Abstract
Introduction
Total knee arthroplasty (TKA) can effectively treat end-stage knee osteoarthritis. For cruciate-retaining (CR) TKA, the posterior tibial slope (PTS) of the reconstructed proximal tibia plays a significant role in restoring normal knee kinematics as it directly affects the tension of the posterior cruciate ligament (PCL) [1]. However, conventional cadaveric testing of the impact of PTS on knee kinematics may damage/stretch the PCL, therefore impact the test reproducibility. The purpose of this study was to assess the reproducibility of a novel method for the evaluation of the effects of PTS on knee kinematics.
Materials and Methods
Cemented CR TKAs (Logic CR, Exactech, Gainesville, FL, USA) were performed using a computer-assisted surgical guidance system (ExactechGPS®, Blue-Ortho, Grenoble, FR) on six fresh frozen non-arthritic knees (PCL presumably intact). The tibial baseplate was specially designed (Fig. 1) with a mechanism to modify the PTS in-situ. Knee kinematics, including anteroposterior (AP) translation, internal/external (IE) rotation, and hip-knee-ankle angles, were evaluated by performing a passive range of motion from extension up to ∼110° of flexion, three separate times at 5 PTSs: 10°, 7°, 4°, 1°, and then 10° again. The repeatability of the test was investigated by comparing the kinematics between the first and the last 10° tests. Any clinically relevant deviation (1.5° for the hip knee ankle angle, 1.5mm for anterior-posterior translation and 3° for internal-external rotation) would reflect damage to the soft-tissue envelope or the PCL during the evaluation. Potential damage of PCL was investigated by comparing the kinematic parameters from the first and last 10° slope tests at selected flexion angles (Table 1) by paired t-test, with statistical significance defined as p<0.05.
Results
The differences in the kinematic parameters between the two sets of acquisitions at 10° of PTS were small, non-clinically relevant (Fig 2), and statistically insignificant (Table 1). For a given knee, the difference was relatively constant over the range of flexion. Knowing that the PCL is not active in extension and early flexion, this finding suggested the differences were mainly caused by the measurement noises.
Discussion
The results suggested our test method does not significantly disrupt the soft tissue environment of the knee. Previous evaluations of the effect of the PTS on passive knee kinematics often overlooked the potential disruption/stretching of the PCL or other soft tissue over the course of aggressive manipulation of the PTS. Other soft tissue preserving test methods for the adjustment of PTS, such as anterior opening wedge osteotomy with gap filling using bone cement [2] but the preservation of the PCL over the course of the experiment hasn't been evaluated. The present study utilized a novel tibial baseplate, which allowed for adjusting the PTS without re-cutting the tibia and removing the components. Knee kinematics can therefore be reliably tested without disrupting the PCL or the soft tissue envelope. As such, the authors promote the proposed test method for future investigations.
