• Recurrent posterior glenohumeral instability is an entity that demands a high clinical suspicion and a detailed study for a correct approach and treatment. Its classification must consider its biomechanics, whether it is due to functional muscular imbalance or to structural changes, volition, and intentionality.

• Due to its varied clinical presentations and different structural alterations, ranging from capsule-labral lesions and bone defects to glenoid dysplasia and retroversion, the different treatment alternatives available have historically had a high incidence of failure.

• A detailed radiographic assessment, with both CT and MRI, with a precise assessment of glenoid and humeral bone defects and of glenoid morphology, is mandatory.

• Physiotherapy focused on periscapular muscle reeducation and external rotator strengthening is always the first line of treatment. When conservative treatment fails, surgical treatment must be guided by the structural lesions present, ranging from soft tissue repair to posterior bone block techniques to restore or increase the articular surface.

• Bone block procedures are indicated in cases of recurrent posterior instability after the failure of conservative treatment or soft tissue techniques, as well as symptomatic demonstrable nonintentional instability, presence of a posterior glenoid defect >10%, increased glenoid retroversion between 10 and 25°, and posterior rim dysplasia. Bone block fixation techniques that avoid screws and metal allow for satisfactory initial clinical results in a safe and reproducible way.

• An algorithm for the approach and treatment of recurrent posterior glenohumeral instability is presented, as well as the author’s preferred surgical technique for arthroscopic posterior bone block.

• Massive rotator cuff tears (MRCTs) present a particular challenge due to high rates of retear that can range from 18 to 94%, failure of healing after repair, and potential for irreparability.

• Management of MRCTs must take into consideration the patient's characteristics, clinical examamination and expectation, number and quality of muscle tendons units involved.

• Conservative treatment, arthroscopic long head of the biceps tenotomy, cuff debridement, partial repair, and superior capsule reconstruction are viable solutions to treat selected patients.

• The goal of tendon transfers is to achieve stable kinematic by restoring rotational strength and force coupling of the shoulder joint.

• The ideal candidate is a young, motivated patient with small degenerative changes of the glenohumeral joint, a massive irreparable cuff tear, significant atrophy, fatty infiltration, and functional deficit.

• Patients with posterosuperior massive tears have impaired shoulder function with external rotation weakness and eventually lag sign If the teres minor is affected.

• Latissimus dorsi transfer is the most used with results lasting for long follow-up and lower Trapezius transfer is becoming a surgical option. For anterosuperior tears, there is still controversial if pectoralis major is the best option when compared to latissimus dorsi although this last has a similar vector force with the supraspinatus tendon.

• Complications associated with tendon transfers include neurovascular injury, infection, and rupture of the transferred tendon.

• Variable definitions of pseudoparalysis have been used in the literature.

• Recent systematic reviews and biomechanical studies call for a grading of loss of force couple balance and the use of the terms ‘pseudoparesis’ and ‘pseudoparalysis’.

• Pain should be excluded as the cause of loss of active function.

• Key players for loss of force couple balance seem to be the lower subscapularis as an anterior inferior checkrein and the teres minor as a posterior inferior fulcrum.

• Loss of three out of five muscle–tendon units counting upper and lower subscapularis separately is predictive of pseudoparalysis.

• Shoulder equator concept: loss of all three posterior, or all three superior, or all three anterior muscle–tendon units is predictive of pseudoparalysis (loss of fulcrum for deltoid force).

• Every effort should be made to prevent propagation of rotator cuff tears into the subscapularis and posterior rotator cuff (infraspinatus and teres minor) to maintain force couple balance (value of partial cuff repair).

• Clinical assessment of active forward elevation, active external rotation, and active internal rotation is important to define and grade the severity of loss of force couple balance.

• Additional features such as patient age, traumatic aetiology, chronicity, fatty infiltration, and stage of cuff tear arthropathy are useful for a specific diagnosis with implications for treatment.

• Decision-making for the treatment of pseudoparalytic shoulders is complex and a high level of experience in shoulder surgery and outcome evaluation is required.

• Management and results depend on clinical findings, tear and tissue quality, patient and surgeon criteria. Clinical findings determine the exact definition and direction of pseudoparesis and pseudoparalysis.

• Tear pattern and tissue quality determine if the rotator cuff is repairable or irreparable. Age and general health are important patient factors.

• Non-operative treatment is the first option for patients with a higher risk profile for reconstruction or arthroplasty, but delineation of its value requires better evidence.

• Tendon transfers are used for irreparable loss of the horizontal force couple balance (rotation). Options include latissimus dorsi, pectoralis minor and major for loss of active internal rotation, and latissimus dorsi ± teres major and lower trapezius for loss of active external rotation (AER).

• Partial cuff repair with or without superior capsular reconstruction using allograft or biceps tendon is an option for loss of active forward elevation.

• Treatment for the combined loss of elevation and external rotation patients is still not clear. Options include lateralised reverse shoulder arthroplasty (RSA) alone or combined RSA with a tendon transfer.

• RSA with loss of AER can be revised by adding a tendon transfer.

• The initial reverse shoulder arthroplasty (RSA), designed by Paul Grammont, was intended to treat rotator cuff tear arthropathy in elderly patients. In the early experience, high complication rates (up to 24%) and revision rates (up to 50%) were reported.

• The most common complications reported were scapular notching, whereas clinically more relevant complications such as instability and acromial fractures were less commonly described.

• Zumstein et al defined a ‘complication’ following RSA as any intraoperative or postoperative event that was likely to have a negative influence on the patient’s final outcome.

• High rates of complications related to the Grammont RSA design led to development of non-Grammont designs, with 135 or 145 degrees of humeral inclination, multiple options for glenosphere size and eccentricity, improved baseplate fixation which facilitated glenoid-sided lateralization, and the option of humeral-sided lateralization.

• Improved implant characteristics combined with surgeon experience led to a dramatic fall in the majority of complications. However, we still lack a suitable solution for several complications, such as acromial stress fracture.

Cite this article: EFORT Open Rev 2021;6:1097-1108. DOI: 10.1302/2058-5241.6.210039

• Early reported complication rates with the Grammont-type reverse shoulder arthroplasty (RSA) were very high, up to 24%.

• A ‘problem’ is defined as an intraoperative or postoperative event that is not likely to affect the patient’s final outcome, such as intraoperative cement extravasation and radiographic changes. A ‘complication’ is defined as an intraoperative or postoperative event that is likely to affect the patient’s final outcome, including infection, neurologic injury and intrathoracic central glenoid screw placement.

• Radiographic changes around the glenoid or humeral components of the RSA are very frequently observed and described in the literature.

• High complication rates related to the Grammont RSA design led to development of non-Grammont designs which led to a dramatic fall in the majority of complications.

• The percentage of radiological changes after RSA is not negligible and remains unsolved, despite a decrease in its occurrence in the last decade. However, such changes should be now considered as simple problems because they rarely have a negative influence on the patient’s final outcome, and their prevalence has dramatically decreased.

• With further changes in indications and designs for RSA, it is crucial to accurately track the rates and types of complications to justify its new designs and increased indications.

Cite this article: EFORT Open Rev 2021;6:1109-1121. DOI: 10.1302/2058-5241.6.210040

• Rotator cuff tears are a common condition of the shoulder, and 20.7% of people with the condition have a full-thickness rotator cuff tear. The purpose of this study was to explore the risk factors for full-thickness rotator cuff tears and to provide evidence to support the accurate diagnosis of full-thickness rotator cuff tears.

• Studies from PubMed, Embase and Web of Science published before 30 January 2021 were retrieved. All cohort studies and cross-sectional studies on risk factors for full-thickness rotator cuff tears were included. A meta-analysis was performed in RevMan 5.3 to calculate the relative risks (RRs) or weighted mean differences (WMDs) of related risk factors. Stata 15.1 was used for the quantitative analysis of publication bias.

• In total, 11 articles from six countries, including 4047 cases, with 1518 cases and 2529 controls, were included. The meta-analysis showed that age (MD = 0.76, 95% CI: 0.24 to 1.28, P = 0.004), hypertension (RR = 1.46, 95% CI: 1.17 to 1.81, P = 0.0007) and critical shoulder angle (CSA) (MD = 2.02, 95% CI: 1.55 to 2.48, P < 0.00001) were risk factors for full-thickness rotator cuff tears.

• Our results also suggested that body mass index, sex, dominant hand, smoking, diabetes mellitus and thyroid disease were not risk factors for full-thickness rotator cuff tears. Early identification of risk factors for full-thickness rotator cuff tears is helpful in identifying high-risk patients and choosing the appropriate treatment.

Cite this article: EFORT Open Rev 2021;6:1087-1096. DOI: 10.1302/2058-5241.6.210027

• Acute distal biceps tendon (DBT) pathology includes bicipitoradial bursitis, tendinosis, partial and complete tears.

• Diagnosis of complete DBT tears is mainly clinical, whereas in partial tears medical imaging is a valuable addition to the clinical diagnosis.

• New insights in clinical and medical imaging of partial tears may reduce time to diagnosis and may guide the treatment plan.

• Most complete tears are best treated with primary repair using either a single-incision or double-incision approach with good clinical outcome.

• The double-incision technique has a higher risk of heterotopic ossification, whereas a single-incision technique carries a higher risk of nerve-related complications.

• Intramedullary fixation may be a viable solution to negate the risk of posterior interosseus nerve lesions in single-incision repairs.

• DBT endoscopy can be used to treat low-grade partial tears and tendinosis.

Cite this article: EFORT Open Rev 2021;6:956-965. DOI: 10.1302/2058-5241.6.200145

• The biomechanics of the shoulder relies on careful balancing between stability and mobility. A thorough understanding of normal and degenerative shoulder anatomy is necessary, as the goal of anatomic total shoulder arthroplasty is to reproduce premorbid shoulder kinematics.

• With reported joint reaction forces up to 2.4 times bodyweight, failure to restore anatomy and therefore provide a stable fulcrum will result in early implant failure secondary to glenoid loosening.

• The high variability of proximal humeral anatomy can be addressed with modular stems or stemless humeral components. The development of three-dimensional planning has led to a better understanding of the complex nature of glenoid bone deformity in eccentric osteoarthritis.

• The treatment of cuff tear arthropathy patients was revolutionized by the arrival of Grammont’s reverse shoulder arthroplasty. The initial design medialized the centre of rotation and distalized the humerus, allowing up to a 42% increase in the deltoid moment arm.

• More modern reverse designs have maintained the element of restored stability but sought a more anatomic postoperative position to minimize complications and maximize rotational range of motion.

Cite this article: EFORT Open Rev 2021;6:918-931. DOI: 10.1302/2058-5241.6.210014

• Despite rapid medical technology development, various challenges exist in three- and four-part proximal humeral fracture (PHF) management. This condition has led to a notably increased use of the reverse total shoulder arthroplasty (RTSA); however, open reduction and internal fixation (ORIF) is still the most widely performed procedure. Thus, these two modalities are crucial and require further discussion. We aim to compare the outcomes of three- or four-part PHF surgeries using ORIF and RTSA based on direct/head-to-head comparative studies.

• We conducted a systematic review and meta-analysis based on the Cochrane handbook and PRISMA guidelines. We searched MEDLINE (PubMed), Embase (Ovid), and CENTRAL (Cochrane Library) from inception to October 2020. Our protocol was registered at PROSPERO (registration number CRD42020214681). We assessed the individual study risk of bias using ROB 2 and ROBINS-I tools, then appraised our evidence using the GRADE approach.

• Six head-to-head comparative studies were included, comprising one RCT and five retrospective case-control studies. We found that RTSA significantly improved forward flexion but was comparable to ORIF in abduction (p = 0.03 and p = 0.47, respectively) and more inferior in external rotation (p < 0.0001). Moreover, RTSA improved the overall Constant-Murley score, but the difference was not significant (p = 0.22). Interestingly, RTSA increased complications (by 42%) but reduced the revision surgery rates (by 63%) compared to ORIF (p = 0.04 and p = 0.02, respectively).

• RTSA is recommended to treat patients aged 65 years or older with a three- or four-part PHF. Compared to ORIF, RTSA resulted in better forward flexion and Constant-Murley score, equal abduction, less external rotation, increased complications but fewer revision surgeries.

Cite this article: EFORT Open Rev 2021;6:941-955. DOI: 10.1302/2058-5241.6.210049