Condition category
Musculoskeletal Diseases
Date applied
Date assigned
Last edited
Prospectively registered
Overall trial status
Recruitment status
No longer recruiting

Plain English Summary

Background and study aims
Osteoarthritis of the knee is a common condition that affects ~25% of the population over the age of 50. It occurs when there is damage to the knee joints that the body isn’t able to repair. The exact cause is not known, but there are a number of factors thought to increase the risk of developing the condition. Symptoms include pain while walking (particularly when climbing the stairs or walking uphill), knees ‘giving way’ or difficulties in straightening the legs. The most common treatment option for osteoarthritis of the knee is a knee replacement. There are currently two main forms of knee replacement used, total knee replacement and unicompartmental knee replacement (used when only one side of the knee joint is damaged). Total knee replacement involves replacing both sides of the knee joint with metal implants separated by a plastic spacer or bearing. Unicompartmental knee replacement involves replacing only the side of the knee joint that is damaged, with smaller metal implants used to replace that side. Total knee replacement successfully provides pain relief in around 80% of cases, but the knee joint never feels ‘normal’ and patients often find that they can’t do more physically demanding activities. Several studies have shown that 10-20% of patients are dissatisfied with the results of their total knee replacement surgery. In comparison, patients who undergo unicompartmental knee replacement surgery tend to have more normal walking patterns and a more normal feeling knee with better function than if they had had a total knee replacement. However, it is estimated that only 25% of patients have osteoarthritis on only one side of the knee and are therefore eligible for the surgery and, as it’s a complex procedure, many surgeons do not offer it as an option. Recently robotic assistive technology has been introduced to help surgeons perform unicompartmental knee replacement. The team at Glasgow Royal Infirmary have used this technology and found that implants are placed more accurately using it and that patients recover from surgery faster and, at least initially, have better outcomes. A natural extension of the unicompartmental knee replacement technique would be to use two unicompartmental knee replacements implanted at the same time on either side of the same knee joint – this is called bi-unicompartmental knee replacement. This technique would allow surgeons to leave knee ligaments intact and replace only the damaged parts of the joint rather than removing the whole knee joint as occurs with total knee replacement. We believe that this surgical option would allow patients to walk more normally (a normal gait) and give them a significantly more ‘normal’ feeling and acting knee than with a conventional total knee replacement. The purpose of the study is to determine if robotically assisted bi-unicompartmental knee replacement allows patients to walk with a more normal gait than is achieved with a traditional total knee replacement.

Who can participate?
Patients that have osteoarthritis on both sides of the knee but have intact knee ligaments.

What does the study involve?
Patents are randomly placed into one of two groups. Those in group one undergo standard total knee replacement surgery while those in group two undergo robotically assisted bi-unicompartmental knee replacement. The progress of each patient will then be followed up after 3 months, and then after 1, 2, 5 and, finally, ten years, after surgery.

What are the possible benefits and risks of participating?
Robotic assisted bi-unicompartmental knee replacement is a new technique and only around 20 cases have been undertaken using this technology worldwide. We therefore cannot tell how well this surgery will perform in the long term. The most significant risks for patients undergoing knee replacement surgery are infection within the new joint and in the longer term wearing out of the implant. We do not think that the risk of infection will be any higher for patients who receive robotic assisted bi-unicompartmental knee replacement. We cannot predict how long robotic bi-unicompartmental knee replacement knee implants will last as the technique is too new. In addition, patients that take part in this study will have at least one CT scan of their knee (some patients will have two CT scans). This will involve additional exposure to X-rays.

Where is the study run from?
Glasgow Royal Infirmary, Scotland, UK

When is the study starting and how long is it expected to run for?
August 2014 to August 2027

Who is funding the study?
Medical Research Council (UK)

Who is the main contact?
Dr Iain Anthony
Dr James Doonan (added 04/10/2019)

Trial website

Contact information



Primary contact

Mr Mark Blyth


Contact details

Orthopaedic Research Unit
Glasgow Royal Infirmary
Gatehouse Building
Castle St
G4 0SF
United Kingdom



Additional contact

Dr James Doonan


Contact details

Gatehouse Building
Glasgow Royal Infirmary
82 Castle street
G4 0RH
United Kingdom

Additional identifiers

EudraCT number number

Protocol/serial number

1.1 18th Sept 2013

Study information

Scientific title

Explanatory comparative study of conventional total knee arthroplasty versus robotic assisted bi-unicompartmental knee arthroplasty



Study hypothesis

We hypothesise that robotic assisted Bi-UCKA surgery undertaken in appropriately selected patients can offer improved knee kinematics and proprioception in comparison to that afforded by TKA. Furthermore we hypothesise that accurate positioning of implants by robotic assistive technology will improve implant survivorship in Bi-UCKA to the levels achieved with TKA and UKA.

Ethics approval

West of Scotland Research Ethics Committee 4 – approval pending

Study design

Randomised Controlled Trial

Primary study design


Secondary study design

Randomised controlled trial

Trial setting


Trial type


Patient information sheet

Not available in web format, please use the contact details below to request a patient information sheet


Osteoarthritis of the knee


Patients will be randomised to receive either a standard total knee replacement or a robotically assisted bi-unicompartmental knee replacement. Randomisation will be via an online web interface and we will stratify by surgeon. Follow- will occur over a 10 year period at the following intervals (3 months, 1,2,5 and 10 years).

Intervention type



Not Applicable

Drug names

Primary outcome measure

Percentage of patients with a bi-phasic (normal) moment curve during gait (level walking) measured at 1 year.

Secondary outcome measures

1. Biomechanical performance: Gait during stair climb/descent and lunge, functional activity assessment (using electrogoniometers) at 1 year
2. Activity: Overall daily activity levels, maximum sport/physical activity, functional activity test times (stair climb, timed up and go) 1,2,5 and 10 years
3. Impairment: Range of motion, proprioception, quadriceps strength (short term outcome) and progression of OA in contralateral knee (long term outcome) at 1,2,5 and 10 years
4. Clinical Outcomes: Clinical knee scores (Oxford Knee Score and American Knee Society Score), pain, analgesic use, complications, implant fixation and satisfaction at 1,2,5 and 10 years
5. Safety profile: Determined by revision rate, adverse events, robotic system errors and accuracy of implantation at 1,2,5 and 10 years
6. Accuracy of surgical implantation, determined by post-op CT analysis, at 1 year

Overall trial start date


Overall trial end date


Reason abandoned (if study stopped)


Participant inclusion criteria

1. Patients with medial and lateral compartment osteoarthritis of the knee with intact cruciate ligaments
2. Patients willing and able to give informed consent

Participant type


Age group




Target number of participants


Participant exclusion criteria

1. Patients with osteoarthritis limited to one compartment of the knee
2. Patients with rheumatoid arthritis
3. Patients with medial or lateral subluxation of the tibia on the femur
4. Patients with a varus or valgus deformity greater than 15º
5. Patients with a flexion contracture greater than 10º
6. Patients with rupture of either the ACL or PCL
7. Active or recent local infection
8. Patello-femoral OA greater than Kellgren and Lawrence grade III
9. Patients who have had previous surgery to the knee which may impact on the outcome of TKA or bi-unicompartmental knee arthroplasty
10. Patients with significant disease in other joints which might impact on their gait
11. Patients unable to give informed consent

Recruitment start date


Recruitment end date



Countries of recruitment

United Kingdom

Trial participating centre

Orthopaedic Research Unit
G4 0SF
United Kingdom

Sponsor information


NHS Greater Glasgow and Clyde (UK)

Sponsor details

NHS GGC R&D Office
Western Infirmary
Dumbarton Road
G11 6NT
United Kingdom

Sponsor type

Hospital/treatment centre



Funder type

Research council

Funder name

Medical Research Council (MRC) (UK) MRC EME (12/12/12)

Alternative name(s)

Funding Body Type

Funding Body Subtype


Results and Publications

Publication and dissemination plan

Planned publication in a high-impact peer-reviewed journal

Intention to publish date


Participant level data

Not provided at time of registration

Basic results (scientific)

Publication list

Publication citations

Additional files

Editorial Notes

27/04/2020: The recruitment start date was changed (as a correction of an editorial error) from 01/08/2018 to 01/09/2014. 24/04/2020: Internal review. 04/10/2019: The following changes were made to the trial record: 1. The recruitment end date was changed from 01/08/2014 to 01/08/2018. 2. The overall end date was changed from 01/08/2027 to 01/08/2028. 3. The intention to publish date was added. 4. A public contact was added. 5. The plain English summary was updated to reflect these changes.