A Rare Case of Double-Headed Psoas Minor Muscle with Review of its Known Variants

Potential Lack of Association Between Three Vestigial Muscles in Humans: A Willed Body Donor Study

PURPOSE

Anatomical agenesis within a population is not well understood, with variations including but not limited to complete absence, unilateral presence, or bilateral presence. Agenesis of human vestigial muscles including the palmaris longus (PL), fibularis tertius (FT), and psoas minor (PM) has been studied; however, the relationship between their presence and absence has not been examined. The purpose of this study is to analyze the prevalence of the PL, FT, and PM muscles, investigate any relationship of prevalence based on sex or race, and investigate any correlation between the presence or absence of each muscle within individual donors.

METHODS

Twenty-three willed body donors were comprehensively dissected by medical students, and the presence or absence of the PL, FT, and PM muscles was recorded.

RESULTS

The PL was present bilaterally in 87% of donors and absent bilaterally in 13%. The FT was present bilaterally in 96% of donors, and present unilaterally in 4% of donors. There was no evidence of total agenesis of the FT within our sample. The PM was present bilaterally in 39% of donors, and absent bilaterally in 61% of donors. No statistically significant relationship was indicated between muscle presence and the sex or race of the donors. No correlation between the presence or absence of each of the muscles was found.

CONCLUSION

In this sample of willed body donors, there was no relationship between muscular agenesis of the vestigial muscles. This suggests that muscle agenesis is a local genetic developmental event at each muscle, and that there is not a single developmental event that leads to agenesis of multiple vestigial muscles. Further understanding of the agenesis of vestigial structures within populations and subpopulations can aid in physician diagnosis and understanding of the anatomical makeup of individuals.

Psoas Minor Muscle: A Cadaveric Morphometric Study

Introduction

The psoas muscle group is part of the posterior abdominal wall and is comprised of long muscles – major, minor, and tertius. Out of those, only the psoas major muscle is an obligatory muscle present in all individuals. The psoas minor muscle (PMM) originates as vertical fascicles inserted in the bodies of the last thoracic and first lumbar vertebrae and inserting into the iliopectineal eminence. The muscle provide flexion of the lumbar spine in a limited fashion. The aim of the study was to establish the frequency of the muscle in the Bulgarian population.

Materials and methods

This study was carried out in the Department of Anatomy and Cell Biology, Medical University, Varna, Bulgaria, by Dr. Paraskev Stoyanov in November 2017, on a total of 10 cadavers. The length, width, and circumference of the muscles were measured. The collected data were interpreted in a descriptive manner.

Results

The PMM was present in six out of ten cadavers (60%). Out of those six cadavers, the muscle was bilateral in three, unilateral on the left side in one, and unilateral on the right side in two cadavers. The average length of the muscle was 19.66 cm (range:14.4 cm - 21.7 cm), average width was 1.73 cm (range: 1.0 cm - 3.2 cm ) and average circumference was 3.48 cm (range: 1.7 cm - maximum 5.6 cm). The male to female ratio of cadavers with a PMM was 1:1.

Conclusion

The frequency of the muscle's variations considering its presence in the Bulgarian population (60%) is higher when compared to its presence in the Indian population (36.67%), virtually identical to the Brazilian population (59%), and lower than that reported in the US (65.6%). The morphometric analyses of the different populations showed a shorter psoas minor in the Bulgarian population.