Reassessing Flexor Tendon Excursion Models with Colour Doppler Ultrasonography

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1 Reassessing Flexor Tendon Excursion Models with Colour Doppler Ultrasonography A.M. KOCIOLEK and P.J. KEIR* Department of Kinesiology, McMaster University, Hamilton, ON, Canada, L8S 4K1 Abstract Patients with carpal tunnel syndrome present with fibrosis of the subsynovial connective tissue (SSCT) next to the flexor tendons, suggesting that shear forces play a role in injury development. Researchers are increasingly utilizing diagnostic imaging to assess musculoskeletal dynamics in vivo. Recent ultrasound studies found that flexor tendon excursions did not match traditional cadaveric models of tendon-joint interaction, which are often used to assess occupational injury risks. To better link ergonomic factors with pathomechanics, ultrasound was used to measure relative motion of the long finger flexor digitorum superficialis (FDS) and adjacent SSCT in the carpal tunnel. Sixteen participants (8, 8 ) completed three cyclical finger movements (metacarpophalangeal, proximal and distal interphalangeal joints, full finger flexion/extension) in three wrist postures (30 flexion, 0, 30 extension) with motion analysis of the wrist and long finger. Full finger movements produced larger tendon excursions than metacarpophalangeal and interphalangeal motions (full finger: 21.7 ± 1.0 mm; metacarpophalangeal: 14.0 ± 0.7 mm; interphalangeal: 11.9 ± 0.6 mm). Relative displacements between the FDS and SSCT increased linearly by 32.3% from 30 wrist extension to 30 wrist flexion (F 2,30 = 16.2, p < 0.01). This relationship was primarily driven by excursion changes of the SSCT, which decreased by 22.1% with wrist flexion (F 2,30 = 9.9, p < 0.01). This study shows that the wrist may be more prone to shear injuries in flexion. We are currently integrating the data into an analytical model that predicts FDS and SSCT motion as well as injury risk in the workplace. Keywords: Carpal tunnel; flexor tendon; subsynovial connective tissue; shear; ultrasound. 1. Introduction The most common findings in patients with carpal tunnel syndrome are fibrosis and thickening of the subsynovial connective tissue (SSCT) surrounding the flexor tendons inside the carpal tunnel (Barr et al., 2004). These pathological changes are exacerbated close to the flexor tendons, indicating that shear forces are involved in injury development (Ettema et al., 2006; Schuind et al., 1990). SSCT fibrosis also affects tendon gliding, resulting in either increased adherence or dissociation between the flexor tendons and the SSCT (Ettema et al., 2006). Frictional forces increase even further, giving rise to a vicious cycle of degradation (Ettema et al., 2006; 2008). Researchers are utilizing sonography more often to assess musculoskeletal dynamics due to advances in image resolution (Ettema et al., 2006; Korstanje et al., 2010; Lopes et al., 2011; Oh et al., 2007; Peolsson et al., 2010; Yoshii et al., 2009). Ettema et al. (2006) used colour Doppler ultrasound to quantify tendon motion of the long finger flexor digitorum superficialis (FDS) and surrounding SSCT. Flexor tendon velocities were significantly higher than the SSCT during both finger flexion and extension. In a similar study, long finger FDS velocities were greater than SSCT velocities for tendon movements exceeding 2. cm/s (Oh et al., 2007). These findings support the injury mechanism of tendon shear in the carpal tunnel. However, there is a need to better understand how tendon dynamics are influenced by occupational risk factors, including awkward (or non-neutral) wrist and finger postures. A recent study calculated index finger FDS excursions from spectral Doppler waveforms, which were acquired with a 12- MHz probe using a 60 angle correction (Lopes et al., 2011). The researchers found that flexor tendon excursions were larger than a traditional cadaveric model of tendon-joint interaction (Armstrong and Chaffin, 1978). Differences were most pronounced during complex movement patterns involving concurrent wrist and finger motions. These results challenge traditional cadaver models that consider each joint *Corresponding author. pjkeir@mcmaster.ca 1

due to repetitive wrist and finger movements, and (b) update ergonomic tools that use flexor tendon motion and shear as a predictor of injury risk in the workplace.

2 independently. There remains a need to quantify excursions of the flexor tendons and adjacent SSCT (in vivo) using ultrasound while simultaneously measuring joint angles to: (a) better assess carpal tunnel shear due to repetitive wrist and finger movements, and (b) update ergonomic tools that use flexor tendon motion and shear as a predictor of injury risk in the workplace. probe scanning head and the palmar wrist to improve acoustic coupling. A 2. Methods 2.1. Participants Sixteen healthy volunteers (8 and 8 ) were recruited for this study. Participants completed a brief questionnaire to document musculoskeletal disorders of the wrist and hand as well as other health conditions that may influence tendon gliding in the carpal tunnel. Briefly, exclusion criteria included peripheral nerve disease, wrist tendinopathy, degenerative joint disease, arthritis, gout, hemodialysis, sarcoidosis, amyloidosis, hypothyroidism, diabetes mellitus, acute injury of the upper extremity, and pain, tingling, or numbness of the hand. Participants provided informed written consent prior to data collection, which was approved by the Hamilton Health Sciences (HHS) / Faculty of Health Sciences (FHS) Research Ethics Board Protocol Each participant was seated at an adjustable table to maintain 120 of elbow flexion with 0 of shoulder abduction and the right forearm was immobilized in a mid-prone posture using a thermoplastic splint (Figure 1A). A custom handgrip fixed the index, ring, and little fingers in a mid-flexed position, allowing only the long finger to move (Figure 1B). Flexor tendon excursions of the long finger were assessed as participants completed three cyclical finger movements (metacarpophalangeal, proximal and distal interphalangeal joints, full finger flexion/extension) in three wrist postures (30 flexion, 0, 30 extension). Ultrasound and motion capture data were recorded as the participants completed each test movement for 10 seconds at comfortable self-selected tempo. Trial order was randomized to mitigate potential learning and fatiguing effects Colour Doppler Ultrasound An ultrasound scanner (Vivid Q, GE Healthcare) equipped with a high-frequency probe (i12l) was used to scan the wrist with colour Doppler imaging (CDI). This method generated a colour map of Doppler shifts superimposed on echograms, which represented velocity of the imaged structures (Figure 2). The probe was positioned cm proximal to the wrist crease with a custom holding device. Transmission gel was applied between the B Figure 1. Experimental setup showing: (a) participant with the forearm immobilized in the apparatus, and (b) custom handgrip to perform long finger movements. Ultrasound scans were collected at 30 frames per second with a 30 beam steering adjustment to achieve a suitable angle of insonation (< 60 ). Velocity-time data of the flexor digitorum superficialis (FDS) and adjacent subsynovial connective tissue (SSCT) were obtained from colour maps overlying the grayscale wrist images using dedicated software (EchoPac, GE Healthcare). Velocity profiles were integrated to determine displacements of the long finger FDS tendon and SSCT. Figure 2. Colour map of the long finger FDS tendon. Colour brightness is associated with velocity of the underlying structure Motion Capture Three-dimensional wrist and long finger joint kinematics were obtained with a 12-camera motion capture system (Raptor-4, Motion Analysis Corporation). Twenty-six reflective hemi-spherical markers (4 mm in diameter) were affixed to the 2

distal upper extremity (Figure 3). Marker trajectories were collected at 120 Hz, which fed into a kinematic model of the wrist and hand (Cocchiarella et al., 2013).

3 distal upper extremity (Figure 3). Marker trajectories were collected at 120 Hz, which fed into a kinematic model of the wrist and hand (Cocchiarella et al., 2013). Wrist and finger joint angles were calculated with an x-y-z sequence (flex/extension-ab/adduction-pro/supination). A FDS Excursion (mm) B Figure 3. Marker configuration used to calculate wrist and long finger joint angles. 2.. Statistical Analyses Repeated measures ANOVAs were used to test the effects of finger movement (metacarpophalangeal, proximal and distal interphalangeal, full finger) and wrist posture (30 flexion, 0, 30 extension). Dependent variables were FDS and SSCT excursions as well as the shear strain index (FDS excursion - SSCT excursion / FDS excursion 100%). Significant main effects and interactions were followed up with Tukey s HSD (ɑ = 0.0). 3. Results Long finger FDS excursions were similar across wrist postures (Figure 4A). Full finger () movements produced larger excursions than metacarpophalangeal () and interphalangeal () motions (F 2,30 = 79.3, p < 0.01; 21.7 ± 1.0 mm; 14.0 ± 0.7 mm; 11.9 ± 0.6 mm). SSCT displacements were smaller than the FDS by 32.% (across all test conditions). However, there was a main effect of wrist posture on excursions of the SSCT (F 2,30 = 9.9, p < 0.01). SSCT displacements increased linearly, by 22.1%, from 30 wrist flexion to 30 wrist extension (Figure 4B). There was also a main effect of finger movement (F 2,30 = 41.8, p < 0.01). produced larger excursions than and (Figure 4B). The shear strain index (a measure of relative motion between the FDS and SSCT) was influenced by wrist posture (F 2,30 = 16.2, p < 0.01). The highest shear strain index occurred at 30 wrist flexion (38.9 ± 1.9 %) and decreased in the neutral (32.4 ± 2.3 %) and extended (26.3 ± 2.0 %) wrist positions (Figure 4C). Type of finger movement (,, ) did not significantly affect shear strain. C SCT Excursion (mm) Shear Strain Index (%) Wrist Posture Figure 4. Displacements of the: (a) FDS, (b) SSCT, and (c) Shear Strain Index (a measure of relative motion between FDS and SSCT). Metacarpophalangeal; Interphalangeal; Full flexion. 4. Discussion We investigated the effects of finger movement and wrist position on absolute and relative displacements of the FDS and SSCT. Both FDS and SSCT excursions were similar to previous cadaver studies (Ettema et al., 2006; Yoshii et al., 2009). However, the current results differed from ultrasound assessment of complex and simple movement patterns by Lopes et al. (2011). The researchers found that multi-joint finger movements 3

4 (such as full finger flexion) resulted in larger tendon excursions than the sum of the individual movement components performed in isolation (i.e. metacarpophalangeal + proximal interphalangeal + distal interphalangeal joint flexion). In this study, full finger motion did not produce larger tendon excursions compared to the sum of the movement components. actually resulted in 16.1% less FDS excursion than and added together. However, this discrepancy is likely due to differences in joint kinematic profiles. We are currently incorporating motion capture data from this study into a regression model that predicts displacements of the FDS and SSCT. Our study also showed that relative displacements between the FDS and SSCT increased linearly by 32.3% from 30 wrist extension to 30 wrist flexion. This relationship was primarily driven by excursion changes of the SSCT, which decreased by 22.1% with wrist flexion. Yoshii et al. (2008) found a similar trend in cadavers; however, significant changes in the shear strain index only occurred with greater wrist flexion (> 60 ). This study indicates that the wrist may be more prone to shear injuries in wrist flexion than determined by previous cadaver studies of flexor tendon and SSCT motion. We are currently integrating these data into an analytical model that predicts FDS and SSCT excursion as well as injury risk in the workplace. Another study is also underway to directly measure tendon motion and friction in cadaveric specimens as a means for further comparison.. Conclusion This study represents an important first step into better understanding wrist and hand disorders during repetitive work tasks. FDS and SSCT excursions from this study showed the importance of finger movement and wrist posture as occupational risk factors. An improved understanding of how work factors influence underlying pathomechanics will ultimately lead to the development and refinement of research-driven ergonomic tools based on tendon motion and shear. Acknowledgement This study was supported by NSERC (Discovery Grant # and RTI # ) and by the Centre of Research Expertise for the Prevention of Musculoskeletal Disord.ers (CRE-MSD Seed Grant #00632). References Armstrong T, Chaffin D, An investigation of the relationship between displacements of the finger and wrist joints and the extrinsic finger flexor tendons. Journal of Biomechanics, 11 (3), Barr A, Barbe M, Clark B, Work-related musculoskeletal disorders of the hand and wrist: epidemiology, pathophysiology, and sensorimotor changes. Journal of Orthopaedic and Sports Physical Therapy, 34 (10), Cocchiarella D, Kociolek A, Keir P, An unconstrained kinematics model of the hand In: Proceedings of the 2 nd International Digital Human Modeling Symposium. Ann Arbor, Michigan. Ettema A, Amadio P, Zhao C, Wold L, O Byrne M, Moran S, An K, Changes in the functional structure of the tenosynovium in idiopathic carpal tunnel syndrome: a scanning electron microscope study. Journal of Plastic and Reconstructive Surgery, 118 (6), Ettema A, An K, Zhao C, O Byrne M, Amadio P, Flexor tendon and synovial gliding during simultaneous and single digit flexion in idiopathic carpal tunnel syndrome. Journal of Biomechanics, 41 (2), Korstanje J, Selles R, Stam H, Hovius S, Bosch J, Development and validation of ultrasound speckle tracking to quantify tendon displacement. Journal of Biomechanics, 43 (7), Lopes M, Lawson W, Scott T, Keir P, Tendon and nerve excursion in the carpal tunnel in healthy and CTD wrists. Clinical Biomechanics, 26 (9), Oh S, Belohlavek M, Zhao C, Osamura N, Zobitz M, An K, Detection of differential gliding characteristics of the flexor digitorum superficialis tendon and subsynovial connective tissue using color Doppler sonographic imaging. Journal of Ultrasound Medicine, 26 (2), Peolsson M, Löfstedt T, Vogt S, Stenlund H, Arndt A, Trygg J, Modelling human musculoskeletal functional movements using ultrasound imaging. BioMed Central (BMC) Medical Imaging, 10 (1), Schuind F, Ventura M, Pasteels J, Idiopathic carpal tunnel syndrome: histologic study of the flexor synovium. Journal of Hand Surgery, 1A (3), Yoshii Y, Villarraga H, Henderson J, Zhao C, An K, Amadio P, Speckle tracking ultrasound for assessment of the relative motion of flexor tendon and subsynovial connective tissue in the human carpal tunnel. Ultrasound in Medicine and Biology, 3 (12),

5 Yoshii Y, Zhao C, Zhao K, Zobitz M, An K, Amadio P, The effect of wrist position on the relative motion of tendon, nerve, and subsynovial connective tissue within the carpal tunnel in a human cadaver model. Journal of Orthopaedic Research, 26 (8),

Transverse Movement of the Median Nerve in the Carpal Tunnel during Wrist and Finger Motion in Patients with Carpal Tunnel Syndrome

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