Fluoroscopic and RSA evaluation of the Triathlon total knee prosthetic design

The performance of total knee replacement (TKR) is dependent on a number of
factors, such as the pre-operative range of motion (ROM) (Argenson et al.,
2005; Nelissen et al., 1995; Ritter et al., 2003) and resulting kinematics of
the joint. The kinematics are determined by the design of the implant,
particularly the geometry of the articulating surfaces, the alignment of the
components with respect to the bone and to each other, and of the surrounding
soft tissue (Dennis et al., 1998b; Karrholm et al., 1994). Because of the
influences of the prosthesis design, it is important to asses the in vivo
characteristics and functional adaptations of the design following TKR (Banks
and Hodge, 2004; Taylor et al., 2003).

Three-dimensional (3D) fluoroscopic analysis is the most accurate measurement
technique to examine the in vivo kinematics of TKR (Banks et al., 1997; Dennis
et al., 1996; Dennis et al., 1998a; Garling et al., 2005; Stiehl et al., 1999).
The position and orientation of 3D computer models of total knee components are
manipulated so that their projections on the image match those captured during
the in vivo knee motion (Garling et al., 2002; Kaptein et al., 2006). It is
also possible to analyse the in vivo kinematics of marked polyethylene bearings
in mobile bearing knee designs (Garling et al., 2005; Nelissen et al., 1998).

Fluoroscopic analysis studies has shown that there is a broad range of
kinematic patterns of the femur with respect to the tibia during dynamic
activities and a significant proportion of implanted knees has abnormal
kinematics (Callaghan et al., 2001; Dennis et al., 1998b; Stiehl et al., 1999).
In the short term, poor kinematics may lead to a feeling of instability and
limits the mobility of the patient. In the long term, abnormal kinematics may
lead to accelerated wear of the articular surfaces (Banks and Hodge, 2004;
Krichen et al., 2006) and excessive stresses in bone-implant interface leading
to aseptic loosening (Taylor and Barrett, 2003).

To decrease the excessive stresses and wear of the articular surface a mobile
bearing design has been developed. The essential point of this design is that
the polyethylene bearing can move with respect to the underlying tibial
component. The conformity between the femoral component and the polyethylene
bearing leads to an increased contact area and thus lower contact stresses in
the bearing in comparison with non-conforming fixed bearings (Andriacchi, 1994;
Stiehl et al., 1997). The broad range of kinematic patterns seen in mobile
bearing knees could be explained by the absence of motion or occurrence of
erratic motion of the polyethylene bearing. This will enhance wear of the
polyethylene surface and could induce more aseptic loosening (Garling et al.,
2005). For this reason, it is important to evaluate the motions of the
polyethylene bearing over a substantial period of time.

The primary objective is the assessment and comparison of the in vivo kinematic
patterns of the knee designs by means of fluoroscopy and EMG.

The secondary objective is to evaluate if the polyethylene bearing in the
mobile bearing is rotating and if this changes over time.

The third objective is to relate the kinematic patterns found by fluoroscopy
with the kinematic patterns found by means of gait analysis.

The last objective will be to evaluate if there is micromotion of the
prosthesis with respect to the bone and if there is a different between the
designs. Also, results of the RSA study will be used to correlate the kinematic
parameters (fluoroscopy and gait analysis) with the migration results in order
to identify factors of risk for the survival of total knee prostheses.

RSA: 0, 6, 12 en 24 months post-operative
Fluoroscopy: 6, 12 en 24 months post-operative
Gaitanalysis: 6 en 12 months post-operative

During each visit, several questionnairs have to be filled in.

The effective radiation dose per RSA-radiograph is 3 µSv. For fluoroscopy the
cumulative effective dose will be 0.02 mSv (3 trials × 2 tasks × 3 seconds of
15 fps imaging). The total effective radiation dose for one patient is
estimated on 0.07 mSv. The additional annual radiation dose is negligible if
the natural annual exposure of 2 mSv is considered and will do the subject no
harm.

The International Commission on Radiological Protection categorizes the
corresponding level of risk qualitative due to radiation as *trivial* with a
quantitative risk of about one in a million or less. The required level of
benefit should be related to *only increase knowledge*.
(http://ec.europa.eu/energy/nuclear/radioprotection/publication/099_en.htm)

For the gait analysis no potential risks are expected.