Role of length of locking screws & surgeon strength in precision of placing locking screws in In-vitro osteoporotic saw bone model
Authors: Kumar Ritabh , Aggrawal Anu , Chawla Pushkar , Vishwakarma Gayatri , Goel Shakti Amar 
Published: March 2022

Locking compression plate technology needs perfect seating of the locking screw head in the corresponding recess in the plate hole for a stable construct. The purpose of this study is to quantify screw-plate angle. In this study, a total of 750 locking screws of different lengths were placed by six residents. The measured angles were compared with Repeated Measures ANOVA method. Significant differences were seen for 40mm, 50mm, 70mm and 80mm screw length (p &#60; 0.05) to assess the deviation of angle in pre-training, post-training and final experiment. The placement of locking screws precisely can help avoid an easily preventable surgical risk factor for fixation failure.

The evolution of Locking Compression Plate (LCP) technology has radically changed the practice of fracture fixation. This technology mandates meticulous detail in surgical technique in placing the locking screw. It demands perfect seating of the locking screw head in the corresponding recess in the plate hole. The purpose of this study is to quantify screw-plate angle i.e., off-axis screw trajectory and its change with an increase in the length of screw and strength of the surgeons.

Six orthopaedic residents were selected. The surgeons were familiarized with the instrumentation. A total of 750 locking screws of different lengths were placed in a locking plate in osteoporotic saw bone models using a torque measuring screw driver. The deviation was assessed for 150 screws inserted in pre-training, post-training and the final test under the supervision of the senior author. Immediate feedback on the performance and objective proof of precision was given within an hour by measuring the angle of deviation on X-ray using InstaPACS.

Collected data was entered in MS Excel sheet. Descriptive statistics were presented in mean ±SD for continuous variables and count with percentage for Categorical variables. Repeated Measures ANOVA was used to assess the difference in deviation of angle pre-training, post-training and final experiment with the length of the screw. IBM SPSS 25.0 software was used for data analysis.

Surgeon grip strength and torque applied had no significant association with the angle of deviation. The surgeons exceeded 10 Newton meter torque in pretraining. This applied torque decreased after training in the post-training and final experiments. The length of the screw and angle of deviation were found to positively correlate in pre-training and final experiment. In this study, 40 out of 150 (26%) studied screw insertions were off-axis. Most of the deviations (29) were only one degree (19.33%). The remaining 11 were more than 2 degrees (6.67%). The maximum off-axis was 4.3 degrees. Significant differences were seen for 40mm, 50mm, 70mm and 80mm screw length (p &#60; 0.05) in pre-training, post-training and the final experiment.

: This study signifies that practice under supervision with immediate and objective feedback is a valuable learning tool. Real time feedback definitely improves the surgical confidence that will result in better patient outcome in placing locking screws. The placement of locking screws precisely can help avoid an easily preventable surgical risk factor for fixation failure.