Page 30 - ISAKOS Newsletter 2016 Volume 1

CURRENT CONCEPTS
Soft Tissue Balancing in Total
Knee Arthroplasty
Finally, postoperative kinematics such as tibial internal rotation and tibial anterior translation are important to achieve better clinical outcomes including high knee flexion angle. With regard to achieving high flexion after TKA, some studies have emphasized that an increase in postoperative tibial internal rotation is observed during knee flexion. Therefore, we investigated the correlation between intraoperative soft tissue balance assessed by the tensor and postoperative knee kinematics assessed by navigation system following all prostheses implanted. The results confirmed a positive correlation between varus ligament balance and tibial internal rotation, which may indicate that looseness of the lateral compartment in relation to the medial side at 60° and 90° flexion permits rotational mobility and results in increased tibial internal rotation.
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In fact, the positive correlation between the lateral compartment gap and tibial internal rotation from mid-to- deep knee flexion was a more sensitive factor than the joint component gap, and the fact that there was no relationship between the medial compartment gap and tibial internal rotation supported this result. Moreover, in another study on assessing correlation between intra and postoperative knee flexion angle and knee kinematics, postoperative knee flexion angle as well as preoperative knee flexion angle were significantly correlated to the postoperative tibial internal rotation. In addition, we reported positive correlation between intraoperative lateral laxity at flexion and postoperative flexion angle in CR TKA, indicating that medial stability with appropriate lateral laxity was important for achievement of high flexion angle. Similarly, Kobayashi reported on postoperative stress radiograph, that lateral laxity at flexion (flexion-valgus, 3.4°: flexion-varus, 6.2°) showed positive correlation with postoperative knee flexion angle [30]. These studies are supported by other studies indicating that the flexion gap in healthy knees is not rectangular and that the lateral joint gap is significantly lax. In summary, to reproduce medial pivot motion after TKA, medial stability with moderate lateral laxity during flexion might lead to appropriate tibial internal rotation and result in a high flexion angle.
28 ISAKOS NEWSLETTER 2016: Volume I
Perspective
Recent advances in sensor technology have provided surgeons with an easy tool for assessment of intraoperative pressure distribution and femoral contact points on tibial trial insert. OrthoSensor® enables surgeons to assess Kinetic TrackingTM feature (force and motion), displaying femoral component motion paths in the medial and lateral compartments (Fig. 02). Recently, Gustke et al introduced a new assessing system and reported better patient satisfaction rate with balanced knee (94.1%) compared to that with unbalanced knee (82.1%), by using the assessment system; Verasense Knee System (OrthoSensor Inc., Dania Beach, Florida). This assessment tool highlights the measurement condition same as offset-type tensor; PF joint reduction throughout the range of motion. However, whereas the measurement with the sensor is focused on natural knee condition with load distribution on tibial insert, offset-type tensor aims to measure the characteristics of soft tissue envelope with distraction force. Both these two measurement methods are important and might be combined in the future.
The most important aspect in soft tissue balancing is the close interaction between the surgical technique and the assessment, in which surgeons should adjust the surgical technique to attain final soft tissue balance. With the measured resection technique for CR TKA, we recently reported the importance of minimal medial release (osteophyte removal and release of deep layer of medial collateral ligament) for varus-type osteoarthritis to maintain appropriate tibial internal rotation and gain high flexion angle. Recently, offset type tensor has been developed to be used for gap technique as well as measured resection technique during TKA. With this new system FuZionTM (Zimmer, Inc.) (Fig. 03), surgeons can assess and correct soft tissue balance after femoral distal and tibial proximal cut, then adjust femoral rotation based on the tensor measurement, and confirm the final balance throughout the range of motion with the femoral component placement. The information available by the use of the tensor during surgery is useful in a real-time manner and essential for the insight of true postoperative kinematics. It allows the surgeon to adjust the soft tissue balance more accurately and thereby expect a better postoperative outcome.
Considering successful clinical outcomes, accurate osteotomy / implantation and soft tissue balancing are essential in TKA. Appropriate bone cut and prosthetic implantation have improved due to advances in surgical instrumentations such as the computer-assisted navigation system, preoperative image-matching technique, or patient- specific instrumentation. Similarly, appropriate soft tissue balancing has become more important than before. With the recent advances in this field described here, improvement of patient satisfaction after TKA is expected in the near future.
03 FuZionTM Instrument (Zimmer, Inc.)
The FuZion Instruments are based on two platforms: the FuZion Spacer Block and FuZion Tensor, and were specifically designed to provide crossover utility, harmonizing measured resection and gap balancing philosophies.