A facet joint is exposed at one side of the spine during surgery. An inclinometer is mounted on an elongated probe, and a pin is fixed on a spinous process near the exposed joint. The probe is swivelled about the pin so that a distal end of the probe contacts the joint and the inclinometer indicates a corresponding first trajectory. A second trajectory from the pin to an unexposed facet joint on the opposite side of the spine is defined as being symmetrical with the first trajectory about the spine axis. The inclinometer is mounted on a guide sleeve, and the sleeve is swivelled about the pin into the second trajectory. A wire is inserted through the sleeve until a tip of the wire penetrates the unexposed joint percutaneously. A facet screw is advanced over the wire and threaded percutaneously into the unexposed facet joint after the sleeve is withdrawn.
