Via Research Recognition Day Program VCOM-Carolinas 2025

Case Reports

Unilateral Hypoplasia of the Trapezius Muscle in a Female Cadaver Alyssa Levien, OMS-I, Avery Savoie, OMS-I, Kelsey Negron, OMS-I, David Jaynes, PhD Edward Via College of Osteopathic Medicine – Carolinas, Spartanburg, SC

Case Report Data

Introduction

Discussion

The trapezius is a superficial posterior axioappendicular muscle that provides direct attachment of the pectoral girdle to the vertebral column and cranium. Proximally, the trapezius attaches to the medial third of the superior nuchal line, the external occipital protuberance, the nuchal ligament, and the spinous processes of C7-T12 vertebrae. The distal attachments include the lateral third of the clavicle, the acromion, and the scapular spine. The trapezius muscle fibers are divided into three parts ● descending fibers elevate the scapula ● middle fibers retract the scapula ● ascending fibers depress the scapula Additionally, the ascending and descending fibers superiorly rotate and fix the scapula on the thoracic wall. A 67-year-old female cadaver, who died of pulmonary carcinoma, was gifted to the anatomy program at The Edward Via College of Osteopathic Medicine. During routine dissection, we observed hypoplasia of the left trapezius muscle. The descending muscle fibers only extended as far superiorly as the ligamentum nuchae at the level of C2. There were no cranial attachments. Inferiorly, the ascending fibers originated at the spinous process of T7. The clavicular, acromial, and scapular insertions were all normal. There were no signs of previous trauma or surgical procedures. Hypoplasia of the trapezius muscle was only noted on the cadaver’s left side. The right trapezius muscle displayed typical fiber orientation and attachments. When the trapezius muscles were reflected, the left rhomboid muscles were considerably enlarged. Case Presentation

Figure 1. Dorsal view of bilateral trapezius muscles outlined in white. Note the significant hypoplasia of the left trapezius muscle.

• Anatomic variations are frequently documented in medical literature. In particular, the musculoskeletal system is rife with structural anomalies. • This case presents a unique variation of unilateral congenital hypoplasia of the left trapezius muscle originating at the spinous process of T7 and ligamentum nuchae of C2 with no cranial attachment. Associated compensatory hypertrophy of the left rhomboids was also observed. • To our knowledge, these observations have not been reported previously. • Comparative studies have described unilateral trapezius hypoplasia in both live patients [1] and cadaveric dissections [2]. Most cases report hypoplasia limited to either the descending or ascending portions [3][4]. Additionally, these reports noted muscle fibers to be largely aponeurotic. • Examination of the intact spinal accessory nerve and typical blood supply yielded no apparent anomalies, suggesting an embryologic etiology. Trapezius muscle development arises from pharyngeal mesoderm and partly from occipital and cervical myotomes [5]. • Our findings display the potential impact this trapezius agenesis may have on structure and function of the left upper extremity. We hope this case serves as a resource for clinicians to recognize the clinical significance that anatomical variations may have.

Figure 2. Bilateral reflection of the trapezius muscles showing the rhomboid muscles. Observe the hypertrophy of the left rhomboid muscle in comparison to the right.

Weight of Trapezius and Rhomboid Muscles

Acknowledgement & References

Muscle

Left Side

Right Side

Trapezius Rhomboids

92.71 70.70

149.63

42.25

The authors would like to thank the person who donated their body to further the education of medical students, as well as their family who supported this decision.

Table 1. Muscle weight in grams.

2025 Research Recognition Day

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