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Trial registered on ANZCTR

Registration number
Ethics application status
Date submitted
Date registered
Date last updated
Type of registration
Retrospectively registered

Titles & IDs
Public title
A Comparison of Different Patellar Implant Designs in Total Knee Replacement.
Scientific title
A prospective randomized comparative trial (pilot study) to compare intra-operative and post-operative outcome measures between inset, onlay round and onlay oval designs of patellar implants in patients undergoing unilateral total knee arthroplasty for degenerative osteoarthritis
Secondary ID [1] 288587 0
Nil Known
Universal Trial Number (UTN)
Trial acronym
Linked study record

Health condition
Health condition(s) or problem(s) studied:
Osteoarthritis 297731 0
Condition category
Condition code
Musculoskeletal 297914 297914 0 0
Surgery 298859 298859 0 0
Surgical techniques

Study type
Description of intervention(s) / exposure
This research will study the outcomes of using different patellar implants in Total Knee Arthroplasty (TKA). Patients with knee osteoarthritis undergoing TKA will be randomized into three groups allocated to one of the three patellar implants' designs. The different patellar designs to be evaluated in this study are:
- Onlay oval: asymmetrical oval patella designs with three projections cemented on the resurfaced patella.
- Onlay round: symmetrical round patella designs with three projections cemented on the resurfaced patella.
- Inset: a round biconvex design with one projection cemented on reamed under-surface of patella.

Intervention will be performed by a fellowship trained surgeons with minimum 10 years experience. The approximate duration of the TKA procedure is around 90 minutes. The duration of performing the selected patellar implants is 5-10 minutes. Adherence to the assigned randomization will be monitored by the assisting fellow. any misconduct or fidelity will be documented and reported in the monthly research meeting.
Intervention code [1] 294775 0
Treatment: Surgery
Intervention code [2] 294814 0
Treatment: Devices
Comparator / control treatment
The Inset design group will be the comparator group.
Control group

Primary outcome [1] 298335 0
Patellar surface coverage: A photograph will be taken to the patella after implanting the trial design with a ruler to the side. Photoshop CS program will be used to calculate the percentage of surface coverage by the implant.
Timepoint [1] 298335 0
Intra-operative: This will be done after implanting the trial patellar design.
Primary outcome [2] 298336 0
Patellar tilt on weight bearing merchant view (x-ray)
Timepoint [2] 298336 0
6 months post surgery
Primary outcome [3] 298337 0
Blood supply to patella using bone scan; to asses for patellar osteonecrosis.
Timepoint [3] 298337 0
6 months post surgery
Secondary outcome [1] 323874 0
Patient's pain and functional scores (Composite secondary outcome): using validated Kujala scores. (Patient self reported outcome score using validated questionnaire. Kujala questionnaire reports on patient's pain, daily activities and functional level)
Timepoint [1] 323874 0
6 months post surgery

Key inclusion criteria
Patients undergoing unilateral total knee arthroplasty for degenerative osteoarthritis
Minimum age
50 Years
Maximum age
85 Years
Both males and females
Can healthy volunteers participate?
Key exclusion criteria
- Revision TKA surgery
- Bilateral simultaneous TKA
- Prior osteotomies around the knee or extra-articular deformities
- Systemic inflammatory disease (e.g. rheumatoid arthritis, Systemic lupus erythematosus, etc)
- Medial and lateral knee ligamentous instability on knee examination.
- TKA for acute trauma and need for allograft
- Prior patellar fracture, ruptured extensor mechanism
- Constrained implants, stemmed components or metal augmentation during surgery.

Study design
Purpose of the study
Allocation to intervention
Randomised controlled trial
Procedure for enrolling a subject and allocating the treatment (allocation concealment procedures)
A computer software will be used for randomization of patients into the three designs options. The study will be patient blinded. and the operating surgeon will be informed about the randomization at surgery time.(Allocation is not concealed)
Methods used to generate the sequence in which subjects will be randomised (sequence generation)
Computerised sequence generation
Masking / blinding
Blinded (masking used)
Who is / are masked / blinded?
The people receiving the treatment/s

Intervention assignment
Other design features
Not Applicable
Type of endpoint(s)
Statistical methods / analysis
Based on power analysis, a sample size of 20 patients in each cohort would provide appropriate power (beta level = 0.80, alpha level = 0.05) to detect an 80% improvement in percentage of patellar surface coverage (as oval onlay design proposed to provide nearly full coverage) and in risk of osteonecrosis by preserving the lateral facet with the oval onlay design. There will be a midterm analysis when 30 patients are recruited to assess whether significance has been reached and whether or not, further patient enrolment is necessary. Means, ranges, and standard deviations will be recorded for percentage of patellar surface coverage, pre-operative and postoperative scores in all groups. ANOVA will be used to compare differences in means between continuous variables. ANOVA will be used to statistically assess pre-operative demographic factors. Fisher's exact test will be used to test for significance in osteonecrosis difference (proportions) between the groups. Statistical significance set at p = 0.05.

Recruitment status
Date of first participant enrolment
Date of last participant enrolment
Date of last data collection
Sample size
Accrual to date
Recruitment in Australia
Recruitment state(s)
Recruitment hospital [1] 5806 0
St George Private Hospital - Kogarah
Recruitment postcode(s) [1] 13248 0
2217 - Kogarah

Funding & Sponsors
Funding source category [1] 293615 0
Name [1] 293615 0
St George Private Hospital
Address [1] 293615 0
1 South St, Kogarah NSW 2217
Country [1] 293615 0
Primary sponsor type
Commercial sector/Industry
Sydney Knee Specialist
Sydney Knee Specialists, Suite 8
19, Kensington St
Kogarah, NSW 2217
Secondary sponsor category [1] 292434 0
Name [1] 292434 0
Address [1] 292434 0
Country [1] 292434 0

Ethics approval
Ethics application status
Ethics committee name [1] 295056 0
Hunters New England research ethics and governance unit
Ethics committee address [1] 295056 0
Research Support and Development Office
Locked bag 1, New Lambton, NSW, 2305
Ethics committee country [1] 295056 0
Date submitted for ethics approval [1] 295056 0
Approval date [1] 295056 0
Ethics approval number [1] 295056 0

Brief summary
To compare the intra-operative and post-operative outcome measures between three different patellar implant designs in patients undergoing total knee arthroplasty (TKA) surgery with regards to patellar bone coverage and tracking, patient-reported outcomes and post-operative radiological and scintigraphic analysis.

Controversy remains regarding whether the patella should be resurfaced in total knee arthroplasty. However, at present the scientific literature supports patellar resurfacing with regards to reduced re-operation risk and improved long term patient satisfaction.
Two basic techniques present for resurfacing the patella; either onlay or inset. In the inset design, a round domed implant is reamed in the patella and fixed with a single central projection (peg). On the other hand, the onlay design has either round (symmetrical) or oval (asymmetrical) shaped patellae with three small peripheral pegs fixed on the cut surface of the patella. When using a round patellar implant, either onlay or inset, some surgeons perform a lateral facetectomy to avoid lateral compression syndrome and enhance patellar tracking. However, neither method has proved to be superior.

A wide range of complications are associated with patellar resurfacing. These include patellar fracture, osteonecrosis related to devascularisation, patellar polyethylene (PE) wear, aseptic loosening, instability, dislocation, overstuffing and rupture of the extensor mechanism. Many of these can be catastrophic. One should always consider the peculiar blood supply to the patella during TKA and patellar resurfacing as iatrogenic disruption of supplying vessels has been identified as a major contributing factor in post-operative patellofemoral complications. The hypothesis of this study is that onlay oval design provides optimal bone coverage, better tracking, better patient reported outcome scores and carries the lowest risk of osteonecrosis in comparison with the other two designs.

Trial Objectives:
To prospectively compare intra-operative observed measures, patient-reported outcome measures and radiological results between inset, onlay round and onlay oval designs of patellar implants in patients undergoing total knee arthroplasty surgery. Specifically, we will compare patellar surface bone coverage, pain and functional scores together with patellar tracking and vascular status of the patella postoperatively.
Trial website
Trial related presentations / publications
Public notes
Attachments [1] 882 882 0 0

Principal investigator
Name 63718 0
Dr Samuel Macdessi
Address 63718 0
Sydney Knee Specialists, Suite 8, 19, Kensington St, Kogarah NSW 2217
Country 63718 0
Phone 63718 0
Fax 63718 0
Email 63718 0
Contact person for public queries
Name 63719 0
Dr Samuel Macdessi
Address 63719 0
Sydney Knee Specialists, Suite 8, 19, Kensington St, Kogarah NSW 2217
Country 63719 0
Phone 63719 0
Fax 63719 0
Email 63719 0
Contact person for scientific queries
Name 63720 0
Dr Samuel Macdess
Address 63720 0
Sydney Knee Specialists, Suite 8, 19, Kensington St, Kogarah NSW 2217
Country 63720 0
Phone 63720 0
Fax 63720 0
Email 63720 0

No information has been provided regarding IPD availability
Summary results
No Results