Intraoperative Nerve Conduction Studies During Open Carpal Tunnel Release: A Pilot Study

Carpal tunnel syndrome (CTS) is a common neuropathy affecting up to 7% of the general population and accounting for up to 90% of all neuropathies.^1,2 More commonly seen in women and older patients, the typical presentation of CTS involves numbness, tingling, burning, or pain resulting from compression of the median nerve.^1,3,4 CTS is diagnosed via a combination of clinical symptoms, physical examination maneuvers (such as Tinel’s sign, Phalen’s maneuver, or 2-point discrimination testing), and electrophysiologic studies, such as nerve conduction velocity (NCV) or electromyography (EMG).^5-7 Characteristic changes in motor and sensory amplitude and latency are hallmarks of the condition. Initial treatment includes a combination of nonsteroidal anti-inflammatory drugs, local corticosteroid injections, and physical therapy, with surgery reserved for refractory cases. Surgical decompression involves release of the transverse carpal ligament (TCL),^8,9 with or without volar antebrachial fascia (VAF) release.¹⁰

Currently, electrophysiologic studies are not used to assess changes in nerve conduction immediately after carpal tunnel release (CTR). Specifically, it is not known what differences in amplitude, if any, can be expected in NCV after CTR. Furthermore, it is not known if a more extensive decompression (including the TCL as well as the VAF) is better than an isolated TCL release. In a 1978 prospective study assessing intraoperative nerve conduction results in 51 hands treated with TCL release, Eversmann and Ritsick found a reduction in the conduction latency across the carpal canal after 10 minutes in all but 7 patients, 2 of whom had diabetes (P < .00001).¹¹ Hongell et al reported that after some operations, recordings of sensory conduction time and microneurographic studies showed an improvement of nerve conduction within 30 minutes of decompression.¹² Furthermore, Rotman et al showed improved distal motor latencies at various points postoperatively, concluding that NCV may be useful in long-term management and monitoring of patients with CTS.⁹ Although further investigations are warranted, these studies suggest that a rapidly reversible mechanical or metabolic block, such as ischemia in the segment of the median nerve, may be responsible for the symptoms of CTS. 

The need for TCL and VAF release to decompress the carpal tunnel in CTS has been demonstrated. Using 5 cadaveric specimens, Means et al showed that release of TCL alone is associated with pressures consistently greater than 30 mm Hg beneath the distal volar forearm fascia despite an overall decrease in pressure.¹⁴ Other studies of CTS anatomy implicate the VAF in its pathology and symptomatology.^15,16 Whereas intraoperative neurodiagnostic studies have been shown to have clinical value in a variety of orthopedic conditions,^17-20 the utility of median nerve conduction studies has not yet been used to demonstrate a difference in outcomes immediately after TCL versus TCL+VAF release. These data may be used to inform surgeons about the success of decompression before leaving the operating room. We conducted a pilot study to identify any differences in intraoperative NCV between TCL release and TCL+VAF release. If no difference was observed, limited releases may be preferred to decrease the risk of iatrogenic nerve injury, decrease pillar pain, and improve cosmesis due to a smaller incision.

Patient Population and Outcomes

A prospective, therapeutic pilot study was conducted on patients aged 18 to 65 years with a diagnosis of idiopathic CTS that failed to respond to conservative management with bracing, therapy, or injections. Institutional review board approval was obtained. Informed consent was obtained from all individual participants included in the study. Patients were excluded if they had a history of surgical median nerve release, diabetes, acute CTS, or cervical spine radiculopathy. Primary outcomes of interest included motor and sensory amplitude and latency. 

 Intraoperative Setup

All patients underwent surgery with general anesthesia. No local anesthetic, tourniquets, or muscle relaxants were used. A Medtronic/Dantec Keypoint Portable EMG/NCS monitor (Natus Global) was used to record motor and sensory amplitude and latency. Surface electrodes were placed on the abductor pollicis brevis (APB), the index finger, and the forearm, approximately 8 cm from the APB. EMG was not performed due to the patients’ inability to participate under general anesthesia. 

The following steps were performed on all patients. Incision was made from Kaplan’s cardinal line to the distal wrist crease in line with the third web space. TCL release was performed under direct visualization, and VAF release was performed through the initial incision site by sliding a Metzenbaum scissor approximately 2 to 3 cm proximal to the wrist after TCL release for each patient. A freer was then used to ensure complete release. Motor and sensory amplitude and latency were recorded at 3 points for each patient: before TCL release (baseline), immediately after TCL release, and then immediately after VAF release. 

Statistics

A paired, single tail t test was performed for all measurements. Significance was defined at an alpha level of 0.05. As the purpose of this pilot study was to provide preliminary data, a power analysis was not needed.

A total of 10 patients were included in this study. Mean age was 53 years. The majority were female (n = 8), and most procedures were performed on the left hand (n = 6). The greatest decrease in measurements from baseline to TCL release was in motor amplitude, with a mean change of -10.8% ±26%, whereas the greatest increase was seen in sensory amplitude, with a mean 8.7% ±60% change (Table 1). The greatest change from TCL to VAF release was in sensory latency, with a mean change of 7.1% ±26%, followed by motor amplitude, with a mean 5.1% ±8.9% change (Table 2). From baseline to TCL and VAF release, the greatest change was in sensory latency, with a mean decrease of -16.0% ±33%, followed by sensory amplitude, with a mean decrease of -14.0% ±33% (Table 3). These changes were not statistically significant (P > .05).

This pilot study shows that the immediate use of intraoperative NCV after TCL and VAF release may not be a reliable measure of improvement. We found no change in mean motor and sensory amplitude or latency from baseline measurements to TCL release and VAF release. Interestingly, from baseline to TCL and VAF release, there was a net decrease in both latency and amplitude in the motor and sensory branches, but these results were not statistically significant. We postulate there are 2 reasons for these data: NCV is not effective in measuring surgical outcome immediately after TCL and VAF release, and/or there is no significant difference between TCL and TCL+VAF release. 

The use of NCV in the immediate postoperative period (seconds to minutes) may not be a reliable measure of nerve function. Our study included patients with chronic, idiopathic CTS. As such, the long-term, low-level ischemia resulting from externally applied compression and increased pressure may not be so acutely reversed.²¹ In patients with severe CTS, the vessels of the median nerve become obliterated, and the epineuria become avascular and fibrotic.²² Although restoration of normal pulsatile blood flow can occur within 1 minute of TCR release,²³ it may take some time for median nerve conduction velocity, and consequent dysesthesias, to recover to a measurable degree. This may also be due to ischemia time, differences in soft tissue temperature, and nerve damage, which are known to affect conduction time.^24-27  

To our knowledge, the study with the earliest measure of NCV after CTR was that of Eversmann et al, who waited approximately 10 minutes before measuring motor nerve latency.¹¹ These authors used a tourniquet, however, and reasoned that the time interval allowed for recovery from tourniquet ischemia. Though no tourniquet was used during our procedures, the effects of chronic ischemia from CTS may still require several minutes to change.

Additionally, it may be possible that there is no measurable difference between TCL and VAF release. There were no significant changes between the NCV studies of either approach, raising the question of whether one approach is superior to the other. The VAF is often released during CTR to ensure maximum decompression of the median nerve, particularly in severe cases where more proximal compression is implicated, but this may lead to more frequent complications.²⁸ To release the VAF, a slightly larger incision is usually made compared with that made during TCL release alone. This can lead to iatrogenic nerve injury and increased pillar pain, which may take several months to resolve.^29-31 The majority of orthopedic hand surgeons favor more limited approaches to avoid these complications,^32,33 despite some suggesting isolated TCL release may not be sufficient for median nerve decompression.¹⁴ Our preliminary data lend favor to the limited approach rather than the extensile approach. These data must be interpreted with caution, however, as the utility of the NCV immediately after CTR may not be reliable.

There are several limitations to our research. As a pilot study with 10 patients in which patients with diabetes were excluded, it is subject to sampling bias and is thus not representative of the CTS population. Our data also came from a single center and a single surgeon, which limits external validity and applicability to the general population. Finally, we did not analyze a correlation with clinical outcomes. 

This pilot study showed no detectable difference in NCV conducted immediately following the release of TCL and TCL+VAF. Our data suggest that NCV may not be an appropriate assessment of objective improvement intraoperatively or as a measure of superior approach in this setting. Future prospective studies with larger numbers of patients may be warranted. These data may provide surgeons with valuable intraoperative information regarding the success rate of CTR before leaving the operating room.

Affiliations: ¹Rutgers Health – New Jersey Medical School Department of Orthopaedics,

Newark, NJ; ²Rutgers Health – New Jersey Medical School Department of Surgery,

Newark, NJ

Correspondence: Robert L. DalCortivo, BBA; dalcort@rutgers.edu

Ethics: Institutional review board approval was obtained, and informed consent was obtained from all individual participants included in the study. The approving group was Rutgers New Jersey Medical School Institutional Review Board. The reference number is Pro20140000654.

Disclosures: Author Michael M Vosbikian, MD receives honorarium for content authorship from The Journal of Bone and Joint Surgery Clinical Classroom and is an editorial board member for ePlasty. The authors do not have any other potential conflicts of interest with respect to this manuscript.