Navio is a new generation of computer navigation systems allowing intraoperative navigation of the bone cuts relative to both ligaments and skeletal axes, prior to bone removal. An improved accuracy is incorporated by the use of robotics in a burr for bone removal.

This study investigates whether this advanced technology leads to better clinical or radiostereometric results, by comparing one group operated with Navio to another group operated with conventional technique.

Background:

The scientific foundation of total knee replacement (TKR) surgery is incomplete. As a national governor of joint replacements, the Norwegian Arthroplasty Register is obligated to strict regulations, demanding high levels of evidence for implants and instruments utilized by Norwegian surgeons. It is well known that 15-20% of patients with a TKR, are dissatisfied. Nevertheless, only a small proportion of these patients have revision surgery.

In this randomized, clinical trial we will use the Journey II BCS total knee system, with a more native anatomical design, intended to improve the kinematics and functional outcomes by mimicking a native knee, with respect to geometry and its interplay with the ligaments and soft tissue envelope of the knee (i.e. the biomechanics; stability, joint line, off-set, sizing etc.). To achieve an optimal placement of the implant, the surgeon needs to assess a lot of information (experience) during the surgical procedure. To secure this process, and to make sure all aspects are taken into account, with respect to an optimal positioning and ligament balancing, the computer navigation technique may offer valuable input, with further enhancement of the accuracy and precision using precision tools like the Navio from Smith & Nephew. The Navio system combines robotics and computer navigation, and represents the newest technology within surgical robotics and haptics. This trial is important in the mandatory evaluation process needed, before introducing new technology into orthopaedic surgery, on a larger scale.

Methods:

The surgeons involved have been trained at a wet lab, and on saw bones, before utilizing this tool in a live setting. After the introduction period, the training will continue in a clinical setting until the surgeons have operated at least 20 Navio assisted cases each, followed by a pilot study of 10 patients. All patients will be randomized to either Navio or Conventional technique.

Surgical method: A tourniquet is used. All implant components are cemented (Palacos R+G bone cement is utilized 10 minutes after retrieval from a 4 degrees Celsius refrigerator). Standard para-patellar approach. ACL and PCL are removed. Closing of the wound and capsule in mid-flexion position, Quill for the capsule, Vicryl for the subcutaneous tissue, continuous overlapping mattress with Ethilon suture for the skin. No drainage. Wrapping of the entire limb with elastic dressings for the first 48 hours. Prophylactic antibiotics and anticoagulants are given. Tranexamic acid to reduce bleeding. Postop pain medication: gabapentin, acetaminophen, naproxen, femoral triangle nerve block (repeated next day if needed).

For the conventional group: The rotational alignment is set according to Whiteside's line, and intramedullary rods with 5, 6 or 7 degrees valgus, are selected for the distal femoral cut (dependent on pre-operatively measured angles on long radiographs (hip-knee-ankle). The entry hole of the rod is plugged with bone from the femur to reduce bleeding from the intramedullary canal. The tibial component (metal) is positioned with a 3 degrees posterior slope.

For the Navio group: The cuts are navigated to optimize ligament balance in flexion and extension, and adjusted for mid-flexion instability when needed. A difference of less than 4 mm between lateral and medial gaps is accepted when the laxity is on the lateral side, preferably in flexion. However, if the gap balancing technique suggests a deviation from mechanical alignment of more than 2 degrees of valgus or 4 degrees of varus, the suggestion is overruled by the mechanical alignment (maximum 2 degrees valgus, less than 4 degrees varus).

Sample size calculations: To detect a clinically important difference of 0.17 in the rate of "high responders" and "non-responders" (OMERACT-OARSI criteria) to the Navio, with a standard deviation of 20, power 80% and a 0.05 significance level, a total of 194 patients must be included in the trial (97 patients in each group). The calculations are based on data from a previous study, by Petursson et al, JBJS Am 2018. When 10% eventual drop-outs are taken into account, the total number of patients to be included is 214 (107 patients in each group).

A large number of patients is important, as the expected difference between the groups is small. A small difference may be less clinically relevant, however, may contribute to an overall better outcome for the patients in total. A small improvement of the tools combined with other small improvements may add up to be clinically important in the end. Small trials with no significant differences may disqualify important small improvements, thus stopping any further development in the field. Consequently, large clinical trials will be valuable.

A radiostereometric analysis constitutes a separate study of the trial. A clinically relevant difference of 0.1 mm between the groups will be detected with a standard deviation of 0.1, power 80% and significance level 0.05, if 17 patients are included in each group. Including eventual drop-outs and an expectation of some failures due to the technically challenging investigation method (the RSA), a total of 30 patients will be included in each group. RSA radiographs will be collected within the first week after the operation, at 3 months, 1 year, 2 years and 5 years follow-ups.

The trial is approved by the regional ethics committee and the data inspectorate of Norway.

Inclusion Criteria:

• Degenerative knee in need of a total knee arthroplasty
• Recruited from the hospital's waiting list
• Informed consent

Exclusion Criteria:

• Severe systemic illness
• Infections
• Severe neurological dysfunction
• Severe cancer disease
• Severe incompensated heart failure
• Severe incompensated lung disease
• Dementia
• Previous fracture or deformity of the limb, making the use of an intramedullary rod impossible (same side hip or ankle implant is not to be excluded if the rod unaffectedly reaches more than the first half of the femoral canal)

Participants are blinded as the Navio system will be switched on at all operations, the outcomes assessors, statisticians and co-researchers will not get access to the randomization information.