Development of a musculoskeletal model of the wrist to predict frictional work dissipated due to tendon gliding resistance in the carpal tunnel.

Carpal tunnel syndrome is an entrapment neuropathy that has been associated with the aggravation of tendon gliding resistance due to forceful, high velocity, awkwardly angled, and repetitive wrist motions. Cadaveric and epidemiological studies have shown that combinations of these risk factors have a more than additive effect. The aim of the current study was to develop a musculoskeletal model of the wrist that could evaluate these risk factors by simulating frictional work dissipated due to the gliding resistance of the third flexor digitorum superficialis tendon. Three flexion angle zones, three extension angle zones, five levels of task repetitiveness, and five levels of task effort were derived from ergonomic standards. Of the simulations performed by systematically combining these parameters, the extreme wrist flexion zone, at peak task repetitiveness and effort, dissipated the most frictional work. This zone dissipated approximately double the amount of frictional work compared to its equivalent zone in extension. For all motions, a multiplicative effect of the combination of task repetitiveness and effort on frictional work was identified by the musculoskeletal model, corroborating previous epidemiological and experimental studies. Overall, these results suggest that the ergonomic standards for wrist flexion-extension may need to be adjusted to reflect equivalent biomechanical impact and that workplace tasks should be designed to minimise exposure to combinations of highly repetitive and highly forceful work, especially when the wrist is highly flexed.

Tricuspid valve endocarditis due to a jet lesion detected by echocardiography in a 27-year old man with congenital ventricular septal defect.

The case of an non-addict young caucasian with isolated tricuspid valve endocarditis in congenital ventricular septal defect (VSD) is presented. Despite antibiotic treatment the patient suffered from recurrent right sided pneumonias. A computed tomography of the chest revealed an abscess localized in the right lower lung with signs of cavitation. Echocardiography identified a vegetation located at the anterior tricuspid leaflet due to a jet lesion through the VSD. ECG-gated MRI revealed normal left ventricular function and localized the septal defect and a jet against the anterior tricuspid valve leaflet. The patient underwent open heart surgery and the VSD was closed. Now, two years later, the patient is free from any symptoms or complications. This case illustrates that noninvasive techniques like echocardiography and ECG-gated MRI can not only accurately image cardiac anatomy in patients with ventricular septal defect but additionally provide information about the pathomechanism of the development of jet lesions resulting in valvular vegetations. Operative correction of underlying cardiac disease in nonaddicts with complicating tricuspid valve endocarditis might be a favourable treatment especially when antibiotic treatment fails to cure the infection.