A controlled study, comparing computer- and conventional jig-assisted total knee replacement in six cadavers is presented. In order to provide a quantitative assessment of the alignment of the replacements, a CT-based technique which measures seven parameters of alignment has been devised and used. In this a multi-slice CT machine scanned in 2.5 mm slices from the acetabular roof to the dome of the talus with the subject's legs held in a standard position. The mechanical and anatomical axes were identified, from three-dimensional landmarks, in both anteroposterior and lateral planes. The coronal and sagittal alignment of the prosthesis was then measured against the axes. The rotation of the femoral component was measured relative to the transepicondylar axis. The rotation of the tibial component was measured with reference to the posterior tibial condyles and the tibial tuberosity. Coupled femorotibial rotational alignment was assessed by superimposition of the femoral and tibial axial images. The radiation dose was 2.7 mSV. The computer-assisted total knee replacements showed better alignment in rotation and flexion of the femoral component, the posterior slope of the tibial component and in the matching of the femoral and tibial components in rotation. Differences were statistically significant and of a magnitude that support extension of computer assistance to the clinical situation.

Purpose Total knee arthroplasty with functional alignment uses pre-resection balancing to determine component position within the soft tissue envelope to achieve balance and restoration of native joint obliquity. The purpose of this study was to assess the balance achievable with a mechanical axis alignment and kinematic axis alignment plan, and the subsequent balance achievable after adjustment of the component position to functional alignment. Methods A prospective cohort of 300 knees undergoing cruciate retaining total knee arthroplasty were included in this study. Of these, 130 were initially planned with mechanical alignment (MA) and 170 with kinematic alignment (KA). Maximal stressed virtual gaps were collected using an optical tracking software system. The gaps were measured medially and laterally in flexion and extension. Following assessment of balance, implant position was adjusted to balance the soft tissues in functional alignment (FA) and the maximal gaps reassessed. Gaps were considered to be balanced when within 2 mm of equality. Incidence of balance within each cohort was compared to independent samples proportions test. Results Functional alignment obtained significantly better balance in extension, medially and overall than both MA and KA alignment without soft tissue release (p < 0.001). Overall balance was observed in 97% of FA knees, 73% of KA knees and in 55% of MA knees. The difference between KA and MA was also significant (p = 0.002). Whilst there was no difference observed in balanced achieved or limb alignment when FA was planned with either MA or KA, the joint line obliquity was maintained with an initial KA plan. Conclusion Functional alignment more consistently achieves a balanced total knee arthroplasty than either mechanical alignment or kinematic alignment prior to undertaking soft tissue release. Utilising an individualised KA plan allows FA to best achieve the stated goals of maintaining joint line plane and obliquity. Level of evidence Level III: retrospective cohort study.

Introduction: The use of robotic technology is becoming a well-recognized alternative to conventional total knee arthroplasty (TKA). The quantitative soft tissue information generated in robotic surgery can be used to balance the knee and achieve functional alignment (FA) of the components. This paper describes a novel FA technique using an individualized preoperative plan that is then adjusted to achieve soft tissue balance. Materials and Methods: We report on surgical technique, indications, considerations, and complications after our experience of performing 650 functionally aligned TKAs. We collected 2-year patient reported outcomes on 165 TKAs in this series (165 of 193 TKAs have reached 2 years follow-up in the series of 650 TKAs; 85% follow-up rate). Results: We found significant postoperative improvements with few infections and no revisions for mechanical reasons 2 years after surgery with this technique. Patients had improved knee range-of-motion (105 degrees° flexion preoperatively vs. 125 degrees flexion postoperatively; P<0.001), higher Forgotten Joint Scores (17 preoperatively vs. 77 postoperatively; P<0.001), improved Oxford Knee Scores (22 preoperatively vs. 43 postoperatively; P<0.001), higher KOOS Jr scores (48 preoperatively vs. 88 postoperatively; P<0.001) and lower visual analogue score pain scores (70 preoperatively vs. 12 postoperatively; P<0.001) 2 years postoperatively. Discussion: The described surgical technique is a promising method for conducting a robotic TKA. Benefits of FA include improved efficiency with preresection balancing, reduced soft tissue releases compared with a mechanical alignment technique, and accurate bony cuts with robotic assistance. Further studies are required to compare this technique with established methods to determine any differences in outcomes.