The kinematic alignment (KA) approach to total knee arthroplasty (TKA) has recently increased in popularity. Accordingly, a number of derivatives have arisen and have caused confusion. Clarification is therefore needed for a better understanding of KA-TKA. Calipered (or true, pure) KA is performed by cutting the bone parallel to the articular surface, compensating for cartilage wear. In soft-tissue respecting KA, the tibial cutting surface is decided parallel to the femoral cutting surface (or trial component) with in-line traction. These approaches are categorized as unrestricted KA because there is no consideration of leg alignment or component orientation. Restricted KA is an approach where the periarthritic joint surface is replicated within a safe range, due to concerns about extreme alignments that have been considered ‘alignment outliers’ in the neutral mechanical alignment approach. More recently, functional alignment and inverse kinematic alignment have been advocated, where bone cuts are made following intraoperative planning, using intraoperative measurements acquired with computer assistance to fulfill good coordination of soft-tissue balance and alignment. The KA-TKA approach aims to restore the patients’ own harmony of three knee elements (morphology, soft-tissue balance, and alignment) and eventually the patients’ own kinematics. The respective approaches start from different points corresponding to one of the elements, yet each aim for the same goal, although the existing implants and techniques have not yet perfectly fulfilled that goal

A technique for performing allograft-augmented revision total knee replacement (TKR) using computer assistance is described, on the basis of the results in 14 patients. Bone deficits were made up with impaction grafting. Femoral grafting was made possible by the construction of a retaining wall or dam which allowed pressurisation and retention of the graft. Tibial grafting used a mixture of corticocancellous and morsellised allograft. The position of the implants was monitored by the computer system and adjusted while the cement was setting. The outcome was determined using a six-parameter, quantitative technique (the Perth CT protocol) which measured the alignment of the prosthesis and provided an objective score. The final outcomes were not perfect with errors being made in femoral rotation and in producing a mismatch between the femoral and tibial components. In spite of the shortcomings the alignments were comparable in accuracy with those after primary TKR. Computer assistance shows considerable promise in producing accurate alignment in revision TKR with bone deficits

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

We performed a prospective, randomised controlled trial of unicompartmental knee arthroplasty comparing the performance of the Acrobot system with conventional surgery. A total of 27 patients (28 knees) awaiting unicompartmental knee arthroplasty were randomly allocated to have the operation performed conventionally or with the assistance of the Acrobot. The primary outcome measurement was the angle of tibiofemoral alignment in the coronal plane, measured by CT. Other secondary parameters were evaluated and are reported.

All of the Acrobot group had tibiofemoral alignment in the coronal plane within 2° of the planned position, while only 40% of the conventional group achieved this level of accuracy. While the operations took longer, no adverse effects were noted, and there was a trend towards improvement in performance with increasing accuracy based on the Western Ontario and McMaster Universities Osteoarthritis Index and American Knee Society scores at six weeks and three months. The Acrobot device allows the surgeon to reproduce a pre-operative plan more reliably than is possible using conventional techniques which may have clinical advantages.

Intra-articular resection of bone with soft-tissue balancing and total knee replacement (TKR) has been described for the treatment of patients with severe osteoarthritis of the knee associated with an ipsilateral malunited femoral fracture. However, the extent to which deformity in the sagittal plane can be corrected has not been addressed. We treated 12 patients with severe arthritis of the knee and an extra-articular malunion of the femur by TKR with intra-articular resection of bone and soft-tissue balancing. The femora had a mean varus deformity of 16° (8° to 23°) in the coronal plane. There were seven recurvatum deformities with a mean angulation of 11° (6° to 15°) and five antecurvatum deformities with a mean angulation of 12° (6° to 15°).

The mean follow-up was 93 months (30 to 155). The median Knee Society knee and function scores improved from 18.7 (0 to 49) and 24.5 (10 to 50) points pre-operatively to 93 (83 to 100) and 90 (70 to 100) points at the time of the last follow-up, respectively. The mean mechanical axis of the knee improved from 22.6° of varus (15° to 27° pre-operatively to 1.5° of varus (3° of varus to 2° of valgus) at the last follow-up. The recurvatum deformities improved from a mean of 11° (6° to 15°) pre-operatively to 3° (0° to 6°) at the last follow-up. The antecurvatum deformities in the sagittal plane improved from a mean of 12° (6° to 16°) pre-operatively to 4.4° (0° to 8°) at the last follow-up.

Apart from varus deformities, TKR with intra-articular bone resection effectively corrected the extra-articular deformity of the femur in the presence of antecurvatum of up to 16° and recurvatum of up to 15°.