1172THE JOURNAL OF BONE AND JOINT SURGERY
Patient-reported outcomes after fixed- versus
mobile-bearing total knee replacement
A MULTI-CENTRE RANDOMISED CONTROLLED TRIAL USING THE
KINEMAX TOTAL KNEE REPLACEMENT
From Bristol Implant
University of Bristol,
? V. Wylde, BSc, Research
? I. Learmonth, FRCS,
Professor of Orthopaedic
University of Bristol
Bristol Implant Research
Centre, Avon Orthopaedic
Centre, Southmead Hospital,
Bristol BS10 5NB, UK.
? A. Potter, BSc,
Department of Orthopaedics
Woodend Hospital, Eday Road,
Aberdeen AB15 6XS, UK.
? K. Bettinson, MSc,
Department of Orthopaedics
Freeman Road, High Heaton,
Newcastle upon Tyne
NE7 7DN, UK.
? E. Lingard, BPhty, MPhil,
MPH, Research Co-ordinator
School of Surgical and
Reproductive Sciences (Trauma
The Medical School, Newcastle
University, Newcastle upon
Tyne NE1 7RU, UK.
Correspondence should be sent
to Miss V. Wylde; e-mail:
©2008 British Editorial Society
of Bone and Joint Surgery
J Bone Joint Surg [Br]
Received 13 March 2008;
Accepted after revision 22 April
We compared patient-reported outcomes of the Kinemax fixed- and mobile-bearing total
knee replacement in a multi-centre randomised controlled trial. Patients were randomised
to the fixed- or the mobile-bearing prosthesis via a sealed envelope method after the bone
cuts had been made in the operating theatre. Randomisation was stratified by centre and
diagnosis. Patients were assessed pre-operatively and at eight to 12 weeks, one year and
two years post-operatively. Validated questionnaires were used which included the Western
Ontario MacMasters University, Short-Form 12, Mental Health Index-5, Knee Injury and
Osteoarthritis Outcome Score for Knee-Related Quality of Life and Function in Sport and
Recreation scales and a validated scale of satisfaction post-operatively. In total, 242 patients
(250 knees) with a mean age of 68 years (40 to 80) were recruited from four NHS orthopaedic
centres. Of these, 132 patients (54.5%) were women.
No statistically significant differences could be identified in any of the patient-reported
outcome scores between patients who received the fixed-bearing or the mobile-bearing
knee up to two-years post-operatively.
Younger and more active patients are now
undergoing total knee replacement (TKR) due
to widening criteria for surgery and changing
demographics of the patient population.1 By
providing a dual-surface articulation, allow-
ing mobility of the bearing surface and
enhancing the conformity of the polyethylene
insert, the theoretical advantage of the
mobile-bearing implant is a reduction of
stress at the bearing surface and thereby a
reduction in failure due to polyethylene
wear.2 These design features should also fol-
low a closer reproduction of normal knee
kinematics, thereby producing an arthro-
plasty that feels more natural to the patient.
The Kinemax Plus mobile-bearing prosthesis
(Stryker-Howmedica, Limerick, Ireland) is an
evolution combining the Kinemax Plus
(Stryker-Howmedica) and an established
mobile-bearing system from the Interax ISA
To date, there is no clear consensus on
whether the mobile-bearing knee produces
better outcomes than the fixed-bearing knee
replacement. Previous research3-9 has failed to
resolve the ongoing debate, and a Cochrane
Review on the subject criticised the methodol-
ogy of previous studies, describing the quality
of the research as ‘silver’,10 meaning it was
found to be poor.
Many of the previous trials comparing out-
comes after fixed- and mobile-bearing implants
have used surgeon-based outcome tools, such as
the Knee Society score (KSS),11 to assess clinical
outcomes. However, tools such as the KSS are
limited because there is a well-documented dis-
crepancy between clinician and patient ratings
of health status, particularly in subjective
domains such as pain and quality of life.12,13 To
address this deficiency, patient-reported out-
come measures, such as the disease-specific
Western Ontario and McMaster University
Osteoarthritis Index (WOMAC)14 and the gen-
eral health Short form (SF)-12,15 have been
developed which can be supplemented by vali-
dated measures of joint-related quality of life
such as the knee injury and osteoarthritis out-
come score (KOOS) quality of life scale16 and a
The aim of this randomised controlled trial
was to compare patient-reported outcomes,
including satisfaction and knee-related quality
of life, after Kinemax Plus fixed- versus mobile-
bearing TKR up to two years after surgery.
Patients and Methods
This prospective, multi-centre randomised
controlled trial involved four NHS orthopae-
dic centres in the United Kingdom (Avon
Orthopaedic Centre, Bristol; Weston General
PATIENT-REPORTED OUTCOMES AFTER FIXED- VERSUS MOBILE-BEARING TOTAL KNEE REPLACEMENT1179
VOL. 90-B, No. 9, SEPTEMBER 2008
functional limitations at two years post-operatively. Pain and
functional impairment strongly influence patient satisfac-
tion, with those who experience more pain and functional
limitations being less likely to be satisfied with the outcome
of surgery.25 In the current study, the levels of dissatisfaction
reflected those of pain and functional limitations, with
12.4% of patients being somewhat or very dissatisfied with
their outcome two years after surgery. Previous research has
reported similarly high rates of chronic pain, disability and
dissatisfaction after TKR,26 suggesting that it is not achieving
its purpose of providing pain relief and restoring functional
ability in a substantial proportion of patients.
In conclusion, no statistically significant differences were
found in patient-reported outcomes between the Kinemax
Plus fixed- and mobile-bearing implants up to two years
The authors wish to acknowledge Kinemax Mobile Group for their contribution
to this study: Avon Orthopaedic Centre, Bristol: A. Blom, J. Newman, A. Weale,
M. Hassaballa and V. Cavendish.
Although none of the authors has received or will receive benefits for profes-
sional use from a commercial party related directly or indirectly to the subject of
this article, benefits have been or will be received but will be directed solely to
a research fund, foundation, educational institution, or other non-profit organi-
sation with which one or more of the authors is associated.
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Table IV. Table IV. Complications
8 to 12 weeks8 to 12 weeks
Urinary track infections
Superficial wound infection
Deep wound infection
Inadequate range of flexion (< 75°)
Severe unexplained pain
Quadriceps tendon tear
Fell on ward and dehisced wound
1 year 1 year
Inadequate range of flexion (< 75°)
Loosening of tibial component
Patella tracking laterally
2 years2 years
Severe unexplained pain
* includes one patient revised one-year post-operatively