Total versus Robotic Assisted Unicompartmental Knee Replacement (TRAKER)

This group will receive a conventional manual Triathlon (Stryker) TKA with a cruciate retaining polyethylene insert. The surgeon will then make bone cuts using a manual jig and a hand held saw to prepare the bone surfaces for the implant. A measured resection technique will be employed with a three degree tibial slope. The surgeon will use a conventional jig alignment technique for intramedullary referencing for the femur and extra medullary referencing for the tibia. Once the implant is in position the knee is then balanced by the "feel" though a range of movement and soft tissue releases will be performed as required to balance the knee in flexion and extension.

Triathlon (Stryker) TKA with a cruciate retaining polyethylene insert.

• Totaler Kniegelenkersatz

This group will receive the cemented Restoris MCK (Mako, Stryker) with a highly crossed linked (X3) polyethylene insert through a less invasive to the knee joint. Instead of using a manual jig and a hand held burr will be used to prepare the bone surfaces for the implant, the MAKO robotic arm will be used by the surgeon to cut the bone at the required alignment. The information from the CT scan will be used to create a 3D model of the patient's bony anatomy and will used to plan the positioning of the implant. Once the trackers are in place registration of the knee joint surface is performed. The specified bone cuts are then performed using the robotic arm, aiming to gap balance the knee through a full range of movement.

The robotic-arm will be used to position a partial knee arthroplasty.

• Roboterarm-assistierte partielle Knieendoprothetik

Knee specific functional outcome measure. It consists of twelve questions assessed on a Likert scale with values from 0 to 4, to give a summative score. This is measured on a scale from 0 (worst) to 48 (best).

The Oxford knee score is a knee specific functional outcome measure. It consists of twelve questions assessed on a Likert scale with values from 0 to 4, to give a summative score. This is measured on a scale from 0 (worst) to 48 (best). The additional Activity and Participation Questionnaire is a higher functioning supplementary questionnaire consisting of a further eight questions scored 0 (worst) to 4 (best).

Knee specific functional outcome. It uses a five-point Likert response format, consisting of 12 equally weighted questions with the raw score transformed to range from zero (worst) to 100 (best) points.

Patient satisfaction will be assessed following surgery by asking four questions with a different focus:

i. "Overall how satisfied are you with the results of your knee replacement surgery?" ii. "How satisfied are you with the results of your knee replacement surgery for improving your ability to do housework or yard work (such as cooking, cleaning, or gardening and raking leaves)?" iii. "How satisfied are you with the results of your knee replacement surgery for improving your ability to do recreational activities (such as taking walks, swimming, bicycling, playing golf, dancing, going out with friends)?" iv. "How satisfied are you with the results of your knee replacement surgery for relieving your pain?" The response to each question will be recorded using a four point Likert scale: very satisfied, somewhat satisfied, somewhat dissatisfied, and very dissatisfied.

Quality of life will be assessed using the EQ-5D-3L general health questionnaire which evaluates five domains (-5D), which include: mobility, self-care, usual activities, pain/discomfort, and anxiety/depression. This is a two page questionnaire that consists of five dimensions, with the responses recorded at three levels (3L) of severity (no problems; some problems or extreme problems). The utility index is on a scale of -0.594 to 1, where 1 represents perfect health and a negative value represents a state perceived as worse than death.

The second page consists of a standard vertical 20cm visual analogue scale (EQ-5D VAS) which is transformed to a scale of 0 (worst) to 100 (best) measuring current health-related quality of life. Each patient's health state, derived from the EQ-5D, will be measured before and after their surgery to determine the change in their health gain or loss after their knee replacement surgery.

A goniometer will be used to measure range of movement by a blinded researcher prior to surgery (baseline), at discharge (immediately post surgery prior to discharge home) and at review appoints. Three measurements will be recorded for extension and flexion of the knee and an average will be documented.

Cost utility analysis will be undertaken to establish the incremental cost effectiveness ratio (ICER). Each patient's health state, derived from the EQ-5D, will be measured before and after their surgery to determine the change in their health gain or loss after their knee replacement surgery. The health state will then be multiplied by the time spent in that state to derive the QALYs gained or lost. The cost per QALY will then be calculated by dividing the cost of the procedure by the QALYs gained after total knee arthroplasty (intervention). A health service resource use questionnaire will be completed by the patient at the 3, 6 and 12 month research assessment. The questionnaire collects data on primary, secondary and community care and associated with the knee replacement over the previous months. Inpatient and surgical data will be collected on the case report forms (CRF's) and complications will be recorded at each visit.

Knee stability (stress testing) and power (power rig) will be measured. A stress will be applied to the knee and the joint space opening will be measured using an ultrasound probe which will be used as a marker of knee stability. The power of the knee joint will be assessed using a standardise power rig Specific assessment of the patient's power output will be evaluated by a Leg Extensor Power Rig (Nottingham, UK), well validated for use with this population group.

The Hospital of Special Surgery Expectation questionnaire is a validated measure of patient pre-operative expectations of surgery. The level of patient expectation is indicated on a 5 point Likert scale as 'very important', 'somewhat important', 'a little important', 'I do not expect this' or 'this does not apply to me'. After surgery patients will complete a similar expectation questionnaire, but are asked whether the same expectations had been fulfilled, which again is assessed on a 5 point Likert scale as: 'greatly', 'a lot', 'a little', 'I did not expect this' or 'this did not apply to me'.