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STUD Y PRO T O C O L Open Access
The Warwick patellofemoral arthroplasty trial:
a randomised clinical trial of total knee
arthroplasty versus patellofemoral arthroplasty
in patients with severe arthritis of the
patellofemoral joint
Michelle Odumenya
1*
, Katie McGuinness
1
, Juul Achten
1
, Nick Parsons
1
, Tim Spalding
2
and Matthew Costa
1
Abstract
Background: Severe arthritis of the knee is a disabling condition, with over 50,000 knee replacements performed
each year in the UK. Isolated patellofemoral joint arthritis occurs in over 10% of these patients with the treatment
options being patellofemoral arthroplasty or total knee arthroplasty. Whilst many surgeons believe total kne e
arthroplasty is the ‘gold standard’ treatment for severe knee arthritis, patellofemoral arthroplasty has certain
potential advantages. Primarily, because this operation allows the patient to keep the majority of their own knee
joint; preserving bone-stock and the patients’ own ligaments. Patellofemor al arthroplasty has also been recognised
as a less ‘ invasive’ operation than primary total knee arthroplasty, facilitating a more rapid recovery. There are
currently no published results of randomised clinical trials comparing the two arthroplasty techniques. The primary
objective of the current study is to ass ess whether there is a difference in functional knee scores and quality of life
outcome assessments at one year post-operation between patellofemoral arthroplasty and total knee arthroplasty.
The seco ndary objective is to assess the complication rates for both procedures.
Methods/design: Patients who ar e deemed suitable, by an Orthopaedic Consultant, for patellofemoral arthroplasty
and medically fit for surgery are eligible to take part in this trial. The consenting patients will be randomised in a
1:1 allocation to a total knee or patellofemoral arthroplasty. The randomisation sequence will be computer
generated and administered by a central independent randomisation service. Following consent, all participants
will hav e their knee function, quality of life and physical activity level assessed through questionnaires. The
assigned surgery will then be performed using the preferred technique and implant of the operating surgeon. The
first post-operative assessments will take place at six weeks, followed by further assessments at 3, 6 and 12 months.
At each assessment time point all complications will be recorded. In addition, community and social care services
usage will be collected using a patient questionnaire at 3, 6 & 12 months. The patients will then be sent an annual
postal questionnaire. The questionnaire will ask about any problems, knee pain and function following their knee
arthroplasty to monitor long-term function and failure rates.
Discussion: This trial is expected to deliver results in early 2013.
Trial Registration: ISRCTN: ISRCTN34863373
UKCRN portfolio ID 6847
* Correspondence: michelle.odumenya@warwick.ac.uk
1
Division of Health Sciences, Warwick Medical School, Universi ty of Warwick,
Clifford Bridge Road, Coventry, CV2 2DX, United Kingdom
Full list of author information is available at the end of the article
Odumenya et al. BMC Musculoskeletal Disorders 2011, 12:265
http://www.biomedcentral.com/1471-2474/12/265
© 2011 Odumenya et al; licensee BioMed Cent ral Ltd. This is an Open Access article distributed under the terms of the Creative
Commons Attribution License (http://creativ ecommon s.org/licenses/by/2.0) , which permits unrestricted use, distribution, and
reprodu ction in any medium, provided the original work is properly cited.
Background
Isolated patellofemoral arthritis and treatment options
Severe arthritis of the knee is a common and disabling
condition. Over 50,000 patients require a knee arthro-
plasty each year in the UK at an estimated cost of 300
million pounds. Arthritis confined to the patellofemoral
joint (the articulation between the patella and the tro-
chlear groove of the femur) occurs in over 10% of these
patients. The average age of those affected by isolated
arthritis of the patellofemoral joint is significantly lower
than those with severe generalised arthritis [1]. Com-
monly, patients complain of anterior knee pain which
limits their daily activities and in severe cases patients
are unable to continue in employment. Initially, these
symptoms can be successfully treated non-operatively.
However, in severe debilitating cases the efficacy of these
non-surgical modalities is minimal and the only alternative
treatment is surgery. The operative treatm ent options for
this disease include arthroscopic procedures, patellectomy
(removal of the knee-cap), Total Knee Arthroplasty (TKA)
and more recently, Patellofemoral Arthroplasty (PFA).
Arthroscopic surgery is seldom beneficial in severe disease
and pa tellectomy often leads to poor long-term function,
therefore the choice for patients is usually between TKA
and PFA.
Whilst many s urgeons believe TKA is the ‘gold stan-
dard’ treatment for severe knee arthritis, PFA has certa in
potential advantages. Primarily, this operation allows the
patient to keep the majority of their own knee jo int; pre-
serving bone-stock and the patients’ own ligaments. PFA
has a lso been recognised as a less ‘invasive’ operation
than TKA, facilit ating a more rapid recovery [2]. Despite
these perceived advantages, early PFA designs yielded
less than satisfactory results due to residual patella mal-
ali gnment, wear of po lyethylene and failure secondary to
disease progressi on in the other parts of the joint [ 3].
More recent studies, however, have shown significantly
better results with PFA. This is due to improved
implants, an appreciation of the need to balance the soft
tissues and more appropriate patient selection when con-
sidering PFA [4].
In a r etrospective case series study, Cartier et al. [5]
reported ex cellent functional outco me in 77% of patients
at a mean of 10 years follow-up. These findings substanti-
ate those of an earlier retrospective consecutive case study,
where good or excellent functional results were reported,
using the Knee Society Score (KSS), in 86% of ‘residual’
cases at 17 years [6]. Most recently, Odumenya et al. [7]
and Stark et al [8] have reported excellent functional out-
comes with 100% survivorship at 5 and 2 years follow-up,
respectively. Therefore, there is some evidence to suggest
that PFA provides positive results for patients with isolated
patellofemoral arthritis. It is however not clear how the
latest generation of PFA compare with the excellent long-
term results of Total Knee Arthroplasty [9]. The majority
of the remaining literature consists of case series with
short-term results and includes only a small number of
studies on the use of TKA for primarily severe patellofe-
moral arthritis. Mont et al. [10] reported 97% good or
excellen t clinical results using the KSS at a mean follow-
up of over 6 years. These results are in agreement with the
findings of Laskin et al. [11] who reported on forty-two
patients managed w ith TKA for primary patellofemoral
arthritis. This study compared the use of TKA in patients
with patellofemoral arthritis and tricompartmental arthri-
tis. They concluded that the results of TKA in the patello-
femoral subgroup were superior to those patients with
tricompartmental arthritis. However, these inferences are
uninformative when deci ding between TKA and PFA for
the treatment of isolated patellofemoral arthritis.
There are currently no published results of randomised
clinical trials comparing the two arthroplasty techniques.
At present the only registered study (ISRCTN22478626)
directly comparing TKA and PFA was not performed.
We therefore propose the first trial comparing TKA wit h
PFA to provide surgeons and patients with accurate
information regarding knee function. The null hypothesis
for this trial is that there is no difference in functional
score (WOMAC - Western Ontario and McMaster
Universities Osteoarthritis Inde x score) at one year post-
operation between Total Knee Arthroplasty and Patell o-
femoral Arthroplasty.
Methods/Design
Design
This is a two-arm, double-blind, randomised clinical trial
performed in a single centre (University Hospitals Coven-
try and Warwickshire NHS Trust) i n the United King-
dom. The participant and assessor (research associate)
are both blinded to the treatment allocation throughout
the e ntire study. This study has been reviewed by the
Coventry Research Ethics Committee under reference
number 09/H1210/9. The study w as approved on the 3
rd
of March 2009. The research carried out is in compliance
with the Helsinki Declaration.
Study participants
Inclusion criteria
The eligibility criteria for participation in this study is
that the patient is medically fit for an operation and has
severe isolated patellofemoral osteoarthritis of the knee
deemed suitable for a patellofemoral arthroplasty by the
responsible consultant orthopaedic surgeon. It is
accepted that all patients deemed suitable for PFA are
also suitable for TKA. These broad eligibility criteria
should ensure that the results of the study can readily be
Odumenya et al. BMC Musculoskeletal Disorders 2011, 12:265
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generalised to the wider population of patients with
severe isolated patellofemoral osteoarthritis.
Exclusion criteria
Contra-indications to surgery include patients with tibio-
femoral osteoarthritis of the knee and those unfit for sur-
gery, defined as: (i) severe cardiac impairment, e.g. heart
or valve replacement, arrhythmia, previous myocardial
infarction, (ii) severe respiratory impairment, e.g. chronic
obstructive pulmonary disease, asthma that has required
hospital admission, or (iii) any other systemic medical
condition that would prod uce a specific contraindication
to a general anaesthetic. There is no fixed age range.
In addition, patients who are unable to adhere to trial
procedures or complet e questionnaires, for reasons such
as dementia or intravenous drug use, will be excluded.
If a recruited patient requires contra-lateral knee arthro-
plasty surgery during the trial period, this second knee will
not be included in the study (i.e. it will not be randomised)
since the result of this intervention would not be indepen-
dent of the first intervention.
Recruitment
Patients will be recruited from orthopaedic clinics at Uni-
versity Hospitals Coventry and Warwickshire NHS Trust.
Upon identification of an eligible patient by the orthopae-
dic consultant, the patient will be referred to the research
associate present in the clinic. The research associate will
provide the patient with the patient information sheet and
verbally explain what the trial entails. The patient will
then be given the opportunity to discuss any issues w ith
the research associate, their consultant as well as members
of their family and friends.
Consent
Informed consent will be obtained by the research associ-
ate, after allowing sufficient time for the patient to con-
sider their decision and ask questions about the trial. Any
new information that arises during the trial that may affect
participants’ willingness to take part will be reviewed by
the Trial Steering Committee, and, if necessary, communi-
cated to all participants by the trial coordinator.
If the participant decides to withdraw, their care will
continue as normal for the hospital. If the participant deci-
destocontinueinthestudytheywillbeaskedsignan
updated consent form.
Post randomisation withdrawals
Patients may withdra w from the trial at any time without
discrimination. If patients decide to have the treatment to
which they were not randomised, they will be followed-up
where feasible and data collected as per the protocol until
completion of the trial. The primary analysis will be on an
intention-to-treat basis with a secondary per-protocol ana-
lysis. If patients have neither treatment during the course
of the trial, they will be followed up in the same way as
the other patients in the trial and included i n the inten-
tion-to-treat analysis.
The Study Intervention
The two treatments in this study are patellofemoral
arthroplasty and total knee arthroplasty. In this pragmatic
trial, each patient will undergo the allocated surgery
according to the preferre d technique and preferred
implants of the operating surgeon.
In summary, the details of the surgery will be left
entirely to the discretion of the surgeon to ensure that the
results of the trial can be generalised to as wide a group of
patients and surgeons as possible.
Patellofemoral Arthroplasty
Patellofemor al joint arthroplasty involves replacement of
the articular surfaces of the femoral trochlear groove with
a contoured metal implant and, usually, the under-surface
of the patella with a plastic ‘button’. Both articulating
areas are resected using jigs and clamps respectively. The
implants are then cemented in place using bone cement
(see Figure 1). The native tibiofemoral joint remains in
situ.
Total Knee Arthroplasty
In total knee arthroplasty, the tibiofemoral ar ticulation is
also replaced. The top of the tibia is resurfaced with a flat
metal plate with a plastic ‘spacer’ on top. The upper part
of the knee joint, the femoral condylar articulating surface,
is replaced with a contoured metal implant that fits
around it and includes the trochlear groove. The patella is
usually resurfaced with a plastic button similar to that
used in the PFA. All the implants are cemented to bone
(see Figure 2).
Rehabilitation
The same standard rehabilitat ion program will be imple-
mented for all patients, as outlined in the University Hos-
pitals Coventry and Warwickshire NHS Trust ‘Knee
Figure 1 AP radiograph showing a Patellofemoral Arthroplasty.
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Replacement: A Guide for Patients’ booklet. This includes
early e xercises, precautions to be followed for the first
three months, how to perform functional activities and
advanced exercises.
Follow-up
Patients will continue in routine clinical follow-up, accord-
ing to their surgeon’s practice. For this trial, the primary
outcome point will be at one year, w ith other scheduled
assessmentsat6weeks,3monthsand6monthspost
operation. At all these assessment time points patients will
come to the clinic to be reviewed by the research associate,
and if necessary an orthopaedic surgeon. Thereafter, an
annual postal questionnaire will be sent to each patient
including the Oxford Knee Score, Euroqol and an addi-
tional treatment questionnaire to monitor long term func-
tion and failure rates.
In this study, we will use techniques common in long
term cohort studies to ensure minimum loss to follow-
up, such as collection of multiple contact addresses and
telephone numbers, mobile telephone numbers and
email addresses. Considerable efforts will be made by the
trial team to keep in touch with p atients. Using these
techniques, with only 64 pa rticipants t o track, we are
confident that loss will not exceed 10%. In the event of a
part icipant being lost to one year follow-up, we will con-
sider, on the advice of the trial statistician, imputing
missing primary outcome data from interim scores.
A system of re minders will be instituted to ensure that
return to clinic at three, six and twelve months is as com-
plete as possible. The research associate will phone parti-
cipants to make an appointment and after two weeks
non-response a le tter will b e sent out to the p atient. The
letter will be followed up by phone call after 1-2 weeks. If
the re is no response from participant, they will be classi-
fied as a ‘non-responder’.
Study objectives
There are two main objectives of this randomised clini-
cal trial:
1. To quantify and draw inferences on observed differ-
ences in primary and secondary outcomes measures
between the trial treatment groups at one ye ar post-
operation.
2. To determine the complication rate of Patellofe-
moral Arthroplasty versus Total Knee Arthroplasty at
one year post-operation.
Outcome measures
The primary outcome measure is: WOMAC (Western
Ontario and McMaster Universities) Osteoarthritis
Index score. This is a validated questionnaire, which is
self-administered (filled out by the patient). It consists of
24 items (5 for pain, 2 for s tiffness and 17 for physical
function), all related to daily tasks, which are directly influ-
enced by poor function resulting from osteoarthritis. The
minimum (best) score attainable is 0 and the maximum
(worst) score is 96 [12].
Five secondary outcome measures will be used in this
trial: (i) Oxford Knee Score (OKS): This is a self-adminis-
tered, validated knee arthroplasty functional outcome
measure consisting of 12 items related to daily activities.
The score ranges from 12 to 60, wh ere 12 represents the
best outcome an d 60 represents the worst outcome [13].,
(ii) American Knee Society Score (AKSS) :Thisisalsoa
validated knee function questionnai re, which is divided
into two sections: knee score and function score. The knee
score is comprised of assessments of range of motion, sta-
bility, alignment, and muscle power of the knee. The func-
tion score includes an assessment of d aily tasks to
deter mine functional ab ility. Both scores range from 0 to
100 points (100 points being the best score). The research
associate fills out this questionnaire [14], (iii) Euroqol
(EQ-5D): This validated quality of life (QoL) questionnaire
consists of 5 domains related to daily activities, each with
a 3 -level answer possibilit y. The combination of ans wers
leads to t he QoL score. The patient completes this form
[15], (iv) Disability Rating Index: a self-administered, 12-
item Visual Analogue Score (VAS) questionnaire assessing
the patient’s own rating of disability [16], (v) UCLA Physi-
cal Activity Ques tionnaire: The Univers ity of California
Los Angeles activity-level rating is a self-rating scale from
level 0-complete inactivity to level 10- participa tion in
impact sports [17]. All complications will be recorded
throughout the duration of the trial.
Figure 2 AP radiograph showing a Total Knee Arthroplasty.
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Sample size
Previou s work has suggested that the WOMAC score is
the most sensitive condition-specific tool for assessing
interventions in knee osteoarthritis [12,18]. Angst et al.
[19] successfully demonstrated the use of the 17-item
functional sect ion of the WOMAC score to determine
sample size.
Thesamplesizecalculationwasbasedonatwo-arm
parallel group design and an assumed approximate normal
distribution for the primary outcome measure (WOMAC).
The required number of patients in each arm of the trial is
29, based on an independent samples t-test and an
assumed population standard deviation of 10.8 points [20]
and a minimum clinically important difference of 8 points
[19]; this gives a relatively lar ge standard effect size of
0.74. The proposed number of patients will provide 80%
power to detect a difference at the 5% level (PS, Power
and Sample Size Calculation Software version 2.1 30th
February 2003, available at http://biostat.mc.vanderbilt.
edu/wiki/Main/PowerSampleSize). To allow for a 10% loss
to follow-up we will aim to recruit 32 patients in each
arm, giving a total of 64 patients.
Randomisation
Those patients who consent to take part in the trial will
be randomised in a 1:1 allocation to TKA or PFA. The
randomisation se quence will be computer generated. An
independent researcher will phone the secure centralised,
telephone r andomisatio n se rvice. The treatment alloca-
tion will then be emailed to the medical secretary of the
operating consultant by t he randomisation service. The
medical secretary will then enter the allocation on to th e
patient’s operation booking form. This will ensure that
the research associates collecting outcome data remain
blind to the treatment allocation,
Blinding
The patients will also be blind to their treatment allocation
to allow for an unbiased comparison to be made between
the two interventions. The surgeons will, of course, not be
blind to the treatment but will take no part in the post-
operative assessment of the patients.
Statistical analysis
Standard statistical summaries (e.g. medians and ranges or
means and variances, dependent on the assumed distribu-
tion of the outcomes) and graphical plots showing correla-
tions will be presented for the primary outcome measure
(WOMAC) and the secondary outcome measures. Base-
line data will be summarized to check comparability
between treatment arms, and to highlight any characteris-
tic differences between those individuals in the study,
those ineligible, and those eligible but withholding con-
sent. The main analysis will investigate differences in the
primary outcome measure, the WOMAC score, between
the two treatment groups on an intention-to-treat basis at
12 months post-ope ration. The significance in responses
between treatment groups will be formally assessed using
an independent samples t-test;basedonanassumed
approximate normal distribution for this outcome mea-
sure. Tests will be two-sided and considered to provide
evidence for a significant difference if p-values are less
than 0.05 (5% significance level). Estimates of treatment
effects will be presented with 95% confidence intervals. A
linear regression analysis will also be undertaken that will
incorporate terms that model the effects of patient age
and gender in addition to the effects of the treatment
groups (TKA and PFA). Results from the unadjusted and
adjusted analyses will be presented graphically, together
with diagnostic plots that check the underlying model
assumptions. Depending on the nature of the data, various
derived variables (e.g. logarithmic transformations of
scores) may be created and analysed, in addition to the
primary outcome. Although missing data is not expected
to be a problem for this study, the nature and pattern of
the missingness will be carefully considered – including in
particular whether data can be treated as missing comple-
tely at random (MCAR). If j udged appropriate, missing
data will be imputed, probably using the multiple imputa-
tion facilities available in R http://www.r-project.org/. A
detailed statistical analysis plan (SAP) will be agreed with
the Data Management Committee (DMC) at the start of
the study. Any subsequent amendments to this initial SAP
will be clearly stated and justified. Interim analyses will be
performed only where directed by the DMC. The routine
statistical analysis will be carried out using R http://www.
r-project.org/.
This trial is expected to deliver results in early 2013.
Abbreviations
PFA: Patellofemoral Arthroplasty; TKA: Total Knee Arthroplasty; WO MAC:
Western Ontario and McMaster Universities Osteoarthritis Index Score.
Acknowledgements
This protocol was developed on behalf of the Patellofemoral Arthroplasty
Group at the University Hospitals Coventry and Warwickshire NHS Trust. The
Patellofemoral Arthroplasty Group consists of, Mr Tim Spalding, Mr Peter
Thompson, Mr Pedro Foguet, Mr Udai Prakash, Mr Steve Krikler, Mr Richard
King and Mr Matthew Costa.
This trial is funded by Action Medical Research (AMR). AMR did not
contribute to the trial protocol, the trial procedures or the writing of any
publications with regards to this trial.
Author details
1
Division of Health Sciences, Warwick Medical School, Universi ty of Warwick,
Clifford Bridge Road, Coventry, CV2 2DX, United Kingdom.
2
University
Hospitals Coventry & Warwickshire NHS Trust, Trauma & Orthopaedic
Department, Clifford Bridge Road, Coventry, CV2 2DX, United Kingdom.
Authors’ contributions
MO developed the protocol, assisted in securing grant funding and is
responsible for recruitment of trial patients. JA developed the protocol,
assisted in securing grant funding and manages the running of the trial. NP
Odumenya et al. BMC Musculoskeletal Disorders 2011, 12:265
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developed the protocol, assisted in securing grant funding and is
responsible for the statistical analysis of the trial. KM developed the protocol
and manages the running of the trial. TS developed the protocol and is
responsible for the recruitment of trial patients. MC developed the protocol,
secured the grant funding, is responsible for the recruitment of trial patients,
management of trial and has overall clinical responsibility for the conduct of
the trial. All authors read and approved the final manuscript.
Competing interests
The authors declare that they have no competing interests. The department
of trauma and orthopaedics at UHCW does not receive funding from
manufacturers of total knee arthroplasty. UHCW has held research grants
from manufacturers of both total hip arthroplasty and patellofemoral
arthroplasty implants, but not in relation to this trial.
Received: 28 September 2011 Accepted: 23 November 2011
Published: 23 November 2011
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Pre-publication history
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Cite this article as: Odumenya et al.: The Warwick patellofemoral
arthroplasty trial: a randomised clinical trial of total knee arthroplasty
versus patellofemoral arthroplasty in patients with severe arthritis of
the patellofemoral joint. BMC Musculoskeletal Disorders 2011 12:265.
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