Aim: To compare results of hemi arthroplasty (Aequalis) and reverse arthroplasty (Delta) in treatment of arthropathy with massive cuff tear. Methods: This was a multicentric study included 142 shoulder arthroplasties (80 reverse and 62 hemiarthroplasties). The pre-op. status was similar in two population according to Constant score, active anterior elevation (AAE) and active external rotation (AER). Results: The patients were evaluated with a mean follow-up of 44 months. There were 7 failures needed 5 revisions (2 in hemi group and 3 in reverse one). The Constant score was significantly better (p< 0,01) in reverse group (65.6) than in hemi group (46.2). AAE was significantly better (p< 0,01) in reverse group (138°) than in hemi group (96°). AER was significantly better (p< 0,05) in hemi group (22°) than in reverse group (11°) but external rotation in elevated position and internal rotation were not different. These results stay similar even with a follow up over 5 years. In reverse group, partial glenoid unscrewing was observed in 3 patients, and a notch in pillar of scapula in 50 cases. In hemi group, upward migration was observed in 32 cases. Conclusions: We found significantly better results for reverse prostheses. The inherent risk of hemiarthroplasties is upward migration wearing the coraco acromialarch. The inherent risk of reverse prosthesis is the notch in scapula, and the strain on glenoid fixation, but the results over 5 years stay satisfactory

Reverse total shoulder arthroplasty (RTSA) has improved the lives of many patients with complex shoulder pathology including rotator cuff arthropathy, glenoid bone defects, post-traumatic arthritis and failed non-constrained total shoulder arthroplasty. However, this non-anatomic replacement has a very different complication profile than has been observed with non-constrained shoulder arthroplasty and the revision of RTSA can be extremely challenging. The purpose of this talk is to review some of the typical complications observed in RTSA including instability, infection, stress fractures, peri-prosthetic fractures and glenoid failures, and discuss the treatment options for dealing with these difficult problems.

A reverse shoulder arthroplasty has become increasingly common for the treatment of proximal humerus fractures. A reverse shoulder arthroplasty is indicated especially in older and osteopenic individuals in whom the osteopenia, fracture type or comminution precludes fixation. However, there are many other ways to treat proximal humerus fractures and many of these are appropriate for different indications. Percutaneous pinning remains an option in certain surgical neck or valgus impacted proximal humerus fractures with minimal or no comminution at the medial calcar. In general, a fracture that is amenable to open reduction and fixation should be fixed. Open reduction and internal fixation should be the gold standard treatment for three-part fractures in younger and middle-aged patients. Four-part fractures should also be fixed in younger patients. Hemiarthroplasty results are less predictable as they are very dependent on tuberosity healing. While a reverse shoulder replacement may be considered in patients with severe comorbidities, patients always have better outcomes in the setting of an appropriately reduced and stably fixed proximal humerus fracture.

There is a large and growing population of patients with shoulder arthritis that are over 70 years old. Many of these patients live alone and sling immobilization after shoulder arthroplasty is problematic. Other than improved internal rotation, there are limited benefits of anatomic shoulder arthroplasty compared to reverse arthroplasty. Anatomic arthroplasty is associated with longer OR time, longer recovery with need for assistance to allow the subscapularis to heal, and more challenging glenoid exposure. The reverse arthroplasty is a faster operation without the need for subscapularis healing and the sphere provides a more forgiving implant position. Additional benefits of reverse arthroplasty include better ability to manage glenoid bone loss and joint subluxation. Data from the Australian Orthopaedic Association National Joint Replacement Registry shows that within the first year of surgery the rate of revision of anatomic shoulder arthroplasty is less than reverse arthroplasty. However, after one year, the overall revision rate of reverse arthroplasty is less than anatomic shoulder arthroplasty. Therefore, increased technical difficulty of anatomic shoulder arthroplasty together with concerns of subscapularis insufficiency, glenoid loosening, and lack of strong evidence of superiority do not warrant changing from reverse for patients over 70 years old

The 2021 Australian Orthopaedic Association National Joint Replacement Registry report indicated that total shoulder replacement using both mid head (TMH) length humeral components and reverse arthroplasty (RTSA) had a lower revision rate than stemmed humeral components in anatomical total shoulder arthroplasty (aTSA) - for all prosthesis types and diagnoses. The aim of this study was to assess the impact of component variables in the various primary total arthroplasty alternatives for osteoarthritis in the shoulder. Data from a large national arthroplasty registry were analysed for the period April 2004 to December 2020. The study population included all primary aTSA, RTSA, and TMH shoulder arthroplasty procedures undertaken for osteoarthritis (OA) using either cross-linked polyethylene (XLPE) or non-cross-linked polyethylene (non XLPE). Due to the previously documented and reported higher revision rate compared to other anatomical total shoulder replacement options, those using a cementless metal backed glenoid components were excluded. The rate of revision was determined by Kaplan-Meir estimates, with comparisons by Cox proportional hazard models. Reasons for revision were also assessed. For a primary diagnosis of OA, aTSA with a cemented XLPE glenoid component had the lowest revision rate with a 12-year cumulative revision rate of 4.7%, compared to aTSA with cemented non-XLPE glenoid component of 8.7%, and RTSA of 6.8%. The revision rate for TMH was lower than aTSA with cemented non-XLPE, but was similar to the other implants at the same length of follow-up. The reason for revision for cemented aTSR was most commonly component loosening, not rotator cuff deficiency. Long stem humeral components matched with XLPE in aTSA achieve a lower revision rate compared to shorter stems, long stems with conventional polyethylene, and RTSA when used to treat shoulder OA. In all these cohorts, loosening, not rotator cuff failure was the most common diagnosis for revision

Durable humeral component fixation in shoulder arthroplasty is necessary to prevent painful aseptic loosening and resultant humeral bone loss. Causes of humeral component loosening include stem design and material, stem length and geometry, ingrowth vs. ongrowth surfaces, quality of bone available for fixation, glenoid polyethylene debris osteolysis, exclusion of articular particulate debris, joint stability, rotator cuff function, and patient activity levels. Fixation of the humeral component may be achieved by cement fixation either partial or complete and press-fit fixation. During the past two decades, uncemented humeral fixation has become more popular, especially with short stems and stemless press fit designs. Cemented humeral component fixation risks difficult and complicated revision surgery, stress shielding of the tuberosities and humeral shaft periprosthetic fractures at the junction of the stiff cemented stem and the remaining humeral shaft. Press fit fixation may minimise these cemented risks but has potential for stem loosening. A randomised clinical trial of 161 patients with cemented vs. press fit anatomic total shoulder replacements found that cemented fixation of the humeral component provided better quality of life, strength, and range of motion than uncemented fixation but longer operative times. Another study found increased humeral osteolysis (43%) associated with glenoid component loosening and polyethylene wear, while stress shielding was seen with well-fixed press fit humeral components. During reverse replacement the biomechanical forces are different on the humeral stem. Stem loosening during reverse replacement may have different factors than anatomic replacement. A systemic review of 41 reverse arthroplasty clinical studies compared the functional outcomes and complications of cemented and uncemented stems in approximately 1800 patients. There was no difference in the risk of stem loosening or revision between cemented and uncemented stems. Uncemented stems have at least equivalent clinical and radiographic outcomes compared with cemented stems during reverse shoulder arthroplasty. Durable humeral component fixation in shoulder arthroplasty is associated with fully cemented stems or well ingrown components that exclude potential synovial debris that may cause osteolysis

Lateralization of the reverse arthroplasty may be desirable to more effectively tension the remaining rotator cuff, decrease scapular notching, improve the cosmetic appearance of the shoulder, and improve stability as well as the arc of motion prior to impingement. There are two primary options to lateralise a reverse shoulder arthroplasty: bone graft with a long post (BIO-RSA) vs. using metal. The two metal options generally include a thicker glenosphere or a thicker glenoid baseplate. Potential benefits of a BIO-RSA include lateralization of the glenoid center of rotation but without placing the center of rotation lateral to the prosthetic-bone interface. By maintaining the position of the center of rotation, the shear forces at the prosthesis-bone interface are lessened and are converted to compressive forces which will minimise glenoid failure. Edwards et al. performed a prospective study on a bony increased offset reverse arthroplasty. Among the 18 shoulders in the BIO-RSA group, the incidence of notching was 78% compared to controls 70%. The graft completely incorporated in 12 (67%), partially incorporated in 4 (22%), and failed to incorporate in 2 (11%). Frankle et al. reported on the minimum 5-year follow-up of reverse arthroplasty with a central compression screw and a lateralised glenoid component. The survivorship was 94% at 5 years. There were seven (9%) cases of scapular notching and no patient had glenoid baseplate loosening or baseplate failure. The authors noted that the patients maintained their improved function and radiographic results at a minimum of five years. In summary, lateralisation of the glenosphere is an attractive option to improve the outcome of reverse arthroplasty. Benefits of lateralisation with metal rather than bone graft include elimination of concern over bone graft healing or resorption. In addition, the procedure has the potential to be more precise with the exact offset amount known pre-operatively as well as improved efficiency of the procedure. Preparing the graft takes additional OR time and there is variable quality of the bone graft

Severe glenoid bone loss in patients with osteoarthritis with intact rotator cuff is associated with posterior glenoid bone loss and posterior humeral subluxation. Management of severe glenoid bone loss during shoulder arthroplasty is controversial and technically challenging and options range from humeral hemiarthroplasty, anatomic shoulder replacement with glenoid bone grafting or augmented glenoid component implantation, to reverse replacement with reaming to correct version or structural bone grafting or metallic augmentation of the bone deficiency. Shoulder replacement with severe glenoid bone loss is technically challenging and characterised by higher rates of complications and revisions. Hemiarthroplasty has limited benefit for pain relief and function especially if eccentric glenoid wear exists. Bone loss with >15 degrees of retroversion likely requires version correction include bone-grafting, augmented glenoid components, or reverse total shoulder replacement. Asymmetric reaming may improve version but is limited to 15 degrees of version correction in order to preserve subchondral bone and glenoid bone vault depth. Bone-grafting of glenoid wear and defects has had mixed results with graft-related complications, periprosthetic radiolucent lines, and glenoid component failure of fixation. Implantation of an augmented wedge or step polyethylene glenoid component improves joint version while preserving subchondral bone, but is technically demanding and with minimal short term clinical follow-up. A Mayo study demonstrated roughly 50% of patients with posteriorly augmented polyethylene had radiolucent lines and 1/3 had posterior subluxation. Another wedge polyethylene design had 66% with bone ingrowth around polyethylene fins at 3 years. Long term outcomes are unknown for these new wedge augmented glenoid components. Reverse shoulder arthroplasty avoids many risks of anatomic replacement glenoid component fixation and stability but is associated with a high complication rate (15%) including neurologic and baseplate loosening and often requires structural bone grafting behind the baseplate with suboptimal outcomes or metallic augmented baseplates with limited evidence and short term outcomes. Reverse replacement with baseplate bone grafting or metal augmentation is technically challenging due to limited native glenoid bone stock available for baseplate component ingrowth and long term fixation. Failure to correct glenoid superior inclination and restore neutral version within 10 degrees increases the risks of reverse baseplate failure of fixation, pull out, and failure of reverse replacement. Reverse baseplate failure rates in patients with severe glenoid bone loss and concomitant glenoid bone grafting range from 5–11%. The minimum native glenoid bony contact with the baseplate is unknown but likely is approximately 1cm of native bone contacting a central ingrowth post and a minority (∼15–25%) of native glenoid contacting the backside of the baseplate. Failure to correct posterior bone loss can lead to retroversion of the baseplate, reduced external rotation, posterior scapular notching, and posteromedial polyethylene wear. In summary, shoulder replacement with severe glenoid bone loss is technically challenging and characterised by higher rates of complication and revision

We present a series of 18 consecutive cases of primary reverse total shoulder arthroplasty for irreparable proximal humerus fractures in patients over 70. Failure of tuberosity union and poor cuff function leads to unsatisfactory results in over half the patients with hemiarthroplasty. Reverse total shoulder arthroplasty does not depend upon a functional rotator cuff and requires little formal rehabilitation. Patients over 70 with irreparable proximal humerus fractures treated with a reverse total shoulder arthroplasty were included in this study. Only primary arthroplasties were included. Reverse arthroplasties for failed hemiarthroplasties were excluded. All arthroplasties were performed using either a deltoid split direct lateral (superior) approach or the antero-lateral MacKenzie approach. The SMR reverse total shoulder prothesis was implanted in all cases using a press-fit glenoid base plate and glenosphere, and press-fit or cemented humerus stem. Tuberosity repair was attempted in 10 cases. The supraspinatus was excised from the greater tuberosity. Patients were allowed self-mobilisation after two weeks in a sling. Patients were recruited and followed up per ethics approved protocol. Outcome measures used were range of motion, dislocation and revision rates radiological signs of loosening and glenoid notching, DASH and Constant scores. Results were compared to another series of cases of reverse shoulder arthroplasty for sequelae of trauma and failed hemiarthroplasties, as well as a series of primary hemiarthroplasties. At an average follow-up of 30 months (minimum 12 months) all patients were satisfied with their results. Average forward elevation was 132 deg. and abduction 108 deg. There was not deterioration of movement at 12 or 24 months. No patient had ongoing pain. The average constant score was 62. There was no evidence of humeral stem loosening apart from one case of early subsidence in a press fit stem. Eleven cases showed glenoid notching, four Nerot grade 1, six Nerot grade 2 and one Nerot grade 3. All notching had stabilised after 12 months. There were no cases of dislocation. No case needed revision, or awaits revision. All cases were pain-free at last review. Overall results for this group of primary reverse arthroplasties for fractures was much better than for reverse arthroplasties for sequelae of trauma. The results were also better than for primary hemiarthroplasties. Irreparable three and four part fractures of the proximal humerus pose management challenges in the elderly. The reverse total shoulder arthroplasty is very attractive option for elderly patients with irreparable proximal humerus fractures. They require little rehabilitation and can give reproducibly good functional results, which do not deteriorate with time

The concept of non-anatomic reversed arthroplasty is becoming increasingly popular. The design medializes and stabilizes the center of rotation, and lowers the humerus relative to the acromion, and lengthens the deltoid muscle up to 18%. Such a surgically created global distraction of muscles is likely to affect nervous structures. When nerves are stretched up to 5–10%, axonal transport and nerve conduction starts to be impaired. At 8% of elongation, venous blood flow starts to diminish and at 15% all circulation in and out of the nerve is obstructed. [. 1. ] To understand nerve dynamics following reversed arthroplasty, we investigated nerve strain and excursion in a cadaver model. In a formalin-embalmed female cadaver specimen, the brachial plexus en peripheral upper limb nerves were carefully dissected and injected with an iodine containing contrast medium. At the same time 1.2 mm-diameter leaded markers were implanted at topographically crucial via points for later enhanced recognition on CT reconstructions. After the first session of CT scanning a plastic replica of the Delta reversed shoulder prosthesis® was surgically placed followed by re-injection of the plexus with the same solution. The preoperative and the postoperative specimen were studied using a helical CT scan with a 0,5 mm slice increment. The Mimics® (Materialise NV, Belgium) software package was used for visualization and segmentation of CT images and 3D rendering of the brachial plexus and peripheral nerves. After surgery, there was an average increase in nerve strain below physiologically relevant amplitudes. In a few local segments of the brachial plexus an increase in nerve strain exceeding 5–10 % was calculated. The largest increase in strain (up to 19%) was observed in a segment of the medial cord. These results suggest there might be a clinically relevant increase in nerve strain following reversed shoulder arthroplasty

Glenoid bone loss is not an uncommon challenge in both primary shoulder arthroplasty surgery and revision surgery. Walch described the classification of glenoid morphology and this has led to an understanding of the expanded role for bone grafting, patient-specific implants and reverse prostheses. While bone grafting of the glenoid in conventional arthroplasty has been shown to be successful in some patients it is more routinely used in combination with reverse prostheses. More recently, augmented glenoid components have been developed for both conventional and reverse arthroplasty, though follow-up is insufficient to confirm their durability at this time

Introduction. Acromial and scapular fractures are a rare but difficult complication with reverse total shoulder arthroplasty (rTSA), with an incidence rate reported from 1–10%. The risk factors associated with these fractures types is largely unknown. The goal of this study is to analyze the clinical outcomes, demographic and comorbidity data, and implant sizing and surgical technique information from 4125 patients who received a primary rTSA with one specific prosthesis (Equinoxe, Exactech, Inc) and were sorted based on the radiographic documentation of an acromial and/or scapula fracture (ASF) to identify factors associated with this complication. Methods. 4125 patients (2652F/1441M/32 unspecified; mean age: 72.5yrs) were treated with primary rTSA by 23 orthopaedic surgeons. Revision and fracture reverse arthroplasty cases were excluded. The radiographic presence of each fracture was documented and classified using the Levy classification method. 61 patients were identified as having ASF, 10 patients had fractures of the Type 1, 32 patients had Type 2, and 18 patients had Type 3 fractures according to Levy's classification. One fracture was not classifiable. Pre-op and post-op outcome scoring, ROM as well as demographic, comorbidity, implant, and surgical technique information were evaluated for these 61 patients and compared to the larger cohort of patients to identify any associations. A two-tailed, unpaired t-test identified differences (p<0.05). Results. The overall rate of ASF was 1.48% with the average time after surgery occurring at 12.9 ± 17.9 months (range 1 day to 78 months). Men had an ASF rate of 0.69% (10 of 1441); whereas women had a rate of 1.92% (51 of 2652). Patients with ASF were observed to be significantly shorter than patients without ASF (65.1 in vs 63.3 in, p=0.0004). ASF were more common in females (p=0.0019), have Rheumatoid Arthritis (p=0.0051), Cuff Tear Arthropathy (p=0.0093), or previous shoulder surgery (p=0.0189). Patient's weight did not correlate, nor did BMI. No difference was observed in humeral stem size, glenosphere diameter, or the humeral tray offset, humeral liner offset, or combined humeral tray+liner offset. The average number of screws used in the fracture group was significantly more than in the non-fracture group (p=0.0327), and 93% of patients in the fracture group had a screw in the superior hole of the baseplate. Pre-operatively, patients who developed ASF had significantly worse ASES (p=0.0104) and SPADI (p=0.0136) scores and also had significantly worse forward elevation (p=0.0237) and internal rotation (p=0.0054) than those who did not develop ASF. At latest follow-up, patients with ASF had significantly worse SST, UCLA, ASES, Constant, and SPADI scores (all p<0.0001); significantly worse abduction, forward elevation, internal rotation, strength (all p<0.0001); and significantly less preop-to-postop improvement in all measured outcomes, except for external rotation (all p<0.0001). Finally, 24% of fractures were identified as being caused by a traumatic event, 28% of patients with fractures had a previous acromioplasty, and 53% of fractures were Levy type 2. Discussion. Acromial and scapular fractures after rTSA are a rare complication, with an incidence of 1.48% in this analysis of 4125 patients with a single rTSA prosthesis. These fractures were observed to occur at an average of 12.9 months after surgery, but were observed as early as 1 day and as late as 6.5 years. Female patients, Rheumatoid Arthritis, Cuff Tear Arthropathy, previous shoulder surgery, relatively worse pre-operative ASES or SPADI scores, relatively decreased pre-operative forward elevation and internal rotation as well as a larger number of screws placed in the baseplate all were significantly associated with the occurrence of ASF. Although 93% of patients with ASF had a screw placed in the superior hole of the baseplate, we cannot conclude that this is a driving factor at this time, as the superior screw number for the non-fracture group was not recorded. Future work should evaluate if usage of a superior glenoid baseplate screw and previous acromioplasty are also risk factors for these fracture types after rTSA. This study is the largest ever performed analysis of this rare complication and provides news insight into the predisposing risk factors to consider when evaluating patients for rTSA

Experience has demonstrated in the hip and knee, related to total joint replacement arthroplasty, polymethyl methacrylate cement fixation can provide problems in terms of loosening, fragmentation, particulate wear and ultimate failure. These same problems have been recognised in total shoulder arthroplasty related to cement fixation of the glenoid. While cement fixation of the humeral component has proven much less problematic, there has been a swelling towards avoidance of using cement to secure the humeral component for fear of difficulty if revision is required. Surprisingly, with the high incidence of lucent lines, bone resorption and frank loosening, representing the most common source of failure in total shoulder arthroplasty, cementless fixation of the glenoid has not been, until now, embraced. The advent of reverse total shoulder arthroplasty has demonstrated the ability for secure cementless fixation to provide long-lasting secure implant retention in implants which have inherently higher shear and stress forces passing through the implant/bone interface. In anatomic total shoulder arthroplasty a woven tantalum anchor (Trabecular Metal) has proven to demonstrate secure cementless fixation as well. This presentation will discuss the use of trabecular metal anchored glenoid implants with and without additional screw fixation for anatomic and convertible reverse arthroplasty baseplates. Avoidance of complications with successful long-lasting outcomes requires meticulous surgical attention to detail

Before reverse shoulder replacement was an option for rotator cuff tear arthropathy the treatment modalities were limited to injections and physical therapy for pain control, arthroscopic debridement with or without biceps tenodesis/tenotomy and hemiarthroplasty. Functional improvement was limited with these treatment options and success for pain control was moderate at best. The destructive nature of the rotator cuff deficient shoulder continued with medialization of the glenoid and erosion of the acromion seen even after replacement with hemiarthroplasty. The end result usually left the patient with a pseudo paralysis of the shoulder region functionally and uncontrolled pain that made later revision with a reverse implant difficult or impossible. Reverse arthroplasty was released for use in United States in 2004 for rotator cuff tear arthropathy. This initial procedure had a number of related complications that have been improved on over time with changes in implant design and better operative techniques. The long term results with reverse total shoulder arthroplasty have made this the procedure of choice for contained cuff tear arthropathy

Is there an optimal way to place a glenoid in reverse total shoulder arthroplasty (RTSA)? Four of the six parameters that a surgeon can control in a RTSA involve the glenoid. The parameters are: inferior tilt, increased lateral or inferior offset and increased glenosphere diameter. The theoretical challenges are further complicated by the normal variations that exist in the bony anatomy of the scapula and pathological abnormalities prevalent in as many as 40% of patients undergoing RTSA. Over the last 5 years there has been a growing body of data and study on the biomechanics, clinical outcomes and complications of this prosthesis. What have we learned? How does a surgeon incorporate this into their practice? The goal of this talk is to briefly review the current status of biomechanics on the impact of glenosphere positioning and offset on the outcome of reverse arthroplasty

A primary goal of shoulder arthroplasty is to place the components in anatomic version. However, traditional instrumentation does not accommodate glenoid wear patterns. Therefore, many investigators have attempted to use computer modeling or CT-based algorithms to create custom targeting guides to achieve this goal. There are some recent studies investigating the use of custom guides. Iannotti et al. published in JBJS-American in 2012 on the use of patient specific instrumentation. There were 31 patients included in the study. The authors found that the planning software and patient specific instrumentation were helpful overall, but particularly of benefit in patients with retroversion in excess of 16 degrees. In this group of patients, the mean deviation was 10 degrees in the standard surgical group and 1.2 degrees in the patient specific instrumentation group. Throckmorton presented a study at the AAOS in 2014 on 70 cadaveric shoulders. There was one high volume surgeon (>100 shoulder arthroplasties a year), two middle volume surgeons (20–50 shoulder arthroplasties a year), and two low volume surgeons (less than 20 shoulder arthroplasties per year). Overall, the custom guide was significantly more accurate than standard instrumentation. The custom guides were found to be especially more accurate among specimens with associated glenoid wear. There were no strong trends to indicate consistent differences between high, medium, and low volume surgeons. The authors concluded that custom guides have narrower standard deviation and fewer significant errors than standard instrumentation. Custom guides continue to evolve for use in shoulder arthroplasty including some guides that allow the surgeon to decide intra-operatively between anatomic shoulder arthroplasty and reverse arthroplasty. Additional studies will be necessary to further define the role of patient specific instrumentation in practice

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.

Periprosthetic joint infection (PPJI) following shoulder arthroplasty is uncommon, with an overall rate of 0.98%. However, the rates following revision arthroplasty and reverse arthroplasty are much higher. Given the rapid increase in the prevalence of shoulder arthroplasty and the increasing revision burden, the cost of PPJI to society will likely increase substantially. The most common organisms found in PPJI following shoulder arthroplasty are Staphylococcus aureus, coagulase-negative Staphylococcus, and Propionibacterium acnes (P. acnes). P. acnes is especially common in males. Traditional testing for PPJI includes aspiration, white blood cell count (WBC), erythrocyte sedimentation rate (ESR), and c-reactive protein (CRP). Aspiration often yields a dry tap and when fluid is obtained for culture, a positive result is helpful but a negative result does not rule out PPJI. Although WBC, ESR, and CRP are often positive with PPJI in the lower extremity, they are most often negative in shoulder PPJI. Although bone scans and WBC labeled scans are used, they are expensive and have low sensitivity and specificity. New testing and techniques have been reported in an attempt to improve sensitivity and specificity for PPJI. These techniques can be divided into tests on serum, synovial fluid, and tissue. Serum Interleukin-6 (IL-6) is highly specific (94%) for shoulder PPJI but has low sensitivity (14%). Synovial fluid can be tested for leukocyte esterase using a simple and cheap technique. In lower extremity PPJI it has shown to be helpful. It is not as helpful in shoulder PPJI with 30% sensitivity and 67% specificity. Alpha defensin has been reported to be more sensitive (63%) and as specific (95%) as traditional techniques but still lacks predictive value. Testing for specific cytokines (IL-2, IL-6, TNF- α) within synovial fluid is not widely used as yet but has shown promise with 80% sensitivity and 90% specificity. Obtaining tissue for culture and other testing is probably the most reliable way of confirming PPJI for the shoulder. Frozen sections taken at the time of revision can be helpful but is very pathologist dependent and institution specific. With a dedicated musculoskeletal pathologist, the finding of 10 or more WBCs per high powered field has been reported to be 72% sensitive and 100% specific for P. acnes and 63% sensitive and 100% specific for other organisms. Cultures from arthroscopic tissue biopsy have also been found to have high sensitivity (100%) and specificity (100%). Genetic testing of tissue biopsy specimens (PCR/NGS) has recently been reported and shows great promise. The significance of positive cultures and other tests, especially for P. acnes is unclear. There is a high rate of positive intra-operative cultures in primary cases of shoulder arthroplasty. In addition, intra-operative cultures taken at the time of revision, even in cases in which infection is not suspected, are frequently positive for P. acnes with weak correlation with rates of post-operative clinical infection. In conclusion, shoulder PPJI is a difficult problem to deal with. The definition of shoulder PPJI is currently unclear and further study is needed. There is no ideal test to confirm it. A reasonable approach is to aspirate for culture, and perform serum tests for WBC, ESR, and C-reactive protein. If any of these is positive in the setting of a painful arthroplasty, PPJI should be assumed until proven otherwise. Operative tissue cultures are probably the most reliable test but the clinical significance is not always obvious. Synovial fluid cytokine profiles and tissue PCR/NGS show promise for the future

There is nothing going to ruin your day like a complication after shoulder arthroplasty, either hemiarthroplasty (HA) anatomical (TSA) or reverse arthroplasty (RTSA). While complications are fortunately uncommon with anatomical shoulder arthroplasty (approximately 8% but as high as 40%), the complication rate for RTSA has been reported as high as 70%. Most complications are multifactorial and cannot all be blamed on the patient. Basically you do not want to operate upon a young patient who is an insulin dependent diabetic, has an ASA of 3 or 4, who smokes, has HIV disease and has a BMI over 40. The most common predictors of failure are determined by the indication for surgery, the type of implant used and the skill of the surgeon. The major risk factors for HA are eccentric glenoids, young age and rotator cuff failure. The biggest risk factors for TSA are metal backed glenoid components, younger age of the patient, rotator cuff pathology and insufficient glenoid bone. The major risk factors for RTSA are the type of component used (Grammont type versus lateral center of rotation designs) and the indication for surgery. Infection risks include previous infected arthroplasty, previous joint infection, immunosuppression (e.g. steroid use, insulin dependent diabetes, HIV disease), ASA 3 or 4 and higher BMI (i.e. over 40). Not all of these risk factors can be prevented in patients but informed consent is critical to the patient understanding the potential outcomes of their surgery

Introduction. Glenoid loosening, still a main complication in shoulder arthroplasty, could be related to glenohumeral orientation and conformity, cementing techniques, fixation design and periprosthetic bone quality [1,2]. While past numerical analyses were conducted to understand the relative role of these factors, so far none used realistic representations of bone microstructure, which has an impact on structural bone properties [3]. This study aims at using refined microFE models including accurate cortical bone geometry and internal porosity, to evaluate the effects of fixation design, glenohumeral conformity, and bone quality on internal bone tissue and cement stresses under physiological and pathological loads. Methods. Four cadaveric scapulae were scanned at 82µm resolution with a high resolution peripheral quantitative computer tomography (XtremeCT Scanco). Images were processed and virtually implantated with two anatomical glenoid replacements (UHMWPE Keeled and Pegged designs, Exactech). These images were converted to microFE models consisting of nearly 43 million elements, with detailed geometries of compact and trabecular bone, implant, and a thin layer of penetrating cement through the porous bone. Bone tissue, implant and cement layer were assigned material properties based on literature. These models were loaded with a central load at the glenohumeral surface, with the opposite bone surface fully constrained. Effects of glenohumeral conformity were simulated with increases of the applied load area from 5mm-radius to a fully conformed case with the entire glenoid surface loaded. The models were additionally subjected to a superiorly shifted load mimicking torn rotator cuff conditions. These models were solved and compared for internal stresses within the structures (Figure 1) with a parallel solver (parFE, ETH Zurich) on a computation cluster, and peak stresses in each region compared by design and related to apparent bone density. Results. Peak cement stresses were generally located at the interface with bone rather than implant (p<0.05), and peak bone stresses occurred around the cemented region. A larger trabecular load share was predicted with the Pegged compared to the Keeled design (Figure 2a). Superior load shift reduced this ratio but resulted in slight stress increase in the cement and implant, with the Keeled design less sensitive to this shift (Figure 2b). These effects were more pronounced with decreased overall bone density (Figure 2c). Increasing conformity significantly affected peak stresses in the cement and implant for both Keeled and Pegged designs (Figure 3) (p<0.041), but only significantly changed bone stresses for the Keeled design (p<0.047). Generally higher peak cement and trabecular bone stresses were predicted for the Pegged design. Discussion. Our detailed microFE analyses suggest that implant fixation design affects the sensitivity of internal stresses to glenohumeral load shifts, in particular within the cement region and through alterations in load sharing in the periprosthetic bone. Future steps including reverse replacements and more physiological loading conditions, combined with experimental validation tests in dynamic loading, will provide improved insights into the clinical incidences of glenoid loosening