Knock and Drill Technique: A Simple Tips for the Instrumentation in Complex Craniovertebral Junction Anomalies without using Fluoroscopy

CONTEXT: Existence of complex variable bony and vertebral artery (VA) anomalies at craniovertebral junction (CVJ) in subset of complex CVJ anomalies demands individualized instrumentation policy and placing screws in each bone requires strategic preoperative planning and intraoperative skills. AIM: To evaluate the clinical accuracy of knock and drill (K and D) technique for the screw placement in complex CVJ anomalies. SETTINGS AND DESIGN: Prospective study and operative technical note. MATERIALS AND METHODS: Totally 36 consecutive patients (16 - pediatrics, 20 - adult patients) of complex CVJ: Complete/partial occipitalized C1 vertebra; at least one hypoplastic (C1/C2) articular mass, rotational component, and variations in the third part of VA were included in this study. Preoperative detail computed tomography (CT) CT CVJ with three-dimensional reconstruction was done for the assessment of CVJ anatomy and facet joint orientation. The accuracy of novel technique was assessed with postoperative CT to evaluate cortical breach in between 5(th) and 7(th) postoperative day in all the patients. All patients were underwent clinico-radiological evaluation at 6-month follow-up. RESULTS: Totally 144 screws were placed using K and D technique (pediatric group - 64 screws, adult patients - 80 screws). Total of 12 screws were placed in C1 lateral mass in both age group without any bony cortical breach and complication. Sixteen C2 pedicle screws and 12 C2 pars screw in pediatrics and 18 C2 pedicle screws in adult patients were placed without any bony breach or VA injury. Out of thirty subaxial lateral mass screws in pediatric group, the bony breach was encountered with one screw (3.3%). Total of 38 C2 pars screws was placed in adult group in which bony breach along with VA injury was encounter with 1screw (2.6%). CONCLUSION: A simple technique of K and D for placing a screw increases the accuracy and spectrum of bony purchase and has the potential to reduce the complication in patients with complex CVJ anomalies.