Persistent symptoms are most commonly caused by incomplete release of the transverse carpal ligament. A recent study analyzing 50 patients who required revision carpal tunnel release found that 58% of patients had persistent symptoms due to incomplete release. Compression occurred at the distal transverse carpal ligament in 56% of cases and at the proximal antebrachial fascia at the wrist crease in 44% of cases [3]. Endoscopic carpal tunnel release has often been cited as a risk factor for incomplete release of the transverse carpal ligament, particularly in early studies of endoscopic release [8]. However, meta-analysis data on endoscopic versus open releases find that endoscopic release is comparable to open release in regard to most complications, including the need for revision surgery and rate of persistent symptoms. The only difference is a slightly higher risk of catastrophic complications with endoscopic release, most commonly from complete transection of the median nerve [9].

Persistent symptoms may also be caused by chronic nerve injury. Relief of pain and numbness in a chronically compressed nerve may take many months to resolve even with complete surgical release. Often, exacerbating symptoms (such as nighttime pain) will be relieved with transverse carpal ligament release, but numbness will persist and gradually improve over time as the median nerve returns to full function [10]. Studies have shown that the best way to monitor gradual nerve function over time is with periodic clinical sensation assessment with Semmes-Weinstein monofilaments [11]. Careful clinical follow-up, therefore, is key in determining gradual improvement, particularly in patients with significant preoperative compression.

Persistent symptoms that fail to resolve should alert the clinician to examine other etiologies of hand and wrist pain. Even with careful history, thorough physical exam, and testing, the diagnosis of carpal tunnel syndrome in the patient with wrist and hand pain is not always straightforward. Hand pain can easily be confused with other common problems such as cervical radiculopathy , radial sensory neuritis, De Quervain’s tenosynovitis , carpal-metacarpal thumb arthritis , ulnar neuropathy at the elbow, or trigger finger. Other metabolic causes for neuropathy must also be considered including diabetes, alcoholism, vitamin deficiencies, HIV, chemotherapy agents, and adverse reactions from medications. In combination with slightly abnormal but clinically inconsequential electrodiagnostic studies, these patients may be incorrectly indicated for carpal tunnel release and result in persistent symptoms after surgery.

Recurrent symptoms are defined as a return of preoperative symptoms after a period of complete or partial relief following surgery. The most common cause of recurrent symptoms is the formation of excessive scar tissue surrounding the median nerve (perineural fibrosis ) or postoperative edema (swelling ) causing median nerve compression. The patient with recurrent symptoms will often complain of the exact same symptoms experienced preoperatively. It is, therefore, essential that clinicians document preoperative symptoms carefully, to aid in evaluation of postoperative recurrent carpal tunnel syndrome.

The time interval to recurrent symptoms can vary widely from patient to patient. In a retrospective review of recurrent carpal tunnel symptoms, the average time from the initial surgery to recurrence was 21 months but ranging from 14 days to 8 years [3]. In another study the average time to recurrence was 4.8 months, with the most common complaint consisting of numbness in the median nerve distribution [12]. While recurrent latency periods vary widely, the key to determining whether a patient has recurrent symptoms is some period of initial relief (which represents full transverse carpal ligament release), followed by return of preoperative symptoms.

Perhaps the most frustrating complaint following carpal tunnel release is the onset of a new symptom that was not present prior to surgical release. While the causes of new onset symptoms are numerous, the most common in the immediate onset is iatrogenic nerve injury. Patients may complain of new onset pain, trigger finger, and incisional “pillar” pain, which are largely separate issues from the original diagnosis. Worsening numbness or loss of two-point discrimination should alert the clinician to suspect iatrogenic nerve injury [13].

While rare, iatrogenic nerve injuries have been shown to occur. In revision surgeries iatrogenic nerve injury occurred in 3–6% of cases [3, 6]. Transection of the median nerve has also been documented, in one series occurring in 1 of 24 revision procedures and in another series in 2 of 200 revision procedures [6, 14]. Iatrogenic injuries can occur to the palmar cutaneous branch, recurrent motor branch, or median nerve as well as to digital nerves [10].

Clinical examination maneuvers, diagnostic studies, and diagnostic injections are all options in evaluating a patient with recurrent carpal tunnel syndrome. These studies are particularly valuable when preoperative studies are available for comparison. Provocative maneuvers, such as Phalen’s and Durkan’s tests and Tinel’s sign , are useful in eliciting compression in the carpal tunnel, especially when compared to the contralateral side and to preoperative assessments. Studies have shown that up to 50% of patients with recurrent carpal tunnel syndrome will have positive Phalen’s and Tinel’s tests, as well as experience loss in grip strength and limitations in performing fine motor tasks [15, 16]. In addition to provocative exams, diagnostic steroid injections have been shown to be helpful isolating pathology to the carpal tunnel. In one study examining patients with recurrent carpal tunnel syndrome, positive Durkan’s and Phalen’s tests in the presence of relief of symptoms from corticosteroid injection combined to provide a clinical diagnosis of median nerve compression with a sensitivity of 100% and a specificity of 80% [16].

Electrodiagnostic (EMG ) studies can also be helpful in determining the etiology of recurrent symptoms, particularly when preoperative studies are available for comparison [3]. EMG studies are particularly helpful when showing either clinical improvement or worsening (Table 15.1). If EMG findings are improved after surgical release, clinicians may monitor for clinical improvement over time. If EMG findings are worsened after surgery, clinicians should suspect iatrogenic nerve injury or exuberant postoperative perineural fibrosis. Equivocal EMG findings are more difficult to interpret and should lead clinicians to examine for other sites of compression or attempt a diagnostic intra-carpal tunnel steroid injection. In addition, imaging studies, particularly MRI, may be helpful to rule out other causes of compression within the carpal tunnel such as overly abundant tenosynovitis, fibrosis, or any space-occupying mass. MRI does not, however, reliably exclude incomplete release of the transverse carpal ligament [17].

Revision carpal tunnel surgery can be difficult due to excessive scar formation and perineural fibrosis distorting normal anatomy and surgical planes. Therefore, it has been recommended that the incision for revision surgery be made ulnar to the prior incision, as the median nerve may be adherent to the underside of the previous incision and is at risk during the initial dissection. In our experience, however, the median nerve usually resides away from the original incision and remains adherent underneath the radial leaflet of the incised transverse carpal ligament in close proximity to the tendon of the flexor pollicis longus. Certain authors also advocate for the extension of the incision, either proximal or distal, to access native tissue planes and identify the median nerve prior to surgical exploration in the prior surgical field [10]. This technique offers significant advantages in the setting of significant perineural fibrosis.