Navigated Versus Convention Total Knee Arthroplasty
Condition: Arthroplasty, Replacement, Knee; Surgery, Computer-Assisted
Study type: Interventional

Summary: 
      The aim of this single blinded randomised control trial study was to assess the accuracy of
      implantation of components and the clinical outcome and complications with the iNAV
      electromagnetic navigation system compared with conventional techniques. Secondary outcome
      measures include Patient reported outcome measures (PROMS) and rates of revision surgery up
      to 10 years post operatively.
    

Detailed description: 
      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.

      Primary outcome measurement Post-operative CT scans were used to determine the accuracy of
      implantation. CT scan analysis was conducted using Mimics 12.0 software (Materialise, Leuven,
      Belgium). Measurements of the femoral and tibial component position in the coronal
      (varus/valgus), sagittal (flexion/extension) and axial (rotational) planes were made. The
      overall mechanical alignment was also calculated from the addition of the femoral and tibial
      coronal angles. The combined component rotation was calculated from the addition of the
      femoral and tibial rotation angles. The rotations were measured using the methods detailed in
      Berger et al (1998). In the coronal plane the investigators aimed to position both femoral
      and tibial implants at 90° to the mechanical axis. In the sagittal plane the investigators
      aimed to position the femoral component with a 5° slope relative to the mechanical axis, in
      line with the anterior cortex of the distal femur. The tibial component was aimed to be
      positioned at a 7° slope, as per the manufacturer's guidelines. For femoral rotation the
      investigators aimed to implant the femoral component in line with the surgical
      trans-epicondylar axis of the femur. The reference for tibial rotation was a line from the
      geometric center of the tibia to the center of the tuberosity. Rotational measurements were
      calculated from a perpendicular line drawn from the posterior surface of the implant. As the
      tuberosity is 18° externally rotated, the investigators considered an 18° internal rotation
      of the implant to be a neutral position. (No obvious deformities of the tibia or previous
      fractures were noted in the study cohort that could have influenced this value.) The
      investigators considered the desired mechanical axis alignment to be 0° with a range of ± 3°.

      Patient-Reported Outcome Measures and Revisions Participants were followed up for 10 years
      after surgery, with clinical assessments by a blinded independent assessor; range of motion
      (ROM) was determined using a hand-held goniometer, and knee-specific outcome measures
      included the American Knee Society Score (AKSS) and Oxford Knee Scores (OKS) and the SF 36
      score used as a general health measure (both physical and mental). Revision surgery was also
      assessed by analyzing the Scottish National Picture Archiving and Communication System. This
      image archiving system stores all imaging for patients undertaken in the National Health
      Service (NHS) in Scotland since 2008. It acts as a valuable resource for identifying patients
      lost to follow-up who have undergone revision surgery in other NHS hospitals in Scotland
      which may have not been identified.

      Statistics A power calculation was performed based in data provided by a randomized
      controlled trial using infra red optical tracking systems. Bathis et al reported 96% of
      patients with mechanical leg alignment within 3° of neutral using navigation compared to just
      78% with conventional instrumentation . In order to detect a difference of this magnitude
      with a power of 90% at alpha = 0.05, the investigators would require 82 patients per group,
      164 in total. As the primary outcome measure was based on post-operative CT scan the
      investigators anticipated a higher than average loss to follow-up for the primary outcome
      measure. The investigators therefore allowed an additional 25% for loss to follow-up, giving
      a total of 103 patients in each group.

      Statistical analysis was performed using SigmaPlot 11.0 (Systat Software Inc). To evaluate
      differences between the surgical groups either a two sample t test (normally distributed
      data) or a Mann Whitney test (non parametric data) was performed. A Chi Squared test was used
      to analysis the male: female ratio. A P value of less that 0.05 was considered significant.
    

Intervention name(s): Electromagnetically navigated total knee arthroplasty; Conventional total knee arthroplasty
Intervention type(s): Device; Device
Intervention description(s): The navigated group had surgery using the iNav portable EM navigation system (Zimmer GmbH, Winterthur, Switzerland and Medtronic, Minneapolis, MN, USA) and the definitive implant used was NexGen LPS implant (Zimmer Inc, Warsaw, IN, USA), a fixed-bearing bicruciate-sacrificing total condylar implant using traditional instrumentation with no patellar resurfacing; The conventional group received surgery using conventional instrumentation and jigs from the implant manufacturer (Zimmer Inc, Warsaw, IN, USA) and the definitive implant used was NexGen LPS implant (Zimmer Inc, Warsaw, IN, USA), a fixed-bearing bicruciate-sacrificing total condylar implant using traditional instrumentation with no patellar resurfacing
Allocation: Randomized
Intervention model: Parallel Assignment
Masking: Double (Participant, Outcomes Assessor)
Primary purpose: Treatment