Background
The function of gravitational (g)-valves is strictly dependent on the angle of verticalization. For even minor axis-deviations have a significant impact on the functional pressure, a strict orientation parallel to the longitudinal body axis is important. Despite the decisive role only 1/166 g-valve-papers (incl. running studies) investigated systematically g-valve-deviations (= failure angles) to the body axis. Furthermore, the more frequent implantation site on the lateral head yet has not been compared to the thoracal site.
Materials and methods
Each 50 consecutive g-valve patients with retroauricular and thoracal implanted gravitational devices were randomly extracted from our medical records of about 650 g-valve-implanted patients. On scout-scans/x-rays the deviations to the body axis were measured. The impact on g-valve-function and additionally the effect of a head elevation of 30 degrees were calculated.
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Results
Only 22% of retroauricular vs. 28% of thoracal implantated devices were correctly placed (<10 degree). Valves placed on the head showed anteversion in 84% and retroversion in 16%. The mean deviation was 21 degrees implying a valve-offset of 72 (126) mm H2O in a 200 (350) mm H2O-g-valve, the maximum was 43 degrees (valve-offset: 136 (239) mm H2O). A nocturnal head elevation of 30 degrees may result in a mean valve-offset of 156 (272) mm H2O calculated with the mean deviation angle and 191 (335) mm H2O in the worst case. In the thoracal position the mean counted 10 degrees in lateral and 16 degrees in anteroposterior direction, implying a valve-offset of 55 (96) mm H2O in 200 (350) mm H2O-valve. Maximal deviation was 52 degrees resulting in valve-offset of 158 (276) mm H2O.
Conclusion
Position failures are common in our series and may declare malfunction of g-valves. The thoracal implantation site is clearly superior to the head position and should therefore be preferred in adults.
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