Comparison of the JOURNEY II Bi-Cruciate Stabilised and GENESIS II Total Knee Arthroplasty in Performance and functional Ability. A Randomised Controlled Trial (CAPAbility). The study protocol.

Background: Osteoarthritis of the knee is a common condition that is expected to rise in the next two decades leading to an associated increase in total knee replacement (TKR) surgery. Although there is little debate regarding the safety and efficacy of modern TKR, up to 20% (Baker et al 2007) of patients report poor functional outcomes following surgery. This study will look at the functional outcome of two TKR; the JOURNEY II Bi Cruciate Stabilised knee, a newer prosthesis designed to provide guided motion and improve knee kinematics by more closely approximating a normal knee and the GENESIS II, a proven existing design. Aim: The aim of the CAPAbility study is to compare the change in patient reported outcome scores, of the JOURNEY II BCS and the GENESIS II from pre-operation to six months post-operation. Methods: CAPAbility is a pragmatic, blinded, two-arm parallel, randomised controlled trial recruiting patients with primary osteoarthritis due to have unilateral knee replacement surgery across two UK hospitals. Eligible participants (n = 80) will be randomly allocated to receive either the JOURNEY II or the GENESIS II BCS knee prosthesis. Baseline measures will be taken prior to surgery, with patients followed at one week, six to eight weeks and six months post-operatively. The primary outcome is the Oxford Knee Score (OKS) at six months post-operatively. Secondary outcomes include: other patient-reported outcome measures (PROMs), biomechanical, radiological (computer tomography, (CT)), clinical efficacy and safety outcomes. An embedded qualitative study will also investigate patients’ perspectives via interview pre and post-surgery on variables known to affect the outcome of knee replacement surgery. A sub-sample (n=30) will have additional in-depth interviews to explore themes identified. The surgeons’ perspectives on the operation will be investigated by a group interview after all participants have had surgery. Discussion: This trial will evaluate two generations of TKR by PROMS and kinematic analysis with additional and predictive


Aims
The principal aim of the trial is to compare the change in PROMs scores of the JOURNEY II BCS and the GENESIS II knee from pre-operation to six months post-operation. Additional aims are as follows: 1.
To determine if the temporal and spatial parameters of gait, the range of movement and static and dynamic balance are closer to aged-matched normative data in those receiving the JOURNEY II BCS compared to those receiving the GENESIS II knee.

2.
To monitor the change in function (aim 1 above) and PROMs of the JOURNEY II BCS and the GENESIS II knee from post-operation to six months post-operation.

3.
From CT scan measures, determine anatomical landmarks and rotational profile around the native knee and following TKR to ascertain the component rotational position post-operatively compared to anatomical landmarks.

4.
Examine the relationship between rotational values determined by CT scanning with pre-and post-operative PROMs and movement analysis.

5.
To develop knowledge and understanding of patient and surgeon experiences, perspectives and satisfaction when receiving or implanting the JOURNEY II BCS compared with the GENESIS II knee, and their experiences of recovery and rehabilitation.

Trial design
This is a pragmatic, triple-blinded, randomised controlled trial of JOURNEY II BCS (Intervention) versus GENESIS II (Control) in patients with primary osteoarthritis undergoing TKR. Embedded in the clinical trial is a qualitative investigation of participants' confidence in the TKR received and their experiences of the recovery process in the first six months after surgery. Surgeons will also be interviewed to investigate their perceptions of the surgery and patient's rehabilitation.
The trial outline is illustrated in Figure 1

Study setting
The sites for this trial have been preselected on the basis of their locality to facilitate data collection (namely the kinematic assessment). Sites include the Norfolk and Norwich University Hospital (NNUH), which is an NHS Foundation Trust where all patients recruited to the trial will be referred for consideration of TKR. The NNUH refers some of its TKR patients to Spire Norwich where the operation and follow-up physiotherapy is delivered and so some CAPAbility participants may be referred for surgery at Spire Norwich. CT scans will be performed at NNUH. The biomechanical assessment will be undertaken in a specialist movement analysis laboratory (MoveExLab) at the University of East Anglia (UEA).

Eligibility criteria
Patients must satisfy the surgeon's general requirements for a TKR, meet all inclusion criteria and none of the exclusion criteria listed in Table 1 to be eligible for the trial.
Patients will be excluded if they are currently enrolled on an interventional trial involving surgery, exercise or rehabilitation. Patients can be co-enrolled into studies given prior agreement from the Trial Management Group (TMG) of both studies. Patients who enter the study are eligible for entry onto the National Joint Registry. Patients currently enrolled on an interventional trial involving surgery, exercise or rehabilitation.
Patients can be co-enrolled into studies not meeting the above criteria given prior agreement from the TMG of both studies. Patients who enter the study are eligible for entry onto the National Joint Registry and in terms of the Journey II BCS, into Beyond Compliance.

Screening
Potential participants will be approached via a single route. Potential participants will be screened by a member of the clinical team in collaboration with research nurses after having been added to the orthopaedic clinic waiting list. Potentially eligible patients who meet the eligibility criteria, will either be handed a patient information sheet (PIS) if still at the clinic, or be posted an invitation letter informing them that the trial is taking place and include the PIS. After having been provided the trial PIS, potential participants will be telephoned by a research nurse. To minimise the possibility of attrition, appointments for outcome measures will be agreed with participants when they enter the trial. In addition, members of the research team will maintain regular contact with participants to ensure attendance at follow up visits and check for any adverse events.

Informed consent
Written informed consent to enter and be randomised into the trial will be taken by a member of the clinical team and will be obtained from participants after explanation of the aims, methods, benefits and potential hazards of the trial. Potential participants will be given as much time as they need to consider whether or not to provide informed consent. Consent will take place before any trial related measures, at a time convenient to the potential participant, preferably at a time to combine with one or more of the measures to reduce participant visits.
If a participant withdraws prior to surgery an additional participant will be randomised to ensure 80 participants complete the surgery.
Patients who, in the opinion of the clinical team do not have capacity to consent will be ineligible for this study. If a participant loses capacity during the course of the trial, they will be withdrawn from the any further assessments but, any data already collected will be retained. Consent will be re-sought if new information becomes available that affects the participant's consent in any way. This will be documented in a revision to the patient information sheet and the participant will be asked to sign an updated consent form.
These will be approved by the ethics committee prior to their use. A copy of the approved consent form is available from the Norwich Clinical Trials Unit (NCTU).

Sample size
Eighty patients will be recruited onto this study. The sample size has been calculated from the Oxford Knee Score (OKS). The OKS ranges from a score of 12 to 60, with 12 being the best outcome. The minimally important clinical difference for OKS is 5 and a standard deviation of 7.4 (Bohm et al 2012). For an 80% power, and an assumed dropout rate of 10%, 80 participants will be randomised to one of the two intervention groups.

Participant timeline
The participant timeline is shown in Figure 1. Where possible trial visits will be combined with standard clinic visits. Should additional visits be necessary, participants will be reimbursed for travel costs.

Interventions
All participants will receive routine care provided by the NHS. Pre-operative and perioperative care is standardised for each TKR participant irrespective of implant.
Surgeons will be high volume arthroplasty surgeons who work at both NNUH and Spire Norwich Hospital. All surgeons and theatre staff have received training on the implantation of the JOURNEY II BCS Implant. All surgeons have undergone training on the JOURNEY BCS II implant in a cadaveric lab and also undertaken a learning curve with the device until they were confident with both techniques. Both devices are CE marked and will be used within indication. Smith and Nephew are providing the JOURNEY II BCS at the same price as the GENESIS II system for this study.

Surgical procedures
Devices will be identified and prepared for the operation by a surgical technician at the surgery site.
Participants allocated to the intervention device will receive the JOURNEY II BCS prosthesis while participants allocated to the control condition will receive the GENESIS II prosthesis.
The type of device implanted, and serial number will be recorded on the trial database, by an unmasked member of the research team.
The surgical procedure will follow the standardised surgical approach and technique. It will be undertaken through a medial parapatellar approach. In both implants and in every case to ensure standardisation of technique, a posterior stabilised prosthesis with patella resurfacing will be used.
It is possible that a decision will be taken prior to or during the operation not to use the allocated device if, in the opinion of the surgeon, the patient is found to have become

Post-operative rehabilitation
Post-operative rehabilitation will follow routine clinical care at NNUH and Spire Norwich.
Whilst an inpatient, participants will be seen by a physiotherapist for routine care at least twice daily to progress on a tailored gait re-education and exercise programme during their hospital admission. This will be recorded in an in-patient hospital rehabilitation log.
Once safe for discharge, patients will be asked to continue a home exercise programme and gait re-education. This will consist of daily (advised) knee flexion range of motion exercises and quadriceps strengthening.
At Week four post-operatively, all participants will attend an exercise group-based intervention delivered by a qualified physiotherapist and a physiotherapy assistant. These sessions will be used to increase participant's knee range of motion, strength, and overall confidence to undertake more strenuous exercises. Participants will attend this class weekly for two to six sessions depending on their need. All rehabilitation interventions will be recorded in a post-discharge rehabilitation log. Participants will be encouraged to continue with their exercises which are prescribed within the group as part of a homeexercise programme.

Outcomes
The schedule of enrolment, interventions, and assessment is shown in Table 2. The PROMs will be administered by research nurses apart from the Week 1 follow-up telephone call undertaken by the research associate performing the qualitative interview. The CT scans will be performed at the NNUH by research radiographers and reported by a consultant radiologist. The biomechanical assessments and qualitative interviews will be performed at the Movement and Exercise laboratory (MoveExLab) at the UEA.

Primary Outcome
The OKS will be used to assess patient-reported functional status at six months postsurgery.

Secondary Outcomes: Clinical Efficacy Outcomes
Clinical efficacy will evaluated by: Surgical-related parameters: need for revision surgery; length of hospital stay and change in pain medication will be collected during inpatient stay and at all the follow-up time points.
Performance-related parameters: knee flexion and extension ranges of movement, measured at six to eight weeks and six months post-operatively by the research associate in the MoveExLab (and by the research physiotherapist at baseline as part of routine care); timed-up-and-go (TUG) and timed six minute walk recorded at the six to eight weeks and six months' time points by the research associate in the MoveExLab.

Secondary Outcomes: Clinical Safety Outcomes
Complications related to the surgery (e.g. anaesthesia-related problems, bleeding, morbidities) will be collected from a notes review, prior to discharge, post-discharge, rehabilitation and follow-up. Additionally, at each visit, participants will be asked if they have received additional treatment since their surgery/previous visit and what that consisted of.

Secondary Outcomes: Biomechanical Outcomes
All biomechanical measures will be collected in the MoveExLab by the research associate.
3D motion capture using 8 cameras (Vicon Motion System, Oxford UK), three built in force plates (BERTEC, Ohio, USA) and surface EMG (Delsys). Participants will be unshod and asked to walk at their self-selected speed. A minimum of three heel strikes from each foot will be used to construct an average.

Radiographs
Pre-operative and post-operative conventional semi-flexed AP and lateral radiographs of the knee will be acquired.

Computed Tomography
A rotational profile CT protocol will be acquired at the NNUH radiology department under standard operating procedure.
This will consist of three separate axial acquisitions through the femoral necks, knees and ankles reconstructed on bone and soft tissue algorithms. The images through the knee will be split into two acquisitions according to the Berger protocol (Berger et al 1998) The preoperative CT will be performed in the time after consent for the study and before TKR. The post-operative CT is not time sensitive and will be performed any time following surgery.
Two independent observers, radiologists under direct supervision of a senior musculoskeletal radiologist, will obtain the following measurements from the CT Pre-operative In the event of an incidental finding being reported, the Clinical Chief Investigator will organise the necessary clinical follow up which may include referral to an appropriate clinician and the organisation of further investigations.

Secondary Outcomes: Qualitative Study
Interviews will be completed either via a telephone call or face-to-face by the research associate. These will be audio-recorded and transcribed for analysis.
All TKR participants will be invited to take part in an interview and complete a selfefficacy questionnaire and the HADS at baseline and a telephone call interview at the seven days (+/-two days) surgery.
Two additional post-surgery interviews will be carried out with a purposive sample of participants (N=30), drawn equally from intervention and control groups. Sampling decisions will be based on the following factors: age; sex; ethnicity; socioeconomic status; OKS; self-efficacy; expectations, mood and symptom management (as ascertained from inspection of baseline interviews). To explore patients' expectations of and hopes for surgery (pre-op only).

2.
To explore patients' experiences and perspectives on: mood, pain and functioneveryday mobility, participation in work, social roles and activities; surgery and postoperative clinical management; rehabilitation and recovery, and social support.
All surgeons, will be invited to consent to a face to face interview after the last participant's surgery to explore their perspective on using each prostheses and their overall experience of surgery.

Allocation
An interactive web randomisation system will be used by a member of the research team who is not blinded to the intervention. Participants will be randomly assigned to either control or experimental group with a 1:1 allocation as per a computer-generated randomisation schedule. Randomisation will occur after the completion of all baseline tests. This will take place four days (+/-three days) prior to the operation to allow the correct TKR to be made available. Randomisation will be stratified by;

Blinding (masking)
It is not possible to blind the surgeon to the trial treatment. However, the participants, the physiotherapists, and all staff involved in assessing outcomes will be blinded. Processes will be in place to maintain blinding. These will include concealment in a sealed envelope, of the surgery notes mentioning the prosthesis implanted in the patient file.
In the unlikely event of a research nurse accidentally becoming unmasked, the contacts, assessments, and data entry for that participant will be undertaken by another member of the research team for the remaining period of this participant in the trial. Accidental unmasking will be logged and monitored to ensure that appropriate steps are taken to prevent this from reoccurring.
The clinical staff providing usual care will also be blinded, and thus the decision to unmasking a single case will be made when knowledge of an individual's allocated treatment is required to enable treatment of a serious adverse event which is likely to be caused by the type of device implanted.
Where possible, requests for emergency unmasking of individuals will be made via the trial manager and agreement of the Clinical Chief Investigator will then be sought.
However, in circumstances where there is insufficient time to make this request or for agreement to be sought, the treating clinician can make the decision to unmask immediately. This can be done via the trial database. The database and associated code have been developed by NCTU Data Management, in conjunction with the CAPAbility trial team. The database software provides a number of features to help maintain data quality, including; maintaining an audit trail, allowing custom validations on all data, allowing users to raise data query requests, and search facilities to identify validation failure/ missing data. After completion of the trial the database will be retained on the servers of NCTU for on-going analysis of secondary outcomes.

Data management
The identification, screening and enrolment logs, linking participant identifiable data to the pseudoanonymised PIN, will be held locally by the trial site. This will either be held in written form in a locked filing cabinet or electronically in password protected form on hospital computers. After completion of the trial the identification, screening and enrolment logs will be stored securely by the sites for 15 years unless otherwise advised by NCTU. The consent form will explain that if a participant wishes to withdraw from the study the data acquired prior to that point will be retained. Reason for withdrawal will be recorded, if given, as will loss to follow up.

Statistical analysis
A full Statistical Analysis Plan (SAP) will be developed between the trial statistician and Chief Investigators and agreed with the trial's governance committees. All analysis will be based on the intention-to-treat principle in which all participants will be analysed according to the group they were allocated regardless of compliance.
Baseline factors will be summarised by group. All continuous variables will be summarised by the mean and standard deviation, or if appropriate, the median and interquartile range.
Categorical variables will be summarised with the number, and percentage, in each category.
The primary comparison for OKS will be made using a general linear model with the stratification factors included as fixed effects. The difference between arms will be summarised using the mean difference and 95% confidence intervals will be presented. A similar analysis will be undertaken for all other outcome measures.
For the temporal gait parameters and kinematic outcomes, each participants 'closeness' to age-matched normative data will be calculated. This will then be compared between groups using a general linear model with the stratification factors included as fixed effects. This data will also be presented graphically via scatter and distributional graphs to describe the deviations from the normative data.
For all the measures of movement listed, a general linear model with the stratification factors included as fixed effects will be used to assess for differences between the groups.
If appropriate adjusted analysis will be undertaken by including baseline factors and fixed effects in the above models.

Assumptions and sensitivity analysis
All the assumptions will be checked via distribution graphs and tests. If the assumptions are not valid then transformation will be considered if none are found then a nonparametric approach will be used. The pattern of missing or incomplete data will be assessed and, if appropriate, then missing data will be imputed. The baseline comparability of the groups will be assessed and if appropriate any factor found to be imbalanced and important will be adjusted for in the analysis.
Exploratory subgroup analysis will be undertaken by including an interaction in the model to assess if the effectiveness of the prosthesis is dependent on age or gender.
All analysis will be conducted using Stata and the full SAP will be produced, and approved, before any comparative analysis is undertaken.

Additional Analyses -CT Scans
All Rotational profile measurements will be performed at NNUH under standard operating procedure on a full diagnostic workstation (Synapse DICOM viewer, Fujifilm, Japan, High resolution 2K monitors, Radiforce RX340 Eizo, Germany) in the BioImaging Laboratory and under the supervision of Prof Andoni Toms.

Reproducibility
Inter-rater reliability will be assessed using intra-class correlation coefficients and 95% limits of agreement derived from Bland-Altman plots.

TKR alignment versus native landmarks
The difference between the post-operative component rotational alignment and the preoperative native landmarks will be assessed using Bland-Altman plots.

Correlation with PROMS
The correlation between the PROMS and the difference between the post-operative component rotational alignment and the pre-operative native landmarks will be assessed using a correlation coefficient. A regression model will also be fitted including the randomisation group to allow for a potential difference in PROMS between these groups.

Correlation with movement analysis
A similar analysis will be undertaken for the correlation between movement analysis and the difference between the post-operative component alignment and the pre-operative native landmarks.

Additional Analyses -Qualitative Study
Interview transcripts will be organised using NVivo qualitative data management software (http://www.qsrinternational.com/nvivo-product). Analysis will follow qualitative content analysis procedures (Graneheim et al 2004). Coding and thematic analysis will be carried out independently by two experienced qualitative researchers. Trustworthiness strategies (Lincoln et al 1985) will be used to increase the credibility, dependability and transferability of analysis and interpretation, including cross-checking and review of codes and themes; constant comparative method (hypothesis testing within and across the data set) and deviant case analysis (the use of 'outliers' as a resource for understanding and interpretation of data) (Silverman 2000).

Analysis Population and Missing Data
The analyses population are defined as: a) intention-to-treat: all randomised individuals b) per-protocol: all randomised individuals who do not have an alternative knee replacement during the follow-up period. Individuals will be included up to the point of the alternative knee replacement.
c) safety population: all randomised individuals who receive the replacement knee.
Missing outcomes data will be multiply imputed to increase precision of the treatment effect estimates. Sensitivity analyses will be conducted to assess the impact of the multiple imputations and a complete case analysis will also be conducted. All imputations will be examined to ensure sensible values are being generated. Imputation models will contain baseline measures, outcome measures and factors predictive of missing data.
No Interim analysis is planned for this study.

Data monitoring
A TMG has been convened to assist with developing the design, co-ordination and strategic management of the trial. A Safety Committee will review safety data and act in Adverse events do NOT include: Readmissions for revision surgery Mild (i.e. not lasting more than 5 days) anaesthetics related complications: Nausea, vomiting, dizziness, drowsiness, vaso-vagal drop, hypotension and constipation.
Medical or surgical procedures; the condition that led to the procedure is the adverse event Pre-existing disease or a condition present that was diagnosed before trial entry and does not worsen Hospitalisation where no untoward or unintended response has occurred e.g. elective surgery, social admissions The Safety Committee will be provided with safety data for each treatment arm including related AEs. The committee will advise on the continuation or early stoppage of the trial in the unlikely event that there are concerns over harm to participants.

Auditing
The Quality Assurance (QA) and Quality Control (QC) considerations for the CAPAbility trial are based on the standard NCTU Quality Management Policy that includes a formal risk assessment, and that acknowledges the risks associated with the conduct of the trial and proposals of how to mitigate them through appropriate QA and QC processes. Risks are defined in terms of their impact on: the rights and safety of participants; project concept including trial design, reliability of results and institutional risk; project management; and other considerations.
NCTU staff will review CRF data for errors and missing key data points. The trial database will also be programmed to generate reports on errors and error rates. Essential trial issues, events and outputs, including defined key data points, will be detailed in the trial DMP. The frequency, type and intensity of routine and triggered on-site monitoring will be detailed in the QMMP. The QMMP will also detail the procedures for review and sign-off of monitoring reports. In the event of a request for a trial site inspection by any regulatory authority, NCTU must be notified as soon as possible.

Research Ethics Approval
The trial is being conducted in accordance with CODEX rules and guidelines for research and the Helsinki Declaration as well as the ICH Guideline for GCP. The study protocol was Committee has also been set up to provide oversight on the trial and to safeguard the interests of the participants

Protocol amendments
The protocol was amended in August 2017 (before trial start at sites) to improve consistency and clarity. To that effect, an additional inclusion criterion was added to match the consent form requiring participants to agree to any incidental findings to be reported to their GP. The exclusion criteria relating to the use of the Warfarin was also improved by the addition of novel anti-coagulants therapies which are increasingly used.
As part of this amendment we also changed the stratification criteria from ASA grade and age to site and age as we became aware that ASA grading is highly subjective and has poor inter-rater reliability. We added the UCLA Activity Score as a secondary outcome measure to provide valuable information on the participant activity levels pre-and postoperatively. The HADS was also added to be taken at baseline as part of the embedded qualitative study. The embedded qualitative study was also simplified by the removal of the physiotherapists' interview after agreeing that these would not add relevant information towards the outcome measure due to recall biases that would be introduced by practical aspects of running these interviews.
Further changes were made in June 2018 allowing further clarifications. This was done following the removal of the BMI requirement enforced by one of our surgery sites. The associated exclusion criteria could therefore be removed opening the recruitment to a wider population and thus improving the representativeness of the study sample as many patients have a BMI greater than 35. In addition to this, the criteria excluding prior knee surgery was refined to exclude only previous surgery of the collateral ligaments of the knee as previous surgery on the cruciate ligaments would not affect the trial outcome as these ligaments are to be removed during surgery. The clarification of this exclusion criteria also permitted for previous non-intra-articular knee surgery (e.g. minor procedures around the knee) which were excluded despite not affecting the trial outcome. The visit windows were also reviewed as part of these changes to increase the baseline window from -21 days to -42 days up to surgery and to change the six month visit timeframe from +/-two weeks to + four weeks. The former ensuring enough time for the assessments to take place before randomisation and the latter that all participants would have a full six months rehabilitation period before undertaking the last follow-up visits.
Additional changes included the addition of the learning curve details for surgeon training to perform the intervention, the addition of the process for participants to be informed of their knee allocation at the end of the trial as part of the result dissemination, the clarification of the non-adherence and non-retention section to confirm that any data collected up to a participant withdrawal will be retained and the clarification of the safety reporting period and responsibilities. This amendment also allowed us to update the compliance section to add the General Data Protection Regulation (GDPR).
Following on the previous amendment additional modifications were made in August 2018 after the agreement that the recruitment of patients with previous TKR could be allowed as long as they are over a year old at the time of the consultation and painless, mildly or moderately painful. This was agreed to create a more representative data set while ensuring that these participants' mobility won't be affected by contralateral pain.
Additional changes were made in December 2018 to include the MVIC of the hamstring and quadriceps muscles on both limbs to assess the known issue of muscle strength loss after TKR (Moon et al 2016). This biomechanical measure evaluates postoperative quadriceps and hamstring muscle strength loss and subsequent recovery in both the non-operative legs and healthy control legs for comparison. The inclusion criteria were also amended to remove "Patient willing to provide full informed consent to the trial, including consent for any incidental findings to be communicated to their GP". This does not need to be an inclusion criteria as a potential participant would not be enrolled on the trial if the consent form, which includes a statement about communicating findings with the GP, was not initialled and signed. In addition the patient information was amended to clarify that baseline data collected for participants that may not progress to randomisation or surgery, for reasons other than withdrawal, will be retained and used as observational data.
Furthermore, the protocol was amended in March 2019 to extend the six to eight week visit window to six to ten weeks to ensure all participants can be seen within the appropriate window. An additional time point for collecting changes in pain medication was also added to the participant timeline at discharge from surgery. This will allow for a comparison between the participant reported pain medications at the Week 1 phone call and what was prescribed at discharge.

Consent or assent
Potential participants will be provided with a PIS and given time to read it fully. Following a discussion with a medical qualified investigator or suitable trained and authorised delegate, any questions will be satisfactorily answered and if the participant is willing to participate, written informed consent will be obtained. During the consent process it will be made clear that the participant is free to refuse to participate in all or any aspect of the trial, at any time and for any reason, affecting their treatment.
Potential participants who, in the opinion of the clinical team do not have capacity to consent will be ineligible for this study. If a participant loses capacity during the course of the trial, they will be withdrawn from the any further assessments but, the data which has already been collected will be retained.
Consent will be re-sought if new information becomes available that affects the participant's consent in any-way. This will be documented in a revision to the patient information sheet and the participant will be asked to sign an updated consent form.
These will be approved by the ethics committee prior to their use. A copy of the approved consent form is available from the NCTU trial team.

Confidentiality
Any paper copies of personal trial data will be kept at the participating site in a secure location with restricted access. Following consent, identifiable data will be kept on the trial database to allow the MoveExLab staff to contact participants in order to arrange appointments. Only authorised trial team members will have password access to this part of the database.
Confidentiality of participant's personal data is ensured by not collecting participant names on CRFs and limiting access to personal information held on the database at NCTU.
At trial enrolment the participant will be issued a participant identification number and this will be the primary identifier for the participant, with secondary identifiers of month and year of birth and initials.
The participant's consent form will carry their name and signature. These will be kept at the trial site, and a copy sent to NCTU for monitoring purposes. They will not be kept with any additional participant data.

Declaration of interests
The investigators named on the protocol have no financial or other competing interests that impact on their responsibilities towards the scientific value or potential publishing activities associated with the trial.

Access to data
Requests for access to trial data will be considered, and approved in writing where appropriate, after formal application to the TMG. Considerations for approving access are documented in the TMG Terms of Reference. The Co-CIs and trial statistician at NCTU will have access to the full trial dataset.

Dissemination policy
The results of the trial will be disseminated regardless of the direction of effect and will be reported following the

Discussion
This protocol describes a trial that will explore the performance and functional ability of two types of total knee implants by comparing them on multiple levels.
The use of validated PROMs as both primary and secondary outcomes will allow the comparison of the Journey II BCS and the Genesis II implants in a standardised manner widely used in the literature. The addition of biomechanical, radiological, clinical efficacy and safety outcomes will permit an in-depth comparison of the implants and to fully assess the performance of both implants' design in a comprehensive way. This will also highlight any relationships between each of these individual aspects and inform future study designs. The biomechanical outcome using every day movement and detailed anatomical information from the rotational profile will both provide invaluable and pragmatic information on the knee implants in situ which will help clinicians in the investigation and management of participants before and after TKR. Additionally, the embedded qualitative study will investigate not only participant related constructs associated with both their total knee replacement and rehabilitation but also provide surgeon's perspectives.
One of the challenges linked with the collection of varied outcome measures is the participant visit burden. This has been considered very carefully and the trial has been designed for most of the study visits to be combined with routine clinical visits or to be undertaken over the phone Declarations Ethics approval and consent to participate The study protocol was approved by the East of England -Cambridge Central Research Ethics Committee (reference 17/EE/0230) prior to the start of the trial. The trial is registered on the International Standard Randomised Controlled Trials Number (ISRCTN) registry (reference ISRCTN32315753). Approval was granted by the Health Research Authority (HRA) and Confirmation of Capacity and Capability to conduct the trial has been provided by the NNUH R&D office. Informed consent will be obtained from all study participants.

Consent for publication
Not applicable

Availability of data and materials
Not applicable

Competing interests
The authors declare that they have no competing interests.

Funding
The CAPAbility trial is an investigator initiated trial funded by Smith and Nephew (JOURNEY BCS II and GENESIS II implant manufacturer) apart from the embedded radiological study (radiological outcomes measures from rotational CT scans) which is funded by the Gwen Fish Orthopaedic Trust.

Authors' contributions
CC, EP and IMN drafted this paper. All authors contributed to revisions of the manuscript, read and approved the final manuscript. All authors contributed to the research funding application and development of the trial protocol. All authors read and approved the final manuscript.
CC is the corresponding Author. Figure 1