. Current models are not able to replicate experimental forces in cadaveric scapulae.

While several biomechanical investigations have measured acromion and scapular spine strains for various pathological conditions to better understand the risk factors for fracture, no study has measured strains in the native shoulder. The objective of this study was to use an ex-vivo shoulder motion simulator to measure principal strain during continuous, unconstrained, muscle-driven motion of the native shoulder. Eight cadaveric specimens (57 ± 6 years) were used to simulate scapular plane abduction (27.5 to 80° of humerothoracic elevation), forward flexion (27.5 to 72.5° of humerothoracic elevation), external rotation (0 to 40° of external rotation), and circumduction (elliptical path) with glenohumeral rotation speeds of 10°/s. Principal strain was measured throughout motion in four clinically relevant regions of the scapular spine and acromion according to the Levy classification using tri-axial strain gauge rosettes. Increases in humeral elevation during scapular plane abduction and forward flexion were associated with increases in deltoid force and scapula strain. However, above approximately 60° of humerothoracic elevation, strains plateaued while deltoid forces continued to increase indicating that scapula strain patterns are influenced by deltoid force magnitude and direction. Scapula strain was higher during scapular plane abduction than forward flexion in all regions but was only significantly higher in Levy 3B (p = 0.038). The highest strains were observed in Levy regions 2 and 3A (p ≤ 0.01) which correspond to regions with the highest clinically observed fracture rates demonstrating that the shape of the acromion and scapular spine may influence strain distribution irrespective of the joint condition.

To determine whether subacromial space (i.e. acromiohumeral distance; AHD, and/or occupation ratio percentage) differs between people with subacromial pain syndrome (SAPS) and those without. To investigate whether there is a correlation between subacromial space and pain or disability in adults with SAPS and whether temporal changes in pain or disability are accompanied by changes in subacromial space. Systematic review and meta-analysis. Fifteen studies with a total of 775 participants were included. Twelve studies were of high quality and three studies were of moderate quality using the modified Black and Downs checklist. There was no between group difference in AHD in neutral shoulder position (mean difference [95% CI] 0.28 [−0.13 to 0.69] mm), shoulder abduction at 45° (−0.02 [−0.99 to 0.96] mm) or 60° (−0.20 [−0.61 to 0.20] mm). Compared to the control group, a greater occupation ratio in neutral shoulder position was demonstrated in participants with SAPS (5.14 [1.87 to 8.4] %). There was no consistent pattern regarding the correlation between AHD and pain or disability in participants with SAPS, and no consistent increase in subacromial space with improvement in pain or disability over time. The results suggest that surgical (e.g. sub-acromial decompression) and non-surgical (e.g. manual therapy, taping, stretching and strengthening) management of subacromial pain syndrome should not focus solely on addressing a potential decrease in subacromial space, but also on the importance of other biopsychosocial factors.

Shoulder pain is a common clinical problem affecting most individuals in their lifetime. Despite the high prevalence of rotator cuff pathology in these individuals, the pathogenesis of rotator cuff disease remains unclear. Position and motion related mechanisms of rotator cuff disease are often proposed, but poorly understood. The purpose of this study was to determine the impact of systematically altering glenohumeral plane on subacromial proximities across arm elevation as measures of tendon compression risk. Three-dimensional models of the humerus, scapula, coracoacromial ligament, and supraspinatus were reconstructed from MRIs in 20 subjects. Glenohumeral elevation was imposed on the humeral and supraspinatus tendon models for three glenohumeral planes, which were chosen to represent flexion, scapular plane abduction, and abduction based on average values from a previous study of asymptomatic individuals. Subacromial proximity was quantified as the minimum distance between the supraspinatus tendon and coracoacromial arch (acromion and coracoacromial ligament), the surface area of the supraspinatus tendon within 2 mm proximity to the coracoacromial arch, and the volume of intersection between the supraspinatus tendon and coracoacromial arch. The lowest modeled subacromial supraspinatus compression measures occurred during flexion at lower angles of elevation. This finding was consistent across all three measures of subacromial proximity. Knowledge of this range of reduced risk may be useful to inform future studies related to patient education and ergonomic design to prevent the development of shoulder pain and dysfunction.

To establish the test–retest reliability of ultrasound measurements on acromio-humeral distance (AHD) and supraspinatus tendon thickness; and to explore their relationships with shoulder rotational strengths. Test–retest observational study. Thirty-seven individuals (age: 21.5±1.4 years) participated in this study. Twenty-four were University volleyball players with 15 healthy and 9 players with shoulder impingement syndrome (SIS). Thirteen participants were healthy untrained individuals. Ultrasound measurements of AHD and supraspinatus tendon thickness were taken, and isokinetic testing of concentric shoulder internal rotation (IR) and external rotation (ER) at a speed of 90°/s was performed. The measurement of the AHD and the supraspinatus tendon thickness indicated excellent reliability (ICC=0.922, and ICC=0.933 respectively), and the minimum detectable difference (MDD) were 2.10mm and 0.64mm respectively. A cut-off AHD distance of 23.9mm had a sensitivity of 0.67 and specificity of 0.71 (area under curve (AUC): 0.70; p=0.05) in identifying individuals with and without SIS. Hence, individuals with AHD larger than 23.9mm had greater possibility of having SIS. Positive correlations were found in AHD with supraspinatus tendon thickness (r=0.36, p<0.05) and shoulder external rotational strengths (r=0.47–0.62, all p<0.05) and ER/IR ratios (r=0.56–0.58, all p<0.05). Ultrasound measurements of AHD and tendon thickness have excellent reliability. The reported cut-off AHD highlighted the potential role of ultrasound measurements in volleyball players for early identification of SIS. The AHD was related to the supraspinatus tendon thickness and shoulder external rotation strengths. Our findings provide a scientific basis for muscle training in overhead athletes such as volleyball players.

The acromial tracker is used to measure scapular rotations during dynamic movements. The method has low accuracy in high elevations and is sensitive to its attachment location on the acromion. The aim of this study was to investigate the effect of the attachment position and shoulder orientation during calibration on the tracker accuracy. The tracker was attached to one of three positions: near the anterior edge of the acromion process, just above the acromial angle and the meeting point between the acromion and the scapular spine. The scapula locator was used to track the scapula during bilateral abduction simultaneously. The locator was used to calibrate the tracker at: no abduction, 30°, 60°, 90° and 120° humerothoracic abduction. ANOVA tests compared RMS errors for different attachment positions and calibration angles. The results showed that attaching the device at the meeting point between the acromion and the scapular spine gave the smallest errors and it was best to calibrate the device at 60° for elevations ≤90°, at 120° for elevations >90° and at 90°or 120° for the full range of abduction. The accuracy of the tracker is significantly improved if attached appropriately and calibrated for the range of movement being measured.

Accurate measurement of joint kinematics is required to understand the musculoskeletal effects of a therapeutic intervention such as upper extremity (UE) ergometry. Traditional surface-based motion capture is effective for quantifying humerothoracic motion, but scapular kinematics are challenging to obtain. Methods for estimating scapular kinematics include the widely-reported acromion marker cluster (AMC) which utilizes a static calibration between the scapula and the AMC to estimate the orientation of the scapula during motion. Previous literature demonstrates that including additional calibration positions throughout the motion improves AMC accuracy for single plane motions; however this approach has not been assessed for the non-planar shoulder complex motion occurring during UE ergometry. The purpose of this study was to evaluate the accuracy of single, dual, and multiple AMC calibration methods during UE ergometry. The orientations of the UE segments of 13 healthy subjects were recorded with motion capture. Scapular landmarks were palpated at eight evenly-spaced static positions around the 360° cycle. The single AMC method utilized one static calibration position to estimate scapular kinematics for the entire cycle, while the dual and multiple AMC methods used two and four static calibration positions, respectively. Scapulothoracic angles estimated by the three AMC methods were compared with scapulothoracic angles determined by palpation. The multiple AMC method produced the smallest RMS errors and was not significantly different from palpation about any axis. We recommend the multiple AMC method as a practical and accurate way to estimate scapular kinematics during UE ergometry.

Robotic exoskeletons can be used to study and treat patients with neurological impairments. They can guide and support the human limb over a large range of motion, which requires that the movement trajectory of the exoskeleton coincide with the one of the human arm. This is straightforward to achieve for rather simple joints like the elbow, but very challenging for complex joints like the human shoulder, which is comprised by several bones and can exhibit a movement with multiple rotational and translational degrees of freedom. Thus, several research groups have developed different shoulder actuation mechanism. However, there are no experimental studies that directly compare the comfort of two different shoulder actuation mechanisms. In this study, the comfort and the naturalness of the new shoulder actuation mechanism of the ARMin III exoskeleton are compared to a ball-and-socket-type shoulder actuation. The study was conducted in 20 healthy subjects using questionnaires and 3D-motion records to assess comfort and naturalness. The results indicate that the new shoulder actuation is slightly better than a ball-and-socket-type actuation. However, the differences are small, and under the tested conditions, the comfort and the naturalness of the two tested shoulder actuations do not differ a lot.

During a four-year period, fourteen individuals (fifteen shoulders) who had been seen at the shoulder service of our institution because of pain in the shoulder had a radiographic finding of an os acromiale. On clinical examination, the pain appeared to be due to an unstable os acromiale because the patients had point tenderness over the acromion and pain on forward elevation of the shoulder. The diagnosis of an os acromiale was confirmed on radiographs, magnetic resonance images, or a bone scan. Eight patients had an associated tear of the rotator cuff. The os acromiale was located in the pre-acromion in one shoulder, the meso-acromion in eleven shoulders, and the meta-acromion in three shoulders. At the operation, the anterior aspect of the acromion was found to be unstable in all shoulders. Eleven patients (twelve shoulders) had open reduction of the os acromiale and insertion of an autogenous iliac-crest bone graft. Of those patients, four (five shoulders) had open reduction and internal fixation with a tension-band procedure with use of pins and wires. Only one of those shoulders had a solid osseous union, and the other four shoulders had a non-union that was due to a disruption of the fixation. The remaining seven patients (seven shoulders) had open reduction and internal fixation with use of cannulated screws and a tension-band construct; a solid osseous union was achieved in all but one of them. One patient had excision of the pre-acromion, which relieved the pain. Two patients who had had failed open reduction and internal fixation had excision of a grossly unstable os acromiale in the meso-acromion; both patients had pain and weakness after this procedure. Of the twelve shoulders that had open reduction and bone-grafting, seven had union of the os acromiale; the average time to radiographic and clinical union was nine weeks (range, seven to twenty weeks). We concluded that, although it is rare, symptomatic unstable os acromiale does occur and can be effectively treated with use of autogenous bone-grafting and internal fixation with a rigid tension-band construct and cannulated screws.

Deficits in trunk control due to spinal cord injury (SCI) lead to slower target-reaching movements of the hand. We investigated whether the movement path is also affected, and whether providing external support for the trunk can abolish the kinematic differences. To compare movement trajectories between individuals with SCI and neurologically normal individuals, with and without external trunk support. Neural Control/Biomechanics Laboratory, University of Illinois, Chicago, USA. Five subjects with levels of injury between C7 and T4 were tested 3-8 years post-injury, and compared with five control subjects. Two targets were employed. Trajectories were recorded by a motion-capture system using infrared emitting markers. Peak speed and path curvature were calculated for the fingertip and for the acromion. Compared with control subjects, the subjects with SCI exhibited lower peak speed of the fingertip but not of the acromion, and less straight paths for both. When the trunk was supported externally, the difference in fingertip speed persisted. The support abolished the difference in path curvature for the fingertip but accentuated that for the acromion. The slower hand movements of individuals with SCI are not simply time-scaled versions of those of normal subjects, and the provision of trunk support does not erase the kinematic differences between the reaching movements of the two groups.