Distribution of bone and tissue morphological properties related to subacromial space geometry in a young, healthy male population

Investigating the reliability and validity of subacromial space measurements using ultrasound and MRI

BACKGROUND

While ultrasound (US) measures of the subacromial space (SAS) have demonstrated excellent reliability, measurements are typically captured by experts with extensive ultrasound experience. Further, the agreement between US measured SAS width and other imaging modalities has not been explored. This research evaluated the agreement between SAS measures captured by novice and expert raters and between US and magnetic resonance imaging (MRI). This study also evaluated the effect of US transducer tilt on measured SAS.

METHODS

Nine men and nine women participated in this study. US images were captured by a novice and expert with the participant in both seated and supine positions. An inclinometer was fixed to the US probe to measure transducer tilt. SAS width was measured in real time from freeze framed images. MRI images were captured, and the humerus and acromion manually segmented. The SAS width was measured using a custom algorithm.

RESULTS

Intraclass correlation coefficients (ICCs) between novice and expert raters were 0.74 and 0.63 for seated and supine positions, respectively. Intra-rater agreement was high for both novice (ICC = 0.83-0.84) and expert (ICC ≥ 0.94) raters. Agreement between US and MRI was poor (ICC = 0.21-0.49) but linearly related.

CONCLUSIONS

Moderate agreement between novice and expert raters was demonstrated, while the agreement between US and MRI was poor. High intra-rater reliability within each rater suggests that US measures of the SAS may be completed by a novice with introductory training.

Between Two Rocks and in a Hard Place: Reflecting on the Biomechanical Basis of Shoulder Occupational Musculoskeletal Disorders

OBJECTIVE

The aim was to review the biomechanical origins of occupational shoulder damage, while considering the complexity of shoulder mechanics and musculoskeletal consequences of diverse task demands.

BACKGROUND

Accessible measures of physical exposures are the primary focus of occupational shoulder assessments and analyses. This approach has led to guidelines and intervention strategies that are often inadequate for mitigating shoulder disorders amongst the complexity of modern workplace demands. Integration of complex shoulder mechanics into occupational assessments, analyses, and interventions is critical for reducing occupational shoulder injury risk.

METHOD

This narrative review describes shoulder biomechanics in the context of common injury mechanisms and consequent injuries, with a particular focus on subacromial impingement syndrome. Several modulators of shoulder injury risk are reviewed, including fatigue, overhead work, office ergonomics considerations, and pushing and pulling task configurations.

RESULTS

Relationships between work requirements, muscular demands, fatigue, and biomechanical tissue loads exist. This review highlights that consideration of specific workplace factors should be integrated with our knowledge of the intricate arrangement and interpersonal variability of the shoulder complex to proactively evaluate occupational shoulder demands and exposures.

CONCLUSION

A standard method for evaluating shoulder muscle exposures during workplace tasks does not exist. An integrated approach is critical for improved work design and prevention of shoulder tissue damage and accompanying disability.

APPLICATION

This review is particularly relevant for researchers and practitioners, providing guidance for work design and evaluation for shoulder injury prevention by understanding the importance of the unique and complex mechanics of the shoulder.

Anatomical variations of the acromial and coracoid process: clinical relevance

PURPOSE

The acromial and coracoid process morphology is of clinical relevance due to associations with functional limitations and shoulder pathology. Our objective was to describe the anatomical characteristics of the acromial and coracoid process using computed tomography (CT).

METHODS

Descriptive, observational, transversal and retrospective study. A total of 155 CT of patients without shoulder pathology, of both genders, and indistinct age were evaluated and grouped by age: Group 1 < 25 years; group 2 25-40 years; group 3 > 40 years. The following parameters were evaluated: Acromial type (AcT), vertical coracoid distance (VCD), acromial tilt (AT), acromial projection (AP), critical shoulder angle (CSA), type of the subcoracoid outlet (TSO), and the area of the subcoracoid outlet (ASO).

RESULTS

Statistically significant differences were found between men and women for VCD (14.44 ± 4.79 vs. 11.76 ± 4.00 mm; p < 0.001) and AP (3.66 ± 4.71 vs. 1.62 ± 4.99 mm; p < 0.05) as well as between age groups 1 and 3 for AT (35.08 ± 11.53 vs. 28.41 ± 6.60; p < 0.05) and ASO (398.99 ± 153.91 vs. 255.56 ± 124.58 mm²; p < 0.001). An unexpected high ASO variation was identified with 11% of S-shaped acromion and 1.3% clock-shaped TSO.

CONCLUSION

The age group between 25-40 years had the most uniform distribution of data. There is a high morphological variability present in an asymptomatic population, which should be considered in the clinical assessment such as shoulder impingement syndrome.

Glenohumeral stabilizing roles of the scapulohumeral muscles: Implications of muscle geometry

Dynamic stability provided by muscles is integral for function and integrity of the glenohumeral joint. Although the high degree of inter-individual variation that exists in musculoskeletal geometry is associated with shoulder injuries, there is limited research associating the effects of muscle geometry on the potential stabilizing capacities of shoulder muscles. The purpose of this investigation was to evaluate the stabilizing functions of the scapulohumeral muscles using computational modeling and to quantify the sensitivity of muscle stabilizing roles to changes in muscle geometry. Muscle stability ratios in the superior/inferior and anterior/posterior directions were computed as the ratio between the muscle's shear components relative to compression throughout arm elevation in the scapular plane. Muscle attachment locations on the clavicle, scapula, and humerus were iteratively adjusted using Monte Carlo simulations. Consistent with previous experimental studies, the rotator cuff muscles were identified as the primary stabilizers of the glenohumeral joint; whereas the deltoids and coracobrachialis have a strong potential for superiorly translating the humerus at low elevation angles. Variations in the stability ratios due to altered muscle geometry were muscle- and angle-specific. In general, the highest variation was observed for the subscapularis and deltoids (at low elevation angles), while the remaining rotator cuff muscles largely maintained their capacity to provide compressive stabilizing forces at the glenohumeral joint. Changes in muscle stability ratios may affect dynamic stability of the humerus that could differentially predispose individuals to greater risk for injury.

Subacromial space volume in patients with rotator cuff tear: The effect of surgical repair

Objective

The aim of this study was to evaluate the effect of the rotator cuff tear repair on subacromial space volume.

Methods

We retrospectively identified 21 eligible patients (5 males and 16 females; mean age: 56.4 (range; 46–71) years) who had shoulder arthroscopy for unilateral full-thickness small to medium rotator cuff tear and normal controlateral shoulder joint. The mean follow-up time was 16.1 (range; 12–25) months. Preoperative and postoperative 1 year bilateral shoulder MRIs and Constant scores were reviewed. Subacromial volume was calculated by using Osirix software. Pre-, postoperative and healthy side (contralateral control group) subacromial volumes were recorded. Paired sample and t-tests were used to compare the pre- and postoperative groups. Independent sample t-tests were used to compare the healthy and pre- and postoperative groups. The correlation between the changes in the subacromial volume and the shoulder Constant score were analyzed using Pearson correlation analyses.

Results

The mean subacromial volume of the preoperative group was 2.95 cm³ (range; 1.53–4.23) and the postoperative group was 3.59 cm³ (range; 2.12–4.84). The volume increase was statistically significant (p < 0.05). The mean subacromial volume of the control group was 3.93 cm³ (range; 2.77–5.03), and the difference between the preoperative group and the control group was statistically significant. There was no significant difference found between the postoperative group and the control group (p = 0.156). There was no significant correlation found between the volume and the constant score changes (r = 0.170, p = 0.515).

Conclusion

The subacromial space volume significantly decreases in full-thickness rotator cuff tears smaller than 3 cm and the surgical repair increases the subacromial volume significantly.

Level of evidence

Level IV; Diagnostic Study.