The treatment of rectal cancer is currently based on surgical resection of the rectum with total excision of the mesorectum, associated with neoadjuvant radiochemotherapy.

Surgical resections with sphincter preservation are frequently (60% of cases) associated with problems related to intestinal and defecatory function, which together are called Anterior Resection Syndrome (ARS) with varying degrees of severity.

Among the different treatments the investigators find posterior tibial nerve stimulation, a simple and non-invasive technique, which is currently used.

The study aims to analyze whether postoperative posterior tibial nerve stimulation in patients undergoing low anterior resection of the rectum has an impact on the incidence and duration of low anterior resection syndrome (LARS) and therefore on the quality of life of patients undergoing this type of intervention.

Therefore, treatment with PNTS is currently established for the management of LARS symptoms. Given that a large percentage of patients operated on for rectal neoplasms will develop this syndrome, the investigators intend to apply this treatment before the onset of symptoms in patients at risk for LARS. It is also an intervention with a low rate of side effects, the benefit that the investigators can obtain from its preventive application is clearly superior to the risk of undergoing such treatment.

The investigators´ hypothesis is: Posterior tibial stimulation for 6 weeks post-operative of low anterior resection with anastomosis has a favorable impact by reducing the incidence and duration of ARS and improving the quality of life of patients undergoing anterior rectal resections for cancer.

Inclusion Criteria:

• Patients undergoing elective surgery (scheduled, non-urgent) who underwent anterior rectal resection or transit reconstruction with low anastomosis (below 10 cm from the anal margin) at the Hospital Álvaro Cunqueiro in Vigo after the start date of the study.
• Anastomotic tightness (absence of dehiscence).
• Patients older than 18 years old.
• Acceptance to participate in the study.

Exclusion Criteria:

• Inability to understand the study instructions and recommendations.
• Dementia or any type of mental disability.
• Palliative surgery.
• Patients with pacemakers.
• Anti-coagulated patients.
• Patients with trophic lesions on the skin of the ankles.

Assignment to one group or the other will be randomized by a simple 1:1 randomization method through the CRF automatically and after hospital discharge.

Double-blind masking will be performed (patients will not know to which group they belong and the investigator will not know to which group each patient is assigned). The only person aware of the outcome of the randomization will be the functional tests nurse, who will apply the PTNS treatment.

Patients in both groups will be appointed in the same way in the functional testing office, although patients in group 2 will not receive PTNS, the tibial nerve puncture will be applied, they will be stimulated until they perceive the corresponding current and then the neurostimulator will be turned off so that they do not receive the treatment.