Robotic knee surgery makes it possible to adopt different alignment philosophies in total knee arthroplasty. The classical operation where the knee is placed in a neutral manner, the so called mechanical alignment, has been used for decades. The kinematical alignment has recently won popularity. With this technique the focus is to render the natural knee anatomy even if this means to end up with a varus or valgus position. In this study, the investigators will compare the mechanical alignment and kinematical alignment and test the patients clinically and with a special CT scan to see if this technique gives equal or better longevity of the implants.

Mechanical alignment (MA) has for many years been the most used surgical alignment technique in total knee arthroplasty (TKA). This means that regardless of constitutional native anatomy (i.e. valgus or varus), one strives to achieve a neutral coronal knee axis on postoperative x-rays (Hip-Knee-Ankle angle, HKA). To achieve MA, the cuts are made perpendicular to the mechanical axis, and subsequent soft tissue balancing is performed if necessary. However, many patients do not have a neutral knee alignment before they develop osteoarthritis. Several authors therefore advocate the personalized alignment (kinematic, KA or functional alignment, FA), where the aim is to restore the patient's original pre-arthritis anatomy and joint line. This means that tibial component placement in varus or valgus is accepted, despite the possible result of a postoperative non-neutral HKA axis. Studies indicate that good clinical results can be achieved in terms of range of motion (ROM) and patient reported outcome measures (PROMs) with these techniques, but it has not been tested properly in terms of activity measurements, strength testing or migration of implants. There is diversity in the literature regarding whether tibial component with too much deviation from a neutral axis can lead to increased migration and eventually aseptic solution. To date, only a few trials, with diverging results, have assessed migration of the implants implanted with KA or FA. The methods are so far perceived as controversial, despite the widespread use.

KA or FA can be performed by manual conventional surgery; however, the newly introduced robotic assisted surgery probably yields higher accuracy and precision of the cuts during surgery. This makes robotic assisted surgery well suited for personalized surgery. Yet, it is claimed that because of diversity of the different features for planning and executing the surgery, each system should be evaluated separately, and not as a group. The investigators therefore planned this study to assess the efficacy of robotic assisted surgery comparing MA and personalized alignment (PA) techniques.

Aims of the trial

1. Evaluate the clinical outcomes of patients who have had TKA with PA and compare it with conventional MA.
2. Analyse and compare the in vivo stability over time of TKA operated with PA vs. MA using CT- based radiostereometric analysis (CT-RSA).
3. Evaluate the postoperative position of the implants using two different alignment philosophies.

Objective Perform TKAs on patients using ROSA® Knee System (Zimmer Biomet, Warsaw, Indiana USA) robotic assisted surgery and randomize the patients to either PA or MA.

Materials and methods

A multiple blinded randomized controlled parallel superiority trial will be performed, where the patients, study nurse, statistician and physiotherapists are blinded to the surgical method (PA or MA). The study will include 152 patients. The study adheres to the consort statement.

Surgery All surgeons involved in the trial are experienced knee surgeons. The surgeons have received thorough tutoring in the use of the ROSA Knee System and the Persona TKA, and both alignment techniques have now been adopted in our standard treatment of end stage OA. The learning curve of robotic assisted surgery is probably very small, and more related to time spent on the procedure rather than placement of the implants. The placement of the tibial implant will be restricted in the coronal plane to maximum 5 degrees of varus and 2 degrees of valgus. In sagittal plane, the slope will be limited to between 0-10 degrees.

The Persona TKA implant although contemporary, is a well-documented implant with very low migration.

The MA and PA techniques are well known and already used in a widespread fashion all around the world. Several clinics in Norway have also adopted the methods.

Implantation of tantalum markers in bone and polyethylene has been performed for more than 40 years in numerous studies without any known complications.

Known but rare complications to robotic surgery are fractures at the site of insertion of the bone pins, and pin site infections. In elderly or osteoporotic patients, the surgeons will consider using unicortical engagement of the pins. Concerning infections, all the default precautions in the OR will be taken, such as preoperative and postoperative administration of antibiotics, strict sterile procedures etc.

Inclusion Criteria:

• femoro-tibial or patello-femoral osteoarthritis (Kellgren-Lawrence, K-L) grade 2-4 with persistent pain, referred to Kristiansund Hospital for primary TKA

Exclusion Criteria:

• serious psychiatric disorders
• dementia
• drug abuse
• patients not able to speak and read Norwegian language making them noncompliant or unable to perform an informed consent
• Patients with ongoing cancer therapy
• Patients with ASA (The American Society of Anesthesiologists physical status class risk stratification system) classification >3
• Patients in the need of walking aid devices
• Patients in need of primary revision arthroplasty or more than 15 degrees of varus or 5 degrees of valgus on preoperative HKA images.

Upon proper request to the corresponding author data will be shared anonymously.

After publication and for 2 years

Patient, nurses and physiotherapists are blinded. Surgeon is of course not blinded.