Lumbosacral Plexus Injuries

Epidemiology and Causative Mechanisms

Described in the medical literature as late as in the 1960s, ¹ posttraumatic injuries of the lumbosacral plexus have received less attention than other nerve lesions, particularly their brachial counterpart. This dearth of information seems related with their presumed rarity; although no precise statistical data are available on their real incidence, it is generally assumed that they occur in 1% of pelvic traumas. Yet in recent years, it has been emphasized that they might simply remain undiagnosed and their real incidence could be between 40 and 52% of pelvic ring traumas. ² Apparently, less than 50% of posttraumatic lumbosacral plexus injuries (LSPIs) are detected on admission or during the early stage of hospitalization. As they generally occur in severe traumas and patients are often unconscious or uncooperative, the massive life-threatening lesions capture the physicians’ attention and these injuries can easily go unnoticed. Moreover in such circumstances, a thorough neurological examination can be extremely difficult and functional deficits can be simply considered the consequence of the concomitant bone injuries. ²^, ³^, ⁴

The traumatic event is often clearly related with the injury pattern, affecting its prognosis and outcome. ³^, ⁴ In more than 60% of cases, the injury occurs during a car crash. Remaining trapped in the vehicle, the patient sustains a pelvic crush that generally causes compression injuries of the lumbosacral plexus. ³^, ⁴ LPSIs due to motorcycle accidents are far less common ³^, ⁴ as well as those occurring during traumas after from falling from high, such as in work accidents (e.g., falling from a scaffold) or suicidal attempts; all these events imply high kinetic energy, mostly resulting in traction injuries. ³^, ⁴

LSPIs due to gunshot are uncommon ( ▶ Fig. 20.1), probably because they are often lethal; on the contrary, iatrogenic injuries (after hip arthroplasty or pelvic and abdominal surgery) are frequently encountered. ³^, ⁴

Fig. 20.1 Clinical examples of lumbosacral plexus injuries. (a) Sequelae of obstetrical lumbosacral plexus palsy due to breech delivery in a 5-year-old boy. (b) Sequelae of sacral plexus palsy in a 32-year-old man after gunshot injury.

During breech delivery, an LSPI can occur, but it is extremely rare ( ▶ Fig. 20.2). ³^, ⁴

Fig. 20.2 Sacral fracture responsible of sacral root compression in the foramina.

20.2 Clinical Pictures

Bilateral lumbosacral plexus impairment of different severity can be encountered. ³^, ⁴^, ⁵

Four injury patterns are usually described: lumbar plexus injury, lumbosacral trunk injury, sacral plexus injury, and complete LSPI (see ▶ Table 20.1). Sacral plexus injuries and lumbosacral trunk injuries are statistically predominant. ²^, ³^, ⁴ In sacral injuries and total palsies, the neurological presentation may include loss of sphincter control, sexual disturbances, and severe, excruciating pain. These symptoms should always raise a red flag as they are associated with root avulsions. ³^, ⁴

**Table 20.1** Clinical presentation according to injury patterns
Injury patterns	Motor impairment	Sensory loss	Remarks
Lumbar plexus injury	Iliopsoas, quadriceps, hip adductors	Anterior, medial, and lateral surfaces of the thigh and medial aspect of the lower leg	Iatrogenic injuries are common Femoral fractures in 50% of cases No avulsions Spontaneous recovery mostly occurs
Lumbosacral trunk injury	Glutei, peronei, tibialis anterior and posterior, extensor digitorum, and hallucis longus	Mainly L5 dermatome	The most frequent injury pattern No avulsions High rates of spontaneous recovery
Sacral plexus injury	Glutei, hamstrings, peronei, gastrocnemius, tibialis anterior and posterior, extensor digitorum, and hallucis longus	Buttock and perineum, posterior surfaces of thigh and calf, anterolateral aspect of the lower leg, sole of foot	The second most frequent clinical presentation High incidence of sacral fractures Possibility to detect lower roots avulsions
Complete lumbosacral plexus injury	All the above	All the above	High incidence of sacroiliac joint dislocation Possibility to detect roots avulsions

As LPSIs are sustained in severe pelvic traumas, fractures, and dislocations concomitant, endopelvic organs and vascular injuries are usually found. Bone injuries occur in more than 90% of patients. ²^, ³^, ⁴ All kinds of pelvic fractures can be encountered, yet some are statistically prevalent and correlated with the typology of causative mechanism (see ▶ Table 20.1). In particular, note that it is clearly stated in the literature that sacroiliac joint separations are regularly associated with root avulsions. ²^, ³^, ⁴

Injuries of endopelvic organs (extraperitoneal bladder rupture, intestinal perforation of the terminal sigmoid colon or rectum) and vascular injuries (gluteal or iliac artery/vein rupture with retroperitoneal bleeding) are, respectively, detected in 30 and 10% of these patients ³^, ⁴ and may require urgent treatment.

20.3 Management

LSPIs should always be suspected in pelvic traumas. Early electromyogram (EMG) has been recently suggested in order to overcome the limits of the neurological examination during the acute phase. ⁶

In sacral fractures allegedly associated with neurological complications, early traction (limiting the rise of the hip bone and the lateral fragment of the aileron) and surgical realignment reduce the compression and clearly favor neurological recovery. ²

In gunshot injuries, the missile wound should receive immediate treatment in order to avoid complications, specially infections.

On the suspicion of a posttraumatic LSPI, investigations to assess the extension and severity of the nerve damage should be prescribed with the main purpose of revealing the presence of root avulsions. Although electrodiagnostic studies performed 3 to 4 weeks after the traumatic event can distinguish between neuroapraxia and more severe forms of nerve damage, it must be noted that information provided by such techniques is inferred but not directly demonstrated. Thus, imaging is the core of the diagnostic assessment. Three-dimensional (3D) magnetic resonance imaging (MRI) should be considered the first choice of investigation. ⁷ It offers high diagnostic accuracy and is not invasive as myelo-CT (computed tomography). It can also reveal muscle denervation in correlation with signal intensity chances. ⁷ Nowadays, it is generally accepted that the absence of pseudomeningoceles does not exclude avulsions and vice versa (intact roots have been visualized inside them). However, these bulky, mushroom-like images subsequent to the dural tear occurring when the roots are violently pulled out from the spinal cord are still fundamental in the diagnostic assessment of plexual injuries. Pseudomeningoceles need a few weeks to form; therefore, neuroradiological studies are conveniently performed 3 to 4 weeks after the trauma.

Apparently avulsions are found in less than 25% of LSPIs and only in sacral plexus and complete LSPIs; L5 and S1 are the most frequently avulsed roots, whereas the upper roots are never found avulsed. ³

Once the diagnostic assessment is accomplished, a peripheral nerve surgeon should evaluate whether the injury is amenable of spontaneous recovery or if surgery should be offered to the patient.

Regardless of the indication for surgery or conservative treatment, early and intensive physiotherapy is strongly recommended to prevent muscle degeneration and joint stiffness. If needed, specific braces should be prescribed.

Severe pain is often reported. In addition to the sequelae of bone injuries, it is often the consequence of deafferentation following root avulsions. Pain management is of paramount importance. Severe and uncontrolled pain is detrimental, strongly limiting or making physiotherapy impossible and completely disrupting the patient’s quality of life. Adequate pain control usually requires a multidisciplinary approach and should encompass medical therapy (e.g., tricyclic antidepressants, opiates, and pregabalin), physical treatments, and psychological counseling. Mirror visual feedback treatment (effective in chronic pain of central origin) could possibly have a role, but no experience is presently available in these cases. The importance of psychological issues has clear evidence. When patients are reintegrated into socially and professionally active lives, pain control is more easily achieved. Nevertheless, it must be admitted that in severe deafferentation pain, treatment is often ineffective and surgical options (e.g., drezotomy) must be taken in account.

Sildenafil is also offered to patients with impaired sexual functions.

20.4 Natural History

Spontaneous recovery of LSPIs occurs in 50 to 70% of cases, usually starting 8 months after the trauma. ³ Average time of recovery is 18 months but can occasionally last up to 36 months. The low rate of avulsions does not seem to be the only explanation for this frequent favorable evolution. The lumbosacral plexus is known to present anatomical variations, with extradural or intradural anastomosis and extradural nerve root divisions. Collateral sprouting from healthy or less severely injured neighboring nerves could contribute to the recovery. ⁵

Follow-up shows that complete, spontaneous recovery seems the rule in lumbar plexus injuries associated with femoral fractures along with the reabsorption of the hematoma that forms around the fracture as well in those cases associated with a hematoma in the psoas. ³

When caused by traction of self-retraining retractors, iatrogenic injuries also present favorable evolution. ³

For the remaining patterns, when no avulsions are detected, spontaneous recovery also occurs in high percentage. However, complete restitutio ad integrum is unlikely and minor sequelae (e.g., hallux extensor and gluteus medius deficits) are common. ²^, ³^, ⁴ In some cases, spontaneous recovery may only involve the sciatic medial trunk with a permanent foot drop. ²^, ³^, ⁴

20.5 Indication for Surgery

In LSPIs where neuroradiological exams reveal multiple avulsions, surgery should be promptly advocated, being the only expendable option not only to regain partial function, but also to relieve pain. Yet it must be admitted that early exploration and repair of LSPIs is not realistic. These patients are generally late referral cases for the consistent delay in diagnosis or the need to postpone the nerve repair after concomitant injuries have been treated.

When the diagnostic assessment rules out avulsions, if a neurotmesis is not deemed a likely event, conservative treatment may be initially offered; however, if no signs of spontaneous recovery appear clinically or at EMG within 5 to 8 months after the traumatic event, indication for surgery should be given.

In long-dating injuries, nerve surgery has unfavorable outcome and functional restoration can be achieved by tendon transfers. Such procedures can be applied also in case of inadequate recovery after nerve repair, provided that a donor muscle is expendable (M4 or more). Transposition always implies a reduction in muscle strength and if the muscle to be transposed is already flabby or weak, the procedure is doomed to fail.

20.6 Main Principles in Repair Strategy

Differently from the brachial plexus, easily and completely explored via an anterior approach, a complete exposure of the lumbosacral plexus is not possible via a single approach. Root transections, contusions, or avulsions require a posterior approach, whereas the lumbar plexus is explored via an anterior approach. Given its hidden position in the pelvis, access to the sacral plexus requires a multidisciplinary approach and encompasses a high rate of complications. On the other hand, surgical outcome has clearly proved remarkably unfavorable in comparison with the brachial counterpart. All this has resulted in a nihilistic attitude toward lumbosacral plexus surgery. Even in cases not amenable of spontaneous recovery, most surgeons refrained from giving an indication for surgery. In more recent times, in the wave of the enthusiasm aroused by the favorable outcome of nerve transfers in brachial plexus injuries, lumbosacral plexus surgery is going through a rebirth of interest. A few reports have been published prompting peripheral nerve surgeons to resume and further develop it. In order to counterbalance such tendency, it must be honestly admitted that the surgical series reported in the literature are statistically not significant, mostly being just case reports with successful outcome. Moreover, nerve transfer often imply the sacrifice of a donor nerve whose value must be carefully assessed in the economy of the general function of the limb. For instance, in a case of a complete palsy where the obturator nerve has been spared, its choice as a donor nerve involves the loss of the adductors necessary when the patient moves from the bed to the wheelchair.

In evaluating the repair strategy in LSPIs, the surgeon must have a clear vision of the advantage that the surgery could actually offer, the adjunctive deficit/s and its/their role on the overall situation according to the donor/s chosen for the possible nerve transfers as well as having a correct idea of the level and the extension of the nerve injury in planning the repair strategy. ⁵^, ⁷ In complete LSPIs, it must be considered that surgical reinnervation may require more than one procedure. ⁵^, ⁷

It must be stated as preliminary remark that distal functional restoration of the lower limb is not possible, but also not necessary. Even a complete palsy of the foot does not impair standing and walking. Surgery aims and may only restore proximal muscles (iliopsoas, glutei muscles, and quadriceps) which control hip and knee stability and leg flexion/extension, basic requirements to allow independent standing and walking instead of being confined to a wheelchair. ⁵^, ⁷

In lumbar plexus injuries, the goal of surgery is to restore iliopsoas and quadriceps; this can be achieved by direct repair of the femoral nerve or, when this may turn out technically impossible, by nerve transfers. Concerning the latter, a transfer from the obturator nerve (generally spared in most lumbar plexus injuries) to the femoral nerve is the technique of choice by most surgeons. ⁷^, ⁸^, ⁹ Alternatively, some authors ⁵^, ¹⁰ have attempted to transfer the 10th and 11th intercostal nerves to the intra-abdominal femoral nerve.

In long-dating lumbar plexus injuries or when femoral nerve reinnervation is impossible or fails, knee extension can be restored by tendon transfer, usually employing a combination of the biceps femoris and semitendinosus muscles. ¹¹

In sacral plexus injuries, hip stability is the main goal of surgery. Intradural repair of ruptured ventral sacral roots is rare and the surgeon usually resorts to other techniques such as homolateral or contralateral root transfer to the distal root stumps or to the gluteal nerves. Alternatively a femoral nerve to the gluteal nerves/medial sciatic trunk can be considered. ⁵^, ⁷

In total palsy, surgery should be focused on restoring iliopsoas, glutei muscles, and quadriceps, and the choice on the expandable repair strategies is dependent on the presence of root avulsions. ⁵^, ⁷

As previously pointed out, spontaneous recovery may be associated with sequelae varying from impairment of toe dorsiflexion or gluteal medius weakness to foot drop. Tendon transfers may contribute to improve hip stability (e.g., vastus lateralis muscle transfer or ventral transposition of the gluteus maximus to completely paralyzed gluteus medius) ¹¹ or can restore foot dorsiflexion (tibialis tendon transfer). ⁷

▶ Fig. 20.3 schematically shows a synopsis of the repair strategies applied in nerve microreconstruction according to the different kinds of LSPIs.