[In vivo biomechanics of unicondylar knee replacement performed using minimally invasive technique]

Disturbed kinematics of the knee plays an important role in early failure of a unicondylar knee prosthesis (UNI). Recent studies on kinematics have shown that an intact anterior cruciate ligament (ACL) is important for a successful UNI. In this study, in vivo fluoroscopic analysis of knee kinematics was performed for 30 patients with a successful medial UNI implanted with the use of minimally invasive technique. The three-dimensional data of the CAD model were used for evaluating the sagittal translation as well as the axial rotation during deep knee bending and one gait cycle. The anteroposterior translation for flexion was, on average, -5.3 mm (-15.7-3.3; standard deviation 5.3). In most cases, the contact point was more posterior compared with the normal knee. During gait, the average anteroposterior translation was 0.8 mm, which is comparable to that of the normal knee. Axial rotation for deep knee bending was, on average, 8 degrees (-1.3-22.0; standard deviation 5.7), whereas 28 of the 30 knees showed normal axial rotation. During gait, an average axial rotation of 0.94 degrees was observed. The kinematic pattern of each of the subjects did not replicate the average pattern in most of the patients. An insufficient ACL may be suspected as the cause of the pathological kinematic pattern observed in some of these patients.