title: The Hakim programmable valve: reasons for reprogramming failures.
abstract: OBJECTIVE
  In patients with hydrocephalus, the pressure settings of a Medos Hakim programmable valve may require adjustments even months after implantation. In some cases, however, adjustment proves to be impossible. The object of this study was to illuminate the reasons for reprogramming failures.
  
  
  METHODS
  Data pertaining to the authors' experience with programmable valves at their clinic were obtained through retrospective review of patient records from 1992 to 1998 and prospectively collected from 1998 to 2006. Between 1992 and 2006, 585 Medos Hakim programmable valves were implanted at the authors' center, and reprogramming failure was observed in 12 of these 585 cases. The authors investigated and recorded the reasons for reprogramming failure. In cases in which the valves had to be explanted, the valves were returned to the manufacturer for further investigation and the results were recorded.
  
  
  RESULTS
  In three of the 12 cases of reprogramming failure, the pressure settings could eventually be adjusted by placing the transmitter upside down against the flow direction. In the remaining nine cases, the valve had to be removed, yielding a rate of valve explantation of approximately 1.5% in this series. In two of these nine cases, the valve was found to be rotated longitudinally along its axis. In two cases the ratchet wheel had become loose and in one the radiopaque marker had become dislodged from the baseplate. Extensive deposits were identified macroscopically and microscopically within four explanted valves.
  
  
  CONCLUSIONS
  The reasons for failed reprogramming of Codman Medos Hakim valves as described in this article have not been mentioned in the literature so far. Failure of adjusting the pressure setting is a very rare event in a Medos Hakim programmable valve. The programming and adjustment mechanism appears to be very reliable. Valve replacement was required due to failed reprogramming in only a few cases.
authors.affiliation: Department of Neurosurgery, Armed Forces Hospital, Ulm, Germany. uwe-max.mauer@dgn.de
authors.forename: Uwe Max
authors.initials: UM
authors.lastname: Mauer
authors.forename: Jens
authors.initials: J
authors.lastname: Schuler
authors.forename: Ulrich
authors.initials: U
authors.lastname: Kunz
mesh_terms: D015170:Cerebrospinal Fluid Pressure; D002557:Cerebrospinal Fluid Shunts / Q000295:instrumentation*; D004868:Equipment Failure; D006801:Humans; D006849:Hydrocephalus / Q000000981:diagnostic imaging / Q000601:surgery*; D011183:Postoperative Complications / Q000209:etiology*; D011859:Radiography; D012189:Retrospective Studies; D012984:Software