Injury to the Lumbar Plexus and its Branches After Lateral Fusion Procedures: A Cadaver Study

Introduction

Neurologic deficits from lumbar plexus nerve injuries commonly occur in patients undergoing lateral approaches. However, it is not yet clear what types of injury occur, where anatomically they are located, or what mechanism causes them. We aimed to study 1) the topographic anatomy of lumbar plexus nerves and their injuries in human cadavers after lateral transpsoas approaches to the lumbar spine, 2) the structural morphology of those injuries, and 3) the topographic anatomy of the lumbar plexus throughout the mediolateral approach corridor.

Methods

Fifteen adult fresh frozen cadaveric torsos (26 sides) underwent lateral approaches (L1-L5) by experienced lateral spine surgeons. The cadavers were subsequently opened and the entire plexus dissected and examined for nerve injuries. The topographic anatomy of the lumbar plexus and its branches, their injuries, and the morphology of these injuries were documented.

Results

Fifteen injuries were found with complete or partial nerve transections (Sunderland IV and V). Injuries were found throughout the mediolateral approach corridor. At L1/2, the iliohypogastric, ilioinguinal, and subcostal nerves were injured within the psoas major muscle, the retroperitoneal space, or the outer abdominal muscles and subcutaneous tissues. Genitofemoral nerve injuries were found in the retroperitoneal space. Nerve root injuries occurred within the retroperitoneal space and psoas muscle. Femoral nerve injuries were found only within the psoas major muscle. No obturator nerve injuries occurred.

Conclusions

Lateral approaches can lead to structural nerve damage. Knowledge of the complex plexus anatomy, specifically its mediolateral course, is critical to avoid approach-related injuries.

Introduction

The lateral transpsoas approach to the lumbar spine is increasingly being used to treat degenerative changes requiring fusion.¹ In contrast to conventional posterior spinal fusion techniques, this minimally invasive approach spares extensive posterior tissue dissection and resection for cage implantation and decreases operative time, blood loss, postoperative pain, and tissue trauma.¹ Although minimally invasive, this procedure has the approach-related potential to cause lumbar plexus (Figure 1) nerve injuries from the insertion and dilation of dilatators or retractors. Plexus injuries are reported in 6%–33% of cases and often present as neuropathic pain as well as motor or sensory deficits.1, 2, 3

Although neurologic deficits commonly occur, nerve injuries from these approaches have so far only been assessed clinically, leaving the following questions unanswered:

• Where can nerve injuries occur? At what spinal level, anatomic compartment (within the psoas major muscle, retroperitoneal space or subcutaneous tissue), and segment of the nerve?

• What type of nerve injuries can occur? Is there structural damage to the nerve?

• Which nerves, not commonly monitored by electromyography (EMG) or not clearly discernable by clinical assessment, are prone to injury?

• Are there surgical recommendations that could help to preclude these plexus injuries?

To answer these questions, we studied the topographic anatomy of the lumbar plexus nerves and their injuries in human cadavers after expert surgeons had performed lateral fusion procedures in the lumbar spine using standard operative techniques.

Several cadaveric anatomic studies on plexus nerve anatomy for lateral approaches have been reported.4, 5 However, to our knowledge, this is the first anatomic study on cadavers to examine the plexus nerves for possible injuries immediately after standard lateral fusion surgery. Our goal was to study which nerves can be encountered and injured throughout the mediolateral approach corridor, what types of injury can potentially occur, and what mechanisms might be involved.