MECHANICAL DYSFUNCTION OF VENTRICULOPERITONEAL SHUNTS CAUSED BY CALCIFICATION OF THE SILICONE-RUBBER CATHETER

Object. The authors studied new and calcified shunt catheters to ident ify the prevalence of failures caused by aging materials in the shunt. Complications associated with these devices have various origins. Amo ng late complications, fracture or migration of the system is related to the subcutaneous adhesion of the distal tubing in a growing child. A review of a cohort of 64 children who underwent shunt placement in 1 980 with barium-impregnated distal catheters showed that 10 of these p atients underwent reoperation for complications related to aging of th e shunt material. This group represents 15% of the whole series and 30 % of those children who were followed for more than 3 years. The true impact of aging of materials on shunt function is probably underestima ted. Methods. The authors performed physical, chemical, and mechanical analyses of the retrieved aged catheters and also of new catheters, r esulting in the following findings: 1) calcifications were observed on ly on the external surface of the catheter, predominantly in its subcu taneous segment at the level of the neck and anterior chest wall; 2) c alcifications contained particles of free silicon and barium sulfate, signifying fragmentation of the polymer; 3) the microstructure of the silicone polymer was modified: microfractures and alteration of the po lymeric network were observed; 4) silanol groups were observed on the external surface of the catheter; and 5) the mechanical properties of the silicone rubber were degraded, and the aged catheters were more br ittle than the new ones, with ruptures at elongations and fracture ene rgy much lower than that seen in new catheters. Furthermore, in vitro testing with a metastable solution of simulated body fluid demonstrate d the critical impact of pH variations in liquid media and surface deg radation of the catheters on the precipitation of hydroxylapatite crys tals. Conclusions. Although most shunt complications can be addressed by better patient management acid surgical technique, late complicatio ns appear to be partly related to aging of the material. Distal tubing calcifications have been observed in barium-impregnated catheters. Th e industry recently responded to these observations by introducing pla in silicone-coated shunt tubing; further evaluation will show what imp rovement can be expected.