The role of diagnostic ultrasound in the examination of carpal tunnel syndrome: an update and systematic review

•Intra- and interrater reliability and known-group validity of cross-sectional area (CSA) measurements of the median nerve taken at the carpal tunnel inlet are consistently well-supported in the literature.•There is conflicting evidence on the concurrent validity of measures of median nerve CSA taken at the carpal tunnel inlet when electrodiagnostic studies are used as the reference standard.•The findings of this scoping review indicate a 3.1%-37% false negative rate and a 0-32.1% false positive rate when diagnosing carpal tunnel syndrome, using inlet CSA cutoff values between 8.5 mm2 to 12.6 mm2.•In comparing data on inlet and outlet CSA measurements, there is more evidence to support the use of measuring CSA at the carpal tunnel inlet. The diagnostic utility values including sensitivity, specificity, and positive and negative likelihood ratios were consistently less for outlet CSA when compared to inlet CSA.•There is conflicting evidence on known-group validity of the flattening ratio when measured at the level of the hamate. Diagnostic ultrasound is becoming more available and has potential for identifying carpal tunnel syndrome (CTS), but there is a lack of consensus on optimal measurement parameters and interpretation. The purpose of this systematic review was to analyze and summarize recent published data evaluating measurement properties of diagnostic ultrasound for use in individuals with CTS. Five databases were searched to identify studies reporting on diagnostic measurement in individuals ≥18 years of age. Thirty-four studies underwent critical appraisal using Center for Evidence Based Medicine guidelines for diagnostic study accuracy. Each team member independently reviewed and scored the studies and consensus was reached through discussion. Seventeen studies evaluating 21 unique nerve or tunnel measurements and 9 measurement ratios were included. Measurements of median nerve cross sectional area (CSA) taken at the carpal tunnel inlet consistently demonstrated good to excellent interrater reliability (ICC=0.83-0.93) and good intrarater reliability (r>0.81). All studies supported inlet CSA in differentiating between individuals with and without CTS. Carpal tunnel inlet CSA measurements demonstrated a moderate correlation to the Padua severity classification (r = 0.71), but this varied between studies. Diagnostic accuracy of CSA measured at the carpal tunnel inlet using diagnostic cutoff values ranging from 8.5 mm2 to 12.6 mm2 resulted in a range