Efficacy and Safety of NAVIO

Primary outcomes

1. Difference in planned and achieved alignment in degrees based on CT scan pre- and postoperatively (first 52 participants)

   Time frame: within 6 weeks pre-surgery and 6 weeks post-surgery

   Difference in preoperatively planned and postoperatively achieved alignment of both the femoral and tibial component of the prosthesis in the frontal, sagittal and coronal plane. Deviations (in degrees varus/valgus, flexion extension, and internal/external rotation) from calculated positions (of both components) to bony anatomic landmarks, used by NAVIO to align the prosthesis, will be obtained.

2. Difference in planned and achieved mechanical axis in degrees based on CT scan pre- and postoperatively (first 52 participants)

   Time frame: within 6 weeks pre-surgery and 6 weeks post-surgery

   Preoperatively planned and postoperatively achieved mechanical axis of the operated leg. The mechanical axis is defined as the angle between a line from the centre of rotation of the hip to the centre of the femoral component and a line from the centre of the tibial plateau to the centre of the ankle.

3. Difference in percentage of outliers of alignment on CT scan pre- and postoperatively (first 52 participants)

   Time frame: within 6 weeks pre-surgery and 6 weeks post-surgery

   Percentage of outliers in alignment (defined as > 3 degrees deviation from positions calculated by software) of the femoral and tibial components in frontal, sagittal and transverse plane.

4. Difference in percentage of outliers of mechanical axis based on CT scan pre- and postoperatively (first 52 participants)

   Time frame: within 6 weeks pre-surgery and 6 weeks post-surgery

   Percentage of outliers (defined as > 3 degrees deviation from neutral) in mechanical axis of the of the operated leg. The mechanical axis is defined as the angle between a line from the centre of rotation of the hip to the centre of the femoral component and a line from the centre of the tibial plateau to the centre of the ankle.

5. Mean change in the visual analogue scale scores

   Time frame: within 6 weeks preoperative, 24 hours post-surgery, day of discharge, 6 weeks post-surgery, 3 months post-surgery, 1 year post-surgery, 2 years post-surgery, 5 years post-surgery, 10 years post-surgery

   Comparison is made between the two study arms, a higher visual analogue pain score means a worse outcome

6. Mean change in the American Knee Society Score

   Time frame: within 6 weeks preoperative, 3 months post-surgery, 1 year post-surgery, 2 years post-surgery, 5 years post-surgery, 10 years post-surgery

   in a total of 50 points, stability, 25 points, and range of motion, 25 points. The maximum score of 100 points . Comparison is made between the two study arms. A higher American Knee Society Score means a better outcome

7. Mean change in the Oxford Knee Score

   Time frame: within 6 weeks preoperative, 3 months post-surgery, 1 year post-surgery, 2 years post-surgery, 5 years post-surgery, 10 years post-surgery

   Comparison is made between the two study arms, score between 0 and 48. Better score means better outcome

8. Mean change in the Lower Extremities Activity scale

   Time frame: within 6 weeks preoperative, day of discharge, 6 weeks post-surgery, 3 months post-surgery, 1 year post-surgery, 2 years post-surgery, 5 years post-surgery, 10 years post-surgery

   Comparison is made between the two study arms, score between 0 and 80. The minimal clinically important difference is 9 scale points. The lower the score the greater the disability.

9. Mean change in the The Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC)

   Time frame: within 6 weeks preoperative, 3 months post-surgery, 1 year post-surgery, 2 years post-surgery, 5 years post-surgery, 10 years post-surgery

   Comparison is made between the two study arms. Five items for pain (score range 0-20), two for stiffness (score range 0-8), and 17 for functional limitation (score range 0-68). The higher the score, the poorer the function

10. Difference in mechanical axis of the prosthesis between the two study arms based on Long-leg X-rays

    Time frame: within 6 weeks preoperative, 6 weeks post-surgery, 1 year post-surgery, 5 years post-surgery, 10 years post-surgery

    Post-operative (at 6 week visit) the baseline mechanical axis will be measured as the angle between a line connecting the center of the femoral head with the center of the knee and the line connecting the center of the knee with the center of the ankle.

11. Difference in positioning of the prosthesis between the two study arms based on Long-leg X-rays

    Time frame: within 6 weeks preoperative, 6 weeks post-surgery, 1 year post-surgery, 5 years post-surgery, 10 years post-surgery

    In order to measure positioning of the prosthesis (coronal alignment), long-leg, weight-bearing, standing anteroposterior and lateral X-rays will be made

12. Difference in wear between the two study arms based on Long-leg X-rays

    Time frame: within 6 weeks preoperative, 6 weeks post-surgery, 1 year post-surgery, 5 years post-surgery, 10 years post-surgery

    In the long term, wear can be roughly measured by measuring again the mechanical axis of the leg and comparing this with baseline mechanical axis and by measuring the distance between medial and lateral femoral condyles and medial and lateral tibial platform respectively.

13. Significant difference in length of hospital stay between the two study arms

    Time frame: 1 day of discharge from the hospital

    Length of hospital stay (in days) will be registered for both groups.

14. Operation Time

    Time frame: intraoperative (Time will be recorded from the moment of incision until bandage is being placed)

    Compare the duration of surgery between the two study arms

15. Significant difference in blood loss between study arms

    Time frame: Intra-operatively until 24 hours post-surgery. .

    Blood loss will be measured intra-operatively and up to 24 hours post-operatively.

    The amount of rinsing liquid will be subtracted from the total amount collected in the suction device to obtain the amount (ml) of intra-operative blood loss. The weight of grids and compresses will be measured post-operatively and dry weight will be subtracted from this value to obtain blood loss not collected in the suction device (1mg = 1ml).

    On day 2 post-operative, Hb and Ht will obtained.

16. Difference in adverse events

    Time frame: through study completion, an average of 10 years

    Complication registration will be done throughout the entire study period

17. Difference in frequency of infection

    Time frame: through study completion, an average of 10 years

    When infection is present, this will be noted on the complication registry form and appropriate action will be taken. Distinction will be made between superficial infections and deep infections.

18. Difference in frequency of trombo-embolic complications

    Time frame: through study completion, an average of 10 years

    Attention will be focused on clinical signs of deep vein thrombosis and pulmonary embolism.

19. Difference in frequency of wound problems

    Time frame: From day of surgery until 5 days post-surgery

    Persistent wound leakage will be registered. Persistent leakage is defined as leakage lasting 5 days after surgery.

20. Difference in frequency of loosening

    Time frame: through study completion, an average of 10 years.

    Loosening of tibial or femoral components of the prosthesis as seen on X-ray.