Effects of shock waves on chondrocytes and their relevance in clinical practice

Extracorporeal shock wave lithotripsy (ESWL) has been used increasingly in clinical practice over the last few years. The aim of this study was to investigate the effects of shock waves on cartilage often unintentionally placed inside the focal volume during ESWL. We investigated whether the physical state of the chondrocytes exposed to shock waves has an influence on cell lethality. Chondrocytes of 12 patients were exposed to shock waves generated by a Piezoson 300. We used 200 shock waves of different energy levels (0.08 and 0.26 mJ/mm(2)) and the cells were prepared in two physical states: a fluid suspension and a viscous alginate. After ESWL the percentage of dead cells was determined by microscopy. DNA electrophoresis was carried out to detect fragmentation of the DNA. A significant increase of dead cells at higher energy levels in suspension (P = 0.001) in contrast to alginate medium (P = 0.263) was detected immediately after ESWL. The long-term survival of chondrocytes was not affected in either substance, as shown in an investigation of the cells three weeks after ESWL. At the molecular level a permeabilisation of the cell membrane was detected. DNA was not affected, even at high-energy levels. Alginate is definitely closer to the real state of cartilage in vivo than suspension. Therefore the negative effects of shock waves which are shown in many investigations that used cells in suspension are not necessarily to be expected in vivo. It can be assumed that side effects will not occur in a clinical setting.