To compare classical pedicle finder versus pedicle finder with impedancemetry on the perioperative radiation exposure of PPTLO. These two devices are already used in common practice.

Inclusion Criteria:

• Men and women between 18 and 80 years-old;
• Patient with an indication of PPTLO for one or two segments
• Patient in a position to understand protocol information;
• Patient who received information about the protocol and who did not show opposition to participate

Exclusion Criteria:

• History of posterior spinal fusion surgery on the spinal level concerned by the study;
• Morbid obesity (body mass index greater than 35 kg / m²);
• Major incapable (safeguard of justice, guardianship) and persons deprived of liberty.
• Simultaneous participation in another research protocol involving the human person