Fig. 36.1
Lumbar plexus from a lateral perspective relevant to the lateral trans-psoas approach [18]
Fig. 36.2
Lateral radiograph of the lumbar spine with overlay dividing the vertebral column into four zones. A generalized “safe zone” is depicted by the highlight in zone 3. Optimal safe trajectories are depicted for each level with white crosses
The most common plexus-related complications observed with the lateral approach are related to neuropraxic injury to the more superficial branches resulting in thigh or hip numbness and pain that is typically self-limited with the majority resolving by 1 month. Less commonly reported complications include thigh and hip pain, radicular pain, and quadriceps weakness. We believe that the following points specifically salient to the known possibility of plexus injury should be reviewed with patients during surgical consent:
Thigh/hip/groin numbness, paresthesias, or pain
Quadriceps weakness related to femoral nerve injury
Rare and typically avoidable (1.7, 4.8 % at L4–L5 level) [6] – most will improve with time and therapy
Psoas weakness
Nearly universal and transient on the ipsilateral side – typically attributed to direct muscular injury – but can occur from damage to some of the small nerve fibers from the plexus that innervate the muscle
The implications of lumbar plexus injuries related to the trans-psoas lateral approach typically involve a patient coping with minor sensory or motor deficits for a relatively short period of time during recovery from the neurapraxia. Reassurance and optimism from the physician are typically appropriate during the early postoperative assessments. Despite potential plexus complications, the majority of patients still demonstrate improved back and leg pain and decreased total disability scores after lateral procedures [3]. However, rare cases of persistent thigh or groin pain or debilitating proximal weakness can become more disabling than the presenting spine symptoms. We therefore advocate for recognition of these complications, careful avoidance, and aggressive treatment when appropriate.
36.2 Sensory Complications
Sensory complications related to stretch injury of the lumbar plexus during lateral trans-psoas approaches to the spine are common. L1–L3 sensory branches run with variable courses through the retroperitoneal fat, are challenging to visualize, and are not reliably detectable with SSEP recording. Because of the complex and overlapping dermatomal distribution of the iliohypogastric, ilioinguinal, and genitofemoral branches, differentiating numbness, pain, or paresthesias from these nerves can be challenging. The relative novelty of upper lumbar plexus anatomy to most spine surgeons and the typically self-resolving transient nature of injury to this region probably contribute to underreporting of sensory complications associated with lateral approaches. While even permanent sensory loss from damage to lumbar plexus sensory branches can be very well tolerated, the difference between the etiology of local anesthesia and a painful neuropathy is not well understood mechanistically, and therefore, we advocate for efforts aimed at accurately characterizing and minimizing injury to sensory portions of the plexus. In this section, we will review the function and anatomy of each sensory branch in the context of the lateral approach. Ultimately, to simplify reporting of sensory deficits relative to postoperative complications of the lateral approach, we recommend the sensory dermal zone (SDZ) classification system (Fig. 36.3) that classifies lumbar plexus sensory deficits into four simplified anterior zones. Pain in any of these zones typically resolves rapidly, but may persist chronically in up to 5.5 % of patients that experience it postoperatively [5]. In patients with a chronic painful neuropathy, a more detailed workup including EMG and selective blocks is warranted to identify candidate nerves for definitive therapy. Table 36.1 reviews the innervation of lumbar plexus nerves, complications associated with lateral trans-psoas procedures, and treatment options.
Fig. 36.3
Sensory dermal zones (SDZs) of the lumbar plexus. Left side – zones to simplify reporting of sensory complications. Right side – approximate dermatomes [17]
Table 36.1
Lumbar plexus nerve innervation, complications, and treatment options for consideration
Nerve | Cutaneous | Motor | Complications | Treatment |
|---|---|---|---|---|
Iliohypogastric | SDZ1 – lat. buttock, suprapubic | Transversus abdominis, internal oblique | Increased risk of direct hernia, pain | R/o direct hernia, paravertebral or superficial blocks, neurectomy, dorsal root ganglionectomy |
Ilioinguinal | SDZ1 – external genitals, medial thigh | Transversus abdominis, internal oblique | Groin pain | Paravertebral or superficial blocks, neurectomy, dorsal root ganglionectomy |
Genitofemoral | SDZ1 – external genitals, anteromedial thigh | Cremaster | Groin pain | Differentiate from ilioinguinal injury, neurectomy or blocks |
LFCN | SDZ2 – lat. thigh | None | Meralgia paresthetica | Medications, nerve block, neurectomy |
Femoral | SDZ3 – anteromedial thigh/leg | Iliopsoas, pectineus, sartorius, quadriceps | Weakness – hip flexion, knee extension, and rotation. Numbness or pain | Early rehabilitation, obturator nerve transfer |
Obturator | SDZ4 – inferomedial thigh | Adductor longus, adductor magnus, obturator externus, gracilis, pectineus | Adductor weakness – rare/unlikely | Early rehabilitation |
36.2.1 Iliohypogastric Nerve (T12, L1): SDZ1
The iliohypogastric nerve emerges from the posterolateral border of the psoas muscle at the L1 level and crosses obliquely behind the kidney, anterior to the quadratus and iliacus muscles, toward the anterior iliac crest. Just above the iliac crest, it divides into lateral and anterior branches with the lateral branch piercing the oblique muscles as it heads cutaneously and the anterior branch running between the transversus abdominis and internal oblique as it heads medially before piercing the internal and external obliques. These branches provide sensory innervation to the lateral buttock and the hypogastric suprapubic regions, respectively (Fig. 36.3).
The dermatomes of the iliohypogastric nerve often have redundancy with other sensory nerves, and isolated injury to this nerve should rarely produce a significant regional numbness. Given its long course through mobile retroperitoneal fat, tethering in multiple muscle and fascial layers, and the inability to reliably detect any changes with electrophysiological monitoring, injury to the iliohypogastric is likely common during the early stages of the lateral lumbar approach [7]. Most injuries are largely asymptomatic and transient and go undetected. The rare painful neuropathy warrants closer investigation if it persists. A potential localizer (which can represent either iliohypogastric or ilioinguinal damage) borrowed from abdominal surgery literature involves searching for a particular hyperalgesic pressure point 2–3 cm medial to the edge of the anterior superior iliac spine (ASIS) with possible relief from local anesthetic administered at this point [8]. Avoiding techniques that utilize a secondary incision for retroperitoneal palpation is recommended as these likely increase the risk of iliohypogastric or ilioinguinal injury [9].
Related posts:
Stay updated, free articles. Join our Telegram channel
Full access? Get Clinical Tree
