gms | German Medical Science

Objective: The filigree adjustment rotor of the Codman-Medos (Medos-P) valve has a relatively soft silicone and plastic housing. Inadequate pumping manoeuvres and shocks are a risk for breaking out or decentering the rotor.

There are only a few reports in the literature about breakage of Medos-P rotors. In all cases the dislocation of the adjustment helix results in an impossibility of readjustment. In addition, an over- or underdrainage may occur in these cases.

Methods: In over 500 implantations between 1990 and 2008, we observed four specimens with a damage of the proximal rotor and three valves with breakage of the distal valve. The failure was diagnosed by clinical shunt dysfunction and x-ray-examination. The verification was made by lab investigation with magnification glasses and macro-photos.

Results: No patient had a relevant head trauma. In one case the valve was powerfully pumped by a non-neurosurgeon. Two patients showed symptoms of overdrainage (headaches in vertical body position) without subdural effusions or haematoma. One patient presented with a chronic subdural haematoma requiring surgical insertion of a drain. In all cases, the helix of the valve was dislocated in the pumping chamber. Surgical revision was necessary in all cases. The distal valve produces 10 mm H₂O resistance only, therefore fractures can be clinically inapparent.

Conclusions: The identical defects in these cases suggest that the housing of the Medos-P-valves is mechanically too weak and can be destroyed even by minor shocks of daily life or pumping manoeuvres.

We propose a reinforcement of the valve body and mechanics, e.g. by titanium or more stable plastics. In cases of overdrainage, a damage of the valve must be thought of.