Introduction and Objective. Kinematic Alignment (KA) is a surgical technique that restores the native knee alignment following Total Knee Arthroplasty (TKA). The association of this technique with a medial pivot implant design (MP) attempts to reestablish the physiological kinematics of the knee. Aim of this study is to analyze the clinical and radiological outcomes of patients undergoing MP-TKA with kinematic alignment, and to assess the effect of the limb alignment and the orientation of the tibial component on the clinical outcomes. Materials and Methods. We retrospectively analyzed 63 patients who underwent kinematic aligned medial pivot TKA from September 2018 to January 2020. Patient-Related Outcomes (PROMs) and radiological measures were collected at baseline, 3 months and 12 months after surgery. Results. We demonstrated a significant improvement in the clinical and functional outcomes starting from 3 months after surgery. This finding was also confirmed at the longest follow-up. The clinical improvement was independent from the limb alignment and from the orientation of the tibial component. The radiological analysis showed that the patient's native limb alignment was restored, and that the joint line orientation maintained the parallelism to the floor when standing. This latter result has a particular relevance, as it may positively influence the outcomes, reducing the risk of wear and mobilization of the implant. Conclusions. The association of kinematic alignment and a medial pivot TKA implant allows for a fast recovery, good clinical and functional outcomes, independently from the final limb alignment and the tibial component orientation

Introduction and Objective. Gait variability is the amplitude of the fluctuations in the time series with respect to the mean of kinematic (e.g., joint angles) or kinetic (e.g., joint moments) measurements. Although gait variability increases with normal ageing or pathological mechanisms, such as knee osteoarthritis (OA). The purpose was to determine if a patient who underwent a total knee arthroplasty (TKA) can reduce gait variability. Materials and Methods. Twenty-five patients awaiting TKA were randomly assigned to receive either medial pivot (MP, m=7/f=6, age=62.4±6.2 years) or posterior stabilized (PS, m=7/f=5, age=63.7±8.9 years) implants, and were compared to 13 controls (CTRL, m=7/f=6, age=63.9±4.3 years). All patients completed a gait analysis within one month prior and 12 months following surgery, CTRLs completed the protocol once. A waveform F-Test Method (WFM) was used to compare the variance in knee biomechanics variables at each interval of the gait cycle. Results. Preoperatively, the PS group had greater sagittal knee angle variability compared to the MP (32–58% gait cycle) and CTRL (21–53% gait cycle) groups. Postoperatively, no difference in sagittal knee angle variability existed between any of the groups. Preoperatively, sagittal knee moment variability was greater in the MP (2–39% gait cycle) and PS (5–19% and 42–57% gait cycle) groups compared to the CTRL. Postoperatively, sagittal knee moment was lower in the MP (49–55% gait cycle) and greater in the PS (23–36% gait cycle) compared to the CTRL. Knee power variability was greater preoperatively in the MP (52–61% gait cycle) and PS (52–62% gait cycle) compared to the CTRL. Postoperatively, knee power variability was lower in the MP (17–22% and 45–50% gait cycle) and PS (6–23%, 34–41% and 45–49% gait cycle) compared to the CTRL group. Conclusions. Preoperatively, knee OA patients have greater variability in knee moments than CTRLs during the transition from double-limb support to single-limb support on the affected limb. This indicates knee instability as patients are adopting a gait strategy that refers to knee muscle contraction avoidance. The MP group showed greater knee stability postoperatively as they had lower knee moment and power variability compared to the CTRL. The significance of having less variability than CTRLs is not well understood at this time. Future research on muscle activity is needed to determine if neuromuscular adaptations are causing these reductions in variability after TKA

Introduction. Femoral periprosthetic fractures above TKA are commonly treated with retrograde intramedullary nailing (IMN). This study determined if TKA design and liner type affect the minimum knee flexion required for retrograde nailing through a TKA. Methods. Twelve cadaveric specimens were prepared for six single radius (SR) TKAs and six asymmetric medial pivot (MP) TKAs. Trials with 9mm polyethylene liners were tested with cruciate retaining (CR), cruciate substituting (CS) and posterior stabilizing (PS) types. The knee was extended to identify the minimum knee flexion required to allow safe passage of the opening reamer while maintaining an optimal fluoroscopic starting point for retrograde nailing. Furthermore, the angle of axis deviation between the reamer and the femoral shaft was calculated from fluoroscopic images. Results. In all specimens, the reamer entry point was posterior to Blumensaat's line. In the SR TKA, the average flexion required was 70, 71 and 82 degrees for CR, CS and PS respectively. The required flexion in PS was significantly greater than the other designs (p=0.03). In the MP TKA, the average flexion required was 74, 84 and 123 degrees for CR, CS and PS respectively. The required flexion was significantly greater in CS and PS designs (p<0.0001). Femoral component size did not affect the minimum flexion required. Furthermore, the entry reamer required 9.2 (SR) and 12.5 (MP) degrees of posterior axis deviation from the femur. Conclusions. Our study illustrates four novel factors to consider when performing retrograde nailing through TKA. First, significant knee flexion is required to obtain an ideal radiographic starting point when retaining the liner. Second, PS implants require more flexion with both TKA designs. Third, femoral component size does not affect the flexion required. Fourth, there is a consistent posterior axis deviation of the entry reamer from the femoral shaft, explaining the commonly created extension deformity

Physiological kinematics is very difficult to restore after total knee arthroplasty (TKA). A new model of medial stabilized (MS) TKA prosthesis has a high spherical congruence of the internal compartment, which guarantees anteroposterior (AP) stability associated with a flat surface of the insert in the lateral compartment, that allows a greater AP translation of the external condyle during knee flexion. The aim of our study is to evaluate, by dynamic radiostereometric analysis (RSA), the knee in vivo kinematics after the implantation of a MS prosthesis during sit to stand and lunge movements. To describe the in vivo kinematics of the knee after MS Fixed Bearing TKA (GMK Sphere (TM) Medacta International AG, Castel San Pietro, Switzerland) using Model Based dynamic RSA. A cohort of 18 patients (72.1 ± 7.4 years old) was evaluated by dynamic RSA 9 months after TKA. The kinematic evaluation was carried out using the dynamic RSA tool (BI-STAND DRX 2), developed at our Institute, during the execution of sit to stand and lunge movements. The kinematic data were processed using the Grood and Suntay decomposition and the Low Point method. The patients performed two motor tasks: a sit-to-stand and a lunge. Data were related to the flexion angle versus internal-external, varus-valgus rotations and antero-posterior translations of the femur with respect to the tibia. During the sit to stand, the kinematic analysis showed the presence of a medial pivot, with a significantly greater (p=0.0216) anterior translation of the lateral condyle (3.9 ± 0.8 mm) than the medial one (1.6 ± 0.8 mm) associated with a femoral internal rotation (4.5 ± 0.9 deg). During the lunge, in the flexion phase, the lateral condyle showed a larger posterior translation than the medial one (6.2 ± 0.8 mm vs 5.3 ± 0.8 mm) associated with a femoral external rotation (3.1 ± 0.9 deg). In the extension phase, there is a larger anterior translation of the lateral condyle than the medial one (5.8 ± 0.8 mm vs 4.6 ± 0.8 mm) associated with femoral internal rotation (6.2 ± 0.9 deg). Analysing individual kinematics, we also found a negative correlation between clinical scores and VV laxity during sit to stand (R= −0.61) and that the higher femoral extra-rotation, the poorer clinical scores (R= 0.65). The finding of outliers in the VV and IE rotations analysis highlights the importance of a correct soft tissue balancing in order to allow the prosthetic design to manifest its innovative features

INTRODUCTION. Useful feedback from a Total Knee Replacement (TKR) can be obtained from post-surgery in-vivo assessments. Dynamic Fluoroscopy and 3D model registration using the method of Banks and Hodge (1996) [1] can be used to measure TKR kinematics to within 1° of rotation and 0.5mm of translation, determine tibio-femoral contact locations and centre of rotation. This procedure also provides an accurate way of quantifying natural knee kinematics and involves registering 3D implant or bone models to a series of 2D fluoroscopic images of a dynamic movement. AIM. The aim of this study was to implement a methodology employing the registration methods of Banks and Hodge (1996) [1] to assess the function of different TKR design types and gain a greater understanding of non-pathological (NP) knee biomechanics. METHODS. Knee function was assessed for five subjects with NP knees (4 males and 1 female, 34.8 ± 10.28 years, BMI 25.59 ± 3.35 Kg/m. 2. ) and five subjects 13.2 (± 1.8) months following a TKR (2 males, 3 females, 68 ± 9.86 years, BMI 30 ± 3 Kg/m. 2. ). The TKR types studied included 1 cruciate retaining, 2 cruciate substituting, 1 mobile-bearing (high flex) and 1 medial pivot). Ethical approval was obtained from the South East Wales Local Research Ethics Committee. Each subject's knee was recorded whilst they performed a step up/down task, using dynamic fluoroscopy (Philips). 3D CAD models of each TKR were obtained for the TKR subjects. 3D bone models of the knee, tibia and femur were created for the 5 NP subjects by segmenting MRI scans (3T GE scanner, General Electric Company) using ScanIP (Simpleware, Ltd.). Using the program KneeTrack (S A Banks, USA), each TKR component and bone model was projected onto a series of fluoroscopic images and their 3D pose iteratively adjusted to match the contours on each image. Joint Kinematics were determined from the 3D pose of each 3D model using Cardan/Euler angles [2]. The contact points and centre of rotation of each TKR were also computed. RESULTS. The mean range of motion (ROM) in the sagittal plane was 61° for the NP cohort and 64° for the TKR cohort. The mean frontal plane ROM was 4° for NP knees and 3° for TKR. A greater axial ROM was achieved by the mobile-bearing (7.5°) and medial pivot TKR (7.0°), compared to the cruciate retaining (4.4°) and substituting (3.6°). The Medial Pivot TKR rotated around a medial centre of rotation, whereas the centre of rotation was located laterally for the other TKR types. This has also been found in other studies of stair climbing activities [3]. CONCLUSIONS. This study demonstrates how this method can be used to quantify and compare the kinematics, contact locations and centre of rotation for a range of TKR designs and NP knees in-vivo. Initial analyses have identified functional differences associated with different TKR designs

Achieving deep flexion after total knee replacement remains a challenge. In this study we compared the soft-tissue tension and tibiofemoral force in a mobile-bearing posterior cruciate ligament-sacrificing total knee replacement, using equal flexion and extension gaps, and with the gaps increased by 2 mm each. The tests were conducted during passive movement in five cadaver knees, and measurements of strain were made simultaneously in the collateral ligaments. The tibiofemoral force was measured using a customised mini-force plate in the tibial tray. Measurements of collateral ligament strain were not very sensitive to changes in the gap ratio, but tibiofemoral force measurements were. Tibiofemoral force was decreased by a mean of 40% (sd 10.7) after 90° of knee flexion when the flexion gap was increased by 2 mm. Increasing the extension gap by 2 mm affected the force only in full extension. Because increasing the range of flexion after total knee replacement beyond 110° is a widely-held goal, small increases in the flexion gap warrant further investigation.