Abstract
Introduction:
One of the important factors for success in TKA is to achieve proper stability of the knee joint. It is currently unknown that how much joint laxity exists in mid-range to deep knee flexion, postoperatively. We hypothesized that retaining the PCL or not during TKA has an influence on the postoperative joint laxity from mid-range to deep knee flexion. The purpose of this study was to investigate the postoperative coronal joint laxity throughout the full range of motion by the 3-dimensional in vivo analysis, both in PS and CR TKA.
Methods:
We implanted 5 knees with a PS TKA using a NexGen LPS-flex and 5 knees with a CR TKA using a NexGen CR-flex. All of them were the osteoarthritis patients. We performed all operations with a measured resection technique. Four weeks after TKA, the valgus- and varus-stress radiographic assessments were performed at the five flexion angles from full extension to maximum flexion. The patients sat on the radiolucent chair with their lower legs hanging down. The examiner held their thigh, and a force of 50N was applied 30 cm distal to the tibiofemoral joint. The series of static fluoroscopic images via a flat panel detector were stored digitally. A 3-dimentional to 2-dimentional techniqueusing an automated shape-matching algorithm was employed to determine the relative 3-dimentional positions of the femoral component and tibial component in each fluoroscopic image (KneeMotion; LEXI, Tokyo). On the coronal plane of the tibial component, the angle between the tangent line of the condyles of the femoral component and the tibial plateau was measured as the joint laxity for valgus (α valgus) or varus (α varus). The flexion angle between the femoral component and tibial component was also measured.
Results:
The total laxity (α valgus + α varus) tended to increase until deep knee flexion in PS TKA. While in CR TKA, the total laxity tended to increase until mid-range of knee flexion and then decreased until maximum flexion (Fig. 1). PS TKA: In varus stress, the mean tilting angles were 2.4, 3.6, 3.6, 4.1, 5.4 degrees at −2.3, 25.3, 42.2, 72.1, 97.1 degrees of knee flexion, respectively. The tilting angle measured at maximum flexion was significantly larger than that measured at full extension (p < 0.05) (Fig. 2). CR TKA: In valgus stress, the mean tilting angles were 0.8, 2.8, 2.8, 2.0, 0.6 degrees at −6.4, 24.1, 35.8, 67.7, 87.8 degrees of knee flexion, respectively. The tilting angles measured at full extension and maximum flexion were significantly smaller than that measured at 24.1 and 35.8 degrees of knee flexion (p < 0.05) (Fig. 3).
Discussion:
In PS TKA, joint laxity for varus at maximum flexion was significantly larger than that at full extension. While in CR TKA, joint laxity for varus indicated no significant differences among at each flexion angle. Moreover, joint laxity for valgus at full extension and maximum flexion were significantly smaller than that at mid-range flexion in CR TKA. Retaining the PCL during TKA has a strong influence on the postoperative coronal joint laxity especially in deep knee flexion.
