How water jets may heal your knees

When you cut your finger while cooking, the cut heals over time. When knee cartilage is damaged, for example by trauma, it is not that simple. Cartilage has no blood cells so that the red blood cells necessary for healing cannot reach the tissue. Bone debridement, in which small holes are drilled into the bone causing the bone to bleed and bone marrow to permeate through the bone, may be a solution. Blood and bone marrow have healing properties. When they come into contact with the damaged cartilage, the cartilage starts growing again. The problem with the treatment is that drilling holes is not a precise procedure.

Drilling holes with pure water jets

This is where the pure water jet comes in. In the Healing Water project, funded by the Dutch Technology Foundation STW, part of the Netherlands Organisation for Scientific Research (NWO),  PhD candidate Steven den Dunnen investigated whether pure water jets can be used for bone debridement treatments. He defends his PhD thesis on Wednesday. A pure water jet directs a pressurised water jet onto a surface, creating a precise cut. In contrast to other types of drilling, the pure water jet does not heat up the drilled material. This means that there is no risk of the cells dying due to overheating.

Dealing with varying bone density

The tests showed that using the pure water jet to drill holes in bones works. However, one problem is varying bone density which makes it hard to predict how deep a regular pure water jet drills. This compromises the safety of the patient.

There are several ways to deal with this though. First, the surgeon can take control by drilling the hole in several parts. In this case, the surgeon must pay attention all the time instead of saving time by letting the instrument do the work. Second, the bone density can be input into a mathematical model to define the water pressure, time and diameter. Developing this model was the most important part of the research. While the model does work, in trauma surgery there might not be time to ascertain the bone density.

The colliding water jet

An even more interesting finding, however, is the third option. A colliding water jet uses two pressurised water streams instead of one. Both streams drill into the bone at an angle. Once the two streams meet, the water dissolves into a spray and the drilling stops. This gives the user precise control over the depth of the drilling by setting the meeting point of the two streams.

Though the technique works, the method has not yet been tested with the size of pure water jets required for orthopaedic surgery. Small prototypes have been developed, but thus far these cannot withstand the high pressure of the water. Den Dunnen has done some research on creating a safe and easy-to-use pure water jet, but says that this research is“not yet ready to be published”. He is talking to companies to follow-up his research.

Steven den Dunnen, Healing water: using pure water jets to perform bone debridement treatments in orthopedic surgery, PhD supervisors Professor Dr Jenny Dankelman, Professor Dr Gino Kerkhoffs and Dr Gabrielle Tuijthof, 12 December 2018

Prototype for the pure water jet. (Photo: Steven den Dunnen)

Nina van Wijk / science editor trainee