Joint line restoration after navigated posterior stabilized total knee replacement

Anterior knee pain is still a major reason for patient unsatisfaction after total knee replacement (TKR). Anterior knee pain may involve up to 30% of patients operated with TKR, with an incidence of revision up to 5-10%. Restoration of joint line is a key consideration In optimising functional results in knees with a posterior stabilized TKR. In the past the measurement of joint line variation before and after TKR was made only with radiograph evaluation. Aim of our study is to measure the variation of the joint line height during TKR using a navigation system. The present prospective study involved 50 consecutive primary TKRs using the Scorpio Posterior Stabilized System. The navigation system used was the Image-free Stryker Knee Navigation System. During the procedure of anatomy survey made by the navigation system, the surface digitisation of the distal femoral condyles and of the medial and lateral tibial compartments have been executed in order to establish the level of osteotomy of the distal femur and of the proximal tibia. The same measurements have been executed after the implant of the femorai and tibial component, with a dedicated probe placed on the respective prosthesis component. To determinate the TKR joint line has been added the polyethylene thickness to the measurement of the tibial component height. To determinate the level of the pre-operative joint line, the most normal tibial plateau has measured respect on the tibial mechanical axis. The mean cranial movement of the joint line was of 0.8±2.2 mm with a maximum of elevation of 8 mm and a maximum of distal movement of 3 mm. Using the navigation system accurate and reliable intraoperative decisions are possible with respect to the mechanical axis and positions of the components. The navigation system obviates the risk of conventional alignment devices and provide reliable determinations of the correct position of the components and joint line restoration.