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In vivo pediatric shoulder muscle volumes and their relationship to 3D strength
Hyun Soo Im1, Katharine E Alter2, Sylvain Brochard3
1Functional and Applied Biomechanics Section, Rehabilitation Medicine Department, National Institutes of Health, Bethesda, MD, USA.
Insights
This study created a pediatric shoulder muscle database, finding that muscle volume strongly correlates with joint torque. These findings are vital for understanding and treating pediatric shoulder injuries.
Area of Science:
- Pediatric orthopedics
- Musculoskeletal biomechanics
- Human anatomy
Background:
- Pediatric shoulder injuries disrupt muscle balance, causing functional deficits.
- Limited in vivo data exists on pediatric shoulder muscle function.
- Musculoskeletal data is essential for advancing pediatric shoulder injury treatment.
Purpose of the Study:
- To develop a pediatric database of in vivo shoulder muscle volumes.
- To correlate these volumes with maximum isometric joint moments (flexion/extension, rotation, abduction/adduction).
Main Methods:
- Developed a methodology to derive 3D shoulder muscle volumes from MRI scans.
- Segmented the deltoid muscle into sub-units based on torque capabilities.
- Analyzed data from eleven typically developing children/adolescents.
Main Results:
- Established normative pediatric shoulder muscle volumes, with deltoid being largest and supraspinatus smallest.
- Found consistent muscle volume percentages across subjects.
- Demonstrated moderate-to-high correlations (0.70-0.94) between individual muscle volumes and maximum voluntary isometric joint torques.
Conclusions:
- Presents a comprehensive database of normative pediatric shoulder muscle volumes.
- Established a clear relationship between shoulder muscle volume and torque production across all rotational degrees-of-freedom.
- Provides a foundation for evaluating pediatric shoulder injury and pathology.
Abstract:
In the pediatric shoulder, injury and pathology can disrupt the muscle force balance, resulting in severe functional losses. As little data exists pertaining to in vivo pediatric shoulder muscle function, musculoskeletal data are crucially needed to advance the treatment of pediatric shoulder pathology/injury. Therefore, the purpose of this study was to develop a pediatric database of in vivo volumes for the major shoulder muscles and correlate these volumes with maximum isometric flexion/extension, internal/external rotation, and abduction/adduction joint moments. A methodology was developed to derive 3D shoulder muscle volumes and to divide the deltoid into sub-units with unique torque producing capabilities, based on segmentation of three-dimensional magnetic resonance images. Eleven typically developing children/adolescents (4F/7M, 12.0 ± 3.2 years, 150.8 ± 16.7 cm, 49.2 ± 16.4 kg) participated. Correlation and regression analyses were used to evaluate the relationship between volume and maximum, voluntary, isometric joint torques. The deltoid demonstrated the largest (30.4 ± 1.2%) and the supraspinatus the smallest (4.8 ± 0.5%) percent of the total summed volume of all six muscles evaluated. The anterior and posterior deltoid sections were 43.4 ± 3.9% and 56.6 ± 3.9% of the total deltoid volume. The percent volumes were highly consistent across subjects. Individual muscle volumes demonstrated moderate-high correlations with torque values (0.70-0.94, p<0.001). This study presents a comprehensive database documenting normative pediatric shoulder muscle volume. Using these data a clear relationship between shoulder volume and the torques they produce was established in all three rotational degrees-of-freedom. This study furthers the understanding of shoulder muscle function and serves as a foundation for evaluating shoulder injury/pathology in the pediatric/adolescent population.
