Reverse Prosthesis Research Articles

Use of the Reverse Prosthesis in Patients in Wheelchairs or Walkers

Use of the Reverse Prosthesis in Patients in Wheelchairs or Walkers

Early Outcomes of Reverse Shoulder Arthroplasty for Tumors of the Humerus

At present in 90% of patients with malignant tumors of long bones and large joints the organ-saving intervention - oncologic joint replacement can be performed. The risk of complications after such operations on the upper extremity is low however the adequate functional results can not be achieved. The analysis and evaluation of oncologic and functional results after application of anatomic (group 1, n=28) and reverse (group 2, n=14) shoulder prostheses in patients with proximal humerus tumors was performed. Mean age of patients made up 32±4 and 38±3 years in the 1st and 2nd groups, respectively. Primary bone tumors were diagnosed in 19 (68%) patients from the 1st and 12 (86%) patients from the 2nd group. Mean follow up period was 42 months. Progression of the disease at terms from 6 to 14 months was observed in 4 patients with primary malignant bone tumors. Functional result by MSTS scale was 60-80% in 3, 40-60% in 6 and under 40% in 19 patients from the 1st group. In 2nd group functional result ranged from 80 to 100% in 6, from 60 to 80% in 6 and from 40 to 60% in 2 patients. Application of modular reverse prosthesis for the treatment of patients with proximal humerus tumors is a perspective technique as it enables to increase functional result and social adaptation of patients significantly.

Analysis of complications of reverse total shoulder arthroplasty.

the aim of this study was to analyze complications of reverse total shoulder arthroplasty (RTSA) used to treat different shoulder diseases. from March 2000 to March 2013, 195 RTSA were implanted by the senior Author. The indications for reverse prosthesis surgery were secondary osteoarthritis (OA) in 49 cases, irreparable rotator cuff tear (RCT) in 48 cases, and complex humeral fractures in 75 cases, while 19 were patients requiring surgical revision for first prosthesis implant. We used different prostheses with different designs. the clinical and radiological results of all the patients were analyzed retrospectively at an average follow-up of 7 years. The cases were divided into four groups on the basis of the diagnosis and complications were classified as perioperative, postoperative, or late. The mean total Constant score improved from 28 to 69 points in the OA group; from 21 to 70.8 points in the irreparable RCT group, to 76.4 in the fracture group, and from 16.6 to 59.8 points in the revision group. Scapular notching was observed in 59 cases (30.2%). Thirty-three other complications (16.9%) were observed, namely: hematomas (n=3), instability of the humeral component (n=1), scapular spine fractures (n=2), ulnar nerve deficit (n=2), long thoracic nerve palsy (n=2), deep infections (n=2), periprosthetic fractures (n=6), glenoid fractures (n=2), implant loosening (n=2), anterior deltoid muscle deficiency (n=2) and periarticular heterotopic calcifications (n=9). the rates of complications, especially fractures, reported in the present study were lower than those reported in the current literature. Level IV, therapeutic case series.

Reverse shoulder arthroplasty for the treatment of three-part and four-part proximal humeral fractures in the elderly

The purpose of this study was to review the survivorship, radiologic and clinical outcomes of reverse shoulder arthroplasty (RSA) used for the treatment of 3-part and 4-part proximal humeral fractures in the elderly. Between 2003 and 2009, 29 shoulders in 28 elderly patients (87% female) with a 3-part or 4-part fractures were managed with RSA in Brisbane, Australia. Clinical and radiologic outcomes of this continuous cohort were retrospectively reviewed at an average follow-up of 54.9 months. Average age at surgery was 79 years. Survivorship and radiologic outcome assessment for all patients was undertaken. Seven patients died, and 1 was unavailable for clinical review, leaving 21 shoulders in 20 patients available for clinical review. There were no revisions of the reverse prosthesis. Mean average pain was 2.19 of 100 (standard deviation [SD], 6.97). Mean American Shoulder and Elbow Surgeons score was 89.3 (SD, 13.65). Mean normalized Constant score was 88.03 (SD, 11.24). Grade 1 scapular notching was observed radiologically in 4 shoulders. A scapular spur was observed in 7 shoulders. Class 1 heterotopic ossification was seen in 4 shoulders. Nonprogressive lucent lines were seen in 2 shoulders. Nonprogressive radiolucency was observed around the superior screw in 3 shoulders. No loosening of the glenoid baseplate or of the humeral component was observed. There was 1 complication of an axillary nerve palsy, which spontaneously resolved by 12 months after surgery. RSA using the shoulder technique described in this series provides good clinical and radiologic outcomes in elderly patients with 3-part and 4-part fractures.

Treatment of proximal humeral fractures with reverse shoulder arthroplasty in elderly patients

Proximal humeral fractures in four or even only three parts, with metaphyseal hinge distances of <8mm, represent a serious and widely debated problem. Reduction is complex and plating is often instable, especially in elderly patients. Failures, sometimes involving necrosis of the head, are frequent. Hemiarthroplasty has long been used for 3- or 4-part complex fractures, even in young patients, although often with sub-optimal results, due to reabsorption of tuberosities. This complication has partly been overcome with reverse shoulder prostheses which, although more invasive than partial ones, may lead to less disappointing results, even in cases of reabsorption of tuberosities. We have data on a homogeneous series of patients treated with reverse shoulder arthroplasty for proximal fractures, with a maximum follow-up of 10years. The aim of this study was mainly to identify which cases can be selected for effective treatment and which technical aspects are best to adopt. There were 33 patients in this study, mean age 76.6years (range 54-85). Fractures were classified according to Neer. Surgery was undertaken on average 4.4days after trauma. The deltopectoral approach was used. Sutures were hooked over the major and lesser tubercles for later reduction and fixation after the prosthesis had been applied. This passage was sometimes not possible in cases of serious degeneration of the rotator cuff. One day after surgery, a shoulder brace providing an abducted angle of 15° was applied for 30days. Patients were re-assessed with DASH and Constant scores (CS), and the ratio between healthy and operated shoulders was calculated. Physical examination was followed by X-rays, mainly to evaluate and classify any infraglenoid scapular notching according to Nerot. Mean follow-up was 42.3months (range 10-121). According to the CS, mean pain was 12.6/15 (range 3-15/15), activities of daily living 16.3/20 (range 8-20/20), ROM 21.8 (range 8-32/40) and power 5.4/25 (range 2-12/25). Total mean CS was 56.4 (range 23-80/100). The mean DASH score was 49.7 (range 32-90). The ratio of the CS parameters between opposite and operated shoulders was on average 72.8% (range 28-90%). Long-term complications were eight cases of scapular notching (24.2%) of which four of grade 2 (12.1%) and four of grade 1 (12.1%). Total reverse prostheses are more invasive because they also compromise the glenoid surface of the scapula, but they do offer good stability, even in cases of damage to the rotator cuff. Reverse prostheses have great advantages as regards to ROM, allowing functional recovery, which is good in cases with re-insertion of tuberosities, and acceptable in cases when tuberosities are not re-inserted or resorbed. In our cases, the first 3 reverse prostheses lasted 10, 8.3 and 7.3years, and we believe that they will become increasingly long-lived, so that applying them in cases of complex fractures becomes more feasible. We prefer the deltopectoral approach because it can reduce and stabilize possible intra-operative diaphyseal fractures. Possible scapular notching must be foreseen when inserting the glenosphere. We had eight cases (24.2%), of which four were Nerot grade 1 and four were grade 2. Applying the Kirschner wire in an infero-anterior position allows the glenosphere to be lowered with a tilt of 10°. Reverse prostheses are suitable for 3- or 4-part complex proximal humeral fractures in patients over 65. Prolonged physiokinesitherapy is essential.

Hemiarthroplasty versus reverse shoulder arthroplasty: comparative study of functional and radiological outcomes in the treatment of acute proximal humerus fracture

To compare functional and radiographic results of reverse prosthesis versus hemiarthroplasty after complex displaced proximal humeral fractures in elderly patients when adequate ORIF cannot be achieved and prosthetic shoulder replacement is required. From 2008 to 2012, 67 patients were treated with hemiarthroplasty or reverse arthroplasty. We evaluated 53 cases with an average follow-up of 27.5months (range 12-64). Twenty-eight patients with an average age of 71.4years were treated with a hemiarthroplasty and 25 patients with an average age of 77.3years with a reverse prosthesis. All patients were assessed before and after surgery by Constant-ASES-DASH score, strength in abduction, ER1, ER2, and X-rays. In hemiarthroplasty group, we observed a mean Constant score of 42.3pt, ASES score 51.3pt, and DASH score 46.1, with an average strength of 1.3lb in abduction and of 3.7lb in ER1 and 1.8lb in ER2. In reverse arthroplasty group, we measured a mean Constant of 56.2pt, ASES 69.3pt, and DASH score 40.4, with an average strength of 4.3lb in abduction and of 3.3lb in ER1 and 3.2lb in ER2. Radiographically, it is interesting to observe that greater tuberosity healing rate was 37% in hemiarthroplasty group compared to 84% in reverse arthroplasty group. About complications, the highest rate was recorded in the hemiarthroplasty group. Reverse shoulder arthroplasty indication is steadily increasing in acute displaced proximal humeral fracture. Pain and articular movement results appear better than those with hemiarthroplasty. Our data are similar to the international literature.

Cuff tear arthropathy is best treated with a reverse total shoulder arthroplasty

Cuff tear arthropathy is the arthritic eroded collapse of the glenohumeral joint with progressive superior humeral migration in the setting of long-standing rotator cuff insufficiency. The ideal management of cuff tear arthropathy remains elusive. Current arthroplasty options include hemiarthroplasty or reverse shoulder arthroplasty. Proper clinical and radiographic evaluation is essential in decision making in order to optimize outcomes. Acromio-humeral distance (AHD), as measured on plain radiographs, as well as fatty degeneration of the rotator cuff muscles on MRI are reliable tools for decision making. AHD < 7mm correlates well with complete tear of the supraspinatus while AHD < 5mm indicates infraspinatus involvement with significant muscular atrophy. Hemiarthroplasty remains an option for providing pain relief; however, continued development of superior migration and glenoid erosion remains a concern. The conversion to reverse total shoulder arthroplasty after hemiarthroplasty can be difficult due to glenoid bone loss. Recent literature supports the use of reverse total shoulder arthroplasty over hemiarthroplasty for cuff tear arthropathy with significant differences in functional outcome. Here, we discuss the radiographic evaluation of cuff tear arthropathy and review the treatment options and why we advocate the use of the reverse prosthesis.

Treatment options for rotator cuff tear arthropathy

Rotator cuff tear arthropathy is characterized by massive and irreparable rotator cuff tears associated with shoulder arthritis. Symptoms include varying degrees of pain, loss of motion, and loss of function, or “pseudo-paralysis” alone. Nonoperative modalities are the treatment mainstay for mildly symptomatic patients, and there are viable medical and surgical treatment options for those whose symptoms are not severe enough to warrant shoulder arthroplasty. The trend toward using reverse total shoulder arthroplasty as the only treatment for this highly variable patient group does not allow a cautious approach to this disease nor recognize the high potential complication rate of the reverse prosthesis.

Indikation zur primären Frakturendoprothetik der Schulter

Although fractures of the proximal humerus are one of the most common osteoporotic fracture types, no generally accepted treatment algorithm exists in the current literature. For young patients with high functional demands and good rehabilitation potential, we recommend humeral head salvage therapy. If symptomatic humeral head necrosis occurs, the implantation of an anatomic endoprothesis is possible on a secondary basis. For patients with a biological age > 70 years suffering from a persisting defect of the rotator cuff along with a humeral head fracture or from a multiple fragment fracture of the humeral head, we increasingly prefer implantation of a reverse shoulder prosthesis due to good clinical results. However, because of technical aspects and a high complication rate, treatment using the reverse fracture prosthesis should be reserved for surgeons with expertise in this particular field. After analyzing the fracture- and patient-specific risk factors and performance expectations, the trauma surgeon can select the best individual therapy with the patient.

Reverse shoulder arthroplasty current concepts

The reverse shoulder arthroplasty (RSA) was introduced in 1987 for cuff tear arthropathy. Over time the prostheses have evolved and its indications have increased. RSA is a semi-constrained reverse ball and socket prosthesis with several key biomechanical advantages, including a fixed centre of rotation which allows the deltoid to function. In this review, the history, key principles, indications, surgical tips and complications are discussed. RSA can provide excellent results with significant improvements in pain and function but is a technically demanding procedure.

Metal-Backed Glenoid Prostheses

Despite the theoretical advantages of uncemented glenoid prostheses, clinical experience with uncemented metal-backed glenoids (MBG) has been disappointing to date. MBG design features have varied widely and, unlike the systematic ‘generational’ refinement of cemented glenoid prostheses, MBG design has been haphazard and unsystematic. The advent of reverse prostheses has rekindled interest in MBGs that allow ‘exchange’ from ‘anatomic’ to ‘reverse’ without baseplate removal. Recent designs, based on earlier prostheses, have proven excellent medium-term results, and there are now some specific indications for the use of MBGs. Further refinements are expected.

Increased-offset reverse shoulder arthroplasty for the treatment of failed post-traumatic humeral head replacement

Late complications after humeral head replacement (HHR) for comminuted proximal humeral fractures are common and may necessitate revision surgery. This study evaluated the outcome of revision surgery of failed post-traumatic HHR with a less medialized reverse shoulder prosthesis. Thirty-three patients with failed post-traumatic HHR due to rotator-cuff insufficiency and glenoid erosion, but with sufficient preservation of the glenoid bone stock to permit primary stability of an inverted glenoid implant, underwent revision using the Bayley-Walker reverse shoulder prosthesis (Stanmore Implants, Elstree, UK) and were monitored up for a mean of 31 months. Outcome measures included the Oxford Shoulder Score, subjective shoulder value, pain rating, active range of motion, and shoulder radiographs. The average postrevision Oxford Shoulder Score and subjective shoulder value improved from 50 ± 6 to 29 ± 11 and from 23 ± 19 to 51 ± 23, respectively (P < .001). Pain level decreased from 6.2 ± 2.1 to 1.4 ± 2.0 (P < .001). Active forward flexion increased from 34° ± 22° to 63° ± 30° and external rotation from 11° ± 14° to 20° ± 16°(P < .01). More patients were able to use their affected arm to reach a functional triangle consisting the mouth, opposite armpit, and ipsilateral buttock after revision (24% vs 73%; P < .001). Seven patients (21%) had postrevision complications. No glenoid loosening or scapular notching occurred. Revision of failed post-traumatic HHR with the Bayley-Walker shoulder offers reliable pain relief and improvement in shoulder function with a complication rate similar to other reverse prostheses. Nevertheless, revision shoulder arthroplasty remains challenging with a high rate of complications.

Multibody System of the Upper Limb Including a Reverse Shoulder Prosthesis

The reverse shoulder replacement, recommended for the treatment of several shoulder pathologies such as cuff tear arthropathy and fractures in elderly people, changes the biomechanics of the shoulder when compared to the normal anatomy. Although several musculoskeletal models of the upper limb have been presented to study the shoulder joint, only a few of them focus on the biomechanics of the reverse shoulder. This work presents a biomechanical model of the upper limb, including a reverse shoulder prosthesis, to evaluate the impact of the variation of the joint geometry and position on the biomechanical function of the shoulder. The biomechanical model of the reverse shoulder is based on a musculoskeletal model of the upper limb, which is modified to account for the properties of the DELTA® reverse prosthesis. Considering two biomechanical models, which simulate the anatomical and reverse shoulder joints, the changes in muscle lengths, muscle moment arms, and muscle and joint reaction forces are evaluated. The muscle force sharing problem is solved for motions of unloaded abduction in the coronal plane and unloaded anterior flexion in the sagittal plane, acquired using video-imaging, through the minimization of an objective function related to muscle metabolic energy consumption. After the replacement of the shoulder joint, significant changes in the length of the pectoralis major, latissimus dorsi, deltoid, teres major, teres minor, coracobrachialis, and biceps brachii muscles are observed for a reference position considered for the upper limb. The shortening of the teres major and teres minor is the most critical since they become unable to produce active force in this position. Substantial changes of muscle moment arms are also observed, which are consistent with the literature. As expected, there is a significant increase of the deltoid moment arms and more fibers are able to elevate the arm. The solutions to the muscle force sharing problem support the biomechanical advantages attributed to the reverse shoulder design and show an increase in activity from the deltoid, teres minor, and coracobrachialis muscles. The glenohumeral joint reaction forces estimated for the reverse shoulder are up to 15% lower than those in the normal shoulder anatomy. The data presented here complements previous publications, which, all together, allow researchers to build a biomechanical model of the upper limb including a reverse shoulder prosthesis.

Differenzialindikationen aktueller Endoprothesensysteme der Schulter

Modern shoulder prostheses adapt to the size, inclination, posterior offset and retrotorsion of the shoulder anatomy. Typical implants are cup prostheses for surface replacement, stemless prostheses that anchor in metaphyseal bone, anatomical prostheses using stems of different lengths, and last but not least reverse prostheses. The main reasons for implantation of shoulder prostheses are primary osteoarthritis, posttraumatic and rheumatoid arthritis, avascular necrosis, arthritis of instability and cuff defect arthropathy.Anatomical hemiprostheses should be used only if the glenoid is intact as total prostheses are functionally better as soon as the arthritis involves the glenoid. Conventional stems are cemented most of the time and cemented glenoids that are convex on the back are standard. Stemless prostheses were developed for posttraumatic indications and can often replace stemmed designs if the bone quality is good. Reverse prostheses were developed for the treatment of cuff tear arthropathies but if used as a revision implant complication rates rise and survival time is shorter.

Conversion of shoulder arthroplasty to reverse implants: clinical and radiological results using a modular system

Revision of a shoulder arthroplasty to a reverse arthroplasty is a highly demanding procedure. The aim of this study is to report the clinical results of hemi and total shoulder prosthesis revisions to reverse implants without removal of the humeral stem, using a modular shoulder replacement system (SMR Lima LTD). We retrospectively reviewed 26 patients who underwent an operation from 2004 to 2009. The patients were divided into two groups: in Group I, 18 patients underwent a revision of hemiarthroplasty implanted for fracture; in Group II, eight patients underwent a revision of anatomical total prosthesis. All patients were evaluated at a mean follow-up of 32.3 (±12.7) months using the Constant score rating scale and by range of motion evaluation, EQ-VAS, X-ray and CT scan. The Constant score of each patient was 47.88 (±5.88) after the revision. The EQ-VAS improved from 40 (±20) to 70 (±10). All patients improved in terms of range of motion. The radiographs and CT scans obtained after revision showed good integration and no signs of loosening of the implant. The mean time of surgery was recorded as 62' (±8'), with a maximum blood loss of less than 300 ml in all cases. Our study demonstrates that using a full modular system at the time of the first implant allows avoidance of the step to remove the humeral stem and metal back in cases of shoulder prosthesis revision to a reverse prosthesis, resulting in a short operative time, few intraoperative complications and a satisfactory clinical outcome at medium-term follow-up.

Duocentric® reversed shoulder prosthesis and Personal Fit® templates: innovative strategies to optimize prosthesis positioning and prevent scapular notching

We describe our experience with a new system of patient-specific template called Personal Fit(®), which is unique in shoulder surgery and used in combination with Duocentric(®) prosthesis. The reverse prosthesis's concept is the invention of Paul Grammont, developed with Grammont's team of Dijon University as from 1981, which led to the first reversed total shoulder prosthesis called Trumpet in 1985. The Duocentric(®) prosthesis developed in 2001 is the third-generation prosthesis, coming from the Trumpet and the second-generation prosthesis Delta(®) (DePuy). This prosthesis provides a novel solution to the notching problem with an inferior overhang integrated onto the glenoid baseplate. Personal Fit(®) system is based on reconstructing the shoulder joint bones in three dimensions using CT scan data, placing a landmark on the scapula and locating points on the glenoid and humerus. That will be used as a reference for the patient-specific templates. We study the glenoid position planned with Personal Fit(®) software relative to native glenoid position in 30 cases. On average, the difference between the planned retroversion (or anteversion in one case) and native retroversion was 8.6°.

Trabecular metal fixation: A new chemical concoction

Secure fixation of metal prosthesis to bone has always been a challenge. Bone cement has been a great help in achieving this goal, but there can be complications, such as cement loosening and breakage. Therefore, it is reasonable to consider types of coating on a metal surface that will allow bone ongrowth or a type of metal (tantalum) that will allow bone ingrowth as it is a porous scaffold. Furthermore the stiffness of tantalum is between subchondral bone and cortical bone, which also promotes ingrowth. This metal can be overlayed on other metal or used by itself as an implant. In primary osteoarthritis of the glenohumeral joint, it can be used for both the humeral and glenoid components allowing for a cementless prosthesis. Thus the complications from the use of bone cement can be avoided. Tantalum can also be used with a reverse prosthesis. It is especially important for the glenoid baseplate component as it will take away stress from the screws that are used for early fixation. Tantalum is also useful in the revision setting where there is bone loss and secure fixation is needed to the remaining bone. Tantalum has been used in the shoulder for more than 5 years successfully and longer in the hip and knee.

Resurfacing arthroplasty for contained cuff tear arthropathy

Cuff tear arthropathy has been among the most difficult management problems faced by the shoulder surgeon. Ability to restore motion and alleviate pain has been challenging and has led Neer to coin the term “limited goals” when discussing outcomes of surgery in this group of patients. Over the past 15 years evidence of improved outcomes has been demonstrated with use of the reverse total shoulder prosthetic implant. However, with longer follow-up, a high rate of complication has also been demonstrated with these implants. Furthermore, their utilization significantly affects the local anatomy and takes away a significant amount of native bone stock. In addition, these implants cost in many cases, three to four times the price of a more conventional prosthesis. Not all patients with cuff tear arthropathy have the same degree of pathology. Many patients retain a “captured” humeral head underneath the coracoacromial arch without demonstrating anterior/superior escape and can be managed with a more conventional prosthesis. Indiscriminate use of the reverse prosthesis on all patients with cuff tear arthropathy presents a relatively reckless and irresponsible use of resources while limiting the ability to perform revision in the face of implant failure. Use of a CTA humeral head implant or cup resurfacing in a valgus position provides a seamless covering over the humeral head, which allows smooth seating within a “socket” formed by the coracoacromial arch. Such patients function quite well with excellent pain relief. Should revision ultimately be needed at a later date, a reverse arthroplasty can easily be performed without damage to the existing architecture. Reverse arthroplasty should be reserved for the physiologically older patient with limited demands and anterior/superior escape of the humeral head. Valgus resurfacing should be the procedure of choice in younger, more active patients whose humeral head remains captured within the coracoacromial arch.

Single-stage revision for peri-prosthetic shoulder infection

There have been only a few small studies of patients with an infected shoulder replacement treated with a single-stage exchange procedure. We retrospectively reviewed 35 patients (19 men and 16 women) with a peri-prosthetic infection of the shoulder who were treated in this way. A total of 26 were available for clinical examination; three had died, two were lost to follow-up and four patients had undergone revision surgery. The mean follow-up time was 4.7 years (1.1 to 13.25), with an infection-free survival of 94%. The organisms most commonly isolated intra-operatively were Staphylococcus epidermidis and Propionibacterium acnes; two patients developed a recurrent infection. Three different types of prosthesis were used: a hemiarthroplasty, a hemiarthroplasty with a bipolar head and reverse prosthesis. The mean Constant-Murley score at final follow-up was 43.3 (14 to 90) for patients with a hemiarthroplasty, 56 (40 to 88) for those with a hemiarthroplasty with a bipolar head and 61 (7 to 90) for those with a reverse prosthesis. The mean hospital stay was 10.6 days (5 to 29). Single-stage exchange is a successful and practical treatment for patients with peri-prosthetic infection of the shoulder.

Activities of daily living with reverse prostheses: importance of scapular compensation for functional mobility of the shoulder

The nonanatomical design of reverse shoulder prostheses induce medial displacement of the center of rotation, impingements and may reduce the mobility of the shoulder. The aim of this study is to test the hypothesis that during activities of daily living functional mobility of the shoulder can be restored by scapular compensation. A numerical 3-dimensional model was developed to reproduce the movement of the scapula and humerus, during 4 activities of daily living measured experimentally. This hypothesis was tested in 4 configurations of the aequalis reverse prosthesis (standard 36-mm glenosphere, 42-mm glenosphere, lateralized 36-mm glenosphere, lateralized Bony Increased-Offset ReverseShoulder Arthroplasty [BIO-RSA]), which were implanted in the virtual model. Allimpingement positions were evaluated, as the required scapular compensation to avoid impingements. With the 36-mm glenosphere, impingements occurred only for rest of hand to back-pocket positions. The 42-mm partly improved the mobility. The 2 lateralized glenospheres were free of impingement. When impingements occurred, the scapular compensation was less than 10°. Most reverse prostheses impingements reported in clinical and biomechanical studies can be avoided, either by scapular compensation or by a glenosphere lateralization. After reverse shoulder arthroplasty, a fraction of the mobility of the gleno-humeral is transferred to the scapulo-thoracic joint.