ULTRASONOGRAPHIC ASSESSMENT OF LONGITUDINAL MEDIAN NERVE AND HAND FLEXOR TENDON DYNAMICS IN CARPAL TUNNEL SYNDROME JAN-WIEBE H. KORSTANJE, MSc, 1 MARJAN SCHELTENS-DE BOER, MD, 2 JOLEEN H. BLOK, PhD, 2 PETER C. AMADIO, MD, 3 STEVEN E.R. HOVIUS, PhD, 4 HENK J. STAM, PhD, 1 and RUUD W. SELLES, PhD 1 1 Department of Rehabilitation Medicine and Physical Therapy, Erasmus MC, University Medical Centre Rotterdam, P.O. Box 2040, 3000CA Rotterdam, The Netherlands 2 Department of Clinical Neurophysiology, Erasmus MC, University Medical Centre Rotterdam, Rotterdam, The Netherlands 3 Orthopedic Biomechanics Laboratory, Division of Orthopedic Research, Department of Orthopedic Surgery, Mayo Clinic, Rochester, Minnesota, USA 4 Department of Plastic and Reconstructive Surgery, Erasmus MC, University Medical Centre Rotterdam, Rotterdam, The Netherlands Accepted 14 November 2011 ABSTRACT: Introduction: Changes in subsynovial connective tissue (SSCT) in carpal tunnel syndrome (CTS) patients may result in altered dynamics; consequently, quantification of these dynamics might support objective diagnosis of CTS. Methods: We measured and compared longitudinal excursion of the flexor digitorum superficialis and profundus tendons, the median nerve, and the SSCT between the most and least affected hands of 51 CTS patients during extension-to-fist motion. Results: Median nerve and flexor digitorum superficialis tendon excursions in the most affected hands were smaller than in the least affected hands of the same patients, whereas the excur- sions of the flexor digitorum profundus were larger. Based on these excursions, logistic regression models classified between 67% and 86% of the hands correctly as having CTS. Conclusions: The altered hand dynamics in CTS patients may have implications for the pathophysiology and clinical evaluation of CTS, and ultrasound-based classification models may further support the diagnosis of CTS. Muscle Nerve 45: 721–729, 2012 Carpal tunnel syndrome (CTS) is the most fre- quently encountered compression neuropathy. In general terms, CTS is defined as an entrapment of the median nerve, but in the majority of patients its precise etiology is unknown. The traditional di- agnosis of CTS is based on clinical symptoms and signs in combination with results of electromyo- graphic (EMG) studies. Although EMG develop- ments have increased the specificity and sensitivity of this technique, there is still ongoing debate on the ‘‘gold standard’’ for diagnosis of CTS. A recent study questioned the added value of EMG studies in the diagnosis of CTS compared with clinical di- agnosis alone. 1 Furthermore, it has been reported that 16–34% of patients with clinically diagnosed CTS have normal EMG findings. 2–4 This justifies exploration of new techniques to complement EMG findings. CTS is associated with an increased cross-sec- tional area of the median nerve. 5–11 A large num- ber of studies have shown that ultrasound (US) measurement of the cross-sectional area of the me- dian nerve can discriminate between patients and controls and is therefore a valuable diagnostic tool. However, at the same time, results seem equivocal due to: (1) optimization toward sensitiv- ity or specificity; (2) operator dependency of US; and (3) the lack of a gold standard for compari- son. 7,11 Recently, a number of studies have addressed not only the cross-sectional area of the median nerve but also the dynamic behavior of the median nerve and hand flexors in CTS patients. 12–15 It has been suggested that thickening and non- inflammatory fibrosis of the subsynovial connective tissue (SSCT) within the carpal tunnel is an essential part of the pathophysiology. The SSCT surrounds the tendons and is connected to them with fibrils. Thickening and fibrosis of the SSCT might change the excursion of the median nerve and hand flexor tendons during hand movement. Therefore, meas- uring the movement of the flexors and median nerve may provide important insights into the spe- cific pathology in individual patients. For the purpose of measuring the longitudinal dynamics of the median nerve and the hand flexor tendons, various approaches have been proposed. Ettema et al. used a video camera to assess the lon- gitudinal excursion of the relevant structures in cadaver hands and perioperatively in patients with CTS during carpal tunnel release. 13,16 This tech- nique is invasive and therefore it may alter tendon dynamics. Alternatively, US techniques such as color Doppler imaging 17 or speckle tracking 15,18 have been employed to measure longitudinal nerve and tendon movement in vivo. However, color Doppler imaging was found to be only moderately accurate, with tracking errors of up to 18%. 17 Simi- larly, tracking accuracy using an industrial speckle tracking algorithm not optimized for tendons Abbreviations: AAEM, American Association of Electrodiagnostic Medi- cine; AVI, audio-video interleave; BCTQ, Boston Carpal Tunnel Question- naire; CMAP, compound muscle action potential; CTS, carpal tunnel syndrome; DIP, distal interphalangeal; DML, distal motor latency; DSL, dis- tal sensory latency; EMG, electromyography; FDP, flexor digitorum profun- dus; FDS, flexor digitorum superficialis; IP, interphalangeal; MCP, metacarpophalangeal; MN, median nerve; NCC, normalized cross-correla- tion; ROI, region of interest; SNAP, sensory nerve action potential; SSCT, subsynovial connective tissue Correspondence to: J. H. Korstanje; e-mail: j.korstanje@erasmusmc.nl V C 2011 Wiley Periodicals, Inc. Published online 18 November 2011 in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/mus.23246 Key words: carpal tunnel syndrome, diagnostic tool, hand dynamics, subsynovial connective tissue, ultrasound Hand Dynamics in CTS MUSCLE & NERVE May 2012 721