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Session: Medical Instruments - Surgery I
Session starts: Friday 25 January, 10:30
Presentation starts: 10:30
Room: Lecture room 557

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Steven den Dunnen (Delft University of Technology)
Lars Mulder (LifeTec Group BV)
Gino Kerkhoffs (Academic Medical Centre)
Jenny Dankelman (Delft University of Technology)
Gabrielle Tuijthof (Delft University of Technology)

Abstract:
The use of waterjets in orthopaedic surgical drilling can be beneficial over conventional rigid instruments, because it allows the design of flexible instruments for easy manoeuvring in joints. For safe application, the drill depth should be controlled, which is challenging as the heterogeneous characteristics of bone tissue can cause variations in hole dimensions despite waterjet drilling under similar circumstances. The bone heterogeneity can be identified by determining the bone density or volume fraction (BV/TV). An increase in BV/TV increases the maximum stress bone can endure, and is therefore expected to reduce the depth of a water jet drilled hole. The goal of this study is to determine whether a correlation is present between BV/TV and drilling depth (Ldepth), which can be used to describe a hole depth prediction model for safe waterjet drilling in various types of articular bone. Two hundred and ten holes were drilled in the articular surfaces of 10 pig tali and 10 femora (4-6 months) by waterjet diameters (dwaterjet) of 0.3 (femora only), 0.4, 0.5 and 0.6mm. Pressure, standoff distance and jet time were kept constant at 700 bar, 8 mm and 5 seconds, respectively. All tests were performed submerged in water to mimic regular arthroscopic treatment. MicroCT scans were used to measure hole depths and the local BV/TV. A Pearson test was used to correlate the BV/TV and nozzle diameters to the drilling depths (p<0.05). A significant linear correlation (R2=0.90, p<0.001) was found for predicting the drilling depth: Ldepth = -18.3 x BV/TV + 31.5 x dwaterjet + 4.1, with Ldepth and dwaterjet in mm. An increase in BV/TV and nozzle diameter will result in shallower and deeper holes, respectively. The results allow prediction of the drilling depth for a given BV/TV and chosen nozzle diameter, which is an important finding for the safe application of waterjet drilling in orthopaedic surgery. Orthopaedic procedures where holes are drilled in bone such as microfracturing treatments and screw fixations can now be considered to be performed with waterjet drilling. Future developments will concentrate on miniaturization of the waterjet instrument for performing minimally invasive surgery.