**15. Use of PediGuard™**

Misplacement and breach of pedicle cortex occurs in approximately 20% of attempted screw placements. Given the much softer consistency of rheumatoid bones, and the importance of avoidance of creating any false tracts down narrow pedicles, it is of utmost importance to ensure that each "screw placement counts". A screw which breaches the pedicle will not be able to contribute its required resistance to flexion, extension or torque forces, and so will significantly weaken the entire construct, perhaps even placing the patient at risk of

Fig. 9. PediGuard™ Picture

developing a significant neurological morbidity. Our practice when placing pedicle screws in such patients is to utilise the Pediguard™, a device which doubles both as a hand-held awl and which also detects changes in electrical conductance at the device tip. Variation of conductivity occurs when passing between different media, such as exiting the osseous pedicle into surrounding soft-tissue, as occurs during an iatrogenic pedicle perforation. Our series demonstrated a sensitivity of >98% in detecting breaches, more than twice the rate reported by surgeons performing the same surgeries (Bolger et al 2007, Anzhsn 2011).
