Abstract
Soft tissue balancing remains the most subjective and most artistic of current techniques in total knee arthroplasty. It is well known that it is more difficult to achieve posterior roll-back with CR than with PS. Extension and flexion gaps on the sagittal plane, and medial and lateral gaps on the coronal plane have to be well balanced. However, it is very difficult to match these four. Biomechanical properties of the soft tissue were obtained during the surgery, using the specially designed system. The system consists of two electric load cells in the tensioning device, digital output indicators, and an XY plotter. Load displacement curves were obtained in extension and in flexion. Interestingly, the stiffness of curves obtained from the lateral in flexion is 1/3 lower than the other three. However, it is very questionable whether we can adjust these materials precisely and constantly or not.
To achieve posterior roll-back and deep knee flexion, ligament balancing is more important in cruciate retaining TKA than in PS Knee. Posterior impingement and anterior lift-off are often seen during surgery. That means “too tight in flexion”. First of all, elementary correction of the coronal deformity is performed by appropriate removal of osteophytes and soft tissue release. A pre-cut is made 2–3 mm distal to the conventional cutting line at the distal femoral end. Femoral component size is determined in accordance with the antero-posterior dimension. Posterior femoral condylar resection is performed. A load is applied in flexion to measure flexion gap. The extension gap is then measured in extension with the same load as that which was applied in flexion. Additional bone re-cut of the femoral distal end is performed.
The technique is very similar to the classic flexion-extension gap balance technique.
However, the most different point I would like to emphasize is that an accurate and constant load is applied to make both the flexion and extension gaps equal. There is no need to release the PCL using this technique. Therefore, I would like to name this technique “Load dependent gap technique” to emphasize that an accurate and constant load can be clearly applied to equalize the gaps.
In future, using this technique, it could be possible to know what percentage of the load applied in extension should be appropriate in flexion when the two gaps are equalized in TKA.
Correspondence should be addressed to Diane Przepiorski at ISTA, PO Box 6564, Auburn, CA 95604, USA. Phone: +1 916-454-9884; Fax: +1 916-454-9882; E-mail: ista@pacbell.net
