Randmised Controlled Trial Comparing Electromagnetically Navigated Versus Conventional Mechanically Aligned Total Knee Arthroplasty

Participants Patients were identified by members of the research team from TKA surgical waiting lists. Patients were invited to participate if they had osteoarthritis of the knee suitable for TKA, were able to provide informed consent, and were aged 18 or over. There were no specific limits imposed on the degree of preoperative coronal or sagittal deformity.

Randomization Overall, 272 patients were screened between July 2007 and August 2010. Of the 272 screened patients, 14 were excluded for other medical reasons, whereas 58 participants decided that they did not want to participate in a research study. The remaining 200 patients were recruited and consented to the study giving a recruitment rate of 74%. Patients were randomized in a 1:1 ratio to either conventional TKA or navigated TKA using a web based computer-generated random number table. Randomization was based on the order of their recruitment and stratified by surgeons to prevent surgeon bias and ensure that similar numbers of patients in each groups were allocated to each surgeon. Randomization was successful in assigning equal preoperative patient demographics between the groups.

Ethical Approval The study was approved by the Glasgow Royal Infirmary Local Ethics Committee and the University of Strathclyde Ethics Committee (07/S0704/6) and approved by the NHS GGC R&D department before commencement of the study.

Surgical Procedure All patients received a cemented posterior stabilized NexGen LPS Flex (Zimmer, Warsaw, Indiana, USA). Participants randomized to the conventional group received a TKA implanted using standard instrumentation, whereas those randomized to the navigated group had surgery using the iNav portable EM navigation system (Zimmer GmbH, Winterthur, Switzerland and Medtronic, Minneapolis, MN, USA). The iNav EM system is imageless and uses small reference frames attached to the femur and tibia which are readily incorporated in the primary incision. There is then a process of joint registration which maps the surface anatomy of the joint. All surgeries including joint surface registration were carried out by, or under the direct supervision of, one of two knee arthroplasty surgeons. Alignment targets were similar in both groups with a neutral HKAA and the aim to implant both femur and tibial components perpendicular to this in the coronal plane.

Ligament balancing was carried out using clinical assessment during the surgical procedure in both groups. In the navigated group, additional information was provided by the system with real-time feedback of the gap in mm between the femoral and tibial component and of the overall HKAA during varus and valgus stress.