The mayfield modified skull clamp (a1059) was returned for evaluation: device history record (dhr): the dhr was reviewed and shows no abnormalities related to the reported failure.Failure analysis: with respect to the returned unit, it passed all specific functional testing requirements, except for the lock having slight rotational movement.When the unit is positioned properly and put under pressure, the unit will function properly.General maintenance and cleaning required at this time.Unit was machined to have heli-coils added to the large starburst threads.Root cause: evaluation found no device deficiencies that would have contributed to the reported complaint.Repairs could not duplicate slippage.Probable root cause is improper positioning of the skull clamp.No further investigation required based on the acceptability of risk and no adverse trends identified.This will be monitored and trended going forward.
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