Neuroma in Continuity

Fig. 17.1

(a) Schematic representation of the cross-section of a normal peripheral nerve showing the connective tissue and nerve tissue components. (b) The cross-section of the peripheral nerve demonstrates a mixed, or sixth degree, injury pattern. This fascicle at the top left is normal. Moving in the counter clockwise direction, fascicle I is a first degree injury (neurapraxia) with segmental demyelination. Fascicle II is a second degree injury (axonotmesis). The second degree involves both the axon and the myelin. The endoneurial tissue is not damaged. Fascicle III demonstrates a third degree injury, with injury to the axon, myelin, and endoneurium. The perineurium is intact and normal. Fascicle IV demonstrates a fourth degree injury, with injury to the axon, myelin, endoneurium, and perineurium. The fascicle is marked by scarring across the nerve, with only the epineurium being intact. Fascicle V is a fifth degree injury in which the nerve is not in continuity and is transected. The surgeon will separate the fourth and fifth degree injury patterns, which will require reconstruction from the normal fascicles and the fascicles demonstrating first, second, and third degree injury patterns. These latter patterns of injury require, at most, neurolysis. (Permission to reprint from Thieme in Nerve Surgery by Mackinnon)

Diagnosis

The evaluation of these patients starts with a detailed history and physical exam. Focus is placed upon the pre- and postoperative symptoms. Patients with an iatrogenic injury to the median nerve resulting in a neuroma in continuity will complain of new neurological symptoms after their CTR, in the form of numbness, weakness, or pain, and these symptoms are often severe (Fig. 17.2). Physical examination can help to identify the area of injury. Careful sensory testing including two-point discrimination, Semmes-Weinstein monofilament testing, and the ten test of both the median innervated digital nerves and the palmar cutaneous branch can determine if all or a portion of the nerve has been injured which will help guide surgical management. Each digital nerve should be separately evaluated in the autonomous area (the volar lateral side of the middle phalanx). We have found the ten test to be very useful in the evaluation of these patients. Patients are given a scale of 1–10 with 10, normal; 5, half; and 0, no sensation. The normal hand is used as the control for 10, and then the injured finger(s) is touched in the same autonomous zone simultaneously with the contralateral side, and the patient reports a number between 0 and 10 [11]. We also use the scratch collapse test ethylene chloride hierarchy to evaluate for persistent and recurrent secondary carpal tunnel, evaluation of the median nerve in the forearm as well as iatrogenic median nerve injury [12]. A Tinel sign can help to localize the area of injury and should be performed proximal to the carpal tunnel as percussion over the carpal tunnel at the level of the injury will often result in severe and intolerable pain for the patient. We call this a “proximal” Tinel and specifically ask the patient to describe the precise distribution of the Tinel. Weakness or atrophy of the abductor pollicis brevis indicates an injury to the recurrent motor branch of the median nerve.

Fig. 17.2

Pain descriptions for neuromatous pain and non-neuromatous pain . The pain evaluation is an important tool for distinguishing types of pain and helping with the diagnosis. Neuromatous pain includes description of focal, brief, intermittent, sharp, often intense, and localizes to a specific nerve territory. Non-neuromatous pain includes description of diffuse and of varying quality and duration. (Permission to reprint from Thieme in Nerve Surgery by Mackinnon)

Nerve conduction studies should be performed during the evaluation of any patient presenting with symptoms of a failed carpal tunnel release, and the results should be compared to preoperative studies. Evidence of worsening median nerve function when compared to previous studies often implies injury to the median nerve or one of its branches and helps guide the decision for surgery. Recording to each median nerve, innervated digital nerve may be necessary to evaluate the VI degree injury pattern. For example, an injury to the third webspace fascicular group may not be noted if the electrodiagnostic reading is from the index finger.

Treatment

General Principles

Surgical treatment of a neuroma in continuity after carpal tunnel release requires careful attention to technique. The original incision site should be ignored in favor of a larger ulnarly placed incision that crosses the proximal wrist crease and carries on distal to the original incision to allow adequate exposure. The median nerve is first identified both proximal to the zone of injury in order to minimize the risk of further iatrogenic injury. Guyon’s canal is then released and the flexor retinaculum divided on the ulnar border. The flexor retinaculum is then retracted, and the injured median nerve will be visualized adherent to the overlying scar from original incision.

Identification and Resection of the Zone of Injury

Internal neurolysis of the internal and external epineurium is performed using microsurgical instrumentation until normal fascicles and bands of Fontana are encountered (Fig. 17.3). The extent of neurolysis required will vary by case and should continue until normal fascicles are encountered. We start the neurolysis proximally above the area of suspected injury and carefully proceed distally. Normal fascicles are first neurolysed to protect their function. All injured fascicles are identified and resected taking care to protect the uninjured, healthy portions of the nerve (Fig. 17.4).

Fig. 17.3

Exposure of median nerve and intraneurolysis . (a) The median nerve was identified proximal and distal to the zone of injury. It was found to have a course within dense scar tissue. (b) The median nerve was isolated from the scar tissue, and distal neurolysis revealed the sensory branches of the median nerve. The intact thenar motor branch and sensory fascicles to the thumb were protected. Suture material was found within the remainder of the injured median nerve. (c) Proximal neurolysis revealed the fascicular anatomy of the median nerve. The third webspace is neurolyzed proximally so that it can be used as graft material. (Permission to reprint from Thieme in Nerve Surgery by Mackinnon)

Fig. 17.4

Neuroma resection and first webspace grafted with a third webspace graft . (a) The zone of injury was identified, and the neuroma was resected with proximal and distal median nerve components identified. The third webspace was further neurolyzed proximally to mobilize graft material. (b) The proximal end of the third webspace fascicle was transected and used as a nerve graft to repair a portion of the median nerve. The proximal remainder of the third webspace was transposed proximally to prevent a painful neuroma. The distal third webspace was end-to-side transferred to the sensory component of the ulnar nerve to provide rudimentary sensation for donor deficit. (Permission to reprint from Thieme in Nerve Surgery by Mackinnon)

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