Role of positioning of femoral component in the anterior-posterior direction on postoperative anterior pain in TKA.

INTRODUCTION AND PURPOSE: The patellofemoral joint has proved to be the most problematic element of modern TKA for postoperative anterior knee pain; the positioning of the femoral component constitutes a critical phase in this issue. The objective of our study was to evaluate the possible role of either anterior positioning or posterior positioning of the femoral shield compared to the reference plane represented by the anterior cortex, on the anterior knee pain after knee arthroplasty. METHODS: Forty-eight patients treated with TKA were followed up approximately 12 months. None of them have been submitted to any patellar treatment. We observed the position of femoral shield with respect to the anterior cortical line of femur dividing patients into three groups: patients with significant notching, patients with no notching (shield corresponding to anterior cortical line) and patients with anterior positioning of shield. We evaluated clinical and functional outcomes with KSS, anterior knee pain with Kujala's score and adverse events such as periprosthetic fractures. RESULTS: We found a better clinical and functional result for patients with femoral shield positioned in line with anterior cortical cortex with respect to both TKAs with femoral notching and to protruding anterior femoral components; there were no main differences in anterior postoperative score by Kujala's system. We observed a periprosthetic fracture in a patient with an important femoral notching. CONCLUSIONS: We cannot consider our study as an objective conclusion to the argument. We need more RCTs in order to study the proper influence of either notching or protrusion of femoral shield component onto anterior postoperative pain. Anyway positioning of femoral shield in anterior-posterior direction could be an interesting new critical object of study about anterior knee pain after TKA.

In vivo kinematics of medial unicompartmental osteoarthritic knees during activities of daily living.

Few studies exist describing unicompartmental osteoarthritic knee kinematics. Moreover, the role of the anterior cruciate ligament (ACL) in the determination of knee kinematics has not been fully described. The objective of the current study was to analyze the in vivo kinematics of knees with medial osteoarthritis (OA) and intact ACL during closed and open chained motion. Eight patients scheduled for UKA diagnosed with primary medial OA underwent knee CT-scans and video-fluoroscopy. Fluoroscopic analysis included stair climbing, chair rising and leg extension. Three-dimensional bone positions were obtained from each image by iterative procedures using a CAD-model-based shape-matching technique. Patterns of axial rotation and anterior-posterior (AP) motion of the medial and lateral femoral condyle were obtained with specific software. The femur reported an overall external rotation relative to the tibia from extension to flexion in all tasks. Average AP translation of the medial femoral condyle were smaller in open-chained tasks than in weight-bearing conditions. Average AP motion of the lateral femoral condyle reported an overall posterior translation with knee flexion. The absent natural "screw-home" mechanism and the lack of medial condyle posterior translation was explained by bone-cartilage defects and meniscal degeneration. Relevant findings were the kinematic pattern differences between weight-bearing and open chained activities, suggesting that in biphasic muscle contraction and unloaded conditions, the function of the cruciate ligaments was not physiological. The kinematics of knees with medial OA and intact ACL differed from healthy knees.