2015 ISAKOS Biennial Congress ePoster #1443
In Vivo Kinematic Effects of Ball and Socket Third Condyle as a Post-Cam Mechanism in Tri-Condylar Knee Implants
Shinichiro Nakamura, MD, PhD, Kyoto JAPAN
Adrija Sharma, PhD, Knoxville, TN UNITED STATES
Kenji Nakamura, MD, Matsue JAPAN
Noboru Ikeda, MD, PhD, Matsue JAPAN
Richard D. Komistek, PhD, Knoxville, TN UNITED STATES
Shuichi Matsuda, MD, PhD, Kyoto JAPAN
University of Tennessee, Knoxville, USA
FDA Status Not Applicable
Summary: The third condyle induced intensive posterior translation of both condyles, and did not prevent axial rotation, which worked as a posterior-stabilizing cam mechanism.
Tri-condylar implants containing a ball and socket third condyle as a post-cam mechanism were developed to accommodate a lifestyle requiring frequent deep flexion activities. This third condyle is expected to replace the function of a post-cam mechanism and also to act as a load-bearing interface in flexion. It is still unknown whether the third condyle actually works as a posterior stabilizer in vivo. The purpose of the current study was to examine the kinematic effects of the ball and socket third condyle during a deep knee bend activity, and to confirm the contact status of the ball and socket joint.
Seventeen knees implanted with tri-condylar implants were analyzed using a 3D to 2D registration approach. A distance of less than 1 mm denoted ball and socket contact. Medial and lateral contact positions and axial rotation were compared before and after contact. Moreover, the contact position at the third condyle and the center of the ball joint were analyzed.
The average angles of full extension and maximum flexion for all subjects were 2.0° (SD = 6.0) and 109.8° (SD = 15.5), respectively. The ball joint came into contact at 64.7° (SD = 8.7) of knee flexion, on average. After the third condyle contact, posterior translation of the medial and lateral contact positions was significantly greater than before contact. Meanwhile, the angular rotation remained still. The average contact position of the ball and socket joint was located within 4 mm from the bottom of the medial and lateral condyles. After the third condyle contact, the contact position remained low through the entire process. The ball center showed anterior and distal movement by 7.5 mm (SD = 1.3) and -10.7 mm (SD = 1.9) from full extension to ball and socket joint contact, respectively, and then showed posterior and distal movement by 0.3 mm (SD = 0.8) and -1.4 mm (SD = 0.6), respectively. The center of the ball joint stayed after contact.
The third condyle induced intensive posterior translation of both condyles, and did not prevent axial rotation. Separating the kinematics before and after the post-cam engagement, and analyzing the contact status of the post-cam, might aid our understanding of the effects of the post-cam mechanism in detail.