The variation of median nerve functionality with wrist postures typical of computer use and a novel ultrasound technique for the diagnosis of carpal tunnel syndrome

Carpal tunnel syndrome (CTS) is an affliction that affects numerous people in an occupational and recreational environment. One area commonly linked to the development of this condition is computer use. This is due to the repetitive movements that occur while undertaking this task. However, a direct link between computer use and CTS development has not been established. Determining the cause and development of CTS will result in a greater understanding of the condition and its influence on the patient. This is necessary for adequate treatment and diagnosis of the condition. Knowing the physical responses or anatomical changes that occur will lead to identification of CTS at an earlier stage and a level of severity to be accurately determined. Establishing a connection between CTS and computer use, involves breaking down computer activities into its individual components. One of these components is wrist posture. Deviation of the wrist from a neutral position has been shown to increase pressure within the carpal tunnel, leading to a reduction in nerve functionality. If this pressure is great enough, it will induce the development of CTS. However, investigations into the wrist postures frequented during computer use or the impact of these postures on the median nerve have been limited. During a computer activity wrist movements occur in extension/flexion and a radial/ulnar direction. However, previous studies have only documented these movements in one direction at a time. To account for complete movement of the wrist, motion analysis techniques were adopted. This allowed for all wrist postures to be calculated and categorised. Once the most prevalent wrist postures were determined, their influence on median nerve functionality was investigated. This was carried out utilising electrodiagnostic techniques. This involved maintaining the most common wrist postures for an extended duration of time and recording the change in nerve response to electrical stimulation. This determined that nerve functionality decreased enough to indicate a significant pressure increase within the carpal tunnel. Even though testing was only conducted on healthy individuals, changes to NCS data occurred. This highlights the possibility of false diagnosis. To overcome this problem an alternative diagnostic modality, which is not influenced by this would be beneficial. One suitable method is sonography. Sonography has previously been investigated for diagnosing CTS, but the accuracy of it has varied significantly in literature. However, the benefits of viewing the carpal tunnel contents and the potential of sonography in CTS diagnosis are evident. For sonography to develop further in the diagnosis of CTS, a new diagnostic criterion needs to be created. This would overcome the variation and problems associated with other criteria. The method proposed in this study is median nerve volume ratio. To calculate median nerve volume, a 3-D model of the median nerve in the forearm and through the carpal tunnel was constructed. This is done from a number of B-scans of the median nerve. Image orientation was calculated using photogrammetric techniques and allowed for alignment of the images to occur. A total of four volumes along the median nerve were calculated. This resulted in three volume ratios, comparing the nerve volume in the carpal tunnel to areas in more proximal locations. The results display a substantial difference between controls and patients for two of the volume ratios calculated. These volume ratios also show a strong trend for severity with better R2 values than current diagnostic methods. To understand the discrepancies in previous sonographic diagnostic criteria, the impact of the sonographer was reviewed. This focused on the transducer force applied during an ultrasound examination. It was found that force had the capacity to alter values used in diagnosis such as flattening ratio. However, it was also noted that area measurement did not alter significantly due to the applied force. Therefore, volume measurement from 3-D models would not be affected. The experimental investigations undertaken revealed a link between computer use and decrease in nerve functionality. This was not simply beneficial in determining how CTS can develop, but also in showing the possibility of incorrect diagnosis occurring. The new sonographic methods presented here show great promise in diagnosing CTS and tackled the problem of false diagnosis associated with NCS.