Abstract
Although the pre- or intraoperative flexion angle in TKA has been commonly considered as a predictor of the postoperative flexion angle, patients with well flexion intraoperatively cannot necessarily obtain deep flexion angle postoperatively. The reason why inconsistencies remains has been unsolved. The intraoperative compressive force between femoral and tibial components has the advantage of the sequential changes during knee motion. However, the relationship between the compressive force and the postoperative ROM has not yet been clarified. We aimed to evaluate the intraoperative femorotibial compressive force during passive knee motion, and determine the relationship between the compressive force and the postoperative flexion angle.
A total of 11 knees in 10 patients who underwent primary cruciate-retaining (CR) TKA (The FINE Total Knee System; Teijin Nakashima Medical Co., Ltd., Okayama, Japan) for osteoarthritis were studied retrospectively, with a mean age of 76 years via a measured resection technique. We developed a customized measurement device mimicking the tibial component with this platform of six load sensors arranged in two rows (medial and lateral) by three tandem sets (anterior, center and posterior): anteromedial (AM), anterolateral (AL); centromedial (CM), centrolateral (CL); and posteromedial (PM), posterolateral compartment (PL) (Fig. 1). At the step of the implant trial, this device was placed on the tibia with compressive force recorded three times, while the knee was subsequently taken from 0° to full flexion manually in 15 seconds with the flexion angle of the knee recorded simultaneously by using an electric goniometer (Fig. 2). Eligibility were evaluated for ROM using a long-armed goniometer preoperatively and at 6 months postoperatively. A p value of < 0.05 was considered significant.
The mean compressive force at AM, AL, CM, CL, PM and PL was 0.7, 0.5, 1.3, 1.2, 3.4 and 2.6 kgf, with the peak force of 4.2, 2.5, 4.1, 2.5, 7.3 and 4.7 kgf, respectively. The mean pre- and postoperative extension and flexion angles were −11° and −6°; and 115° and 113°, respectively. There were no significant correlations between the mean force in any region of interest (AM to PL) and the postoperative flexion angle. The peak force in PM showed little correlation with the postoperative flexion angle (r = −0.17, p = 0.54), however, that in PL was strongly negatively correlated with the postoperative flexion (r = −0.86, p < 0.01).
The current results suggest the presence of less force on the lateral side in flexion. We speculate that lower compressive force at the lateral side is essential for deep flexion as it has been reported that the lateral structure has more laxity than the medial side during flexion in healthy knees. Measurement between the femoral and tibial compressive force can contribute an achievement of more flexion angle following CR-TKA.
