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Reverse shoulder arthroplasty may be performed using components that medialize or lateralize the center of rotation. The purpose of this prospective study was to directly compare 2 reverse shoulder arthroplasty designs. Two treatment groups and 1 control group were identified. Group I comprised 9 patients using a medialized Grammont-style (GRM) prosthesis with a neck-shaft angle of 155°. Group II comprised 9 patients using a lateralized (LAT) prosthesis with a neck-shaft angle of 135°. Pre- and postoperative assessment of range of motion, American Shoulder and Elbow Surgeons score, and visual analog scale pain score were performed. Radiographic measurements of lateral humeral offset and acromiohumeral distance were compared. The GRM prosthesis achieved greater forward flexion (143.9° vs 115.6°; Reverse shoulder arthroplasty may be performed using components that medialize or lateralize the center of rotation. The purpose of this prospective study was to directly compare 2 reverse shoulder arthroplasty designs. Two treatment groups and 1 control group were identified. Group I comprised 9 patients using a medialized Grammont-style (GRM) prosthesis with a neck-shaft angle of 155°. Group II comprised 9 patients using a lateralized (LAT) prosthesis with a neck-shaft angle of 135°. Pre- and postoperative assessment of range of motion, American Shoulder and Elbow Surgeons score, and visual analog scale pain score were performed. Radiographic measurements of lateral humeral offset and acromiohumeral distance were compared. The GRM prosthesis achieved greater forward flexion (143.9° vs 115.6°; P =.05), whereas the LAT achieved greater external rotation (35.0° vs 28.3°; P =.07). The lateral humeral offset was greater for the LAT prosthesis compared with the GRM prosthesis, but this distance was not significantly different from that found in the control group. The acromiohumeral distance was significantly greater in the GRM prosthesis group compared with both the LAT and the control groups. The results of this study confirm that different reverse shoulder arthroplasty designs produce radiographically different anatomy. Whereas the GRM prosthesis significantly alters the anatomy of the shoulder, the LAT design can preserve some anatomic relationships found in the normal shoulder. The clinical outcomes indicate that this may have an effect on range of motion, with traditional designs achieving greater forward flexion and lateralized designs achieving greater external rotation. [ Orthopedics. 2015; 38(12):e1098–e1103.]

The acquisition of terrestrial, limb-based locomotion during tetrapod evolution has remained a subject of debate for more than a century 1 , 2 . Our current understanding of the locomotor transition from water to land is largely based on a few exemplar fossils such as Tiktaalik 3 , Acanthostega 4 , Ichthyostega 5 and Pederpes 6 . However, isolated bony elements may reveal hidden functional diversity, providing a more comprehensive evolutionary perspective 7 . Here we analyse 40 three-dimensionally preserved humeri from extinct tetrapodomorphs that span the fin-to-limb transition and use functionally informed ecological adaptive landscapes 8 – 10 to reconstruct the evolution of terrestrial locomotion. We show that evolutionary changes in the shape of the humerus are driven by ecology and phylogeny and are associated with functional trade-offs related to locomotor performance. Two divergent adaptive landscapes are recovered for aquatic fishes and terrestrial crown tetrapods, each of which is defined by a different combination of functional specializations. Humeri of stem tetrapods share a unique suite of functional adaptations, but do not conform to their own predicted adaptive peak. Instead, humeri of stem tetrapods fall at the base of the crown tetrapod landscape, indicating that the capacity for terrestrial locomotion occurred with the origin of limbs. Our results suggest that stem tetrapods may have used transitional gaits 5 , 11 during the initial stages of land exploration, stabilized by the opposing selective pressures of their amphibious habits. Effective limb-based locomotion did not arise until loss of the ancestral ‘L-shaped’ humerus in the crown group, setting the stage for the diversification of terrestrial tetrapods and the establishment of modern ecological niches 12 , 13 . Analysis of humeri from fossils that span the fin-to-limb transition reveal that the change in the humerus shape is driven by both ecology and phylogeny, and is associated with functional trade-offs related to locomotor performance.

Spaceflight is known to induce severe systemic bone loss and muscle atrophy of astronauts due to the circumstances of microgravity. We examined the influence of artificially produced 2G hypergravity on mice for bone and muscle mass with newly developed centrifuge device. We also analyzed the effects of microgravity (mostly 0G) and artificial produced 1G in ISS (international space station) on mouse bone mass. Experiment on the ground, the bone mass of humerus, femur and tibia was measured using micro-computed tomography (μCT), and the all bone mass was significantly increased in 2G compared with 1G control. In tibial bone, the mRNA expression of bone formation related genes such as Osx and Bmp2 was elevated. The volume of triceps surae muscle was also increased in 2G compared with 1G control, and the mRNA expression of myogenic factors such as Myod and Myh1 was elevated by 2G. On the other hand, microgravity in ISS significantly induced the loss of bone mass on humerus and tibia, compared with artificial 1G induced by centrifugation. Here, we firstly report that bone and muscle mass are regulated by the gravity with loaded force in both of positive and negative on the ground and in the space.

Background Reverse total shoulder arthroplasty (RTSA) is widely used; however, the effects of RTSA geometric parameters on joint and muscle loading, which strongly influence implant survivorship and long-term function, are not well understood. By investigating these parameters, it should be possible to objectively optimize RTSA design and implantation technique. Questions/purposes The purposes of this study were to evaluate the effect of RTSA implant design parameters on (1) the deltoid muscle forces required to produce abduction, and (2) the magnitude of joint load and (3) the loading angle throughout this motion. We also sought to determine how these parameters interacted. Methods Seven cadaveric shoulders were tested using a muscle load-driven in vitro simulator to achieve repeatable motions. The effects of three implant parameters—humeral lateralization (0, 5, 10 mm), polyethylene thickness (3, 6, 9 mm), and glenosphere lateralization (0, 5, 10 mm)—were assessed for the three outcomes: deltoid muscle force required to produce abduction, magnitude of joint load, and joint loading angle throughout abduction. Results Increasing humeral lateralization decreased deltoid forces required for active abduction (0 mm: 68% ± 8% [95% CI, 60%–76% body weight (BW)]; 10 mm: 65% ± 8% [95% CI, 58%–72 % BW]; p = 0.022). Increasing glenosphere lateralization increased deltoid force (0 mm: 61% ± 8% [95% CI, 55%–68% BW]; 10 mm: 70% ± 11% [95% CI, 60%–81% BW]; p = 0.007) and joint loads (0 mm: 53% ± 8% [95% CI, 46%–61% BW]; 10 mm: 70% ± 10% [95% CI, 61%–79% BW]; p < 0.001). Increasing polyethylene cup thickness increased deltoid force (3 mm: 65% ± 8% [95% CI, 56%–73% BW]; 9 mm: 68% ± 8% [95% CI, 61%–75% BW]; p = 0.03) and joint load (3 mm: 60% ± 8% [95% CI, 53%–67% BW]; 9 mm: 64% ± 10% [95% CI, 56%–72% BW]; p = 0.034). Conclusions Humeral lateralization was the only parameter that improved joint and muscle loading, whereas glenosphere lateralization resulted in increased loads. Humeral lateralization may be a useful implant parameter in countering some of the negative effects of glenosphere lateralization, but this should not be considered the sole solution for the negative effects of glenosphere lateralization. Overstuffing the articulation with progressively thicker humeral polyethylene inserts produced some adverse effects on deltoid muscle and joint loading. Clinical Relevance This systematic evaluation has determined that glenosphere lateralization produces marked negative effects on loading outcomes; however, the importance of avoiding scapular notching may outweigh these effects. Humeral lateralization’s ability to decrease the effects of glenosphere lateralization was promising but further investigations are required to determine the effects of combined lateralization on functional outcomes including range of motion.

It is accepted that the metabolic response of bone tissue depends on the intensity of the mechanical loads, but also on the type and frequency of stress applied to it. Physical exercise such as running involves stresses which, under certain conditions, have been shown to have the best osteogenic effects. However, at high intensity, it can be deleterious for bone tissue. Consequently, there is no clear consensus as to which running modality would have the best osteogenic effects. Our objective was to compare the effects of three running modalities on morphological and micro-architectural parameters on forelimb bones. Forty male Wistar rats were randomly divided into four groups: high intensity interval training (HIIT), continuous running, combined running ((alternating HIIT and continuous modalities) and sedentary (control). The morphometry, trabecular microarchitecture and cortical porosity of the ulna, radius and humerus were analyzed using micro-tomography. All three running modalities resulted in bone adaptation, with an increase in the diaphyseal diameter of all three bones. The combined running protocol had positive effects on the trabecular thickness in the distal ulna. The HIIT protocol resulted in an increase in both medio-lateral diameter and cortical bone area over total area (Ct.Ar/Tt.Ar) at the ulnar shaft compared with sedentary condition. Moreover, the HIIT protocol decreased the mean surface area of the medulla (Ma.Ar) according to sedentary condition at the ulnar shaft. This study has shown that HIIT resulted in a decrease in trabecular bone fraction in favor of cortical bone area at the ulna.

Shoulder kinematics and muscle activity vary depending on the elevation plane of the upper limb. However, how muscle coordination, which plays a crucial role in controlling shoulder kinematics, differs among elevation planes remains unclear. This study compared shoulder kinematics, muscle synergies, and muscle activation levels across different elevation planes to better understand the neuromuscular mechanisms underlying shoulder kinematics. Shoulder kinematics and muscle activity were recorded during three upper limb elevation tasks (sagittal, scapular, and frontal plane elevation) in 12 subjects (7 males and 5 females). Muscle synergies were extracted using nonnegative matrix factorization, and individual muscle activity levels were calculated as a percentage of maximum voluntary contraction. Glenohumeral elevation was greatest during the sagittal plane elevation task and smallest during the frontal plane elevation task (maximum difference of 14.1°). The differences in kinematics among these elevation planes were suggested to be attributable to the early-stage activity level during elevation of one of the two extracted muscle synergies—specifically, the synergy believed to contribute to humeral head stabilization—and the activation amplitude of the anterior deltoid. Differences in scapular kinematics among three elevation plane tasks could not be explained by variations in muscle synergies but were instead suggested to result primarily from differences in the activation amplitudes of the three parts of the trapezius. To results suggest that shoulder kinematics are controlled by subtle changes in muscle synergy activation patterns and individual muscle activation levels.

The ‘sprawling-parasagittal’ postural transition is a key part of mammalian evolution, associated with sweeping reorganization of the postcranial skeleton in mammals compared to their forebears, the non-mammalian synapsids. However, disputes over forelimb function in fossil synapsids render the precise nature of the ‘sprawling-parasagittal’ transition controversial. We shed new light on the origins of mammalian posture, using evolutionary adaptive landscapes to integrate 3D humerus shape and functional performance data across a taxonomically comprehensive sample of fossil synapsids and extant comparators. We find that the earliest pelycosaur-grade synapsids had a unique mode of sprawling, intermediate between extant reptiles and monotremes. Subsequent evolution of synapsid humerus form and functional traits showed little evidence of a direct progression from sprawling pelycosaurs to parasagittal mammals. Instead, posture was evolutionarily labile, and the ecological diversification of successive synapsid radiations was accompanied by variation in humerus morphofunctional traits. Further, synapsids frequently evolve toward parasagittal postures, diverging from the reconstructed optimal evolutionary path; the optimal path only aligns with becoming increasingly mammalian in derived cynodonts. We find the earliest support for habitual parasagittal postures in stem therians, implying that synapsids evolved and radiated with distinct forelimb trait combinations for most of their recorded history.

Understanding 3D shoulder girdle kinematics is essential for applications in medicine, sports, and computational biomechanics, where reference data help quantify deviations from the standard. Unfortunately, existing datasets on shoulder kinematics based on gold-standard measurements are often inconsistent in data collection methods, segment definitions, and joint kinematics computation, limiting their relevance. This study reviews and aggregates available datasets to establish Spartacus, a comprehensive reference for normal shoulder girdle kinematics. We gathered 20 datasets, published between 2000 and 2023, and aligned them, when possible, with the International Society of Biomechanics recommendations to enable population-wide analysis. Spartacus comprises data recorded in vivo (70 %) or ex vivo (30 %) on 245 shoulders using intracortical pins (55 %) or imaging (45 %), primarily during active dynamic (65 %) movements. The dataset predominantly covers arm elevation records in the scapular (70 %), frontal (50 %), and sagittal (50 %) planes, but also includes internal-external rotation and horizontal flexion. Both rotations and translations are represented across all shoulder girdle joints, with scapulothoracic rotations being the most frequent (75 %). Our approach corrects or at least compensates for six identified deviations in local coordinate system definitions and joint kinematics computation methods. Substantial inconsistencies across existing datasets reveal a need for improved standardisation to facilitate reliable data comparisons. Spartacus, openly available, will enable researchers to explore normal shoulder girdle kinematics, and provides a foundation for future clinical and biomechanical studies.

Accurate measurement of internal/external rotation joint angle is critical in assessing the shoulder function, especially in the clinical practice as it plays a key role in evaluating activities of daily living and monitoring the rehabilitation progress. This study analyzed the effectiveness of using a marker cluster placed over the proximal epiphysis of the ulna to measure humeral axial rotation with respect to the thorax, comparing it with the traditional method that uses a cluster placed on the upper arm. Data were collected simultaneously using the proposed indirect approach and a conventional marker cluster to analyze three internal/external rotations performed in the Ski-Pose, frontal, and sagittal plane. Linear regressions for time series comparison reported a coefficient of determination R2 > 0.9919 in all tasks.The linear coefficients (a1) were as follows: Ski-Pose (a1 = 0.64 ± 0.10), frontal plane (a1 = 0.74 ± 0.05), and sagittal plane (a1 = 0.73 ± 0.04). Three additional planar tasks were recorded for concurrent validity and RMSE was reported for the main joint angle, obtaining a maximum of 3.87° for the pure flexion/extension task and 1.94° for the abduction/adduction task. A forearm pronation/supination task without axial rotation yielded a maximum error standard deviation of 2.64°. Proximal ulna tracking showed a statistically higher maximum range of motion than humeral tracking in pure axial rotation tasks. This indirect tracking approach is a promising alternative to the traditional cluster technique due to its reduced sensitivity to soft tissue artifacts.

Measurement of axial rotation of the humerus using marker-based motion capture is compromised due to soft tissue artefact. The aim of this study was to quantify the elastic deformation of markers on the humerus and evaluate the combined effects of elastic deformation and rigid displacement of the markers on humeral kinematics during axial rotation. Thirteen wheelchair users performed active humeral internal rotation whilst a Vicon motion capture system tracked 12 retro-reflective markers placed on the arm. Elastic deformation was quantified using the Optimal Common Shape Technique (OCST) and Ordinary Procrustes Analysis (OPA). The combined effects of elastic deformation and rigid marker displacement were quantified by comparing kinematics derived from only the humeral markers to the kinematics derived using the forearm segment (benchmark measurement). Elastic deformation of the markers demonstrated a systematic variation in the deformation pattern across the arm where the proximal markers lagged and the distal markers proceeded the OPA fitted reference shape of the marker cluster. There was a significant 48.7° underestimation in the range of axial rotation (P < 0.001). A secondary analysis was performed utilising only the distal arm markers on the humerus. The underestimation in axial rotation range of motion reduced to 25.9° and was not significantly different to the benchmark measurement from neutral through to internal rotation. Systematic elastic deformation of markers was present across the upper limb segment that adversely affected the estimation of humeral axial rotation. Careful selection of marker position for the arm cluster is needed minimise the effect of soft tissue artefact.