Baseplate Positioning Research Articles

Current Controversies in Reverse Total Shoulder Arthroplasty.

Reverse total shoulder arthroplasty can restore forward elevation in pseudoparalytic shoulders, can reduce pain, and can increase quality of life for patients; however, there are a number of issues with regard to the design and ideal implantation technique of reverse total shoulder arthroplasties that remain controversial. Glenospheres with a Grammont, medialized center of rotation and designs with a more lateralized center of rotation have specific pros and cons. Medialized designs have historically decreased glenosphere loosening but increase scapular notching, and lateralized designs decrease notching and improve range of motion but historically have resulted in increased baseplate failure. As such, a concrete conclusion with regard to medialization or lateralization of the glenosphere cannot be made at this time. Caudal, inferior placement of the glenosphere increases internal rotation, external rotation, abduction, and adduction while reducing notching. Superior baseplate positioning and tilt are correlated with baseplate failure and therefore should be avoided. It remains unclear whether neutral or slightly inferior tilt is preferred. The ideal humerosocket inclination angle remains unclear. The 135[degrees] designs appear to have a lower rate of scapular notching than the Grammont-style 155[degrees] humerosockets. The implications of this angle for instability remain unclear as, to our knowledge, there have been no randomized comparisons and the largest meta-analysis was confounded by other implant variables.

Optimizing baseplate position in reverse total shoulder arthroplasty in small-sized Japanese females: technical notes and literature review.

The management of cuff tear arthropathy (CTA) has always been a challenge for shoulder surgeons. Introduction of reverse total shoulder arthroplasty (RTSA) helped in providing pain relief and improved shoulder function in patients with CTA. In this study, we aimed to evaluate the short-term clinical results and some clinical details regarding the types of available prosthesis, positioning, and size of the components for RTSA in a population of short-stature female Japanese. In our seven cases, the average glenoid size was 23.9 mm in width and 34.2 mm in height. The average width was smaller than the size of all available baseplates. We implanted reverse shoulder prostheses with baseplate that measured 28 mm in diameter and two locking screws. The center of the baseplate was shifted to allow slight anterior overhang relative to the anatomical center to avoid breakage of the posterior cortex and to achieve firm fixation. One case of humeral shaft fracture occurred while inserting the humeral stem and required encircling wiring. In our experience, the short term clinical results of RTSA were excellent, but a new prosthesis that is designed to fit the short stature of Asians with smaller glenoid and humerus should be considered.

Challenges in Reverse Shoulder Arthroplasty: Addressing Glenoid Bone Loss

Reverse shoulder arthroplasty (RSA) was designed for the treatment of elderly patients with cuff tear arthropathy. Because of its success, the indications for RSA have expanded beyond cuff tear arthropathy to include acute fractures, fracture sequelae, massive rotator cuff tears, inflammatory arthritis, and revision shoulder arthroplasty. Consequently, the number of RSAs performed has increased steadily. Glenoid bone loss is not uncommon in patients undergoing primary or revision RSA. Failure to appreciate and address glenoid bone loss during RSA can lead to improper baseplate positioning and early failure or complications such as dislocation or scapular notching. The authors present a review of the current literature as well as recommended strategies for characterization of glenoid bone loss and preferred surgical techniques for addressing bone loss during RSA.

Analyse fonctionnelle comparative du positionnement de l’implant glénoïdien d’une prothèse d’épaule inversée entre une méthode 3D interactive et une méthode traditionnelle

Introduction A previous study by our group suggested that surgeons were not able to achieve the same accuracy in computer surgeries without full vision of scapulae. However, it is unknown whether planned prosthetic position for correcting alignment would result in better functional outcomes. The aim of this study is to analyze the effect of glenoid component positioning on the postoperative impingement free range of motion during standard glenohumeral kinematics. Materials and methods Thirty 3D-CT scapulas with highly eroded glenoid were involved. Two surgeons (A and B) performed blind RSA in Mimics software, when only the glenoid was visible. Surgeon A performed full 3D structure assisted virtual surgery on the same group of scapulae, and achieved high accuracy in correcting tilt and version. For each subject, the center of the frontal surface of glenoid metaglene from 3D assisted surgeries was defined as the planned position for baseplate. Translation of baseplate was measured in sagittal plane (anterior-posterior and superior-inferior directions) as the distance from the planned position to the center of baseplate from blind surgeries. For three postoperative situations, four standard glenohumeral kinematics (abduction, forward flexion, and internal external rotation) were simulated. Impingements between the humeral prosthesis, humerus and scapula during motion were recorded. Results Relative to the planned position from 3D assisted surgeries, no statistical difference was found on positioning by different surgeons for the anterior-posterior and superior-inferior translations of the baseplate. No statistical difference was found in impingement free range of motion among three operative conditions for each activity. Compared to the planned positions, more inferiorly translated baseplates resulted in increased impingement free range of motion in forward flexion ( P P P P P Discussion Without the guidance of the full 3D structure, the location deviation of baseplate positioning for both surgeons were similar, but showed significant variability. However, surgical plans focusing only on alignment accuracy in RSA may not result in better positioning of glenoid component, therefore may not improve impingement free range of motion for patients. A more inferior and posterior position may be advantageous for a better functional outcome. Future studies should integrate better designs for both alignment and positioning accuracy.

Optimal baseplate rotational alignment for locking-screw fixation in reverse total shoulder arthroplasty: a three-dimensional computer-aided design study

Baseplate loosening in reverse total shoulder arthroplasty (RTSA) remains a concern. Placing peripheral screws into the 3 pillars of the densest scapular bone is believed to optimize baseplate fixation. Using a 3-dimensional computer-aided design (3D CAD) program, we investigated the optimal rotational baseplate alignment to maximize peripheral locking-screw purchase. Seventy-three arthritic scapulae were reconstructed from computed tomography images and imported into a 3D CAD software program along with representations of an RTSA baseplate that uses 4 fixed-angle peripheral locking screws. The baseplate position was standardized, and the baseplate was rotated to maximize individual and combined peripheral locking-screw purchase in each of the 3 scapular pillars. The mean ± standard error of the mean positions for optimal individual peripheral locking-screw placement (referenced in internal rotation) were 6°±2° for the coracoid pillar, 198°±2° for the inferior pillar, and 295°±3° for the scapular spine pillar. Of note, 78% (57 of 73) of the screws attempting to obtain purchase in the scapular spine pillar could not be placed without an in-out-in configuration. In contrast, 100% of coracoid and 99% of inferior pillar screws achieved full purchase. The position of combined maximal fixation was 11°±1°. These results suggest that approximately 11° of internal rotation is the ideal baseplate position for maximal peripheral locking-screw fixation in RTSA. In addition, these results highlight the difficulty in obtaining optimal purchase in the scapular spine.

Comparing conventional and computer-assisted surgery baseplate and screw placement in reverse shoulder arthroplasty

Preoperative planning and intraoperative navigation technologies have each been shown separately to be beneficial for optimizing screw and baseplate positioning in reverse shoulder arthroplasty (RSA) but to date have not been combined. This study describes development of a system for performing computer-assisted RSA glenoid baseplate and screw placement, including preoperative planning, intraoperative navigation, and postoperative evaluation, and compares this system with a conventional approach. We used a custom-designed system allowing computed tomography (CT)-based preoperative planning, intraoperative navigation, and postoperative evaluation. Five orthopedic surgeons defined common preoperative plans on 3-dimensional CT reconstructed cadaveric shoulders. Each surgeon performed 3 computer-assisted and 3 conventional simulated procedures. The 3-dimensional CT reconstructed postoperative units were digitally matched to the preoperative model for evaluation of entry points, end points, and angulations of screws and baseplate. Values were used to find accuracy and precision of the 2 groups with respect to the defined placement. Statistical analysis was performed by t tests (α=.05). Comparison of the groups revealed no difference in accuracy or precision of screws or baseplate entry points (P>.05). Accuracy and precision were improved with use of navigation for end points and angulations of 3 screws (P<.05). Accuracy of the inferior screw showed a trend of improvement with navigation (P>.05). Navigated baseplate end point precision was improved (P<.05), with a trend toward improved accuracy (P>.05). We conclude that CT-based preoperative planning and intraoperative navigation allow improved accuracy and precision for screw placement and precision for baseplate positioning with respect to a predefined placement compared with conventional techniques in RSA.

Decreased scapular notching with lateralization and inferior baseplate placement in reverse shoulder arthroplasty with high humeral inclination.

Background:Scapular notching is a radiographic finding of unknown clinical significance following reverse total shoulder arthroplasty (RTSA). The purpose of this study was to determine how baseplate position affects the incidence of scapular notching and measure the clinical outcomes.Hypothesis:We hypothesized that low base plate position on the glenoid and new prosthesis design with a higher humeral inclination angle would decrease the incidence of notching at 2 years follow-up.Materials and methods:A total of 54 patients with an average follow-up of 30 months met inclusion criteria and underwent radiographic analysis of scapular notching and radiographic measures to determine glenoid component placement. Clinical measures including visual analog score, American Shoulder and Elbow Surgeons (ASES) scores, and range of motion (ROM) were prospectively collected.Results:Thirty-nine of the 54 patients had no notching. 7 had Grade 1 notching, 7 had Grade 2 notching, one had Grade 3, and one had Grade 4 notching. Notching was associated with higher placement of the glenoid component as measured by peg-glenoid rim distance and base plate distance. All patients with no evidence of notching at 1-year, continued to have no notching after multi-year follow-up. Clinical outcome measures including ASES scores, ROM, and visual analog pain scores were improved at follow-up.Conclusion:We concluded that lower neck-shaft angle and low baseplate positioning led to a low incidence of significant scapular notching as only 6 out of 57 (16%) patients had notching Grade 2 and above. At short-term follow-up, this RTSA results in excellent clinical outcomes and a significantly lower scapular notching rate than traditional techniques.

Scapular Notching in Reverse Shoulder Arthroplasty: Is It Important to Avoid It and How?

Scapular notching, erosion of the scapular neck related to impingement by the medial rim of the humeral cup during adduction, is a radiographic sign specific to reverse shoulder arthroplasty (RSA). Its clinical and radiological consequences remain unclear. Therefore, we: (1) determined the incidence of notching in a large series, (2) described the natural history of notching, (3) determined whether notching is related to functional scores or (4) radiographic signs of failure, and (5) identified factors related to notch development. We retrospectively reviewed 448 patients who underwent a Grammont-type RSA (461 shoulders) with a mean followup of 51 months (range, 24-206 months). RSA was implanted for cuff tear arthropathy or osteoarthritis with cuff deficiency. We assessed scapular notching using AP views standardized under fluoroscopy. Clinical assessment included Constant-Murley score and range of motion. Aside from notching, radiographic assessment included evaluation of humeral and glenoid radiolucent lines. Notching occurred in 68% of cases. It appeared early, but its later evolution was variable. Notching was associated with followup, strength, passive and active elevation, humeral radiolucent lines, and glenoid lucent lines. It also correlated with a higher rate in patients with preoperative superior erosion. Scapular notching is frequent, generally progresses, and is associated with deterioration of some clinical parameters and radiolucent lines. We believe the preoperative pattern of glenoid erosion is of particular importance due to its influence on the surgeon's glenoid preparation and base-plate positioning. It is crucial to avoid cranial position and superior tilt. Level IV, Therapeutic study. See Guidelines for Authors for a complete description of levels of evidence.

Can medio-lateral baseplate position and load sharing induce asymptomatic local bone resorption of the proximal tibia? A finite element study

BackgroundAsymptomatic local bone resorption of the tibia under the baseplate can occasionally be observed after total knee arthroplasty (TKA). Its occurrence is not well documented, and so far no explanation is available. We report the incidence of this finding in our practice, and investigate whether it can be attributed to specific mechanical factors.MethodsThe postoperative radiographs of 500 consecutive TKA patients were analyzed to determine the occurrence of local medial bone resorption under the baseplate. Based on these cases, a 3D FE model was developed. Cemented and cementless technique, seven positions of the baseplate and eleven load sharing conditions were considered. The average VonMises stress was evaluated in the bone-baseplate interface, and the medial and lateral periprosthetic region.ResultsSixteen cases with local bone resorption were identified. In each, bone loss became apparent at 3 months post-op and did not increase after one year. None of these cases were symptomatic and infection screening was negative for all. The FE analysis demonstrated an influence of baseplate positioning, and also of load sharing, on stresses. The average stress in the medial periprosthetic region showed a non linear decrease when the prosthetic baseplate was shifted laterally. Shifting the component medially increased the stress on the medial periprosthetic region, but did not significantly unload the lateral side. The presence of a cement layer decreases the stresses.ConclusionLocal bone resorption of the proximal tibia can occur after TKA and might be attributed to a stress shielding effect. This FE study shows that the medial periprosthetic region of the tibia is more sensitive than the lateral region to mediolateral positioning of the baseplate. Medial cortical support of the tibial baseplate is important for normal stress transfer to the underlying bone. The absence of medial cortical support of the tibial baseplate may lead to local bone resorption at the proximal tibia, as a result of the stress shielding effect. The presence of a complete layer of cement can reduce stress shielding, though. Despite the fact that the local bone resorption is asymptomatic and non-progressive, surgeons should be aware of this phenomenon in their interpretation of follow-up radiographs.

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The influence of tibial baseplate position on stress distribution of tibial bone after total knee arthroplasty

The influence of tibial baseplate position on stress distribution of tibial bone after total knee arthroplasty

Critical speeds for a flexible spinning disk

A flexible uniform elastic disk is clamped at its inner radius and rotates at constant speed. It is shown that certain critical speeds exist at which the spinning disk is unable to support arbitrary spatially fixed transverse loads. These critical speeds are in the range of rotational speeds relevant in certain floppy disk magnetic recording applications. It is then shown that the inclusion of an elastic foundation parameter into the governing equations can raise the critical speeds of rotation. In the case of the floppy disk this corresponds to the use of a baseplate located in close proximity to the spinning disk. The results presented are the effect of the foundation stiffness parameter and clamping radius ratio on the critical speeds. Also included, for the magnetic recording application, is the effect of the baseplate position on the critical speeds.