In the Netherlands about 36.000 total hip prostheses are implanted every year. Survival of these prostheses at 10 year follow-up is 90% in patients older than 70 years at the index operation. In younger patients these results decrease to about 80–85% at 10 years follow-up. The main cause of failure in total hip replacement is aseptic (mechanical) loosening which is caused by a biological response to wear products of the articulation of the joint. This foreign body reaction is associated with periprosthetic bone resorption and subsequent formation of periprosthetic fibrous (interface) tissue. As a result the implant is becoming increasingly loosened, causing debilitating pain on ambulation. At present, patients with loosened prostheses can only undergo revision surgery. This procedure is often extensive (3–5 hr surgery and over 1 liter of blood loss), due to the necessity of removing the prosthesis and all interface tissue; thereafter a new prosthesis is implanted. This revision surgery has a high complication rate in elderly patients with comorbidities (e.g. cardiovascular disease, diabetes etc), which can even result into death in a small percentage. Because of this high complication rate, this demanding procedure cannot be performed in patients with a poor general health, thus these patients remain with this debilitating pain. Therefore, we investigated the possibilities of an alternative minimally invasive refixation procedure that leaves the prosthesis in place, but relies on removing the periprosthetic interface membrane and replacing it with bone cement. Before the refixation procedure can be executed this way, an instrument to remove the interface tissue needs to be developed. @en

Mechanical loosening of implants is in the majority accompanied with a periprosthetic interface membrane, which has to be removed during revision surgery. The same is true if a minimal invasive (percutaneous) refixation of a loose implant is done. We describe the requirements for a waterjet applicator for interface tissue removal for this percutaneous hip refixation technique. The technical requirements were either obtained from a literature review, a theoretical analysis, or by experimental setup. Based on the requirements, a waterjet applicator is designed which is basically a flexible tube (outer diameter 3 mm) with two channels. One channel for the water supply (diameter 0.9 mm) and one for suction to evacuate water and morcellated interface tissue from the periprosthetic cavity. The applicator has a rigid tip (length 6 mm), which directs the water flow to create two waterjets (diameter 0.2 mm), both focused into the suction channel. The functionality of this new applicator is demonstrated by testing a prototype of the applicator tip in an in vitro experimental setup. This testing has shown that the designed applicator for interface tissue removal will eliminate the risk of water pressure buildup; the ejected water was immediately evacuated from the periprosthetic cavity. Blocking of the suction opening was prevented because the jets cut through interface tissue that gets in front of the suction channel. Although further development of the water applicator is necessary, the presented design of the applicator is suitable for interface tissue removal in a minimally invasive hip refixation procedure.

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