Carpal Tunnel Syndrome (CTS) is a common condition where pressure on the median nerve in the wrist causes pain, numbness, and weakness in the hand. Surgery to release the carpal tunnel is often performed to relieve these symptoms.

This study will evaluate the changes in the median nerve after surgery and how these changes relate to symptom improvement. Investigators will use ultrasound imaging to measure the nerve size before and at three and six months after surgery. Patients will also complete questionnaires about their symptoms and hand function, and undergo tests to assess strength and sensation.

The investigator's goal is to determine whether changes observed on ultrasound are associated with the rate of patient recovery. This may help doctors better monitor healing and improve care for people with CTS.

This is a prospective observational cohort study designed to evaluate structural and functional recovery in patients with primary carpal tunnel syndrome undergoing open carpal tunnel release. The study also aims to identify prognostic factors associated with clinical and functional improvement after surgery. Patients will be consecutively recruited from the Hand Surgery and Microsurgery Department of a tertiary University Hospital.

All participants will undergo a standardized surgical procedure performed by experienced hand surgeons as part of routine clinical care. Ultrasonographic assessments of the median nerve cross-sectional area (CSA) at the carpal tunnel inlet and outlet will be conducted by an experienced radiologist using a high-resolution linear transducer (7-16 MHz) at three time points: preoperatively, and at 3 and 6 months after surgery. Secondary outcomes, including the Boston Carpal Tunnel Questionnaire (BCTQ), QuickDASH, quantitative grip and pinch strength measured with calibrated dynamometers, and tactile sensibility testing with Semmes-Weinstein monofilaments, will be assessed at the same time points by an occupational therapist specializing in hand therapy. This evaluation schedule is designed to characterize both morphological and functional recovery after surgery longitudinally.

The primary outcome is the change in median nerve CSA between baseline and follow-up. Secondary outcomes include changes in BCTQ and QuickDASH scores, grip strength, pinch strength, and sensory thresholds. All analyses will be two-sided with an alpha level of 0.05 and 95% confidence intervals. Data normality will be assessed with the Shapiro-Wilk test. Continuous outcomes will be compared pre- and postoperatively using paired t-tests or Wilcoxon signed-rank tests, as appropriate. Associations between CSA change and secondary outcomes will be examined with univariate and multivariable linear regression, adjusting for age, sex, symptom duration, and dominant hand involvement, with interaction terms to assess potential effect modification. Exploratory subgroup analyses for age, sex, and symptom duration will follow the same statistical approach, and categorical variables, if applicable, will be compared using Chi-square or Fisher's exact tests.

The prognostic value of baseline CSA will be explored using receiver operating characteristic (ROC) curve analysis for clinically meaningful improvement in secondary outcomes at 3 and 6 months. The Youden index will determine the optimal cutoff, and the area under the curve (AUC) will quantify discriminative ability. This cutoff will then stratify patients for exploratory comparisons over time. The sample size was calculated for a paired comparison of pre- and postoperative CSA, assuming a mean detectable difference of 1.0 mm² and a standard deviation of paired differences of 3.29 mm², with an alpha level of 0.05 and 80% power. This yields a requirement of 85 patients; allowing for 20% missingness, the final target is 107 participants.

All analyses will be performed using MedCalc version 23.2.7 (64-bit). Standardized protocols will be applied for all assessments, with regular data validation, source-data verification against medical records, and maintenance of a detailed data dictionary. Standard Operating Procedures will guide recruitment, data collection, and management. Missing data will be addressed using appropriate statistical methods such as multiple imputation or sensitivity analyses, depending on the mechanism and extent of missingness. No experimental interventions will be introduced; the study is observational in nature. Results will contribute to improved understanding of prognostic indicators in carpal tunnel syndrome and support evidence-based postoperative monitoring.

Inclusion Criteria:

• Clinical diagnosis of primary carpal tunnel syndrome (CTS), confirmed by characteristic symptoms, physical examination findings, and a cross-sectional area superior to 10 mm² in the ultrasonography baseline.
• Indication for open carpal tunnel release as part of routine clinical care.

Exclusion Criteria:

• Secondary CTS due to inflammatory arthritis, prior wrist trauma, or space-occupying lesions.
• History of previous carpal tunnel release in the affected hand.
• Concomitant peripheral neuropathies (e.g., diabetic polyneuropathy) or cervical radiculopathy
• Inability to undergo ultrasound assessment

Participants will be recruited from patients referred to the Hand Surgery and Microsurgery Department at Hospital das Clínicas, a tertiary care academic hospital affiliated with the University of São Paulo Medical School in São Paulo, Brazil.

Individual participant data (IPD) that underlie the results reported in the publication (after de-identification) will be shared. This includes clinical and ultrasonographic data collected before and after surgery. Supporting documents such as the study protocol, statistical analysis plan, and analytic code will also be available upon request. Data sharing will comply with ethical approvals and patient consent requirements.

Beginning 12 months after publication of the primary results and available for 3 years.

Data will be made available to researchers whose proposed use of the data has been approved by an independent review committee (data access committee). Access requests should include a methodologically sound proposal and will be evaluated for scientific merit and ethical compliance.