Introduction. Total knee replacement (TKR) is an established and effective surgical procedure in case of advanced osteoarthritis. However, the rate of satisfied patients amounts only to about 75 %. One common cause for unsatisfied patients is the anterior knee pain, which is partially caused by an increase in patellofemoral contact force and abnormal patellar kinematics. Since the malpositioning of the tibial and the femoral component affects the interplay in the patellofemoral joint and therefore contributes to anterior knee pain, we conducted a computational study on a cruciate-retaining (CR) TKR and analysed the effect of isolated femoral and tibial component malalignments on patellofemoral dynamics during a squat motion. Methods. To analyse different implant configurations, a musculoskeletal multibody model was implemented in the software Simpack V9.7 (Simpack AG, Gilching, Germany) from the SimTK data set (Fregly et al.). The musculoskeletal model comprised relevant ligaments with nonlinear force-strain relation according to Wismans and Hill-type muscles spanning the lower extremity. The experimental data were obtained from one male subject, who received an instrumented CR TKR. Muscle forces were calculated using a variant of the computed muscle control algorithm. To enable roll-glide kinematics, both tibio- and patellofemoral joint compartments were modelled with six degrees of freedom by implementing a polygon-contact-model representing the detailed implant surfaces. Tibiofemoral contact forces were predicted and validated using data from experimental squat trials (SimTK). The validated simulation model has been used as reference configuration corresponding to the optimal surgical technique. In the following, implant configurations, i.e. numerous combinations of relative femoral and tibial component alignment were analysed: malposition of the femoral/tibial component in mediolateral (±3 mm) and anterior-posterior (±3 mm) direction. Results. Mediolateral translation/malposition of the tibial component did not show high influence on the maximal patellofemoral contact force. Regarding the mediolateral translation of the femoral component, similar tendencies were observed. However, lateralisation of the femoral component (3 mm) clearly increased the lateral patella shift and medialisation of the tibial component (3 mm) led to a slightly increased lateral patella shift. Compared to the reference model, pronounced posterior translation of the tibial and femoral component resulted in a lower patellofemoral contact force, further increasing with higher anterior translation of the components. The translation of the tibial component showed smaller influence on the patellofemoral contact force than the translation of the femoral component. Discussion. In our present study, the mediolateral malposition of the femoral and tibial component showed no major impact on patellofemoral contact force and contribution to anterior knee pain in patients with CR TKR. However, the influence of implant component positioning in anterior-posterior direction on patellofemoral contact force is evident, especially for the femoral component. Our generated musculoskeletal model can contribute to computer-assisted preclinical testing of TKR and may support clinical decision-making in preoperative planning

Introduction. Conventional pre-operative planning for total hip arthroplasty mostly relies on the patient radiologic anatomy for the positioning and choice of implants. This kind of planning essentially remains a static approach since dynamic aspects such as the joint kinematics are not taken into account. Hence, clinicians are not able to fully consider the evolving behavior of the prosthetic joint that may lead to implant failures. In fact, kinematics plays an important role since some movement may create conflicts within the prosthetic joint and even provoke dislocations. The goal of our study was to assess the relationship between acetabular implant positioning variations and resultant impingements and loss of joint congruence during daily activities. In order to obtain accurate hip joint kinematics for simulation, we performed an in-vivo study using optical motion capture and magnetic resonance imaging (MRI). Methods. Motion capture and MRI was carried out on 4 healthy volunteers (mean age, 28 years). Motion from the subjects was acquired during routine (stand-to-sit, lie down) and specific activities (lace the shoes while seated, pick an object on the floor while seated or standing) known to be prone to implant dislocation and impingement. The hip joint kinematics was computed from the recorded markers trajectories using a validated optimized fitting algorithm (accuracy: translational error ≍ 0.5 mm, rotational error < 3°) which accounted for skin motion artifactsand patient-specific anatomical constraints (e.g. bone geometry reconstructed from MRI, hip joint center) (Fig. 1). 3D models of prosthetic hip joints (pelvis, proximal femur, cup, stem, head) were developed based on variations of acetabular cup's inclination (40°, 45°, 60°) and anteversion (0°, 15°, 30°) parameters, resulting in a total of 9 different implant configurations. Femoral anteversion remained fixed and determined as “neutral” with the stem being parallel to the posterior cortex of the femoral neck. Motion capture data of daily tasks were applied to all implant configurations. While visualizing the prosthetic models in motion, a collision detection algorithm was used to locate abnormal contacts between both bony and prosthetic components (Fig. 2). Moreover, femoral head translations (subluxation) were computed to evaluate the joint congruence. Results. Simulations showed collisions occurring at maximal ranges of motion in the anterosuperior part of the acetabulum. Both prosthetic and bony impingements were observed, especially while lacing shoes and lying down. The more the inclination and anteversion were important, the lower the frequency of impingements was noted (e.g. 23% at 40°/0°, 13% at 45°/15°, 5% at 60°/30°). Subluxations followed the same trend (e.g. 4.0 mm at 40°/0°, 1.5 mm at 45°/15°, 0.2 mm at 60°/30°). They occurred in a posterior direction as a consequence of impingements. Conclusion. Daily tasks could expose the prosthetic hip to subluxation and impingement located in anterosuperior position. This location could be explained by the high hip flexion required to execute the motions (≥ 95°). Considering the kinematics solely, increasing inclination and anteversion seems to decrease possible conflicts, but mechanical aspects (stress, wear) should also be considered in the definition of ideal cup positioning

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

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).

Introduction. Reverse total shoulder arthroplasty (RTSA) can partially restore lost range of motion (ROM). Active motion restoration is largely a function of RTSA joint constraint, limiting impingement, and muscle recruitment; however, it may also be a function of implant design. The aim of this computational study was to examine the effects of implant design parameters, such as neck-shaft (N-S) angle and glenoid lateralization, on impingement-free global circumduction range of motion (GC-ROM). GC-ROM summarizes the characteristically complex, wide-ranging envelope of glenohumeral motion into a single quantity for ease of comparison. Methods. Nine computational models were used to investigate implant parameters. The parameters examined were N-S angles of 135°, 145°, and 155° in combination with glenoid lateralizations (0, 5, and 10 mm). Static positioning of the humerus was defined by an elevation direction angle, elevation angle, and rotation. The humerus was rotated from the neutral position (0° of rotation and elevation), and then elevated in different elevation directions until impingement was detected. Abduction occurred at an elevation direction angle of 0°, while flexion and extension occurred at elevation direction angles of 90° and −90°, respectively. Elevation direction angles ranged from −180° to 180°. Elevation ranged from 0° and 180°. Rotations ranged from −45° to 90°, where negative and positive rotations represented external and internal rotation, respectively. For each rotation angle, a plot of maximum elevation in each elevation plane was created using polar coordinates (radius = elevation, angle = elevation direction). The area enclosed by the resulting points, normalized with respect to the implant with a 145° N-S angle and 5 mm lateralization, was calculated. The sum of these areas defined the GC-ROM. Results. Figure 1 depicts the maximum ROM curves at each angle of rotation for a 145° N-S angle humeral implant with 5 mm of glenoid lateralization. Table 1 shows the normalized areas within the maximum ROM curves for each implant configuration at each angle of rotation, where 0% indicates that the corresponding angle of rotation could not be achieved without impingement. The effect of varying N-S angle (constant lateralization of 5 mm) and lateralization (constant N-S angle of 145°) is shown for 0° rotation (Figures 2A and 2B, respectively). Conclusions. In general, increasing glenoid lateralization increases GC-ROM; however, the unintuitive poor performance of all 10 mm lateralized configurations at rotations of −90° highlights the complex relationships between implant parameters and ROM. Interestingly, the 135° N-S implant had greater flexion and extension ROM, while the 155° N-S implant had greater abduction ROM, suggesting that there are trade-offs between N-S angles pertaining to the elevation direction in which maximum elevation is obtained. The results of this study highlight the need to incorporate multi-directional motion when assessing the effect of varying implant parameters on the impingement-free GC-ROM. Future studies will include the application of the presented technique to a broader range of implant and surgical parameters

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

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 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

Introduction. The possibility of corrosion at the taper junction of hip replacements was initially identified as a concern of generating adverse reactions in the late 1980s. Common clinical findings of failure are pain, clicking, swelling, fluid collections, soft tissue masses, and gluteal muscle necrosis identified intra operatively. Methodology. The joint replacement surgery was performed utilizing a posterior approach to the hip joint. The data from all surgical, clinical and radiological examinations was prospectively collected and stored in a database. Patients were separated into two groups based on bearing material, where group 1 had a CoC bearing and ABG modular stem whilst group 2 had a MoM bearing and SROM stem, with each group having 13 cases. Pre-operative revision surgery and post-operative blood serum metal ion levels we collected. Cup inclination and anteversion was measured using the Ein-Bild-Roentgen-Analyse (EBRA) software. A range of 2–5 tissue sections was examined per case. 2 independent observers that were blinded to the clinical patient findings scored all cases. The tissue grading for the H&E tissue sections were graded based on the presence of fibrin exudates, necrosis, inflammatory cells, metallic deposits, and corrosion products. The corrosion products were identified into 3 groups based on visible observation and graded based on abundance. A scanning electron microscope (SEM) Hitachi S3400 was used to allow for topographic and compositional surface imaging. Unstained tissue sections were used for imaging and elemental analysis. X-Ray diffraction was the analytical technique used for the taper debris that provided identification on the atomic and molecular structure of a crystal. Result. Group 1 patients showed a significant reduction (p = 0.0002) in the Co, however the decrease of Cr ion concentration had no statistical significance (p = 0.48). The Co (p = 0.001) and Cr (p = 0.02) levels significantly reduced after revision surgery for patients within group 2. The largest differences in the abundance between the two groups were for the brown/red corrosion particles where group 2 is highly significant (p<0.001) compared to group 1. The specific identification was determined using a mapping technique that showed the red/brown colour consisted of evenly scattered Ti (green) and Cr (red) particles (figure 1). Elemental analysis of the green shards showed chromium as a major metallic element with traces of cobalt (figure 2). The ABG modular collected debris matched the peaks of the following crystaline strucutes: chromium oxide (CrO), titantium oxide (TiO2), and chromium oxide (Cr2O3), and iron titanium oxide (Fe2Ti3O9) (figure 2). The peaks from the XRD scan were assessed against these possible elements which showed the most were aluminium nitride and chromium oxide (Cr2O3). Both implant configurations produced an ALTR response indicative from the tissue sections graded and visually observed. Conclusion. This study has characterized the corrosion products produced at taper junctions. The histology presented with similar results across the two groups suggestive that due to the same corrosion products found between both groups this was expected

Introduction. Total shoulder arthroplasty is the fastest growing joint replacement in recent years, with projected compound annual growth rates of 10% for 2016 through 2021 – higher than those of both the hip and knee combined. Reverse total shoulder arthroplasty (RTSA) has gained particular interest as a solution for patients with irreparable massive rotator cuff tears and failed conventional shoulder replacement, for whom no satisfactory intervention previously existed. As the number of indications for RTSA continues to grow, so do implant designs, configurations, and fixation techniques. It has previously been shown that continuous implant migration within the first two years postoperatively is predictive of later loosening and failure in the hip and knee, with aseptic loosening of implant components a guaranteed cause for revision in the reverse shoulder. By identifying implants with a tendency to migrate, they can be eliminated from clinical practice prior to widespread use. The purpose of this study is to, for the first time, evaluate the pattern and magnitude of implant component migration in RTSA using the gold standard imaging technique radiostereometric analysis (RSA). Methods. Forty patients were prospectively randomized to receive either a cemented or press-fit humeral stem, and a glenosphere secured to the glenoid with either autologous bone graft or 3D printed porous titanium (Aequalis Ascend Flex, Wright Medical Group, Memphis, TN, USA) for primary reverse total shoulder arthroplasty. Following surgery, partients are imaged using RSA, a calibrated, stereo x-ray technique, at 6 weeks (baseline), 3 months, 6 months, 1 year, and 2 years. Migration of the humeral stem and glenosphere at each time point is compared to baseline. Preliminary results are presented, with 15 patients having reached the 6-month time point by presentation. Results. Implant migration of ten participants at the 3-month time point is presented. Maximum total point motion (MTPM) is a measure of translation and rotation of the point on the implant that has moved the most from baseline. Average MTPM ± SD of the humeral stem is 1.18 ± 0.65 mm and 0.98 ± 0.46 mm for press-fit (n = 6) and cemented (n = 4) stems, respectively; and 0.25 ± 0.09 mm and 0.47 ± 0.24 mm for bone graft (n = 4) and porous titanium (n = 6) glenosphere fixations, respectively, at the 3-month time point. Conclusion. There is a trend towards increased migration with the use of press-fit humeral stems and porous titanium glenosphere fixation, though no conclusions can be made from the current sample size. Further, though differences in migration magnitude may be observed at early postoperative time points, it is expected that all fixation techniques will show stability from 1 to 2 years postoperatively

Introduction:. Given that factors like center of rotation (COR), neck shaft angle, glenosphere diameter and component tilt alter the biomechanics of reverse total shoulder arthroplasty (rTSA), the performance of the total rTSA system is of interest. This study compared the composite performance of two rTSA systems that were designed around a medialized or lateralized glenohumeral COR. The objective was to quantify the following outcome measures: 1) COR & humeral position; 2) range of glenohumeral abduction; 3) force to abduct; and 4) range of internal (IR)/external (ER) rotation. Methods:. Seven pairs of shoulders were tested with a biomechanical shoulder simulator. Beads were implanted in the scapula and humerus to quantify bone positions with a fluoroscope. Spectra lines simulated the deltoid and the rotator cuff. Linear actuators simulated muscle excursion while load cells recorded applied force. Diode arrays were used to quantify arm position and calculate the humeral center of rotation. Native specimens were tested where a motion path was recorded from resting to peak glenohumeral abduction in the scapular plane. The trajectory was replayed and deltoid force vs. arm position was recorded. With the elbow flexed, the arm was articulated to maximal internal and external rotation to determine ROM limits due to impingement or soft tissue constraint. Specimens were implanted with a Tornier Aequalis Reversed Shoulder prosthesis (“A,” 36 mm glenosphere, 10° humeral retroversion, 9 mm poly insert – “medial”) or a DJO Surgical Reverse Shoulder Prosthesis (“R,” 32 mm, 30° retroversion, neutral insert/shell – “lateral”). Implants were randomized between shoulders in a pair. After implantation the test protocol was repeated. Paired-t tests (p ≤ 0.050) were adjusted with Holm's step-down correction for multiple comparisons. Results:. Joint COR shifted inferiorly (A = 7 ± 3 mm, R = 4 ± 2 mm) and medially (A = 19 ± 4 mm, R = 12 ± 3 mm) for both systems with respect to native (p≤0.007, between systems p≤0.037). All humeri shifted inferiorly with respect to native (Fig. 1, p = 0.000, between systems p = 0.718). The RSP maintained a nearly anatomic medial/lateral humerus position, whereas the Aequalis medialized the humerus (p = 0.007). Both rTSA systems showed adduction deficit versus native arms (Fig. 2, p ≤ 0.046). Peak passive abduction, IR and ER were not significantly different between systems (p ≥ 0.113) or with respect to native (p ≥ 0.085). Deltoid force required to elevate the arm decreased ∼25% after rTSA (p ≤ 0.049), but did not differ between systems (p ≥ 0.117). Discussion:. Understanding the implications of implant configuration is imperative to improving implant design and optimizing patient outcomes. As tested, the configurations represent over 70% of respective clinical cases. The systems varied in COR offset, humeral component version/tilt, glenosphere placement, and insert thickness, yet few kinematic differences arose. The RSP COR was more lateral than the Aequalis, yet both were medial to native. Accordingly, both systems provided a similar mechanical advantage by reducing the abduction forces. The RSP had the least adduction deficit, which could indicate increased inferior clearance around the more lateral COR. Inferior and medial humerus shift could negatively impact external rotation capability by moving the posterior cuff line of action below the COR and reducing muscle tension (Fig. 3)

Statement of Purpose. Meniscal tears are common knee injuries that subsequently lead to degenerative arthritis, attributed to changes in stress distribution in the knee. In such cases there is need to protect the articular cartilage by repairing or replacing the menisci. While traditionally, meniscal replacement involves implantation of allografts, problems related to availability, size matching, cost and risk of disease transmission limit their use. Another optional treatment is that of biodegradable scaffolds which are based principally on tissue engineering concepts. The variability in body response to biodegradable implants and the quality of the tissue formed still pose a problem in this respect, under intense knee loading conditions. Moreover, biological solutions are mostly limited to younger patients <40 years old. Therefore, the goal of this study was, to develop a synthetic meniscal implant which can replace the injured meniscus, restore its function, and relieve pain. Methods. A composite, non-fixed self-centering discoid-shaped meniscus implant (NUsurafce®, AIC, Memphis, TN), composed of polycarbonate-urethane (PCU) and reinforced circumferentially with UHMWPE fibers is proposed (Fig. 1). The implant geometry was based on an extensive MRI study of over 100 knee scans [1]. The proposed structure aims to mimic the circumferential collagen reinforcement of the natural meniscus. Biomechanical evaluation of the implant was focused on in-vitro measurements of contact pressure under the implant in cadaver knees and computational finite element (FE) analyses [2,3]. Pressure distribution on the tibial plateau (under the meniscus implant) was measured by pressure sensitive films (Tekscan, MA) and quantified with respect to the natural meniscus. FE analyses were used to evaluate internal stress and strains, and to support the selection of optimal implant configuration. The last pre-clinical step was a large-animal (sheep) study in which the cartilage condition was evaluated microscopically over six months [4]. Results. Contact pressure distributions on the tibia, were in good agreement with those measured under the natural meniscus (Fig. 2). Specifically, peak and average pressures developed under the implant were found to similar to those of the natural meniscus. The contact area measured under the implant (658±135mm. 2. ) was also restored when compared to the natural meniscus (642±96mm. 2. ). FE models confirmed that internal strains/stresses within the device components remained within the materials' allowed limits. The evaluation of an implant adapted to sheep showed no signs of wear or degradation of the materials. Histology showed relatively mild cartilage degeneration that was dominated by loss of proteoglycan content and cartilage structure. First clinical results for the implant, with up to 2 years follow-up, demonstrate encouraging prospects for this concept in terms of pain relief. Conclusions. In the current study, we presented the development of a novel PCU meniscal implant for the medial compartment of the knee, along with an overview of essential tests. It was found that (a) the implant is able to reduce the overall cartilage load associated with meniscectomy by effectively distributing joint loads, and (b) the implant completely prevents contact between opposing cartilage surfaces. The results of implantation in sheep can be considered favourable in arresting joint degeneration, and first implantations have shown that arthroscopic implantation of the device is short and uncomplicated. Results. Contact pressure distributions on the tibia, were in good agreement with those measured under the natural meniscus (Fig. 2). Specifically, peak and average pressures developed under the implant were found to similar to those of the natural meniscus. The contact area measured under the implant (658±135mm. 2. ) was also restored when compared to the natural meniscus (642±96mm. 2. ). FE models confirmed that internal strains/stresses within the device components remained within the materials' allowed limits. The evaluation of an implant adapted to sheep showed no signs of wear or degradation of the materials. Histology showed relatively mild cartilage degeneration that was dominated by loss of proteoglycan content and cartilage structure. First clinical results for the implant, with up to 2 years follow-up, demonstrate encouraging prospects for this concept in terms of pain relief. Conclusions. In the current study, we presented the development of a novel PCU meniscal implant for the medial compartment of the knee, along with an overview of essential tests. It was found that (a) the implant is able to reduce the overall cartilage load associated with meniscectomy by effectively distributing joint loads, and (b) the implant completely prevents contact between opposing cartilage surfaces. The results of implantation in sheep can be considered favourable in arresting joint degeneration, and first implantations have shown that arthroscopic implantation of the device is short and uncomplicated