Physiological studies have revealed that the central nervous system controls groups of muscle fibers in a very efficient manner. Within a single skeletal muscle, the central nervous system independently controls individual muscle segments to produce a particular motor outcome. Mechanomyographic studies on the deltoid muscle have revealed that the deltoid muscle, commonly described as having three anatomical segments, is composed of at least seven functional muscle segments, which all have the potential to be at an important level independently coordinated by the central nervous system.[. 1. ] In this study we tried to anatomically describe and quantify these different functional segments within the deltoid muscle, based on the branching out pattern of the axillary nerve. Forty-four deltoids of 22 embalmed adult cadavers, were analyzed. The axillary nerve was carefully dissected together with his anterior and posterior branch upon invasion into the muscle. According to the pattern of fiber distribution and their fascial embalmment, we then carefully splitted the deltoid muscle into different portions each being innervated by a major branch of the axillary nerve. The position and volume of each segment in relation to the whole muscle was derived. In 3 cases the axillary nerve branched out in 8 major divisions. In 22 out of 44 cases (50%), the axillary nerve branched out in 7 principal parts. A branching out pattern of 6 major divisions occurred in 14 out of 44 cases. Finally we found a division in 5 major branches in 5 of the specimens. In general, both posterior and anterior peripheral segments seemed to have the largest volume. In nearly all (93%) cases, the central segments were smaller in weight and volume compared to the more peripheral segments. Based on the innervation pattern of the deltoid muscle a segmentation in 5 up to 8 major segments seem to be found. This confirms from anatomical point of view earlier reports of functional differentiation within the deltoid muscle

Tear pattern and tendon involvement are risk factors for the development of a pseudoparalytic shoulder. However, some patients have similar tendon involvement but significantly different active forward flexion. In these cases, it remains unclear why some patients suffer from pseudoparalysis and others with the same tear pattern show good active range of motion. Moment arms (MA) and force vectors of the RC and the deltoid muscle play an important role in the muscular equilibrium to stabilize the glenohumeral joint. Biomechanical and clinical analyses were conducted calculating different MA-ratios of the RC and the deltoid muscle using computer rigid body simulation and a retrospective radiographic investigation of two cohorts with and without pseudoparalysis and massive RC tears. Idealized MAs were represented by two spheres concentric to the joints centre of rotation either spanning to the humeral head or deltoid origin of the acromion. Individual ratios of the RC /deltoid MAs on antero-posterior radiographs using the newly introduced Shoulder Abduction Moment (SAM) Index was compared between the pseudoparalytic and non-pseudoparalytic patients. Decrease of RC activity and improved glenohumeral stability (+14%) was found in simulations for MA ratios with larger diameters of the humeral head which also were consequently beneficial for the (remaining) RC. Clinical investigation of the MA-ratio showed significant risk of having pseudoparalysis in patients with massive tears and a SAM Index <0.77 (OR=11). The SAM index, representing individual biomechanical characteristics of shoulder morphology has an impact on the presence or absence of pseudoparalysis in shoulders with massive RC tears

The surgical technique for treatment of massive rotator cuff tears, more than 5 cm, with loss of substance and tendon retraction, is still not well defined by the international orthopaedic community. A specific rehabilitation regimen or arthroscopic débridement may be insufficient in active patients who continue to suffer from pain and muscular fatigue in active forward elevation. We treated 20 patients, 14 men and 6 women, with an average age of 52 years (range 40–69) with the surgical technique consisting in acromion decompression, stabilisation of the cuff lesion with anchors, application of a prolene membrane and using a deltoid muscular flap as reinforcement. Deltoid flap is created by splitting the deltoid muscular fibres in front of the anterior border of the acromion. The inferior part of deltoid is sutured to the tendon above the synthetic membrane.

The mean patient follow-up was 24 months. The pain was completely relieved in 85% of subjects, The joint mobility increased significantly in flexion, abduction and external rotation; however, the internal rotation did not improve.

We propose this surgical technique as the procedure of choice for treating retracted ruptures of the supraspinatus associated with lesions of the supra- and the infra-spinatus.

Reverse total shoulder arthroplasty (RTSA) is an increasingly common treatment for osteoarthritic shoulders with irreparable rotator cuff tears. Although very successful in alleviating pain and restoring some function, there is little objective information relating geometric changes imposed by the reverse shoulder and arm function, particularly the moment generating capacity of the shoulder muscles. Recent modeling studies of reverse shoulders have shown significant variation in deltoid muscle moment arms over a typical range of humeral offset locations in shoulders with RTSA. The goal of this study was to investigate the sensitivity of muscle moment arms as a function of varying the joint center and humeral offset in three representative RTSA subjects that spanned the anatomical range from our previous study cohort. We hypothesized there may exist a more beneficial joint implant placement, measured by muscle moment arms, compared to the actual surgical implant configuration. A 12 degree of freedom, subject-specific model was used to represent the shoulders of three patients with RTSA for whom fluoroscopic measurements of scapular and humeral kinematics during abduction had been obtained. The computer model used subject-specific in vivo abduction kinematics and systematically varied humeral offset locations over 1521 different perturbations from the surgical placement to determine moment arms for the anterior, lateral and posterior aspects of the deltoid muscle. The humeral offset was varied from its surgical position ±4 mm in the anterior/posterior direction, ±12mm in the medial/lateral direction, and −10 mm to 14 mm in the superior/inferior direction. The anterior deltoid moment arm varied up to 20 mm with humeral offset and center of rotation variations, primarily in the medial/lateral and superior/inferior directions. Similarly, the lateral deltoid moment arm demonstrated variations up to 20 mm, primarily with humeral offset changes in the medial/lateral and anterior/posterior directions. The posterior deltoid moment arm varied up to 15mm, primarily in early abduction, and was most sensitive to changes of the humeral offset in the superior/inferior direction. The goal of this study was to assess the sensitivity of the deltoid muscle moment arms as a function of joint configuration for existing RTSA subjects. High variations were found for all three deltoid components. Variation over the entire abduction arc was greatest in the anterior and lateral deltoid, while the posterior deltoid moment arm was mostly sensitive to humeral offset changes early in the abduction arc. Moment arm changes of 15–20 mm represent a significant amount of the total deltoid moment arm. This means there is an opportunity to dramatically change the deltoid moment arms through surgical placement of the joint center of rotation and humeral stem. Computational models of the shoulder may help surgeons optimize subject-specific placement of RTSA implants to provide the best possible muscle function, and assist implant designers to configure devices for the best overall performance

Reverse total shoulder arthroplasty (RTSA) is an increasingly common treatment for osteoarthritic shoulders with irreparable rotator cuff tears. Although very successful in alleviating pain and restoring some function there is little objective information relating geometric changes imposed by the reverse shoulder and the moment generating capacity of the shoulder muscles. Recent modeling studies of reverse shoulders have shown significant variation in deltoid muscle moment arms over varied joint centers for shoulders with RTSA. The goal of this study was to investigate the sensitivity of muscle moment arms as a function of varying the joint center in one representative RTSA subject. We hypothesized there may exist a more beneficial joint implant placement, measured by muscle moment arms, compared to the actual surgical implant placement. A 12 degree of freedom, subject-specific model was used to represent the shoulder of a patient with RTSA for whom fluoroscopic measurements of scapular and humeral kinematics during abduction had been obtained. The computer model used these abduction kinematics and systematically varied joint center locations over 1521 different perturbations from the surgical placement to determine moment arms for the anterior, lateral and posterior aspects of the deltoid muscle. The joint center was varied from its surgical position ±4 mm in the anterior/posterior direction, 0–24 mm in the medial/lateral direction, and −10 mm to 14 mm in the superior/inferior direction. The anterior deltoid moment arm varied up to 16mm with center of rotations variations, primarily in the medial/lateral and superior/inferior directions (Figure 2, Table 1(Figure 1)). Similarly, the lateral deltoid moment arm demonstrated variations up to 13 mm, primarily with joint center changes in the anterior/posterior and superior/inferior directions. The posterior deltoid moment arm varied up to 10mm, primarily in early abduction, and was most sensitive to changes of the joint center in demonstrated a sensitivity of 6 mm corresponding to variations in the superior/inferior directions (Figure 2). The goal of this study was to assess the sensitivity of the deltoid muscle moment arms as a function of joint configuration for an existing RTSA subject. High variations were found for all three deltoid components. Variation over the entire abduction arc was greatest in the anterior and lateral deltoid, while the posterior deltoid moment arm was mostly sensitive to joint center changes early in the abduction arc. Moment arm changes of 10–16mm represent a significant amount of the total deltoid moment arm. This means there is an opportunity to dramatically change the deltoid moments arms through surgical placement of the joint center of rotation. Computational models of the shoulder may help surgeons optimize subject-specific placement of RTSA implants to provide the best possible muscle function, and assist implant designers to configure devices for the best overall performance

Background:. An upper extremity model of the shoulder was developed from the Stanford upper extremity model (Holzbaur 2005) in this study to assess the muscle lengthening changes that occur as a function of kinematics for reverse total shoulder athroplasty (RTSA). This study assesses muscle moment arm changes as a function of scapulohumeral rhythm (SHR) during abduction for RTSA subjects. The purpose of the study was to calculate the effect of RTSA SHR on the deltoid moment arm over the abduction activity. Methods:. The model was parameterized as a six degree of freedom model in which the scapula and humeral rotational degrees of freedom were prescribed from fluoroscopy. The model had 15 muscle actuators representing the muscles that span the shoulder girdle. The model was then uniformly scaled according to reflective markers from motion capture studies. An average SHR was calculated for the normal and RTSA cohort set. The SHR averages were then used to drive the motion of the scapula and the humerus. Lastly 3-dimensional kinematics for the scapula and humerus from 3d-2d fluoroscopic image registration techniques were used to drive the motion of model. Deltoid muscle moment arm was calculated. Results:. Muscle moment arms were calculated for the anterior, lateral and posterior heads of the deltoid. Significant changes (>1 mm) were only found in comparing the anterior deltoid muscle moment arm predictions between the normal and RTSA group. The anterior deltoid for RTSA had a moment arm range from −12.5–20.6 mm over the max abduction arc. The anterior deltoid for normal group had a moment arm range from −14.5–22.6 mm over the max abduction arc. There is a difference of 2 mm between the normal and RTSA anterior deltoid moment arm that converges to 0 at 45° of elevation. The 2 mm difference is also seen again as the difference diverges again (Figure 1). There were no significant differences found between normal and RTSA groups for the lateral and posterior deltoid. The most significant difference between moment arm calculations for the RTSA and normal group was found in the Anterior deltoid. (Figure 1). Conclusion:. It was found that the muscle moment arms in the RTSA group were significantly different than in the normal group for the anterior deltoid. No other significant differences were found. In the initial 40° of elevation there is a 2 mm difference in anterior deltoid muscle moment arm between the normal and RTSA group. This difference is also found is seen from 60°–90° of elevation. From 35° −55° there is no difference between RTSA and normal groups. SHR for the RTSA (1.8: 1) is significantly lower than in the normal (2.5: 1) group. Differences found in muscle moment arms over the abduction arc between RTSA and normal groups point to the significant change of the anterior deltoid after RTSA. This study primary objective was to assess the differences in muscle moment arms as a function of SHR (Kinematic differences). Significant differences found may improve implant design, surgical technique, and rehabilitative strategies for reverse shoulder surgery

Purpose of the study: The aim of this biomechanical study was to assess the performance of the deltoid muscle in the absence of a rotator cuff using different models for shoulder prosthesis. Material and methods: A computer model reproducing the three dimensions of the glenohumeral joint was use to analyze the force of the deltoid muscle during abduction movements in shoulders devoid of a rotator cuff. The three heads of the deltoid were analyzed in order to determine the most effective level of muscle tension. The lever arm of the deltoid was measured from 0–90° abduction. Using this 3D model, we simulated implantation of six different models of reversed prostheses in order to assess the biomechanical situation which would be the most favorable for the deltoid. Performance of the normal deltoid was compared with the performance of the deltoid after implantation of an anatomic prosthesis and after implantation of an reversed prosthesis. Several variables were studied: medial offset of the center of rotation, lateral offset of the humerus, lengthening of the deltoid muscle. Results: Optimal deltoid performance (especially from 60–90° abduction) was observed if the center of rotation was offset medially and the humerus was offset laterally and lowered. A 10% increase in the length of the muscle fibres increased muscle performance 18%. Exaggerated lateral offest of the humerus increased deltoid performance between 30 and 60° abduction but lost its beneficial effect at 90° abduction. From 15° abduction, a scapular notch appeared when the humerus was off set medially. This could be avoided if the humerus was offset laterally with a less medial center of rotation. Beyond 150° abduction, superior impingement appeared irrespective of the type of prosthesis. Discussion and conclusion: This biomechanical study proved the superiority of reversed prostheses compared with anatomic prostheses for massive rotator cuff tears. Medial offset of the center of rotation reduced shear forces on the glenoid. Lateral offset of the humerus increase via a pulley effect the lowering force of the deltoid. Lowering the humerus pulled on the muscle fibers of the deltoid and increased their performance. Dosing these three variables with an appropriate («ideal») design for the reversed prosthesis would optimize deltoid performance in patients with deficient rotator cuffs

Background. Though many advantages of reverse total shoulder arthroplasty (RTSA) have been demonstrated, a variety of complications indicate there is much to learn about how RTSA modifies normal shoulder function. This study assesses how RTSA affects deltoid muscle moment arms post-surgery using a subject-specific computational model driven by in vivo kinematic data. Methods. A subject-specific 12 degree-of-freedom (DOF) musculoskeletal model was used to analyze the shoulders of 26 subjects (14 RTSA, 12 Normal). The model was modified from the work of Holzbaur et al. to directly input 6 DOF humerus and scapula kinematics obtained using fluoroscopy. Results. The moment arm of the anterior, lateral and poster aspects of the deltoid was found to be significantly different when comparing RTSA and normal cohorts. Anterior and lateral deltoid moment arms were found to be larger at initial elevation. There was large inter-subject variability within the RTSA group. Conclusion. Placement of implant components during RTSA can directly affect the geometric relationship between the humerus and scapula and the muscle moment arms in the RTSA shoulder. RTSA shoulders maintain the same anterior and posterior deltoid muscle moment arm patterns as healthy shoulders, but they show much greater inter-subject variation and larger moment arm magnitudes. These observations provide a basis for determining optimal implant configuration and surgical placement to maximize RTSA function in a patient-specific manner

Reverse Total shoulder arthroplasty (RTSA) has become an increasingly used solution to treat osteoarthritis and cuff tear arthropathy. Though successful there are still 10 to 65% complication rates reported for RTSA. Complication rates range over different reverse shoulder designs but a clear understanding of implant design parameters that cause complications is still lacking within the literature. In efforts to reduce complication rates (Implant fixation, range of motion, joint stiffness, and fracture) and improve clinical/functional outcomes having to do with proper muscle performance we have employed a computational approach to assess the sensitivity of muscle performance to changes in RTSA implant geometry and surgical placement. The goal of this study was to assess how changes in RTSA joint configuration affect deltoid performance. An approach was developed from previous work to predict a patient's muscle performance. This approach was automated to assess changes in muscle performance over 1521 joint configurations for an RTSA subject. Patient-specific muscle moment arms, muscle lengths, muscle velocities, and muscle parameters served as inputs into the muscle prediction scheme. We systematically varied joint center locations over 1521 different perturbations from the in vivo measured surgical placement to determine muscle activation and normalized operating region for the anterior, lateral and posterior aspects of the deltoid muscle. The joint center was varied from the RTSA subject's nominal surgical position ±4 mm in the anterior/posterior direction, ±12mm in the medial/lateral direction, and −10 mm to 14 mm in the superior/inferior direction. Overall muscle activity varied over 1521 different implant configurations for the RTSA subject. For initial elevation the RTSA subject showed at least 25% deltoid activation sensitivity in each of the directions of joint configuration change(Figure 1). Posterior deltoid showed a maximal activation variation of 84% in the superior/inferior direction(Figure 1c). Deltoid activation variations lie primarily in the superior/inferior and anterior/posterior directions. An increasing trend was seen for the anterior, lateral and posterior deltoid outside of the discontinuity seen at 28°(Figure 1). Activation variations were compared to subject's experimental data. Reserve actuation for all samples remained below 4Nm(Figure 2). The most optimal deltoid normalized operating length was implemented by changing the joint configuration in the superior/inferior and medial/lateral directions(Figure 3). Current shoulder models utilize cadaver information in their assessment of generic muscle strength. In adding to this literature we performed a sensitivity study to assess the effects of RTSA joint configurations on deltoid muscle performance in a single patient-specific model. For this patient we were able to assess the best joint configuration to improve the patients muscle function and ideally their clinical outcome. With this information improvements can be made to the surgical placement and design of RTSA on a patient-specific basis to improve functional/clinical outcomes while minimizing complications. For any figures or tables, please contact authors directly (see Info & Metrics tab above).

Reverse Total shoulder arthroplasty (RTSA) has become an increasingly used solution to treat osteoarthritis and cuff tear arthropathy. Though successful there are still 10 to 65% complication rates reported for RTSA. Complication rates range over different reverse shoulder designs but a clear understanding of implant design parameters that cause complications is still lacking within the literature. In efforts to reduce complication rates (Implant fixation, range of motion, joint stiffness, and fracture) and improve clinical/functional outcomes having to do with proper muscle performance we have employed a computational approach to assess the sensitivity of muscle performance to changes in RTSA implant geometry and surgical placement. The goal of this study was to assess how changes in RTSA joint configuration affect deltoid performance. An approach was developed from previous work to predict a patient's muscle performance. This approach was automated to assess changes in muscle performance over 1521 joint configurations for an RTSA subject. Patient-specific muscle moment arms, muscle lengths, muscle velocities, and muscle parameters served as inputs into the muscle prediction scheme. We systematically varied joint center locations over 1521 different perturbations from the in vivo measured surgical placement to determine muscle activation and normalized operating region for the anterior, lateral and posterior aspects of the deltoid muscle. The joint center was varied from the RTSA subject's nominal surgical position ±4 mm in the anterior/posterior direction, ±12mm in the medial/lateral direction, and −10 mm to 14 mm in the superior/inferior direction. Overall muscle activity varied over 1521 different implant configurations for the RTSA subject. For initial elevation the RTSA subject showed at least 25% deltoid activation sensitivity in each of the directions of joint configuration change(Figure 1A–C). Posterior deltoid showed a maximal activation variation of 84% in the superior/inferior direction(Figure 1C). Deltoid activation variations lie primarily in the superior/inferior and anterior/posterior directions(Figure 1). An increasing trend was seen for the anterior, lateral and posterior deltoid outside of the discontinuity seen at 28°(Figur 1A–C). Activation variations were compared to subject's experimental data (Figure 1). Reserve actuation for all samples remained below 4Nm. The most optimal deltoid normalized operating length was implemented by changing the joint configuration in the superior/inferior and medial/lateral directions. Current shoulder models utilize cadaver information in their assessment of generic muscle strength. In adding to this literature we performed a sensitivity study to assess the effects of RTSA joint configurations on deltoid muscle performance. With this information improvements can be made to the surgical placement and design of RTSA to improve functional/clinical outcomes while minimizing complications

Aims: The authors reported an original technique for proximal humerus reconstruction followed tumor resection using a delta composite prosthesis. Seven patients undergoing this technique Technique: Proximal humeral resection was conducted usually. The host tendons of rotator cuff were resected; the deltoid muscle must be preserved. The glenosphere was inserted with three screws. A long humeral stem was used to provide a distal anchorage of 10 cm; this stem was cemented into the allograft and into the humerus host. The patient was immobilized in 90¡ of abduction during 6 weeks. Results: 7 patients aged 38 to 56 years, who presented a chondro-sarcoma or an osteosarcoma of the proximal humerus were enrolled in this study. The mean follow-up was 20 months (6 to 24). None patient presented with pain and the mean of active abduction was 120¡. No local or general recurrence was detected. Discussion: The Delta prosthesis of Gramon is usually used for shoulder arthritis with rotator cuff rupture. In our experience, reconstruction of the proximal humerus with composite prosthesis provides good functional results but after 3 years, a graft resorption was observed and the functional results decrease. The delta prosthesis could provide good functional results without reconstruction of the rotator cuff. In our technique, we sutured the rotator cuff to avoid dislocation. However, the glenoid þxation is incertain for a long term because its a constrained prosthesis. This technique could be used when the deltoid muscle can be preserved

Reverse total shoulder arthroplasty (R-TSA) converts the glenohumeral joint into a ball-and-socket articulation by implanting a metal glenosphere on the glenoid and a concave polyethylene articulation in the humerus. This design increases the stability of the shoulder and is indicated for the treatment of end-stage shoulder arthropathy with significant rotator cuff deficiency. To minimise the risk of loosening, the glenosphere is often medialised (to keep the center of rotation within glenoid bone). Since bone grafting under the glenosphere is recommended as an alternate method to medialisation, we studied the effect of glenosphere placement on the biomechanical efficiency of the deltoid. A musculoskeletal model of the shoulder was constructed using BodySIM (LifeModeler, Inc, San Clemente, CA). The model simulated active dynamic glenohumeral and scapulothoracic abduction in a shoulder implanted with an R-TSA. Muscle forces and gleno-humeral contact forces were computed during shoulder abduction. The following conditions were simulated:. R-TSA with the center of rotation unchanged;. medialisation of center of rotation by 16 mm;. medialisation reduced to 10 mm with a 6-mm bone graft; and. inferior placement of R-TSA by 4 mm to preserve soft-tissue tension and prevent scapular notching. We validated our model by comparing peak glenohumeral contact forces (85% body weight) with previously reported in vivo measurements (Bergmann, J Biomech 2007). Inferior placement of the glenosphere component increased the mechanical advantage of deltoid muscle at 90° abduction by 25%. Medialisation of the glenosphere had little effect on deltoid forces. Reducing the medialisation (to 10 mm, by simulating the effect of a bone graft under the glenosphere) also did not change the mechanical advantage relative to full medialisation (16 mm). One disadvantage of R-TSA is that a center of shoulder rotation outside (lateral) to the glenoid increases the tendency for glenosphere loosening. Unfortunately, medialisation of the glenosphere reduces the tension on the deltoid, increases the incidence of prosthetic impingement resulting in scapular notching, and produces a shoulder contour that is cosmetically undesirable. To counter these disadvantages, reduced medialisation is proposed by bone grafting under the glenosphere and placing the glenosphere inferiorly. Our model indicates that the major mechanical advantage of the R-TSA is provided by the inferior placement of the glenosphere, which increases the moment arm of the deltoid muscle. On the other hand, the extent of glenosphere medialisation had an insignificant effect. These results support the use of reduced medialisation and bone grafting in the presence of other advantages, such as reduced notching and maintenance of infraspinatus tension and improved shoulder contour

Manufacturers of reverse shoulder arthroplasty (RSA) implants have recently designed innovative implants to optimise performance in rotator cuff deficient shoulders. These advancements are not without tradeoff and can have negative biomechanical effects. The objective of this study was to develop an integrated FEA kinematic model to compare the muscle forces and joint reaction force (JRF) of 3 different RSA designs. A kinematic model of a normal shoulder joint was adapted from the Delft model and integrated with the OpenSim shoulder model. Static optimisations then allowed for calculation of the individual muscle forces, moment arms and JRF relative to net joint moments. Three dimensional computer models of humeral lateralised design (HLD), glenoid lateral design (GLD), and Grammont design (GD) RSA 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 and external rotation. The joint reactive forces in abduction and flexion decreased similarly for all RSA designs compared to 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 kinematic differences most prominently seen in the deltoid muscle and overall joint reactive forces. Further research utilising this novel integrated model can help guide continued optimisation of RSA design and clinical outcomes

Last decade, a shift towards operative treatment of midshaft clavicle fractures has been observed [T. Huttunen et al., Injury, 2013]. Current fracture fixation plates are however suboptimal, leading to reoperation rates up to 53% [J. G. Wijdicks et al., Arch. Orthop. Trauma Surg, 2012]. Plate irritation, potentially caused by a bad geometric fit and plate prominence, has been found to be the most important factor for reoperation [B. D. Ashman et a.l, Injury, 2014]. Therefore, thin plate implants that do not interfere with muscle attachment sites (MAS) would be beneficial in reducing plate irritation. However, little is known about the clavicle MAS variation. The goal of this study was therefore to assess their variability by morphing the MAS to an average clavicle. 14 Cadaveric clavicles were dissected by a medical doctor (MH), laser scanned (Nikon, LC60dx) and a photogrammetry was created with Agisoft photoscan (Agisoft, Russia). Subsequently a CT-scan of these bones was acquired and segmented in Mimics (Materialise, Belgium). The segmented bone was aligned with the laser scan and MAS were indicated in 3-matic (Materialise, Belgium). Next, a statistical shape model (SSM) of the 14 segmented clavicles was created. The average clavicle from the SSM was then registered to all original clavicle meshes. This registration assures correspondences between source and target mesh. Hence, MAS of individual muscles of all 14 bones were indicated on the average clavicle. Mean area is 602 mm. 2. ± 137 mm. 2. for the deltoid muscle, 1022 mm. 2. ±207 mm. 2. for the trapezius muscle, and 683 mm. 2. ± 132 mm. 2. for the pectoralis major muscle. The sternocleidomastoid muscle has a mean area of 513 mm. 2. ± 190 mm. 2. and the subclavius muscle had the smallest mean area of 451 mm. 2. ± 162 mm. 2. Visualization of all MAS on the average clavicle resulted in 72% coverage of the surface, visualizing only each muscle's largest MAS led to 52% coverage. The large differences in MAS surface areas, as shown by the standard deviation, already indicate their variability. Difference between coverage by all MAS and only the largest, shows that MAS location varies strongly as well. Therefore, design of generic plates that do not interfere with individual MAS is challenging. Hence, patient-specific clavicle fracture fixation plates should be considered to minimally interfere with MAS

Reverse Total shoulder arthroplasty (RTSA) has become an increasingly used solution to treat osteoarthritis and cuff tear arthropathy. Though successful there are still 10 to 65% complication rates reported for RTSA. Complication rates range over different reverse shoulder designs but a clear understanding of implant design parameters that cause complications is still lacking within the literature. In efforts to reduce complication rates (Implant fixation, range of motion, joint stiffness, and fracture) and improve clinical/functional outcomes having to do with proper muscle performance we have employed a computational approach to assess the sensitivity of muscle performance to changes in RTSA implant geometry and surgical placement. The goal of this study was to assess how changes in RTSA joint configuration affect deltoid performance. An approach was developed from previous work to predict a patient's muscle performance. This approach was automated to assess changes in muscle performance over 1521 joint configurations for an RTSA subject. Patient-specific muscle moment arms, muscle lengths, muscle velocities, and muscle parameters served as inputs into the muscle prediction scheme. We systematically varied joint center locations over 1521 different perturbations from the in vivo measured surgical placement to determine muscle normalized operating region for the anterior, lateral and posterior aspects of the deltoid muscle. The joint center was varied according to previous published work from the RTSA subject's nominal surgical position ±4 mm in the anterior/posterior direction, ±12mm in the medial/lateral direction, and −10 mm to 14 mm in the superior/inferior direction (Walker 2015 et al. Table 2). Overall muscle normalized operating length varied over 1521 different implant configurations for the RTSA subject. Ideal muscle normalized operating length variations were found to be in all the fundamental directions that the joint was varied. The anterior deltoid normalized operating length was found to be most sensitive with joint configurations changes in the anterior/posterior medial/lateral direction. It lateral deltoid normalized operating length was found to be most sensitive with joint configurations changes in the medial/lateral direction. It posterior deltoid normalized operating length was found to be most sensitive with joint configurations changes in the medial/lateral direction. Reserve actuation for all samples remained below 1 Nm. The most optimal deltoid normalized operating length was implemented by changing the joint configuration in the superior/inferior and medial/lateral directions. Current shoulder models focus on predicting muscle moment arms. Although valuable it does not allow me for active understanding of how lengthening the muscle will affect its ability to generate force. Our study provides an understanding of how muscle lengthening will affect the force generating capacity of each of the heads of the deltoid. With this information improvements can be made to the surgical placement and design of RTSA to improve functional/clinical outcomes while minimizing complications. For any figures or tables, please contact the authors directly

Introduction. Reverse Shoulder Arthroplasty (RSA) improves the mechanics of rotator cuff deficient shoulders. To optimize functional outcomes and minimize failures of the RSA manufacturers have recently made innovative design modifications with lateralized components. However, these innovations have their own set of biomechanical trade-offs, such as increased shear forces along the glenoid bone interface. The objective of this study was to develop an efficient musculoskeletal model to evaluate and compare both the muscle forces and joint reactive force of a normal shoulder to those implanted with varied RSA implant designs. We believe these findings will provide valuable insight into possible advantages or shortcomings of this new RSA design. Methods. A kinematic model of a normal shoulder joint was adapted from publically available musculoskeletal modeling software. Static optimizations then allowed for calculation of the individual muscle forces, moment arms and joint reactive forces relative to net joint moments. An accurate 3D computer models of humeral lateralized design (HLD) (Equinoxe, Exactech, Gainesville FL, USA), glenoid lateral design (GLD) (Encore, DJO Global, Vista CA, USA), and Grammont design (GD) (Aequalis, Tornier, Amsterdam, NV) reverse shoulder prostheses was also developed and parametric studies were performed based on the numerical simulation platform. Results. As expected, there were decreases in muscle forces in all RSA models (Table 1). These decreases were greatest in the middle deltoid of the HLD model for abduction and flexion (Figure 1) and in the rotator cuff muscles under both internal and external rotation (Figure 2). In all RSA models the muscle forces of the rotator cuff were diminished to near zero in all range of motions. The joint reactive forces in abduction and flexion decreased similarly for all RSA models compared to the normal shoulder model, with the greatest decrease again seen in the HLD model (Table 1). Conclusion. These findings demonstrate that the design characteristics implicit in these modified RSA prostheses result in kinematic differences most prominently seen in the deltoid muscle and overall joint reactive forces. These differences could have a profound effect on the ultimate clinical success and long term outcomes for RSA. These results can help guide continued optimization of RSA design and clinical outcomes. The developed innovative shoulder modeling simulation could serve as a prototype for testing of future implant design concepts

Reverse Shoulder Arthroplasty (RSA) has been widely accepted for the treatment of rotator cuff arthropathy. There are a number of other shoulder pathologies where the reverse shoulder prosthesis can salvage previously untreatable shoulder conditions and restore function to the shoulder. This is a series of cases where RSA has been used to treat shoulder fractures. Material. Our indications for the reverse prosthesis in fracture management were:. Revision of failed fracture fixation with a deficient rotator cuff – 2 patients;. Acute 3 and 4 part fractures in the elderly, osteoporotic – 1 patient;. Acute 4 part fracture dislocation in elderly, osteoporotic – 1 patient;. Revision of non-union and malunions – 5 patients;. Revision of hemiarthroplasties which were initially done for fracture management – 5 patients. Results. There were a total of 14 cases treated for fractures out of 123 reverse shoulder arthroplasties performed. The average age for the fracture cases was 68 years (range 47–87) and for non-fracture RSA cases 73 years (range 51–88). The average follow-up Constant Score was 53 for fracture cases and 67 for non-fracture RSA cases. Complications included 1 dislocation and 1 deep infection. The problem with treatment of complex cases is there is an increased risk of complications. Problems encountered in the use of reverse shoulder arthroplasty in complex diagnoses include: instability, notching of scapula, scapula fractures, sepsis, lack of bone stock, poor quality soft-tissue and deficient deltoid muscle due to numerous previous surgical procedures, distortion of anatomy due to trauma, subscapularis deficiency and problems encountered from metal implants in situ. Conclusion. RSA is a good salvage procedure for cuff deficient shoulder fracture cases

Reverse polarity shoulder replacements are indicated in cases of gleno-humeral arthritis with the presence of rotator cuff muscle dysfunction. Despite some studies demonstrating early improvement in function and pain, limited information still exists regarding the durability and longer term outcomes of these prostheses. The reported complication rates have been reported to range from 0–68%. Post-operative clinical complication rates of three commonly used reverse polarity total shoulder replacements (Delta, Verso and Equinoxe) were evaluated against those mentioned in the literature to predict satisfactory outcome. A retrospective review of 54 patients (3.5F:1M) and 64 operations (27L:37R) between 2004–2011 was carried out. Post-operative complications were searched for through medical records, the local hospital database (BLuespearIT) and the Picture Archiving and Imaging System (PACS). All operations were performed by two experienced consultant-grade orthopaedic shoulder surgeons. The mean age at time of operation was 75.9 years (range 64–94). 33 Delta, 19 Equinoxe and 12 Verso prostheses were inserted. Three patients were excluded from the study due to insufficient information from medical records and radiography. Total complications were seen in 25 % of operated cases:- dislocation (6), fracture (4), deep infection (2), significant post-operative pain (1) and deltoid muscle dysfunction (3). Complications categorised according to prosthesis type were:- Delta (24%), Equinoxe (32%) and Verso (8%). Short to medium term complication rates using reverse polarity total shoulder replacements are higher than the majority of the current literature suggests. The Verso is associated with the least number of complications which may correlate with its minimally invasive approach

Reverse total shoulder arthroplasty (RTSA) is increasingly used in the United States since approval by the FDA in 2003. RTSA relieves pain and restores mobility in arthritic rotator cuff deficient shoulders. Though many advantages of RTSA have been demonstrated, there still are a variety of complications (implant loosening, shoulder impingement, infection, frozen shoulder) making apparent much still is to be learned how RTSA modifies normal shoulder function. The goal of this study was to assess how RTSA affects deltoid muscle moment generating capacity post-surgery using a subject-specific computational model driven by in vivo kinematic data. A subject-specific 12 degree-of-freedom (DOF) musculoskeletal model was used to analyze the shoulders of 27 subjects (14-RTSA, 12-Normal). The model was modified from the work of Holzbaur et al. to directly input 6 DOF humerus and scapula kinematics obtained using fluoroscopy. Model geometry was scaled according to each subject's skeletal dimensions. In vivo abduction kinematics for each subject were input to their subject-specific model and muscle moment arms for the anterior, lateral and posterior aspects of the deltoid were measured over the arc of motion. Similar patterns of muscle moment arm changes were observed for normal and RTSA shoulders. The moment arm of the anterior deltoid was positive with the arm at the side and decreased monotonically, crossing zero (the point at which the muscle fibers pass across the joint center) between 50°–60° glenohumeral abduction (Figure 1a). The average moment arm of the lateral deltoid was constant and positive in normal shoulders, but showed a decreasing trend with abduction in RTSA shoulders (Figure 1b). The posterior deltoid moment arm was negative with the arm at the side, and increased monotonically to a positive value with increasing glenohumeral abduction (Figure 1c). Subject-specific moment arm values for RTSA shoulders were highly variable compared to normal shoulders. 2-way repeated measures ANOVA showed significant differences between RTSA and normal shoulders for all three aspects of the deltoid moment arm, where the moment arms in RTSA shoulders were smaller in magnitude. Shoulder functional capacity is a product of the moment generating ability of the shoulder muscles which, in turn, are a function of the muscle moment arms and muscle forces. Placement of implant components during RTSA can directly affect the geometric relationship between the humerus and scapula and, therefore, the muscle moment arms in the RTSA shoulder. Our results show RTSA shoulders maintain the same muscle moment arm patterns as healthy shoulders, but they show much greater inter-subject variation and smaller moment arm magnitudes. These observations show directly how RTSA configuration and implant placement affect deltoid moment arms, and provide an objective basis for determining optimal implant configuration and surgical placement to maximize RTSA function in a patient-specific manner

Aims

Steroid injections are used for subacromial pain syndrome and can be administered via the anterolateral or posterior approach to the subacromial space. It is not currently known which approach is superior in terms of improving clinical symptoms and function. This is the protocol for a randomized controlled trial (RCT) to compare the clinical effectiveness of a steroid injection given via the anterolateral or the posterior approach to the subacromial space.