Study to Evaluate Patient Outcomes and Safety and Effectiveness of Robotic Assisted Unicompartmental Knee Replacements Versus Conventional Unicompartmental Knee for Subjects With Primary Arthritis of the Knee Joint Involving One (UKA) Compartment (Medial or Lateral)

The overall aim of this trial is to compare functional and patient-reported outcomes and to assess the safety and effectiveness and long-term performance of the Smith+Nephew Robotic Systems for Unicompartmental Knee Replacements to non-robotic, conventionally implanted Unicompartmental Knee Replacements.

There are two phases for this study:

* Phase 1: The primary objective of this study is to compare Forgotten Joint Score (FJS) 12-month patient reported outcome scores, in patients undergoing robotic assisted Unicompartmental Knee Replacements as compared to those undergoing conventionally implanted Unicompartmental Knee Replacements
* Phase 2: The primary objective of Phase 2 of this study is evaluate the revisions rates of the JII UK unicompartmental knee at 10 years

Research participants / locations:

280 research participants will be recruited from up to 15 sites in the UK, US and Europe. There will be 140 participants undergoing robotic assisted Unicompartmental Knee Replacements and 140 participants undergoing non-robotic, conventionally implanted Unicompartmental Knee Replacements.

Eligibility Criteria:
Inclusion Criteria:

1. The subject or, legal guardian (in the case of difficulty reading and/or writing,) must provide written informed consent, including consent for any incidental findings to be reported to their General Practitioner (reference section 7.5).
2. Subjects eighteen (18) years and older and considered to be skeletally mature at the time of surgery.
3. Willing and able to make all required study visits (for both phases of the study, up to 10 years postoperatively).
4. Able to follow instructions and deemed capable of completing all the study questionnaires.
5. The subject has primary arthritis of the knee joint involving one (UKA) compartment (medial or lateral), and is suitable for JOURNEY II UK in the opinion of the surgeon.
6. The subject can, and is willing to have radiographic images taken to include non-standard of care imaging (for long leg radiographs at follow up).

Exclusion Criteria:

1. Contraindications or hypersensitivity to the use of the JII UK implant components (e.g., oxinium femoral, Tibial Baseplate, XPLE insert).
2. The subject is contraindicated for the use of robotic-assisted knee arthroplasty.
3. Participation in the treatment period of another clinical trial within thirty (30) days of the preoperative visit, or during the study.
4. Women who are pregnant, nursing, or of child-bearing potential who are not utilizing highly effective birth control measures.
5. Any subject that meets the definition of a Vulnerable Subject per ISO 14155 Section 3.55.
6. Subjects who have participated previously in this trial through UKR on other knee.
7. The subject is listed for a simultaneous bilateral knee arthroplasty
8. Subjects experiencing severe pain in both knees and consequently anticipating bilateral surgery within 12 months.
9. The subject requires a complex implant or any other implant, other than a standard UKR (e.g. stems, augments or custom-made devices)
10. Subject has an active infection or sepsis or has had previous intra-articular infections
11. Subjects with a history of poor compliance with medical treatment
12. The subject, in the opinion of the investigator, has a neuromuscular disorder (e.g. Charcot joint) that prohibits control of the index joint
13. Cases where bone stock is poor and would therefore make the procedure unjustifiable
14. Subjects with a BMI of 40 or higher
15. Those with incomplete/sufficient soft tissue around the joint.
16. Subjects with Conditions that tend to place increased loads on implants such as age, weight, and activity level, which are incompatible with a satisfactory long-term result.
17. Subjects with a medical or physical condition that, in the opinion of the Investigator, would preclude safe subject participation in the study.