2015 ISAKOS Biennial Congress ePoster #1430

Influence Of 1mm Pitch Different Insert on Intraoperative Kinematics in Cruciate-Retaining and Posterior Stabilized Total Knee Arthroplasty

Nobuhiro Abe, MD, PhD, Prof., Okayama JAPAN
Yoshinori Tojo, MD, Okayama JAPAN
Toshinori Tamada, MD, PhD, Okayama JAPAN
Kazuki Shimamoto, MD, Okayama JAPAN
Keiya Mori, MD, PhD, Okayama JAPAN
Kazuto Hirai, MD, Okayama JAPAN

Department of Orthopaedic Surgery and Sport Medicine, Kawasaki Hospital, Kawasaki Medical School, Okayama, JAPAN

FDA Status Cleared

Summary: In CR type of TKA, 1mm difference insert was influence to anterior-posterior translation (APT), axial rotation (AR), and moreover flexion extension gap (FEG). The kinematics of PS TKA was mostly regulated by implant design with post-cam mechanism. One mm thicker insert was made the limitation of extension with the small difference of APT, AR, and moreover FEG.

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Abstract:

Purpose

Total knee arthroplasty (TKA) is a relatively safe surgical procedure and most patients improve with regard to pain and physical functioning and quality of life. But only 75 to 89% of the patients are satisfied. This satisfaction is reported to be associated with postoperative range of motion, knee alignment, high expectations and pain reduction while performing daily activities. Especially, the patients feel a degree of dissatisfaction with ascending stairs, get in or out of the car and rising from bed because of a sensation of the mid-flexion instability. Newly developed total knee system has been to stabilize and reproduce smooth motion during knee kinematics. This system offers many sizes of implants and inserts according to individual patient variations. The purpose of this study was to evaluate the kinematics in both of the crucial retained (CR) and the posterior stabilized (PS) knee implants with small variations of the inserts using an intra-operative navigation system.

Materials And Methods

Modern TKA was performed in 14 knees (14 women, average aged 75.6 year old) with image-free navigation system (KolibliTM) under general anesthesia. In 7 CR and 7 PS TKA, measured resection method was performed according to the navigation system. The implant kinematics was regulated to the medial pivot motion from 0 to 120 degree and the bi-condylar rollback motion from 120 degree to full flexion angle as the normal knee kinematics reported by MRI studies. The kinematics with applying various size of insert thickness was evaluated about flexion extension gap (FEG), anterior-posterior translation (APT) and axial rotation (AR) with passive motion under general anesthesia with image free navigation system.

Results

In the crucial retained (CR) type, no medial pivot motion was observed, and thus the kinematics showed the bi-condylar roll-back pattern even the gap balancing between medial and lateral compartment was nearly equal during whole range of motion. However, the medial pivot motion was gradually started from early flexion angle and bi-condylar rollback was strated from around 100 degree when the joint gap was reduced with a 1-mm thinner insert to regulate the appropriate ligament balancing, even in the same knee.
In case of PS kinematics, the medial pivot motion was observed during flexion. And the gap balancing between medial and lateral compartment was nearly equal during whole range. The medial pivot was recognized around at 40 degree flexion and the cental pivot was seen at 60 degree flexion and bi-condylar rollback was started from 90 degree, which was related to the post-cam mechanism. The various thickness of insert showed the small difference of APT, AR, and moreover FEG throughout the whole range of motion. But 1mm thicker insert was caused to the limitation of extension.

Discussion

In CR type of TKA, 1mm difference insert was influence to APT, AR, and moreover FEG. The kinematics of PS TKA was mostly regulated by implant design with post-cam mechanism. One mm thicker insert was made the limitation of extension with the small difference of APT, AR, and moreover FEG.
The PCL releasing technique is so various and sometimes difficult to have proper ligament balancing. One mm pitch different insert would give us the good option to have the reasonable kinematics in CR TKA.