Impact on Safety of Pre-operative Ultrasound for Carpal Tunnel Release: A Case Series - SOMOS 2023

Smith M, Yuan X, Smith J, deal b, Nanos G, Tintle S, Reece D, Miller M

Abstract accepted for presentation at the 2023 SOMOS Annual Meeting

Carpal Tunnel Syndrome (CTS) is the most common peripheral entrapment neuropathy, impacting the health of the general population, as well as the performance and readiness of active duty service members (ADSMs) and military beneficiaries.1-2 CTS occurs when the median nerve (MN) is compressed beneath the transverse carpal ligament (TCL) within the carpal tunnel (CT). Within the general workforce, the incidence of CTS is between 1.5 and 3.5 per 1,000 person-years.3 According to Wolf et al., the raw incidence of CTS in the United States (U.S.) military is 3.98 per 1,000 person-years.4 CTS risk factors include female gender, increasing age, poor wrist posture, and occupations that involve repetitive movements, forceful grip, and exposure to vibration.3-5 Occupational risk factors are particularly relevant in the setting of the Military Health System (MHS), as different military occupational specialties may predispose ADSMs to CTS. Notably, CTS can impact operational readiness, prompting the need to improve diagnostic and treatment options for this common health condition, focusing on safety and efficiency to facilitate quicker return to duty. To this end, high-frequency ultrasound (HFUS) has demonstrated utility in CTS diagnosis and may serve as a valuable tool to improve overall safety during CTS treatment.

CTS diagnosis and treatment are typically guided by patient complaints, physical examination, and electrodiagnostic studies (EDX). The 2012 American Association of Neuromuscular and Electrodiagnostic Medicine (AANEM)’s evidence-based guideline on the use of neuromuscular ultrasound (US) in the diagnosis of CTS concluded that US adds diagnostic value to EDX, focusing specifically on measuring the MN cross-sectional area (CSA) at the wrist as a diagnostic tool.6 Additionally, the guideline recommended that US be considered in screening for anatomic abnormalities. However, the 2016 American Academy of Orthopedic Surgeons’ clinical practice guidelines indicate limited evidence in support of routine US pre-operative exams, specifying a need for higher-level evidence regarding the utility of US, with a focus on establishing optimal measurement and cut-off values, in alignment with AANEM's guidelines for future research.7 More recently, studies have demonstrated that utilizing a cut-off CSA of 10-12 mm2 can differentiate between patients with normal versus abnormal EDX.8-9 However, Chen et al. demonstrated that US measurements were unable to differentiate levels of severity, indicating EDX remains a useful tool for grading CTS severity.9

CTR by endoscopic (ECTR) or mini-open (mOCTR) approach is the current standard of care (SOC) in the MHS for management of refractory CTS. CTR techniques have continued to evolve to further reduce post-operative symptoms and iatrogenic injury risk, while promoting quicker recovery and better functional outcomes. CTR using Ultrasound Guidance (CTR-US) is a promising treatment option for military beneficiaries with CTS, currently under rigorous study in a single-site pragmatic randomized controlled feasibility trial at a military medical center. Both ECTR and CTR-US involve smaller incisions and alternative means of visualization (i.e., endoscope or US). Although rare, intra-operative complications can occur during CTR secondary to anatomic variations. Multiple surgeons have emphasized the need for increased awareness of anatomic variations of the muscles, nerves, and vasculature within the CT region to promote procedural safety.15-17 Neurovascular injury can result in increased post-operative pain, persistent paresthesias, and/or excessive bleeding, all of which may contribute to an extended, complicated post-operative course, impacting return to work/duty and overall quality of life.

Key variations in neurovascular anatomy include a high bifurcation of the median nerve (approximately 6%), transligamentous thenar motor branch of the MN (TMB; <10%), multiple TMBs (<1% in patients with normal versus hypertrophic thenar musculature), ulnar course of the palmar cutaneous branch of the MN (PCBMN; <3%), persistent median artery (PMA; 1.2 – 23%), and superficial ulnar artery (UA; <10%).15-19 Prior studies have demonstrated that HFUS can be utilized to reliably identify these key variations that are at risk during CTR.10-14 Therefore, pre-operative US exams can identify anatomic variations and aid decision-making of the most appropriate CTR approach. This case series presents three participants in the feasibility trial of CTR-US who received pre-operative diagnostic US examinations, which detected distinct anatomic variants that were integral to subsequent treatment planning for CTR.