Prosthetic component relationship of the reverse Delta III total shoulder prosthesis in the transverse plane of the body

Three-dimensional evaluation of stem placement accuracy with the conventional guide in reverse shoulder arthroplasty and its relevance to clinical outcomes

Background

Placement of retroversion of the stem (RS) is important in reverse shoulder arthroplasty. A conventional guide, based on the forearm, has been used for stem placement; however, only a few studies have reported the accuracy of stem placement using conventional guides. In this study, a three-dimensional postoperative evaluation software was used to investigate the accuracy of RS placement using a conventional guide and its effect on postoperative outcomes.

Methods

This retrospective study was performed by a single surgeon (a board-certified specialist with more than 15 years of experience in performing reverse shoulder arthroplasty) using the Exactech Equinoxe Reverse Shoulder System (Exactech Inc., Gainesville, FL, USA). Forty-nine patients who were followed up for at least 2 years were included. The target RS angle of the humeral component was set to 20°. Postoperative implant placement, including RS, was assessed with a three-dimensional planning software using computed tomography images obtained postoperatively. Postoperative range of motion and its relationship with clinical outcomes were also evaluated as clinical assessment. Furthermore, a subanalysis was performed comparing the 0-20° RS group with the other groups.

Results

The mean postoperative RS was 13.2 ± 11.9° and was placed within 0-20° in 31/49 patients (63.3%). A correlation was observed between postoperative external rotation and RS (r = 0.30, P = .03). In a further subanalysis, the Constant-Murley score was significantly higher in the 0-20° RS group (P = .03).

Conclusion

Placement of the RS using a conventional guide varied from the target position. RS correlated with postoperative external rotation, and RS within 0-20° significantly improved clinical outcomes. These results suggested that accurate placement of the RS may improve clinical outcomes. Therefore, the development of surgical assistive technologies for accurate placement is necessary to ensure accurate stem placement to avoid human error.

Patients posture affects clinical outcomes and range of motion after reverse total shoulder arthroplasty: A clinical study

Background

Movement limitations following implantation of reverse total shoulder arthroplasty (rTSA) have been observed in some patients postoperatively, with implant design and positioning recognized as important influential factors. Recent analyses have identified patient's posture, measured as scapula internal rotation on computed tomography (CT), as an additional factor influencing the functional outcome after rTSA. However, no clinical study has correlated the preoperatively photo-documented posture to functional outcome. It was the aim of this study to correlate preoperatively photo-documented posture to scapula orientation using CT and analyze the influence on functional outcome following rTSA implantation.

Methods

A prospectively enrolled rTSA database was retrospectively reviewed to include a total of 360 patients with a minimum follow-up of 2 years. Patient's posture was analyzed using standardized preoperative photo and video documentation. The posture was defined following the classification system of Moroder et al as type A (upright posture, retracted scapulae), type B (intermediate), and type C (kyphotic posture with protracted scapulae). In addition, CT data were used to measure scapula position (internal rotation). Correlation analyses between them were conducted. Postoperative range of motion (ROM) and clinical outcomes (absolute Constant-Murley Score and relative Constant-Murley Score) were compared between the different posture types.

Results

According to the photo-documented posture types, the patients were divided into posture types A (n = 59), B (n = 253) and C (n = 48). Average absolute Constant-Murley Score differed significantly among the groups (69 ± 16 vs. 69 ± 14 vs. 64 ± 16, P < .05) favoring patients with posture types A and B over type C. In terms of ROM, flexion, abduction, and internal rotation significantly differed among the groups. Types A and B exhibited better flexion and abduction (flexion 124 ± 26° and 123 ± 23° vs. 113 ± 25°, abduction 140 ± 34° and 137 ± 30° vs. 128 ± 34°). Patients with posture type A demonstrated superior internal rotation (CS points: 5.9 ± 2.9 vs. 5.0 ± 2.7 vs. 4.4 ± 2.8, P < .05). External rotation was better for type A compared to type C (A: 33 ± 17° vs. B: 30 ± 16° vs. C: 28 ± 18°). Correlation analysis of posture classification using photo documentation and CT scan showed poor reliability (r = 0.35).

Conclusion

Patients with clinical posture types A and B exhibited improved ROM values compared to type C postures. Clinical outcome scores were also notably superior in types A and B. However, the measurement of scapula internal rotation on supine CT does not reliably correlate with photo documentation of patient's posture. Preoperatively, patient's posture should be considered in rTSA planning because of the potential influence on ROM and clinical outcomes.

Practical considerations for determination of scapular internal rotation and its relevance in reverse total shoulder arthroplasty planning

BACKGROUND

Scapulothoracic orientation, especially scapular internal rotation (SIR) may influence range of motion in reverse total shoulder arthroplasty (RTSA) and is subjected to body posture. Clinical measurements of SIR rely on apical bony landmarks, which depend on changes in scapulothoracic orientation, while radiographic measurements are often limited by the restricted field of view (FOV) in CT scans. Therefore, the goal of this study was (1) to determine whether the use of CT scans with a limited FOV to measure SIR is reliable and (2) if a clinical measurement could be a valuable alternative.

METHODS

This anatomical study analyzed the whole-body CT scans of 100 shoulders in 50 patients (32 male and 18 female) with a mean age of 61.2 ± 20.1 years (range 18; 91). (1) CT scans were rendered into 3D models and SIR was determined as previously described. Results were compared to measurements taken in 2D CT scans with a limited FOV. (2) Three apical bony landmarks were defined: (the angulus acromii (AA), the midpoint between the AA and the coracoid process tip (C) and the acromioclavicular (AC) joint. The scapular axis was determined connecting the trigonum scapulae with these landmarks and referenced to the glenoid center. The measurements were repeated with 0°, 10°, 20°, 30° and 40° anterior scapular tilt.

RESULTS

Mean SIR was 44.8° ± 5.9° and 45.6° ± 6.6° in the 3D and 2D model, respectively (p < 0.371). Mean difference between the measurements was 0.8° ± 2.5° with a maximum of 10.5°. Midpoint AA/C showed no significant difference to the scapular axis at 0° (p = 0.203) as did the AC-joint at 10° anterior scapular tilt (p = 0.949). All other points showed a significant difference from the scapular axis at all degrees of tilt.

CONCLUSION

2D CT scans are reliable to determine SIR, even if the spine is not depicted. Clinical measurements using apical superficial scapula landmarks are a possible alternative; however, anterior tilt influenced by posture alters measured SIR.

Humeral and Glenoid Version in Reverse Total Shoulder Arthroplasty: A Systematic Review

There is increasing interest in reverse total shoulder arthroplasty (RTSA) as a reliable treatment for arthritic, rotator cuff deficient shoulders. Humeral and glenoid version are controversial parameters that can influence internal and external rotation, muscular forces, and implant stability as outcomes of RTSA. The aim of this study was to obtain an overview of the current knowledge on the effect of both humeral component version and glenoid component version and give recommendations on their most optimal degree for RTSA. A comprehensive quantitative review of the published literature on the effect of humeral version and glenoid version in RTSA was performed, to identify its influence on the range of movement, muscle forces, and intrinsic stability of the reverse prosthesis. Eleven studies were included: nine were biomechanical studies, one was a clinical-radiographic study, and one was an implant design consideration. Anterior stability can be improved by implanting the humeral component in neutral or with some anteversion. Glenoid component retroversion has been proven to reduce the likelihood of subluxation, while increasing ER and ROM at the same time. The study was conducted considering 5° anteversion; neutral; and 5°, 10°, and 20° retroversion of the glenoid component. Although a final opinion has not been yet expressed on the matter, the general consensus tends to agree on restoring 0° to 20° of retroversion of the humeral and glenoid component to yield the best outcomes.

Clinical and Functional Results of Reverse Total Shoulder Arthroplasty and Postoperative Rehabilitation Protocol

Purpose

This retrospective study aims to analyze the clinical and functional results obtained over a seven-year period of performing reverse total shoulder arthroplasty (RTSA) and the subsequent postoperative rehabilitation protocol.

Methods

We analyzed data from 80 patients who were evaluated at a preoperative, as well as monthly postoperative outpatient consultation, until the discharge from the rehabilitation program, using Constant Score (CS).

Results

A comparison of preoperative and postoperative (after rehabilitation protocol) results revealed an improved functional score of absolute CS (20.8 increase), normal relative CS (29.1 increase), and individual relative CS (31.7 increase) with statistical significance (p<0.05). From the analysis of CS subscores, there was a positive evolution of the pain subscore, as well as flexion, abduction, and external rotation combined with abduction range of motion (ROM). Contrarily, there was a negative evolution of the combined internal rotation, extension, and adduction ROM, as well as deltoid muscle strength. No statistically significant correlations were found between age and postoperative CS, as well as between the time interval from surgery to the beginning of outpatient rehabilitation and CS evolution.

Conclusion

Our study demonstrates that RTSA is an effective therapeutic option that, if combined with a well-structured rehabilitation program, can improve pain, mobility, and upper limb functionality.

The Evolution of Reverse Total Shoulder Arthroplasty-From the First Steps to Novel Implant Designs and Surgical Techniques

PURPOSE OF REVIEW

The purpose of this review is to summarize recent literature regarding the latest design modifications and biomechanical evolutions of reverse total shoulder arthroplasty and their impact on postoperative outcomes.

RECENT FINDINGS

Over the past decade, worldwide implantation rates of reverse total shoulder arthroplasty have drastically increased for various shoulder pathologies. While Paul Grammont's design principles first published in 1985 for reverse total shoulder arthroplasty remained unchanged, several adjustments were made to address postoperative clinical and biomechanical challenges such as implant glenoid loosening, scapular notching, or limited range of motion in order to maximize functional outcomes and increase the longevity of reverse total shoulder arthroplasty. However, the adequate and stable fixation of prosthetic components can be challenging, especially in massive osteoarthritis with concomitant bone loss. To overcome such issues, surgical navigation and patient-specific instruments may be a viable tool to improve accurate prosthetic component positioning. Nevertheless, larger clinical series on the accuracy and possible complications of this novel technique are still missing.

The influence of posture and scapulothoracic orientation on the choice of humeral component retrotorsion in reverse total shoulder arthroplasty

BACKGROUND

The literature suggests implantation of the humeral component in reverse total shoulder arthroplasty (RTSA) in 0°-40° of retrotorsion without further specification. We hypothesized that optimal humeral component retrotorsion to avoid notching and gain balanced rotational capacity would depend on scapular position and posture.

METHODS

We investigated 200 shoulders in 100 patients with available whole-body computed tomography scans and created 3-dimensional models. Implantation of a humeral component in 20° of retrotorsion was simulated, and a correction angle (CA) to yield perfect opposition to the glenosphere was calculated. Patient-specific variables such as age, sex, posture, and scapular orientation parameters were correlated with this CA.

RESULTS

Scapular orientation showed large interindividual differences. A highly significant correlation was seen between the CA and scapular internal rotation (R = 0.71, P < .001) and protraction (R = 0.39, P < .001). When the CA was adjusted for glenoid retroversion, the correlation coefficient of scapular internal rotation increased even further (R = 0.91, P < .001). Scapular internal rotation itself showed a correlation with thoracic kyphosis (R = 0.27, P < .001), protraction (R = 0.57, P < .001), tilt (R = 0.29, P < .001), and scapular translation (R = -0.23, P < .001).

CONCLUSION

Scapular orientation and posture should be integrated into the determination process of humeral component retrotorsion in RTSA. In theory, implantation of the humeral component with increased retrotorsion leads to improved neutral opposition of the RTSA components in patients with extensive internal rotation of the scapula. On the basis of varying scapular internal rotation, we propose the distinction of 3 different posture types (A-C) for enhanced appraisal of scapulothoracic orientation.

Short-Term Outcomes of the Grammont Reverse Shoulder Arthroplasty: Comparison between First and Second Generation Delta Prosthesis

Purpose  This article compares short-term outcomes of two series of patients, who underwent reverse total shoulder arthroplasty (RTSA) with two different implants, both based on Grammont's principles: the Delta III (D-3) and the Delta Xtend (D-XT) prostheses. Methods  The D-3 group included a consecutive series of 26 patients (mean age 75 years), that were treated between 2000 and 2006; the D-XT group included a consecutive series of 31 patients (mean age 72.5 years), for a total of 33 implants performed between 2011 and 2015. In both groups the most common diagnoses were cuff tear arthropathy (18 and 22 shoulders, respectively) and malunion of proximal humerus fractures (3 and 5). All procedures were performed by the same surgeon. Constant-Murley score (CMS) was used to assess clinical and functional outcomes. Radiographic evaluation included the true anteroposterior and axillary views. Results  Twenty-three patients of the D-3 group and 22 patients (24 shoulders) of the D-XT group were evaluated at a mean follow-up of 42 months (range 26-84) and 44 months (range 26-66), respectively. Four complications occurred in the D-3 group (1 partial deltoid detachment, 1 dislocation, and 2 glenoid component loosening), while one early postoperative infection occurred in the D-XT group. Increases in elevation and CMS between preoperative and postoperative period were observed in both groups; only the D-XT group showed a slight improvement in rotations. The incidence of scapular notching was significantly different between the two groups: 100% for D-3 and 22.2% for D-XT in patients with a minimum follow-up of 5 years. Conclusion  Prosthetic design evolution and greater acquaintance with this surgery have undoubtedly led to an improvement in short-term outcomes with second generation implants of RTSA. Future studies will have to ascertain whether newer implants, relying on biomechanical solutions alternative to Grammont's original concept, might provide additional advantages and minimize drawbacks.

Impact of scapular notching on reverse total shoulder arthroplasty midterm outcomes: 5-year minimum follow-up

BACKGROUND

The impact of scapula notching on reverse total shoulder arthroplasty (rTSA) clinical outcomes is controversial. The purpose of this study was to conduct a sufficiently statistically powered analysis to quantify the impact of scapular notching on midterm rTSA outcomes.

METHODS

There were 324 rTSA patients with 5 years of minimum follow-up evaluated. Patients were stratified according to the presence of a scapular notch at latest follow-up; radiographs were also assessed at each time point for patients with notching to determine the time for notch grade development. A 2-tailed, unpaired t-test compared preoperative, postoperative, and preoperative to postoperative outcomes between cohorts.

RESULTS

There were 324 patients having an average follow-up of 75.1 months assessed; 47 (14.5%) patients had scapular notching. For scapular notching patients, the average notching grade was 1.7 ± 0.8 (24 grade 1, 15 grade 2, and 8 grade 3). The average time to notch development was 51.4 ± 24.1 months; grade 1, grade 2, and grade 3 notches developed at 49.0 ± 22.1 months, 57.5 ± 22.6 months, and 71.6 ± 15.8 months, respectively. No preoperative differences were observed between cohorts. At latest follow-up, scapular notching patients had significantly worse outcome scores and significantly less active abduction, forward flexion, and strength. Finally, scapular notching patients had significantly more complications, revisions, and humeral radiolucent lines.

CONCLUSIONS

Scapular notching patients had significantly worse clinical outcomes and less range of motion than patients without scapular notching; these differences exceeded the minimal clinically important difference threshold for several outcome metrics. Based on these results, we recommend minimizing scapular notching through patient and implant selection and technique modification.

Reverse shoulder arthroplasty with a cementless short metaphyseal humeral prosthesis without a stem: survivorship, early to mid-term clinical and radiological outcomes in a prospective study from an independent centre

INTRODUCTION

The use of reverse total shoulder arthroplasty has increased for the management of cuff-deficient glenohumeral joint arthritis and fractures. With bone preservation being a major target in reverse shoulder arthroplasty, metaphyseal humeral components without a stem were developed. The aim of this study is to present the survivorship, functional and radiological outcomes of a novel short metaphyseal prosthesis without a diaphyseal stem from an independent centre.

METHODS

Clinical function and radiological features of patients undergoing stemless reverse shoulder arthroplasty were prospectively recorded. Patients' demographics, indications for surgery, complications, functional and radiological assessment at the final follow-up as well as survivorship with the end point of revision for any reason were recorded.

RESULTS

Between 2009 and 2016, 36 patients received 37 reverse shoulder arthroplasties with the stemless Verso prosthesis. Mean age of the patients was 76.9 years. The most common indication for surgery was cuff tear arthropathy. Mean follow-up was 3 years (range 1-7 years). Oxford shoulder score improved from an average of 11 pre-operatively (range 2-19) to 44 post-operatively (range 29-48) (p < 0.0001). There was one case of a deep post-operative infection that needed washout, liner exchange with retention of the prosthesis. Radiographic analysis showed no lucencies, or stress shielding around the humeral or glenoid components. Constant score at the final follow-up was on average 63 (range 35-86). Activities of daily living with requirement for internal and external rotation score (ADLEIR) was on average 12 pre-operatively (range 0-27) and 31 post-operatively (range 18-36) (p < 0.0001). There was 100% survivorship of the prosthesis in this early to mid-term study.

CONCLUSION

This early to mid-term prospective study demonstrates excellent survivorship and radiological results of the Verso reverse shoulder replacement. It needs a simple reproducible technique, and the results have been replicated at an independent centre. This study underlines its survivorship in the early to mid-term and confirms lower incidence of complications such as instability, notching, loosening and the need for revision surgery. Most importantly, it conserves the humeral bone stock for revision arthroplasties in the future. Our results are similar to those of the currently published literature.

Long-term results of the Delta Xtend reverse shoulder prosthesis

BACKGROUND

Reverse shoulder arthroplasty has become the standard treatment for cuff tear arthropathy and complex fractures of the proximal humerus. The Delta Xtend prosthesis (DePuy Synthes, Warsaw, IN, USA) was launched in 2006 and has shown good short-term results. Longer-term results are not yet available.

METHODS

There were 126 primary Delta Xtend prostheses implanted in our center by 1 surgeon from October 2006 until December 2009. Of these, 38 patients died, 12 were lost to follow-up, and 2 needed early revision of the prosthesis. Follow-up of at least 8 years was available for 74 patients. At preoperative and postoperative visits, shoulder function and pain were evaluated using the age- and sex-adjusted Constant-Murley score (aCS). The satisfaction rate was evaluated on a visual analog scale (VAS).

RESULTS

The mean follow-up in our population was 113.1 months. The mean aCS was 44.6% (standard deviation [SD], 19.2) preoperatively. It increased significantly (P < .001) after surgery to 75.8% (SD, 12.5) at 3 months and 91.1% (SD, 11.8) at 5 years. At the latest follow-up, the mean aCS was only 79.9% (SD, 17.7), which was significantly lower (P = .002) than the aCS at 5 years postoperatively. An overall survival rate of more than 97% was seen at 8 years of follow-up.

CONCLUSION

This study confirms that the promising short-term results of the Delta Xtend prosthesis can be extended in the longer-term. However, further follow-up will be necessary to check whether the statistically significant decrease in the Constant-Murley score at latest follow-up, which was driven by a decrease in range of motion and power, continues or not.

Impact of scapular notching on clinical outcomes after reverse total shoulder arthroplasty: an analysis of 476 shoulders

BACKGROUND

Scapular notching is a complication unique to reverse total shoulder arthroplasty (rTSA), although its clinical implications are unclear and remains controversial.

METHODS

We retrospectively reviewed rTSA patients of a single implant design in 476 shoulders with a minimum 2-year clinical and radiographic follow-up. Clinical measures included active range of motion and American Shoulder and Elbow Surgeons scores, in addition to one or more of the Constant score, Shoulder Pain and Disability Index, Simple Shoulder Test (SST), and University of California, Los Angeles Shoulder Rating Scale. Complications and rates of humeral radiolucencies were also recorded.

RESULTS

Scapular notching was observed in 10.1% (48 of 476) of rTSAs and was associated with a longer clinical follow-up, lower body weight, lower body mass index, and when the operative side was the nondominant extremity. Patients with scapular notching had significantly lower postoperative scores on the Shoulder Pain and Disability Index, Constant, Simple Shoulder Test, and University of California, Los Angeles, Shoulder Rating Scale compared with patients without scapular notching. Patients with scapular notching also had significantly lower active abduction, significantly less strength, and trended toward significantly less active forward flexion (P = .0527). Finally, patients with scapular notching had a significantly higher complication rate and trended toward a significantly higher rate of humeral radiolucent lines (P = .0896) than patients without scapular notching.

CONCLUSIONS

This large-scale outcome study demonstrates that patients with scapular notching have significantly poorer clinical outcomes, significantly less strength and active range of motion, and a significantly higher complication rate than patients without scapular notching. Longer-term follow-up is necessary to confirm that these statistical observations in the short-term will result in greater clinically meaningful differences over time.

Is there any influence of humeral component retroversion on range of motion and clinical outcome in reverse shoulder arthroplasty? A clinical study

PURPOSE

Reverse shoulder arthroplasty becomes more widely used as treatment for patients with complex cuff arthropathy. Theoretically, a higher retroversion of the humeral component leads to an increase in external rotation ROM and a decrease in internal rotation ROM. There is no consensus in optimal retroversion orientation. We retrospectively describe the effect of retroversion of the humeral component. We hypothesize that 20° humeral retroversion improves postoperative ROM, strength or clinical outcome scores compared to neutral retroversion.

METHODS

A retrospective clinical study is performed. An Aequalis reverse shoulder prosthesis was placed in 65 shoulders from 58 patients with a mean age of 73.8 years (95% CI 72.0-75.6). Between October 2006 and May 2012, the humeral component was placed in neutral retroversion in 36 shoulders (55%). From June 2012 to June 2014, it was placed in 20° retroversion in 29 shoulders (45%). After a mean follow-up of 36 months with a minimum of 12 months, patients were invited for a study visit. ROM, strength, Constant-Murley and Oxford Scores were measured.

RESULTS

ROM, strength and Constant-Murley and Oxford Scores did not differ significantly between both groups.

CONCLUSIONS

With the Aequalis prosthesis, no significant effect of 0° or 20° retroversion on external and internal rotation ROM, strength or functional outcome scores was found.

Reverse shoulder arthroplasty with a cementless short metaphyseal humeral implant without a stem: clinical and radiologic outcomes in prospective 2- to 7-year follow-up study

BACKGROUND

Reverse shoulder prostheses are increasingly used in recent years for treatment of glenohumeral arthropathy with deficient rotator cuff. Bone preservation is becoming a major goal in shoulder replacement surgery. Metaphyseal humeral components without a stem were developed to minimize bone resection and preserve bone. This study evaluated the clinical and radiologic outcomes at 2 to 7 years using a novel short metaphyseal reverse total shoulder arthroplasty (rTSA) prosthesis without a diaphyseal stem.

METHODS

Between 2005 and 2010, 102 consecutive patients underwent rTSA with this implant, and 98 (20 men, 78 women) were available for follow-up. Mean age was 74.4 years (range, 38-93 years). Indications were cuff tear arthropathy, 65; fracture sequelae, 12; rheumatoid arthritis, 13; failed rotator cuff repair, 3; cuff deficiency with loosening of anatomic prosthesis, 3; and acute trauma, 2; with 17 of these as revisions.

RESULTS

Patients' satisfaction (Subjective Shoulder Value) improved from 8 of 100 to 85 of 100. The Constant score improved from 14 to 59 (age- and sex-adjusted, 86; P < .0001). Range of motion improved from 47° to 129° in elevation, 10° to 51° in external rotation, and 21° to 65° in internal rotation. Radiographic analysis showed no lucencies, subsidence, or stress shielding around the humeral or glenoid components. Glenoid notching was found in 21 patients (18 grade 1-2; 3 grade 3).

CONCLUSIONS

The short metaphyseal rTSA design without a diaphyseal stem shows encouraging short- to midterm results, with excellent pain relief and shoulder function, restoration of good active range of motion, and high patient satisfaction scores. The design of this implant seems to result in improved rotational movements, low incidence of glenoid notching, and no implant loosening, subsidence, or stress shielding.

Combined effect of change in humeral neck-shaft angle and retroversion on shoulder range of motion in reverse total shoulder arthroplasty - A simulation study

BACKGROUND

We studied combined effect of change in humeral neck shaft angle and retroversion on shoulder ROM in reverse total shoulder arthroplasty using 3-dimensional simulations.

METHODS

Using a 3D model construct based on the CT scans of 3 males and a 3-dimensional analysis program, a humeral component of reverse total shoulder arthroplasty was implanted in 0°, 10°, 20°, 30°,40° retroversion and 135°, 145°, and 155° neck shaft angle. Total horizontal range of motion (sum of horizontal adduction and abduction) at 30° and 60° scaption, adduction in the scapular plane and IR behind the back were measured for various combinations of neck shaft angle and retroversion.

FINDINGS

Change in retroversion didn't show any effect on total horizontal range of motion. Total horizontal range of motion at both 30° and 60° scaption, showed maximum values at 135° neck shaft angle and minimum values at 155° neck shaft angle. With any combination of retroversion angles, adduction deficit was maximum at 155° neck shaft angle and no adduction deficit at 135° neck shaft angle. Every 10° decrease in neck shaft angle resulted in an average 10.4° increase in adduction. For every 10° increase in retroversion, there was loss of internal rotation behind the back up to at least one vertebral level.

INTERPRETATION

135° neck shaft angle resulted in maximum total horizontal range of motion both at 30° and 60° scaption regardless of retroversion angles. 135° neck shaft angle also reduced the chances of scapular impingement. Decrease in retroversion angle resulted in more amount of internal rotation behind the back.

Biomechanics of reverse total shoulder arthroplasty

Reverse total shoulder arthroplasty is an effective procedure for treatment of glenohumeral joint disease among patients with severe rotator cuff deficiency. Improvements in prosthetic design are the result of an evolved understanding of both shoulder and joint replacement biomechanics. Although modern generations of the reverse shoulder prosthesis vary in specific design details, they continue to adhere to Grammont's core principles demonstrated by his original Delta III prosthesis. This review article discusses the biomechanics of reverse total shoulder arthroplasty with a focus on elements of implant design and surgical technique that may affect stability, postoperative complications, and functional outcomes.

Relationship of the Medial Clavicular Head to the Manubrium in Normal and Symptomatic Degenerated Sternoclavicular Joints

BACKGROUND

Clavicular prominence is common in patients with symptomatic degenerative sternoclavicular arthritis. It is unclear if this is caused by enlargement or subluxation of the clavicle. The aim of this report is to describe a reproducible measurement technique to evaluate the relationship of the medial clavicular head to the manubrium.

METHODS

One hundred normal sternoclavicular joints, twenty-five sternoclavicular joints with symptomatic degenerative arthritis, and twenty-five non-symptomatic sternoclavicular joints on the contralateral side were studied with three-dimensional (3D) reconstruction with use of computer modeling. The greatest width (anterior-posterior distance) and height (superior-inferior distance) of the clavicle in the sagittal plane were measured, and the positions of the anterior and superior borders of the medial clavicle and their distances to the frontal and axial planes, respectively, were evaluated. The ratio of the anterior-posterior distance to the anterior-frontal plane distance was measured to evaluate the anterior-posterior position of the clavicle and the ratio of the superior-inferior distance to the superior-axial plane distance was measured to evaluate its superoinferior position. If the ratio was not in the 95% normal range, the clavicle was defined as subluxated. The reproducibility of this technique was evaluated on the basis of the interobserver and intraobserver reliability.

RESULTS

This technique showed good interobserver and intraobserver reliability. The mean anterior-posterior and superior-inferior distances were significantly larger in association with symptomatic sternoclavicular arthritis than in the normal sternoclavicular joints (p < 0001). The clavicle was subluxated anteriorly in twenty-two of the twenty-five cases of symptomatic sternoclavicular arthritis, but it was not subluxated superiorly.

CONCLUSIONS

The medial clavicular head in patients with degenerative sternoclavicular arthritis is significantly larger than it is in the normal population, and it is usually subluxated anteriorly.

Influence of glenoid component design and humeral component retroversion on internal and external rotation in reverse shoulder arthroplasty: a cadaver study

BACKGROUND

A common disadvantage of reverse shoulder arthroplasty is limitation of the range of arm rotation. Several changes to the prosthesis design and implantation technique have been suggested to improve rotation range of motion (ROM).

HYPOTHESIS

Glenoid component design and degree of humeral component retroversion influence rotation ROM after reverse shoulder arthroplasty.

MATERIAL AND METHODS

The Aequalis Reversed™ shoulder prosthesis (Tornier Inc., Edina, MN, USA) was implanted into 40 cadaver shoulders. Eight glenoid component combinations were tested, five with the 36-mm sphere (centred seating, eccentric seating, inferior tilt, centred with a 5-mm thick lateralised spacer, and centred with a 7-mm thick lateralised spacer) and three with the 42-mm sphere (centred with no spacer or with a 7-mm or 10-mm spacer). Humeral component position was evaluated with 0°, 10°, 20°, 30°, and 40° of retroversion. External and internal rotation ROMs to posterior and anterior impingement on the scapular neck were measured with the arm in 20° of abduction.

RESULTS

The large glenosphere (42 mm) was associated with significantly (P<0.05) greater rotation ROMs, particularly when combined with a lateralised spacer (46° internal and 66° external rotation). Rotation ROMs were smallest with the 36-mm sphere. Greater humeral component retroversion was associated with a decrease in internal rotation and a significant increase (P<0.05) in external rotation. The best balance between rotation ROMs was obtained with the native retroversion, which was estimated at 17.5° on average in this study.

DISCUSSION

Our anatomic study in a large number of cadavers involved a detailed and reproducible experimental protocol. However, we did not evaluate the variability in scapular anatomy. Earlier studies of the influence of technical parameters did not take humeral component retroversion into account. In addition, no previous studies assessed rotation ROMs.

CONCLUSION

Rotation ROM should be improved by the use of a large-diameter glenosphere with a spacer to lateralise the centre of rotation of the gleno-humeral joint, as well as by positioning the humeral component at the patient's native retroversion value.

The impact of scapular notching on reverse shoulder glenoid fixation

BACKGROUND

Scapular notching is a well-documented complication of reverse shoulder arthroplasty. The effect of scapular notching on glenoid fixation is unknown.

MATERIALS AND METHODS

This study dynamically evaluated reverse shoulder glenoid baseplate fixation and assessed the effect of scapular notching on fixation in composite scapulae. A cyclic test was conducted to simulate 55° of humeral abduction in the scapular plane as a 750-N axial load was continuously applied to induce a variable shear and compressive load. Before and after cyclic loading, a displacement test was conducted to measure glenoid baseplate displacement in the directions of the applied static shear and compressive loads.

RESULTS

For the scapulae without a scapular notch, glenoid baseplate displacement did not exceed the generally accepted 150-μm threshold for osseous integration before or after cyclic loading in any component tested. For the scapulae with a scapular notch, glenoid baseplate displacement exceeded 150 μm in 2 of the 7 samples before cyclic loading and in 3 of the 7 samples after cyclic loading. The average pre-cyclic glenoid baseplate displacement in the direction of the shear load was significantly greater in scapulae with a scapular notch than those without a scapular notch both before (P = .003) and after (P = .023) cyclic loading.

CONCLUSIONS

Adequate glenoid baseplate fixation was achievable in most cases in scapulae with a severe scapular notch; however, the fact that this micromotion threshold was not met in all scapulae with a notch is concerning and implies that severe notching may play a role in initial glenoid baseplate stability.

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

HYPOTHESIS

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.

MATERIAL AND METHODS

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 Reverse Shoulder Arthroplasty [BIO-RSA]), which were implanted in the virtual model. All impingement positions were evaluated, as the required scapular compensation to avoid impingements.

RESULTS

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°.

CONCLUSION

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.

Scapular notching and osteophyte formation after reverse shoulder replacement: Radiological analysis of implant position in male and female patients

This study provides recommendations on the position of the implant in reverse shoulder replacement in order to minimise scapular notching and osteophyte formation. Radiographs from 151 patients who underwent primary reverse shoulder replacement with a single prosthesis were analysed at a mean follow-up of 28.3 months (24 to 44) for notching, osteophytes, the position of the glenoid baseplate, the overhang of the glenosphere, and the prosthesis scapular neck angle (PSNA). A total of 20 patients (13.2%) had a notch (16 Grade 1 and four Grade 2) and 47 (31.1%) had an osteophyte. In patients without either notching or an osteophyte the baseplate was found to be positioned lower on the glenoid, with greater overhang of the glenosphere and a lower PSNA than those with notching and an osteophyte. Female patients had a higher rate of notching than males (13.3% vs 13.0%) but a lower rate of osteophyte formation (22.9% vs 50.0%), even though the baseplate was positioned significantly lower on the glenoid in females (p = 0.009) and each had a similar mean overhang of the glenosphere. Based on these findings we make recommendations on the placement of the implant in both male and female patients to avoid notching and osteophyte formation.

Effect of deltoid tension and humeral version in reverse total shoulder arthroplasty: a biomechanical study

BACKGROUND

No clear recommendations exist regarding optimal humeral component version and deltoid tension in reverse total shoulder arthroplasty (TSA).

MATERIALS AND METHODS

A biomechanical shoulder simulator tested humeral versions (0°, 10°, 20° retroversion) and implant thicknesses (-3, 0, +3 mm from baseline) after reverse TSA in human cadavers. Abduction and external rotation ranges of motion as well as abduction and dislocation forces were quantified for native arms and arms implanted with 9 combinations of humeral version and implant thickness.

RESULTS

Resting abduction angles increased significantly (up to 30°) after reverse TSA compared with native shoulders. With constant posterior cuff loads, native arms externally rotated 20°, whereas no external rotation occurred in implanted arms (20° net internal rotation). Humeral version did not affect rotational range of motion but did alter resting abduction. Abduction forces decreased 30% vs native shoulders but did not change when version or implant thickness was altered. Humeral center of rotation was shifted 17 mm medially and 12 mm inferiorly after implantation. The force required for lateral dislocation was 60% less than anterior and was not affected by implant thickness or version.

CONCLUSION

Reverse TSA reduced abduction forces compared with native shoulders and resulted in limited external rotation and abduction ranges of motion. Because abduction force was reduced for all implants, the choice of humeral version and implant thickness should focus on range of motion. Lateral dislocation forces were less than anterior forces; thus, levering and inferior/posterior impingement may be a more probable basis for dislocation (laterally) than anteriorly directed forces.

Effect of humeral component version on impingement in reverse total shoulder arthroplasty

HYPOTHESIS

Reverse shoulder arthroplasty is growing in popularity for patients with deficient rotator cuffs; however, the phenomenon of scapular notching continues to be a concern. This study examined the effects of humeral component version in the Aequalis Reversed Shoulder Prosthesis (Tornier, Edina, MN) on impingement of the humeral prosthesis against the scapula to test the hypothesis that the mechanical contact of the humeral component with the scapular neck is influenced by the version of the humeral component.

MATERIALS AND METHODS

Seven shoulders from deceased donors were tested after the Aequalis Reversed Shoulder was implanted. The deltoid, pectoralis major, and latissimus dorsi were loaded based on physiologic cross-sectional area. The degree of internal and external rotation when impingement, subluxation, or dislocation occurred was measured at 0°, 30°, and 60° glenohumeral abduction in the scapular plane. Testing was performed with the humeral component placed in 20° of anteversion, neutral version, 20° of retroversion, and 40° of retroversion.

RESULTS

Maximum external rotation at 0° abduction was -1° ± 4° at 20° anteversion, 15° ± 3° at neutral, 28° ± 4° at 20° retroversion, and 44° ± 5° at 40° retroversion (P < .05). Maximum internal rotation at 0° abduction was 128° ± 9° at 20° anteversion, 112° ± 9° at neutral, 99° ± 8° at 20° retroversion, and 83° ± 8° at 40° retroversion (P < .05). Maximum external rotation at 30° abduction was 70° ± 6° at 20° anteversion, 84° ± 7° at neutral, 97° ± 6° at 20° retroversion, and 110° ± 5° at 40° retroversion (P < .05). There was no limitation to internal rotation at 30° abduction. No impingement occurred at 60° abduction.

DISCUSSION

Version of the humeral component plays a role in range of motion and impingement in reverse total shoulder arthroplasty. Anteversion can significantly decrease the amount of external rotation achievable after reverse total shoulder surgery.

CONCLUSION

Placing the Aequalis Reversed Shoulder humeral component at between 20° and 40° of retroversion more closely restores a functional arc of motion without impingement.

Prosthetic overhang is the most effective way to prevent scapular conflict in a reverse total shoulder prosthesis

BACKGROUND AND PURPOSE

Despite good clinical results with the reverse total shoulder arthroplasty, inferior scapular notching remains a concern. We evaluated 6 different solutions to overcome the problem of scapular notching.

METHODS

An average and a "worst case scenario" shape in A-P view in a 2-D computer model of a scapula was created, using data from 200 "normal" scapulae, so that the position of the glenoid and humeral component could be changed as well as design features such as depth of the polyethylene insert, the size of glenosphere, the position of the center of rotation, and downward glenoid inclination. The model calculated the maximum adduction (notch angle) in the scapular plane when the cup of the humeral component was in conflict with the scapula.

RESULTS

A change in humeral neck shaft inclination from 155° to 145° gave a 10° gain in notch angle. A change in cup depth from 8 mm to 5 mm gave a gain of 12°. With no inferior prosthetic overhang, a lateralization of the center of rotation from 0 mm to 5 mm gained 16°. With an inferior overhang of only 1 mm, no effect of lateralizing the center of rotation was noted. Downward glenoid inclination of 0º to 10º gained 10°. A change in glenosphere radius from 18 mm to 21 mm gained 31° due to the inferior overhang created by the increase in glenosphere. A prosthetic overhang to the bone from 0 mm to 5 mm gained 39°.

INTERPRETATION

Of all 6 solutions tested, the prosthetic overhang created the biggest gain in notch angle and this should be considered when designing the reverse arthroplasty and defining optimal surgical technique.

One-stage revision for patients with a chronically infected reverse total shoulder replacement

We retrospectively reviewed 11 consecutive patients with an infected reverse shoulder prosthesis. Patients were assessed clinically and radiologically, and standard laboratory tests were carried out. Peroperative samples showed Propionbacterium acnes in seven, coagulase-negative Staphylococcus in five, methicillin-resistant staphylococcus aureus in one and Escherichia coli in one. Two multibacterial and nine monobacterial infections were seen. Post-operatively, patients were treated with intravenous cefazolin for at least three days and in all antibiotic therapy was given for at least three months. Severe pain (3 of 11) or severe limitation of function (3 of 11) are not necessarily seen. A fistula was present in eight, but function was not affected. All but one patient were considered free of infection after one-stage revision at a median follow-up of 24 months, and without antibiotic treatment for a minimum of six months. One patient had a persistent infection despite a second staged revision, but is now free of infection with a spacer. Complications included posterior dislocation in one, haematoma in one and a clavicular fracture in one. At the most recent follow-up the median post-operative Constant-Murley score was 55, 6% adjusted for age, gender and dominance.

A one-stage revision arthroplasty reduces the cost and duration of treatment. It is reliable in eradicating infection and good functional outcomes can be achieved.

The effect of component positioning on intrinsic stability of the reverse shoulder arthroplasty

HYPOTHESIS

Anterior instability is one of the most common complications in reverse shoulder replacement. This study hypothesized that intrinsic stability of a reverse prosthesis varies with the degree of version of the humerus and glenoid components. This should provide guidelines on how to best position the implant components to decrease the rate of dislocation.

MATERIALS AND METHODS

Resistance to anterior dislocation of a reverse implant was measured in a mechanical testing machine by means of the stability ratio (ratio of peak dislocation/axial compressive forces). Versions of the humeral and glenoid components were modified in 10 degrees steps in the 90 degrees abducted and resting positions.

RESULTS

In both tested positions, the effect of humeral component version was highly significant. Only a glenoid component retroversion of 20 degrees led to a statistically significant drop in stability ratio for the 20 degrees abducted position. Intrinsic stability in the typical component positioning (neutral glenoid version and 20 degrees humeral retroversion) yielded comparably low intrinsic stability, which could only be improved by increasing anteversion of the humeral component.

DISCUSSION

Version of the humeral component is the critical factor for intrinsic stability. Version of the glenoid component is less important for intrinsic stability, but special care should be given to avoid retroversions of more than 10 degrees . Within this range, the surgeon can concentrate primarily on other parameters critical for long-term outcome (range of motion, secure fixation) when choosing the appropriate glenoid version.

CONCLUSION

Anterior stability can be improved by implanting the humeral component in neutral or with some anteversion.