The objective of this study was to evaluate the correlations between deformation and displacement of median nerve and flexor tendons during finger motion in the carpal tunnel for both carpal tunnel syndrome (CTS) patients and healthy controls. Sixtytwo wrists of 31 asymptomatic volunteers and fifty-one wrists of 28 idiopathic CTS patients were evaluated by ultrasound. The displacement of the median nerve and the middle finger flexor digitorum superficialis (FDS) tendon, as well as area, perimeter, aspect ratio of a minimum enclosing rectangle, and circularity of the median nerve were measured in finger extension and flexion positions. Deformation indices were defined as the ratios of indices in finger extension and flexion positions. The correlations between displacement and deformation indices were evaluated. There were significant correlations between nerve palmar-dorsal displacement and deformation indices (p < 0.05). The aspect ratio deformation index showed the strongest correlation to palmar-dorsal displacement of the nerve (À0.572, p < 0.01). This study showed that there is a relationship between median nerve deformation indices and nerve palmar-dorsal displacement in the carpal tunnel. Since the highest correlations were between palmar-dorsal nerve displacement direction and aspect ratio deformation index, these parameters may be helpful to understand the pathophysiology of CTS. Keywords: carpal tunnel syndrome; median nerve; displacement; deformation; ultrasound Carpal tunnel syndrome (CTS) is a compression neuropathy of the median nerve at the wrist. The diagnosis of CTS is mostly clinical, and usually confirmed with nerve conduction studies. Recently, cross-sectional ultrasound imaging has been proposed for the diagnosis of CTS. Static ultrasonography can detect pathological changes such as thickening and alteration of the echogenicity of the flexor tendons and flexor retinaculum, synovial proliferation and flattening of the median nerve in the carpal tunnel. 1-7 These findings can distinguish patients with CTS from normal subjects.Peripheral nerve trunks slide over considerable length with movements of the extremity. 8 However, in the case of chronic compression, fibrosis of the perineurium and endoneurial edema 9 may alter the motion and deformation characteristics of the median nerve. Thus, to fully understand the pathophysiology of CTS, to the clinician should consider the deformation and displacement of the nerve and tendons.An ultrasound method to observe the movement of the structures in the carpal tunnel during finger motion has been described, 10 and several ultrasound indices of deformation have been identified which may be helpful in the assessment of patients with CTS. 11 The median nerve shape is affected more by the flexor digitorum superficialis (FDS) tendons than by the flexor digitorum profundus tendons, because the FDS tendons lie closer to the median nerve. There is a changed pattern of median nerve motion in association with middle finger, index, and thumb motion, when co...

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The purpose of this study was to measure the compliance of the carpal tunnel in candidate animal models of carpal tunnel syndrome (CTS), by measuring the resistance when passing a tapered metal rod through the carpal tunnel. Forepaws from 10 dogs, 10 rabbits, and 10 rats with intact carpal tunnels, and 10 fresh frozen human wrist cadavers were used. The slopes of the linear part of the force-displacement curve (a measure of stiffness), normal force, and increasing area ratio (InAR) were significantly different among the four species (p < 0.05). Post hoc analysis indicated that the mean slopes for the human carpal tunnel were the largest, indicating the least compliance, whereas those of the rat were the least (p < 0.05). The features of the compliance for the dog carpal tunnel were closest to the human. The development of animal models of CTS should consider the compliance of the carpal tunnel, as it will be more difficult to increase pressure in a more compliant tunnel. Keywords: carpal tunnel syndrome; disease models; animals; human; biomechanics Carpal tunnel syndrome (CTS) is a common hand disease in which the median nerve is compressed at the wrist. 1 Most cases are idiopathic. 2 Although repetitive hand use is suspected in some cases, 3-5 the correlation with activity in most cases is still unclear. 6 The three pathological hallmarks of CTS are elevated carpal tunnel pressure, 7-12 fibrosis of the subsynovial connective tissue (SSCT), [13][14][15][16] and abnormal nerve function. 17 More recent studies have suggested that the neuropathy is also associated with changes in the gliding characteristics 18,19 and permeability 20 of the SSCT.Clinical studies of CTS are limited by the difficulty of evaluating the early stages of its pathology. Thus, a validated animal model of CTS is an important need. A good animal model would have comparable anatomy: a carpal tunnel containing the median nerve, tendons, and SSCT, as the human carpal tunnel does. In addition, because CTS is characterized by increased carpal tunnel pressure, the animal carpal tunnel model should have mechanical characteristics similar to the human carpal tunnel. A model with a very complaint carpal tunnel might not be useful if the goal is to investigate changes in biology within the tunnel that might induce pressure elevation, such as gradual thickening of the SSCT.Previous studies have reported animal models of CTS in the rabbit, 21-24 rat, 25,26 and dog. 27 The rabbit model is commonly used to study CTS. 28,29 Lim et al. 22 determined the dose-responsiveness for an acute pressureinduced median neuropathy model of human acute CTS in the rabbit, using saline infusion, showing that significant electrophysiological changes were caused by pressures greater than 30 mmHg. Diao et al. 21 also investigated the relationship between pressure and median nerve function in the carpal tunnel in the rabbit model. Angioplasty catheters were placed in the carpal tunnel to create pressures ranging from 50 to 80 mmHg, with similar findings. These experi...

Background Trigger finger is most common in the ring finger, but the reason for this is not known. We hypothesized that the compliance of the A1 pulley might be one of the factors responsible for this phenomenon. The purpose of this study was therefore to compare the compliance of the normal A1 pulley of the thumb, index, middle, ring and little fingers using human cadavers. Methods Eight normal thumbs, index, middle, ring and little fingers from eight fresh frozen human hand cadavers were used in this experiment. The compliance of the A1 pulley was measured by the resistance when passing a tapered metal rod through the A1 pulley. The slopes of the linear region of radial force/increasing area ratio curve were calculated and analyzed. Findings The mean slope of the linear region of the radial force/increasing area ratio curve was significantly different among the five digits (p<0.05). Post hoc analysis indicated that the mean slope for the middle finger A1 pulleys was larger than the thumb and little finger A1 pulleys (p<0.05). Interpretation The findings did not support our clinical hypothesis that A1 pulley stiffness would parallel the relative frequency of trigger finger by digit.