title: Two-Finger Tightness: What Is It? Measuring Torque and Reproducibility in a Simulated Model.
abstract: OBJECTIVE
  Residents in training are often directed to insert screws using "two-finger tightness" to impart adequate torque but minimize the chance of a screw stripping in bone. This study seeks to quantify and describe two-finger tightness and to assess the variability of its application by residents in training.
  
  
  METHODS
  Cortical bone was simulated using a polyurethane foam block (30-pcf density) that was prepared with predrilled holes for tightening 3.5 × 14-mm long cortical screws and mounted to a custom-built apparatus on a load cell to capture torque data. Thirty-three residents in training, ranging from the first through fifth years of residency, along with 8 staff members, were directed to tighten 6 screws to two-finger tightness in the test block, and peak torque values were recorded. The participants were blinded to their torque values.
  
  
  RESULTS
  Stripping torque (2.73 ± 0.56 N·m) was determined from 36 trials and served as a threshold for failed screw placement. The average torques varied substantially with regard to absolute torque values, thus poorly defining two-finger tightness. Junior residents less consistently reproduced torque compared with other groups (0.29 and 0.32, respectively).
  
  
  CONCLUSIONS
  These data quantify absolute values of two-finger tightness but demonstrate considerable variability in absolute torque values, percentage of stripping torque, and ability to consistently reproduce given torque levels. Increased years in training are weakly correlated with reproducibility, but experience does not seem to affect absolute torque levels. These results question the usefulness of two-finger tightness as a teaching tool and highlight the need for improvement in resident motor skill training and development within a teaching curriculum. Torque measuring devices may be a useful simulation tools for this purpose.
authors.affiliation: *Department of Orthopaedic Surgery, University of Michigan, Ann Arbor, MI;†Department of Mechanical Engineering, Texas A&M University, College Station, TX;‡Department of Mechanical Engineering, University of Michigan, Ann Arbor, MI.
authors.forename: William B
authors.initials: WB
authors.lastname: Acker
authors.forename: Bruce L
authors.initials: BL
authors.lastname: Tai
authors.forename: Barry
authors.initials: B
authors.lastname: Belmont
authors.forename: Albert J
authors.initials: AJ
authors.lastname: Shih
authors.forename: Todd A
authors.initials: TA
authors.lastname: Irwin
authors.forename: James R
authors.initials: JR
authors.lastname: Holmes
mesh_terms: D040761:Biomimetic Materials; D001863:Bone Screws; D001842:Bone and Bones / Q000601:surgery*; D017276:Friction; D000070856:High Fidelity Simulation Training / Q000379:methods*; D008954:Models, Biological; D019919:Prosthesis Implantation / Q000379:methods*; D013314:Stress, Mechanical; D019415:Torque