RECOGNISING MATERIAL STIFFNESS WITH AN ARTHROSCOPIC PROBE

Abstract

Surgical long shape tools, such as the arthroscopic hooked probe, are used during knee-arthroscopy procedures by surgeons to manipulate tissues and diagnose problems. These procedures allows surgeons to assess the physical properties of tissues (such as wear, tear, inflammation, stiffness, etc), which are impossible to evaluate using real-time video observation or MRI and CT mapping. This study focuses on the dynamic properties of the hooked probe and its ability to deliver tactile information, created at the tip of the hook as the tissue is being manipulated, to the handle where the surgeon is grasping the instrument.

From previous studies, it is known that when a probe comes into contact with hard tissues, such as bones, vibrations can occur that enhance the tactile feedback. To better understand the importance of the dynamic influence on the tactile feedback, initially a vibration analysis of the probe (Model 8399.95 by Richard Wolf UK Ltd) was performed; a stepped sine sweep was carried out to evaluate the dynamic behaviour of the probe, including its resonance response frequencies and the damping behaviour. Several vibration modes were identified in a range up to 2000Hz parallel and perpendicular to the probe. The measurement values were correlated to a finite element model of the probe and an error of less than 5% was found for all relevant resonance response frequencies, thereby validating the accuracy of the model.

Measurement and simulation results show that tapping on different materials excites different modes of the probe at different levels, leading to a tactile feedback that harder materials “shift” the probe resonances to higher levels. To verify this, a tapping experiment was performed and the resulting vibrations, while tapping on different materials, were recorded. The study shows that the dynamic behaviour of the probe are somewhat influenced by the fact that the probe is being held in hand leading to a slight reduction in its natural frequencies.

A study on an individual’s ability to discriminate between the stiffness of different materials while tapping on them using an arthroscopy hooked probe is currently underway. Ten subjects are being asked to sort five materials (silicon, latex, rubber, plastic, steel) from the softest to the hardest by simple tapping. During the test, each subject is exposed to two materials each time, iteratively until the sort is complete. The subjects are blindfolded and white noise is played through headphones, to blur the sounds of tapping. The resulting dynamic response of the probe is recorded, using an accelerometer, along with the impact forces on the material, measured by a force sensor. Results to date show that subjects can distinguish quite accurately between the soft materials (silicon and latex), but find it difficult to distinguish between stiffer materials (plastic and steel), but comprehensive statistics are not yet available.