Design and manufacture of a novel system to simulate the biomechanics of basic and pitching shoulder motion.

OBJECTIVES: Cadaveric models of the shoulder evaluate discrete motion segments using the glenohumeral joint in isolation over a defined trajectory. The aim of this study was to design, manufacture and validate a robotic system to accurately create three-dimensional movement of the upper body and capture it using high-speed motion cameras. METHODS: In particular, we intended to use the robotic system to simulate the normal throwing motion in an intact cadaver. The robotic system consists of a lower frame (to move the torso) and an upper frame (to move an arm) using seven actuators. The actuators accurately reproduced planned trajectories. The marker setup used for motion capture was able to determine the six degrees of freedom of all involved joints during the planned motion of the end effector. RESULTS: The testing system demonstrated high precision and accuracy based on the expected versus observed displacements of individual axes. The maximum coefficient of variation for displacement of unloaded axes was less than 0.5% for all axes. The expected and observed actual displacements had a high level of correlation with coefficients of determination of 1.0 for all axes. CONCLUSIONS: Given that this system can accurately simulate and track simple and complex motion, there is a new opportunity to study kinematics of the shoulder under normal and pathological conditions in a cadaveric shoulder model.

Ultrasonographic control of the puncture level for lumbar neuraxial block in obstetric anaesthesia.

BACKGROUND: Errors in the judgement of puncture level during neuraxial anaesthesia can lead to significant complications. The aim of this study was to assess, in obstetric anaesthesia, the accuracy of clinical determination of the lumbar spinal interspace level, using surface ultrasound imaging as control. METHODS: At the anaesthesia follow-up visit, women who had received lumbar neuraxial anaesthesia during labour were prospectively included. The intervertebral level of needle insertion, located by the needle scar position, was identified by ultrasonography and compared with the clinical level reported on the chart by the anaesthetist who performed the block. RESULTS: Ninety-nine women were studied. The clinical puncture level was accurate in 36.4% of patients. Ultrasound examination showed the puncture level to be more cephalad than the level noted in the anaesthetic record in almost 50% of patients. In 15% of patients, the puncture level was more caudad than the anaesthetist had assessed. Factors including type of anaesthesia, indication, time period, level of anaesthetic experience, BMI, and spinal pathology did not seem to influence the frequency of errors. CONCLUSIONS: The observed differences between clinical and ultrasonic identification of spinal puncture level highlight the potential for serious complications associated with the performance of neuraxial blocks above the spinous process of L3 in the parturient. With the increase in popularity of techniques involving puncture of the dura mater for labour anaesthesia, we feel that awareness of this risk is important.