Fluoroscopic and RSA evaluation of the ROCC total knee prosthesis

Three-dimensional (3D) fluoroscopic analysis is the most accurate measurement
technique to examine the in vivo kinematics of total knee replacement (TKR)
(Banks et al., 1997; Dennis et al., 1996; Dennis et al., 1998a; Garling et al.,
2005; Stiehl et al., 1999). 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). Because of
the influences of the prosthesis design on the kinematics, 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).

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 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 of the in vivo kinematic patterns of a
mobile bearing knee prosthesis (ROCC, Biomet Europe BV, The Netherlands) over
time by means of fluoroscopy and to evaluate if the polyethylene bearing is
rotating.

The secondary objective will be to evaluate if there is micromotion of the
prosthesis with respect to the bone and if it changes over time.

The last objective will be to compare the kinematic patterns found by
fluoroscopy of the mobile bearing knee prosthesis with the kinematic patterns
found by external movement registration.

Evaluations will be performed at 6, 12 and 24 months post-operative. At 0
months a RSA examination will be performed.

Post operative evaluation will consist of:
•Age, gender, length, weight, affection, side TKA
•RSA assessment
•Performing tasks (fluoroscopy, external movement registration, ground reaction
forces and EMG)
•Questionnaires: Womac, Knee Society Score, Rand-36
•Post-operative procedure information (physiotherapy (how long and how much,
when totally loaded)

Burden
•3 questionnaires (Knee Society Score, Womac, Rand-36)
•Fluoroscopic assessment
•RSA assessment
•EMG measurements will be performed for eight muscles. For this reason, two
electrodes are placed on the subject for each muscle.
•External movement registration will be performed. For this reason, a cluster
of three LED*s will be placed on several segments (foot, lower leg, upper leg,
pelvis and trunk).

The subject is asked to perform two tasks (step-up task and lunge movement).
During these tasks, EMG, ground reaction forces and segment angels are measured
synchronised with fluoroscopic images. The burden for the subjects during this
study will not be different with respect to normal daily activities.

Potential risks
The effective radiation dose per RSA-radiograph is 3 µSv. For fluoroscopy, a
follow up consisting of three fluoroscopic sessions (involving each 3 trials ×
2 tasks × 3 seconds of 15 fps imaging) the cumulative effective dose will be
0.06 mSv. The total effective radiation dose for this protocol 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)

Other potential risks are risks associated with normal knee replacements such
as infection, migration, bone loss, pain, loosening of components, metal
sensitivity reactions and tromboembolic complications.

Potential benefits
While the patients participating in this study may not directly derive any
immediate benefits, the results of the study should improve the understanding
of knee prostheses. This information will be extremely useful in optimizing
total knee prosthesis implant designs and improve long-term results.