The lumbar and sacral plexuses

The lumbar plexus is derived from the anterior primary rami of L1, L2, L3, and part of L4. It may also receive a contribution from T12. Its major derivatives are the femoral and the obturator nerves. The sacral plexus arises from the anterior primary rami of the five sacral nerves and the coccygeal nerve, together with the lumbosacral trunk, an important contribution which comprises the whole of L5 together with a contribution from L4. Its terminal branches are the sciatic and the pudendal nerve. In addition, both plexuses have numerous collateral muscular and cutaneous branches, and the sacral plexus gives rise to the pelvic parasympathetic outflow from S2 and S3.     

Extent of blockade with various approaches to the lumbar plexus

The extent of blockade when four different techniques were used for blocking the lumbar plexus was prospectively evaluated in 80 adult patients. The extent of blockade was measured by testing motor function of all nerves except the lateral and posterior femoral cutaneous nerves, which were evaluated by pinprick response. The posterior approaches of Dekrey at L3 (n = 20) and Chayen at L4-5 (n = 20) proved similarly effective in producing blockade of the femoral, obturator, and lateral femoral cutaneous nerves, as well as the nerves to the psoas muscle. The anterior approach of Winnie (femoral sheath or 3-in-1 block) using paresthesia (n = 20) or peripheral nerve stimulation (n = 20) proved effective in producing blockade of the femoral and lateral femoral cutaneous nerves, but ineffective for obturator nerve blockade. None of the four techniques produced blockade of the sacral plexus. Perhaps our means of assessing blockade (motor) is what produced the difference between our findings and those of others.     

创伤性腰骶丛神经根损伤的临床分型

  目的 探讨腰骶丛神经根性损伤的临床分型。 方法2004 年11 月至2011 年8 月, 共为 36 例创伤性腰骶丛神经根损伤患者进行腹膜后腰神经丛及(或)盆腔内骶神经丛及(或)腰骶管神经根 手术探查。男24 例, 女12 例;年龄7~49 岁, 平均29.5 岁。伤后时间为2~36 个月, 平均9.3 个月。对每 例患者术中探查的神经根损伤情况与其术前临床表现、物理查体一并进行分析、归纳, 总结出不同组合 的腰骶丛神经根联合损伤的临床表现特点并进行临床分型。 结果 将腰骶丛神经根损伤分为六型:腰 骶丛神经根完全损伤型(L1~S3)4 例, 腰丛+上骶丛损伤型(L1~S1)6 例, 骶丛神经损伤型(L4~S3)9 例, 上骶 丛损伤型(L4~S1)11 例, 下骶丛损伤型(S2, 3)4例, 腰丛神经损伤型(L1~4)2 例。全腰骶丛神经根损伤型、腰 丛+上骶丛损伤型及骶丛神经根损伤型者共19 例, 73.7%(14/19)的损伤部位位于椎管内, 且均发生神经 根的断裂或撕脱。而上骶丛、下骶丛及腰丛神经根损伤共17 例, 其中64.7%(11/17)的损伤部位在盆内 段及(或)骶前孔处, 均为挫伤或牵拉伤。 结论 上述临床分型基本涵盖腰骶丛神经根损伤的常见类型, 为腰骶丛神经根损伤范围的判定提供科学依据。此外, 不同类型的腰骶丛神经根损伤, 其损伤部位及性 质明显不同, 对预后的判定及治疗方案的选择具有重要意义。     

Anatomy and anaesthesia of the lumbar somatic plexus

Cadaveric dissection demonstrated the lumbar plexus to lie within the substance of psoas major, with the major branches of the lumbar plexus emerging into the psoas compartment adjacent to the L5 vertebra. Within psoas major, the lateral femoral cutaneous and femoral nerves were separated from the obturator nerve by a muscular fold in 36 of 60 plexuses. Anatomical variations were common, with the accessory obturator nerve being identified in 12 per cent of plexuses. All previously described lumbar plexus block approaches positioned the needle within close proximity to the lumbar plexus. Modifications to these approaches may increase efficacy and reduce complication rates.     

闭孔神经移位修复腰骶丛神经根撕脱伤的解剖学观察及临床应用

目的 观察闭孔神经移位修复腰骶丛神经根撕脱伤的可行性及临床疗效.方法 取15具成人尸体标本,显露双侧闭孔神经及腰骶丛神经根.测量闭孔神经从主干起始部至闭孔入口处的长度及其在闭孔入口处的横径和纵径,计算横截面积,并在高倍显微镜下计数有髓神经纤维数目.以相同方法测量并计算股神经相应指标.2002年1月至2007年9月,共为5例腰骶丛损伤患者进行闭孔神经移位术.行健侧闭孔神经经椎体前腹膜后通路移位与患侧股神经直接吻合4例,闭孔神经移位与同侧S1神经根直接吻合1例.结果 闭孔神经的平均长度为(10.51±0.9)cm,横径(2.03±0.37)mm,纵径(2.78±0.29)mm,有髓神经纤维数目(5974±1996)根;股神经横径(3.79±0.58)mm,纵径(6.53±0.61)mm,有髓神经纤维数目(15 860±4350)根.术后3～7 d,所有患者供肢内收肌肌力均减弱至2～3级;术后3个月,4级2例,3级2例,2级1例(至术后1年时,内收肌肌力恢复3级).4例修复患侧股神经的患者,术后分别随访8个月～5年,股四头肌肌力4级2例,2级1例,1级1例;1例行闭孔神经移位与同侧S1神经根直接吻合的患者,术后11个月时小腿三头肌及屈趾肌肌力恢复至3级.结论 闭孔神经可作为一个安全有效的动力神经源,用其修复腰骶丛神经根撕脱伤可获得满意疗效.     

Lumbar plexus and psoas major muscle: not always as expected

BACKGROUND AND OBJECTIVES: Conflicting definitions concerning the exact location of the lumbar plexus have been proposed. The present study was carried out to detect anatomical variants regarding the topographical relation between the lumbar plexus and the psoas major muscle as well as lumbar plexus anatomy at the L4-L5 level. METHODS: Sixty-three lumbar plexuses from 32 embalmed cadavers were dissected to determine the topographical relation between lumbar plexus and psoas major muscle. At the L4-L5 levels variability in the course of the femoral as well as obturator nerve were described. RESULTS: The lumbar plexus was situated within the psoas major muscle in 61 of 63 cases. In 2 of 63 cases the entire plexus was localized posterior to the psoas major muscle. In the 61 of 63 cases in which the lumbar plexus was situated within the psoas major muscle, emergence of the individual nerves most often occurred on the posterior or posterolateral surface. CONCLUSIONS: Our results synthesize contrasting assumptions in previous literature, by demonstrating that both locations of the lumbar plexus may be encountered in clinical practice: within and posterior to the psoas major muscle. However, the latter situation represents a minor variant. At the level of L4-L5 the femoral nerve, showing a remarkable degree of branching, as well as the obturator nerve, were found within the psoas major muscle in the vast majority of specimens.     

Anatomy of the spinal nerves and dermatomes

There are 31 pairs of spinal nerves: eight cervical, 12 thoracic, five lumbar, five sacral and one coccygeal. They form by fusion of a posterior sensory spinal root (bearing its posterior root ganglion) with an anterior motor root. These join at each intervertebral foramen. Typically, the nerve then divides into a posterior and an anterior primary ramus. The former supplies the vertebral muscles and dorsal skin. The anterior primary ramus in the thoracic region bears a white ramus communicans to the sympathetic ganglion. Each spinal nerve receives a grey ramus from the sympathetic chain. The nerves T2–T12 supply the skin and muscles of the trunk sequentially. The other nerves are arranged into the cervical, brachial, lumbar and sacral plexuses. The cervical plexus supplies the skin and anterior muscles of the neck and forms the phrenic nerve (C3–C5), while the brachial plexus supplies the skin and muscles of the upper limb, and the lumbar and sacral plexuses supply the skin of the lower limb and perineum and the muscles of the posterior abdominal wall, pelvis, perineum and lower limb. The segmental nerves are arranged to supply the skin (dermatomes), while the segmental supply to the limb muscles, the myotomes, is more complex.     

A review of approaches and techniques for lower extremity nerve blocks

PURPOSE: The purpose of this narrative review is to summarize the evidence derived from randomized controlled trials (RCTs) regarding approaches and techniques for lower extremity nerve blocks. SOURCE: Using the MEDLINE (January 1966 to April 2007) and EMBASE (January 1980 to April 2007) databases, medical subject heading (MeSH) terms "lumbosacral plexus", "femoral nerve", "obturator nerve", "saphenous nerve", "sciatic nerve", "peroneal nerve" and "tibial nerve" were searched and combined with the MESH term "nerve block" using the operator "and". Keywords "lumbar plexus", "psoas compartment", "psoas sheath", "sacral plexus", "fascia iliaca", "three-in-one", "3-in-1", "lateral femoral cutaneous", "posterior femoral cutaneous", "ankle" and "ankle block" were also queried and combined with the MESH term "nerve block". The search was limited to RCTs involving human subjects and published in the English language. Forty-six RCTs were identified. PRINCIPAL FINDINGS: Compared to its anterior counterpart (3-in-1 block), the posterior approach to the lumbar plexus is more reliable when anesthesia of the obturator nerve is required. The fascia iliaca compartment block may also represent a better alternative than the 3-in-1 block because of improved efficacy and efficiency (quicker performance time, lower cost). For blockade of the sciatic nerve, the classic transgluteal approach constitutes a reliable method. Due to a potentially shorter time for sciatic nerve electrolocation and catheter placement than for the transgluteal approach, the subgluteal approach should also be considered. Compared to electrolocation of the peroneal nerve, electrostimulation of the tibial nerve may offer a higher success rate especially with the transgluteal and lateral popliteal approaches. Furthermore, when performing sciatic and femoral blocks with low volumes of local anesthetics, a multiple-injection technique should be used. CONCLUSIONS: Published reports of RCTs provide evidence to formulate limited recommendations regarding optimal approaches and techniques for lower limb anesthesia. Further well-designed and meticulously executed RCTs are warranted, particularly in light of new techniques involving ultrasonographic guidance.     

Anatomy of the posterior approach to the lumbar plexus block

The purpose of this study was to describe the relation of the lumbar plexus with the psoas major and with the superficial and deep landmarks close to it. Four cadavers were dissected and 22 computed tomography files of the lumbosacral region studied. Cadaver dissections demonstrated that the lumbar plexus, at the level of L₅, is within the substance of the psoas major muscle rather than between this muscle and the quadratus lumborum. The femoral nerve lies between the lateral femoral cutaneous and obturator nerves. However, while the lateral femoral cutaneous nerve is in the same fascial plane as the femoral nerve, the obturator nerve can be found in the same plane as the two other nerves or in its own muscular fold. Radiological data provided the following measurements: the femoral nerve is at a depth of 9.01 ± 2.43 cm; the psoas major medial border is at 2.73 ± 0.64 cm from the median sagital plane; and its lateral border is at 6.41 ± 1.61 cm from the same plane. It is concluded that the lumbar plexus is within the psoas major, that the obturator nerve localization within the psoas major varies and that computed tomography data define precisely the relationship of the lumbar plexus with superficial and deep landmarks.     

The suprasacral parallel shift vs lumbar plexus blockade with ultrasound guidance in healthy volunteers – a randomised controlled trial

Surgical anaesthesia with haemodynamic stability and opioid‐free analgesia in fragile patients can theoretically be provided with lumbosacral plexus blockade. We compared a novel ultrasound‐guided suprasacral technique for blockade of the lumbar plexus and the lumbosacral trunk with ultrasound‐guided blockade of the lumbar plexus. The objective was to investigate whether the suprasacral technique is equally effective for anaesthesia of the terminal lumbar plexus nerves compared with a lumbar plexus block, and more effective for anaesthesia of the lumbosacral trunk. Twenty volunteers were included in a randomised crossover trial comparing the new suprasacral with a lumbar plexus block. The primary outcome was sensory dermatome anaesthesia of L2–S1. Secondary outcomes were peri‐neural analgesic spread estimated with magnetic resonance imaging, sensory blockade of dermatomes L2–S3, motor blockade, volunteer discomfort, arterial blood pressure change, block performance time, lidocaine pharmacokinetics and complications. Only one volunteer in the suprasacral group had sensory blockade of all dermatomes L2–S1. Epidural spread was verified by magnetic resonance imaging in seven of the 34 trials (two suprasacral and five lumbar plexus blocks). Success rates of the sensory and motor blockade were 88–100% for the major lumbar plexus nerves with the suprasacral technique, and 59–88% with the lumbar plexus block (p > 0.05). Success rate of motor blockade was 50% for the lumbosacral trunk with the suprasacral technique and zero with the lumbar plexus block (p < 0.05). Both techniques are effective for blockade of the terminal nerves of the lumbar plexus. The suprasacral parallel shift technique is 50% effective for blockade of the lumbosacral trunk.     

直肠癌根治术中保留骨盆自主神经的神经解剖学基础及临床意义

目的　探讨直肠癌根治术中保留神经的解剖学基础。　方法　解剖 6例完整尸体标本(男 4例 ,女 2例 )和 4例直肠及盆腔未受破坏的矢状半骨盆标本 ,观察骨盆神经组成及走行。　结果　显露下腹神经干 ,确定其在第 5腰椎处分为左、右下腹神经。其特点是较为粗大 ,位置固定 ,在腹主动脉分叉处易找到 ,呈网状联系 ,质地较实 ,为灰白色 ,与腹主动脉较近。分叉后左右下腹神经还有较粗大分支。骨盆内脏神经在大体标本上较难辨认 ,在矢状半骨盆标本中见到发自骶前孔 2～ 4的骨盆内脏神经 ,该神经较纤细 ,在侧韧带处呈丛状的细小纤维。　结论　保留下腹神经临床上较易完成。保留骨盆内脏神经则须细心操作 ,预保留神经的一侧在侧韧带水平的手术操作应尽量贴近直肠进行。     

Magnetic resonance imaging of the distribution of local anesthetic during the three-in-one block

The three-in-one technique of simultaneously blocking the femoral, the lateral femoral cutaneous (LFC), and the obturator nerves by a single injection of a local anesthetic was first described in 1973, and it was suggested that the underlying mechanism was one of cephalad spread resulting in a blockade of the lumbar plexus. Today, the technique is widely used in surgery and pain management of the lower limb. Many investigators have, however, reported suboptimal analgesia levels, particularly in the obturator nerve. The purpose of this prospective study was to trace the distribution of a local anesthetic during a three-in-one block by means of magnetic resonance imaging (MRI). Seven patients scheduled for surgery of the lower limb were analyzed with the aid of a primary MRI and then received three-in-one blocks using 30 mL of bupivacaine 0.5% under the guidance of a nerve stimulator. A secondary MRI was performed to determine the distribution pattern of the local anesthetic. It emerged that the local anesthetic blocks the femoral nerve directly, the LFC nerve through lateral spread, and the anterior branch of the obturator nerve by slightly spreading in a medial direction. No involvement of the proximal and posterior portions of the obturator nerve was observed, nor was there any cephalad spread that could have resulted in a lumbar plexus blockade. We therefore conclude that the basis of the three-in-one block is confined to lateral, medial, and caudal spread of the local anesthetic, which effectively blocks the femoral and LFC nerves, as well as the distal anterior branch of the obturator nerve. IMPLICATIONS: We demonstrate by using magnetic resonance imaging that the mechanism of a three-in-one block is one of lateral, caudal, and slight medial spread of a local anesthetic with subsequent blockade of the femoral, the lateral femoral cutaneous, and the anterior branch of the obturator nerves. It does not involve cephalad spread of the local anesthetic with blockade of the lumbar plexus.     

The cutaneous nerves encountered during laparoscopic repair of inguinal hernia

BACKGROUND: With an incidence rate of 2%, injury to the nerves of the lumbar plexus is the most common complication of laparoscopic hernioplasty, particularly when the transabdominal preperitoneal (TAPP) technique is used. METHODS: The course of the genitofemoral nerve, lateral femoral cutaneous nerve, and ilioinguinal nerve within the operation site was investigated in 53 adult dissecting-room bodies. Their relationship to the deep inguinal ring, iliopubic tract, and anterior superior iliac spine was also examined. RESULTS: Both the femoral and genital branches of the genitofemoral nerve may penetrate the abdominal wall lateral to the deep ring and cranial to the iliopubic tract. The lateral femoral cutaneous nerve and the ilioinguinal nerve may run immediately lateral to the anterior superior iliac spine. CONCLUSION: Contrary to the previously accepted opinion, dissection and the placement of staples either cranial to the iliopubic tract or lateral to the anterior superior iliac spine can result in injury to the nerves.     

Continuous three-in-one block for postoperative pain after lower limb orthopedic surgery: where do the catheters go?

Continuous three-in-one block is widely used for postoperative analgesia after proximal lower limb surgery, but location of the catheter has not been well addressed in the literature. We prospectively studied, in 100 patients, the characteristics of catheter threading under the iliac fascia and the correlations between catheter tip location and effective sensory and motor blockade of the three principal nerves of the lumbar plexus. Postoperatively, in conscious patients, 16 to 20 cm of a catheter was placed in the fascial sheath after femoral nerve location with a nerve stimulator. Contrast media (3 mL Iopamidol 390) was injected, and the catheter tip was located by means of an anteroposterior pelvic radiograph. An equal-volume mixture of 0.5% bupivacaine/2% lidocaine with epinephrine (30 mL) was injected through the catheter. Patient and catheter-insertion characteristics were noted. Thirty minutes after injection, sensory blockade was evaluated in the cutaneous territories of the lateral femoral cutaneous, femoral, and obturator nerves, along with motor blockade of the last two nerves. Pain scores at 30 min were also recorded. Seven block failures were noted. The tip of the catheter reached the lumbar plexus (Group 1) in 23% of the patients and lay deep to the medial (Group 2) or lateral (Group 3) part of the fascia iliaca in 33% and 37% of the patients, respectively. Demographic data and catheter threading characteristics were comparable among the groups. A three-in-one block was noted in 91% of Group 1 patients, but in only 52% and 27% of Group 2 and 3 patients, respectively (P < 0.05). Comparing Group 2 and 3 patients, sensory block was achieved in respectively 100% and 94% for the femoral nerve, 52% and 94% for the lateral femoral cutaneous nerve (P < 0.05), and 82% and 27% for the obturator nerve (P < 0.05). Visual analog scale pain scores on movement were significantly lower in Group 1 patients (P < 0.05). We conclude that during a continuous three-in-one block, the threaded catheter rarely reached the lumbar plexus. The quality of sensory and motor blockade and initial pain relief depend on the location of the catheter tip under the fascia iliaca. IMPLICATIONS: The course of a continuous three-in-one block catheter is unpredictable. Only 23% of the catheters lie near the lumbar plexus. The success of sensory and motor blocks, as well as postoperative analgesia, depend on the position of the catheter under the fascia iliaca.     

Vascular entrapment of the sciatic plexus causing catamenial sciatica and urinary symptoms

Aim of the video / Introduction

Pelvic congestion syndrome is a well-known cause of cyclic pelvic pain (Ganeshan et al., Cardiovasc Intervent Radiol 30(6):1105–11, 2007). What is much less well known is that dilated or malformed branches of the internal or external iliac vessels can entrap the nerves of the sacral plexus against the pelvic sidewalls, producing symptoms that are not commonly seen in gynecological practice, such as sciatica, or refractory urinary and anorectal dysfunction (Possover et al., Fertil Steril 95(2):756–8. 2011). The objective of this video is to explain and describe the symptoms suggestive of vascular entrapment of the sacral plexus, as well as the technique for the laparoscopic decompression of these nerves.

Method

Two anecdotal cases of intrapelvic vascular entrapment are used to review the anatomy of the lumbosacral plexus and demonstrate the laparoscopic surgical technique for decompression at two different sites, one on the sciatic nerve and one on the sacral nerve roots.

Result

After surgery, the patient with the sciatic entrapment showed full recovery of the sciatica and partial recovery of the myofascial pain. The patient with sacral nerve root entrapment showed full recovery with resolution of symptoms.

Conclusion

The symptoms suggestive of intrapelvic nerve entrapment are: perineal pain or pain irradiating to the lower limbs in the absence of a spinal disorder, and lower urinary tract symptoms in the absence of prolapse of a bladder lesion. In the presence of such symptoms, the radiologist should provide specific MRI sequences of the intrapelvic portion of the sacral plexus and a team and equipment to expose and decompress the sacral nerves should be prepared.

     

Bloc ≪ 3 en 1 ≫ ou bloc femoral. Que faut-il faire et comment le faire ?

The “3 in 1” block and the femoral nerve block are widely used for lower limb surgery and postoperative analgesia. Whether these blocks are in fact a same regional block with two different names or represent definitively two different blocks remains controversial. A large number of anatomical as well as functional variations of the lumbar plexus have been described and complicate a rational analysis of the spread of local anaesthetics following these blocks. Anatomical, radiological and especially clinical data seem to confirm that these blocks are to be distinguished from one another. Femoral nerve block requires the use of a nerve stimulator and has a high success rate in the territory of the femoral nerve; a spread towards other lumbar nerves, especially the lateral femoral cutaneous nerve, is sometimes observed. The “3 in 1” block is supported by the idea of diffusion within a space that is located after going through two fascial layers. Even in experienced hands, the success predictive value is not high. However, once the “3 in 1” block is well performed, a complete anaesthesia covering the territories of the femoral nerve, the lateral femoral cutaneous nerve, and the obturator nerve occurs. Specific indications of each technique are different: major knee surgery and postoperative analgesia for the “3-in-1” block and leg surgery for femoral nerve block. The best approach for knee arthroscopy remains open for discussion.     

Continuous lumbosacral block using a Tuohy needle and catheter technique

Three cases are reported where continuous lumbosacral block was performed using a catheter through an epidural needle technique. Good unilateral lower limb surgical anaesthesia was achieved in all three cases with successful blockade of the lumbar and sacral plexuses. A 17-gauge Tuohy needle was positioned between the transverse processes of L4 and L5 and an epidural catheter inserted into the space between the quadratus lumborum and psoas muscles. Forty to seventy millilitres of local anaesthetic were injected and resulted in good surgical anaesthesia within 12-20 min. Radiographic studies in these patients confirmed placement of the catheter in close proximity to the lumbosacral plexus. Experience in a further 12 cases is also reported. There were no side-effects. The technique is successful and is recommended when unilateral lower limb anaesthetic is required and when spinal and epidural anaesthesia are contraindicated.     

健侧骶1为动力源神经移位修复骶丛撕脱伤病例报告及文献回顾

目的 探讨健侧S1作为动力源神经修复1例骶丛撕脱伤的安全性与有效性.方法 2007年11月收治1例骨盆骨折伴左下肢功能障碍3个月患者,男性,10岁.术前检查:左臀部、大腿后侧、小腿外侧及足部皮肤感觉麻木或缺失,左髋外展、左膝屈曲和足踝部活动丧失.X线片示左骶髂关节分离术后、左耻骨上下支骨折.椎管照影显示左侧L4～S1根部假性硬膜囊肿.肌电图检查提示骶丛神经损伤.在全身麻醉下行左侧骶丛神经探查+健侧S1移位、腓总神经移植修复臀上神经和股二头肌肌支,左侧闭孔神经移位、腓总神经移植修复部分胫神经术.结果 该患者手术时间为5h,术中出血量约2000 mL,输血量为1600 mL.术后患者伤口一期愈合.术后4d右侧下肢髋外展、后伸、屈膝与踝关节跖屈、背伸活动基本无影响,踝关节外翻稍减弱;足底、足趾外侧部分皮肤感觉减退,面积约4cm×12 cm;术后20 d,皮肤感觉减退面积约为2 cm×6 cm.术后18个月随访,右足底皮肤感觉减退区消失,感觉恢复正常,右下肢感觉、运动功能恢复正常;左侧髋关节外展、膝关节屈曲肌力达3级,踝关节功能无恢复.结论 利用S1作为新动力源神经移位修复骶丛撕脱伤可能是一种安全而有效的手术术式.     

Continuous psoas compartment block for postoperative analgesia after total hip arthroplasty: new landmarks,technical guidelines,and clinical evaluation

A computed tomographic scan was obtained in 35 patients to measure the depth and the relationship of the branches of the lumbar plexus to the posterior superior iliac spine projection and the vertebral column. In addition, we prospectively studied 80 patients scheduled for total hip arthroplasty who received a continuous psoas compartment block (CPCB) in the postoperative period. CPCB was performed after surgical procedures by using modified Winnie's landmarks and nerve stimulation. From 5 to 8 cm of catheter was inserted. Radiographs were obtained after injection of 10 mL of contrast medium. An initial loading dose (0.4 mL/kg) of 0.2% ropivacaine was injected, followed by continuous infusion of 0.2% ropivacaine for 48 h. The depth of the lumbar plexus and the distance between the lumbar plexus and the L4 transverse process were measured. Visual analog scale values of pain at 1, 12, 24, and 48 h were obtained at rest and during mobilization. Amounts of rescue analgesia were also recorded. Sensory blockade of the principal branches of the lumbosacral plexus was noted at 1 and 24 h, as were adverse events related to the technique. There was a significant difference between men and women in depth of the lumbar plexus (median values, 85 vs 70 mm for men and women, respectively). There was a positive correlation between the body mass index and skin-lumbar plexus distances. In contrast, there was no difference regarding the distance between the transverse process of L4 and the lumbar plexus. The catheter tip lay within the psoas major muscle in 74% of the patients and between the psoas and quadratus lumborum muscles in 22%. In three patients, the catheter was improperly positioned. At 1 h, sensory blockade of the femoral, obturator, and lateral femoral cutaneous nerves was successful in, respectively, 95%, 90%, and 85% of patients. At 24 h, these rates were 88%, 88%, and 83%, respectively. During the 48-h study period, median visual analog scale values of pain were approximately 10 mm at rest and from 18 to 25 mm during physiotherapy. Five patients received 5 mg of morphine at 1 h. Five cases of unilateral epidural anesthesia were noted after the bolus injection. We conclude that CPCB with 0.2% ropivacaine allows optimal analgesia after hip arthroplasty, with few side effects and a small failure rate. Before lumbar plexus branch stimulation and catheter insertion, anesthesiologists should be aware of the L4 transverse process location and lumbar plexus depth. IMPLICATIONS: Lumbar plexus depth is correlated with the patient's body mass index and differs between men and women, but this is not true of the lumbar plexus-transverse process distance. Considering new landmarks, a continuous psoas compartment block promotes optimal analgesia after hip arthroplasty, with few side effects.