Split Femoral Nerve Due to Psoas Tertius Muscle: A Review with Other Cases of Variant Muscles Traversing the Femoral Nerve

A multiply split femoral nerve and psoas quartus muscle

The femoral nerve is the largest branch of the lumbar plexus. It is normally composed of the ventral rami of spinal nerves L2 to L4. The psoas major has proximal attachments onto the T12 to L5 vertebrae and related intervertebral discs, fuses with the iliacus deep to the inguinal ligament and then attaches onto the lesser trochanter of the femur. Normally, the anatomical relationship is that the femoral nerve is located between the iliacus and psoas major. Herein, we report a case of the psoas quartus muscle related to several splits of the femoral nerve within the pelvis. Although the embryology for this is unclear, surgeons and physicians should be aware of such anatomical variants in order to better understand pain and entrapment syndromes and during surgical maneuvers in this region such as lateral transpsoas approaches to the lumbar spine.

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.