Normal Shoulder Research Articles

A Simulation Study of Latissimus Dorsi Tendon Transfer (LDTT) for Irreparable Massive Rotator Cuff Tears (MRCT): Investigating the Ideal Fixation Point

Investigating the ideal fixation point for Latissimus dorsi tendon transfer in irreparable massive rotator cuff tear. Latissimus dorsi tendon transfer (LDTT) represents preferred treatment for younger, active individuals with posterosuperior irreparable Massive Rotator Cuff Tears(MRCT), which has been shown to decrease pain and increase range of motion (ROM). The study seeks to find out the ideal fixation points for LDTT in posterosuperior irreparable MRCTs. A computer model named “Stanford upper extremity model (SUEM)” and Opensim 3.3.0 software were modified to simulate conditions of normal shoulder, posterosuperior irreparable MRCT and posterosuperior irreparable MRCT with LDTT. We compare the moment, muscle arm and muscle force of the models above and evaluate Five possible transfer locations adjacent to greater tuberosity to pursue the acceptable fixation point. In posterosuperior irreparable MRCT patients, there was up to 1/3 moment decrease at 0 degree abduction and 6/7 moment decrease at 20 to 30 degree external rotation. LDTT did not enhance abduction moment remarkably. However, the transferred Latissimus dorsi made contribution to enhance the external rotation moment up to 2 times than that of irreparable MRCT. When evaluating the ideal fixation point, we found superior point had a better moment generating potential for it could produce up to 5 Nm for shoulder abduction. When it came to external rotation, both posterior and anterior points’ peak absolute moment were larger than that of other ones. During surgery, LDTT fixation point could be placed posterior to the imagined line between center and superior point.

Midterm results of surface replacement of the shoulder

PurposeThis study was undertaken to determine the midterm results of resurfacing hemiarthroplasty of the shoulder, evaluate the inclination of prosthesis and correlate the effect of valgus or varus positioning on clinical outcomes. MethodsBetween 2007 and 2014, fifty-seven humeral head surface replacements were performed in our hospital for the osteoarthritis of shoulder. One patient expired and 6 shoulders were lost to follow-up. Forty-seven patients with 3 patients having bilateral humeral head replacements, were assessed thoroughly at the mean period of 4.4+2.3years (Range 2–9 years). All fifty shoulders were evaluated using the VAS, ASES and Constant and Murley score. ResultsHumeral head surface replacement produced satisfactory results in 96% of the patients at a mean follow-up of 4.4 years. We found that the difference in mean postoperative ASES, Constant and VAS score in normal and valgus inclination angle shoulders was not significant whereas the difference in normal and varus inclination angle shoulders was significant. Three patients had severe pain with VAS score (range 0 to 10) of 7, 5 and 4 postoperatively though in all 3 patient’s inclination angle was normal. No revision surgery was performed till recent follow-up. ConclusionsIn conclusion mid-term outcomes of the uncemented Global C.A.P. resurfacing prosthesis are promising. Inclination of the implant has effect on functional outcome of patients.

A Systematic Review of Electromyography Studies in Normal Shoulders to Inform Postoperative Rehabilitation Following Rotator Cuff Repair

Study Design Systematic review. Background Electromyography (EMG) has previously been used to guide postoperative rehabilitation progression following rotator cuff repair to prevent deleterious loading of early surgical repair. Objective To review the current literature investigating EMG during rehabilitation exercises in normal shoulders, and to identify exercises that meet a cut point of 15% maximal voluntary isometric contraction (MVIC) or less and are unlikely to result in excessive loading in the early postoperative stages. Methods An electronic search of MEDLINE via Ovid, Embase, CINAHL, SPORTDiscus, PubMed, and the Cochrane Library for all years up to June 2016 was performed. Studies were selected in relation to predefined selection criteria. Pooled mean MVICs were reported and classified as low (0%-15% MVIC), low to moderate (16%-20% MVIC), moderate (21%-40% MVIC), high (41%-60% MVIC), and very high (greater than 60% MVIC). Results A search identified 2159 studies. After applying the selection criteria, 20 studies were included for quality assessment, data extraction, and data synthesis. In total, 43 exercises spanning passive range of motion, active-assisted range of motion, and strengthening exercises were evaluated. Out of 13 active-assisted exercises, 9 were identified as suitable (15% MVIC or less) to load the supraspinatus and 10 as suitable to load the infraspinatus early after surgery. All exercises were placed in a theoretical-continuum model, by which general recommendations could be made for prescription in patients post rotator cuff repair. Conclusion This review identified passive and active-assisted exercises that may be appropriate in the early stages after rotator cuff repair. J Orthop Sports Phys Ther 2017;47(12):931-944. Epub 13 Jul 2017. doi:10.2519/jospt.2017.7271.

Mid-term to long-term outcome of the open Bankart repair for recurrent traumatic anterior dislocation of the shoulder

The purpose of this study was to assess the long-term outcome of the open Bankart repair for traumatic, recurrent anterior dislocation of the shoulder by evaluation of recurrence, range of motion, return to sports, arthritis, patient satisfaction, and outcome measures. Of 162 patients, 127 patients (mean age, 31 years) were evaluated at a mean follow-up of 17.1 years (5-24) after undergoing an open Bankart repair using suture anchors. An independent orthopedic surgeon obtained a history and examined each for range of motion. Radiographs for arthritis and osteolysis were obtained unless the patient refused. Questionnaires including return to sports and function as well as satisfaction and outcome measures were completed by all patients. There was 1 recurrent dislocation (0.8%) and 1 recurrent subluxation (0.8%) but no pain or apprehension. All remaining shoulders were stable. Compared with the normal shoulder, there was statistical difference in external rotation in abduction and at the side as well as in internal rotation but not in forward elevation or abduction. However, no patient considered any measurable loss functionally significant. Of 107 patients who participated in sports, 98 returned to the sport; 7 of the remaining 9 discontinued for reasons other than the shoulder. There were 91 patients who agreed to radiography; 48 had normal findings, 34 had mild arthrosis, 9 had moderate arthrosis, and none had severe arthrosis. Mean postoperative outcome scores were as follows: American Shoulder and Elbow Surgeons, 93.53; Rowe, 91.41; and Western Ontario Shoulder Instability Index, 327.7. There were 125 patients who were satisfied and would undergo the procedure again. The open Bankart procedure remains the standard by which other techniques can be measured for treatment of recurrent, traumatic anterior dislocation of the shoulder.

Comparison of Scapular Kinematics and Range of Motion Between Normal and Post-operative Shoulders Following Subpectoral Biceps Tenodesis

Objectives:Though many surgeons advocate biceps tenodesis for treatment of intra-articular biceps pathology, little is known about the biomechanical effects this may have on the glenohumeral joint. The purpose of the present study is to describe in detail the effect of biceps tenodesis on shoulder muscle strength, range of motion, and scapular motion. We hypothesized that post-surgical shoulders would not show significant differences in range of motion, strength, and kinematics when compared to the uninvolved shoulder.Methods:22 patients underwent a subpectoral biceps tenodesis and were evaluated at least 6 months following the procedure. We evaluated range of motion, strength, and scapular kinematics. Measures included glenohumeral abduction, internal and external rotation, elbow flexion and extension, internal and external rotation strength, and scapular kinematics. Subjects also completed the DASH questionnaire.Results:The average DASH score was 5.3 +/- 6.3 following surgery. The post-surgical shoulder showed a significant 8.3 degree decrease (p = 0.003) in glenohumeral abduction external rotation compared to the uninvolved shoulder. However, there were no significant differences in other measurements of glenohumeral motion or strength. Kinematic data revealed significantly increased scapular internal rotation (p = 0.02) and anterior tipping (p = 0.019) while reaching for the contralateral shoulder.Conclusion:The majority of outcome measures were equivalent when comparing the post-surgical and uninvolved shoulder function and biomechanics. Significant findings include a loss of glenohumeral abduction external rotation after surgery as well as anterior scapular tipping and rotation while reaching for the contralateral shoulder. Overall, subjects expressed minimal disability following surgery, as evidenced by their DASH scores. Nonetheless, we recommend a vigilant focus on regaining external rotation following open subpectoral biceps tenodesis in an attempt to limit or prevent loss of shoulder motion.

Increased Glenoid Index is a Risk Factor for Pediatric Anterior Glenohumeral Dislocation: An MRI-Based Case-Control Study

Objectives:In the adult population, anterior glenohumeral instability has been associated with a tall and narrow glenoid morphology, assessed using glenoid index (GI). This morphological association has not been assessed in children and adolescents. This study was designed to examine the association of GI with anterior glenohumeral dislocation in patients 19 years old and younger using a case-control study design.Methods:An institutional radiology database was queried over a 10-year period to identify patients 19 years old and younger who underwent glenohumeral MRI arthrography and were diagnosed with anterior shoulder dislocation (cases) and those without dislocation and normal shoulder arthrogram studies (controls). Those with bony Bankart lesions were excluded. Glenoid index (glenoid height-to-width ratio) was measured by an attending pediatric musculoskeletal radiologist and a fellowship-trained attending orthopedic surgeon. Comparative analysis between the two groups was performed using Student’s t-test for each variable, followed by receiver-operating-characteristic (ROC) analysis to determine discriminative ability when statistically significant.Results:Thirty-three males and 22 females (mean age: 15.4±2.1 years old) meeting inclusion and exclusion criteria were identified. Mean glenoid index in the dislocator group was significantly greater than the control group (1.55±0.14 vs. 1.38±0.08, P<0.001). ROC analysis revealed adequate discrimination of glenoid index in predicting glenohumeral dislocation (area under the curve [AUC] = 0.88). A glenoid index ≥1.45 was 83% sensitive and 79% specific for predicting dislocation in the study cohort.Conclusion:Patients with anterior glenohumeral dislocation were noted to have increased glenoid index (taller and narrower glenoid morphology) than controls. Glenoid index may help identify patients at risk for primary or recurrent anterior glenohumeral instability events, and can help guide treatment and anticipatory guidance.

Isometric shoulder strength in young swimmers.

The prevalence of shoulder pain in young swimmers is high. Shoulder rotation strength and the ratio of internal to external rotation strength have been reported as potential modifiable risk factors associated with shoulder pain. However, relative strength measures in elevated positions, which include flexion and extension, have not been established for the young swimmer. The aim of this study was to establish clinically useful, normative shoulder strength measures and ratios for swimmers (14-20 years) without shoulder pain. Cross-sectional, observational study. Swimmers (N=85) without a recent history of shoulder pain underwent strength testing of shoulder flexion and extension (in 140° abduction); and internal and external rotation (in 90° abduction). Strength tests were performed in supine using a hand-held dynamometer and values normalised to body weight. Descriptive statistics were calculated for strength and strength ratios (flexion:extension and internal:external rotation). Differences between groups (based on gender, history of pain, test and arm dominance) were explored using independent and paired t tests. Normative shoulder strength values and ratios were established for young swimmers. There was a significant difference (p<0.002) in relative strength between males and females for all tests with no differences in strength ratios. Relative strength of the dominant and non-dominant shoulders (except for extension); and for swimmers with and without a history of shoulder pain was not significantly different. A normal shoulder strength profile for the young swimmer has been established which provides a valuable reference for the clinician assessing shoulder strength in this population.

Effects of short malunion of the clavicle on in vivo scapular kinematics

Short malunion of the clavicle after fracture can change scapular kinematics and alter clinical outcome. However, the effects of malunion on kinematics and outcomes remains poorly understood because there have been no in vivo studies measuring changes during active motion with malunion. This study aimed to measure and to compare in vivo 3-dimensional (3D) scapular kinematics between normal shoulders and shoulders with short malunion using 3D-2-dimensional model image registration techniques. Fifteen patients with clavicle fracture who had been treated conservatively were enrolled in this study. In these patients, the angle of scapular upward rotation, posterior tilting, and external rotation were compared between shoulders with short malunion and contralateral, normal shoulders. A 3D-2-dimensional model image registration technique was used to determine the 3D orientation of the scapula. Scapular upward rotation increased following increase of the arm elevation angle and also showed a significant difference by arm elevation in both groups (P = .04). Posterior tilting of the scapula gradually increased as the arm abduction angle increased, and this varied significantly between groups (P = .01). Shoulders with short malunion also showed a more internally rotated position than the contralateral, normal shoulders between 100° and the maximum abduction angle (P = .04). Our results suggest that clavicle shortening of >10% greatly affects scapular kinematics in vivo. Further studies will be needed to determine the clinical implications of short malunion of the clavicle.

Optoelectronic Plethysmography Characterises Thoracic Excursion In The Evaluation Of Dysfunctional Breathing (DB)

PURPOSE: Ventilatory pattern and thoracic excursion, can vary during exercise and impact on ventilatory performance. A deviation away from an optimal trunk lumbo-pelvic recruitment pattern may affect lung volumes, work of breathing and may be relevant in the development of exertional dyspnoea. The aim of the study was to investigate the effect of different postural positions on the ventilatory excursion using optoelectronic plethysmography (OEP) and a spirometer. METHODS: Fifteen healthy male athletes (Mean ± SD age: 30.3±6.5 yrs.) completed the study. Ninety reflective markers were placed on the chest, abdomen and back (Figure 1). Participants underwent simultaneous OEP and spirometry data collection in two conditions, in a randomised order: (C1) with normal shoulder position or (C2) with hunched shoulders. Forced vital capacity (FVC) was assessed by the spirometer and data was gathered on the chest wall volume (CW) and the compartmental volumes of the rib cage (RC) and the abdomen (AB) by OEP. RESULTS: The correlation between the two instruments in measuring FVC was good in both normal (R2=0.89) and hunched (R2=0.84) positions. FVC was significantly lower in hunched position during both spirometry (5.22±0.69 L vs. 5.35±0.69 L; p=0.03) and OEP measurements (5.22±0.62 L vs. 5.42±0.69 L; p=0.01). When volume contributions in the two conditions were compared the RC/AB ratio was significantly lower in hunched position (1.84±0.74 vs. 2.12±0.79; p=0.01). CONCLUSIONS: These findings suggest that respiratory excursion and lung volume compartmentalisation are affected by the position of the shoulders. Specifically, a hunched should position leads to increased abdominal motion to vital capacity and decreased lung volumes. OEP may be a useful tool to detect altered parameters associated with developement of exertional dyspnoea.Figure

Posture During Exercise Effects Breathing Pattern And Reports Of Dyspnoea

PURPOSE: The posture an athlete holds during exercise may alter breathing pattern and increase reports of exercise induced respiratory symptoms. The purpose of this study was to investigate the effect of different postural positions during high-intensity cycling on breathing frequency (BF), tidal volume (VT), rating of perceived exertion (RPE) and dyspnoea. METHODS: Fifteen healthy male athletes (Mean +/- SD age: 26.1±7.0 yrs.) performed a 10-minute cycling test at 70% of their peak power in two conditions, in a randomised order: with normal shoulder position (C1) and with hunched shoulders (C2). BF and VT were continuously monitored during exercise. RPE and dyspnoea were gauged by using Borg RPE and Borg-10 scales, respectively. RESULTS: BF and VT showed no significant difference between conditions at any time point, however an alteration in BF was observed in C2 (Figure 1). Significant main effects of time emerged for BF, RPE and dyspnoea in both conditions (all p values <0.001). CONCLUSIONS: Cycling with hunched shoulders at high intensities over a prolonged period leads to altered breathing mechanics and as a consequence, an increase in perceived exertion and dyspnoea. These findings suggest that posture may contribute to reports of respiratory symptoms during exercise in the absence of cardio-pulmonary disease.

In Vivo Analysis of Three-Dimensional Dynamic Scapular Dyskinesis in Scapular or Clavicular Fractures.

The three-dimensional (3D) kinematics of the scapula were analyzed in vivo in 10 patients with scapular and 10 patients with clavicular fracture. Both the injured shoulder and normal contralateral shoulder were evaluated by computed tomography in the neutral and fully elevated positions. 3D rotational and translational movements of the scapula relative to the thorax during arm elevation were analyzed. A computer simulation program was used to compare rotational elevation/depression in the coronal plane, anterior/posterior tilting in the sagittal plane and protraction/retraction in the axial plane between the normal and affected sides. Anterior/ posterior translational movement along the X-axis, upward/downward movement along the Y-axis, and lateral/ medial movement along the Z-axis in the Euler space during forward elevation were also compared. In scapular fracture, rotational elevation of the scapula decreased in the coronal plane and posterior tilting of the scapula increased in the sagittal plane. Anterior and superior translation were higher in scapular fracture than in the corresponding normal sides. However, no significant abnormal rotational and translational kinematic changes were observed during elevation in clavicular fracture. In vivo 3D computerized motion analysis was useful for evaluating scapular dyskinesis. Scapular fracture can cause scapular dyskinesis, but not all clavicular fractures alter scapular motion biomechanics.

A comparative study of the behaviors of normal and frozen shoulder: A finite element study

Frozen shoulder is a common condition characterized by a stiff shoulder. Thickening of an axillary pouch and a coracohumeral ligament, which are the passive stabilizers of the shoulder joint, is widely known as a manifestation of frozen shoulder. In this study, the effect of frozen shoulder on the shoulder behavior was investigated by using five finite element shoulder models. Finite element analysis was performed for the shoulder motions. The rotational angle, strain distribution, and the stress distribution were assessed relatively. The mean rotational angle was 54.9 ± 4.5° in external rotation, 35.9 ± 2.8° in internal rotation, 21.2 ± 6.0° in adduction, and 28.2 ± 2.1° in abduction. The resultant angle was decreased 4.1° in external rotation, 4.6° in internal rotation, 1.5° in adduction, and 2.3° in abduction from the normal shoulder to frozen shoulder respectively. The thickening of the AP had more effect on the rotational motions and abduction, on the other hand, the thickening of the CHL had more effect on adduction. The overall strain distribution was similar between the normal and frozen shoulder, however, the high-strain area and the strain value were reduced in frozen shoulder.

Anatomical and biomechanical framework for shoulder arthroplasty rehabilitation

This article provides an anatomical and biomechanical framework for the postoperative management and progression of treatment for shoulder arthroplasty. The clinical relevance of normal shoulder anatomy, biomechanics, and pathomechanics related to this surgery is emphasized to provide the reader with an understanding of the rationale for treatment. We review the rehabilitation implications of surgical indications and technique for both traditional total shoulder arthroplasty and reverse total shoulder arthroplasty procedures with an emphasis on biomechanical considerations. Relevant factors that affect rehabilitation outcomes are discussed along with supporting evidence from the literature. Principles to guide and progress treatment are highlighted with a discussion on return to sports with the ultimate objective of providing a comprehensive approach for successful rehabilitation.

Effects of asymptomatic rotator cuff pathology on in vivo shoulder motion and clinical outcomes

The incidence of asymptomatic rotator cuff tears has been reported to range from 15% to 39%, but the influence of asymptomatic rotator cuff pathology on shoulder function is not well understood. This study assessed the effects of asymptomatic rotator cuff pathology on shoulder kinematics, strength, and patient-reported outcomes. A clinical ultrasound examination was performed in 46 asymptomatic volunteers (age: 60.3 ± 7.5 years) with normal shoulder function to document the condition of their rotator cuff. The ultrasound imaging identified the participants as healthy (n = 14) or pathologic (n = 32). Shoulder motion was measured with a biplane x-ray imaging system, strength was assessed with a Biodex (Biodex Medical Systems, Inc., Shirley, NY, USA), and patient-reported outcomes were assessed using the Western Ontario Rotator Cuff Index and visual analog scale pain scores. Compared with healthy volunteers, those with rotator cuff pathology had significantly less abduction (P = .050) and elevation (P = .041) strength, their humerus was positioned more inferiorly on the glenoid (P = .018), and the glenohumeral contact path length was longer (P = .007). No significant differences were detected in the Western Ontario Rotator Cuff Index, visual analog scale, range of motion, or acromiohumeral distance. The differences observed between the healthy volunteers and those with asymptomatic rotator cuff pathology lend insight into the changes in joint mechanics, shoulder strength, and conventional clinical outcomes associated with the early stages of rotator cuff pathology. Furthermore, these findings suggest a plausible mechanical progression of kinematic and strength changes associated with the development of rotator cuff pathology.

Complete deltoid resection in early childhood without muscle transfer results in normal shoulder function at long-term follow-up: a case report

BackgroundMusculoskeletal tumors involving the deltoid muscle and necessitating its complete resection are rare. The function after complete deltoid resection is reported to be limited, and several authors consider muscle transfer to improve shoulder motion. However, it still remains unclear whether such transfer adds function. To the best of our knowledge, all reports on complete deltoid resection refer to adult patients, and it is unknown what function results after deltoid resection in childhood. The remaining muscles may have the potential to compensate for the loss of deltoid function.Case presentationHere we report the case of a 5-year-old white boy with complete (isolated) deltoid muscle resection in infancy for a large aggressive soft tissue tumor. No reconstructive procedure or muscle transfer was performed at the time of index surgery. Pathology revealed an angiomatoid fibrous histiocytoma. His postoperative course was uneventful. At 11 years of follow-up, he remained disease-free and had excellent shoulder function, including normal range of motion.ConclusionsThis report implies that major muscles such as the deltoid can be resected in a child without compromising long-term function. Therefore, a muscle transfer at index surgery is probably not necessary.

Quantitative Anatomical Differences in the Shoulder.

This study explored the radiographic and anatomical differences in normal shoulders between men and women, as well as factors such as race, height, weight, and age. A total of 205 patients with documented normal anatomical radiographs comprised the study population. Five fellowship-trained orthopedic surgeon reviewers measured head diameter, humeral head size, head to tuberosity distance, greater tuberosity width, neck-shaft angle, surface-arc angle, glenoid neck length, and distance from the lateral acromion process to the greater tuberosity on anteroposterior radiographs with the shoulder in external rotation. After the reviewers identified and marked defined anatomical landmarks, a comprehensive automated calculator was used to compute all parameters. Between men and women, head diameter (P<.001), humeral head size (P<.001), greater tuberosity width (P<.001), distance from the lateral acromion process to the greater tuberosity (P<.001), and glenoid neck length (P<.001) were significantly different, whereas race was not significantly different for any anatomical parameter. Using Spearman's rho, there was a strong correlation between head diameter/humeral head height and height (rs=0.77/rs=0.68), weight (rs =0.62), and greater tuberosity width (rs=0.66/rs= 0.61); there also was a strong negative correlation between head to tuberosity distance and neck-shaft angle (rs=-0.80). This study demonstrated precisely defined proximal humeral anatomical relationships and sizes using an advanced standardized imaging software program. With these data, orthopedic surgeons and implant designers can better understand the anatomy and glenohumeral relationships to re-create when performing total shoulder arthroplasty. [Orthopedics. 2017; 40(3):155-160.].

Friction Stir Welding Tool Design and Their Effect on Welding of AA-6082 T6

Friction stir welding (FSW) is a solid state joining process; it is a new technique with no melting of work piece during welding. The temperature approaches but remain below the solidus temperature; hence the welds have superior properties compared to fusion weld. A parametric study was carried out to understand how the normal force and different shoulder feature effect on welding operation on AA-6082-T6 material for different input traverse speed, rotation speed by considering the different tool shoulder input forces. Concave shoulder with tapered threaded pin tool gives a most favorable result, compared with other tools such as (Flat shoulder, concentric shoulder, Scroll shoulder).

Comparison of normal shoulder and rotator cuff injury in motion analysis of shoulder

Comparison of normal shoulder and rotator cuff injury in motion analysis of shoulder

Osteoid osteoma of the scapula mimicking a pathology of the shoulder

A 14-year-old patient presented with chronic shoulder pain evolving since three years. The pain persisted despite the various medicated and physical treatments followed. The clinical examination noted a normal shoulder examination with pain facing the right scapula without local inflammatory signs. There were no abnormalities in the biological examinations, in particular absence of biological inflammatory syndrome, rheumatoid factor negative and normal calcemia. Radiographs of the shoulder and scapula were normal. Bone scintigraphy showed hyperfixation of the radiotracer regarding the right scapular spine evoking an osteoid osteoma (A). CT scan of the right scapula showed a very limited osteolytic lesion without osteocondensation edges with a non-enhanced hypodense matrix after injection of contrast agent (B). MRI showed lesion of the right scapular spine in hypersignal T1 and T2 without cortical rupture or periosteal reaction suggestive of a benign lesion such as osteoid osteoma (C, D). The patient had a biopsy with surgical resection of the lesion. The diagnosis of osteoid osteoma was confirmed histologically. The peculiarity of this observation lies in the rarity of this localization and the deceptive clinical picture suggesting a shoulder pathology in first intention. In cases of diagnostic doubt and in the presence of normal radiographs, the most specific examination is thin-section CT scans, the sensitivity of which can be improved by association with an MRI.

Effect of lateralized design on muscle and joint reaction forces for reverse shoulder arthroplasty

Manufacturers of reverse shoulder arthroplasty (RSA) implants have recently designed innovative implants to optimize performance in rotator cuff-deficient shoulders. These advancements are not without tradeoffs and can have negative biomechanical effects. The objective of this study was to develop an integrated finite element analysis-kinematic model to compare the muscle forces and joint reaction forces (JRFs) of 3 different RSA designs. A kinematic model of a normal shoulder joint was adapted from the Delft model and integrated with the well-validated OpenSim shoulder model. Static optimizations then allowed for calculation of the individual muscle forces, moment arms, and JRFs relative to net joint moments. Three-dimensional computer models of 3 RSA designs-humeral lateralized design (HLD), glenoid lateralized design, and Grammont design-were integrated, and parametric studies were performed. Overall, there were decreases in deltoid and rotator cuff muscle forces for all 3 RSA designs. These decreases were greatest in the middle deltoid of the HLD model for abduction and flexion and in the rotator cuff muscles under both internal rotation and external rotation. The JRFs in abduction and flexion decreased similarly for all RSA designs compared with the normal shoulder model, with the greatest decrease seen in the HLD model. These findings demonstrate that the design characteristics implicit in these modified RSA prostheses result in mechanical differences most prominently seen in the deltoid muscle and overall JRFs. Further research using this novel integrated model can help guide continued optimization of RSA design and clinical outcomes.