Peripheral Neuropathies

Pathogenesis

Injuries to peripheral nerves have several etiologies. It is commonly accepted that stretch, compression, generalized ischemia, or any combination thereof contribute to postoperative sensory or motor deficits. Compression can be from direct contact with a surface from positioning or it may be indirect as the nerve is stretched over a bony prominence. All of these factors ultimately result in ischemia or mechanical damage that lead to structural and/or functional derangement of the affected nerve (12). Alvine and Schurrer have suggested that subclinical neuropathies are present in many patients who suffer a postoperative nerve injury (13). This conclusion is based on the fact that nerve conduction velocities were abnormally slow in both the affected and contralateral ulnar nerves in patients with postoperative ulnar neuropathies. Most studies note an average time to onset of symptoms of three to five days (Table 2).

Brachial Plexus Palsy

The brachial plexus is at risk of injury due to stretching from surgical positioning. The brachial plexus (C5-T1) courses from its vertebral foramina into the axilla and lies near several bony prominences that can act as a fulcrum, contributing to stretch injury. Stretch is thought to be maximal at 90° abduction and slight extension (14). When positioning the patient, it would be prudent to avoid the combination of extension and abduction. The clinical sequelae of brachial nerve injury vary according to which part of the plexus, upper versus lower, is injured. Stretch injury usually affects the upper plexus (C5-C7). Injury to this part of the plexus usually results in decreased strength and weakness of the affected arm, and is usually painless, though radicular pain may occur. There also may be a sensory deficit of the first three digits and the lateral forearm. Lower plexus injury is rarely due to surgical positioning.

When it occurs, brachial plexus palsy is usually due to Trendelenburg positioning, with the patient supported by shoulder pads. Thus, the potential for this type of injury exists in patients undergoing laparoscopic radical prostatectomy and laparoscopic radical cystectomy, or any other procedure in which the patient is in steep Trendelenburg for a prolonged period of time.

TABLE2 ■ Summary of Peripheral Neuropathies

Nerve

Position

Cause of injury

Prevention of injury

Deficit

Brachial plexus

Shoulder abduction +

Stretch of the nerve roots

Avoiding 90° of abduction

Usually painless weakness of

(C5-T1)

extension or use of

with extension and avoiding

affected arm (C5-C7) or

shoulder braces in

use of shoulder braces

"waiter's tip" deformity (C8-T1)

steep Trendelenburg

Ulnar nerve

Elbow flexion and

Nerve compression as it

Avoid extreme elbow flexion

Numbness or pain at elbow and

pronation

passes through cubital

and adding pressure to

along fifth digit. Weakness of

tunnel

elbow with tape

flexion of fourth and fifth digits

Median nerve

Complete extension

Nerve stretch

Avoid complete elbow

Pain or tingling of thumb, index,

of elbow

extension by padding

and middle fingers. Thenar

under forearm

muscle weakness

Peroneal nerve

Lithotomy

Nerve compression by

Ensure weight of leg is

Numbness of foot dorsum,

(L4, 5; S1, 2)

stirrups as nerve passes

supported by heal in

weakness of foot and

over head of fibula

stirrup, proper padding

toe extension

of lateral aspect of leg

Femoral nerve

Any

Direct surgical trauma

Care to avoid prolonged

Numbness of anterior and medial

(L2-4)

to nerve

pressure or trauma to

thigh and weakness of

iliopsoas muscle

quadriceps muscles

intraoperatively

Obturator nerve

Any, but usually

Direct surgical trauma

Careful intraoperative

Pain radiating through

(L2- 4)

lithotomy

to nerve

dissection and use of

medial thigh

electrocautery

When it occurs, brachial plexus palsy is usually due to Trendelenburg positioning, with the patient supported by shoulder pads. Thus, the potential for this type of injury exists in patients undergoing laparoscopic radical prostatectomy and laparoscopic radical cystectomy, or any other procedure in which the patient is in steep Trendelenburg for a prolonged period of time.

Wolf et al. noted that none of their cases of pelvic laparoscopy with the patient in steep Trendelenburg suffered upper extremity injuries (3), but this was prior to the era of laparoscopic prostatectomy and cystectomy. Should injury to the lower portion of the plexus occur, it usually manifests as a motor deficit, with the arm favoring an adducted and posteriorly extended position known as a "waiter's tip deformity."

Ulnar Neuropathy

Symptoms of ulnar neuropathy are that of pain about the elbow or along the fifth digit and that side of the hand. Alternatively, the patient may experience tingling, paresthesia, hypesthesia, and/or numbness in the ulnar distribution (Fig. 3). Motor deficits include weakness in flexion of the fourth and fifth digits. Alvine et al. noted that six of their 17 patients with ulnar neuropathy were positioned in the flank position, and in all of these patients, the injury occurred in the arm contralateral to the side that was in contact with the operating table (12). Nerve damage is due to compression of the ulnar nerve in the cubital tunnel that results from elbow flexion. The nerve is more susceptible to external compression when in the pronated position. Thus, when positioning a patient, avoidance of prolonged and extreme elbow flexion as well as pronation is advisable. When taping the arm as it is brought across the body, as for laparoscopic nephrectomy in the modified flank position, it is best to avoid placing the tape directly over the unpadded elbow, because it may contribute to compression of the ulnar nerve.

Median Neuropathy

According to Warner, muscular patients with large biceps who do not usually fully extend their elbows are susceptible to stretch injury of the median nerve when the elbow is fully extended under anesthesia (Fig. 10) (11). Although not specific to laparoscopy, this scenario could potentially occur during laparoscopic surgery. Symptoms include pain or tingling in the middle finger, index finger, and thumb, and weakness of the thenar muscles. Prevention of this injury includes padding of the forearm to keep the elbow slightly flexed.

Peroneal Neuropathy

The common peroneal nerve is susceptible to compression injury because it courses around the head of the fibula (Fig. 6). Poor positioning in a leg holder can easily compress this bony prominence because it has little overlying tissue for natural padding. The peroneal nerve of the downside leg can also be compressed if not carefully padded when the patient is in flank position. Symptoms of peroneal neuropathy include weakness of foot and toe extension and numbness over the dorsum of the foot (Figs. 7 and 8). Positioning the foot in the leg holder with the weight of the legs supported by the heel and avoidance of direct contact with the fibular head or generous padding of this area will help prevent injury to the peroneal nerve.

Femoral Neuropathy

Femoral nerve injury results most commonly from retractor placement during open surgery and is therefore unlikely to be encountered after laparoscopic procedures. It is thought that retractors stretch the nerve or cause ischemia as they apply pressure to the iliopsoas muscle. It is conceivable that a direct injury could occur during laparoscopy from dissection along the pelvic sidewall. Femoral neuropathy manifests as weakness of the quadriceps muscles and sensory deficits of the anterior and medial thigh (Fig. 5).

Obturator Neuropathy

Direct surgical trauma to the nerve, rather than positioning, causes obturator neuropathy. Wolf et al. reported this in two of 405 patients undergoing pelvic laparoscopic surgery (3). Stolzenburg noted a higher incidence of obturator nerve injury occurring in two of 70 patients undergoing laparoscopic prostatectomy (15), a series representing the authors' initial experience with that procedure. Symptoms of obturator neuropathy include pain radiating from the groin down to the medial thigh and weakness of the thigh adductor muscles.

Abdominal Wall Neuralgias

Wolf et al. defined abdominal wall neuralgias as pain, impaired sensation, or hyperes-thesia radiating from a port site (3). These were the most common type of neuromuscular complication reported in their survey, with an incidence of 1%. It is interesting to note that patients experiencing abdominal wall neuralgias had relatively low-body mass index, perhaps indicating a greater statistical likelihood of a trocar injury to a cutaneous nerve in patients with relatively less surface area compared to larger patients.

Direct surgical trauma to the nerve, rather than positioning, causes obturator neuropathy.

FIGURE 10 ■ Stretching of the median nerve with full extension of the elbow.

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