The effect of glenosphere diameter in reverse shoulder arthroplasty on muscle force, joint load, and range of motion

Development and Application of a Novel Metric to Characterize Comprehensive Range of Motion of Reverse Total Shoulder Arthroplasty

Active range of motion (ROM) of reverse total shoulder arthroplasty (rTSA) can be limited by bony impingement, muscle inability, and joint instability. The aim of this study was to develop a novel metric representative of comprehensive ROM of rTSA, which is evaluated in the context of all three factors. It was hypothesized that the metric, termed global circumduction ROM (GC-ROM), would capture differences resulting from directional changes in rTSA design parameters known to increase ROM. GC-ROM was calculated for a set of 18 rTSA configurations with humeral polyethylene cup depths of 6 and 8.1 mm, glenosphere lateralization (GLat) distances of 0, 5, and 10 mm, and neck-shaft angles (NSA) of 135°, 145°, and 155°. For any implant configuration, arm positions were defined by internal/external (IE) rotation angle and two spherical coordinates representing the elevation plane angle and elevation angle. At each IE rotation angle, incremental positions with variable elevation plane and elevation angles were checked for feasibility based on impingement, muscle ability, and risk of instability. Coordinates of feasible positions were mapped to unit spheres and connected to form regions, of which the surface area was calculated to represent allowable circumduction ROM. ROMs were averaged across all IE rotation angles to produce a single metric, GC-ROM. The results showed that decreasing cup depth and increasing GLat and NSA increased GC-ROM. In conclusion, a novel metric to characterize comprehensive ROM, evaluated based on several ROM-limiting factors, was developed as a performance metric through which rTSA designs can be compared. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 38:880-887, 2020.

The biomechanics of subscapularis repair in reverse shoulder arthroplasty: The effect of lateralization and insertion site

Functional outcomes of subscapularis (SSc) repair following reverse shoulder arthroplasty (RSA) remains controversial. SSc repair in combination with glenosphere lateralization was reported to yield worse clinical outcomes compared with the non-lateralized glenosphere. The aim of this biomechanical study was to investigate how glenosphere lateralization and different re-insertion sites can affect the biomechanics of the SSc after RSA. Nine patient-specific RSA shoulder models were created from patients' computed tomography scans. Moment arms and SSc length were calculated for abduction, forward flexion, and internal rotation in 20° and 90° abduction for three configurations of glenosphere lateralization (standard/+0, +5, and +10 mm) and three SSc repair sites (native, superior, and inferior) and compared with the native shoulder. When compared with the native shoulder, RSA resulted in large adducting SSc moment arms that were antagonistic to the deltoid. Glenosphere lateralization had no effect on SSc moment arms in any motion. However, lateralization increased SSc tension beyond its anatomic length for +5 and +10 mm of lateralization when attached to its native insertion. A superior SSc repair site created the least adductive moment arm as well as the least amount of SSc lengthening. Increased glenosphere lateralization showed a significant increase in the SSc length, which in combination with its adductive moment arm can be antagonistic to deltoid function. However, a superior SSc repair site may help reduce the adductive SSc moment arm and allow for reduced tension on the repair as its length in that location is less than that of the native SSc. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 38:888-894, 2020.

Effect of humeral stem and glenosphere designs on range of motion and muscle length in reverse shoulder arthroplasty

PURPOSE

To determine how different combinations of humeral stem and glenosphere designs for reverse shoulder arthroplasty (RSA) influence range of motion (ROM) and muscle elongation.

METHODS

A computed tomography scan of a non-pathologic shoulder was used to simulate all shoulder motions, and thereby compare the ROM and rotator cuff muscle lengths of the native shoulder versus 30 combinations of humeral components (1 inlay straight stem with 155° inclination and five onlay curved stems with 135°, 145° or 155° inclinations, using concentric, medialized or lateralized trays) and glenospheres (standard, large, lateralized, inferior eccentric and bony increased-offset (BIO-RSA)).

RESULTS

Only five of the 30 combinations restored ≥ 50% of the native ROM in all directions: the 145° onlay stem (concentric tray) combined with lateralized or inferior eccentric glenospheres and the 145° stem (lateralized tray) combined with either a large, lateralized or inferior eccentric glenosphere. Lengthening of the supraspinatus and infraspinatus, observed for all configurations, was greatest using onlay stems (7-30%) and BIO-RSA glenospheres (13-31%). Subscapularis lengthening was observed for onlay stems combined with BIO-RSA glenospheres (5-9%), while excessive subscapularis shortening was observed for the inlay stem combined with all glenospheres except the BIO-RSA design (> 15%).

CONCLUSIONS

The authors suggest implanting 145° onlay stems, with concentric or lateralized trays, together with lateralized or inferior eccentric glenospheres.

Bone grafting in primary and revision reverse total shoulder arthroplasty for the management of glenoid bone loss: A systematic review

Purpose

We performed a systematic review of the studies including clinical/functional outcomes and complications of bone grafting for glenoid defects in reverse total shoulder arthroplasty (RTSA).

Methods

The PubMed and Cochrane databases were searched for relevant papers.

Results

Thirteen articles were included. The mean clinical/functional subjective scores significantly improved postoperatively. The implant revision rate for primary and revision RTSA was 3.1% and 21.1% respectively. The reoperation rate was 3.5% and 24.4% respectively.

Conclusions

There was moderate evidence that bone grafting is effective for glenoid defects in primary RTSA. Further high-quality research is required about revision RTSA for moderate-to-severe glenoid defects.

Factors associated with internal rotation outcomes after reverse shoulder arthroplasty

BACKGROUND

Reverse shoulder arthroplasty (RSA) was introduced in 1985 by Grammont for patients with gleno-humeral osteoarthritis and severe rotator cuff damage. Internal rotation (IR) is limited in some patients after RSA. The objective of this study was to identify pre- and intra-operative factors associated with good IR outcomes 6 months after RSA.

HYPOTHESIS

The condition of the residual cuff (usually the sub-scapularis and teres minor) and inferior glenosphere overhang are the main factors associated with IR outcomes after RSA.

MATERIAL AND METHOD

A total of 36 patients who underwent RSA between 2 November 2015 and 10 January 2017 were enrolled prospectively. The inclusion criterion was massive rotator cuff tear with or without osteoarthritis and gleno-humeral osteoarthritis with asymmetrical glenoid wear. The pre-operative work-up included determination of the Constant score, Subjective Shoulder Value (SSV), and passive and active motion ranges; standard radiographs; and computed tomography. The same clinical and radiological parameters were recorded in all patients during a visit 6 months after surgery.

RESULTS

After surgery, all motion ranges were improved except IR with the elbow by the side (IR1, ability to place the hand on the back). IR1 to or above L3 was significantly associated with a lower body mass index (p=0.04), good passive IR before surgery (p=0.056), a smaller pre-operative glenoid inclination angle, and greater glenosphere overhang (p=0.03). Neither the condition of the sub-scapularis nor sub-scapularis repair were significantly associated with post-operative IR1. IR1 was significantly more limited in patients whose teres minor was normal.

CONCLUSION

Satisfactory active IR1 correlated with good passive IR1. IR1 was better in thin individuals who had non-concentric gleno-humeral osteoarthritis. Inferior glenosphere overhang of 6mm or more was associated with a greater range of IR.

LEVEL OF EVIDENCE

IV, prospective observational cohort study.

Lateralization in reverse shoulder arthroplasty: a descriptive analysis of different implants in current practice

INTRODUCTION

Since its first description, the concept of reverse shoulder arthroplasty (RSA) has evolved. The term lateralization remains unclear and is used to describe implants that lateralize on the glenoid side, the humeral side, or both. The objective of this study was to provide a clear definition of lateralization and to measure the lateralization achieved by the most commonly used implants.

MATERIALS AND METHODS

Twenty-eight different configurations with 22 different implants were analyzed. Glenoid, humeral, and global lateralization was measured on digitized templates. Implant lateralization was normalized to the lateral offset of the Delta III. Each implant was defined as a combination of one of two glenoid categories (medialized glenoid (MG), lateralized glenoid (LG), and one of four humeral categories (medialized humerus (MH), minimally lateralized humerus (LH), lateralized humerus (LH+). In addition, implants were separated in categories of 5-mm increments for global offset (medialized RSA (M-RSA), minimally lateralized RSA (ML-RSA), lateralized RSA (L-RSA), highly lateralized RSA (HL-RSA), and very highly lateralized RSA (VHL-RSA).

RESULTS

The global lateral offset of the Delta III was 13.1 mm; global lateral offset of all designs in this study varied between 13.1 and 35.8 mm. Regarding their global lateral offset, five implants are M-RSA (lateral offset < 18.1 mm), five ML-RSA (18.1-23.1 mm), seven L-RSA (23.1-28.1 mm), six HL-RSA (28.1-33.1 mm), and one VHL-RSA (33.1-38.1 mm).

CONCLUSION

There is high variability in the amount of lateralization provided by the majority of RSAs currently available. This descriptive analysis can help surgeons understand the features of implants in the market based on their lateralization in order to adapt the surgical technique depending on the expected lateral offset of the design being implanted.

Effect of humeral tray placement on impingement-free range of motion and muscle moment arms in reverse shoulder arthroplasty

BACKGROUND

It has been suggested that onlay humeral tray placement in reverse shoulder arthroplasty can affect impingement and muscle functionality. This study investigates biomechanical changes to the reversed shoulder using a variety of tray positional configurations.

METHODS

The reconstructed scapula and humerus from 12 CT scans were used to customise a 3D biomechanical model of the shoulder. Each model underwent virtual RSA surgery using a commercially available prosthesis that was reconstructed from an explant. 17 tray positions were tested: the default location with no offset and 16 offset locations (2.5 and 5 mm radial offsets over 45° circumferential intervals). Impingement and muscle moment arms were measured during three standardised activities, and impingement was measured during an activity of daily living.

FINDINGS

Offset direction was found to have an effect (P < 0.05) on extra-articular impingement and muscle moment arms for all activities; whereas, offset distance did not (P > 0.05). Overall, impingement-free range of motion was maximised using a posterolateral tray offset and muscle moment arms were maximised using a medial tray offset. An antagonistic relationship between changes to impingement and muscle moment arms due to tray placement was identified and, consequently, the simultaneous maximisation of both outcome measures was not possible.

INTERPRETATION

The functional outcomes of reverse shoulder arthroplasty can be improved by altering onlay humeral tray placement. Due to the antagonistic relationship between the impingement and muscle moment arms, placement of the tray should be guided by patient-specific characteristics.

Reverse shoulder arthroplasty in recent proximal humerus fractures

Reverse shoulder arthroplasty is now the standard treatment for displaced, three- or four-part, proximal humeral fractures in patients older than 70 years. Inadequate tuberosity repair or inappropriate humeral stem position are associated with poorer outcomes, notably regarding rotation and stability. Strict operative technique during prosthesis implantation is therefore crucial to obtain reliable and reproducible outcomes. The objective of this article is to describe the surgical technique for reverse shoulder arthroplasty used to treat recent proximal humerus fractures.

Instability in Reverse Total Shoulder Arthroplasty

Recently, indications for reverse total shoulder arthroplasty have expanded to include glenohumeral arthritis, rotator cuff arthropathy, irreparable rotator cuff tears, complex proximal humerus fractures, sequelae of trauma, and failed shoulder prostheses. Dislocation is a common complication, with rates ranging from 1.5% to 31%. The literature pertaining to management of instability in reverse total shoulder arthroplasty is scanty. Assessment of the patient and biomechanical and surgical factors is critical in determining the best course of treatment. Future studies involving patient selection, prosthetic design, surgical technique, and biomechanics may help reduce the rate of instability.

Outcomes of reverse shoulder arthroplasty in small- and large-stature patients

BACKGROUND

As the worldwide use of reverse shoulder arthroplasty (RSA) increases, a range of implant sizes may be required to match regional and ethnic variation in patients' stature. Size-mismatched implants may possibly result in poorer surgical outcomes. The purpose of this study was to compare the outcomes of primary RSA in patients at the extreme ends of the growth curve with those in average-stature patients in the United States.

METHODS

A multicenter shoulder arthroplasty database was retrospectively reviewed to identify all primary RSAs using a single implant system with a minimum 2-year follow-up. Small patients were defined as the height of <155 cm, tall as >183 cm, and average as 162-178 cm. Active range of motion (ROM), visual analog scale pain score, and patient-reported outcomes (PROs) were compared among the 3 groups.

RESULTS

The study included 552 shoulders (130 small, 384 average, and 38 tall stature). Preoperatively, the average height group had significantly less ROM than the other groups, but there were no significant differences in postoperative ROM. This resulted in poorer improvements in postoperative ROM in the small and tall groups, with the small-stature patients having significantly less ROM improvement compared with average-stature patients. However, these differences did not result in poorer PROs between groups.

DISCUSSION

Small- and large-stature patients showed inferior improvements in ROM after RSA compared with average-stature patients. Our results suggest that current implants optimize ROM gains for average-stature patients and improve PROs independently of patient stature at a minimum 2-year follow-up.

The effect of humeral polyethylene insert constraint on reverse shoulder arthroplasty biomechanics

BACKGROUND

There is little information on the effects of altering reverse shoulder arthroplasty (RSA) polyethylene constraint on joint load, load angle and deltoid force. The present biomechanical study aimed to investigate the effects of changing RSA polyethylene constraint on joint load, load angle, deltoid force and range of motion.

METHODS

A custom RSA implant capable of measuring forces across the joint with varying polyethylene constraint was tested in six cadaveric shoulders. Standard-, low- and high-constraint (retentive) polyethylene liners were tested, and joint kinematics, loads and muscle forces were recorded.

RESULTS

When polyethylene constraint was altered, joint load and load angle during active abduction were not affected significantly (p > 0.19). Additionally, the force required by the deltoid for active abduction was not affected significantly by cup constraint (p = 0.144). Interestingly, active abduction range of motion was also not affected significantly by changes in cup constraint (p > 0.45).

CONCLUSIONS

Altering polyethylene cup constraint in RSA to enhance stability does not significantly alter resultant joint loads and deltoid forces. Surprisingly, terminal abduction range of motion was also not significantly different with varying cup constraint, indicating that terminal impingement may be tuberosity related rather than polyethylene.

Neer Award 2017: wear rates of 32-mm and 40-mm glenospheres in a reverse total shoulder arthroplasty wear simulation model

BACKGROUND

Larger glenosphere diameters have been used recently to increase prosthesis stability and impingement-free range of motion in reverse total shoulder arthroplasty. The goal of this study was to evaluate the rate of polyethylene wear for 32-mm and 40-mm glenospheres.

METHODS

Glenospheres (32 mm and 40 mm, n = 6/group) and conventional polyethylene humeral liners underwent a 5-million cycle (MC) wear simulation protocol. Abduction-adduction and flexion-extension motion profiles were alternated every 250,000 cycles. At each interval, mass loss was determined and converted to volume loss and wear rate. At 0, 2.5 MC, and 5 MC, liners were imaged using micro-computed tomography to determine surface deviation. White light interferometry was performed on liners and glenospheres at 0 and 5 MC to quantify surface roughness. Wear particle morphology was characterized by environmental scanning electron microscopy.

RESULTS

Total volume loss was significantly higher in 40-mm liners from 1.5 MC onward (P < .05). Overall, volumetric wear rate was significantly higher in 40-mm liners compared with 32-mm glenospheres (81.7 ± 23.9 mm³/MC vs. 68.0 ± 18.9 mm³/MC; P < .001). However, micro-computed tomography surface deviation results demonstrated increased linear penetration on 32-mm glenospheres compared with 40-mm glenospheres (0.36 ± 0.03 µm vs. 0.28 ± 0.01 µm; P = .002). Surface roughness measurements showed no difference for liners; however, increased roughness was noted for 40-mm glenospheres at 5 MC compared with 32 mm (P < .05).

CONCLUSION

Larger glenospheres underwent significantly greater polyethylene volume loss and volumetric wear rates, whereas smaller glenospheres underwent greater polyethylene surface deviations. The enhanced stability provided by larger glenospheres must be weighed against the potential for increased polyethylene wear.

Does Humeral Component Lateralization in Reverse Shoulder Arthroplasty Affect Rotator Cuff Torque? Evaluation in a Cadaver Model

BACKGROUND

Humeral component lateralization in reverse total shoulder arthroplasty (RTSA) may improve the biomechanical advantage of the rotator cuff, which could improve the torque generated by the rotator cuff and increase internal and external rotation of the shoulder.

PURPOSE

The purpose of this in vitro biomechanical study was to evaluate the effect of humeral component lateralization (or lateral offset) on the torque of the anterior and posterior rotator cuff.

METHODS

Eight fresh-frozen cadaveric shoulders from eight separate donors (74 ± 8 years; six males, two females) were tested using an in vitro simulator. All shoulders were prescreened for soft tissue deficit and/or deformity before testing. A custom RTSA prosthesis was implanted that allowed five levels of humeral component lateralization (15, 20, 25, 30, 35 mm), which avoided restrictions imposed by commercially available designs. The torques exerted by the anterior and posterior rotator cuff were measured three times and then averaged for varying humeral lateralization, abduction angle (0°, 45°, 90°), and internal and external rotation (-60°, -30°, 0°, 30°, 60°). A three-way repeated measures ANOVA (abduction angle, humeral lateralization, internal rotation and external rotation angles) with a significance level of α = 0.05 was used for statistical analysis.

RESULTS

Humeral lateralization only affected posterior rotator cuff torque at 0° abduction, where increasing humeral lateralization from 15 to 35 mm at 60° internal rotation decreased external rotation torque by 1.6 ± 0.4 Nm (95% CI, -0.07 -1.56 Nm; p = 0.06) from 4.0 ± 0.3 Nm to 2.4 ± 0.6 Nm, respectively, but at 60° external rotation increased external rotation torque by 2.2 ± 0.5 Nm (95% CI, -4.2 to -0.2 Nm; p = 0.029) from 6.2 ± 0.5 Nm to 8.3 ± 0.5 Nm, respectively. Anterior cuff torque was affected by humeral lateralization in more arm positions than the posterior cuff, where increasing humeral lateralization from 15 to 35 mm when at 60° internal rotation increased internal rotation torque at 0°, 45°, and 90° abduction by 3.2 ± 0.5 Nm (95% CI, 1.1-5.2 Nm; p = 0.004) from 6.6 ± 0.6 Nm to 9.7 ± 0.6 Nm, 4.0 ± 0.3 Nm (95% CI, 2.8-5.0 Nm; p < 0.001) from 1.7 ± 1.0 Nm to 5.6 ± 0.9 Nm, and 2.2 ± 0.2 Nm (95% CI, 1.4-2.9 Nm; p < 0.001) from 0.6 ± 0.6 Nm to 2.8 ± 0.6 Nm, respectively. In neutral internal and external rotation, increasing humeral lateral offset from 15 to 35 mm increased the internal rotation torque at 45˚ and 90˚ abduction by 1.5 ± 0.3 Nm (95% CI, 0.2-2.7 Nm; p = 0.02) and 1.3 ± 0.2 Nm (95% CI, 0.4-2.3 Nm; p < 0.001), respectively.

CONCLUSIONS

Humeral component lateralization improves rotator cuff torque.

CLINICAL RELEVANCE

The results of this preliminary in vitro cadaveric study suggest that the lateral offset of the RTSA humeral component plays an important role in the torque generated by the anterior and posterior rotator cuff. However, further studies are needed before clinical application of these results. Increasing humeral offset may have adverse effects, such as the increased risk of implant modularity, increasing tension of the cuff and soft tissues, increased costs often associated with design modifications, and other possible as yet unforeseen negative consequences.

The influence of humeral neck shaft angle and glenoid lateralization on range of motion in reverse shoulder arthroplasty

BACKGROUND

Recent developments in reverse shoulder arthroplasty (RSA) have focused on changes in several design-related parameters, including humeral component design, to allow for easier convertibility. Alterations in humeral inclination and offset on shoulder kinematics may have a relevant influence on postoperative outcome. This study used a virtual computer simulation to evaluate the influence of humeral neck shaft angle and glenoid lateralization on range of motion in onlay design RSA.

METHODS

Three-dimensional RSA computer templating was created from computed tomography (CT) scans in 20 patients undergoing primary total shoulder arthroplasty for concentric osteoarthritis (Walch A1). Two concurrent factors were tested for impingement-free range of motion: humeral inclination (135° vs. 145°) and glenoid lateralization (0 mm vs. 5 mm).

RESULTS

Decreasing the humeral neck shaft angle demonstrated a significant increase in impingement-free range of motion. Compared to the 145° configuration, extension was increased by 42.3° (-8.5° to 73.5°), adduction by 15° (10° to 23°), and external rotation with the arm at side by 15.1° (8.5° to 26.5°); however, abduction was decreased by 6.5° (-1° to 12.5°). Glenoid lateralization led to comparable results, but an additional increase in abduction of 7.6° (-1° to 16.5°) and forward flexion of 26.6° (6.5° to 62°) was observed.

CONCLUSION

Lower humeral neck shaft angle and glenoid lateralization are effective for improvement in range of motion after RSA. The use of the 135° model with 5 mm of glenoid lateralization provided the best results in impingement-free range of motion, except for abduction.

A Critical Review on Prosthetic Features Available for Reversed Total Shoulder Arthroplasty

Reversed total shoulder arthroplasty is a popular treatment in rotator cuff arthropathy and in displaced proximal humeral fractures in elderly. In 2016, 29 models of commercially available designs express this popularity. This study describes all the different design parameters available on the market. Prosthetic differences are found for the baseplate, glenosphere, polyethylene, and humeral component and these differences need to be weighed out carefully for each patient knowing that a gain in one mechanical parameter can balance the loss of another. Patient specific implants may help in the future.

Influence of glenosphere size on the development of scapular notching: a prospective randomized study

HYPOTHESIS

The objective of the study was to evaluate the development of scapular notching in reverse shoulder arthroplasty by comparing larger glenospheres (42 mm) with smaller glenospheres (38 mm).

METHODS

This was a prospective randomized study of 81 patients who had undergone reverse shoulder arthroplasty with a 2-year follow-up. Patients were randomized to receive either a 42-mm glenosphere (38 patients) or a 38-mm glenosphere (43 patients). Scapular notching development was assessed with an anteroposterior radiograph at the end of the follow-up. Functional outcome was assessed with the Constant score before surgery and at the end of follow-up. An independent blinded observer carried out radiologic and clinical assessments.

RESULTS

Scapular notching was present in 48.8% of the patients receiving a 38-mm glenosphere and in 12.1% of the patients receiving one of 42 mm, with significant differences between both (P < .001). No significant differences were noted between the 2 glenosphere size groups in terms of the total Constant score. Patients with a 42-mm glenosphere had a mean glenoid-glenosphere overhang of 6.1 mm, whereas patients with a 38-mm glenosphere had one of 4.2 mm, with significant differences between them (P < .001). No significant differences in the total Constant score were found between the patients whether they had scapular notching or not.

CONCLUSION

Bigger glenospheres (42 mm) significantly reduce development of scapular notching compared with smaller glenospheres (38 mm). Glenosphere size has no significant influence on functional outcomes measured with the Constant score.

The rotator cuff muscles are antagonists after reverse total shoulder arthroplasty

INTRODUCTION

There is disagreement regarding whether, when possible, the rotator cuff should be repaired in conjunction with reverse total shoulder arthroplasty (RTSA). Therefore, we investigated the effects of rotator cuff repair in RTSA models with varying magnitudes of humeral and glenosphere lateralization.

METHODS

Six fresh frozen cadaveric shoulders were tested on a validated in vitro muscle-driven motion simulator. Each specimen was implanted with a custom adjustable, load-sensing RTSA after creation of a simulated rotator cuff tear. The effects of 4 RTSA configurations (0 and 10 mm of humeral lateralization and glenosphere lateralization) on deltoid force and joint load during abduction with and without rotator cuff repair were assessed.

RESULTS

Deltoid force was significantly affected by increasing humeral lateralization (-2.5% ± 1.7% body weight [BW], P = .016) and glenosphere lateralization (+7.7% ± 5.6% BW, P = .016). Rotator cuff repair interacted with humeral and glenosphere lateralization (P = .005), such that with no humeral lateralization, glenosphere lateralization increased deltoid force without cuff repair (8.1% ± 5.1% BW, P = .012). This effect was increased with cuff repair (12.8% ± 7.8% BW, P = .010), but the addition of humeral lateralization mitigated this effect. Rotator cuff repair increased joint load (+11.9% ± 5.1% BW, P = .002), as did glenosphere lateralization (+13.3% ± 3.7% BW, P < .001). These interacted, such that increasing glenosphere lateralization markedly increased the negative effects of cuff repair (9.4% ± 3.2% BW [P = .001] vs. 14.4% ± 7.4% BW [P = .005]).

CONCLUSION

Rotator cuff repair, especially in conjunction with glenosphere lateralization, produces an antagonistic effect that increases deltoid and joint loading. The long-term effects of this remain unknown; however, combining these factors may prove undesirable. Humeral lateralization improves joint compression through deltoid wrapping and increases the deltoid's mechanical advantage, and therefore, could be used in place of rotator cuff repair, thus avoiding its complications.

Influence of Glenosphere Design on Outcomes and Complications of Reverse Arthroplasty: A Systematic Review

Background

Different implant designs are utilized in reverse shoulder arthroplasty. The purpose of this systematic review was to evaluate the results of reverse shoulder arthroplasty using a traditional (Grammont) prosthesis and a lateralized prosthesis for the treatment of cuff tear arthropathy and massive irreparable rotator cuff tears.

Methods

A systematic review of the literature was performed via a search of two electronic databases. Two reviewers evaluated the quality of methodology and retrieved data from each included study. In cases where the outcomes data were similar between studies, the data were pooled using frequency-weighted mean values to generate summary outcomes.

Results

Thirteen studies met the inclusion and exclusion criteria. Demographics were similar between treatment groups. The frequency-weighted mean active external rotation was 24° in the traditional group and 46° in the lateralized group (p = 0.0001). Scapular notching was noted in 44.9% of patients in the traditional group compared to 5.4% of patients in the lateralized group (p = 0.0001). The rate of clinically significant glenoid loosening was 1.8% in the traditional group and 8.8% in the lateralized group (p = 0.003).

Conclusions

Both the traditional Grammont and the lateralized offset reverse arthroplasty designs can improve pain and function in patients with diagnoses of cuff tear arthropathy and irreparable rotator cuff tear. While a lateralized design can result in increased active external rotation and decreased rates of scapular notching, there may be a higher rate of glenoid baseplate loosening.

Wear simulation strategies for reverse shoulder arthroplasty implants

Reverse total shoulder arthroplasty is a clinically accepted surgical procedure; however, its long-term wear performance is not known. The purpose of this work is to review wear simulator testing of reverse total shoulder arthroplasty, to develop a wear simulator protocol for reverse total shoulder arthroplasty, and to test it by performing a pilot study. The review of wear simulator testing in the literature revealed considerable variation in protocols. A combination of our own cadaveric testing and those of other research groups helped in determining the magnitude and direction of joint loading for the development of the present protocol. A MATCO orbital-bearing simulator was adapted using custom fixtures to simulate a circumduction motion of the shoulder under mildly adverse conditions, and a pilot study gave wear rates within the wide range found in the literature. Arguments were presented in support of the currently developed protocol, but it was also suggested that, rather than rely on one protocol, a series of simulator wear protocols should be developed to fully test the implant wear performance in reverse total shoulder arthroplasty.

Impact of glenosphere size on clinical outcomes after reverse total shoulder arthroplasty: an analysis of 297 shoulders

BACKGROUND

Although increasing glenosphere diameter has been found to increase passive range of motion (ROM) in simulated models of reverse total shoulder arthroplasty (rTSA), the clinical implications of glenosphere size are unclear. The purpose of our study was to determine the impact that glenosphere size had on short-term and midterm clinical outcomes, specifically American Shoulder and Elbow Surgeons (ASES) scores and ROM.

METHODS

Prospectively collected data comparing patients receiving an rTSA with either a 38- or 42-mm glenosphere after a minimum 2-year follow-up were obtained. Clinical outcome measures included active ROM and ASES scores.

RESULTS

We included 297 primary rTSAs in 290 patients: a 38-mm-diameter glenosphere was used in 160 shoulders and a 42-mm-diameter glenosphere in 137 shoulders. Of the patients, 191 were women and 99 were men. The mean age at the time of surgery was 72 years (range, 50-88 years). At last follow-up, improvements in active forward elevation (aFE) and active external rotation (aER) were significantly greater in shoulders with a 42-mm glenosphere (+59° vs +44° for aFE and +24° vs +18° for aER). Female shoulders treated with a 42-mm glenosphere had significantly greater improvements in aFE, aER, and functional scores. Male shoulders treated with a 38-mm glenosphere had significantly greater improvements in pain levels and ASES scores but less improvement in aFE. Complications and rates of scapular notching were similar between glenosphere sizes.

CONCLUSIONS

Patients treated with 42-mm glenospheres had greater improvements in aFE and aER when compared with 38-mm glenospheres. Our results suggest a potential association among gender, glenosphere size, and improvement in clinical outcome scores.

LEVEL OF EVIDENCE

Level III; Retrospective Cohort Design; Treatment Study.

Effect of size and dimensional tolerance of reverse total shoulder arthroplasty on wear: An in-silico study

Although huge research efforts have been devoted to wear analysis of ultra-high molecular weight polyethylene (UHMWPE) in hip and knee implants, shoulder prostheses have been studied only marginally. Recently, the authors presented a numerical wear model of reverse total shoulder arthroplasties (RTSAs), and its application for estimating the wear coefficient k from experimental data according to different wear laws. In this study, such model and k expressions are exploited to investigate the sensitivity of UHMWPE wear to implant size and dimensional tolerance. A set of 10 different geometries was analysed, considering nominal diameters in the range 36-42mm, available on the market, and a cup dimensional tolerance of +0.2, -0.0mm (resulting in a diametrical clearance ranging between 0.04-0.24mm), estimated from measurements on RTSAs. Since the most reliable wear law and wear coefficient k for UHMWPE are still controversial in the literature, both the Archard law (AR) and the wear law of UHMWPE (PE), as well as four different k expressions were considered, carrying out a total of 40 simulations. Results showed that the wear volume increases with the implant size and decreases with the dimensional tolerance for both the wear laws. Interestingly, different trends were obtained for the maximum wear depth vs. clearance: the best performing implants should have a high conformity according to the AR law but low conformity for the PE law. However, according to both laws, wear is highly affected by both implant size and dimensional tolerance, although it is much more sensitive to the latter, with up to a twofold variation of wear predicted. Indeed, dimensional tolerance directly alters the clearance, and therefore the lubrication and contact pressure distribution in the implant. Rather surprisingly the role of dimensional tolerance has been completely disregarded in the literature, as well as in the standards. Furthermore, this study notes some important issues for future work, such as the validation of wear laws and predictive wear models and the sensitivity of k to implant geometry.

Contact mechanics of reverse total shoulder arthroplasty during abduction: the effect of neck-shaft angle, humeral cup depth, and glenosphere diameter

BACKGROUND

Implant design parameters can be changed during reverse shoulder arthroplasty (RSA) to improve range of motion and stability; however, little is known regarding their impact on articular contact mechanics. The purpose of this finite element study was to investigate RSA contact mechanics during abduction for different neck-shaft angles, glenosphere sizes, and polyethylene cup depths.

METHODS

Finite element RSA models with varying neck-shaft angles (155°, 145°, 135°), sizes (38 mm, 42 mm), and cup depths (deep, normal, shallow) were loaded with 400 N at physiological abduction angles. The contact area and maximum contact stress were computed.

RESULTS

The contact patch and the location of maximum contact stress were typically located inferomedially in the polyethylene cup. On average for all abduction angles investigated, reducing the neck-shaft angle reduced the contact area by 29% for 155° to 145° and by 59% for 155° to 135° and increased maximum contact stress by 71% for 155° to 145° and by 286% for 155° to 135°. Increasing the glenosphere size increased the contact area by 12% but only decreased maximum contact stress by 2%. Decreasing the cup depth reduced the contact area by 40% and increased maximum contact stress by 81%, whereas increasing the depth produced the opposite effect (+52% and -36%, respectively).

DISCUSSION

The location of the contact patch and maximum contact stress in this study matches the area of damage seen frequently on clinical retrievals. This finding suggests that damage to the inferior cup due to notching may be potentiated by contact stresses. Increasing the glenosphere diameter improved the joint contact area and did not affect maximum contact stress. However, although reducing the neck-shaft angle and cup depth can improve range of motion, our study shows that this also has some negative effects on RSA contact mechanics, particularly when combined.

Implant impingement during internal rotation after reverse shoulder arthroplasty. The effect of implant configuration and scapula anatomy: A biomechanical study

BACKGROUND

Internal rotation after reverse shoulder arthroplasty is essential to perform fundamental daily living activities. The purpose of this study was to examine the impact of anatomical and implant related factors on impingement-free internal rotation of the glenohumeral joint.

METHODS

CT-scans of 13 human shoulder specimens with implanted reverse shoulder prostheses were carried out and scapula neck length, lateral pillar angle, and implantation height of the metaglene were measured. Internal rotation testing of all specimens was performed by the use of a robot assisted shoulder simulator. Biomechanical variables were analyzed using a three-way ANOVA. Spearman's rank correlations were performed to determine the relationship between biomechanical and anatomical data.

FINDINGS

The maximum internal rotation angle for a 38 mm centric glenosphere and a standard onlay was 93.4(SD 34.9°). The change of the diameter of the glenosphere resulted in no significant increase of the maximum rotation angle (P=0.16), while change of the glenosphere type from concentric to eccentric (P=0.005) as well as the change of the onlay type from standard to a more shallow one (P=0.002) both had a significant effect on the internal rotation. The distance between the inferior rim of the metaglene and the inferior aspect of the glenoid (P=0.21), scapula pillar angle (P=0.13) as well as the scapula neck length (P=0.81) showed no significant correlation with the maximum internal rotation angle.

INTERPRETATION

Implant component selection shows strong influence on the impingement-free internal rotation. The use of an eccentric glenosphere and a shallow humeral cup may improve internal rotation after reverse shoulder arthroplasty.

The effect of glenosphere size on functional outcome for reverse shoulder arthroplasty

PURPOSE

Reverse shoulder arthroplasty (RSA) is an effective surgery for a variety of patients with difficult shoulder pathology. Since postsurgical outcomes are often variable, there has been great effort made to optimize the design and use of these implants. Previous studies demonstrated an association between increased glenosphere size and improved range of motion. The purpose of this study is to assess the relationship between glenosphere size, range of motion, and functional outcome scores.

METHODS

This is a retrospective cohort study of 140 patients (148 shoulders) undergoing reverse shoulder arthroplasty. All patients were assessed pre- and postoperatively for range of motion, Constant score, ASES score, and Subjective Shoulder Value. Improvements in these variables were compared for patients treated with three different glenosphere sizes (36, 40, 42 mm).

RESULTS

All groups had a mean improvement in range of motion and functional outcome scores, but there were no statistically significant differences between groups when controlling for preoperative differences.

CONCLUSIONS

Our findings do not support a strong role for glenosphere size as a singular factor affecting range of motion or patient-reported outcome following RSA. These problems are most likely due to the multifactorial nature of shoulder dynamics. For this reason, assessing the effect a single surgical or biomechanical parameter on function has been challenging.

Numerical and experimental investigations for the evaluation of the wear coefficient of reverse total shoulder prostheses

In the present study, numerical and experimental wear investigations on reverse total shoulder arthroplasties (RTSAs) were combined in order to estimate specific wear coefficients, currently not available in the literature. A wear model previously developed by the authors for metal-on-plastic hip implants was adapted to RTSAs and applied in a double direction: firstly, to evaluate specific wear coefficients for RTSAs from experimental results and secondly, to predict wear distribution. In both cases, the Archard wear law (AR) and the wear law of UHMWPE (PE) were considered, assuming four different k functions. The results indicated that both the wear laws predict higher wear coefficients for RTSA with respect to hip implants, particularly the AR law, with k values higher than twofold the hip ones. Such differences can significantly affect predictive wear model results for RTSA, when non-specific wear coefficients are used. Moreover, the wear maps simulated with the two laws are markedly different, although providing the same wear volume. A higher wear depth (+51%) is obtained with the AR law, located at the dome of the cup, while with the PE law the most worn region is close to the edge. Taking advantage of the linear trend of experimental volume losses, the wear coefficients obtained with the AR law should be valid despite having neglected the geometry update in the model.

Implant Design Variations in Reverse Total Shoulder Arthroplasty Influence the Required Deltoid Force and Resultant Joint Load

BACKGROUND

Reverse total shoulder arthroplasty (RTSA) is widely used; however, the effects of RTSA geometric parameters on joint and muscle loading, which strongly influence implant survivorship and long-term function, are not well understood. By investigating these parameters, it should be possible to objectively optimize RTSA design and implantation technique.

QUESTIONS/PURPOSES

The purposes of this study were to evaluate the effect of RTSA implant design parameters on (1) the deltoid muscle forces required to produce abduction, and (2) the magnitude of joint load and (3) the loading angle throughout this motion. We also sought to determine how these parameters interacted.

METHODS

Seven cadaveric shoulders were tested using a muscle load-driven in vitro simulator to achieve repeatable motions. The effects of three implant parameters-humeral lateralization (0, 5, 10 mm), polyethylene thickness (3, 6, 9 mm), and glenosphere lateralization (0, 5, 10 mm)-were assessed for the three outcomes: deltoid muscle force required to produce abduction, magnitude of joint load, and joint loading angle throughout abduction.

RESULTS

Increasing humeral lateralization decreased deltoid forces required for active abduction (0 mm: 68% ± 8% [95% CI, 60%-76% body weight (BW)]; 10 mm: 65% ± 8% [95% CI, 58%-72 % BW]; p = 0.022). Increasing glenosphere lateralization increased deltoid force (0 mm: 61% ± 8% [95% CI, 55%-68% BW]; 10 mm: 70% ± 11% [95% CI, 60%-81% BW]; p = 0.007) and joint loads (0 mm: 53% ± 8% [95% CI, 46%-61% BW]; 10 mm: 70% ± 10% [95% CI, 61%-79% BW]; p < 0.001). Increasing polyethylene cup thickness increased deltoid force (3 mm: 65% ± 8% [95% CI, 56%-73% BW]; 9 mm: 68% ± 8% [95% CI, 61%-75% BW]; p = 0.03) and joint load (3 mm: 60% ± 8% [95% CI, 53%-67% BW]; 9 mm: 64% ± 10% [95% CI, 56%-72% BW]; p = 0.034).

CONCLUSIONS

Humeral lateralization was the only parameter that improved joint and muscle loading, whereas glenosphere lateralization resulted in increased loads. Humeral lateralization may be a useful implant parameter in countering some of the negative effects of glenosphere lateralization, but this should not be considered the sole solution for the negative effects of glenosphere lateralization. Overstuffing the articulation with progressively thicker humeral polyethylene inserts produced some adverse effects on deltoid muscle and joint loading.

CLINICAL RELEVANCE

This systematic evaluation has determined that glenosphere lateralization produces marked negative effects on loading outcomes; however, the importance of avoiding scapular notching may outweigh these effects. Humeral lateralization's ability to decrease the effects of glenosphere lateralization was promising but further investigations are required to determine the effects of combined lateralization on functional outcomes including range of motion.

Reverse shoulder prosthesis to treat complex proximal humeral fractures in the elderly patients: results after 10-year experience

PURPOSE

The aim of this study is to report the clinical and radiological results of reverse total shoulder arthroplasty (rTSA) in elderly patients who have been treated for complex humeral fractures.

MATERIALS AND METHODS

From January 2005 to December 2014, we have implanted rTSA for proximal humeral fractures in 95 patients (80 women, 15 men) about 75 years old on average (range 62-95 years). All rates and results on intraoperative and postoperative complications have been collected in a specific database. In all cases we have used a modular implant prosthesis (Lima Corporate, San Daniele del Friuli, Italy). The prosthesis was implanted cementless in 92 cases. Because of the presence of a high percentage of comorbidities in the elderly patients, we have retrospectively analyzed the necessity of a secondary hospitalization, from a week to a 6-month time after the discharge, due to general health problems and specific postoperative shoulder complications. The mean follow-up was 5 years (range 1-9 years) for 70 of 95 patients, 50 of whom had adequate radiographic controls.

RESULTS

None of 95 patients has required a reoperation or a hospitalization for general health problems from 1 week to 6 months postoperative. No early or late infection of prosthesis has been observed. There were seven cases of perioperative complications, three humeral vertical bone fissuring, two glenoid fractures and two cases of deltoid muscle damage. We have had three cases of postoperative hematoma and one case of ulnar nerve neuropathy. The mean constant score was 85.4, and the mean simple shoulder test was 7.4. We have observed a grade 1 scapular notching in 15 cases (30 %). In the remaining 35 reviewed cases, there was no notching. Peri-articular heterotopic ossifications were found in 11 cases (22 %).

CONCLUSION

Reverse shoulder prosthesis in complex humeral fractures in the elderly can be considered as a reliable surgical procedure, which leads to very good clinical and radiological results in case of cementless prosthesis, as well.