No  method before ileostomy closure assess accurately the continence. But is it useful?. You have to test the continence before the rectal resection and decide if you perform the anastomosis or not. If you have already done the anastomosis and ileostomy, the only thing to do is to close the stoma. Morever after ileosotmy closure the functionnal result improve during the firts post operative year. The result immediately after ileosotmy closure will not be the functionnal permanant result.

We use a clinical exploration, if we observe an aceptable muscular tone we considere to operate, but if theres isa low tone we ask for a manometry previous to the surgical procedure.

Si el paciente no tiene incontinencia previa, no es necesario realizar evaluación alguna

I agree, assessment of sphincter function before resection an important consideration. Generally speaking you need to be more concerned about faecal incontinence mainly  in certain subgroups after low resection, e.g. Males with good anal sphincter tone will usually be able to compensate, but older females who have had previous vaginal deliveries and consequent poor anal sphincter function will not be able to. Irrespective of sphincter function, taking away the entire rectum itself is a risk factor for faecal urgency, frequency and probably also incontinence as the reservoir and compliance function of the rectum is lost. Hence, TME ultra low resection with good sphincters can also lead to problems with leakage and urgency.

There is some evidence that loperamide used for faecal incontinence may have an independent role in improving anal sphincter muscle tone, so it is worth trying this.

I would advise reverse, see what happens and manage conservatively. The worst case scenario is that the patient may ask for faecal diversion with intractable diarrhoea, but this us rare. Most of the conservative measures used will relieve symptoms to some degree.

I have started measuring rectal compliance by filling the rectum with barium and if the patient can hold more than 100mls without leak and urgency, they seem to have good continence after ileostomy reversal.

This technique is simple and worth a try.

Schwandner F, Klimars U, Gock M, et al. The Water-Holding Procedure for Ensuring Postoperative Continence Prior Restoring Intestinal Continuity. J Gastrointest Surg. 2020;24(2):411-417. doi:10.1007/s11605-019-04171-7

A standardized water-holding test can function as an easy and reliable method before stoma reversal to predict sufficient postoperative fecal continence. In case of a sufficient water-holding test despite low manometric pressure levels, the risk for postoperative anal incontinence seems to be low. Preoperative manometric pressure levels do not appear to predict postoperative continence.