Kinematic analysis of dynamic shoulder motion in patients with reverse total shoulder arthroplasty

Preoperative Planning Software Does Not Accurately Predict Range of Motion in Reverse Total Shoulder Arthroplasty

BACKGROUND

The purpose of this study was to determine whether preoperative planning software (PPS) accurately predicts clinical range of motion (ROM) in patients with reverse total shoulder arthroplasty 1 year postoperatively with preoperative and postoperative computed tomography (CT) scans.

METHODS

This was a retrospective study of 16 reverse total shoulder arthroplasty patients with preoperative and postoperative (CT) scans obtained at least 1 year postoperatively. Clinical ROM was measured in abduction, external rotation at resting abduction, extension, and flexion at a minimum of 1 year postoperatively. All clinical measurements were obtained before generation of PPS ROM values. Using postoperative CT scans, the achieved implant component positions were quantified and then replicated in PPS on the preoperative CT scans. The preoperative predicted ROM was then recorded, both with and without osteophyte removal. Bland-Altman plots were generated within each motion comparing the differences between clinically measured motion and software-predicted motion.

RESULTS

The variation in clinically measured ROM in abduction, external rotation at resting abduction, extension, and flexion were 118 ± 27 (65° to 180°), 33 ± 16 (10° to 75°), 56 ± 8 (50° to 65°), and 137 ± 25 (80° to 160°), respectively. Clinically measured motion differed greatly from PPS-predicted ROM, with mean differences of 33 ± 29 (-32 to 93) for abduction, 44 ± 25 (-38 to 57) for external rotation, 44 ± 25 (-35 to 65) for extension, and 54 ± 50 (-51 to 147) for flexion with no significant correlations between clinically measured and PPS-predicted ROM ( P > 0.05). With humeral or humeral and glenoid osteophyte resection, correlations for only flexion became significant ( P = 0.002 for both).

CONCLUSION

The passive glenohumeral impingement-free ROM generated from PPS incompletely predicts clinically measured active humerothoracic ROM, possibly because of the unmeasured factors of soft-tissue tension, muscular strength, humeral torsion, resting scapular posture, and, most importantly, scapulothoracic motion.

LEVEL OF EVIDENCE

IV.

Reversed total shoulder arthroplasty for rotator cuff arthropathy is associated with increased scapulothoracic motion: A longitudinal two-year kinematic study

BACKGROUND

Reversed total shoulder arthroplasty (RTSA) is a standard surgical procedure for the treatment of rotator cuff tear arthropathy (CTA), aimed at restoring active arm elevation. Shoulder elevation relies on both scapulothroacic (ST) and glenohumeral (GH) motion, but RTSA computer planning primarily focuses on the GH joint due to challenges in visualizing scapulothroacic (ST) motion.

RESEARCH QUESTION

Does the scapulohumeral rhythm, by means of the relative contributions of ST rotation and GH elevation per degree of arm elevation, in a longitudinal setting for up to two years postoperatively after RTSA for CTA change?

METHODS

In a prospective longitudinal study, shoulder kinematics were studied in 20 patients (22 shoulders) before and at three, six, 12, and 24 months after RTSA implantation for CTA. Skin markers were tracked using 3D motion analysis. The relative ST and GH contributions per degree of arm elevation were assessed and were compared using statistical non-parametric mapping with Bayesian inference.

RESULTS

Mean arm elevation was 89 ± 33° preoperatively, 135 ± 28° at 3 months, 161 ± 20° at 6 months, 169 ± 18° at 12 months, and 165 ± 19° at 24 months. Between 48-66°, 62-93°, 53-94°, 60-97° and 72-104° of arm elevation at the measurement time points pre, 3-months, 6-months, 12-months and 24-months postoperatively, respectively, the ST rotation had a significantly greater contribution to arm elevation compared to GH elevation; a pattern that was not found in controls.

SIGNIFICANCE

While RTSA successfully restored active arm elevation through improved GH and ST motion, the scapulohumeral rhythm exhibited a consistent pattern up to two years postoperatively, resembling the preoperative state. In the midrange of motion, ST rotation dominated over GH elevation, potentially contributing to muscular fatigue and explaining the documented decline in functional outcomes over time after RTSA. The findings highlight the importance of incorporating ST kinematics into modern computer planning for RTSA.

Analysis of in vivo humeral rotation of reverse total shoulder arthroplasty patients during shoulder abduction on the scapular plane with a load

BACKGROUND

Few studies have investigated the kinematics after reverse total shoulder arthroplasty (RTSA). This study aimed to compare the shoulder kinematics in RTSA patients during shoulder abduction on the scapular plane with and without a load and yield information regarding the function of stabilizing the joints against gravity for the functional assessment of the shoulder after RTSA, which could lead to changes in postoperative rehabilitation treatment.

METHODS

Twenty RTSA patients (7 men, 13 women; mean age: 78.1 [64-90] years) were examined. First, active shoulder abduction in the scapular plane was captured using single-plane fluoroscopic X-ray images. Imaging was performed by stipulating that one shoulder abduction cycle should be completed in 6 s. Two trials were conducted: one under a load equivalent to 2% of body weight and one without a load. Next, a three-dimensional (3D) model of each humeral and scapular component was matched to the silhouette of the fluoroscopic image to estimate the 3D dynamics. By using the 3D dynamic model obtained, the kinematics of the glenosphere and humeral implant were calculated relative to the shoulder abduction angle on the scapular plane and were compared between groups with and without a load. A one-way analysis of variance and a post hoc paired t-test with a statistical significance level of 0.05 were performed.

RESULTS

The humeral internal rotation decreased with a load at shoulder abduction between 40° and 90° on the scapular plane (P < 0.01, effect size: 0.15). No significant differences in scapular upward rotation (P = 0.57, effect size: 0.022), external rotation (P = 0.83, effect size: 0.0083) and posterior tilting (P = 0.74, effect size: 0.013) were observed between groups with and without a load. The main effect was not observed with and without a load (P = 0.86, effect size: 0.0072). However, the scapulohumeral rhythm was significantly greater without a load during shoulder joint abduction between 40° and 60° on the scapular plane.

CONCLUSION

In RTSA patients, the glenohumeral joint was less internally rotated, and the scapulohumeral rhythm decreased under loaded conditions. It was stabilized against the load through the mechanical advantage of the deltoid muscle and other muscles.

Comparison of Outcomes After Reverse Total Shoulder Arthroplasty in Patients With Proximal Humerus Fractures Versus Rotator Cuff Arthropathy

INTRODUCTION

Indications for reverse total shoulder arthroplasty (rTSA) has expanded to encompass complex proximal humerus fractures (PHFs) in recent years. The purpose of this study was to report and assess whether PHF patients treated with rTSA could achieve similar functional outcomes and short-term survivorship to patients who underwent rTSA for rotator cuff arthropathy (RTCA).

METHODS

All consecutive patients with a preoperative diagnosis of PHF or RTCA, 18 years or older, treated with rTSA at a single academic institution between 2018 and 2020 with a minimum 2-year follow-up were retrospectively reviewed. Primary outcomes were survivorship defined as revision surgery or implant failure analyzed using the Kaplan-Meier survival curve, and functional outcomes, which included Quick Disabilities of the Arm, Shoulder, and Hand, and range of motion (ROM) were compared at multiple follow-up time points up to 2 years. Secondary outcomes were patient demographics, comorbidities, surgical data, length of hospital stay, and discharge disposition.

RESULTS

A total of 48 patients were included: 21 patients (44%) were diagnosed with PHF and 27 patients (56%) had RTCA. The Kaplan-Meier survival rate estimates at 3 years were 90.5% in the PHF group and 85.2% in the RTCA group. No differences in revision surgery rates between the two groups (P = 0.68) or survivorship (P = 0.63) were found. ROM was significantly lower at subsequent follow-up time points in multiple planes (P < 0.05). A greater proportion of patients in the PHF group received cement for humeral implant fixation compared with the RTCA group (48% versus 7%, P = 0.002). The mean length of hospital stay was longer in PHF patients compared with RTCA patients (2.9 ± 3.8 days versus 1.6 ± 1.8 days, P = 0.13), and a significantly lower proportion of PHF patients were discharged home (67% versus 96%, P = 0.015).

CONCLUSION

The rTSA implant survivorship at 3 years for both PHF and RTCA patients show comparable results. At the 2-year follow-up, RTCA patients treated with rTSA were found to have better ROM compared with PHF patients.

Recovery of the shoulder kinematics after reverse shoulder arthroplasty

BACKGROUND

There is very limited information about the changes in shoulder kinematics in patients with reverse shoulder arthroplasty. The aim of the study was to investigate the changes in the scapulohumeral rhythm and shoulder kinematics over time after the reverse shoulder procedure.

METHODS

Nineteen patients with reverse shoulder arthroplasty (age: 65.8 ± 10.3 years) were included to the study. During arm elevation in the sagittal and scapular planes, operated shoulder kinematics (humerothoracic elevation, glenohumeral elevation, scapulohumeral rhythm, and scapular rotations) were assessed using an electromagnetic tracking system at the postoperative 3rd, 6th, and 18th months. Asymptomatic shoulder kinematics were also assessed at the postoperative 18th month. Shoulder function was assessed using The Disabilities of the Arm Shoulder and Hand score at the postoperative 3rd, 6th, and 18th months.

FINDINGS

Maximum humerothoracic elevation increased from 98° to 109° over the postoperative period (p = 0.01). The scapulohumeral rhythm was similar on the operated and asymptomatic shoulders at the final follow-up (p = 0.11). Both the operated and asymptomatic shoulder demonstrated similar scapular kinematics at the postoperative 18th month (p > 0.05). The Disabilities of the Arm Shoulder and Hand score decreased over time in the postoperative period (p < 0.05).

INTERPRETATION

Shoulder kinematics may be improved after reverse shoulder arthroplasty in the postoperative period. Focusing on scapular stabilization and deltoid muscle control in the postoperative rehabilitation program may enhance the shoulder kinematics and upper extremity function.

Preoperative Planning for Reverse Shoulder Arthroplasty: Does the Clinical Range of Motion Match the Planned 3D Humeral Displacement?

INTRODUCTION

The functional outcome after reverse shoulder arthroplasty (RSA) is closely linked to how much the humerus shifts because of the implants. While two-dimensional (2D) angle measurements have been used to capture this shift, it can be measured in three dimensions (3D) as the arm change position (ACP). In a previous study, the ACP was measured using 3D preoperative planning software with the passive virtual shoulder range of motion obtained after RSA. The main objective of this study was to evaluate the relationship between the ACP and the actual active shoulder range of motion measured after RSA. The hypothesis was that the ACP and the active clinical range of motion are related such that the ACP is a reliable parameter to guide the preoperative planning of an RSA. The secondary objective was to assess the relationship between 2D and 3D humeral displacement measurements.

MATERIALS AND METHODS

This prospective observational study enrolled 12 patients who underwent RSA and had a minimum follow-up of 2 years. The active range of motion in shoulder flexion, abduction, and internal and external rotation was measured. At the same time, ACP measurements were taken from a reconstructed postoperative CT scan, in addition to the radiographic measurements of humeral lateralization and distalization angles on AP views in neutral rotation.

RESULTS

The mean humeral distalization induced by RSA was 33.3 mm (±3.8 mm). A non-statistically significant increase in shoulder flexion was observed for humeral distalization beyond 38 mm (R² = 0.29, p = 0.07). This "threshold" effect of humeral distalization was also observed for the gains in abduction, as well as internal and external rotations, which seemed better with less than 38 mm or even 35 mm distalization. No statistical correlation was found between the 3D ACP measurements and 2D angle measurements.

CONCLUSION

Excessive humeral distalization seems to be detrimental to joint mobility, especially shoulder flexion. Humeral lateralization and humeral anteriorization measured using the ACP seem to promote better shoulder range of motion, with no threshold effect. These findings could be evidence of tension in the soft tissues around the shoulder joint, which should be taken into consideration during preoperative planning.

The Real Post-Operative Range of Motion Differs from the Virtual Pre-Operative Planned Range of Motion in Reverse Shoulder Arthroplasty

INTRODUCTION

The purpose of this study was to analyze the real range of motion (RoM) measured in patients operated on for reverse shoulder arthroplasty (RSA) and compare it to the virtual RoM provided by the preoperative planning software.

HYPOTHESIS

There was a difference between virtual and real RoM, which can be explained by different factors, specifically the scapula-thoracic (ST) joint.

METHODS

Twenty patients with RSA were assessed at a minimum follow-up of 18 months. Passive RoM in forward elevation abduction, without and with manually locking the ST joint, and in external rotation with arm at side were recorded. The humerus, scapula, and implants were manually segmented on post-operative CTs. Post-operative bony structures were registered to preoperative bony elements. From this registration, a post-operative plan corresponding to the real post-operative implant positioning was generated and the corresponding virtual RoM analysis was recorded. On the post-operative anteroposterior X-rays and 2D-CT coronal planning view, the glenoid horizontal line angle (GH), the metaphyseal horizontal line angle (MH), and the gleno-metaphyseal angle (GMA) were measured to assess the extrinsic glenoid inclination, as well as the relative position of the humeral and glenoid components.

RESULTS

There were some significant differences between virtual and post-operative passive abduction and forward elevation, with (55° and 50°, p < 0.0001) or without ST joint participation (15° and 27°, p < 0.002). For external rotation with arm at side, there was no significant difference between planning (24° ± 26°) and post-operative clinical observation (19° ± 12°) (p = 0.38). For the angle measurements, the GMA was significantly higher (42.8° ± 15.2° vs. 29.1°± 18.2°, p < 0.0001), and the GH angle, significantly lower on the virtual planning (85.2° ± 8.8° vs. 99.5° ± 12.5°, p < 0.0001), while the MH was not different (p = 0.33).

CONCLUSIONS

The virtual RoM given by the planning software used in this study differs from the real post-operative passive RoM, except for external rotation. This can be explained by the lack of ST joint and soft tissues simulation. However, in focusing on the virtual GH participation, the simulation looks informative. Some modifications between the glenoid and humerus starting positions before running the motion analysis could be provided for making it more realistic and predictive of the RSA functional results.

LEVEL OF EVIDENCE

III.

High and low performers in internal rotation after reverse total shoulder arthroplasty: a biplane fluoroscopic study

BACKGROUND

Internal rotation in adduction is often limited after reverse total shoulder arthroplasty (rTSA), but the origins of this functional deficit are unclear. Few studies have directly compared individuals who can and cannot perform internal rotation in adduction. Little data on underlying 3D humerothoracic, scapulothoracic, and glenohumeral joint relationships in these patients are available.

METHODS

Individuals >1-year postoperative to rTSA were imaged with biplane fluoroscopy in resting neutral and internal rotation in adduction poses. Subjects could either perform internal rotation in adduction with their hand at T12 or higher (high, N = 7), or below the hip pocket (low, N = 8). Demographics, the American Shoulder and Elbow Surgeons score, Simple Shoulder Test, and scapular notching grade were recorded. Joint orientation angles were derived from model-based markerless tracking of the scapula and humerus relative to the torso. The 3D implant models were aligned to preoperative computed tomography models to evaluate bone-implant impingement.

RESULTS

The Simple Shoulder Test was highest in the high group (11 ± 1 vs. 9 ± 2, P = .019). Two subjects per group had scapular notching (grades 1 and 2), and 3 high group and 4 low group subjects had impingement below the glenoid. In the neutral pose, the scapula had 7° more upward rotation in the high group (P = .100), and the low group demonstrated 9° more posterior tilt (P = .017) and 14° more glenohumeral elevation (P = .047). In the internal rotation pose, axial rotation was >45° higher in the high group (P ≤ .008) and the low group again had 11° more glenohumeral elevation (P = .058). Large rotational differences within subject groups arose from a combination of differences in the resting neutral and maximum internal rotation in adduction poses, not only the terminal arm position.

CONCLUSIONS

Individuals who were able to perform high internal rotation in adduction after rTSA demonstrated differences in joint orientation and anatomic biases versus patients with low internal rotation. The high rotation group had 7° more resting scapular upward rotation and used a 15°-30° change in scapular tilt to perform internal rotation in adduction versus patients in the low group. The combination of altered resting scapular posture and restricted scapulothoracic range of motion could prohibit glenohumeral rotation required to reach internal rotation in adduction. In addition, inter-patient variation in humeral torsion may contribute substantially to postoperative internal rotation differences. These data point toward modifiable implant design and placement factors, as well as foci for physical therapy to strengthen and mobilize the scapula and glenohumeral joint in response to rTSA surgery.

Scapulohumeral rhythm in shoulders with reverse shoulder arthroplasty measured with a new portable three-dimensional scapular kinematics assessment system

BACKGROUND

Reverse shoulder arthroplasty (RSA) is a valid and increasingly popular treatment option in eccentric arthrosis and cuff arthropathy. We know that the deltoid is the motor of RSA. However, the role of scapular motion has been poorly documented in the literature. The aim of our study is to analyze and quantify the role of the scapular contribution in the functional outcome of patients undergoing RSA.

MATERIALS AND METHODS

Fourteen patients who underwent primary RSA were included in the study. In all cases, a reverse prosthesis with lateralizing stem was implanted. All patients underwent clinical examination, video recording, and motion analysis. X-ray and postoperative CT examinations were collected to evaluate positioning and any loosening. ShowMotion (NCS Lab srl, Modena, Italy) 3D kinematic tracking system was used to evaluate and measure the scapular motion in 3 planes.

RESULTS

All patients show substantial amount of posterior tilting and lateral rotation starting at 30° in forward elevation. A further difference is the anticipation of the retraction during the range of motion in the RSA side. The contribution of scapular motion in the RSA shoulder was greater than in the healthy shoulder. In patients with bilateral RSA, the contribution of scapular motion was higher in tilting and lateral rotation in the worse shoulder side in terms of range of motion. This means that to compensate for the loss of glenohumeral motion in RSA, more scapula-thoracic motion is needed to obtain the same thoraco-humeral elevation angle.

CONCLUSIONS

In the light of what has been measured, the post-RSA scapular kinematics has typical characteristics that must be achieved in order to obtain a good functional outcome. We can conclude that on the RSA side, the patients anticipate upward rotation both in flexion and abduction. The contribution of the upward rotation to elevation in the RSA group is therefore more significant. In addition to this, to facilitate elevation movements, there is an anticipation of the scapular retraction and a more prominent tilt resulting in different scapular kinematics. The analysis of scapular motion could be useful in the postoperative follow-up of patients undergoing RSA surgery and improve adaptative physiotherapy protocols. It potentially can even be included in future arthroplasty planning systems.

The quantification of muscle activities during arm elevation following reverse shoulder arthroplasty or superior capsular reconstruction for irreparable rotator cuff tears using positron emission tomography

BACKGROUND

Reverse shoulder arthroplasty (RSA) and superior capsular reconstruction (SCR) are recognized as surgical options for an irreparable rotator cuff tear. However, the postoperative changes of the muscle activity patterns remain unclear. The purpose of this study was to investigate the quantified muscle activities on shoulder elevation in patients treated with RSA or SCR using fluorine-18-labelled fluorodeoxyglucose-positron emission tomography.

METHODS

Asymptomatic shoulders that underwent RSA or SCR and those without a rotator cuff tear were analyzed as the RSA, SCR, and control groups. All subjects underwent shoulder elevation exercise, followed by a fluorine-18-labelled fluorodeoxyglucose-positron emission tomography examination. Using previously established methods to quantify the uptake of each muscle on positron emission tomography images, the standard uptake values (SUVs) for 16 portions of the deltoid, rotator cuff, and periscapular muscles were obtained to compare the muscle activity patterns among 3 groups.

RESULTS

The deltoid muscle showed the most characteristic differences according to the surgeries. The mean SUVs of the anterior, middle, and posterior deltoid were 3.3, 3.7, and 1.5 for the RSA group; 2.7, 4.2, and 1.5 for the SCR group; and 1.3, 2.0, and 0.9 for the control group, respectively. In comparison to the control group, both the RSA and SCR groups showed significantly increased SUVs at all portions of the deltoid muscle. The RSA group showed similar SUVs for the anterior and middle deltoid, whereas the SCR and control groups showed greatest SUVs at the middle deltoid. In addition, the serratus anterior, levator scapulae, and upper portion of the trapezius in the RSA group showed greater SUVs than in the control group.

CONCLUSION

The deltoid muscle showed increased activity in the RSA and SCR groups. The middle deltoid was mainly used in the SCR group, whereas the anterior and middle deltoid, as well as the upward rotator muscles of the scapula, were mainly used in the RSA group.

Reverse total shoulder glenoid component inclination affects glenohumeral kinetics during abduction: a cadaveric study

BACKGROUND

Optimal implant placement in reverse total shoulder arthroplasty (rTSA) remains controversial. Specifically, the optimal glenoid inclination is unknown. Therefore, a cadaveric shoulder simulator with 3-dimentional human motion specific to rTSA was used to study joint contact and muscle forces as a function of glenoid component inclination.

METHODS

Eight human cadaver shoulders were tested before and after rTSA implantation. Scapular plane abduction kinematics from control subjects and those with rTSA drove a cadaveric shoulder simulator with 3-dimentional scapulothoracic and glenohumeral motion. Glenoid inclination varied from -20° to +20°. Outputs included compression, superior-inferior (S/I) shear, and anterior-posterior shear forces from a 6° of freedom load cell in the joint, and deltoid and rotator cuff muscle forces. Data were evaluated with statistical parametric mapping and t-tests.

RESULTS

Inferior glenoid inclination (-) reduced S/I shear by up to 125% relative to superior inclination, with similar compression to the neutral condition (0°). Superior inclinations (+) increased the S/I shear force by approximately the same magnitude, yet decreased compression by 25% in the most superior inclination (+20°). There were few differences in deltoid or rotator cuff forces due to inclination. Only the middle deltoid decreased by approximately 7% for the most inferior inclination (-20°). Compared with native shoulders, the neutral (0°) rTSA inclination showed reduced forces of 30%-75% in the anterior deltoid and a trend toward decreased forces in the middle deltoid. Force demands on the rotator cuff varied as a function of elevation, with a trend toward increased forces in rTSA at peak glenohumeral elevation.

CONCLUSIONS

Inferior inclination reduces superior shear forces, without influencing compression. Superior inclination increased S/I shear, while decreasing compression, which may be a source of component loosening and joint instability after rTSA. Inferior inclination of the rTSA glenoid may reduce the likelihood of glenoid loosening by reducing the magnitude of cyclic shear and compressive loading during arm elevation activities, although this may be altered by specific-subject body habitus and motion. These factors are especially important in revision rTSA or glenoid bone grafting where there is already a 3-fold increase in glenoid baseplate loosening vs. primary rTSA.

Reverse Total Shoulder Arthroplasty Alters Humerothoracic, Scapulothoracic, and Glenohumeral Motion During Weighted Scaption

BACKGROUND

Reverse total shoulder arthroplasty (rTSA) typically restores active arm elevation. Prior studies in patients with rTSA during tasks that load the arm had limitations that obscured underlying three-dimensional (3D) kinematic changes and the origins of motion restrictions. Understanding the scapulothoracic and glenohumeral contributions to loaded arm elevation will uncover where functional deficits arise and inform strategies to improve rTSA outcomes.

QUESTIONS/PURPOSES

In a cohort of patients who had undergone rTSA and a control cohort, we asked: (1) Is there a difference in maximum humerothoracic elevation when scapular plane elevation (scaption) is performed with and without a handheld weight? (2) Is maximum humerothoracic elevation related to factors like demographics, patient-reported outcome scores, isometric strength, and scapular notching (in the rTSA group only)? (3) Are there differences in underlying 3D scapulothoracic and glenohumeral motion during scaption with and without a handheld weight?

METHODS

Ten participants who underwent rTSA (six males, four females; age 73 ± 8 years) were recruited at follow-up visits if they were more than 1 year postoperative (24 ± 11 months), had a BMI less than 35 kg/m 2 (29 ± 4 kg/m 2 ), had a preoperative CT scan, and could perform pain-free scaption. Data from 10 participants with a nonpathologic shoulder, collected previously (five males, five females; age 58 ± 7 years; BMI 26 ± 3 kg/m 2 ), were a control group with the same high-resolution quantitative metrics available for comparison. Participants in both groups performed scaption with and without a 2.2-kg handheld weight while being imaged with biplane fluoroscopy. Maximum humerothoracic elevation and 3D scapulothoracic and glenohumeral kinematics across their achievable ROM were collected via dynamic imaging. In the same session the American Shoulder and Elbow Surgeons (ASES) score, the Simple Shoulder Test (SST), and isometric strength were collected. Data were compared between weighted and unweighted scaption using paired t-tests and linear mixed-effects models.

RESULTS

When compared with unweighted scaption, maximum humerothoracic elevation decreased during weighted scaption for patients who underwent rTSA (-25° ± 30°; p = 0.03) but not for the control group (-2° ± 5°; p = 0.35). In the rTSA group, maximum elevation correlated with the ASES score (r = 0.72; p = 0.02), and weighted scaption correlated with BMI (r = 0.72; p = 0.02) and the SST (r = 0.76; p = 0.01). Scapular notching was observed in three patients after rTSA (Grades 1 and 2). Four of 10 patients who underwent rTSA performed weighted scaption to less than 90° humerothoracic elevation using almost exclusively scapulothoracic motion, with little glenohumeral contribution. This manifested as changes in the estimated coefficient representing mean differences in slopes in the humerothoracic plane of elevation (-12° ± 2°; p < 0.001) and true axial rotation (-16° ± 2°; p < 0.001), scapulothoracic upward rotation (7° ± 1°; p < 0.001), and glenohumeral elevation (-12° ± 1°; p < 0.001), plane of elevation (-8° ± 3°; p = 0.002), and true axial rotation (-11° ± 2°; p < 0.001). The control group demonstrated small differences between scaption activities (< |2°|), but a 10° increase in humerothoracic and glenohumeral axial rotation (both p < 0.001).

CONCLUSION

After rTSA surgery, maximum humerothoracic elevation decreased during weighted scaption by up to 88° compared with unweighted scaption, whereas 4 of 10 patients could not achieve more than 90° of elevation. These patients exhibited appreciable changes in nearly all scapulothoracic and glenohumeral degrees of freedom, most notably a near absence of glenohumeral elevation during weighted scaption. Patients with rTSA have unique strategies to elevate their arms, often with decreased glenohumeral motion and resultant compensation in scapulothoracic motion. In contrast, the control group showed few differences when lifting a handheld weight.

CLINICAL RELEVANCE

Functional deficiency in activities that load the shoulder after rTSA surgery can affect patient independence, and they may be prevalent but not captured in clinical studies. Pre- or postoperative rehabilitation to strengthen scapular stabilizers and the deltoid should be evaluated against postoperative shoulder function. Further study is required to determine the etiology of deficient glenohumeral motion after rTSA, and the most effective surgical and/or rehabilitative strategies to restore deficient glenohumeral motion after rTSA.

Development of a framework to assess the biomechanical impact of reverse shoulder arthroplasty placement modifications

Reverse shoulder arthroplasty biomechanics can be improved by modifying the placement of prosthesis. Biomechanical studies have quantified the impact of placement modifications on the mobility and stability of the reverse shoulder. While these studies have provided detailed insights, direct comparisons between their finding are obfuscated by their use of differing methodologies. The aim of our study was to develop an assessment framework which used musculoskeletal simulations to consistently evaluate the biomechanics of various placement modifications. We conducted musculoskeletal simulations of humeral elevations and rotations using 15 reverse shoulder models. For each model, these simulations were conducted for a reference configuration of the prosthesis, established using surgical guidelines, and 34 modified configurations, which were based on commonplace adaptations to the placement of the glenosphere and humeral tray. The effect of each modified configuration on deltoid elongation, deltoid moment arm (DMA), joint stability, and impingement-free range of motion (IFROM) was determined relative to the reference configuration. We found that 16 of the 34 modified placements had an overall beneficial impact on reverse shoulder biomechanics. Within this subset, we identified two biomechanical trade-offs. First, there is an antagonistic relationship between IFROM and both the DMA and joint stability. Second, functional requirements differ between humeral elevations and rotations. Furthermore, we found that posteromedial translation of the humeral tray had the most beneficial impact on joint stability and inferior translation of the glenosphere had the most beneficial impact on IFROM and DMA.

Nonoperative treatment of acromial fractures following reverse shoulder arthroplasty: clinical and radiographic outcomes

BACKGROUND

Acromion/scapular spine fractures (ASFs) remain a challenging complication following reverse shoulder arthroplasty (RSA). Historically, nonoperative management has been the treatment of choice, with variable results. The purpose of this study is to report on both clinical and radiographic outcomes of nonoperative treatment. A new subclassification of Levy type II acromion fractures will be proposed, and outcomes will be evaluated in relation to the modified Levy classification.

METHODS

Forty-four patients diagnosed with ASF following RSA were matched 1:3 to a control group based on gender, age, and preoperative function. All ASF patients were treated nonoperatively. Patient-reported outcome measures, consisting of American Shoulder and Elbow Surgeons Standardized Shoulder Assessment Form, Simple Shoulder Test, Single Assessment Numerical Evaluation, visual analog scale pain and function scores, satisfaction, and active range of motion were gathered preoperatively and at the most recent follow-up. Outcomes were stratified based on fracture type. Radiographic findings including fracture union, scapular rotation, progressive notching, and osteolysis were reviewed from latest follow-up and compared with initial postoperative films.

RESULTS

ASFs were identified at a median of 2 months following RSA (8 type I; 22 type II; 14 type III), followed for a median of 37 months and compared to 108 matched controls. Patients with ASF had inferior clinical outcomes with a higher rate of dissatisfaction (27.8%) when compared to controls. Lateral fracture subtypes (I and IIA) were similar to controls and had little impact on outcomes. However, medial fracture subtypes (type IIB, IIC, and III) demonstrated inferior outcomes when compared to controls, with type III fracture patients demonstrating no improvement from baseline. The overall nonunion rate was 61.4%, with high rates of scapular rotation and osteolysis in medial fracture subtypes. Nonunion was associated with a higher incidence of secondary radiographic findings, including scapular rotation, progressive notching, and osteolysis.

CONCLUSION

Results of nonoperative treatment of ASF following RSA differs based on fracture location. Fractures that occur at or medial to the glenoid face (IIB, IIC, III) demonstrate high rates of unsatisfactory results and worse clinical outcomes. Concerning radiographic findings of scapular tilt, progressive scapular notching and osteolysis were seen at a higher rate with medial fracture types and fracture nonunions.

Implant characteristics affect in vivo shoulder kinematics during multiplanar functional motions after reverse shoulder arthroplasty

The purpose of this study was to determine how implant characteristics affect in vivo shoulder kinematics after reverse shoulder arthroplasty (RSA). Kinematics of the affected upper limb were measured in 32 participants during five motions (scapular plane abduction, hand-to-head, hand-to-back, internal/external rotation at 90° abduction, and circumduction) using optical motion capture. Shoulder abduction, plane of elevation, and internal/external rotation range of motion (ROM), peak angles, and continuous kinematics waveforms were calculated for each motion. Multiple regression was used to identify associations between kinematics and implant characteristics of lateralization, humeral retroversion, glenosphere size, glenosphere tilt, glenoid eccentricity, and implant neck-shaft angle (135° or 145°). Less humeral retroversion was associated with greater shoulder rotation ROM (p = 0.036) and greater plane of elevation ROM (p = 0.024) during circumduction, while less eccentricity was associated with more posterior plane of elevation during hand-to-back (p = 0.021). The 145° implant was associated with greater internal/external shoulder rotation ROM (p < 0.001), greater internal shoulder rotation (p = 0.002), and greater plane of elevation ROM (p = 001) during the hand-to-back. The 145° implant was also associated with more internal/external rotation ROM (p = 0.043) during shoulder rotation and more abduction ROM during circumduction (p = 0.043). During the hand-to-back motion, individuals having 135° neck-shaft angle implants were more abducted from 21 to 51% of the motion and were less internally rotated from 70 to 100% of the motion, while more lateralization was associated with less internal rotation from 90 to 100% of the motion. Retroversion and implant neck-shaft angle are the primary implant characteristics associated with in vivo shoulder kinematics during complex motions after RSA.

Three-dimensional kinematic evaluation of scapulohumeral rhythm after reverse shoulder arthroplasty: a systematic review and meta-analysis

Background

The movement of the arm relative to the trunk results from 3-dimensional (3D) coordinated movements of the glenohumeral (GH) and scapulothoracic (ST) joints and dictates the scapulohumeral rhythm (SHR). Alterations in SHR increase joint overload and may lead to low functional scores, pain, and failures in patients undergoing reverse total shoulder arthroplasty (RSA). The goal of this systematic review and meta-analysis was to examine 3D SHR kinematics after RSA and compare it to that of asymptomatic shoulders.

Methods

A systematic review and meta-analysis of articles in English were performed using PubMed, Embase, Cochrane Library, and SciELO. Additional studies were identified by searching bibliographies. Search terms included "Reverse shoulder arthroplasty", "3D", and "scapula". It was selected cross-sectional studies that reported SHR with 3D motion analysis systems in patients who underwent RSA and asymptomatic controls. Two authors independently performed the extraction of articles using predefined data fields, including study quality indicators.

Results

Data from four studies were included in quantitative analysis, totaling 48 shoulders with RSA and 63 asymptomatic shoulders. Pooled analyses were based on random-effects model (DerSimonian-Laird). A statistically smaller SHR ratio was observed in the RSA group than that in the control group (P < .00001), meaning a greater contribution of ST joint in relation to GH joint for arm elevation. The standardized mean difference was -1.16 (95% confidence interval: -1.64, -0.67). A sensitivity analysis with three more studies that had imputed data on control group did not change the direction of the effect. The standardized mean difference on sensitivity analysis was -0.60 (P = .03; 95% confidence interval: -1.13, -0.06). It was detected as "not important heterogeneity" within the comparison (I2: 22%). Chi-square was not statistically significant (Chi2: 3.85), and I2 was 22%. Tau2 was not zero (Tau2: 0.05). Sensitivity analysis showed an I2 of 74%, which might represent substantial heterogeneity, Chi-square was not statistically significant (Chi2: 23.01), and Tau2 was not zero (Tau2: 0.37).

Conclusion

This study found that RSA shoulders have an increased contribution of ST joint during arm elevation, compared with asymptomatic shoulders. More movement in ST joint in proportion to GH joint increases GH joint contact forces, which could lead to component loosening or other complications. Further studies should address the clinical implications of this kinematic finding.

Biomechanics of anatomic and reverse shoulder arthroplasty

The biomechanics of the shoulder relies on careful balancing between stability and mobility. A thorough understanding of normal and degenerative shoulder anatomy is necessary, as the goal of anatomic total shoulder arthroplasty is to reproduce premorbid shoulder kinematics.With reported joint reaction forces up to 2.4 times bodyweight, failure to restore anatomy and therefore provide a stable fulcrum will result in early implant failure secondary to glenoid loosening.The high variability of proximal humeral anatomy can be addressed with modular stems or stemless humeral components. The development of three-dimensional planning has led to a better understanding of the complex nature of glenoid bone deformity in eccentric osteoarthritis.The treatment of cuff tear arthropathy patients was revolutionized by the arrival of Grammont's reverse shoulder arthroplasty. The initial design medialized the centre of rotation and distalized the humerus, allowing up to a 42% increase in the deltoid moment arm.More modern reverse designs have maintained the element of restored stability but sought a more anatomic postoperative position to minimize complications and maximize rotational range of motion. Cite this article: EFORT Open Rev 2021;6:918-931. DOI: 10.1302/2058-5241.6.210014.

A kinematic and electromyographic comparison of a Grammont-style reverse arthroplasty combined with a l'Episcopo transfer compared to a lateralized humeral component reverse for restoration of active external rotation

PURPOSE

To assess kinematic and electromyographic findings of two designs of reverse total shoulder arthroplasty (RTSA). We tested two hypotheses: (H₁) Grammont-style (RTSA) with l'Episcopo tendon transfer gains similar postoperative kinematic findings of a lateralized humeral component RTSA without a tendon transfer; (H₂) RTSA with lateralized humeral component induces earlier shoulder muscle activation during shoulder motion compared with standard Grammont prosthesis with l'Episcopo transfer.

METHODS

Twenty-five patients with a cuff tear arthropathy, pseudoparalysis, and a positive dropping sign were sequentially included. A Grammont-style RTSA with a l'Episcopo tendon transfer was implanted in 13 patients (medialized humerus and transfer group) and an on-lay curved-stem RTSA in 12 (lateralized humerus group). Constant score; the disabilities of the arm, shoulder, and hand (DASH) score; and active shoulder range of motion (flexion, abduction, external rotation, and internal rotation) were measured pre- and postoperatively. Upper limb kinematic and surface electromyography (EMG) (anterior and posterior deltoid; upper, middle, and lower trapezius; and the upper and lower latissimus dorsi muscles) were recorded during active range of motion.

RESULTS

At > 24 months of follow-up, the Constant and DASH scores and active shoulder range of motion improved in both groups (p < 0.0001). Internal rotation was significantly higher in the lateralized humerus group than in the medialized humerus and transfer group (p = 0.004). The dropping sign was found in 0/12 patients in the lateralized humerus group and in 5/13 patients in the medialized humerus and transfer group (p < 0.001). Kinematic findings were similar between groups (p = 0.286). A pattern of earlier muscle activation in the lateralized humerus group was found as compared to the transfer group as follows: (i) posterior deltoid during external rotation (p = 0.004); (ii) upper latissimus dorsi and middle and lower trapezius during flexion (p = 0.004, p = 0.005, and p = 0.042, respectively); (iii) lower latissimus dorsi during abduction (p = 0.016).

CONCLUSION

RTSA with a lateralized humeral component provided similar active external rotation restoration to a Grammont-style RTSA with a l'Episcopo procedure in patients with a dropping sign. The posterior deltoid muscle underwent earlier activation during active external rotation in the lateralized humerus RTSA group as compared to the tendon transfer group. Our findings demonstrated the H₁ and only partially demonstrated the H₂ of the study.

Scapular and humeral elevation coordination patterns used before vs. after Reverse Total Shoulder Arthroplasty

The purpose of this study was to compare scapulohumeral coordination used before and after Reverse Total Shoulder Arthroplasty (RTSA) during the ascent phase of scapular plane arm elevation tasks performed with varied shoulder rotations (neutral, external rotation, and internal rotation). We expected that after RTSA, participants would decrease scapulothoracic upward rotation angular displacement and increase the scapulohumeral rhythm (SHR) vs. before RTSA. 11 RTSA patients (12 shoulders) participated in this study before and after RTSA while optical motion capture measured kinematics of the humerus and scapula relative to the thorax. Angular kinematics were compared pre vs. post-RTSA within-participant using One Dimensional Statistical Parametric Mapping (SPM) t-tests (α = 0.05) and across-participants, using paired t-tests (α = 0.05) adjusted for multiple comparisons. As a group, during arm elevation with neutral rotation, the mean (SD) SHR pre-RTSA was 1.5 (0.5) and increased to 1.7 (0.3) post-RTSA, though, not significantly (p = 0.182). In contrast, during arm elevation with external rotation, the mean (SD) SHR pre-RTSA was 1.3 (0.4) and significantly increased (p = 0.018) post-RTSA to 1.7 (0.3). Likewise, during arm elevation with internal rotation, the mean (SD) SHR pre-RTSA was 1.2 (0.3) and significantly increased (p < 0.001) post-RTSA to 1.7 (0.2). In addition to these and other group trends, participant-specific patterns were uncovered through SPM analyses - with some participants significantly increasing and others significantly decreasing scapulothoracic angular displacements across humerothoracic elevation ranges. Both before and after RTSA, scapulohumeral rhythm ratios were within the range of those previously reported in post-RTSA patients and were smaller than those used by healthy populations.

Factors influencing functional internal rotation after reverse total shoulder arthroplasty

Background

Functional internal rotation (fIR) of the shoulder is frequently limited after reverse shoulder arthroplasty (RTSA). The objective of this study was to study a cohort of satisfied patients after RTSA who had comparable active mobility except for fIR and to identify factors associated with selective loss of fIR.

Methods

A retrospective cohort study was conducted to compare 2 patient groups with either poor (≤ 2 points in the Constant-Murley score [CS]) or excellent (≥8 points in CS) fIR after RTSA at a minimum follow-up of 2 years. Influencing factors (demographic, surgical or implant related, radiographic parameters) and clinical outcome were analyzed.

Results

Fifty-two patients with a mean age of 72.8 (±9.3) and a mean follow-up of 41 months were included in the IR≤2 group and 63 patients with a mean age of 72.1 (±8.0) and a mean follow-up of 59 months in the IR≥8 group. All patients had undergone RTSA with the same implant type and only 2 different glenosphere sizes (36 and 40) for comparable indications. A multivariate analysis identified the following significant risk factors for poor postoperative fIR: poor preoperative fIR (pts in CS: 3 [range: 2-6] vs. 6 [range: 4-8], P<.0001), smoking (17.3% vs. 6.5%, P = .004), male gender (59.6% vs. 31.7%, P = .002), less preoperative to postoperative distalization of the greater tuberosity (Δ 19.4 mm vs. 22.2 mm, P = .026), a thin humeral insert (≤3 mm: 23.1% vs. 54.8%, P = .039), and a high American Society of Anesthesiologists score (≤ III: 30.8% vs. 14.3%, P = .043). Subscapularis repair status and glenosphere size had no influence on fIR. Clinical outcome scores improved in both groups from preoperatively to last follow-up. The IR≥8 group had overall significantly better outcome scores compared to the IR≤2 group (Δ 9.3% SSV and Δ 9.5% relative CS, P < .0001). There was no difference in CS between the cohorts when the score for fIR was discarded.

Conclusion

Independent risk factors for poor postoperative fIR after RTSA are poor preoperative fIR, smoking, male gender, less preoperative to postoperative distalization of the greater tuberosity, a thin humeral insert height, and a high American Society of Anesthesiologists score. Except for male gender, these factors are modifiable. These findings may be a valuable addition to patient counselling as well as preoperative planning and preoperative and intraoperative decision-making. The relevance of fIR for overall satisfaction is substantiated by this study.

Is limited shoulder abduction associated with poor scapulothoracic mobility after reverse shoulder arthroplasty?

INTRODUCTION

The contribution of the glenohumeral joint to shoulder abduction is acknowledged as an important factor for reverse total shoulder arthroplasty (RTSA) patients. In contrast, the degree of scapulothoracic joint contribution and its relation to RTSA patients with poor to excellent shoulder abduction are unclear.

MATERIALS AND METHODS

Twenty-three selectively recruited patients (74 ± 7 years, 11 males) with shoulder abduction ranging from poor to excellent at least 6 months after primary, unilateral RTSA participated in this study. Individual scapulothoracic and glenohumeral contributions at maximum shoulder abduction in the scapular plane were measured using 3D motion capture and correlations between scapulothoracic and glenohumeral contributions to shoulder abduction were assessed. Multiple regression analysis was used to determine the influence of age, body mass index, follow-up period, abduction strength and passive glenohumeral mobility on scapulothoracic and glenohumeral function.

RESULTS

Maximum shoulder abduction (range 48°-140°) was not significantly correlated with the scapulothoracic contribution (range 39°-75°, r = 0.40, p = 0.06), but there was a strong and significant correlation with the glenohumeral contribution (range - 9°-83°, r = 0.91, p < 0.001). Abduction strength was strongly associated with glenohumeral (p = 0.006) but not scapulothoracic (p = 0.34) joint contributions.

CONCLUSIONS

Limited shoulder abduction is not associated with insufficient scapulothoracic mobility, which rather provides a basic level of function for RTSA patients. Good to excellent shoulder abduction could only be achieved by increasing the glenohumeral contribution that was associated with postoperative abduction strength.

In vivo three-dimensional scapular kinematic alterations after reverse total shoulder arthroplasty

BACKGROUND

In vivo three-dimensional (3D) kinematics of the scapula after reverse total shoulder arthroplasty (rTSA) have been sparsely investigated. The aim of this study was to analyze static and dynamic kinematic alterations of the scapula after rTSA in vivo with the use of computer-aided 3D reconstruction program.

METHODS

A total of 15 patients with cuff tear arthropathy treated by rTSA participated. Scapulae with rTSA and the contralateral scapulae were evaluated with computed tomography scan data in 0° and 120° forward flexion positions of the glenohumeral joint. To examine static scapular kinematic alterations, the angular position and distance from the thorax were evaluated in the shoulder neutral position. 3D rotational and translational movements of the scapula in relation to the thorax were also measured during arm elevation to evaluate dynamic scapular kinematic alterations.

RESULTS

Scapulae with rTSA were more anteriorly tilted in the sagittal plane and more internally rotated in the axial plane than were the contralateral scapulae. However, no significant differences were observed in the upward rotated position in the coronal plane or in the distance from the thorax in any plane between the scapulae with rTSA and the contralateral scapulae. In dynamic analyses, upward rotational movement in the coronal plane, external rotation in the axial plane, and posterior tilting in the sagittal plane showed significant differences between the scapulae with rTSA and the contralateral scapulae during elevation. In contrast, translational movements in coordination revealed no statistical differences between the two scapular groups except for lateral translation.

CONCLUSION

Data from the 3D reconstruction program showed that rTSA might result in static positional changes and dynamic movement alterations.

LEVEL OF EVIDENCE

Therapeutic, IV.

Age-related differences in humerothoracic, scapulothoracic, and glenohumeral kinematics during elevation and rotation motions

Age affects gross shoulder range of motion (ROM), but biomechanical changes over a lifetime are typically only characterized for the humerothoracic joint. Suitable age-related baselines for the scapulothoracic and glenohumeral contributions to humerothoracic motion are needed to advance understanding of shoulder injuries and pathology. Notably, biomechanical comparisons between younger or older populations may obscure detected differences in underlying shoulder motion. Herein, biplane fluoroscopy and skin-marker motion analysis quantified humerothoracic, scapulothoracic, and glenohumeral motion during 3 static poses (resting neutral, internal rotation to L4-L5, and internal rotation to maximum reach) and 2 dynamic activities (scapular plane abduction and external rotation in adduction). Orientations during static poses and rotations during active ROM were compared between subjects <35 years and >45 years of age (N=10 subjects per group). Numerous age-related kinematic differences were measured, ranging 5–25°, where variations in scapular orientation and motion were consistently observed. These disparities are on par with or exceed mean clinically important differences and standard error of measurement of clinical ROM, which indicates that high resolution techniques and appropriately matched controls are required to avoid confounding results of studies that investigate shoulder kinematics. Understanding these dissimilarities will help clinicians manage expectations and treatment protocols where indications and prevalence between age groups tend to differ. Where possible, it is advised to select age-matched control cohorts when studying the kinematics of shoulder injury, pathology, or surgical/physical therapy interventions to ensure clinically important differences are not overlooked.

Kinematics and EMG activity in Reverse Total Shoulder Arthroplasty

INTRODUCTION

Patients undergoing a Reverse Total Shoulder Arthroplasty (RTSA) often have functional limitations that affect the range of motion of the shoulder. These limitations are not mechanical in nature, but instead linked to a reduced ability to generate muscle force. The specific aims of this study was to offer a comparison between the muscle activity generated by a post-operative RTSA shoulder in a patient to that of their contralateral shoulder during a series of functional activities.

MATERIAL & METHODS

A convenience sample of 10 subjects between the ages of 50-75 years of age were recruited. EMG and kinematic data were concomitantly collected while subjects completed tasks that included common activities of daily living.

RESULTS

The main findings of this study were that all sub regions of the deltoid functioned as abductors, versus the native shoulder where the middle deltoid primarily works in abduction. For the scapular elevation activity there was a significant difference in flexion between the surgical and contralateral shoulder (p < .001), with the surgical shoulder having nearly 30° less range of motion.

CONCLUSION

Anticipating limitations in functional outcomes and range of motion for patients after RTSA may inform patient decision-making and improve clinical evaluations. The finding of increased mid deltoid function during lifting activity has implications for rehabilitation and encouraging protocols that strengthen the deltoid in concentric motions. Additionally, the decreased scapular elevation found in this study may guide rehabilitation focusing on regaining range of motion post-operatively.

How Do Scapulothoracic Kinematics During Shoulder Elevation Differ Between Adults With and Without Rotator Cuff Arthropathy?

BACKGROUND

Rotator cuff arthropathy with loss of active arm elevation can be successfully treated with nonanatomic reverse total shoulder arthroplasty to restore active elevation. Shoulder kinematics in this context predominantly focus on glenohumeral motion, neglecting scapular motion, although both substantially contribute to global shoulder motion. Because scapular kinematics are difficult to assess clinically and in the laboratory, they are not well understood and therefore are often reduced to glenohumeral models with a static scapula.

QUESTIONS/PURPOSES

(1) Does the scapulohumeral rhythm (scapular rotation/glenohumeral elevation ratio) change during arm elevation? (2) Is there any scapular motion before arm elevation becomes clinically visible? (3) How do scapulothoracic kinematics during shoulder elevation differ between adults with and without rotator cuff arthropathy?

METHODS

This was a comparative kinematics study of 20 young adult volunteers (reference group) without rotator cuff impairment (seven females, 13 males; mean age: 27 ± 3.5 years) and 20 patients (22 shoulders) with cuff tear arthropathy (10 females, 10 males; mean age: 74 ± 6.2 years). We used a three-dimensional (3-D) motion analysis system from Vicom with eight high-speed infrared cameras (frame rate 200 Hz) and 25 skin markers. Kinematics were studied for scapulothoracic and glenohumeral movements using the Upper Limb Evaluation in Movement Analysis (ULEMA) open-source model. The main motion studied was active arm elevation in the scapular plane. After data cleaning, modeling, and normalization, changes of scapulohumeral rhythm and scapular motion at the beginning of arm elevation were analyzed qualitatively, and statistical parametric mapping was applied to study the difference in scapulothoracic kinematics between adults with and without rotator cuff arthropathy.

RESULTS

The scapular rhythm changes continuously during elevation. Whereas in people without rotator cuff arthropathy, a homogenous proportional relative angular contribution between 85° and 120° could be observed, this regular pattern was disturbed in patients with rotator cuff arthropathy. We observed medial scapular rotation before arm elevation became visible, followed by low lateral or even medial scapular rotation (approximately up to 25°) at the beginning of arm elevation. Patients with rotator cuff arthropathy exhibited more scapulothoracic motion between 50° and 93° of elevation than the reference group.

CONCLUSIONS

Our study introduces a double-normalized data analysis that allows for a more detailed assessment of complex scapular kinematics in a noninvasive way. Scapulothoracic motion is more complex than previously reported, especially in patients with rotator cuff arthropathy. The scapulohumeral rhythm changes dynamically throughout arm elevation. There is counter-directed scapular rotation because of muscular engagement before clinically visible arm elevation. Compared with the homogenous shoulder kinematics in the reference group, patients with rotator cuff arthropathy show a different pattern with predominantly scapular motion in the range between 50° and 93° of arm elevation.

CLINICAL RELEVANCE

The findings of this study suggest that there is a specific pattern of scapular motion during arm elevation in patients with rotator cuff arthropathy. Our study introduces a new noninvasive method that allows for simultaneous analysis of glenohumeral and scapular kinematics. This will enable to investigators explore whether active arm elevation and the physiological motion pattern can be restored after, for example, reverse total shoulder arthroplasty despite a nonanatomic prosthesis configuration.

Scapulohumeral rhythm in patients after total shoulder arthroplasty compared to age-matched healthy individuals

PURPOSE

The coordination of the glenohumeral joint and the shoulder girdle has been known as scapulohumeral rhythm. The effects of anatomical total shoulder arthroplasty (aTSA) are still subject to research. Former studies showed a higher amount of scapula lateral rotation to compensate for reduced glenohumeral elevation. The purpose of the present study was to confirm this mechanism and examine additional effects on the sternoclavicular and acromioclavicular joints' kinematics.

METHODS

3D motion analysis was used to examine 23 shoulders of 16 patients with a mean age of 71.2 (SD: 5.2) years with a mean follow up of 5.4 (SD: 2.1) years after aTSA and to compare kinematics and coordination to 22 shoulders of 11 healthy age-matched individuals with a mean age of 69.6 (SD: 5.3) years while performing elevation movement in frontal and sagittal plane.

RESULTS

The ratio of glenohumeral to shoulder girdle contribution was reduced compared to healthy individuals: Shoulder girdle contribution to elevation was 36.5% (SD: 8.1) in the aTSA group vs. 28.5% (SD: 8.2) in the control group in the sagittal plane and 38.1% (SD: 9.1) vs. 30.2% (SD: 7.1) in the frontal plane. Kinematics of the sternoclavicular and acromioclavicular joints showed significantly different patterns.

CONCLUSION

Patients after aTSA showed altered shoulder girdle kinematics and higher contribution of the shoulder girdle towards elevation. Whether this is a result of the surgery, of limited glenohumeral range of motion or due to the preoperative status remains unclear. Further investigation with a prospective study design is necessary.

Rehabilitation After Anatomic and Reverse Total Shoulder Arthroplasty: A Critical Analysis Review

Postoperative rehabilitation is believed to be essential in optimizing clinical outcome and function following shoulder arthroplasty. Despite this long-held notion, there is a paucity of high-quality evidence to guide rehabilitation protocols and practice. For patients undergoing anatomic total shoulder arthroplasty (ATSA), there are insufficient comparative data regarding type or duration of sling utilization. Based on current evidence, there is no appreciable benefit to early motion compared with a delayed-motion protocol following ATSA. There is insufficient literature to support the use of formal physical therapy over a physician-directed program following ATSA. At the present time, no high-quality evidence exists to guide the postoperative rehabilitation of patients undergoing reverse total shoulder arthroplasty (RTSA). Prospective randomized controlled trials evaluating postoperative management and rehabilitation following ATSA and RTSA are needed to guide best practices and optimize clinical outcomes.

Difficulty in performing activities of daily living associated with internal rotation after reverse total shoulder arthroplasty

BACKGROUND

Reverse total shoulder arthroplasty (RSA) is a widely accepted treatment for irreparable massive rotator cuff tear (mRCT) and cuff tear arthropathy (CTA), but its impact on activities of daily living (ADLs) remains unclear.

METHODS

We retrospectively analyzed 77 patients (age range, 54-87 years; follow-up range, 36.1-120.3 months) with irreparable mRCT and CTA treated by medialized RSA between 2008 and 2015. Ten activities considered essential for daily living were selected and scored from 0 to 3.

RESULTS

The mean visual analog scale scores during motion and University of California at Los Angeles and Constant scores significantly improved at final follow-up (all P < .001). Active forward flexion, external rotation at the side, and internal rotation to the posterior (IRp) were 92.5%, 79.6%, and 48.4% of the contralateral side, respectively, at final follow-up. Active forward flexion and external rotation at the side recovered within 6 months after surgery, similar to the level at final follow-up, but IRp did not reach the preoperative status until final follow-up. ADLs with mean scores of less than 2.0 at final follow-up were "wash the opposite shoulder," "wash the opposite axilla," "use a back pocket," "manage the toilet," and "wash the back" (only 36.4% of patients were able to wash their back at final follow-up).

CONCLUSIONS

RSA for irreparable mRCT and CTA showed satisfactory clinical outcomes. However, IRp was associated with a limited range compared with the other shoulder motions; therefore, all ADLs associated with internal rotation demonstrated lower recovery rates than expected.

Reverse total shoulder arthroplasty and resting radiographic scapular rotation

BACKGROUND

It remains unclear whether changes in scapular rotation influence the surgeon's ability to achieve resting radiographic neutral or inferior baseplate tilt at final follow-up. The purposes of this study were (1) to determine whether reverse total shoulder arthroplasty (RTSA) changes the resting scapular rotation, (2) to determine the association between glenoid inclination with respect to the scapula (β angle) and resting scapular rotation, and (3) to determine the β angle threshold that will most likely lead to resting radiographic neutral or inferior baseplate tilt relative to the thorax.

METHODS

This was a retrospective radiographic study. Patients with adequate-quality standing anteroposterior and Grashey radiographs obtained preoperatively and after primary RTSA at a minimum of 1 year were included. Glenoid inclination (β angle) was measured between the supraspinatus fossa and the glenoid. Resting scapular rotation was measured between the supraspinatus fossa and a vertical line. Baseplate tilt was then calculated as the angle between the glenoid and a vertical line.

RESULTS

The study included 74 patients with a mean follow-up period of 3 years (range, 1-9 years). Scapular rotation changed 2° ± 12° (mean ± standard deviation) into upward rotation (P = .048). No association was found between the β angle and scapular rotation. In 71% of patients with a neutral or inferior baseplate tilt, a postoperative β angle greater than 85° was found.

CONCLUSIONS

Resting radiographic scapular rotation changed 2° into upward rotation with RTSA and was not associated with the β angle. If the β angle is greater than 85°, resting radiographic baseplate tilt will most likely be inferior or neutral.

Clinical Predictors for Optimal Forward Elevation in Primary Reverse Total Shoulder Arthroplasty

Background

Few studies in the literature analyze clinical factors associated with superoptimal and suboptimal forward elevation in primary reverse total shoulder arthroplasty (RTSA). We investigate the functional outcome stratified by shoulder elevation 12 months after primary RTSA and its correlation with selected clinical patient factors.

Methods

We analyzed prospectively collected data within a comprehensive surgical database on patients who had undergone primary RTSA between June 2004 and June 2013. Two hundred eighty-six shoulders were stratified into 2 groups: group I for shoulders that had achieved at least 145° of active forward elevation 12 months postoperatively (90th percentile of active forward elevation, 29 shoulders) and group II for shoulders that never achieved at least 90° of active forward elevation 12 months postoperatively (10th percentile of active forward elevation, 28 shoulders). Statistical analysis associated independent clinical variables with postoperative motion using univariate analysis followed by logistic regression.

Results

Active shoulder elevation of at least 90° was achieved 12 months postoperatively in 259 subjects (90%). Upon comparison with group II (<90° elevation), subjects in group I (≥145° elevation) were found to have improved postoperative active elevation and relatively younger age, lower American Society of Anesthesiologists score, increased preoperative active elevation, increased shoulder strength, increased passive elevation, decreased elevation lag, increased active and passive external rotation, and improved validated outcome scores. When assessing significant preoperative variables, the only independent predictor of improved postoperative forward elevation was preoperative active forward elevation.

Conclusion

These findings illuminate significant factors in the ability to achieve functional active shoulder elevation after primary RTSA. They may help surgeons appropriately counsel patients about anticipated functional prognosis following primary RTSA.

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.

Scaption kinematics of reverse shoulder arthroplasty do not change after the sixth postoperative month

BACKGROUND

Changes over time in shoulder kinematics and function after reverse shoulder arthroplasty have not been reported. The purpose of this study was to compare shoulder kinematics and function at 6 months and 1 year after reverse shoulder arthroplasty.

METHODS

Twenty patients with a mean age of 74 years (range, 63-91 years) were enrolled in this study. Fluoroscopic images during scapular plane elevation were recorded at the mean of 6 months (range, 5-8 months) and 14 months (range, 11-21 months). CT-derived glenosphere models and computer-aided design humeral implant models were matched with the silhouette of the implants in the fluoroscopic images using model-image registration techniques. Glenosphere and humeral implant kinematics during scaption were compared between the two time points. Patients were also clinically examined with active range of motion and Constant score, and postoperative improvement in shoulder function were assessed.

RESULTS

Active flexion and Constant score improved after surgery (p < 0.001 for both), but there was no significant improvement after six months. There was no significant improvement in active external rotation at either postoperative exam. There were no significant differences in glenosphere or humeral kinematics between six months and one year.

INTERPRETATION

There was no significant additional improvement in either shoulder kinematics during scapular plane elevation or function between the sixth and twelfth postoperative months. We can assess kinematics at six months after reverse shoulder arthroplasty to determine how the shoulder will move. Clinically, treatment in the first six postoperative months should be emphasized to achieve better surgical outcomes.

Assessment of anatomical and reverse total shoulder arthroplasty with the scapula-weighted Constant-Murley score

AIM OF THE STUDY

To evaluate total (TSA) and reverse total shoulder arthroplasty (RTSA) using the Constant-Murley score (CMS) and the scapula-weighted (SW) CMS, an integrated outcome measure that takes into account the compensatory movements of the scapula.

METHODS

Twenty-five consecutive patients, 12 with TSA and 13 with RTSA, underwent kinematic analysis before and after shoulder replacement. Measurements included flexion (FLEX) and abduction (ABD) for the humerus and Protraction-Retraction (PR-RE), Medio-Lateral rotation (ME-LA), and Posterior-Anterior tilting (P-A) for the scapula. They were recorded at baseline (T0) and at six (T1) and 12 months (T2). Reference data were obtained from 31 control shoulders.

RESULTS

At T1, differences in CMS and SW-CMS were not significant in either group, whereas values at T2 were significantly lower in RTSA patients (p = 0.310 and p = 0.327, respectively). In TSA shoulders, the compensatory scapular movements in FLEX were all reduced from T0 to T2, whereas P-A was increased in ABD. In RTSA patients, the compensatory scapular movements in FLEX showed a general reduction at T1, with an increase in P-A at T2, whereas in ABD, all increased at T1 and decreased at T2 except for P-A, which did not decrease.

DISCUSSION

The SW-CMS showed that the physiological scapulothoracic motion was not restored in TSA and RTSA patients; it may be used as a reference for the gradual progression of deltoid and scapular muscle rehabilitation.

CONCLUSIONS

The worse CMS and SW-CMS scores found in RTSA patients at six months may be due to the biomechanics of the reverse prosthesis and to the weakness of deltoid and periscapular muscles.

Dynamic thoracohumeral kinematics are dependent upon the etiology of the shoulder injury

Obtaining kinematic patterns that depend on the shoulder injury may be important when planning rehabilitation. The main goal of this study is to explore whether the kinematic patterns of continuous and repetitive shoulder elevation motions are different according to the type of shoulder injury in question, specifically tendinopathy or rotator cuff tear, and to analyze the influence of the load handled during its assessment. For this purpose, 19 individuals with tendinopathy and 9 with rotator cuff tear performed a repetitive scaption movement that was assessed with stereophotogrammetry. Furthermore, static range of motion (ROM) and isometric strength were evaluated with a goniometer and a dynamometer, respectively. Dynamic measurements of maximum elevation (Emax), variablility of the maximum angle (VMA), maximum angular velocity (Velmax), and time to maximum velocity (tmaxvel) were found to be significantly different between the tendinopathy group (TG) and the rotator cuff tear group (RTCG). No differences were found in the ROM assessed with goniometry and the isometric strength. The effect of increasing the load placed in the hand during the scaption movement led to significant differences in Emax, VMA, tmaxvel and repeatability. Therefore, only the dynamic variables showed sufficient capability of detecting differences in functional performance associated with structural shoulder injury. The differences observed in the kinematic variables between patients with tendinopathy and rotator cuff tear seem to be related to alterations in thoracohumeral rhythm and neuromuscular control. Kinematic analysis may contribute to a better understanding of the functional impact of shoulder injuries, which would help in the assessment and treatment of shoulder pain.

Kinematic analysis of the shoulder complex after anatomic and reverse total shoulder arthroplasty: A cross-sectional study

BACKGROUND

The movement of the arm relative to the trunk results from coordinated 3D glenohumeral and scapulothoracic movements. Changes in scapula kinematics may occur after total shoulder arthroplasty and could affect clinical and functional outcomes.

OBJECTIVES

To assess the 3D movement of the scapula during arm elevation after anatomic and reverse total shoulder arthroplasty.

DESIGN/METHODS

This was a single-centre, non-randomized, controlled cross-sectional study. Patients with anatomic (n = 14) and reverse total shoulder arthroplasty (n = 9) were prospectively enrolled and were compared to age-matched asymptomatic controls (n = 23). 3D scapular kinematics were assessed by a non-invasive, electromagnetic method during arm abduction and flexion. 3D scapular rotations and 3D linear displacements of the barycentre (geometrical centre) at rest and at 30°, 60° and 90° arm elevation; as well as scapulohumeral rhythm were analysed. Participant groups were compared using one-way ANOVA and Bonferroni post-hoc testing for normally distributed data, and Mann-Whitney U test for non-normally distributed data.

RESULTS/FINDINGS

Total range of scapular lateral rotation and barycentre displacement were increased, and scapulohumeral rhythm was reduced, in patients with anatomic and reverse total shoulder arthroplasty compared with age-matched controls; however, the global scapular kinematic pattern was preserved.

CONCLUSION/INTERPRETATION

For patients after total shoulder arthroplasty, the increased contribution of the scapula to arm elevation is consistent with a compensatory mechanism for the reduced glenohumeral mobility. The stability of the global scapula kinematic pattern reflects its mechanical and neuromotor strength.

Three-Dimensional Scapular Kinematics in Patients with Reverse Total Shoulder Arthroplasty during Arm Motion

Background

There have been few reports on altered kinematics of the shoulder after reverse total shoulder arthroplasty (RTSA). We investigated differences in 3-dimensional (3D) scapular motions assessed using an optical tracking system between RTSA treated shoulders and asymptomatic contralateral shoulders during arm motion.

Methods

Thirteen patients who underwent RTSA were assessed for active arm elevation in 2 distinct elevation planes (sagittal plane flexion and scapular plane abduction). Their mean age was 72 years (range, 69 to 79 years) and the mean follow-up was 24.4 months (range, 13 to 48 months). The dominant side was the right side in all the 13 patients, and it was also the side treated with RTSA. Scapular kinematics was recorded with an optical tracking system. The scapular kinematics and the scapulohumeral rhythm (SHR) of the RTSA shoulders and asymptomatic contralateral shoulders were recorded and analyzed during arm elevation.

Results

There were no significant differences in internal/external rotation and anterior/posterior tilting of the scapula between shoulders during arm motion (p > 0.05). However, upward rotation of the scapula differed significantly during arm motion (p = 0.035 for sagittal plane flexion; p = 0.046 for scapular plane abduction). There were significant differences in the SHR between the two shoulders (p = 0.016 for sagittal plane flexion; p = 0.021 for scapular plane abduction).

Conclusions

The shoulder kinematics after RTSA showed significant differences from the contralateral asymptomatic shoulders. Increased upward rotation and decreased SHR after RTSA indicate that RTSA shoulders use more scapulothoracic motion and less glenohumeral motion to elevate the arm.

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.

Computational reverse shoulder prosthesis model: Experimental data and verification

The reverse shoulder prosthesis aims to restore the stability and function of pathological shoulders, but the biomechanical aspects of the geometrical changes induced by the implant are yet to be fully understood. Considering a large-scale musculoskeletal model of the upper limb, the aim of this study is to evaluate how the Delta reverse shoulder prosthesis influences the biomechanical behavior of the shoulder joint. In this study, the kinematic data of an unloaded abduction in the frontal plane and an unloaded forward flexion in the sagittal plane were experimentally acquired through video-imaging for a control group, composed of 10 healthy shoulders, and a reverse shoulder group, composed of 3 reverse shoulders. Synchronously, the EMG data of 7 superficial muscles were also collected. The muscle force sharing problem was solved through the minimization of the metabolic energy consumption. The evaluation of the shoulder kinematics shows an increase in the lateral rotation of the scapula in the reverse shoulder group, and an increase in the contribution of the scapulothoracic joint to the shoulder joint. Regarding the muscle force sharing problem, the musculoskeletal model estimates an increased activity of the deltoid, teres minor, clavicular fibers of the pectoralis major, and coracobrachialis muscles in the reverse shoulder group. The comparison between the muscle forces predicted and the EMG data acquired revealed a good correlation, which provides further confidence in the model. Overall, the shoulder joint reaction force was lower in the reverse shoulder group than in the control group.

Kinematic analysis of reaching movements of the upper limb after total or reverse shoulder arthroplasty

Studies have analyzed three-dimensional complex motion of the shoulder in healthy subjects or patients undergoing total shoulder arthroplasty (TSA) or reverse shoulder arthroplasty (RSA). No study to date has assessed the reaching movements in patients with TSA or RSA. Twelve patients with TSA (Group A) and 12 with RSA (Group B) underwent kinematic analysis of reaching movements directed at four targets. The results were compared to those of 12 healthy subjects (Group C). The assessed parameters were hand-to-target distance, target-approaching velocity, humeral-elevation angular velocity, normalized jerk (indicating motion fluidity), elbow extension and humeral elevation angles. Mean Constant score increased by 38 points in Group A and 47 in Group B after surgery. In three of the tasks, there were no significant differences between healthy subjects and patients in the study groups. Mean target-approaching velocity and humeral-elevation angular velocity were significantly greater in the control group than in study groups and, overall, greater in Group A than Group B. Movement fluidity was significantly greater in the controls, with patients in Group B showing greater fluidity than those in Group A. Reaching movements in the study groups were comparable, in three of the tasks, to those in the control group. However, the latter performed significantly better with regard to target-approaching velocity, humeral-elevation angular velocity and movement fluidity, which are the most representative characteristics of reaching motion. These differences, that may be related to deterioration of shoulder proprioception after prosthetic implant, might possibly be decreased with appropriate rehabilitation.

The effects of progressive lateralization of the joint center of rotation of reverse total shoulder implants

BACKGROUND

There has been a renewed interest in lateralizing the center of rotation (CoR) in implants used in reverse shoulder arthroplasty. The aim of this study was to determine the sensitivity of lateralization of the CoR on the glenohumeral joint contact forces, muscle moment arms, torque across the bone-implant interface, and the stability of the implant.

METHODS

A 3-dimensional virtual model was used to investigate how lateralization affects deltoid muscle moment arm and glenohumeral joint contact forces. This model was virtually implanted with 5 progressively lateralized reverse shoulder prostheses. The joint contact loads and deltoid moment arms were calculated for each lateralization over the course of 3 simulated standard humerothoracic motions.

RESULTS

Lateralization of the CoR leads to an increase in the overall joint contact forces across the glenosphere. Most of this increased loading occurred through compression, although increases in anterior/posterior and superior/inferior shear were also observed. Moment arms of the deltoid consistently decreased with lateralization. Bending moments at the implant interface increased with lateralization. Progressive lateralization resulted in improved stability ratios.

CONCLUSIONS

Lateralization results in increased joint loading. Most of that loading occurs through compression, although there were also increases in shear forces. Anterior/posterior shear is currently not accounted for in implant fixation studies, leaving its effect on implant fixation unknown. Future studies should incorporate shear forces into their models to more accurately assess fixation methods.

Scapulohumeral rhythm in shoulders with reverse shoulder arthroplasty

BACKGROUND

Little is known about kinematic function of reverse total shoulder arthroplasty (RTSA). Scapulohumeral rhythm (SHR) is a common metric for assessing muscle function and shoulder joint motion. The purpose of this study was to compare SHR in shoulders with RTSA to normal shoulders.

METHODS

Twenty-eight subjects, more than 12 months after unilateral RTSA, were recruited for an Institutional Review Board-approved study. Subjects performed arm abduction in the coronal plane with and without a 1.4-kg hand-held weight. Three-dimensional model-image registration techniques were used to measure orientation and position for the humerus and scapula from fluoroscopic images. Analysis of variance and Tukey tests were used to assess groupwise and pairwise differences.

RESULTS

SHR in RTSA shoulders (1.3:1) was significantly lower than in normal shoulders (3:1). Below 30° abduction, RTSA and normal shoulders show a wide range of SHR (1.3:1 to 17:1). Above 30° abduction, SHR in RTSA shoulders was 1.3:1 for unweighted abduction and 1.3:1 for weighted abduction. Maximum RTSA shoulder abduction in weighted trials was lower than in unweighted trials. SHR variability in RTSA shoulders decreased with increasing arm elevation.

CONCLUSION

RTSA shoulders show kinematics that are significantly different from normal shoulders. SHR in RTSA shoulders was significantly lower than in normal shoulders, indicating that RTSA shoulders use more scapulothoracic motion and less glenohumeral motion to elevate the arm. With these observations, it may be possible to improve rehabilitation protocols, with particular attention to the periscapular muscles, and implant design or placement to optimize functional outcomes in shoulders with RTSA.

A quantitative analysis of the effect of baseplate and glenosphere position on deltoid lengthening in reverse total shoulder arthroplasty

CONTEXT

Optimizing deltoid tension is important to achieve maximal function after reverse total shoulder arthroplasty (RTSA), but the effects of baseplate and glenosphere positions on deltoid tension have not been quantified.

AIMS

To quantify deltoid elongation and elongation to failure under physiologic loads with three baseplate-glenosphere configurations with increasing inferior offset.

SETTINGS AND DESIGN

Cadaver biomechanical study.

MATERIALS AND METHODS

Twenty-four cadaver shoulders were divided into three groups. The starting point for baseplate insertion in Group 1 was the center of the glenoid, with glenospheres placed in minimal inferior offset (0.5 mm). Groups 2 and 3 baseplates were placed 2 mm inferior to the center point and glenospheres in minimal (2.5 mm) offset (Group 2) or maximal (4.5 mm) offset (Group 3). Tensile testing was done to quantify deltoid elongation and evaluate failure.

STATISTICAL ANALYSIS USED

A one-way analysis of variance was performed to detect statistically significant differences among treatment groups. A post-hoc Neuman-Keul's comparison was conducted to perform discrete comparisons among treatment groups.

RESULTS

Deltoid elongation after loading decreased with increasing inferior offset of >2.5 mm. No significant difference in deltoid yield load was found among groups. The percent of elongation was decreased significantly between groups 2 and 3. Deltoid displacement at failure decreased from 33.3 mm for Group 2-17.3 mm for Group 3. 16 of the 24 specimens (67%) failed by anterior deltoid detachment from the acromion.

CONCLUSIONS

Increasing inferior offset in RTSA constructs appears to increase stretch forces on the deltoid, resulting in a diminished ability of the deltoid to further elongate under physiologic loads, (most pronounced when the inferior offset exceeds 2.5 mm) and significantly decreasing the yield displacement of the construct.

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.

The active and passive kinematic difference between primary reverse and total shoulder prostheses

BACKGROUND

Reverse shoulder arthroplasty (RSA) and total shoulder arthroplasty (TSA) effectively decrease pain and improve clinical outcome. However, indications and biomechanical properties vary greatly. Our aim was to analyze both active and passive shoulder motion (thoracohumeral [TH], glenohumeral [GH], and scapulothoracic [ST]) and determine the kinematic differences between RSAs and TSAs.

METHODS

During 3 range-of-motion (ROM) tasks (forward flexion, abduction, and axial rotation), the motion patterns of 16 RSA patients (19 shoulders), with a mean age of 69 ± 8 years (range, 58-84 years), and 17 TSA patients (20 shoulders), with a mean age of 72 ± 10 years (range, 53-87 years), were measured. The mean length of follow-up was 22 ± 10 months (range, 6-41 months) for RSA patients and 33 ± 18 months (range, 12-87 months) for TSA patients. Kinematic measurements were performed with a 3-dimensional electromagnetic tracking device.

RESULTS

All patients showed better passive than active ROM. This difference was significantly larger for RSA patients than for TSA patients (TH in sagittal plane, 20° vs 8° [P = .001]; GH in sagittal plane, 16° vs 7° [P = .003]; TH in scapular plane, 15° vs 2° [P < .001]; GH in scapular plane, 12° vs 0° [P < .001]; and ST in scapular plane, 3° vs -2° [P = .032]). This finding also showed that in the scapular plane, TSA patients showed hardly any difference between active and passive ROM. Furthermore, TSA patients had 16° to 17° larger active TH motion, 15° larger active GH motion, and 8° larger active ST motion compared with RSA patients. The GH-ST ratios showed similar figures for both types of prostheses.

CONCLUSION

TSA patients have larger active TH motion because in the scapular plane, they completely use the possible GH motion provided by the prosthetic design. This larger active ROM in TSA patients only applies for elevation and abduction, not for axial rotation or passive ROMs.

Optimal positioning of the humeral component in the reverse shoulder prosthesis

INTRODUCTION

Total reverse shoulder arthroplasty is becoming more and more the standard therapeutic practice for glenohumeral arthropathy with massive lesions of the rotator cuff. The biomechanical principle of this prosthesis is represented by the reversion of the normal anatomy of the shoulder joint. This non-anatomical prosthesis leads to a medialization of the rotation centre of the glenohumeral joint and also to a distalization of the humeral head. All that causes a deltoid tension increasing so allowing a larger abduction of the arm. Main complications of the reverse shoulder prosthesis are due to the joint instability, the scapular notching and the wear of the polyethylene insert.

PURPOSE

The main goal of the present work is to study the effect of the positioning of the humeral component on the intrinsic stability of the reverse shoulder prosthesis. In particular, through finite element method simulations, the variation of the stability ratio of the shoulder joint has been calculated for both vertical and horizontal dislocating loads depending on the humeral stem version angle. Moreover, in order to estimate the wear of the polyethylene cup, some analyses have been developed to calculate the pressures on the polyethylene insert.

RESULTS

The obtained results demonstrate the dislocation of a shoulder prosthesis and the wear of the polyethylene insert can be prevented or limited by conveniently varying the version angle of the humeral component.

How does reverse shoulder replacement change the range of motion in activities of daily living in patients with cuff tear arthropathy? A prospective optical 3D motion analysis study

BACKGROUND

Reverse total shoulder arthroplasty (RSA) can improve function in cuff tear arthropathy (CTA) shoulders, but limited exact data are available about the maximum values in 3D motion analysis, and as to how improvements translate into the normal range of motion (ROM) in activities of daily living (ADLs).

METHODS

This study included nine consecutive patients (n = 9) who received RSA for CTA without muscle transfers. We measured shoulder movement by a novel 3D motion analysis using the Heidelberg upper extremity model (HUX) which can eliminate compensatory movements of the scapula, and the trunk. The measurement included active maximum values, and four ADLs.

RESULTS

Comparing the pre- to the 1-year postoperative status, RSA was associated with a significant increase in the mean maximum values for active flexion of about 43° (SD ± 31) from 66° to 109° (p = 0.001), for active abduction of about 37° (SD ± 26) from 57° to 94° (p = 0.001), and for the active adduction of about 28° (SD ± 10) from 5° to 33° (p = 0.002). Comparing the preoperative to the postoperative ROM in the ADLs in flexion/extension, ROM improved significantly in all ADLs, in abduction/adduction in three of four ADLs. No significant changes were observed in internal/external rotation in any ADLs.

CONCLUSION

RSA improves the active maximum ROM for flexion, abduction, and adduction. The patients are able to take advantage of this ROM increase in ADLs in flexion and in most ADL in abduction, but only in trend in internal and external rotation.