The reliability of a new guidance tool voor accurate cuppositioning in total hip arthroplasty

Osteoarthritis of the hip is one of the most common disease in Holland. About
257.400 people in the Netherlands are suffering from this disease. In the Isala
Clinics about 700 primary total hip arthroplasties are performed each year.
Because osteoarthritis is age related the demand for this procedure will
increase. Joint replacing surgery is now world wide one of the most performed
procedures. For this reason the occurence of complications should be kept to a
minimum.

The most important complications are luxation, infection and loosening of
components. Malposistioning of the cup is highly related to luxation and
loosening of components.

The orientation of the acetabular component is defined in anteversion and
inclination. Anteversion is the angle used to define the version of the opening
of the cup to the front of the pelvis. Inclination is the angle which the cup
forms with a horizontal line. Lewinnek defined a *safe zone* in which the cup
would have an optimal position in the pelvis. This safe zone is defined as: 15
+/- 10 degrees anteversion and 45 +/- 10 degrees inclination. In this safe zone
there is an optimal correlation between *range of motion* and stability of the
prosthesis. Correct placement of the cup is usually difficult because of the
absence of reliable intra-operative "landmarks". For this reason, about 50% of
the cups are placed in a different position than the surgeon estimated while
placing the cup during the procedure. It is clear that a method for more
accurate cupposistioning is higly needed.

In deze studie zal de nauwkeurigheid van peroperatieve meting van de
cuppositie door een nieuw ontworpen, onlangs gepatenteerd, meetinstrument
worden onderzocht. In de toekomst kan, indien het meetinstrument betrouwbaar
blijkt, peroperatief de cuppositie op geleide van de metingen van het
instrument worden aangepast en dus het postoperatieve complicatierisico
verlagen.

In this study the accuracy of a new device will be tested for placement of the
acetabular component in total hip arthroplasty. In the future this instrument
can contribute to more accurate placement of the acetabular component, so the
incidence of complications can be decreased.

prospective cohort study.

placement of a screw in the pelvis, and increase of operationtime of
approximately 10 minutes.

during the operation a screw is inserted in the bone. The screw is about 2 mm
in diameter and is placed in the pelvis (Spina Iliaca Anterior Superior). . The
depth of these pins in the bone is about 1 to 2.0 cm. the risk of this
intervention can be expressed in postoperative pain and infection. A few days
after the procedure a CT-scan will be made. This exposes the patient to some
degree of radiation.

The benefit of participation is that the precise orientation of the
actebularcomponent is known (CT-scan). This is of great importance for the
prognosis of the implant. If malpostioning has occured we can instruct the
patient so that the risk of complications can be reduced.