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As an alternative to the well-established surgical procedures for the treatment of disk herniation, percutaneous nucleotomy has proved to be very satisfactory. In several cases this approach has brought complete relief to the patient without sacrifice of bone and without causing soft tissue damage as would have been inevitable with the usual surgical methods. Percutaneous nucleotomy is also a true alternative to chemical nucleolysis when leakage of contrast agent into the spinal canal has already been observed during diskography. Furthermore, this method avoids disagreeable complications encountered in chemical nucleotomy, for example, anaphylactic shock or the escape of the nucleolytic agent into the spinal canal. The method basically consists of removing the nucleus pulposus (or a major part of it) by means of a forceps that is introduced to the site through a cannula. In this manner a reduction of volume of the disk is achieved. The procedure can easily be carried out under local anesthesia. This method should be avoided in the case of prolapse within the spinal canal and especially when displacement beyond the level of the disk has occurred. In the period between 1979 and 1985 we carried out percutaneous nucleotomies in 51 patients with herniation mostly combined with a narrow spinal canal orspondylolisthesis. The clinical results from 32 of 51 patients can be assessed as very good, good, or satisfactory. We consider the proportion of patients showing good clinical results to be high, bearing in mind that the indication was not just disk herniation alone but, in most cases, combined with other lumbar pathologies as well.

Cavitation damage tests of iron and steel have been carried out using two types of experimental facilities. One is a water tunnel system which presumably simulates the field conditions fairly closely and the other is a magnetostriction vibratory unit commonly used for accelerated cavitation erosion testing of metals. A comparison between water tunnel and vibratory tests shows a difference in mechanism of cavitation damage. Consequently, it has been concluded that the application of the test results obtained in a magnetostriction vibratory apparatus should be limited to provide rough data for the primary selection of proper materials to be used in the construction of hydraulic units and other industrial systems, unless damage is caused under similar conditions to that of the vibratory apparatus.