TightRight : augmenting screwdrivers to reduce bone stripping rates and optimise tightness when inserting non-locking screws

Objectives: Non-locking screws remain one of the most commonly used orthopaedic implants, however they are often poorly inserted. Exceeding the stripping torque for a screw hole reduces pullout strength. The aims of this study were firstly to quantify stripping rates and screw tightness for surgeons and secondly to assess how these change when using a screwdriver that indicates when optimum tightness is reached. Methods: At the AO Davos Courses 2018 (Davos, Switzerland), 302 orthopaedic surgeons tightened 20 screws in two phases: Phase 1 - screws tightened to the surgeon’s perception of optimum tightness. Phase 2 - using an augmented screwdriver that indicated, by audibly alarming and vibrating, when a predetermined optimum tightness was reached (defined as 70% of the maximum stripping torque). Within each phase, 10 partially inserted 3.5 mm non-locking cortical screws were tightened through a 3.5 mm plate into 4 mm thick artificial bone analogue of 0.32 g/cm3. The stopping torque for each screw was recorded and compared to the stripping torque; if the stopping torque greatly exceeded the stripping torque, tightness values >100% were possible. A confidence value in each screw’s purchase was recorded, 1-10. Following tests of normality, Student t-tests were performed to compare different phases and insertion confidences. Results: For phases 1 and 2 respectively, stripping rates were 58 ±32% and 15 ±25% (p<0.0001) and the tightness for all screws was 190% ±255% (n=3020) and 87 ±49% (n=3020) (p<0.0001). Considering only unstripped insertions, tightness was 81 ±12% (n=1242) and 71 ±12% (n=2579) respectively. In phase 1, confidence was 7 ±2 (out of 10) for screws found to have not unstripped and 6 ±2 for stripped insertions (p=0.441), and 7 ±2 and 7 ±2 (p=0.216) in phase 2 respectively. Conclusion: With an unaugmented screwdriver (Phase 1), stripping rates were high, though varied greatly amongst surgeons. Using an augmented screwdriver (Phase 2) greatly improved insertion, with optimum tightness being achieving alongside a significantly reduced rate of bone stripping. Further work incorporating these techniques into surgical education and clinical practice are recommended.