Jones, Neil F. M.D.; Ahn, Hee Chang M.D., Ph.D.; Eo, SuRak M.D., Ph.D.
Since Learmonth performed the first surgical treatment for carpal tunnel syndrome in 1933, carpal tunnel release has become the most frequently performed hand operation in the United States.1 In addition to the classic open technique, newer endoscopic techniques have been introduced by Chow, Okutsu, Teo, and Agee.1,2 Although complications are not common after carpal tunnel release, a small number of patients may continue to experience persistent symptoms or may experience new and different symptoms in the postoperative period.
The persistence of preoperative symptoms may occur after either open or endoscopic carpal tunnel release and correlates with incomplete release of the transverse carpal ligament.3 On the contrary, recurrence is defined as “documented carpal tunnel syndrome in which the symptoms had resolved following surgical release, but then recurred, requiring a re-release of the carpal tunnel.”4 Although possible reasons for recurrent carpal tunnel syndrome have been hypothesized by some hand surgeons,4,5 its pathogenesis is still not clear. A retrospective review of 50 consecutive patients who required a second operation performed by the senior author (N.F.J.) for persistent or recurrent symptoms after initial carpal tunnel release in 55 hands was performed to analyze the surgical findings and patients' outcomes.
MATERIALS AND METHODS
After institutional review board approval, medical records were analyzed to identify patients who had undergone revision carpal tunnel surgery performed by a single surgeon (N.F.J.) at the University of California, Los Angeles Medical Center over a 6-year period from March of 2001 through February of 2007. Documentation of preoperative symptoms, physical examination, and electrodiagnostic studies before the revision carpal tunnel operation were recorded. Associated systemic conditions and the technique of the initial carpal tunnel release were obtained from the chart review. Details of displacement of the median nerve, scarring, site of incomplete release, and visible injury to the median nerve were collected from the operative reports. Patients' outcomes at least 1 year postoperatively were documented as either complete, improved, or unchanged symptomatic relief.
Fifty-five hands in 50 consecutive patients underwent a second operation after an initial carpal tunnel release over a 6-year period performed by a single surgeon. Forty-seven patients had their carpal tunnel release at another institution and three patients had been treated by other surgeons in our institution. Twenty-nine were men and 21 were women. The initial carpal tunnel release was an endoscopic technique in 34 hands and an open technique in 21 hands. The affected hand was the dominant hand in 46 of the 50 patients; there 14 left hands and 31 right hands, and five were affected bilaterally.
Thirty-four hands in 30 patients had persistent symptoms after primary carpal tunnel release (Table 1). Reexploration revealed incomplete release of the flexor retinaculum distally in 18 hands and intact antebrachial fascia proximally at the wrist in 14 hands (Table 2). Two patients had “double-crush” syndrome caused by pronator syndrome. Eighteen hands in 17 patients developed recurrent symptoms after initial relief of their original symptoms following primary carpal tunnel release an average of 21 months after the initial operation (range, 7 months to 8 years). Three patients developed completely different symptoms after their initial carpal tunnel release. One patient presented with weakness of thumb abduction and thenar atrophy after the primary carpal tunnel release, and one patient presented with numbness and paresthesias down the ulnar aspect of the long finger and the radial aspect of the ring finger after the primary carpal tunnel release.
The average interval between the first carpal tunnel release and the second operation was 1 year 5 months (range, 3 months to 8 years) (Fig. 1). All patients presented with both clinical symptoms and signs and electrodiagnostic criteria of compromised median nerve function.
Systemic diseases or associated conditions are summarized in Table 3. Trigger thumb developed in three hands after the primary carpal tunnel release. Other nerve compression syndromes, including the “double-crush” phenomenon, occurred in three patients.
The most common intraoperative finding at surgical reexploration was incomplete release of the flexor retinaculum in 32 hands (58 percent) (Fig. 2). Obviously, incomplete release was associated with persistent symptoms. In 18 hands (32.7 percent), the distal few millimeters of the transverse carpal ligament had not been completely released, and in 14 hands (25.5 percent), the antebrachial fascia at the wrist crease remained intact. The location of the incomplete release did not correlate with the original endoscopic or open technique. Circumferential fibrosis of the median nerve within the carpal tunnel was seen in all cases, including patients with persistent, recurrent, and new symptoms. Severe scarring of the palmaris longus tendon over the median nerve was observed in four hands (7.3 percent). Severe synovial proliferation was found in four hands (7.3 percent), and rice bodies, amyloid deposits, and calcinosis were found in one hand each. Two ganglions were discovered at the second carpal tunnel release. Reexploration of two of the three patients who had developed completely new symptoms after their initial carpal tunnel surgery revealed transection of the motor branch of the median nerve after open carpal tunnel release and a neuroma-in-continuity (Fig. 3) of the common digital nerve to the long/ring finger web space after an endoscopic carpal tunnel release. There were no specific abnormal intraoperative findings to explain the symptoms in three patients (5.5 percent). Five patients underwent an ancillary procedure such as cubital tunnel, radial tunnel, or pronator syndrome release.
Formal external neurolysis was performed in 41 hands, neurolysis under the operating microscope was performed in 18 hands, and epineurectomy was performed in 15 hands (Fig. 4 and Table 4). Coverage of the median nerve was performed using a synovial or hypothenar fat flap in eight patients (Fig. 5) and a reverse radial forearm adipofascial flap in three patients.
Postoperatively, abductor pollicis brevis strength, evaluated by the senior surgeon on a five-point scale, was improved in 24 patients (48 percent). Pain, numbness, and paresthesias resolved completely or improved in 40 patients (80 percent) and 45 hands after reoperation, but remained unchanged in 10 patients (20 percent), five of whom (10 percent) required a third operation. Eight of these 10 patients underwent second carpal tunnel surgery for recurrent symptoms and two patients underwent second carpal tunnel surgery for persistent symptoms. Operative findings associated with a poor result included severe circumferential fibrosis around the median nerve, proliferative tenosynovitis, and amyloidosis. Workers' compensation insurance and a painful hypersensitive incisional scar before the second operation were also associated with a worse prognosis.
Of the 34 primary endoscopic carpal tunnel releases, symptoms improved in 26 hands (76 percent); symptoms were relieved completely in 19 (56 percent) and unchanged in eight hands (24 percent). Of the 21 primary open carpal tunnel releases, symptoms improved in 19 hands (90 percent), 12 (57 percent) had complete relief of their symptoms, but there was no improvement in two hands (9.5 percent) (Table 5). Five hands required a third operative procedure.
Carpal tunnel release has become one of the most common and successful hand surgery procedures performed, regardless of the various surgical techniques used—the original open method,6 endoscopic techniques,1,4,6,7 and the limited mini-incision techniques.8 However, complications and failures have been shown to occur in 3 to 19 percent in large series,3,9 necessitating reexploration in up to 12 percent.5,10
Tung and Mackinnon11 classified the indications for secondary carpal tunnel surgery into three general types: persistent, recurrent, and new symptoms. Symptoms may persist after surgery, with little or no improvement. Although Proubasta et al.12 described the “fat pad” and “little finger pulp” signs to confirm complete release of the transverse carpal ligament intraoperatively, incomplete release of the transverse carpal ligament is the most common cause of persistent symptoms after carpal tunnel release, with a reported incidence of 7 to 20 percent.3,13 The most distal portion of the transverse carpal ligament and the proximal antebrachial fascia are the most likely sites of ongoing compression because of the difficulty of adequate exposure in endoscopic and limited mini-incision techniques. However, it has been difficult to determine the true contribution of incomplete release, because many patients have also been found to have other contributing factors such as fibrous proliferation or tenosynovitis.14 In addition, compression of the median nerve more proximally in the forearm (pronator syndrome) or in the neck may lead to a misdiagnosis of carpal tunnel syndrome, and persistent symptoms may be caused by a “double-crush” syndrome.5,15 It is imperative that surgeons consider an incorrect diagnosis as the cause of persistent symptoms rather than automatically assuming incomplete release.
Recurrent carpal tunnel syndrome implies that there has been significant improvement or complete relief of the patient's symptoms that lasts for a definite period of time after the initial carpal tunnel release. Eventually, however, similar symptoms develop again. We have defined recurrent carpal tunnel syndrome as symptoms recurring after a minimum of 6 months of complete relief of the original symptoms after the primary carpal tunnel release. Epineurial fibrosis, interstitial scar, and soft-tissue adhesions to the nerve are common causes of recurrence after carpal tunnel release.16–18 Pizzillo et al.19 and Hunter20 described traction neuropathy when the epineurial surface of the median nerve is surrounded by scar tissue that is irritated by repetitive wrist and finger flexion and extension. Proliferation of fibrous scar tissue may form directly around the median nerve and either externally compress the nerve or “spot-weld” the nerve to surrounding structures (Fig. 6, above), preventing normal nerve gliding and leading to traction neuritis of the nerve whenever the wrist or digits are flexed or extended. Contributing factors may include poor hemostasis, prolonged immobilization, and overzealous physical therapy.
Finally, completely new symptoms may develop following primary carpal tunnel release that are quite distinct from the patient's initial complaints. Neuropathic pain out of all proportion to the surgery, or new areas of numbness or paresthesias, or marked weakness of the thenar muscles implies iatrogenic injury to the median nerve or its branches, usually the palmar cutaneous branch or the thenar motor branch after open carpal tunnel release, or the common digital nerve to the long/ring finger web space after endoscopic carpal tunnel release. Vascular injury to the superficial palmar arch or a common digital artery, “pillar” pain, a painful incisional scar, and trigger finger are infrequently encountered after carpal tunnel surgery.11
Evaluation of a patient with an unfavorable result following carpal tunnel surgery begins with a detailed history, specifically regarding whether the patient's symptoms are similar to those preoperatively or whether they are new symptoms such as pain, numbness, or paresthesias. Iatrogenic injury to the median nerve or its branches should always be suspected in the presence of pain out of all proportion to the carpal tunnel surgery. Examination should include the position and length of the previous carpal tunnel incision, tenderness or a Tinel sign over the incision, Phalen sign, weakness of the abductor pollicis brevis muscle compared with the contralateral normal thumb, or atrophy of the thenar muscles. Two-point discrimination and Semmes-Weinstein monofilament testing of each of the digital nerves within the median nerve distribution and the palmar cutaneous branch of the median nerve should be performed. We have found the Phalen sign, comparison of the strength of the abductor pollicis brevis muscle, and subjective “splitting” of the ring finger sensibility to be the most informative signs on physical examination. The possibility of pronator syndrome should be excluded by examining for tenderness or a Tinel sign over the median nerve in the proximal third of the forearm; weakness of the flexor pollicis longus and flexor digitorum profundus muscles to the index and long fingers; and several provocative maneuvers including the pronator compression test, resisted flexion of the proximal interphalangeal joint of the long finger, the resisted pronation test and the elbow flexion test.
Nerve conduction studies should be repeated and compared with any preoperative nerve conduction study to determine whether they are the same, have improved, or are worse. If the repeated nerve conduction studies are worse or electromyography shows signs of denervation of the thenar muscles, this implies either injury to the median nerve or its branches and provides objective evidence to proceed with surgical reexploration. If the repeated nerve conduction study is the same or slightly improved compared with the initial nerve conduction study, this does not really help in determining whether to perform reexploration. Repeated nerve conduction studies may potentially detect other compression neuropathies or other diagnoses that may have been missed on the initial, possibly less detailed, nerve conduction study. Ultrasound and magnetic resonance imaging may help define pathologic anatomy,14 but absolute indications for their use have not been defined. The operative report from the initial carpal tunnel release should be obtained and reviewed for any hints of difficulty, poor visualization, or excessive bleeding.
Patients with both persistent and new symptoms are usually treated conservatively with scar massage, hand therapy, and a removable wrist splint for 9 months after the initial carpal tunnel release operation, unless objective signs and nerve conduction studies are suspicious for an iatrogenic injury to the median nerve or its branches, in which case early reexploration is indicated. A protective padded glove and scar-modifying gels may be appropriate for patients with complaints of painful or hypersensitive scars. Occasionally, a steroid injection just proximal to the wrist crease in patients with persistent or recurrent symptoms may be diagnostic if it results in a temporary improvement in the patient's symptoms.
Our approach to reexploration has been to extend the previous incision both proximally and distally. For patients who have previously undergone an Agee endoscopic carpal tunnel release, the transverse endoscopic incision can be extended distally from one end of the transverse limb and proximally from the opposite end of the transverse limb. The median nerve is identified in normal tissues proximal to the previous incision and traced in a proximal-to-distal direction. Similarly branches of the median nerve are identified in normal tissues in the palm and traced in a distal-to-proximal direction.
The surgeon should look specifically for remaining intact transverse fibers of the distal end of the transverse carpal ligament that had not been released at the initial carpal tunnel release, or intact antebrachial fascia proximally at the level of the wrist crease (Fig. 2). The palmaris longus tendon may be found acting as a secondary site of compression, passing either in a radial-to-ulnar or ulnar-to-radial direction across the median nerve, in which case it should be resected. The median nerve may be displaced radially beneath the radial leaf of the transverse carpal ligament and should be mobilized gently into a more direct central course. We have observed in 46 percent of patients with recurrent symptoms after previous open carpal tunnel releases that there is a separate synovial layer beneath the median nerve with a cavity between this synovial layer and the underlying flexor tendons (Fig. 6, center and below). Although Henry et al.21 implied that there is little therapeutic benefit to splinting after carpal tunnel release, our findings suggest that the median nerve may sublux slightly palmar with respect to the flexor tendons, possibly as a result of not splinting the wrist in extension immediately after the initial carpal tunnel release.
Although intuitively it would seem that a patient with persistent symptoms would simply require identification and release of the remaining site of incomplete release, unfortunately, these patients develop varying amounts of scar tissue around the median nerve in the interval between the primary carpal tunnel operation and the second operation (average, 17 months; minimum, 3 months). Therefore, the median nerve has to be dissected from scar tissue, and this usually requires a formal external neurolysis under loupe magnification. Especially in patients with recurrent symptoms, areas of significant epineurial scarring may require external neurolysis under the operating microscope and occasionally even epineurectomy. However, internal neurolysis of the median nerve is contraindicated.
If one of the common digital nerves is found to have been transected, either a secondary nerve repair or nerve graft or nerve conduit can be performed. If a neuroma of the palmar cutaneous branch of the median nerve is found, the neuroma can be translocated or, if both ends of the nerve can be identified, a nerve graft performed. If the motor branch of the median nerve is found to have been transected, direct nerve repair can occasionally be performed; otherwise, an opposition tendon transfer is performed either at the same time or at a later stage.
After external neurolysis of the median nerve, controversy exists as to whether a biological barrier should be interposed between the median nerve and the overlying skin or the underlying flexor tendons. If a definitive cause for the patient's persistent symptoms is discovered at the second operation, such as incomplete release of the transverse carpal ligament, or if the median nerve can be easily mobilized from surrounding scar tissue, or if the median nerve can be relocated from a palmarly displaced position back into its normal position, coverage of the nerve is probably unnecessary. If the carpal tunnel is heavily scarred with fibrous proliferation around the median nerve, several authors have suggested that soft-tissue coverage is necessary to prevent recurrent scarring of the anterior surface of the median nerve to the radial and ulnar leaves of the transverse carpal ligament or to the palmar skin. Local muscle flaps including abductor digiti minimi,22 pronator quadratus,23 and palmaris brevis24; the hypothenar fat flap25; a synovial flap (Fig. 5)26; a dermal graft27; and more recently synthetic membranes have all been advocated for coverage of the anterior surface of the median nerve. More complex pedicled flaps and free flaps have also been described, including the reverse radial forearm adipofascial flap,28 free omental transfer,29 and small free muscle and fascial flaps.30,31 For the very severely scarred median nerve that has undergone multiple operations, Jones30 introduced the concept of “circumferential wrapping” the median nerve to insulate the median nerve from both the underlying flexor tendons and the overlying skin, to allow gliding of the previously scarred nerve, and to revascularize the ischemic nerve, analogous to the insulation of an electrical cable. Circumferential wrapping of a scarred median nerve with the intimal surface of a vein graft has also been described,19,32,33 although the vein graft is itself a dead piece of tissue that needs to become revascularized and may produce additional fibrous scar tissue.
According to Hulsizer et al.,10 patients with persistent or recurrent symptoms following a prior endoscopic carpal tunnel release have a better chance of improvement or resolution of their symptoms compared with patients who had a prior open carpal tunnel release. However, our results suggest slightly better improvement after open carpal tunnel release (90 percent) compared with 76 percent after endoscopic carpal tunnel release, although patients achieving complete relief of their symptoms are similar after open (57 percent) or endoscopic (56 percent) release. Only 25 percent of patients who undergo reoperation for a failed carpal tunnel release seem to be completely satisfied without any residual symptoms after the second carpal tunnel operation, with the incidence of residual symptoms ranging from 41 to 90 percent16,34–37 and 20 percent of patients require a third operation. Although the description “residual symptoms” in the literature is not synonymous with our criteria of “no improvement,” 56 percent of our patients had complete relief of their symptoms after the second operation and only 10 percent went on to require a third operation. Poor outcomes after a second carpal tunnel release have been associated with workers' compensation insurance, normal nerve conduction studies before the second operation, and symptoms within the ulnar nerve distribution.34 Because carpal tunnel syndrome is occupationally related in 42 percent of patients,20 these patients appear to have higher recurrence rates and poorer outcomes.
The results of both open and endoscopic carpal tunnel release are generally good, but not all patients obtain complete and long-lasting relief. Persistent, recurrent, or new different symptoms following carpal tunnel release remain a vexing problem for both hand surgeons and patients. Based on our series, incorrect diagnosis and incomplete release of the transverse carpal ligament were the main causes of persistent symptoms. Fibrous proliferation and subtle palmar subluxation of the median nerve compounded by repetitive motion were the main causes of recurrent symptoms. Revision carpal tunnel surgery should be avoidable by reducing technical errors during the primary carpal tunnel release, ensuring complete release of the transverse carpal ligament and avoiding iatrogenic injury to the median nerve.
This information prepared by Dr. Raymund Janevicius is intended to provide coding guidance.
* Release of the transverse carpal ligament is reported with code 64721. This code is reported for both primary and recurrent carpal tunnel surgery.
Table. No title avai...Image Tools
* Code 64721 includes epineurectomy and external neurolysis.
* Internal neurolysis using the operating microscope is reported with code 64727. If fascicular groups are dissected using loupe magnification, code 64727 is not to be used.
* Code 64727 is an add-on code and never stands alone. It must be used with a primary neuroplasty code, in this case, 64721.
* A hypothenar fat flap is an adjacent tissue transfer and is reported with code 14040.
1. Einhorn N, Leddy JP. Pitfalls of endoscopic carpal tunnel release. Orthop Clin North Am. 1996;27:373–380.
2. Teoh LC, Tan PL. Endoscopic carpal tunnel release for recurrent carpal tunnel syndrome after previous open release. Hand Surg. 2004;9:235–239.
3. Kulick MI, Gordillo G, Javidi T, Kilgore ES Jr, Newmayer WL III. Long-term analysis of patients having surgical treatment for carpal tunnel syndrome. J Hand Surg Am. 1986;11:59–66.
4. Concannon MJ, Brownfield ML, Puckett CL. The incidence of recurrence after endoscopic carpal tunnel release. Plast Reconstr Surg. 2000;105:1662–1665.
5. Stütz N, Gohritz A, van Schoonhoven J, Lanz U. Revision surgery after carpal tunnel release: Analysis of the pathology in 200 cases during a 2 year period. J Hand Surg Br. 2006;31:68–71.
6. Palmer AK, Toivonen DA. Complications of endoscopic and open carpal tunnel release. J Hand Surg Am. 1999;24:561–565.
7. Luria S, Waitayawinyu T, Trumble TE. Endoscopic revision of carpal tunnel release. Plast Reconstr Surg. 2008;121:2029–2034; discussion 2035–2036.
8. Ruch DS, Seal CN, Bliss MS, Smith BP. Carpal tunnel release: Efficacy and recurrence rate after a limited incision release. J South Orthop Assoc. 2002;11:144–147.
9. Cobb TK, Amadio PC, Leatherwood DF, Schleck CD, Ilstrup DM. Outcome of reoperation for carpal tunnel syndrome. J Hand Surg Am. 1996;21:347–356.
10. Hulsizer DL, Staebler MP, Weiss AP, Akelman E. The results of revision carpal tunnel release following previous open versus endoscopic surgery. J Hand Surg Am. 1998;23:865–869.
11. Tung TH, Mackinnon SE. Secondary carpal tunnel surgery. Plast Reconstr Surg. 2001;107:1830–1843.
12. Proubasta IR, Lluch A, Lamas CG, Oller BT, Itarte JP. “Fat pad” and “little finger pulp” signs are good indicators of proper release of carpal tunnel. Neurosurgery 2007;61:810–813; discussion 813–814.
13. Gelberman RH, Pfeffer GB, Galbraith RT, Szabo RM, Rydevik B, Dimick M. Results of treatment of severe carpal tunnel syndrome without internal neurolysis of the median nerve. J Bone Joint Surg Am. 1987;69:896–903.
14. Botte MJ, von Schroeder HP, Abrams RA, Gelman H. Recurrent carpal tunnel syndrome. Hand Clin. 1996;12:731–743.
15. Eason SY, Belsole RJ, Greene TL. Carpal tunnel release: Analysis of suboptimal results. J Hand Surg Br. 1985;10:365–369.
16. Rose EH. The use of the palmaris brevis flap in recurrent carpal tunnel syndrome. Hand Clin. 1996;12:389–395.
17. Phalen GS. The carpal tunnel syndrome: Seventeen years' experience in diagnosis and treatment of six hundred fifty-four hands. J Bone Joint Surg Am. 1966;48:211–228.
18. Assmus H, Dombert T, Staub F. Reoperations for CTS because of recurrence or for correction (in German). Handchir Mikrochir Plast Chir. 2006;38:306–311.
19. Pizzillo MF, Sotereanos DG, Tomaino MM. Recurrent carpal tunnel syndrome: Treatment options. J South Orthop Assoc. 1999;8:28–36.
20. Hunter JM. Recurrent carpal tunnel syndrome, epineural fibrous fixation and traction neuropathy. Hand Clin. 1991;7:491–504.
21. Henry SL, Hubbard BA, Concannon MJ. Splinting after carpal tunnel release: Current practice, scientific evidence, and trends. Plast Reconstr Surg. 2008;122:1095–1099.
22. Milward TM, Stott WG, Kleinert HE. The abductor digiti minimi muscle flap. Hand 1977;9:82–85.
23. Dellon AL, Mackinnon SE. The pronator quadratus muscle flap. J Hand Surg Am. 1984;9:423–427.
24. Rose EH, Norris MS, Kowalski TA, Lucas A, Flegler EJ. Palmaris brevis turnover flap as an adjunct to internal neurolysis of the chronically scarred median nerve in recurrent carpal tunnel syndrome. J Hand Surg Am. 1991;16:191–201.
25. Plancher KD, Idler RS, Lourie GM, Strickland JW. Recalcitrant carpal tunnel: The hypothenar fat pad flap. Hand Clin. 1996;12:337–349.
26. Wulle C. Treatment of recurrence of the carpal tunnel syndrome. Ann Chir Main 1987;6:203–209.
27. McLinton MA. The use of dermal-fat grafts. Hand Clin. 1996;12:357–364.
28. Luchetti R, Riccio M, Papini Zorli I, Fairplay T. Protective coverage of the median nerve using fascial, fasciocutaneous or island flaps. Handchir Mikrochir Plast Chir. 2006;38:317–330.
29. Harii K. Clinical application of free omental flap transfer. Clin Plast Surg. 1978;5:273–281.
30. Jones NF. Treatment of chronic pain by “wrapping” intact nerves with pedicle and free flaps. Hand Clin. 1996;12:765–772.
31. Dahlin LB, Lekholm C, Kardum P, Holmberg J. Coverage of the median nerve with free and pedicled flaps for the treatment of recurrent severe carpal tunnel syndrome. Scand J Plast Reconstr Hand Surg. 2002;36:172–176.
32. Varitimidis SE, Riano F, Vardakas DG, Sotereanos DG. Recurrent compressive neuropathy of the median nerve at the wrist: Treatment with autogenous saphenous vein wrapping. J Hand Surg Br. 2000;25:271–275.
33. Varitimidis SE, Herndon JH, Sotereanos DG. Failed endoscopic carpal tunnel release. J Hand Surg Br. 1999;24:465–467.
34. Ellis RA, Novak CB, Mackinnon SE, Cheng CJ. Workers' compensation, return to work, and patient satisfaction after carpal tunnel decompression. Am J Orthop (Belle Mead NJ.) 2007;36;E63–E66.
35. Amadio PC. Interventions for recurrent/persistent carpal tunnel syndrome after carpal tunnel release. J Hand Surg Am. 2009;34:1320–1322.
36. O'Malley MJ, Evanoff M, Terrono AL, Millender LH. Factors that determine reexploration treatment of carpal tunnel syndrome. J Hand Surg Am. 1992;17:638–641.
37. Unglaub F, Wolf E, Goldbach C, Hahn P, Kroeber MW. Subjective and functional outcome after revision surgery in carpal tunnel syndrome. Arch Orthop Trauma Surg. 2008;128:931–936.