In the recording of biomedical signals, a significant noise component is introduced by the electrode. The magnitude of this noise is considerably higher than the equivalent thermal noise from the electrode impedance. As the noise in surface electrodes limits the resolution of biopotential recordings, it is important to understand its origin. It was found that the noise mainly originates in the electrolyte-skin interface and that it is highly dependent on the electrode gel used and the skin properties of the test subject. Depending on skin treatment, magnitudes between 1 and 20 microVrms were measured among subjects. When the metal-electrolyte interface was allowed time to stabilise, electrodes of different metals measured face to face all showed a negligibly small noise magnitude (< 1 microVrms). In pre-gelled electrodes, where the metal-electrolyte interface has stabilised, no difference in noise properties was found between Ag-AgCl electrodes and other metals when measured on the skin. In subjects at rest, the contribution of EMG signals to the total noise level was shown to be negligibly small compared with the noise contribution of the electrolyte-skin interface. The magnitude of the noise of electrodes appeared to be inversely proportional to the square root of the area of the electrode on the skin.

In the first part of the review the various mechanisms that could be the cause of interference in bioelectric recordings are considered. It is demonstrated that the performance of a good amplifier can be seriously degraded in its functioning if the whole measurement situation is not taken into account. Several techniques used to reduce interference, of which guarding and driven right leg circuits are the most important, are analysed. In the second part of the review some examples of the application of the theory in practical situations are presented. The instrumentation amplifier circuit normally used in bioelectric recordings is improved for measurements under difficult circumstances. Another application is a low-cost 64-channel amplifier for multichannel ECG recordings. The third application is a device that can be added to bioelectric measurement systems and will provide a major reduction in interference.

Malunion after a distal radius fracture is very common and if symptomatic, is treated with a so-called corrective osteotomy. In a traditional distal radius osteotomy, the radius is cut at the fracture site and a wedge is inserted in the osteotomy gap to correct the distal radius pose. The standard procedure uses two orthogonal radiographs to estimate the two inclination angles and the dimensions of the wedge to be inserted into the osteotomy gap. However, optimal correction in 3-Dspace requires restoring three angles and three displacements. This paper introduces a new technique that uses preoperative planning based on 3-D images. Intraoperative 3-D imaging is also used after inserting pins with marker tools in the proximal and distal part of the radius and before the osteotomy. Positioning tools are developed to correct the distal radius pose in six degrees of freedom by navigating the pins. The method is accurate ( d 1.2 mm, ϕ 0.9°, m TRE = 1.7 mm), highly reproducible (SE (d) < 1.0 mm, SE (ϕ) ≤ 1.4°, SE (m) (TRE) = 0.7 mm), and allows intraoperative evaluation of the end result. Small incisions for pin placement and for the osteotomy render the method minimally invasive.

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