Stryker (Netherlands)

Ligament balancing during total knee arthroplasty (TKA) often relies on subjective surgeon experience. Although instrumented tibial trays facilitate an objective assessment of intraoperative joint balance through quantification of intra-articular joint loads, postoperative clinical assessment of joint balance relies on passive stress tests quantifying varus–valgus joint laxity. This study aimed at correlating the intraoperative and postoperative metrics used to assess joint balance while also comparing joint loads obtained during passive assessment and active functional motions. Four experienced surgical fellows were assigned a fresh-frozen lower limb each to plan and perform posterior-stabilised TKA. An instrumented tibial insert measured intraoperative intra-articular loads. Specimens were then subjected to passive flexion–extension, open-chain extension, active squatting, and varus–valgus laxity tests on a validated knee simulator. Intra-articular loads were recorded using the instrumented insert and tibiofemoral kinematics using an optical motion capture system. A negative correlation was observed between mean intraoperative intra-articular loads and corresponding mean postoperative tibial abduction angle during laxity tests (medial: R = −0.93, p = 0.02; lateral: R = −0.88, p = 0.04); however, this was not observed for each specimen. Peak intra-articular load distribution for active squatting was lateral-heavy, contrasting to the medial-heavy distribution observed in passive intraoperative measurements, for all specimens. These aspects should be given due consideration while assessing intraoperative and postoperative joint stability following TKA.

In the total knee arthroplasty (TKA), kinematic benefits of the cruciate retaining (CR) mobile-bearing total knee arthroplasty are important. The current study aimed to assess how kinematic features of the anterior-posterior glide CR mobile-bearing TKA are different from those of normal knees or CR fixed-bearing TKA. Using a 3D/2D registration method, CT-derived 3D knee models were registered to sequential 2D X-ray images taken during knee flexion. Full range of knee flexion was 127.6° (SD 5.9) for normal knees, which was always larger than 110.8° (SD 14.0) of Nexgen CR fixed-bearing TKA or 108.1° (SD 8.0) of e.Motion CR mobile-bearing TKA. The rotation path of e.Motion CR mobile-bearing TKA demonstrated a small amount of internal or external femoral rotation from full extension over 40° flexion, steep increase in external femoral rotation from 40° to 90° flexion, then turned down in external rotation from 90° to full flexion. In contrast, Nexgen CR fixedbearing TKA did not demonstrate any consistent kinematic pattern among subjects. e.Motion CR mobile-bearing TKA can be more preferable because it showed a rotational turning point at 90° flexion that was comparable to normal knees’ rotational turning point at 80° flexion.