Abstract
Introduction
The purpose of this study was to examine whether three types of mobile-bearing PCL sacrificing TKA could restore the native knee translation and rotation. The primary hypothesis was that there are differences in knee kinematics and laxity between three different cruciate-substituting TKA designs: 1 with post-cam mechanism, 2 post-cam mechanism based on an inter-condylar ‘third condyle’ concept, 3 anterior stabilized with deep-dished highly congruent tibial insert; specifically, showing different femoral external rotation with flexion, different femoral translation with flexion and different laxity under stress test. The secondary hypothesis was that there is different clinical outcome between the three TKA designs at 2 years follow-up.
Methods
We recruited 3 cohorts consisting of 30 patients each divided according 3 different TKA designs. All patients were operated with navigated procedure. During surgery preoperative and postoperative kinematics were recorded, in terms of femoral antero-posterior translation and tibial rotation during knee flexion, as also preoperative and postoperative at 2 years follow-up clinical scores have been acquired.
Results
Preoperative rotation pattern were superimposable for all three cohorts of patients. All patients showed an average external rotation of 12±5° in extension. In the first part of flexion (0°-30°) screw-home mechanism was present with an internal tibial rotation of about 8°. After this the rotation of the tibia remained stable within 1° up to 120°.
After implant, compared to preoperative status, all patients had less external rotation in extension, (6.5±7.1° for First; 4.6±5.3° for Gemini; 5.6±7.2° for Noetos), even if this reduced external rotation did not change significanlty with respect to preoperative conditions (Fig.2). Screw home mechanism was distributed in a larger flexion range (0–90° for HLS Noetos, 0–100° for FIRST, 0–110° for Gemini) with respect to native knee.
Pre-operative translation of medial and lateral compartments of femur had similar pattern in all three cohorts
After implant, knee was in a more anterior position in extension, especially in the medial compartment.
For all implants femoral position in flexion (range 90–120°) was similar to native knee.
After implant all clinical scores were significantly improved (p<0.001). No differences were found between the three cohorts both in the pre-operative and post-operative values.
CONCLUSION
All clinical scores, of the three cohorts of patients, were significantly improved postoperatively compared to the preoperative values.
Rotating platform MB TKA reproduced femoral translation and tibial rotation postoperatively compared to preoperative knees, despite design variations. Moreover, no superiority of one design over another in clinical function was observed.
