Is there a specific time for stay of such tubes in the tympanic membrane?
The cause of stay of shah type of grommet tube might be
1.During insertion in to tympanic member only small incision is required, which hold the tube in place for longtime
2. This grommet has a ‘shoehorn’ type tab on its inner flange that resists extrusion.
3. The thicker flange lies on the outer surface of the tym panic membrane which also resists extrusion
There is not a lot of evidence in this area. In the UK, median grommet extrusion is approx 14 months.
Song et al (PMID: 20607075) reported that Korean patients with glue/pus effusions took longer to extrude their grommets that patients with serous effusion but this was only in 82 children. Mean extrusion was about 36 weeks.
Passive smoking may have some effect too: in 606 UK children, those who were exposed to passive smoking had median extrusion at 59 weeks versus 84 weeks for those who weren't (Praveen & Terry PMID: 15992470).
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