Influence of the medial offset of the proximal humerus on the glenohumeral destabilising forces during arm elevation: a numerical sensitivity study

Convolutional LSTM: a deep learning approach to predict shoulder joint reaction forces

We developed a Convolutional LSTM (ConvLSTM) network to predict shoulder joint reaction forces using 3D shoulder kinematics data containing 30 different shoulder activities from eight human subjects. We considered simulation outcomes from the AnyBody musculoskeletal model as the baseline force dataset to validate ConvLSTM model predictions. Results showed a good correlation (>80% accuracy, r ≥ 0.82) between ConvLSTM predicted and AnyBody estimated force values, the generalization of the developed model for novel task type (p-value = 0.07 ∼ 0.33), and a better prediction accuracy for the ConvLSTM model than conventional CNN and LSTM models.

The clinical outcomes and tuberosity healing after reverse total shoulder arthroplasty for acute proximal humeral fracture using the turned stem tension band technique

BACKGROUND

Recent studies have reported the clinical effectiveness of tuberosity healing after reverse total shoulder arthroplasty in patients with proximal humeral fractures with respect to joint stability, long-term survival, and postoperative range of motion. However, it is challenging to achieve robust fixation of the fragile bone fragments in elderly patients. This study aimed to report on the radiographic and clinical outcomes of patients who underwent reverse total shoulder arthroplasty for acute proximal humeral fractures using a Turned stem Tension Band technique-a simple suture configuration that can apply a compressive force on both tuberosities at the same time.

METHODS

Eighteen patients who underwent reverse total shoulder arthroplasty for complex proximal humeral fractures (age 80.4 ± 4.7 years, range 70-87 years), using our Turned stem Tension Band technique, were included in this study and evaluated postoperatively for range of motion, American Shoulder and Elbow Surgeons score, Numerical Rating Scale, and tuberosity healing, with minimum 2-years follow-up (mean 34.5 months, range 24-60 months).

RESULTS

At the final follow-up, mean range of motion results were active flexion, 119 ± 34°; active abduction, 116 ± 35°; active external rotation, 27 ± 12°; and active internal rotation, L3. Six of 11 (55%) patients with 4-part dislocated fractures had neurological disorders from the time of injury; of these, three patients obtained shoulder elevation under 90° at the final follow-up. The mean American Shoulder and Elbow Surgeons score was 77.3 ± 10.7, and the mean Numerical Rating Scale was 1.2 ± 0.9. Fifteen of 18 (83%) patients were satisfied with the results. The tuberosity healing rate was 100% (18 of 18).

CONCLUSIONS

The Turned stem Tension Band technique in reverse total shoulder arthroplasty for proximal humeral fractures provides a robust fixation, regardless of the fracture pattern, which results in a high tuberosity healing rate.

Reverse Shoulder Arthroplasty Biomechanics

The reverse total shoulder arthroplasty (rTSA) prosthesis has been demonstrated to be a viable treatment option for a variety of end-stage degenerative conditions of the shoulder. The clinical success of this prosthesis is at least partially due to its unique biomechanical advantages. As taught by Paul Grammont, the medialized center of rotation fixed-fulcrum prosthesis increases the deltoid abductor moment arm lengths and improves deltoid efficiency relative to the native shoulder. All modern reverse shoulder prostheses utilize this medialized center of rotation (CoR) design concept; however, some differences in outcomes and complications have been observed between rTSA prostheses. Such differences in outcomes can at least partially be explained by the impact of glenoid and humeral prosthesis design parameters, surgical technique, implant positioning, patient-specific bone morphology, and usage in humeral and glenoid bone loss situations on reverse shoulder biomechanics. Ultimately, a better understanding of the reverse shoulder biomechanical principles will guide future innovations and further improve clinical outcomes.

Radiographic restoration of native anatomy: a comparison between stemmed and stemless shoulder arthroplasty

BACKGROUND

Shoulder arthroplasty is a reliable procedure for patients with degenerative glenohumeral disease, and reproduction of native shoulder anatomy leads to superior outcomes. The aim of this study was to compare the ability of stemmed and stemless implants to radiographically restore native glenohumeral anatomy.

METHODS

Shoulder arthroplasties were performed in 79 patients, with 58 receiving a stemless implant and 21 receiving a stemmed implant. Preoperative and postoperative radiographs were assessed for humeral head height, humeral head centering, humeral head medial offset, humeral head diameter, humeral neck angle, and lateral humeral offset by 2 independent viewers. Measurements were scored and summed to identify the anatomic reconstruction index (ARI). Radiographic measurements were compared using the Student t test, and significance was set at P < .05 for all statistical analyses. Interobserver agreement of radiographic analyses was assessed using the intraclass correlation coefficient, finding excellent reliability (intraclass correlation coefficient, 0.92).

RESULTS

Five of six radiographic measurements along with the calculated ARI demonstrated no differences between stemmed and stemless shoulder implants (humeral head diameter, P = .651; humeral head height, P = .813; humeral head medial offset, P = .592; lateral humeral offset, P = .311; humeral head centering, P = .414; and ARI, P = .862). Stemless implants showed improved restoration of the native humeral neck angle (0° for stemless vs. -3° for stemmed, P = .017).

CONCLUSION

Radiographic restoration of anatomy is similar for stemmed and stemless shoulder arthroplasty implants.

Morphologic Variability of the Shoulder between the Populations of North American and East Asian

Background

The aim of this study was to determine if there were significant differences in glenohumeral joint morphology between North American and East Asian populations that may influence sizing and selection of shoulder arthroplasty systems.

Methods

Computed tomography reconstructions of 92 North American and 58 East Asian patients were used to perform 3-dimensional measurements. The proximal humeral position was normalized in all patients by aligning it with the scapular plane utilizing anatomic landmarks. Measurements were performed on the humerus and scapula and included coronal and axial humeral head radius, humeral neck shaft and articular arc angles, glenoid height and width, and critical shoulder angle. Glenohumeral relationships were also measured and included lateral distance to the greater tuberosity and acromion, abduction lever arm, and acromial index. Parametric and nonparametric statistical analyses were used to compare population metrics.

Results

East Asian glenohumeral measurements were significantly smaller for all linear metrics (p < 0.05), with the exception of acromial length, which was greater than in the North American cohort (p < 0.001). The increase in acromial length affected all measurements involving the acromion including abduction lever arms. No difference was found between the neck shaft and articular angular measurements.

Conclusions

The East Asian population exhibited smaller shoulder morphometrics than their North American cohort, with the exception of an extended acromial overhang. The morphologic data can provide some additional factors to consider when choosing an optimal shoulder implant for the East Asian population, in addition to creating future designs that may better accommodate this population.

Kinematic impact of size on the existing glenohumeral joint in patients undergoing reverse shoulder arthroplasty

BACKGROUND

Glenohumeral relationships in reverse shoulder arthroplasty patients have not been previously reported. The purpose of this study was to quantify and compare the shoulder spatial relationships and moment arms. Measurements were used to define general size categories and determine if sizes scale linearly for all metrics.

METHODS

Ninety-two shoulders of patients undergoing primary reverse shoulder arthroplasty for functionally-deficient massive rotator cuff tear without bony deformity or deficiency were evaluated using three-dimensional CT reconstructions and computer-aided design software. Multiple glenohumeral relationships (including moment arm) were measured and evaluated for size stratification and linearity. Generalized linear modeling was used to investigate how predictive glenoid height, coronal humeral head diameter, and gender were of greater tuberosity positions.

FINDINGS

The 92 shoulders were grouped based on glenoid height: small (<33.4mm), medium (33.4-38.0mm), and large (>38.0mm). All relationships varied between groups. The humeral head size, glenoid width, lateral offset, and moment arm all independently increased linearly (r(2)≥0.92) but the rate of increase varied (slope range: 0.59-1.92). Glenoid height, coronal humeral head diameter and gender predicted the greater tuberosity position within mean 1.09mm (standard deviation (SD) 0.84mm) of actual position in 90% of the population.

INTERPRETATION

Distinct groups exist based on the size of the glenoid in shoulder arthroplasty patients. Shoulder modeling should account for size groups, sex, and non-uniform linear scaling of morphometric parameters. Prediction of the greater tuberosity offset can be made using sex and size parameters. Clinical implications include appropriate prosthetic size selection and avoiding large deviations in non-anatomic reconstructions.

Muscle load in reaching movements performed by a wheelchair user: a case study

PURPOSE

The aim of this study was to analyse the load on the shoulder muscles during reaching movements that are specific to wheelchair users in relation to the risk of impingement.

METHOD

Three activities of daily living were performed: putting a book on a shelf in front and at the side and putting a pack of water bottles on a table. The AnyBody shoulder model was used to calculate the activity and forces of the shoulder muscles.

RESULTS

Handling the pack of bottles caused the highest forces in the deltoideus, trapezius, serratus anterior and rotator cuff muscles. For handling the book, the highest forces were found in the deltoideus (scapular part) and the serratus anterior, especially during the put phase.

CONCLUSIONS

Handling heavy objects such as a pack of bottles or a wheelchair produces high forces on the rotator cuff muscles and can lead to early fatigue. Therefore, these activities seem to be associated with a high risk of developing impingement syndrome. Implications for Rehabilitation In a single patient, this study demonstrates that the load on the rotator cuff is high during reaching movements. Handling a pack of water bottles, which resembles wheelchair handling, represents an activity associated with a high risk of developing impingement syndrome. Shoulder muscles must be trained in a balanced way to provide stabilization at the shoulder joint and prevent fatigue.

Clinical applications of musculoskeletal modelling for the shoulder and upper limb

Musculoskeletal models have been developed to estimate internal loading on the human skeleton, which cannot directly be measured in vivo, from external measurements like kinematics and external forces. Such models of the shoulder and upper extremity have been used for a variety of purposes, ranging from understanding basic shoulder biomechanics to assisting in preoperative planning. In this review, we provide an overview of the most commonly used large-scale shoulder and upper extremity models and categorise the applications of these models according to the type of questions their users aimed to answer. We found that the most explored feature of a model is the possibility to predict the effect of a structural adaptation on functional outcome, for instance, to simulate a tendon transfer preoperatively. Recent studies have focused on minimising the mismatch in morphology between the model, often derived from cadaver studies, and the subject that is analysed. However, only a subset of the parameters that describe the model's geometry and, perhaps most importantly, the musculotendon properties can be obtained in vivo. Because most parameters are somehow interrelated, the others should be scaled to prevent inconsistencies in the model's structure, but it is not known exactly how. Although considerable effort is put into adding complexity to models, for example, by making them subject-specific, we have found little evidence of their superiority over current models. The current trend in development towards individualised, more complex models needs to be justified by demonstrating their ability to answer questions that cannot already be answered by existing models.