Aims. The Mathys Affinis Short is the most frequently used stemless total shoulder prosthesis in the UK. The purpose of this prospective cohort study is to report the survivorship, clinical, and radiological outcomes of the first independent series of the Affinis Short prosthesis. Methods. From January 2011 to January 2019, a total of 141 Affinis Short prostheses were implanted in 127 patients by a single surgeon. Mean age at time of surgery was 68 (44 to 89). Minimum one year and maximum eight year follow-up (mean 3.7 years) was analyzed using the Oxford Shoulder Score (OSS) at latest follow-up. Kaplan-Meier survivorship analysis was performed with implant revision as the endpoint. Most recently performed radiographs were reviewed for component radiolucent lines (RLLs) and proximal humeral migration. Results. Five shoulders underwent revision surgery (3.5%); three for rotator cuff failure, one for infection, and one for component malposition. Survivorship of the implant was 95.4% (95% confidence interval 90.1% to 97.9%) at five and nine years. Mean OSS improved significantly compared to preoperative values from 19.0 (1 to 35) to 43.3 (7 to 48) (p < 0.001). Radiological analysis was undertaken for 99 shoulders. This revealed humeral RLLs in one case (1%), glenoid RLLs in 15 cases (15.2%), and radiological rotator cuff failure in 22 cases (22.2%). Conclusion. This prospective cohort study shows encouraging short- to mid-term survivorship and clinical and radiological results for the Mathys Affinis Short, Short Stem Total Shoulder Prosthesis. Level of Evidence: IV. Cite this article: Bone Jt Open 2021;2(1):58–65

Abstract. Aim. Excessive glenoid retroversion and posterior wear leads to technical challenges when performing anatomic shoulder replacement. Various techniques have been described to correct glenoid version, including eccentric reaming, bone graft, posterior augmentation and custom prosthesis. Clinical outcomes and survivorship of a Stemless humeral component with cemented pegged polyethylene glenoid with eccentric reaming to partially correct retroversion are presented. Patients and Methods. Between 2010– 2019, 115 Mathys Affinis Stemless Shoulder Replacements were performed. 50 patients with significant posterior wear and retroversion (Walch type B1, B2, B3 and C) were identified. Measurement of Pre-operative glenoid retroversion and Glenoid component version on a post op axillary view was performed by method as described by Matsen FA. Relative correction was correlated with clinical and radiological outcome. Results. 4 were lost to follow up. 46 patients were therefore reviewed. The mean follow up was 4 years (2–8.9 years). Walch B1, Pre op Retroversion: 12 (8–20), post op retroversion :11.8 (−4 to 19), correction= 0.2. Walch B2, Pre op Retroversion :18.4 (10–32), post op retroversion: 13.2 (1 −22), correction= 5.2. Walch B3, Pre op Retroversion: 19.1 (13–32)post op retroversion : 16.1 (9–25), correction= 3.0. Walch C, Pre op Retroversion: 33.3 (28–42) post op retroversion: 16.0 (6–27), correction= 17.3. 3 patients required revision surgery for rotator cuff failure. Conclusion. Partial correction of glenoid retroversion with eccentric reaming and implantation of cemented pegged polyethylene component leads to satisfactory clinical outcomes at midterm follow up. No revisions for aseptic loosening of the glenoid were required

Introduction: In most of the reported series, scapular notching in inverse shoulder arthroplasty has been identified as a major problem. Therefore, a novel concept has been developed in order to minimize the incidence and the evolution (pathophysiology) of scapular notching. The current cohort study is now large enough to examine the results with special attention on notching. Methods: A dual peg design of the metaglene with CaP coating provides high primary and secondary stability. “Geometrical” notching is reduced by inferior (eccentric) fixation of the glenosphere on the metaglene, beveling of the medial part of the humeral inlay, and by the choice of three different sizes of the glenosphere (36, 39 and 42). “Biological” notching is addressed by inversion of the components: the epiphysis – as the mobile part – is metallic. Its contact to the scapula, should this occur, cannot lead to polyethylene wear. This study is a prospective multicentric study on Affinis Inverse and Affinis Fracture Inverse shoulder prosthesis (Mathys Ltd Bettlach, Switzerland), which is running in 7 European hospitals since December 2007. All cases but two (lost to follow-up) are included. Preoperative and all postoperative radiographs were reviewed. Notching has been graded 0 to 4, on a scale adapted after Sirveaux. Results: At submission deadline for the abstract, 163 cases were included. Grade 1 notching was detected in 8 cases (4.9%), and grade 2 notching in one. In those cases, notching developed early, but was not progressive over time. There were no cases of grade 3 or 4. In 17 cases, the X-rays were not assessable and therefore it was impossible to definitively rule out a possible grade 1 notching. None of the Affinis Fracture Inverse prostheses produced any notching. New bone apposition on the inferior aspect of the scapula was detected in 15 cases. We postulate this to be a metaplasia of the long head of the triceps due to local periosteal stimulation. Conclusions: The present design leads to a very low rate of scapular notching. Even in the 9 cases where notching was present, it appears that the epiphysis only created the space it needed, without any ongoing osteolytic process beyond this. Specific prosthetic design improves both quantity and quality of scapular notching

Over the last decade stemless shoulder arthroplasty has become increasingly popular. However, stability of metaphyseal loading humeral components remains a concern. This study aimed to assess the stability of the Affinis stemless humeral component using Radiostereometric analysis (RSA). Patients underwent total shoulder arthroplasty via a standardised technique with a press-fit stemless humeral component and a cemented pegged glenoid. Tantalum beads were inserted into the humerus at the time of operation. RSA of the relaxed shoulder was completed at weeks 1, 6, 13, 26, 52 and 104 post-operatively. Stressed RSA with 12 newtons of abduction force was completed from week 13 onwards. ABRSA 5.0 software (Downing Imaging Limited, Aberdeen) was used to calculate humeral component migration and induced movement. 15 patients were recruited. Precision was: 0.041, 0.034, 0.086 and 0.101 mm for Superior, Medial, Posterior and Total Point Motion (TPM) respectively. The mean TPM over 2 years was 0.24 (0.30) mm, (Mean (Standard deviation)). The mean rate of migration per 3 month time period decreased from 0.45 (0.31) to 0.02 (0.01) mm over 2 years. Mean inducible movement TPM peaked at 26 weeks at 0.1 (0.08) mm, which reduced to 0.07 (0.06) mm by 104 weeks when only 3 patients had measurable inducible motion. There was no clear trend in direction of induced movement. There were no adverse events or revisions required. We conclude migration of the humeral component was low with little inducible movement in the majority of patients implying initial and 2 year stability of the stemless humeral component

Problem: The displacement of the rotation centre of the humeral head in relation to the shaft axis strongly varies individually. In order to measure the position of the pivot points of the head, the Affinis shoulder prosthesis has a double eccentric adjustment possibility that permits to adapt the head to the medial and dorsal offset. So far, such examinations took place exclusively on the anatomical preparation. This raises the question of whether the need for such a prosthetic system can be derived from the anatomical variation of the pivot points. Method: In 126 patients with an Affinis shoulder prosthesis, we calculated the individual rotation centres of the head from the position of the adjustable prosthetic cone and the eccentric position of the head. In addition, we used the Constant Score to record the clinical function. Results: We found great variation of the rotational centres. Therefore we needed the entire setting range of 12mm mediolateral and 6mm dorsoventral. The examination showed that none of the found anatomic head centres could have been reconstructed exactly with a conventional prosthesis. Prosthesis with a single eccentricity would allow correct adjustment in only 22 cases, as the adjustable rotational centres of the head are situated on a circle, which limits the setting possibilities. The Constant Score of the total group improved from 29% preoperatively to 94% after 2 years. Conclusions: The high variation of the head centres indicates the necessity of a freely adjustable system, such as in a double eccentric bearing. This is the only way that permits an optimal reconstruction of the anatomical conditions – it prevents an increased tension of the rotator cuff, reduces the eccentric loading of the glenoid and creates the prerequisites for the anatomical kinematics. The good clinical results speak for the need to observe bony balancing

The aim of our biomechanical study was to find out whether the prosthetic design, especially of the metaphyseal part, and the type of tuberosity fixation influences the primary stability in shoulder arthroplasty. Materials and Methods: 16 fresh frozen human cadaveric humeri were dissected until only the rotator cuff remained. A four-part fracture was simulated by osteotomy. In a first step two types of shoulder prosthesis (open stem versus closed stem) were used. The Tornier Aequalis prosthesis (open stem) using suture fixation and the Mathys Affinis fracture prosthesis (closed stem) using cable fixation were implanted according to standard techniques. The specimens were then loaded into a servo-pneumatic testing device in 25° of abduction. In 20 consecutive cycles traction of 40 Newton was alternating exerted on the subscapularis and infraspinatus tendon, while a continuous force of 40 Newton was exerted on the greater tuberosity to simulate the pull of the m. supraspinatus. The motion of the fragments was recorded by 2 high speed cameras. The following parameters were investigated : Failure of osteosynthesis, intertuberosity motion, motion lesser tuberosity-shaft, motion greater tuberosity-shaft, motion metaphysis-shaft. After completing the first series the cable fixation exposed to be more stable. In a second series we compared cable versus suture fixation in the Affinis fracture prosthesis to find out whether the stability was depending on the prosthesis design. Results:. Series 1: The intertuberosity motion was significantly lower in the cable prosthesis. The tuberosity-shaft motion was significantly lower in the cable group for greater and lesser tuberosity. The metaphysis - shaft motion did not significantly differ in both groups. Series 2: The intertuberosity motion was significant lower when the tuberosities were fixed by cable. The tuberosity-shaft motion was significantly lower when cable fixation was used. The metaphysis-shaft motion was not significantly diverse. Conclusion: Highest primary stability of tuberosity fixation in trauma-arthroplasty of the shoulder was measured in cable fixation and closed stem. We proved that the kind of fixation was the most important factor determing the stability. Metaphyseal design was less important

Aims

The liner design is a key determinant of the constraint of a reverse total shoulder arthroplasty (rTSA). The aim of this study was to compare the degree of constraint of rTSA liners between different implant systems.

PURPOSE. To validate the efficacy and accuracy of a novel patient specific guide (PSG) and instrumentation system that enables minimally invasive (MI) short stemmed total shoulder arthroplasty (TSA). MATERIALS AND METHODS. Using Amirthanayagam et al.'s (2017) MI posterior approach reduces incision size and eliminates subscapular transection; however, it precludes glenohumeral dislocation and the use of traditional PSGs and instruments. Therefore, we developed a PSG that guides trans-glenohumeral drilling which simultaneously creates a humeral guide tunnel/working channel and glenoid guide hole by locking the bones together in a pre-operatively planned pose and drilling using a c-shaped drill guide (Figure 1). To implant an Affinis Short TSA system (Mathys GmbH), novel MI instruments were developed (Figure 2) for: humeral head resection, glenoid reaming, glenoid peg hole drilling, impaction of cruciform shaped humeral bone compactors, and impaction of a short humeral stem and ceramic head. The full MI procedure and instrument system was evaluated in six cadaveric shoulders with osteoarthritis. Accuracy was assessed throughout the procedure: 1) PSG physical registration accuracy, 2) guide hole accuracy, 3) implant placement accuracy. These conditions were assessed using an Optotrak Certus tracking camera (NDI, Waterloo, CA) with comparisons made to the pre-operative plan using a registration process (Besl and McKay, 1992). RESULTS. 3D translational accuracy of PSG physical registration was: humeral PSG- 2.2 ± 1.1 mm and scapula PSG- 2.5 ± 0.7 mm. The humeral and scapular guide holes had angular accuracies of 6.4 ± 3.2° and 8.1 ± 5.1°, respectively; while the guide hole positional accuracies on the articular surfaces (which will control bone preparation translational accuracy) were 2.9 ± 1.2 mm and 2.8 ± 1.3 mm. Final implantation accuracy in translation was 2.9 ± 3.0 mm and 5.7–6.8 ± 2.2–4.0° across the implants’ three rotations for the humerus and in translation was 2.8 ± 1.5 mm and 2.3–4.3 ± 2.2–4.4° across the implants’ three rotations for the scapula (Figure 3). DISCUSSION. The overall implantation accuracy was similar to results of previously reported open, unassisted TSA (3.4 mm & 7–12°, Hendel et al., 2012, Nguyen et al., 2009). Analysis of the positional PSG registration accuracy very closely mirrors the final implantation accuracy (humerus:2.2 mm vs 2.9 mm, and scapula:2.2 mm vs 2.8mm), thus, this is likely the primary predictor of implantation accuracy. Furthermore, the greatest component of PSG registration error was mediolateral translation (i.e. along the guiding axis) and thus should not affect guide hole drilling accuracy. The drilled guide hole positional and angular error was low for the humerus (2.9 mm and 6.4°) but somewhat higher in rotation (8.1°) for the glenoid which may indicate a slight shift in the PSG prior to guide hole drilling due to the weight of the arm applied when the PSGs are locked together. In conclusion, this work has detailed the step-by-step surgical errors associated with the developed system and demonstrated that it achieves similar accuracy to open, unassisted TSA, while avoiding complications related to muscular transection and dislocation. Therefore, we believe this technique is worthy of clinical investigation