Carpal tunnel syndrome is a very common hand condition, which after a failure of conservative treatment can be treated successfully with surgical decompression in either an open or endoscopic manner. On comparing the two techniques there may be some subtle differences; however, both can provide an excellent outcome. This article provides a detailed review of each technique as well as their comparative differences in terms of technique, outcomes, and complications.
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A solid understanding of the applied surgical anatomy and surface landmarks is preeminent to a successful carpal tunnel release.
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Concerns about the safety and potential increased cost of an endoscopic release have led to the modification of the standard open approach.
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On comparing endoscopic with open carpal tunnel release, there may be some subtle differences; however, both can provide an excellent outcome.
Introduction
Sir James Paget first described compression of the median nerve at the wrist following a distal radius fracture in 1854. More than 150 years later, carpal tunnel syndrome (CTS) is today the most common compressive disorder in the upper extremity. In 2007, the American Academy of Orthopaedic Surgeons (AAOS) created a clinical practice guideline that defined CTS as a symptomatic compression neuropathy of the median nerve at the level of the wrist, characterized physiologically by evidence of increased pressure within the carpal tunnel and decreased function of the median nerve in the hand.
Anatomy and pathophysiology
Nine flexor tendons and the median nerve traverse the carpal tunnel, which is bordered dorsally by the concave arch of the carpus, and volarly by the transverse carpal ligament (TCL). The median nerve is the most superficial structure beneath the TCL, and divides into multiple sensory branches and one motor branch after passing through the carpal tunnel. The motor branch, of particular concern during surgical release of the TCL, has been shown to have significant anatomic variation. The motor fascicles arise from the radiopalmar aspect of the nerve in approximately 80% of cases, but may arise centrally or, rarely, ulnarly. Poisel identified 3 major patterns by which the recurrent branch passes through the TCL: extraligamentous, subligamentous, and transligamentous. In his 1977 review of 246 cases, Lanz found the nerve to be extraligamentous in 46%, subligamentous in 31%, and transligamentous in 23% of cases.
Gelberman and colleagues studied the effects of wrist position on interstitial pressure within the carpal tunnel. This study found 2.5 mm Hg to be the normal pressure with the wrist in neutral position, whereas with the wrist in maximal extension and wrist flexion the pressure increased to 30 and 31 mm Hg, respectively. A decrease in epineural blood flow occurs when pressure reaches 20 to 30 mm Hg, and pressures greater than 30 mm Hg diminish nerve conduction. In patients with CTS, interstitial canal pressures were 32 mm Hg in neutral, 94 mm Hg in full flexion, and 110 mm Hg in wrist extension.
Diagnosis
The diagnosis of CTS remains primarily a clinical one, although current trends indicate increased reliance on electrodiagnostic testing (EDX). Nevertheless, as discussed by Bickel, the role of EDX remains unclear. The lack of an appropriate gold-standard test and reliance on EDX testing may lead to the withholding of effective treatment for patients with CTS. To this end, Graham and colleagues performed a literature review in 2006 that yielded 6 clinical criteria (CTS-6) proved to correlate positively with a diagnosis of CTS, and stated that the value added by EDX testing was minimal. The 6 clinical criteria are nocturnal numbness, median nerve paresthesia, thenar muscle atrophy, positive Phalen test, positive Tinel test, and loss of 2-point discrimination.
Techniques of carpal tunnel release
A solid understanding of the applied surgical anatomy and surface landmarks is preeminent to a successful carpal tunnel release. The Kaplan cardinal line correlates to the distal extent of the TCL. It begins with a line drawn at the apex of the first web space, parallel to the proximal palmar crease, and ends just distal to the hook of the hamate. The point where this line intersects with the flexed long finger typically represents the location of the recurrent branch of the median nerve. The palmar cutaneous branch is generally radial to the palmaris longus tendon. A “safe zone” for release may be reproduced by determining the intersection of the longitudinal axis of the flexed ring finger with the distal wrist crease, or alternatively a longitudinal line drawn parallel with the third web space, ending proximally just ulnar to the palmaris longus.
Open carpal tunnel release (OCTR) has long been considered the gold-standard surgical treatment for CTS. The technique involves placement of a longitudinal incision at the base of the hand. The subcutaneous tissue, the superficial palmar fascia, and the muscle of the palmaris brevis (if present) are also incised in line with the incision, thereby exposing the TCL. Scar tenderness, pillar pain, weakness, and delays in return to work can occasionally be seen following an OCTR. These limitations resulted in the development of newer techniques to minimize surgical morbidity and hasten recovery. In 1989, Okutsu and colleagues introduced the concept of an endoscopic carpal tunnel release (ECTR). This landmark technique used a single small incision 3 cm proximal to the wrist crease and released the TCL under direct visualization using a hook knife. In the same year, Chow described a novel ECTR technique using 2 skin incisions. In his report he describes a transbursal approach with one incision just proximal to the wrist flexion crease ulnar to the palmaris longus tendon, and a second longitudinal incision 4 to 5 mm distal to the distal edge of the TCL to allow passage of the endoscope and dissecting instruments superficial to the arch and digital nerves. Agee and colleagues modified the Okutsu technique by also using a single incision but instead used a trigger-deployed blade elevated from the tip of the device. Release of the TCL is performed in a distal to proximal direction. At present many systems are available to perform an ECTR. Furthermore, with the advent of high-definition (HD) monitors and HD arthroscopic cameras, even greater visualization is now possible.
Recently, the standard OCTR has also undergone modifications to minimize surgical morbidity and expedite return to work. These techniques have resulted into what is now referred to as limited-open or mini-open. Lee and colleagues described an approach that attempted to meld the benefits of a minimally invasive release while decreasing the risk of nerve injury. This approach describes a 2.5- to 3.0-cm longitudinal incision placed in line with the radial border of the ring finger or the third web space (although some now only use a 1.5–2.5-cm incision). Dissection is carried to the distal extent of the TCL, and the distalmost aspect of the ligament is incised with a scalpel for approximately 1 cm in a distal to proximal direction, starting ulnar to the midline of the ligament. Next a series of instruments are used to create an unimpeded pathway for the passage of a cutting tome device, which bisects the ligament in a distal to proximal direction, resulting in a complete release with preservation of the palmar fascia and palmaris brevis muscle.
Comparative analysis of open versus endoscopic carpal tunnel release
The debate among hand surgeons in favor of ECTR versus OCTR is as unresolved today as it was during the 1990s. Proponents of both camps cite literature supporting their preferred method, and despite multiple randomized controlled trials no consensus has been reached. The proposed benefit of ECTR versus OCTR is that by dividing the TCL from below, the overlying skin and muscle are preserved, potentially improving postoperative morbidity, facilitating an earlier return to work, and preserving grip strength. Proponents of an open release caution against an increased risk of catastrophic nerve or artery injury owing to limited visualization, a steep learning curve, longer surgical time, and increased cost. In addition, as the paradigm shifts to smaller open incisions, the morbidity associated with the mini-open approaches is potentially lessened.
Return to Work
CTS is one of the most common major disabling workplace injuries, with an incidence of 1 to 3 cases per 1000 subjects per year and a prevalence of 50 cases per 1000 subjects per year. According to the US Bureau of Labor Statistics, in 2005 there was a median loss of 27 workdays with each claim. Foley and colleagues, in their analysis of the economic burden of CTS in Washington State, found that workers recovered only half the preinjury earnings of claimants after 6 years, compared with patients treated for upper extremity fractures during the same period. A Scandinavian study showed a permanent failure to return to work in 11% of CTS claimants, imparting a significant socioeconomic cost to society.
In 2001, Gerristen and colleagues undertook a review of 14 different randomized clinical trials comparing several different surgical techniques for release of the TCL. Included in their review is a section on 7 randomized clinical trials comparing ECTR and OCTR. Their analysis showed slight support with conflicting evidence for an earlier return to work and/or activities of daily living following ECTR, with 4 in favor of ECTR and 3 showing no difference. A 2004 meta-analysis of 13 randomized clinical trials by Thoma and colleagues compared OCTR with ECTR, and analyzed data pooled from 3 studies showing no significant difference between the two techniques.
In 2008, the AAOS published evidence-based guidelines on the treatment of CTS. In its report the Academy specifically addressed pain outcomes, functional status, symptom severity, return to work, grip and pinch strength, infections, wound-related complications, reversible nerve damage, and total complications. Ten studies were identified specifically addressing return to work, 3 of which favored ECTR.
In their 2009 review of the surgical treatment of CTS, the Cochrane Collaboration evaluated a total of 16 studies comparing ECTR with OCTR, and 4 studies comparing minimally invasive OCTR with ECTR. Fourteen studies specifically addressed return to work or activities of daily living, with 8 studies favoring ECTR, 5 showing no difference, and 1 favoring OCTR. In addition, data were pooled and a meta-analysis provided, based on 3 studies, showing a weighted mean difference in time to return to work as 6 days earlier in the ECTR group.
Short-Term Data
The theoretical benefit of preserving the palmar musculature and skin has not been borne out in the literature. Grip and pinch strength have been used as surrogate measures of overall hand function. Thoma and colleagues performed a meta-analysis pooling 3 randomized clinical trials for outcomes of grip strength, and 2 studies for pinch strength at 12 weeks. The investigators concluded that grip and pinch strength are more likely to be preserved with ECTR at 12 weeks. Data from both this study and that by Gerristen and colleagues showed no statistical difference in terms of short-term pain outcomes and short-term symptom relief. Similarly, the AAOS report favored ECTR in terms of pinch strength at 12 weeks. The AAOS also identified 5 studies that evaluated grip strength at 12 weeks with trends favoring ECTR; however, the meta-analysis showed significant heterogeneity, and the investigators were unable to draw a conclusion on differences in functional status at 12 weeks postoperatively. The Cochrane review evaluated short-term data from 11 of 16 studies comparing ECTR with OCTR, 8 of which found no significant difference at 3 months or less. Meta-analysis was performed on 3 studies slightly favoring ECTR in terms of symptom severity scores and functional scores at 12 weeks. In his evidence-based review regarding ECTR versus OCTR, despite inconsistencies in the data, Abrams concluded that the data slightly favor restoration of grip and pinch strength with ECTR. However, these differences have been shown to normalize at 1 year, with equivalent outcomes at 5-year follow-up as well.
Complications
Although much of the skepticism surrounding ECTR during its infancy has waned, many still consider endoscopic release to be dangerous secondary to a lack of visualization and concern for nerve or arterial injury. Palmer and Toivonen sent questionnaires on self-reporting any complications following CTR procedures to 1253 members of the American Society for Surgery of the Hand, and received 708 responses regarding ECTR and 616 regarding OCTR. One hundred median nerve injuries, 88 ulnar nerve injuries, 77 digital nerve injuries, and 121 vessel injuries were reported for ECTR. The OCTR respondents reported 147 median nerve injuries, 29 ulnar nerve injuries, 59 digital nerve injuries, and 34 vessel injuries. An alarming number of major complications are thus occurring with both procedures.
Benson and colleagues reviewed 80 publications from 1966 through 2001 yielding 22,327 cases of ECTR and 5669 cases of OCTR. The investigators reported on neuropraxias, and nerve, artery, and tendon injuries. Major nerve injuries were seen in 0.13% compared with 0.10% for ECTR and OCTR patients, respectively. ECTR had a rate of 0.03% for digital nerve injuries and 0.39% for OCTR. Arterial arch injuries occurred in 0.02% of the ECTR group, with no cases in the OCTR group. The most striking difference was in the rate of transient neuropraxias, which were reported in 1.45% of ECTR cases compared with 0.25% of OCTR cases. After exclusion of transient neuropraxia, the rate of major nerve, vessel, or tendon injury was shown to be lower in the ECTR group, at 0.19% compared with 0.49% for the OCTR subset. Similarly, Boecksyns and Sorensen reported a rate of 0.3% for irreversible nerve damage in the ECTR group, and 0.2% for the OCTR group.
Gerristen and colleagues found ECTR to have a higher incidence of transient nerve problems, with OCTR having more wound problems such as infection, hypertrophic scar, and scar tenderness. Thoma and colleagues demonstrated a benefit to ECTR with respect to scar tenderness, but stated that patients were 3 times as likely to experience transient neuropraxia. The AAOS report found 8 studies regarding wound-related complications, with 7 of 8 favoring ECTR. Reversible nerve damage was once again found to be more likely with ECTR, and the AAOS failed to show a statistical difference in terms of general complications or infection. The Cochrane review found no major complications resulting in permanent nerve damage or major impairments, and supported an increased likelihood of transient nerve injury with ECTR and an increase in wound problems (such as infection, hypertrophic scar, and scar tenderness) with OCTR. In addition, they addressed the need for revision surgery. Six studies met criteria for analysis of relative complication risk. Twelve of 513 cases required revision surgery in the ECTR subset versus 5 of 370 OCTR cases.
There would appear to be a relative consensus that major irreversible nerve damage is extremely rare with either procedure, and that both procedures can be performed safely and effectively. There appear to be more wound complications associated with OCTR and more reversible nerve injuries with ECTR. There also appears to be a higher reoperation rate with ECTR.
The Learning Curve
Much has been made about the added cost and time associated with educating hand surgeons regarding ECTR. Despite significant evidence supporting ECTR as a safe and reliable option for release of the TCL, persistent concern about a steep learning curve has been expressed. Macowiec and colleagues addressed this topic in a cadaveric study reviewing the results of ECTR on 573 hands performed in a teaching environment where orthopedic surgeons were being taught the procedure. Incomplete release in 30% of hands was noted using the extrabursal technique and in 42% using the transbursal technique. There were 8 ulnar artery injuries, 7 superficial arch injuries, 2 median nerve injuries, and 1 ulnar nerve injury. The investigators concluded that there is still a significant learning curve in the use of ECTR.
Recently, Beck and colleagues conducted a retrospective review of patients undergoing ECTR by a single surgeon in the first 2 years of practice, comparing results from months 1 to 6, 7 to 12, and 13 to 24 to determine whether a learning curve was present. Results show that during the first 6 months, 8 of 71 ECTRs were converted to OCTR, 1 of 72 were converted during the second 6 months, and 3 of 215 were converted during the second year of practice. No major complications were observed, there was no increase in morbidity for those patients who underwent conversion to OCTR, and there was a 0.28% complication rate in the study. The investigators concluded that despite the presence of a learning curve during the first 6 months of practice, there was no increase in morbidity transferred to the patient.
Cost
Approximately 500,000 carpal tunnel surgeries are performed in the United States annually, costing more than $2 billion per year. Of these, approximately 50,000 are performed endoscopically. Given the huge cost to society, both sides of the debate have cited cost to support their treatment of choice. Chung and colleagues released a cost analysis comparing OCTR with ECTR using quality-adjusted life-years (QALYs). These investigators used 2 randomized clinical trials comparing ECTR with OCTR and derived QALYs from questionnaire results, and concluded that ECTR seemed to be a cost-effective procedure; however, their analysis was extremely sensitive to major complications. As such, their findings may have been biased in favor of ECTR because 1 of the 2 randomized clinical trials had a major nerve complication rate of 1.5% in the OCTR group, compared with 0% for ECTR. However, the incidence of major nerve complications, as discussed earlier, is likely similar when comparing the 2 groups outright.
Vasen and colleagues performed a decision analysis that used a direct cost basis, and applied data to a model using assumptions of risks for complications. Using their model, a complication rate of greater than 6.2% would favor OCTR, a return-to-work difference of less than 21 days would favor OCTR, and a greater than 0.1% incidence of major nerve injury would favor OCTR. The investigators concluded that ECTR was less costly when considering the cost of the procedure and lost wages when using their base assumptions. These base assumptions, however, had several flaws. For one, they assumed a 10-fold increased relative risk of major nerve laceration with ECTR, which has not been borne out in the literature. Furthermore, they failed to factor in any cost associated with a tender scar or pillar pain, and applied an estimate of 365 days of lost wages for any complication encountered (including neuropraxia). This assumption is likely grossly overestimated. In addition, they estimated the difference in return to work between groups to be 28 days, with more recent analysis indicating perhaps only a 6-day improvement in return-to-work outcomes.
Two randomized clinical trials looked directly at surgical costs on comparing OCTR with ECTR. Saw and colleagues estimated an increased cost to ECTR related to initial capital expenditure and the relatively high cost of the single-use blade. These investigators estimated an incremental cost of ECTR to be £98, which was offset by a savings to industry of £67 per day, and an earlier return to work by 8 days. Trumble and colleagues performed a prospective, randomized, multicenter trial on 192 hands in 147 patients. Direct costs were recorded and calculated using surgeon fees, anesthesia fees, cost of equipment (including endoscopic blades), and operating room costs. The mean time from administration of anesthesia to transport from the operating room was 42 minutes for ECTR and 49 minutes for OCTR. The mean cost of OCTR was $3940 compared with $3750 for ECTR. From these results, Trumble and colleagues concluded that there is a significant benefit to ECTR, with not only the direct costs of ECTR being lower but also the indirect cost to society given a 20-day improvement in return-to-work outcomes in the ECTR group.
Mini-Open Versus Endoscopic Carpal Tunnel Release
Concerns about the safety and potential increased cost of an endoscopic release have led to modification of the standard open approach. Theoretically this approach could offer the safety of better visualization of the TCL and an implied decrease in associated neuropraxias seen with the endoscopic approach, while still providing decreased scar tenderness and pillar pain, and better early postoperative grip strength and earlier return to work. Limited data exist that directly compare endoscopic with a minimally invasive open approach; however the Cochrane Collaboration identified 4 studies that directly addressed this comparison.
In their prospective trial, Mackenzie and colleagues reported a slight but significant improvement in early function and comfort, and faster recovery of pinch and grip strength at 2 to 4 weeks, but not at later follow-up in the endoscopic group. Wong and colleagues found improved outcomes in the limited incision group, with improved pain scores at 2 to 4 weeks, no difference in strength, and surprisingly decreased pillar pain at 2 to 4 weeks, but not at later follow-up. Rab and colleagues found no statistically significant difference between the two groups at any time point in terms of grip and pinch strength, hand function, or symptom severity scores. One study favored ECTR in terms of revision surgery, with 1.5% undergoing revision compared with 9% in the modified open-incision group. No studies addressed return to work or activities of daily living.
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