Background: To develop experience, orthopedic surgeons train their own proprioception to detect torque during screw insertion. This experience is acquired over time and when implanting conventional/non-locked screws in osteopenic cancellous bone the experienced surgeon still strips between 38-45%. Technology needs to be investigated to reduce stripping rates. Acoustic-Emission technology has the ability to detect stress wave energy transmitted through a screw during insertion into synthetic bone. Our hypothesis is Acoustic-Emission waves can be detected through standard orthopedic screwdrivers while advancing screws through purchase and overtightening in cancellous human bone with different bone mineral densities replicating the clinical state.Methods: 77 non-locking 4mm and 6.5mm diameter cancellous bone screws were inserted through to stripping into the lateral condylar area of 6 pairs of embalmed distal femurs. Specimens had varying degrees of bone mineral density determined by quantitative CT. Acoustic-Emission energy and axial force were detected for each test.
Results:The tests showed a significant high correlation between bone mineral density and Acoustic-Emission energy with R=0.74. A linear regression model with the mean stripping load as the dependent variable and mean Acoustic-Emission energy, bone mineral densities and screw size as the independent variables resulted in r 2 =0.94.Interpretation: This experiment succeeded in testing real time Acoustic-Emission monitoring of screw purchase and overtightening in human bone. Acoustic-Emission energy and axial compressive force have positive high correlation to bone mineral density. The purpose is to develop a known technology and apply it to improve the bone-metal construct strength by reducing human error of screw overtightening.
The silicone was slightly tougher to practise on than for example dental rolls, but we feel that it provides useful information regarding 'tissue' handling as every grip is apparent on the model, and can therefore be used by the trainer as a way of evaluating the trainee. A more forceful grip will lead to the tearing of the silicon, and the path of the needle is easily seen within the tendon. We recommend this silicone model as a simple and accessible training tool for all hand and plastic surgery trainees, as a means of learning the correct suture configurations in the various repairs.
ReferencesRCS Eng. Basic surgical skills: participant handbook. London, The
A preliminary study of Acoustic Emission during orthopaedic screw fixation was performed using polyurethane foam as the bone-simulating material. Three sets of screws, a Dynamic Hip Screw, a small fragment screw and a large fragment screw were investigated, monitoring acoustic emission activity during the screw tightening. Some specimens were overtightened on purpose to investigate the possibility of identifying the stripping torque before stripping actually occurred. One set of data was supported by load cell measurements to directly measure the axial load through the screw.Data showed that Acoustic Emission can give good indications of impending screw stripping; such indications are not available to the surgeon at the current state of the art using traditional torque measuring devices, and current practice relies on the surgeon's experience alone. The results suggest that Acoustic Emission may have the potential to prevent screw overtightening and bone tissue damage, eliminating one of the commonest sources of human error in such scenarios.
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