Surg Radiol Anat (2010) 32:409–414 DOI 10.1007/s00276-009-0546-3 A N A T O M I C V A R I A T IO N S Anatomical variations of lumbosacral plexus Viktor Matejbík Received: 14 April 2009 / Accepted: 6 August 2009 / Published online: 21 August 2009 © Springer-Verlag 2009 Abstract Basis Deviations detected during spinal operations have motivated us to start research related to variations of lumbosacral plexus formation. Aim of this work was to Wnd out deviations of its formation from ascension of particular roots from foramen invertebrale and foramina sacralia up to formation of terminal branches. Set One hundred lumbosacral plexi have been examined in 50 adult cadavers for a purpose to Wnd out an incidence of neural variations. We have observed participation of Th12 root, L4 and L5 roots in its formation, as well as various deviations from ascension of particular plexiform roots up to their ending branches. For lumbal plexus, we have observed four nerve roots and six lumbal nerves; for sacral one, three sacral roots with a share of S4 and lumbosacral trunk formed of L4 and L5 roots and four sacral nerves. We have considered also their course, anastomoses and thickness. We highlight motoric innervation particularities in relation to diagnostics besides anatomical complexity and variability. Results Variations on the level of neural roots were common, nerve formations were uncommon. Thickness of neural roots, formation or their absence were dependent on the type of plexus, particularly in sacral area. For lumbal plexus, L1 root was the thinnest and L4 root was the thickest. L3 root was the thickest in six cases. Fifth lumbal root usually completely Wlled foramen invertebrale. We have observed double ascension of L4 root from foramen invertebrale in 25 cases and plexiform in Wve cases. In other cases it was branched in various distance following ascension from foramen invertebrale. Plexiform ascension of L3 root along with L4 root was present in two cases. Double ascension of L3 root was present in four cases. L2, L3 along with L5 roots were doubled in two cases. Iliohypogastric nerve was the longest, ilioinguinal was the thinnest and nervus femoralis was the thickest. Changes in sacral plexus on the level of neural roots have been observed 41-times. Double ascension of L5 root was present in eight cases and plexiform in four cases. Double S1 root at ascension from foramina sacralia was present 16 times, S2 8 times, S3 once and S1 along with S2 4 times. S1, S2 and S3 roots were branched in various distance following ascension from foramina sacralia in 15 cases. Truncus lumbosacralis was thickened in 19 cases, a share from L4 root was thicker as L5 root in 11 cases. Low level of connection between truncus lumbosacralis and S1 root was observed in 10 cases. Nervus ischiadicus has branched into tibial and peroneal portions already in minor pelvis in two cases. The level of distance of n. (nervus) gluteus superior, n. gluteus inferior, n. cutaneus femoris posterior and n. pudendus was dependent on the plexus type. Conclusion This study enabled us to Wnd out and to describe extraordinary anatomical deviations in formation of neural roots and nerves of lumbal and sacral plexus, undescribed yet. V. Matejbík (&) Department of Neurosurgery, Derer’s Faculty Hospital, Comenius University, Limbova 5, 833 05 Bratislava, Slovak Republic e-mail: [email protected] Introduction Keywords Lumbosacral plexus · Sacral plexus · Lumbal plexus · Anatomical variations Lumbal plexus is formed by ventral branches of L1–L4 in musculus psoas major with a share of Th12 or without it. It 123 410 is located on internal surface of dorsal abdominal wall, ventrally from processus transversus of coxal vertebrae [1, 2]. It is protected with layers of the muscle and bone structures. As well-protected and safely located structure, it provides better safety to the plexus. Lumbosacral plexopathies are therefore less frequent peripheral lesion aVecting lower extremities. Sacral plexus is formed by ventral branches of S1–S3 with a share of S4 and very important lumbosacral trunk formed of L4 and L5 roots. It extends above sacroiliac junction and consequently connects with sacral nerves forming n. ischiadicus. Depending of Th12 root presence, we say on high cranial preWxed plexus or low caudal one. Boundary root participating in the plexi formation is L4 root, which in some cases is largerly involved in lumbal plexus formation and sacral in others. Its proportion in that or the other plexus helps to characterize the whole plexus—as cranial preWxed with a share or caudal postWxed without a share of Th12. It is necessary to realize that L4 root does not play, always, the role of boundary root; sometimes it is L5 root [3]. As for literature available for us, we have met only with orphan works devoted to these problems [1–8]. Materials and methods The study is related to 50 fresh cadavers without innate or detected abnormalities, tumour diseases, orthopaedic deformities and spinal operations. Ethics committee approval was obtained prior to the study. However, to the best of our literature search, we could not come across any study performed by the use of those reference structures or points. Therefore, we were not able to discuss our Wndings on the topography lumbosacral plexus and roots with the results of others. Lumbosacral plexi were clariWed in all of them, bilaterally from anterior access following evisceration. Lumbal plexus was clariWed following thorough dissection of m. psoas major. We have observed extraforaminal deviations of particular root formation up to their ending branches, and participation of Th12 and L4 roots, L5, respectively, in its formation. Main lumbal neural roots were localized along with the surface of the most dorsal part of vertebral bodies and intervertebral discs. Lumbal plexus is formed laterally from intervertebral foraminas and passes through m. psoas major. Each lumbal root ascends through superior part of corresponding intervertebral foramina. Ascending from foramina, it extends downward along with lateral surface of caudal pedicle. Here it is crossed by intertransversal ligament with an aim 123 Surg Radiol Anat (2010) 32:409–414 to maintain ventrolateral routing. Most of neural sleeves are anchored on cranial pedicle and only small space between lower bound of pedicle and neural roots is present. Minor motoric branches are depleted directly in m. psoas major, while longer ones leave the muscle on various sites and extend aslope downward into pelvic area and leave it under ligamentum inguinale. N. obturatorius leaves the pelvis through foramen obturatorius. Lumbal nerves—n. iliohypogastric, n. ilioinguinal, n. genitofemoral, n. cutaneus femoris lateralis, n. obturatorius, n. femoralis and sacral nerves—n. ischiadicus, n. gluteus superior, n. gluteus inferior, n. cutaneus femoris posterior and n. pudendus, were identiWed bilaterally. Nerves of sacral plexus are located on anterior area of m. piriformis. Branches of iliac vessels are in the vicinity of S1, S2 and S3 roots. Results As with upper extremity, neural trunks of lower extremity in high cranial form also receive more fascicles from above located nerves in comparison with low caudal form. Th12 and L1 roots are thicker in preWxed type. Then L4 root contributes more signiWcantly to sacral plexus and S3 and S4 roots are absent. If L4 root does not contribute to sacral plexus or contributes only minimally, L5 root is thiner, S1–S3 roots are thicker and S4 root is present too. L5 Table 1 Variations of lumbal plexus roots Number of L plexus root Double root ascension Plexiform root ascension L2 2 – L3 4 – L4 25 5 – 2 2 – 33 7 L3 + L4 L2 + L3 + L5 Total Table 2 Variations of sacral plexus roots Number of S plexus root Double root ascension Plexiform root ascension L5 8 4 S1 16 – S2 8 – S3 1 – S4 – – 4 – 37 4 S1 + S2 Total Surg Radiol Anat (2010) 32:409–414 root is the largest nerve contributing to sacral plexus in postWxed type. When determining the type of plexus, the most appropriate was L4 root, eventually also L5 root. PreWxed type has been occured in 19 cases, postWxed in Wve cases. Variations in the area of plexi were most frequently on the level of neural root formation (Tables 1, 2). Foramen intervertebrale is the narrowest on the level of L5/S1. It was usually completely Wlled with Wfth lumbal root. L4 root participated in truncus lumbosacralis formation in every case. L5 root did not contribute to lumbal plexus in no case. The branch from L4 root to L5 root was thicker as L5 root itself in 11 cases (Fig. 1). Thin connection of L4 root with L5 root was present in majority of cases. Thick truncus lumbosacralis was present in 19 cases (Figs. 2, 3). We have observed junctions of L3 root to L4–L5–S1 roots in 12 cases. Double ascension of roots in lumbal plexus was observed in 33 cases and plexiform in seven cases. Among them, three roots of L2, L3, L5 simultaneously in two cases (Fig. 4). Double ascension of L2 root was observed in two cases, L3 in four cases, L4 in 25 cases. For 411 other cases, L4 root was branched in various distance following ascension from foramen intervertebrale. Plexiform ascension of L4 root was observed in Wve cases, and L3 along with L4 roots in two cases. L1 root was the thinnest and L4 was the thickest root of lumbal plexus. Iliohypogastric nerve was the longest, ilioinguinal nerve was the thinnest and n. femoralis was the thickest. We have observed most deviations of its formation in its case. Shares of L2, L3 roots were dominant in 40 cases and L4 share was minor, also from L1 root in 1 case. Common trunk formation of n. femoralis may be more distal, must not be formed respectively, six cases. L3 root was the thickest in six cases. Participation of L4 root in sacral plexus formation was observed in every case. Absence of junction between the plexi was not observed in any case. In cases of preWxed plexus—thick truncus lumbosacralis in sacral plexus formation, only S1 and S2 roots were present and nerves of sacral plexus ascended from L5, S1 and S2 roots. For postWxed type, truncus lumbosacralis was thin, S1, S2 roots were thicker (Fig. 5). S3 and S4 roots were present too. For other cases, truncus lumbosacralis and S1, S2, S3 Fig. 1 PreWxed type of lumbosacral plexus, right side, front view, in craniocaudal direction, surrendered branches of the spine from left to right: a branch from L4 root (1) is thicker than L5 root (2), thick truncus lumbosacralis (3), S1 root (4), S2 root (5) Fig. 2 Thick truncus lumbosacralis, left side, front view, in craniocaudal direction, from right to left: thin S1 and S2 roots, a branch from L4 root (1), L5 root (2), truncus lumbosacralis (3), S1 root (4), S2 root (5), S3 root (6) 123 412 Surg Radiol Anat (2010) 32:409–414 Fig. 3 Thick truncus lumbosacralis (1), left side, front view, in craniocaudal direction, from right to left: thin S1 (2) and S2 (3) roots branching following ascension from foramina sacralia Fig. 4 Double ascension of L2 and L3 roots, right side, front view, in craniocaudal direction, from left to right: L5 root (1), L4 root (2), L3 root (3), L2 root (4) Fig. 5 PostWxed type of lumbosacral plexus, right side, front view, in craniocaudal direction, from left to right: thin branch from L4 root (1) to L5 root (2), truncus lumbosacralis (3), S1 root (4), S2 root (5), S3 root (6), S4 root (7), n. obturatorius (8), n. femoralis (9) roots were present. Changes in sacral plexus on the level of neural roots were observed 41 times. Double ascension of L5 root (Fig. 6) was present in eight cases. Plexiform ascension of L5 root in four cases (Fig. 7). Double ascension of S1 root following ascension from foramina sacralia 16 times, S2 8 times and S3 once. S1 + S2 roots simulaten- 123 ously 4 times (Fig. 8). S1, S2 and S3 roots were branched in various distance following ascension from foramina sacralia in 15 cases. N. ischiadicus was branched into tibial and peroneal portion already in minor pelvis in two cases. N. cutaneus femoris posterior leaves S1 root and takes shares of S2 and S3 roots. Surg Radiol Anat (2010) 32:409–414 413 Fig. 6 Double ascension of L5 root, left side, front view, in craniocaudal direction, from right to left: S1 root (1), L5 root (2, 3), L4 root (4), a branch from L4 root to L5 root (5), n. obturatorius (6), n. femoralis (7) Fig. 7 Plexiform ascension of L5 root, left side, front view, in craniocaudal direction, from right to left Fig. 8 Double S1 root, right side, front view, in craniocaudal direction, from left to right: a branch from L4 root (1), L5 root (2), truncus lumbosacralis (3), S1 root (4), S2 root (5), S3 root (6) N. pudendus was formed depending on the plexus type from S2 and S3 roots. If main trunk of n. pudendus leaves S3 root, it takes a share of S2 root. Discussion Lumbosacral plexus is an analogue of brachial one. DiVerences in lumbosacral plexus formation are demonstrated in that manner that segmental participation of certain nerves, as well as their participation in tissue innervation may be changed, as in brachial one on the periphery. Nevertheless, interest in details of both plexi formation is not the same. It is because injuries as well as variations of lumbosacral plexus formation are less frequent in comparison with brachial one. Indications for reconstructive operations of lumbosacral plexus are exceedingly rare. There are a lot of variations of standard pattern related to innervation from lumbosacral plexus, but innervation from the Wrst two sacral nerves is quite constant. S2 root also innervates glutei and musculus biceps femoris. N. gluteus superior innervates musculus gluteus medius—so-called “deltoid” of coxal joint, musculus gluteus minimus and extends forward, innervating m. tensor fascia lata, while S3 root usually innervates Xexors of big toe and only rarely other muscles on the extremity. S4 root innervates no muscles on the extremity. L4 root contributes to lumbal and sacral plexi and therefore it is called branched or furcate “furcal nerve”. With the exception of L4 root, in the literature we did not Wnd any cases of root duplication or root fragmentation of lumbosacral plexus that could constitute real operational pitfalls for neurosurgeon and anaesthetist during regional anaesthesia. Weber [8] pointed out to some variations of lumbal plexus. Following Bergman et al. [9], both plexi—lumbal and sacral—are connected with furcal nerve in 91.8%. The connection was not found in 7.4%. Iczi et al. [6] has seen only one case of furcal nerve and had not observed any variation of the connection between lumbal and sacral plexus. 123 414 Erbil et al. [4] has described an occurence of preWxed type on one side and postWxed type on the other in the casuistics. These variations are very rare. Lumbal structures forming plexus are located in longer mutual distances than in brachial plexus. Therefore less signiWcant neurological failures are developed in the case of injuries of lumbal plexus. TraYc accidents may be a cause of lumbal plexus injuries connected with root avulsion [3]. Lumbal injuries (penetrating, non-penetrating)—tumours of posterior abdominal wall, vessel pathologies (aneurysms, bleeding, haematomas), abdominal operations and infarctions of m. psoas major—are the most frequent cause of lumbal plexopathies in diabetics [5, 10]. Lumbal and sacral plexi play an important role in regional anaesthesis, particularly in sacroiliac and pelvic surgery. For its surgical treatment is important to put attention to vessel structures. Artery of glutea inferior is the branch from artery of iliac interna and leads into numerous branches damaging of which is necessary to have in mind in operation, because they may be retracted into pelvis and may bleed. Components of lumbosacral plexus spread on lower extremity, similarly as brachial plexus spread on upper extremity. Lumbal nerves spread similarly as nerves from medial and lateral fascicle of brachial plexus, and sacral nerves spread similarly as nerves from posterior fascicle of brachial plexus. Many variations of lumbosacral plexus formation are a source of diagnostic confusions besides atypical clinical and electromyographic Wndings. It is important to understand what neural functions are transferred in particular parts of the plexus. It is also necessary to bear in mind that muscle innervation may change independently on number of the root entering the plexus due to presence of various connections between plexus roots. Neural roots in preWxed type take more Wlaments from above located spinal nerves. Injuries of highly located neural roots or nerves are accompanied with much more prevalent lesion on the periphery in comparison with the same injuries in postWxed type. S3 root in postWxed type may have many Wlaments normally born by S2 root and the share of S4 may be greater. It is supposed that the deviations in lumbosacral plexus formation are caused by a deviation from normal development process, during the fourth week of foetal development [11, 12]. 123 Surg Radiol Anat (2010) 32:409–414 Conclusion Anatomical organization of lumbosacral plexus has its particularities. Neuroanatomical variations are the cause of unexpected radicular patterns. It is necessary to take into account individual speciWc variants in formation of clinical picture, its diagnostics and surgical treatment. Injuries may be prevented or lessened to a minimum level through detailed knowledge of the topographic features and variations. Injuries may be prevented or lessened to a minimum level through a detailed knowledge on the topographic features and variations. Understanding the structure and course of lumbosacral plexus is important during all interventions to these regions due to the potential damage on the nerve itself. Importance in spinal anaesthesia, spinal operations in spondylosurgery, endoscopic operations in retroperitoneal approach in laser discectomy, ozonotherapy, etc. References 1. Williams PL, Bannister LH, Berry MM, Collins P, Dyson M, Dussek JE, Fergusson MWJ (1995) Gray’s anatomy, 38th edn. Churchill Livingstone, London, pp 1258–1274 2. Williams PL, Warwick R (1985) Gray’s anatomy, 36th edn. Churchill Livingstone, London, pp 1106–1110 3. Chin Ch, Chew KC (1997) Lumbosacral nerve root avulsion. Injury 28:674–678 4. Erbil K, Onderoglu S, Basar R (1998) Unusual branching in lumbar plexus. Case report. Folia Morphol (Warsz) 57:377–381 5. Hope EE, Bodensteiner JB, Thong N (1985) Neonatal lumbar plexus injury. Arch Neurol 42:94–95 6. Iczi Y, Gürkanlar D, Ozan H, Gönül E (2005) The morphological aspects of lumbar plexus and roots. An anatomical study. Turk Neurosurg 15:87–92 7. Urbanowitz Z (1981) Connections between the lumbal and sacral plexus in man. Folia Morphol (Warsz) 40:271–279 8. Weber RH (1961) Some variations in the lumbal plexus of nerves in man. Acta Anat 44:336–345 9. Bergman RA, Thompson SA, AWW AK, Saddeh FA (1988) Compendium of human anatomical variations. Urban and Schwarzenburg, Baltimore, pp 138–139 10. Haigh PI (1999) Soft-tissue images. Abdominal aortic aneurism causing lumbar plexus neuropraxis. Can J Surg 42:329 11. Marieb EN, Mallat J (2005) Základy embryologie, kapitola 3. In: Marieb EN, Mallat J (eds) Anatomie lidského t5la. Computer Press, a.s., Brno, pp 62–67 12. O’Rahilly R, Muller F, Meyer DB (1990) The human vertebral column at the end of the embryonic periods proper. 4. The sacrococcygeal region. J Anat 168:95–111
