VOL. 90-B, No. 1, JANUARY 200843
Total knee replacement with and without
A PROSPECTIVE, RANDOMISED TRIAL USING THE PROFIX TOTAL
A. J. Smith,
D. J. Wood,
From the University
of Western Australia,
D. J. Wood, FRCS, FRACS,
M.-G. Li, MD, PhD, Senior
School of Surgery and
University of Western
Australia, Gate 3, Verdun
Street, Nedlands, Western
Australia 6009, Australia.
A. J. Smith, BSc, PhD,
Correspondence should be sent
to Dr A. J. Smith; e-mail:
©2008 British Editorial Society
of Bone and Joint Surgery
J Bone Joint Surg [Br]
Received 4 December 2006;
Accepted after revision 20
We have examined the differences in clinical outcome of total knee replacement (TKR) with
and without patellar resurfacing in a prospective, randomised study of 181 osteoarthritic
knees in 142 patients using the Profix total knee system which has a femoral component
with features considered to be anatomical and a domed patellar implant.
The procedures were carried out between February 1998 and November 2002. A total of
159 TKRs in 142 patients were available for review at a mean of four years (3 to 7). The
patients and the clinical evaluator were blinded in this prospective study. Evaluation was
undertaken annually by an independent observer using the knee pain scale and the Knee
Society clinical rating system. Specific evaluation of anterior knee pain, stair-climbing and
rising from a seated to a standing position was also undertaken.
No benefit was shown of TKR with patellar resurfacing over that without resurfacing
with respect to any of the measured outcomes. In 22 of 73 knees (30.1%) with and 18 of 86
knees (20.9%) without patellar resurfacing there was some degree of anterior knee pain
(p = 0.183). No revisions related to the patellofemoral joint were performed in either group.
Only one TKR in each group underwent a re-operation related to the patellofemoral joint. A
significant association between knee flexion contracture and anterior knee pain was
observed in those knees with patellar resurfacing (p = 0.006).
While total knee replacement (TKR) is com-
monly carried out for end-stage degenerative
arthritis of the knee, orthopaedic surgeons are
still seeking clarification as to the indications
for patellar resurfacing during this pro-
Recent meta-analyses have been
unable to relate the design of the arthroplasty
to patellofemoral outcome.
tures of the femoral component may be an
important consideration regarding the out-
come after TKR when the patella has not been
From the results of
studies it appears that there may be optimal
design factors for the femoral component, such
as a deep-set, contoured femoral trochlea
extending sufficiently proximally and posteri-
orly to maintain contact with the patella.
studies after TKR do not
exactly replicate the forces occurring at the
, and cannot account for time-
dependent biological changes. Therefore, well-
designed clinical trials are necessary to confirm
the clinical benefit of a more anatomically-
designed patellofemoral joint in TKR.
We have examined the differences in the
clinical outcome between TKR with and with-
out patellar resurfacing using the Profix Total
The design fea-
Knee System (Smith & Nephew Richards Inc.,
Memphis, Tennessee), which has a femoral
component designed for compatibility with the
native patella. It was thought that TKR with
and without patellar resurfacing would result
in comparable outcomes at a minimum follow-
up of three years, given the anatomical design
of the femoral component. The primary out-
come compared was the difference in the knee
pain score before and after surgery. Secondary
outcomes were the incidence and severity of
anterior knee pain after operation, the rate of
re-operation, the Knee Society clinical rating
the functional ability related to
the patellofemoral joint and patient satisfac-
Patients and Methods
Between February 1998 and November 2002,
all patients with osteoarthritis (OA) under-
going primary TKR at two university-affiliated
teaching hospitals were evaluated for inclusion
in the study, which was approved by both the
university and hospital ethics committees.
Patients with inflammatory arthritis, a history
of patellar fracture, patellectomy, patello-
femoral instability or prior unicondylar knee
TOTAL KNEE REPLACEMENT WITH AND WITHOUT PATELLAR RESURFACING 49
VOL. 90-B, No. 1, JANUARY 2008
be less susceptible to malposition because of its spherical
Altered kinematics in the resurfaced patellofemoral
joint may play a role in the genesis of anterior knee pain.
A six-camera computerised gait analysis of a subset of the
patients in our study revealed a trend toward decreased
knee extension at heel-strike 0in those knees with patellar
resurfacing (10˚ vs 7˚, p = 0.023).26 Furthermore, in vivo
fluoroscopic studies have shown that TKR with dome-
shaped patellae have more superior contact points on the
patella and a greater patellar tilt angle in the superior-
inferior direction than that with native or mobile-bearing
patellae.27,28 It may be that the domed patellar design is
more susceptible to the effect of a flexion contracture and
lateral patellar displacement than the non-resurfaced
patella, perhaps because of increased patellofemoral con-
tact stress or shear stress. It has also been hypothesised
that increased patellofemoral contact stress in resurfaced
TKR may be a consequence of the material properties of a
metal/polyethylene interface, which may result in a
decreased ability for expansion under load of both sur-
faces, and thus decreased potential for pressure dissipa-
The statistical analysis for our study was carried out on
the number of knees rather than number of patients. This
is a potential problem because of a violation of the
assumption of independence of observations, and may
result in an underestimation of the standard error of the
mean. However, in our study, there were no patients with
bilateral TKR who contributed both knees to either treat-
ment group. Furthermore, the results were checked by
selecting only the knee with the highest level of pain for
analysis. The results did not differ substantially or alter
the conclusions of the study in terms of the difference in
knee pain scale score change (4.0, p = 0.711, 95% CI -6.5
to 9.5), or the risk of anterior knee pain for TKR without
patellar resurfacing (OR 0.51, p = 0.092, 95% CI 0.24 to
The results of our study indicate no superiority of patel-
lar resurfacing over patelloplasty in a TKR system with an
anatomical femoral component and a domed patellar
component. They contrast strongly with those of our
previous study, suggesting that the design of both the fem-
oral and patellar components may be an important
consideration in the decision as to whether or not to resur-
face the patella.
The authors would like to acknowledge Mr K. Kozak and Professor B. Nivbrant
as participating surgeons and Ms V. Petrov for her assistance with data collec-
The author or one or more of the authors have received or will receive bene-
fits for personal or professional use from a commercial party related directly or
indirectly to the subject of this article. In addition, benefits have been or will be
directed to a research fund, foundation, educational institution, or other non-
profit organisation with which one or more of the authors are associated.
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