[Use of a water jet for synovectomy: in vitro study of feasibility]. / Der Druckwasserstrahl zum selektiven Abtrag der Synovialis--In-vitro-Studie zur Machbarkeit eines neuen Synovektomieverfahrens.

AIM: The selectivity of a water jet (WJ) is already used with clinical advantage in the surgery of liver, brain, kidney and herniated lumbar discs. The aim of the present study was to determine whether a WJ can be used for synovectomy without damaging the joint capsule and the cartilage. METHOD: 60 human cadaver knee specimens (67 +/- 14 years) were dissected into synovial and cartilage samples. They were randomly assessed to four pressure groups (pW = 3; 6; 9; 12 MPa) and three jet surface angles (beta = 30; 60; 90 degrees) The nozzle diameter was dD = 0.12 mm, the stand off distance of the jet was s = 10 mm with a feed rate of vV = 2 mm/s. The acquired parameters were depth of the cuts, histological layer, and change of the samples thickness. RESULT: There was a correlation of the cutting depth and the pressure (pW), whereas the jet-surface angle (beta) showed no correlation. The synovial layer of the cut likewise correlated with the pressure. At pW = 6 MPa the stratum subsynoviale could be cut selectively without damaging the fibrous capsule or the cartilage. The increase of the samples thickness was caused by an interstitial oedema. CONCLUSION: The different mechanical properties of the joint capsule and the stratum subsynoviale lead to the selective cutting of the water jet. Since the joint capsule was not damaged, the feasibility of WJ synovectomy has been proven. The device can be used for synovectomy in parts of the joint that are not visible as well as in very small joints.

[Water jet discotomy with microinvasive approach--in vitro testing and initial clinical aspects of a new procedure]. / Die Wasserstrahldiskotomie im mikroinvasiven Zugang--In-vitro-Testung und erste klinische Aspekte eines neuen Verfahrens.

AIM: The difference in consistence of the nucleus pulposus and the annulus fibrosus allows the water jet to selectively remove the nucleus in a closed vertebral disc at a certain pressure range. The aim of the study was to investigate the use of water jet cutting in microinvasive spinal surgery. METHODS: A comparison in terms of efficiency between the water jet and those of the laser and APLD (automatic percutaneous lumbar discotomy) was achieved by plastic reconstruction of the resected spaces using the in-vitro-model of the spinal column of young pigs. The in-vitro-study was followed by a prospective clinical study with 21 patients. RESULTS: The in-vitro-employment of the three different methods showed that there were no significant differences in volume of the removed nucleus material. During the use of the hydro jet at 50 bar and simultaneous suction the intradiscal pressure measured in vitro remained below 1 bar. Clinical tests on the 21 patients showed good to very good results in 71% of the patients tested (mean follow-up 5.8 months). No complications were found. As working mechanism the pure mechanical effect and the influence on chemical processes within the nucleus remain points for discussion. CONCLUSION: The current studies results demonstrate that hydrojet spinal surgery might be a safe new method for surgery of disc protrusion and contained prolapse.

[Water jet cutting for bones and bone cement--parameter study of possibilities and limits of a new method]. / Water Jet Cutting zur Bearbeitung von Knochen und Knochenzement--Parameterstudie zu Möglichkeiten und Grenzen einer neuen Methode.

Water jet techniques have been used in industrial cutting, drilling and cleaning applications for more than 30 years. Plain water is typically used for the cutting of non-metallic materials. The addition of abrasive substances to the stream allows almost any material to be cut. The first medical applications were reported in the early 1980s, when the water jet was used to cut organs. The present study investigates the use of water jet cutting technology for endoprosthesis revision surgery. Bone and PMMA (polymethylmethacrylate) samples were cut at different pressures using an industrial water jet cutting device. Using plain water at 400 bar, PMMA was cut selectively without damaging the bone; above 400 bar, bone was also cut, but the cutting depths in PMMA were significantly greater (p < 0.05). Adding a water-soluble abrasive disaccharide to the water results in a significantly higher removal rate for both materials (p < 0.05), but selectivity is lost, although the differences in cutting depth between the two materials was significant (p < 0.05). With an abrasive, the quality of the cut was better for both materials. The water jet technology--in particular the abrasive technique--can be used to cut biomaterials such as bone and bone cement. The diameter of the jet is a great advantage when working in the confined area at the prosthesis interface. The cutting process is essentially cold, thus eliminating a thermal effect, and the jet reaction forces are relatively low. Accurate manipulation of the hydro jet nozzle is possible both manually and by robot. The results obtained show that it is possible to remove prostheses with this cutting technique, rapidly and with little damage to the surrounding tissue. Problem areas are the development of sterile pumps and the "depth control" of the jet.