Summary Statement. The current biomecahnical study demonstrated that the stemless peripheral leg humeral component prototype and central screw humeral component prototype achieved similar initial fixation as stemmed Global Advantage humeral component in terms of resultant micromotion in total shoulder arthroplasty. Introduction. A stemless humeral component may offer a variety of advantages over its stemmed counterpart, e.g. easier implantation, preservation of humeral bone stock, fewer humeral complications, etc. However, the initial fixation of a stemless humeral component typically depends on cementless metaphyseal press-fit, which could pose some challenges to the initial stability. Long-term success of cementless implants is highly related to osseous integration, which is affected by initial implant-bone interface motion. 1. The purpose of the study was to biomechanically compare micromotion at the implant-bone interface of three humeral components in total shoulder arthroplasty. Patients & Methods. Three humeral components were evaluated: Global Advantage, a central screw prototype, and a peripheral leg prototype. All components were the smallest sizes available. Global Advantage is a stemmed design. Both central screw prototype and peripheral leg prototype are stemless designs. Five specimens were tested for each design. Composite analogue humeral models were utilized to simulate the humeral bone. The cortical wall had a thickness of 3 mm and a density of 481 kg/m. 3. , while the cancellous density was 80 kg/m. 3. The model was custom fabricated to accommodate 40 mm humeral component and had a 45° resected surface and a square base to facilitate test setup. Each humeral component was implanted per its surgical technique. The construct was clamped in a vise with the humeral shaft angled at 27°. A MTS test system was employed to conduct the test. A sinusoidal compressive load from 157 N to 1566 N (2BW) was applied to the humeral component at 1 Hz for 100 cycles. The implant-bone interface micromotion was measured with a digital image correlation system which had a resolution of less than 1 micron. The micromotion measurement was transformed to 2 components: 1 was parallel and the other perpendicular to the humeral resection surface. Peak-valley micromotion from the last 10 cycles were averaged and utilised for data analyses. A one-way ANOVA and post-hoc Tukey tests were performed to compare the micromotion of different designs (α=0.05). Results. Micromotion of Global Advantage parallel to the resection (X-Axis) was significantly less than that of central screw prototype and peripheral leg prototype. Micromotion of peripheral leg prototype perpendicular to the resection (Y-Axis) was significantly less than Global Advantage and central screw prototype. There was no significant difference between different designs in resultant micromotion. Discussion/Conclusion. Clinical studies have shown that current stemless shoulder prosthesis yielded encouraging results in mid-term follow-ups. Particularly, the stemless Arthrex Eclipse humeral component, a central screw design, has been reported to have a secure bony fixation and ingrowth at an average of 23 months postoperatively. 4. The current study demonstrated that the stemless peripheral leg prototype and central screw prototype achieved similar initial fixation as stemmed Global Advantage in terms of resultant micromotion, and provided biomechanical evidence that stemless humeral components could have comparable initial stability to stemmed counterparts

The purpose of this study is to report the clinical and radiological outcomes of patients undergoing primary or revision reverse total shoulder arthroplasty using custom 3D printed components to manage severe glenoid bone loss with a minimum of 2-year follow-up. After ethical approval (reference: 17/YH/0318), patients were identified and invited to participate in this observational study. Inclusion criteria included: 1) severe glenoid bone loss necessitating the need for custom implants; 2) patients with definitive glenoid and humeral components implanted more than 2 years prior; 3) ability to comply with patient reported outcome questionnaires. After seeking consent, included patients underwent clinical assessment utilising the Oxford Shoulder Score (OSS), Constant-Murley score, American Shoulder and Elbow Society Score (ASES), and quick Disabilities of the Arm, Shoulder, and Hand Score (quickDASH). Radiographic assessment included AP and axial projections. Patients were invited to attend a CT scan to confirm osseointegration. Statistical analysis utilised included descriptive statistics (mean and standard deviation) and paired t test for parametric data. 3 patients had revision surgery prior to the 2-year follow-up. Of these, 2/3 retained their custom glenoid components. 4 patients declined to participate. 5 patients were deceased at the time of commencement of the study. 21 patients were included in this analysis. The mean follow-up was 36.1 months from surgery (range 22–60.2 months). OSS improved from a mean 16 (SD 9.1) to 36 (SD 11.5) (p < 0.001). Constant-Murley score improved from mean 9 (SD 9.2) to 50 (SD 16.4) (p < 0.001). QuickDASH improved from mean 67 (SD 24) to 26 (SD 27.2) (p = 0.004). ASES improved from mean 28 (SD 24.8) to 70 (SD 23.9) (p = 0.007). Radiographic evaluation demonstrated good osseointegration in all 21 included patients. The utility of custom 3D-printed components for managing severe glenoid bone loss in primary and revision reverse total shoulder arthroplasty yields significant clinical improvements in this complex patient cohort

Introduction and Objective. In recent years, along with the extending longevity of patients and the increase in their functional demands, the number of annually performed RSA and the incidence of complications are also increasing. When a complication occurs, the patient often needs multiple surgeries to restore the function of the upper limb. Revision implants are directly responsible for the critical reduction of the bone stock, especially in the shoulder. The purpose of this paper is to report the use of allograft bone to restore the bone stock of the glenoid in the treatment of an aseptic glenoid component loosening after a reverse shoulder arthroplasty (RSA). Materials and Methods. An 86-years-old man came to our attention for aseptic glenoid component loosening after RSA. Plain radiographs showed a complete dislocation of the glenoid component with 2 broken screws in the neck of glenoid. CT scans confirmed the severe reduction of the glenoid bone stock and critical bone resorption and were used for the preoperative planning. To our opinion, given the critical bone defect, the only viable option was revision surgery with restoration of bone stock. We planned to use a bone graft harvested from distal bone bank femur as component augmentation. During the revision procedure the baseplate with a long central peg was implanted “on table” on the allograft and an appropriate osteotomy was made to customize the allograft on the glenoid defect according to the CT-based preoperative planning. The Bio-component was implanted with stable screws fixation on residual scapula. We decided not to replace the humeral component since it was stable and showed no signs of mobilization. Results. The new bio-implant was stable, and the patient gained a complete functional recovery of the shoulder. The scheduled radiological assessments up to 12 months showed no signs of bone resorption or mobilization of the glenoid component. Conclusions. The use of bone allograft in revision surgery after a RSA is a versatile and effective technique to treat severe glenoid bone loss and to improve the global stability of the implant. Furthermore, it represents a viable alternative to autologous graft since it requires shorter operative times and reduces graft site complications. There are very few data available regarding the use of allografts and, although the first studies are encouraging, further investigation is needed to determine the biological capabilities of the transplant and its validity in complex revisions after RSA

We have studied the three-dimensional geometry of the proximal humerus on human cadaver specimens using a digitised measuring device linked to a computer. Our findings demonstrated the variable shape of the proximal humerus as well as its variable dimensions. The articular surface, which is part of a sphere varies individually in its orientation as regards inclination and retroversion, and it has variable medial and posterior offsets. These variations cannot be accommodated by the designs of most contemporary humeral components. Although good clinical results can be achieved with current modular and non-modular components their relatively fixed geometry prevents truly anatomical restoration in many cases. To try to restore the original three-dimensional geometry of the proximal humerus, we have developed a new type of humeral component which is modular and adaptable to the individual anatomy. Such adaptability allows correct positioning of the prosthetic head in relation to an individual anatomical neck, after removal of the marginal osteophytes. The design of this third-generation prosthesis respects the four geometrical variations which have been demonstrated in the present study. These are inclination, retroversion, medial offset and posterior offset

Summary Statement. Reverse shoulder design philosophy can impact external rotation moment arms. Lateralizing the humerus can increase the external rotator moment arms relative to normal anatomy. Introduction. The design of reverse shoulders continues to evolve. These devices are unique in that they are not meant to reproduce the healthy anatomy. The reversal of the fulcurm in these devices impacts every muscle that surrounds the joint. This study is focused on analyzing the moment arms for the rotator cuff muscles involved in internal and external rotation for a number of reverse shoulder design philosophies. Methods. Four of the most common design philosophies were chosen. The first, a Grammont style prosthesis, with a center of rotation (COR) on the glenoid face and a humeral cup countersunk into the proximal humerus (MGMH). The second concept is the MGMH design lateralised by a 10mm bone graft (BIO). The third concept has a lateralised glenosphere COR and a humeral component inside the proximal humerus (LGMH). The fourth design has a medialised COR with a humeral component placed on top of the humerus (MGLH). This places the humerus further lateral than the previous designs. For each component set, a representative implant was modeled based on published specifications. Each design was implanted into the same digital bone models (consisting of a humerus, scapula, clavicle, and ribcage) following the manufacturer's recommended surgical technique. The muscles analyzed were the posterior-deltoid (PD), subscapularis (SSC), infraspinatus (IS), and teres minor (TM). These muscles were allowed to wrap around the bone of the scapula and proximal humerus through the range of motion. All muscle origin and insertion points were kept constant throughout the analysis. The assemblies were externally rotated from an initial position of 45° internal rotation to 45° of external rotation of the humerus with the arm at 0° of abduction. The moment arms for all muscles were compared to those calculated for the anatomic shoulder. Results. All the rotator cuff muscles displayed a similar trend with the reverse shoulder. The external rotators all had similar moment arm values at neutral (IS∼22mm, TM∼20mm), but increased at rates proportional to their humeral offsets with external rotation (IS-MGLH 32.3mm, LGMH 27.5mm, MGMH and BIO 26.25mm; TM-MGLH 31.3mm, LGMH 27.8mm, MGMH and BIO 26.5mm). The SSC internal rotation moment arm remains roughly constant at 20mm for the anatomic shoulder, but varies widely from 45° external to 45° internal rotation with the different designs (MGLH 31.4mm to 6.7mm; MGMH 25.1mm to 11.2mm; LGMH 26.2mm to 10.8mm; BIO 25.4mm to 4.8mm). The PD moment arm is increased relative to the anatomic shoulder during external rotation for the MGLH design (9.3mm vs. 7.4mm). The other designs exhibit a decrease in the moment arm of this muscle relative to the anatomic design (LGMH 7.3mm, MGMH 5.8mm, BIO 6.4mm). Discussion. The lateral offset between the center of humeral axis and the muscle insertion on the humerus dominates the external rotation moment arm value through this range of motion. This is evident by the increase in the moment arms with external rotation for the different reverse shoulder designs. The increase in external rotation efficiency for the external rotators and PD could play a critical role in post-operative external rotation strength and motion

Introduction. Glenoid loosening, still a main complication for shoulder arthroplasty, was suggested to be related implant design, surgical aspects, and also bone quality. However, typical studies of fixation do not account for heterogeneity in bone morphology and density which were suggested to affect fixation failure. In this study, a combination of cyclic rocking horse tests on cadaver specimens and microCT-based finite element (microFE) analysis of specimens of a wide range of bone density were used to evaluate the effects of periprosthetic bone quality on the risks of loosening of anatomical keeled or pegged glenoid implants. Methods. Six pairs of cadaveric scapulae, scanned with a quantitative computer tomography (QCT) scanner to calculate bone mineral density (BMD), were implanted with either cemented anatomical pegged or keeled glenoid components and tested under constant glenohumeral load while a humeral head component was moved cyclically in the inferior and superior directions. Edge displacements were measured after 1000, 4000 and 23000 test cycles, and tested for statistical differences with regards to changes or implant design. Relationships were established between edge displacements and QCT-based BMD below the implant. Four other specimens were scanned with high-resolution peripheral QCT (82µm) and implanted with the same 2 implants to generate virtual models. These were loaded with constant glenohumeral force, varying glenohumeral conformity and superior or inferior load shifts while internal stresses at the cement-bone and implant-cement interfaces were calculated and related to apparent bone density in the periprosthetic zone. Results. Mean displacements at the inferior and superior edges showed no statistical difference between keeled and pegged designs (p>0.05). Compression and distraction were however statistically different from the initial reference measurement at even 1000 and 4000 cycles for both implant designs (p<0.05). For both implant designs, superior and inferior distractions were generally highest at each measurement time in specimens where BMD below the lifting edge was lower, showing a trend of increased distraction with decreased BMD. Moreover, the microFE models predicted higher bone and cement stresses for specimens of lower apparent bone density. Finally, highest peak stresses were located at the cement-bone interface, which seemed the weaker part of the fixation. Discussion. With this combined experimental and numerical study, it was shown that implant distraction and stresses in the cement layer are greater in glenoids of lower bone density for both implant designs. This indicates that fixation failure will most likely occur in bone of lower density, and that fixation design itself may play a secondary role. These results have important impact for understanding the mechanisms of glenoid component failure, a common complication of total shoulder arthroplasty

Wear of polyethylene is associated with aseptic loosening of orthopaedic implants and has been observed in hip and knee prostheses and anatomical implants for the shoulder. The reversed shoulder prostheses have not been assessed as yet. We investigated the volumetric polyethylene wear of the reversed and anatomical Aequalis shoulder prostheses using a mathematical musculoskeletal model. Movement and joint stability were achieved by EMG-controlled activation of the muscles. A non-constant wear factor was considered. Simulated activities of daily living were estimated from in vivo recorded data.

After one year of use, the volumetric wear was 8.4 mm³ for the anatomical prosthesis, but 44.6 mm³ for the reversed version. For the anatomical prosthesis the predictions for contact pressure and wear were consistent with biomechanical and clinical data. The abrasive wear of the polyethylene in reversed prostheses should not be underestimated, and further analysis, both experimental and clinical, is required.

Objectives

The need for bone tissue supplementation exists in a wide range of clinical conditions involving surgical reconstruction in limbs, the spine and skull. The bone supplementation materials currently used include autografts, allografts and inorganic matrix components; but these pose potentially serious side-effects. In particular the availability of the autografts is usually limited and their harvesting causes surgical morbidity. Therefore for the purpose of supplementation of autologous bone graft, we have developed a method for autologous extracorporeal bone generation.