• Daniel D Bohl, Bryce A Basques, Nicholas S Golinvaux, Jason O Toy, Erika A Matheis, Brandon S Bucklen, and Jonathan N Grauer.
• *Department of Orthopaedics and Rehabilitation, Yale School of Medicine, New Haven, CT †Department of Orthopaedic Surgery, Rush University Medical Center, Chicago, IL ‡Department of Orthopaedic Surgery and Rehabilitation, Vanderbilt School of Medicine, Nashville, TN; and §Globus Medical Inc., Audubon, PA.
• Spine. 2015 Jun 15;40(12):E729-34.

Study DesignSurvey of spine surgeons and biomechanical comparison of screw pullout forces.ObjectiveTo investigate what may be a suboptimal practice regularly occurring in spine surgery.Summary Of Background DataIn order for a tap to function in its intended manner, the pitch of the tap should be the same as the pitch of the screw. Undertapping has been shown to increase the pullout force of pedicle screws compared with line-to-line tapping. However, given the way current commercial lumbar pedicle screw systems are designed, undertapping may result in a tap being used that has a different pitch from that of the screw (incongruent pitch).MethodsA survey asked participants questions to estimate the proportion of cases each participant performed in the prior year using various hole preparation techniques. Participant responses were interpreted in the context of manufacturing specifications of specific instrumentation systems. Screw pullout forces were compared between undertapping with incongruent pitch and undertapping with congruent pitch using 0.16 g/cm polyurethane foam block and 6.5-mm screws.ResultsOf the 3679 cases in which participants reported tapping, participants reported line-to-line tapping in 209 cases (5%), undertapping with incongruent pitch in 1156 cases (32%), and undertapping with congruent pitch in 2314 cases (63%). The mean pullout force for undertapping with incongruent pitch was 56 N (8%) less than the mean pullout force for undertapping with congruent pitch. This is equivalent to 13 lb.ConclusionThis study estimates that for about 1 out of every 3 surgical cases with tapping of lumbar pedicle screws in the United States, hole preparation is being performed by undertapping with incongruent pitch. This study also shows that undertapping with incongruent pitch results in a decrease in pullout force by 8% compared with undertapping with congruent pitch. Steps should be taken to correct this suboptimal practice.Level Of Evidence3.

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