Orthopedic surgery is a surgical discipline that is concerned with the treatment of the musculoskeletal system. Many orthopedic treatments involve cutting or drilling in bones by using rigid drills or oscillating saws. Using waterjets instead of conventional instruments can be beneficial due to the absence of thermal damage and a consistent sharp cut. Additionally, waterjet technology allows the development of flexible instruments that facilitate maneuvering through complex or narrow joint spaces. Therefore, the aim of this thesis is to develop a compliant or flexible arthroscopic surgical instrument, based on water jet technology, that is able to drill in bone tissue.@en

Objective: Surgical microfracture is considered a first-line treatment for talar osteochondral defects. However, current rigid awls and drills limit access to all locations in human joints and increase risk of heat necrosis of bone. Using a flexible water jet instrument to drill holes can improve the reachability of the defect without inducing thermal damage. The aim of this feasibility study is to determine whether water jet drilling is potentially safe compared with conventional microfracture awls by studying side effects and perioperative complications, as well as the quality of cartilage repair tissue. Design: Talar chondral defects with 6-mm diameter were created bilaterally in 6 goats (12 samples). One defect in each goat was treated with microfracture created with conventional awls, the contralateral defect was treated with holes created with 5-second water jet bursts at a pressure of 50 MPa. Postoperative complications were recorded and after 24 weeks analyses were performed using the ICRS (International Cartilage Repair Society) macroscopic score and modified O’Driscoll histological score. Results: Several practical issues using the water jet in the operating theatre were noted. Water jet drilling resulted in fibrocartilage repair tissue similar to the repair tissue from conventional awls. Conclusions: These results suggest that water jet drilling gives adequate fibrocartilage repair tissue. Furthermore, the results highlight essential prerequisites for safe application of surgical water jet drilling: stable water pressure, water jet beam coherence, stable positioning of the nozzle head when jetting, and minimizing excessive fluid extravasation.@en

In orthopaedic surgery, water jet drilling provides several advantages over classic drilling with rigid drilling bits, such as the always sharp cut, absence of thermal damage and increased manoeuvrability. Previous research showed that the heterogeneity of bone tissue can cause variation in drilling depth whilst water jet drilling. To improve control over the drilling depth, a new method is tested consisting of two water jets that collide directly below the bone surface. The expected working principle is that after collision the jets will disintegrate, with the result of eliminating the destructive power of the coherent jets and leaving the bone tissue underneath the focal point intact. To assess the working principle of colliding water jets (CWJ), the influence of inhomogeneity of the bone tissue on the variation of the drilling depth and the impact of jet time (twj) on the drilling depth were compared to a single water jet (SWJ) with a similar power. 98 holes were drilled in 14 submerged porcine tali with two conditions CWJ (impact angle of 30° and 90°) and SWJ. The water pressure was 70 MPa for all conditions. The water jet diameter was 0.3 mm for CWJ and 0.4 mm for SWJ. twj was set at 1, 3, 5 and 8 s. Drilling depth and hole diameter were measured using microCT scans. A non-parametric Levene's test was performed to assess a significant difference in variance between conditions SWJ and CWJ. A regression analysis was used to determine differences in influence of twj on the drilling depth. Hole diameter differences were assessed using a one way Anova. A significance level of p<0.05 was set. Condition CWJ significantly decreases the drilling depth variance caused by the heterogeneity of the bone when compared to SWJ. The mean depth for CWJ was 0.9 mm (SD 0.3 mm) versus 4.8 mm (SD 2.0) for SWJ. twj affects the drilling depth less for condition CWJ (p<0.01, R2=0.30) than for SWJ (p<0.01, R2=0.46). The impact angle (30° or 90°) of the CWJ does not influence the drilling depth nor the variation in depth. The diameters of the resulting holes in the direction of the jets is significantly larger for CWJ at 90° than for 30° or a single jet. This study shows that CWJ provides accurate depth control when water jet drilling in an inhomogeneous material such as bone. The maximum variance measured by using the 95% confidence interval is 0.6 mm opposed to 5.4 mm for SWJ. This variance is smaller than the accuracy required for bone debridement treatments (2–4 mm deep) or drilling pilot holes. This confirms that the use of CWJ is an inherently safe method that can be used to accurately drill in bones.@en

Using water jets for orthopedic procedures that require bone drilling can be beneficial due to the absence of thermal damage and the always sharp cut. Previously, the influence of the water jet diameter and bone architectural properties on the drilling depth have been determined. To develop water jet instruments that can safely drill in orthopedic surgery, the impact of the two remaining primary factors were determined: the jet time (tjet [s]) and pressure (P [MPa]). To this end, 84 holes were drilled in porcine tali and femora with water jets using Ø 0.4 mm nozzle. tjet was varied between 1, 3 and 5 s and P between 50 and 70 MPa. Drilling depths Lhole (mm), diameters Dhole (mm) and the volume of mineralized bone per unit volume (BV/TV) were determined with microCT scans. A non-linear regression analysis resulted in the predictive equation: Lhole= 0.22 * tjet0.18 * (1.2–BV/TV) * (P–29) (R2=0.904). The established relation between the machine settings and drilling depth allows surgeons to adjust jet time and pressure for the patient׳s BV/TV to drill holes at a predetermined depth. For developers, the relation allows design decisions to be made that influence the dimensions, flexibility and accuracy of water jet instruments. For a pressure of 50 MPa, the potential hole depth spread indicated by the 95% confidence interval is <1.6 mm for all tested jet times. This maximum variance is smaller than the accuracy required for bone debridement treatments (2–4 mm deep), which confirms that water jet drilling can be applied in orthopedic surgery to drill holes in bone with controlled depth. @en