03 May 2025
: Case report 
Psoas Quartus and Femoral Nerve Branching: A Case Report and Potential Clinical Implications
Congenital defects / diseases
Joshua Wang
ABCDEF 1, Chun Yeung ABCDEF 1, Eric Chang ABCDEF 1, Jason M. Bourke ABCDE 2*
DOI: 10.12659/AJCR.945927
Am J Case Rep 2025; 26:e945927
Table 1 Comparison of reported psoas quartus descriptions.
| Study | Sex | Location | Proximal attachment | Distal attachment | Splitting pattern of femoral nerve |
|---|---|---|---|---|---|
| Clarkson (1889) []6 | Male | Bilateral pelvis | RT: TP of L5 & anterior surface of the lower and inner part of the quadratus lumborum LT: TP of L4/L5 | Fuse with the tendons of the psoas major at the level of the inguinal ligament | Limited description of the femoral nerve. Small branches of the femoral nerve were noted supplying each division of the psoas muscles |
| Tubbs (2006) []7 | Male | Left pelvis | L3 & medial aspect of quadratus lumborum | Tendons of the psoas major and tertius mm deep to the inguinal ligament | No abnormal splitting. Femoral nerve sits anterior to quartus w/branches supplying the quartus |
| Wong (2019) []9 | Female | Left pelvis | Anteromedial surface of quadratus lumborum & TP of L5 vertebra | Fuse with the tendons of the psoas major deep to the inguinal ligament | Femoral nerve splits into 4 branches; no muscles pierced by femoral nerves |
| Parker (2021) []8 | Male | Left pelvis | Anteromedial aspect of quadratus lumborum & TP of L5 | Fused with aberrant iliacus minor prior to fusing with the psoas major and iliacus deep to the inguinal ligament | Femoral nerve splits into 3 branches. One femoral nerve travels between a split psoas quartus; another nerve travels between a split iliacus muscle |
| This study (2023) | Male | Left pelvis | L5 & anteromedial aspect quadratus lumborum | Merged w/psoas major and iliacus deep and slightly inferior to the inguinal ligament | Femoral nerve splits into 3 branches: 2 anterior to quartus, 1 posterior to quartus |
| TP – transverse process; L4 – lumbar vertebrae 4; L5 – lumbar vertebrae 5; RT – right; LT – left. | |||||