Anatomical Variations of the Lumbar Plexus: A Descriptive Anatomy Study with Proposed Clinical Implications

Abstract

Evidence-based practice emphasizes the examination and application of evidence from clinical research into diagnosis, prognosis, and outcomes based on a formal set of rules 1 . One method of evaluating evidence is to assign levels of evidence 2 . In this evidence hierarchy, extrapolations from basic science research are classified as the lowest level of evidence. However, especially in situations where higher-level research evidence is insufficient, such extrapolation based on a thorough knowledge of relevant anatomy often still serves to guide clinical reasoning. This importance of anatomy remains recognized within physical therapy education in the United States, both as part of program entrance requirements 3 and as a part of the required basic sciences content in entry-level curricular content 4 . In those circumstances where clinical diagnosis is solely based on anatomical extrapolation, knowledge of anatomical deviations with a potential impact on interpretation of test results becomes even more important.The lumbar plexus originates from the ventral rami of the L1-L4 nerve roots and projects laterally and caudally from the intervertebral foramina, posterior to the psoas major muscle. A communicating branch from the T12, also known as the subcostal nerve, often joins the first lumbar nerve [5][6][7][8][9][10] . The L2-L4 ventral rami first bifurcate into an anterior and posterior primary division. The T12 and L1 nerves and the L2-L4 anterior primary divisions supply muscular branches to the psoas major and quadratus lumborum. Both primary divisions then enter the lumbar plexus and give rise to six peripheral nerves. Within this plexus, the L1 nerve splits into a cranial and caudal branch. The cranial branch bifurcates into the iliohypogastric and ilioinguinal nerves, the former also formed by the subcostal nerve in people where this nerve contributes to the lumbar plexus. The caudal branch of the L1 nerve unites with the anterior division of the L2 nerve to form the genitofemoral nerve. The anterior divisions of the L2-L4 roots form the obturator nerve. The lateral femoral cutaneous nerve arises from the posterior divisions of the L2 and L3 roots; the posterior divisions of L2, L3, and L4 join to create the femoral nerve (Figure 1). Table 1 presents a summary of the normal presentation of nerves of the lumbar plexus based upon a review of several authoritative anatomical texts commonly used in physical therapy education [5][6][7][8][9][10] . The purpose of this study was to describe the anatomical variations in the lumbar plexus from the origin at the ventral roots of (T12) L1-L4 to the exit from the pelvic cavity based on our descriptive anatomy study of human cadavers as compared to the above description of normal anatomy [5][6][7][8][9][10] . Comparing our findings to anatomical variation described elsewhere in the literature, we will also suggest possible clinical implications ABSTRACT: This study used dissection of 34 lumbar plexes to look at the prevalence of anatomical variations in the lumbar plexu...

Previously Unreported Variation in the Innervation of the Psoas Major Muscle

“…Depending on the specific innervation of the AON, patients may present with diverse symptomology. Due to its innervation of the hip joint, a differential diagnosis for groin pain could be compression of the AON [6]. If there is variation in the of the AON, as in the presently reported case, it could lead to weakness in flexion of the hip due to the innervation of the psoas major by the AON.…”

“…The branches of the lumbar plexus and its association with the psoas major muscle is important to understand, especially during surgery in that region or when performing anesthetic blocks. Variations of the plexus and their associated clinical implications have been documented in the literature [6].…”

“…For example, the AON can be selectively compressed as it travels over the superior pubic ramus, leading to neuropathy of that nerve [6]. Depending on the specific innervation of the AON, patients may present with diverse symptomology.…”

“…The majority of branches from the lumbar plexus cross the psoas major muscle proximally [9]. As these nerves transverse the muscle, motor branches from the anterior rami of (L1-L4) are given off to innervate the psoas major [6]. The AON mainly arises from the anterior branches of the third and fourth lumbar ventral rami, but can also have contributions from L1 and L2 [1,5,10].…”

Is L2 Paravertebral Block Comparable to Lumbar Plexus Block for Postoperative Analgesia After Total Hip Arthroplasty?

“…LPB provides mostly favorable postoperative analgesia but can produce incomplete analgesia. Incomplete analgesia may perhaps be due to the various components of the lumbar plexus being physically separated by muscle tissue such that the infused local anesthetic solution cannot reach them all [1,2,10]. The case reports of Lee et al [12] demonstrated that L1-L2 PVBs provided adequate pain relief in patients undergoing hip arthroscopy; however, the study of Bogoch et al [6] demonstrated that opioid consumption was significantly less during the first 4 hours after performing paravertebral blocks compared to a sham procedure in patients undergoing THA, but no significant difference was seen in opioid consumption thereafter.…”