Introduction

An aneurysmatic bone cyst (ABC) is a benign cystic lesion of bone composed of blood-filled spaces separated by connective septa.

The most common treatment is curettage with or without bone grafting. Curettage with bone grafting and Ethibloc injection therapy have a comparable recurrence rate. Ethibloc is a radiopaque alcohol solution of corn protein which is percutaneously injected in the ABC.

Purpose of the study: Congruence between the femoral component and the insert has been proposed to decrease wear in total knee arthroplasty (TKA). This congruence should favour unidirectional movement between the components because multidirectional movements carry a risk factor for wear up to 30-fold higher than unidirectional movements. This study explored in vivo displacements between the insert and the femoral component of a prosthesis in order to determine whether they meet the required kinematic criteria.

Material and methods: Twelve patients (7 women, 5 men) aged 45 to 79 years with BMI from 23 to 35 underwent knee surgery for osteoarthritis and were included in this study. The prosthesis was a mobile plateau pros-thesis implanted by the same surgeon using a navigation system. During the procedure, four tantalum beads were implanted in the polyethylene under stereotaxic guidance. The postoperative evaluation was performed at six months with the clinical evaluation (KSS, WOMAC) a 3D fluoroscopic protocol (walking, stairs, get up and go) and a radiostereometric analysis (RSA).

Results: Active flexion under weight bearing was 118 (range 102–125) and the mean KSS 165. The videofluoroscopy combined with RSA showed congruent axial rotation between the femoral component and the insert in the flexion arc 0/60 with a mean difference of 0.38 per degree of flexion (SD 1.85). Beyond 60° flexion, the posterior displacement of the condyle was greater than the insert rotation.

Discussion: Compared with other 3D videofluoroscopic studies, this analysis adds greater accuracy due to the implantation of tantalum beads in the insert, enabling a study of insert displacement in relation to the metal components. This method demonstrates that for the implant studied here, rotation of the insert follows the displacement of the femoral component exactly from 0 to 60° flexion, this is a gliding displacement. Then beyond 60°, a gliding plus rolling movement occurs displacing the femoral component posteriorly.

Conclusion: This in vivo study in patients with a mobile plateau knee prosthesis demonstrates that the insert has a rotation exactly like the femoral component and that complete congruency is maintained between the femoral component and the insert with a pure gliding contact from 0 to 60° flexion. The prerequisite criteria for this type of prosthesis designed to reduce the wear factor are thus confirmed.

Introduction: Using navigation the AP alignment of a total knee arthroplasty (TKA) improves. However, much less is known on the influence of navigation on the rotation of the femoral component.

The rotation of the femoral component is of high importance considering the balancing of the knee and the patellofemoral joint. The aim of our study was to evaluate the accuracy of the femoral component rotation when using navigation.

Materials and Methods: We evaluated twenty navigated TKA’s. The Vector Vision system of Brainlab was used during surgery. The preoperative data considering the rotation were stored. On postoperative CT scans the rotation of the femoral component was measured twice at different times by two observers. The posterior condylar angle (the angle between the posterior condylar line and the epicondylar line) was used to define the rotation. The definite position was compared to the per-operative data. The difference between the preoperative determined rotation and the postoperative rotational position was analyzed. The Cohen’s kappa coefficient was used to compare the agreement of results.

Results: The postoperative CT scan showed an average measured rotation of the femoral component (posterior condylar angle) of 3,8 degrees. The average rotation based on the navigation data was 5.8 degrees. The difference between the preoperative data and the definite position measured on the CT was 2,8 degrees with a large range. We found a moderate agreement between the two observers and a good agreement within the two observers.

Conclusion: The rotation of the femoral component is important in the knee kinematics and patellofemoral joint. Using navigation, it is (yet) not possible to accurately determine or improve the rotational position of the femoral component. Further development of the software and method of determining the epicondylar axis during surgery is needed to be able to improve the rotational position of the femoral component.