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Trial registered on ANZCTR

Registration number
Ethics application status
Not yet submitted
Date submitted
Date registered
Date last updated
Date data sharing statement initially provided
Type of registration
Prospectively registered

Titles & IDs
Public title
A comparison of mechanical and kinematic alignment principles in total knee joint replacement using a medial pivot design prosthesis
Scientific title
A randomised controlled trial comparing patient specific instrumentation (PSI)-kinematic alignment with PSI-mechanical alignment using a medial pivot design prosthesis to assess patient-reported functional outcomes
Secondary ID [1] 301776 0
Nil known
Universal Trial Number (UTN)
Trial acronym
Linked study record

Health condition
Health condition(s) or problem(s) studied:
Knee osteoarthritis 318244 0
Condition category
Condition code
Musculoskeletal 316256 316256 0 0
Surgery 316958 316958 0 0
Surgical techniques

Study type
Description of intervention(s) / exposure
Patients will receive their total knee replacement according to kinematic alignment principles. A CT scan 3-4 weeks prior to surgery will be used to manufacture patient specific guides. These guides are positioned on the patients' femurs and tibias to make bone resections according to KA. The control group will also have a CT scan to manufacture their PSI.
Kinematic principles position the knee replacement in a way that respects the natural joint line and rotational axis of the knee. Each surgery will take approximately 2 hours. No difference between groups is expected as both use patient specific instrumentation to determine bone cuts for the femur and the tibia. The surgeons performing the surgeries have a minimum of 6 and 20 years of experience as orthopaedic consultants.

To monitor compliance/fidelity to the protocol of each group's alignment principles, the amount of bone resection from the tibia and femur will be measured using a validated caliper, recorded and cross checked with the 'expected' bone resections. This is the standard method for checking resections using this particular implant.
Intervention code [1] 318074 0
Treatment: Surgery
Comparator / control treatment
Patients who have been randomised to this group will receive their knee replacement in the more traditional way and places the implant perpendicular to the mechanical axis. This is more widely accepted way of performing knee replacement surgery called, mechanical alignment. The length of surgery will be the same as those randomised to the intervention (KA) group
Control group

Primary outcome [1] 324437 0
Patient function using the Forgotten Joint Score (FJS)
Timepoint [1] 324437 0
Preoperative (within 2 months of the date of surgery), and at three (primary time point) and 12 months after surgery
Secondary outcome [1] 384643 0
Knee function using the Oxford knee score (OKS)
Timepoint [1] 384643 0
At baseline/preoperative (within 2 months), and at three and 12 months after surgery
Secondary outcome [2] 384644 0
Long leg xrays to determine overall alignment
Timepoint [2] 384644 0
Preoperative (within 2 months of date of surgery) and at 1 year after surgery
Secondary outcome [3] 384645 0
Range of motion measured by an independent outcomes assessor using a standardised protocol. This includes the use of a goniometer, with the patient in a supine position measuring degrees of flexion and extension.
Timepoint [3] 384645 0
Preoperative (within 2 months of date of surgery), and at three and 12 months after surgery
Secondary outcome [4] 384646 0
Return to theatre (for any reason) after index surgery
This will be assessed by searching electronic and medical records for the following 30 days after index surgery.
Timepoint [4] 384646 0
Within 30 days of the knee replacement surgery
Secondary outcome [5] 385579 0
Knee function using the Knee Injury and Osteoarthritis Outcome Score (KOOS)
Timepoint [5] 385579 0
Preoperative (within 2 months of date of surgery) and at 3 and 12 months after surgery
Secondary outcome [6] 385580 0
Western Ontario and McMaster Universities Arthritis Index (WOMAC)
Timepoint [6] 385580 0
Preoperative (with 2 months of date of surgery) and at 3 and 12 months after surgery
Secondary outcome [7] 385581 0
Quality of Life using the EQ-5D score
Timepoint [7] 385581 0
Preoperative (with 2 months of date of surgery) and at 3 and 12 months after surgery

Key inclusion criteria
Patients with end-stage osteoarthritis (Kellgren-Lawrence grade 3 or 4) deemed suitable for total knee arthroplasty and have exhausted non operative management
Minimum age
45 Years
Maximum age
No limit
Both males and females
Can healthy volunteers participate?
Key exclusion criteria
Coronal > 15 degrees and sagittal deformity of >20 degrees
Mechanical lateral distal femur angle of 85-95 degrees and mechanical medial proximal tibia angles of 85-95 degrees
Patients who had previous open knee surgery that involved infection, osteotomy or fracture fixation
Patients with significant concomitant hip or spinal pathology making functional assessment of the knee replacement inaccurate
Contralateral knee pathology
Patients unable to complete or understand patient reported outcome assessment
BMI > 40kg/m2
History of previous knee infection
Patients with neurological disease or neurosensory deficiency
inflammatory arthritis

Study design
Purpose of the study
Allocation to intervention
Randomised controlled trial
Procedure for enrolling a subject and allocating the treatment (allocation concealment procedures)
After consent has been obtained, patients are sent for a computed tomography (CT) scan of their knee which will instruct manufacture of the patient specific instrumentation (PSI) guides intended to be used for each patient. At this appointment, the radiographer, independent from the study, is given specific instructions to reveal patients’ group allocations and document their group (KA or MA) on their computed data sheet. The radiographer is told not to inform the patient of their respective group. This information in addition to the CT data will be sent to Medacta International in preparation for their PSI jig manufacture in conjunction with the group allocation (KA or MA). The surgical plan is then presented to the surgeon for approval, and once approved the PSI jigs are manufactured.

Group allocation envelopes will all be stored in the radiographer’s office numbered 1 to 140. Once the group allocation has been documented in the data sheet, the envelope is then discarded.
Methods used to generate the sequence in which subjects will be randomised (sequence generation)
Using computer generated random allocation, patients will be randomised to either the KA or MA groups four weeks prior to their procedure with a ratio of 1:1.
Masking / blinding
Blinded (masking used)
Who is / are masked / blinded?
The people receiving the treatment/s

The people assessing the outcomes
The people analysing the results/data
Intervention assignment
Other design features
Not Applicable
Type of endpoint(s)
Statistical methods / analysis
There is no defined minimally clinically important difference (MCID) for the FJS yet reported in the literature. There is however a minimal important change (MIC) of 14 points for FJS that has been reported in the literature using predictive modelling methods. Though the authors caution the reader to avoid using the MIC as a surrogate for the MCID when comparing mean improvements between groups.

Using a distribution-based approach to determining the MCID for the FJS the standard deviation method was used. This method uses the pooled standard deviation of a known population’s groups of scores. The value of 0.5 SD has been shown by Norman et al to correspond to the MCID across a variety of studies. They argue that the value of 0.5 SD represents the limit in a patient’s mental discriminative capacity and determines if this change/difference in score is an important one, or not.

We used data from Young et al whose population is similar to the one we serve to assist with determining an appropriate sample size for the primary outcome of FJS at 1 year. To give an indication of cohort similarities, geographically this centre is less than a 2 hour drive from our centre.

The planned sample size for this study was 63 patients per treatment arm. This was based on a 13 point difference (calculated MCID = 0.5 x SD) in the mean FJS with a pooled SD of 26, 80% power, and a two-sided significance level of 5%. We anticipated an attrition rate of 10% at 1 year and therefore an additional 6 patients were included into the target patient number, bringing the target to a minimum of 69 participants in each group.

Descriptive analysis for continuous variables used means, SD, range (minimum and maximum), and for categorical variables used frequencies and percentages. The change from preoperative to the 1 year time point for the quality-of-life parameters was analyzed with analysis of covariance (ANCOVA) for repeated measures. For each quality of life parameter, the absolute scores at 1 year were analysed with analysis of variance for repeated measurements (ANOVA). The treatment group difference (kinematic-control) was the least squares mean (LSM) difference with 95% CI. The significance level was set to 0.05 without adjustments for multiple comparisons.

Young SW, Walker ML, Bayan A, Briant-Evans T, Pavlou P, Farrington B. The Chitranjan S. Ranawat Award: No Difference in 2-year Functional Outcomes Using Kinematic versus Mechanical Alignment in TKA: A Randomized Controlled Clinical Trial. Clin Orthop. 2017 Jan;475(1):9–20

Recruitment status
Not yet recruiting
Date of first participant enrolment
Date of last participant enrolment
Date of last data collection
Sample size
Accrual to date
Recruitment outside Australia
Country [1] 22740 0
New Zealand
State/province [1] 22740 0

Funding & Sponsors
Funding source category [1] 306206 0
Name [1] 306206 0
Northland Orthopaedics Research Charitable Trust
Address [1] 306206 0
Private Bag 9742
Whangarei Mail Centre
Whangarei 0148
Country [1] 306206 0
New Zealand
Primary sponsor type
Whangarei Hospital
Whangarei Hospital
Maunu Road, Private Bag 9742,
Whangarei, 0148
New Zealand
New Zealand
Secondary sponsor category [1] 306684 0
Name [1] 306684 0
Address [1] 306684 0
Country [1] 306684 0

Ethics approval
Ethics application status
Not yet submitted
Ethics committee name [1] 306418 0
Health and Disability Ethics Committee
Ethics committee address [1] 306418 0
Ministry of Health
Health and Disability Ethics Committees
PO Box 5013
Wellington 6140
Ethics committee country [1] 306418 0
New Zealand
Date submitted for ethics approval [1] 306418 0
Approval date [1] 306418 0
Ethics approval number [1] 306418 0

Brief summary
Total knee arthroplasty (TKA) is regarded as a successful surgical procedure that alleviates the morbidity associated with end-stage osteoarthritis (OA). Despite this, around 15-20% of people are dissatisfied with their result and surgeons are striving to understand the reasons why.
One thought is that the more traditional, mechanical alignment (MA) principle, changes the natural joint kinematics by altering the joint line obliquity and altering its rotational axes. Implanting a prosthesis in this manner may place undue stress on the soft tissue causing pain and dysfunction. More recently, surgeons have strived to attain a more natural alignment to respect an individual’s joint obliquity and rotational axes so that the soft tissue envelope and surrounding musculature is not at odds with the implanted prosthesis hereby, reducing the kinematic conflict. This philosophy is referred to by knee arthroplasty surgeons as kinematic alignment (KA).
Great interest in the kinematic doctrine has been prompted by a handful of level 1 trials with some demonstrating promising results. Ten randomised control trials (RCT) comparing MA with KA in unconstrained prostheses of which five showed a mild improvement in mid-term functional outcomes and five demonstrated no difference. In the period 2017 to 2019, four systematic reviews and meta-analyses have reported comparable functional outcomes in the medium follow-up.
Implant design is also implicated in trying to recreate a more natural knee kinematics. The medial pivot (MP) design attempts to mimic natural medial pivot and lateral femoral rollback during flexion that has been observed in the native, non arthritic knee. On the medial side the implant is a ball and socket design, whereas the lateral compartment is relatively flat allowing the femur to slide posteriorly during flexion.
To date, only one non randomised trial has investigated a medial pivot prosthesis in the setting of KA principles demonstrating superior function compared to a cruciate retaining TKA at 2 years.
We hypothesised that combining a medial pivot design implant with the principle of KA may improve patient functional outcomes. This study aims to 1) compare medium term functional outcomes between mechanically and kinematically aligned TKA when using a MP prosthesis, and 2) evaluate TKA kinematics when a medial pivot designed prosthesis is used for both alignment principles and how these might compare with the native, non arthritic knee
Trial website
Trial related presentations / publications
Public notes

Principal investigator
Name 103806 0
Dr Mike van Niekirk
Address 103806 0
Whangarei Hospital
Maunu Road, Private Bag 9742,
Whangarei, 0148
Country 103806 0
New Zealand
Phone 103806 0
+64 9 430 4100
Fax 103806 0
Email 103806 0
Contact person for public queries
Name 103807 0
Dr Mike van Niekirk
Address 103807 0
Whangarei Hospital
Maunu Road, Private Bag 9742, Whangarei, 0148
Country 103807 0
New Zealand
Phone 103807 0
+64 9 430 4100
Fax 103807 0
Email 103807 0
Contact person for scientific queries
Name 103808 0
Dr Mike van Niekirk
Address 103808 0
Whangarei Hospital
Maunu Road, Private Bag 9742, Whangarei, 0148
Country 103808 0
New Zealand
Phone 103808 0
+64 9 430 4100
Fax 103808 0
Email 103808 0

Data sharing statement
Will individual participant data (IPD) for this trial be available (including data dictionaries)?
What data in particular will be shared?
All individual participant data collected underlying published results only after de-identification and as the ethics committee allows
When will data be available (start and end dates)?
Immediately following publication and without an end date
Available to whom?
Case by case basis - for example to researchers who provide a methodologically sound research proposal and within the limits of what the ethical committee allows.
Available for what types of analyses?
For meta analyses.
How or where can data be obtained?
Access subject to approvals by the principal investigator or their research team (
What supporting documents are/will be available?
No other documents available
Summary results
No Results