Biomechanical Assessment of a High Congruency Knee Bearing

This is a double blind randomised controlled trial. The aim of the study is to compare the biomechanical performance of knee replacements with different bearing designs to that of a native or natural knee. The hypothesis is that a mobile bearing design with a high congruency bearing will allow the knee replacement to work more like the native knee and give more natural movement when carrying out everyday tasks.

The current evidence on whether fixed or mobile, low or high congruency bearings give the most natural movement or provide better knee function is sparse. By carrying out a randomised controlled trial including a cohort of healthy individuals and taking indepth functional assessments of a number of different common activities of daily living it should be possible to show what level of functional outcome the three bearings being used give.

Ninety patients scheduled for total knee arthroplasty under the care of four consultant orthopaedic surgeons at the Golden Jubilee National Hospital who meet the inclusion/exclusion criteria will be recruited and randomised into one of the three study groups (low congruency fixed bearing, high congruency fixed bearing or high congruency mobile bearing).

Invitation letters and participant information sheets will be sent out to suitable patients prior to their preoperative consultation. They will be approached at their consultation visit to seek consent to take part in the study. At this time they will be given the opportunity to ask questions about the study. Following written consent, the patient will be randomised using sequentially numbered opaque sealed envelopes. A nominated person, independent of the approach and consent of the patient, will sign and open the envelope and inform the hospital research team of the randomisation. The patient and the university research team will be blinded to randomisation. For each patient arrangements will be made for their preoperative movement analysis testing session. Subsequently, they will have their surgery and rehabilitation prior to discharge according to standard hospital practice. Participants will then return to the hospital for standard follow up appointments at six weeks and one year. At the same time arrangements will be made for them to attend their follow up movement analysis sessions. Clinical data recorded at preoperative assessment and postoperative follow up appointments, such as range of movement, Oxford Knee Score, patient satisfaction, EQ5D and radiographic measurements will be collected for study patients to compare to the functional outcomes measured during the movement analysis sessions.

Participants will be asked to attend movement analysis testing sessions at the University of Strathclyde in Glasgow on three separate occasions; preoperatively, at 4 to 8 weeks postoperatively and at one year postoperatively. Each of these sessions will follow the same procedure. Prior to data collection, participants will be asked to change into the tight fitting shorts and vest tops provided (male participants will be asked to forego the vest tops) in the changing rooms within the laboratory facility. Measurements of weight and body dimensions will be taken (required for processing the data) and then reflective markers will be attached to the legs, pelvis, torso and arms. These will be attached using toupee tape or elasticated straps as required. They will be asked to wear a headband (provided) with another four markers attached on their head. There will be eight activities of daily living (ADLs) in the test protocol, which will be carried out in one of two laboratories; one a standard motion capture laboratory (S) and the other in a laboratory with a CAREN system (Motek Medical, Amsterdam, Netherlands) which consists of a virtual reality screen, moving platform and treadmill (M). The ADLs will be:

1. Level walking in a straight line (S)
2. Level walking along a curved pathway (S)
3. Sit to stand to sit (S)
4. Sit to stand to walk (S)
5. Ascending and descending stairs (S)
6. Getting into and out of a car (S)
7. Single leg balance (M)
8. Walking on an incline (M)

Participants will be asked to perform each ADL in a fixed order several times until three good sets of data have been collected. Participants will be given instructions on how to perform each ADL prior to performing it and will be asked to practice them before data is collected. During the demanding tasks, participants will be supported by a harness to prevent falls and hand rails will be provided on the test staircase. Participants will be allowed rest breaks between each ADL and during tests if required. At the end of each task the participant will be asked a set of questions about how they found performing the task. On completion of the test protocol, the markers will be removed, the participant will get changed and will be free to leave. It is expected that each testing session will last up to 4 hours.

The three good data sets will be averaged to reduce variability. Statistical analysis will be carried out using an appropriate statistical package to determine if any significant differences exist in the data between the three patient groups and between the patient groups and the control group. All data will be tested for parametricity. Parametric data will be analysed using analysis of variance (ANOVA) tests with post hoc Bonferroni correction. If the data is found to be nonparametric, KruskalWallis tests will be used. For data over time appropriate repeated measures analysis will be used. A 95% confidence level will be used throughout.

The study is being funded over a three year period. The first year involves the set up and development of the protocol and the recruitment of the control participants. It is hoped that the recruitment of the patients will start nine months into the study period and will take 25 months to complete the data collection and analysis. This will allow two months for the reporting of the study.