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Outcomes and early revision rate after medial unicompartmental knee arthroplasty: Prospective results from a non-designer single surgeon

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Background: This prospective study evaluates outcomes and reoperation rates for unicompartmental knee arthroplasty (UKA) from a single non-designer surgeon using relatively extended criteria of degenerative changes of grade 2 or above in either or both non-operated compartments. Methods: 187 consecutive medial mobile bearing UKA implants were included after history, clinical assessment and radiological evaluation. 91 patients had extended clinical outcomes. Post-operative assessment included functional scoring with the Oxford Knee Score (OKS) and radiographic review. Survivorship curves were constructed using the life-table method, with 95% confidence intervals calculated using Rothman's equation. Separate endpoints were examined: revision for any reason and revision for confirmed loosening. Results: The mean follow-up was 3.5 years. The pre-operative OKS improved from a mean of 21.2 to 38.9 (Mann-Whitney U Test, p = < 0.001). Twelve Patients required further operations including 9 revisions. No patients developed deep infection and no surviving implants were loose radiographically. Survivorship at 7 years with endpoints of re-operation, revision and aseptic loosening at surgery or radiographically was 88.4% (95% CI 79.6-93.7), 93.1% (95% CI 85.5-96.9) and 97.3% (95% CI 91.2-99.2) respectively. The presence of pre-operative mild contralateral tibiofemoral or any extent of patellofemoral joint degeneration was of no consequence. Discussion: The indications for UKA are being expanded to include patients with greater deformity, more advanced disease in the patellofemoral joint and even certain features in the lateral compartment indicative of an anteromedial pattern of osteoarthritis (OA). However, much of the supporting literature remains available only from designer centres. This study represents a group of patients with what we believe to be wider indications, along with decisions to treat made on clinical grounds and radiographs alone. Conclusion: This study shows comparable clinical outcomes of UKA for extended indications from a high volume, high-usage non-designer unit.
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R E S E A R C H A R T I C L E Open Access
Outcomes and early revision rate after
medial unicompartmental knee
arthroplasty: prospective results from a
non-designer single surgeon
Jonathan R. B. Hutt
1
, Avtar Sur
1*
, Hartej Sur
1
, Aine Ringrose
1
and Mark S. Rickman
2
Abstract
Background: This prospective study evaluates outcomes and reoperation rates for unicompartmental knee
arthroplasty (UKA) from a single non-designer surgeon using relatively extended criteria of degenerative changes of
grade 2 or above in either or both non-operated compartments.
Methods: 187 consecutive medial mobile bearing UKA implants were included after history, clinical assessment and
radiological evaluation. 91 patients had extended clinical outcomes. Post-operative assessment included functional
scoring with the Oxford Knee Score (OKS) and radiographic review. Survivorship curves were constructed using the
life-table method, with 95% confidence intervals calculated using Rothmans equation. Separate endpoints were
examined: revision for any reason and revision for confirmed loosening.
Results: The mean follow-up was 3.5 years. The pre-operative OKS improved from a mean of 21.2 to 38.9 (Mann-
Whitney U Test, p = < 0.001). Twelve Patients required further operations including 9 revisions. No patients developed
deep infection and no surviving implants were loose radiographically. Survivorship at 7 years with endpoints of re-
operation, revision and aseptic loosening at surgery or radiographically was 88.4% (95% CI 79.693.7), 93.1% (95% CI 85.
596.9) and 97.3% (95% CI 91.299.2) respectively. The presence of pre-operative mild contralateral tibiofemoral or any
extent of patellofemoral joint degeneration was of no consequence.
Discussion: The indications for UKA are being expanded to include patients with greater deformity, more advanced
disease in the patellofemoral joint and even certain features in the lateral compartment indicative of an anteromedial
pattern of osteoarthritis (OA). However, much of the supporting literature remains available only from designer centres.
This study represents a group of patients with what we believe to be wider indications, along with decisions to treat
made on clinical grounds and radiographs alone.
Conclusion: This study shows comparable clinical outcomes of UKA for extended indications from a high volume,
high-usage non-designer unit.
Keywords: Unicompartmental, Arthroplasty, Outcomes, Survivorship, Indications
* Correspondence: avtarsur@doctors.org.uk
1
Department of Trauma and Orthopaedics, St Georges University Hospitals
NHS Foundation Trust, London, UK
Full list of author information is available at the end of the article
© The Author(s). 2018 Open Access This article is distributed under the terms of the Creative Commons Attribut ion 4.0
International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and
reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to
the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver
(http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.
Hutt et al. BMC Musculoskeletal Disorders (2018) 19:172
https://doi.org/10.1186/s12891-018-2099-2
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Background
The Oxford unicompartmental knee arthroplasty (UKA)
(Biomet, Warsaw, Indiana) is a well-established implant
and reports from the designer centre demonstrate good
results for the medial UKA out into the second decade
[1] and into the midterm for its lateral counterpart [2].
Whilst the initial indications were relatively narrow, in-
creased experience has led to an expansion of potential
inclusion criteria, particularly with regard to the level of
deformity and disease presence elsewhere in the knee
[35]. The performance of the Oxford UKA in the wider
orthopaedic community has been variable, with units
reporting conflicting results, some equally favourable
[610], and others less so [1114]. Much of the concern
regarding UKA in general has come from the analysis of
registry data. The Australian, the New Zealand and the
UK implant registries all report higher revision rates for
unicompartmental prostheses [1517]. There is a debate
as to what registry data can reveal about the success of
an implant or technique, and analysis of published litera-
ture on the subject will be biased by numerous reports
from the designing centre [1820]. As such, reports
from surgeons independent of such centres add valuable
information on outcomes from the use of implants by
the wider orthopaedic community.
Between 2005 and 2013, the senior author implanted
187 consecutive UKAs in 173 patients, a caseload of 23
per year. During the same period, the senior author per-
formed 604 TKAs, and 12 lateral UKAs. 14 bilateral
UKA procedures were performed sequentially. This cor-
responds to a usage of 30% in keeping with recommen-
dations that 30% of a surgeons total knee arthroplasties
should be UKAs to achieve optimum results [7,21,22].
The aim of this study was to prospectively evaluate the
early outcomes and revision rate from a single high vol-
ume non-designer practice of unicompartmental knee
replacement as well as the effect of using relatively ex-
tended criteria with regards to other compartments in
the knee.
Methods
Patients presenting to the senior author with symptom-
atic knee arthritis are evaluated for their suitability for
UKA as follows: The history and clinical examination fo-
cuses on presence of isolated unicompartmental knee
pain severe enough to justify joint replacement and an-
terior cruciate ligament (ACL) integrity. Clinical evi-
dence of sagittal instability and the presence of
inflammatory disease remain absolute contraindications
to UKA. Maximum acceptable pre-operative deformity
is 15 degrees of varus that is correctable to neutral and
10 degrees of fixed flexion. No patients have been re-
fused UKA based on BMI. Radiographic evaluation is
with standing AP and Rosenberg views along with
standard lateral and skyline views. The presence of
bone-on-bone contact was considered an indication to
proceed with UKA. Stress radiographs and MRI scans
are not used. Evidence of mild disease of the contralat-
eral compartment, for example marginal osteophytes, is
not considered a contra-indication in the setting of min-
imal joint space narrowing. Degeneration of the patello-
femoral joint (PFJ) is considered irrelevant unless pain is
wholly anterior, and specifically worse on stairs than
with simple walking. No arthroscopic examinations are
performed solely to evaluate the knee for
decision-making purposes. For this study, both the patel-
lofemoral and contralateral tibiofemoral compartment
were evaluated on pre-operative radiographs according
to the Kellgren-Lawrence grading. We considered pa-
tients with evidence of degenerative change of grade 2
or above in either or both non-operated compartments
to have relatively extended indications for UKA. At sur-
gery, ACL integrity is assessed clinically with examin-
ation under anaesthesia (EUA) and direct inspection and
the lateral compartment is also directly inspected. Intra-
operative findings of patellofemoral joint degeneration,
whatever the severity, are not considered a contraindica-
tion to UKA. Within the time frame of the study, no pa-
tients were converted to TKR based on concerns with
ACL integrity at operation. Three patients scheduled for
a UKA received a TKA due to significant lateral disease
that was not identified on pre-operative radiographs.
Surgical technique was per manufacturer guidelines
using a tourniquet and thigh support with free draping
of the limb using the described minimally invasive ap-
proach [23]. All patients underwent a standardized
post-operative recovery physiotherapy programme of im-
mediate full weight bearing, range of motion and
strengthening exercises without restrictions.
Post-operative review was at 6 weeks, 6 months and
then annually, including functional scoring with the Ox-
ford Knee Score (OKS) and radiographs with standard
AP standing and lateral views. All patients were followed
prospectively and reviewed by independent examiners.
For this study, patients undergoing combined UKA and
ACL reconstruction have been excluded.
Statistical analysis
Data was tested for normality using DAgostinosK
2
test.
Pre-and post-operative OKS were thus compared using
the Mann-Whitney U-test with significance set at p<
0.05. Correlations for age and BMI used Spearmans rank
test. Complication rates for extended indications were
compared using Fishers exact test. Survivorship curves
were constructed using the life-table method, with 95%
confidence intervals calculated using Rothmans equa-
tion [24,25]. Separate endpoints were examined: revi-
sion for any reason and revision for confirmed
Hutt et al. BMC Musculoskeletal Disorders (2018) 19:172 Page 2 of 6
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loosening. Patients who died or were lost to follow-up
were treated as censored data.
All procedures performed in studies involving human
participants were in accordance with the ethical standards
of the Clinical Research Facility of St Georges Hospital.
All patients provided written informed consent to their
data being part of this study as part of their surgical consent.
Results
Between 2005 and 2013, the senior author implanted
187 consecutive UKAs in 173 patients. During the same
period, the senior author performed 604 TKAs, and 12
lateral UKAs. 14 bilateral UKA procedures were per-
formed sequentially. Patient demographics are shown in
Table 1. The mean overall follow-up was 3.5 years. 5 pa-
tients died from unrelated causes, all with
well-functioning implants. 7 patients (3.7%) were lost to
follow-up and proved untraceable. 2 had data at
6 months, whilst 5 had no follow-up data available. The
pre-operative OKS improved from a mean of 21.2 to
38.9 (Fig. 1, p = < 0.001). There was no correlation be-
tween the post-op OKS and either age (p= 0.88) or BMI
(p= 0.47).
Twelve patients required 13 further operations. Two
required bearing revision after dislocation within
6 months. One of these was later revised at 7 yrs. for
progression of osteoarthritis (OA) in the lateral compart-
ment, whilst the other had no further problems. Four
patients had revision to total knee arthroplasty (TKA)
for pain alone, without evidence of component loosening
at surgery. Three patients had revision for femoral com-
ponent loosening, all with single peg components. Two
were converted to TKA and 1 had a revision of the UKA
femoral component alone to a twin peg design. One pa-
tient was revised to a TKA for progression of arthritis
following multiple haemarthroses for a familial bleeding
disorder. Two further patients had additional lateral
compartment and patellofemoral arthroplasty respect-
ively without revision of the original UKA. No patients
developed deep infection and no surviving implants were
loose radiographically.
Survivorship at 7 years with endpoints of re-operation,
revision and aseptic loosening at surgery or radiograph-
ically was 88.1% (95% CI 79.193.5), 92.9% (95% CI
85.196.8) and 97.3% (95% CI 90.999.2) respectively.
All revisions were included for the re-operation end-
point. Only operations where the UKA implant was re-
moved or replaced were included for the revision
endpoint. The full survivorship curves and confidence
intervals for the three outcomes are shown in Fig. 2a-c.
The complete life tables for each outcome including
confidence intervals and effective number at risk each
year are provided in Additional file 1.
Effect of degeneration in other compartments
96 patients (51%) had no pre-operative extended indica-
tions, compared with 91 (49%) who did. The outcomes
for patients with extended indications in various combi-
nations are set out in Table 2. The extended indications
group had a significantly higher OKS (p= 0.01), a differ-
ence which remained significant for any case with PFJ de-
generation (p = 0.01) or with isolated PFJ degeneration (p
= 0.05). However, as the differences are less than 5 points,
an accepted minimally important clinical difference for
the OKS, this may not translate into clinical significance.
No other comparisons reached statistical significance; im-
portantly, patients without extended indications did not
demonstrate superior post-operative outcomes when com-
pared with any subgroups of patients with extended indi-
cations including those with a PFJ grade of 3 or 4 (p=
0.15). Only one patient with extended indications had a
revision to a TKA for arthritis progression this was the
patient with a familial bleeding disorder. Overall, patients
with extended indications had significantly lower rates of
re-operation and revision (p=0.003).
Discussion
The indications for UKA are being expanded to include
patients with greater deformity, more advanced disease
in the patellofemoral joint and even certain features in
the lateral compartment indicative of an anteromedial
pattern of OA [35]. However, much of the supporting
literature remains available only from designer centres.
Table 1 Cohort Demographics
UKA Patients
Number 187
M:F 92:95
Mean BMI, Range 29.7 (17.945.1)
Mean Age at Surgery / Years, Range 64.2 (4984)
Mean Follow-up / Years, Range 3.6 (0.58)
Fig. 1 Pre-and post-operative OKS
Hutt et al. BMC Musculoskeletal Disorders (2018) 19:172 Page 3 of 6
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This study represents a group of patients with what we
believe to be wider indications, along with decisions to
treat made on clinical grounds and radiographs alone.
Only very rarely was the procedure changed based on
intra-operative findings.
The senior author implanted 187 consecutive UKAs in
173 patients, a caseload of 23 per year. During the same
period, the senior author performed 604 TKAs, and 12
lateral UKAs. 14 bilateral UKA procedures were per-
formed sequentially. This corresponds to a usage of 30%
in keeping with recommendations that 30% of a sur-
geons total knee arthroplasties should be UKAs to
achieve optimum results Despite the broad criteria and
the fact that the senior author receives patients from
other consultants in the hospital for consideration of
UKA, the ratio of UKA:TKA for patients presenting with
symptomatic knee arthrosis in the period of this study
was approximately 1:3.
Nine UKA implants have been revised so far, and we
are not aware of any currently at risk. Four revisions
were for unexplained but persistent medial pain. All
were uncomplicated revisions to a TKA using simple
primary implants and no obvious cause for pain was
identified in any case. Whilst 3 patients have gone on to
a reasonable result, one continues to have unexplained
pain. None of these patients had extended indications as
we have defined. Three femoral components were re-
vised for aseptic loosening. All were of the single peg de-
sign, which has been noted in the past to be associated
with an incidence of early loosening [26]. One was re-
vised to a twin peg design and continues to function well
(recent OKS 47), whilst the other 2 cases were revised to
total knee arthroplasty, with satisfactory outcomes. Dur-
ing this series of patients, the twin-peg design for the
femoral component became available. Within the litera-
ture there are no reports of femoral loosening issues for
this iteration. Similarly, there were no failures of the
twin peg femoral component in this series. It is possible
therefore that these 3 revisions could have been avoided
with the use of the newer design implants.
There were 2 bearing dislocations; one undoubtedly due
to surgical error, with residual cement at the back of the tib-
ial component leading to anterior dislocation in full flexion.
At revision, an identical bearing was replaced after removal
Table 2 Outcomes for Extended Indications
Number of
Patients
Mean Post-
op OKS
Re-operation, Revision or
Aseptic Loosening
No Extended
Indications
96 37.6 12
Either Extended
Indication
91 40.3 1
PFJ +/Lateral
grade > 2
93 40.2 0
Lateral +/PFJ
grade > 2
27 40.8 0
Isolated PFJ
grade > 2
64 40.1 0
Isolated Lateral
grade > 2
3 44.0 1
PFJ Grade III/IV 39 39.5 0
Fig. 2 aSurvivorship curve with 95% Confidence Intervals for Re-
operation. bSurvivorship curve with 95% Confidence Intervals for
Revision. cSurvivorship curve with 95% Confidence Intervals for
Aseptic Loosening
Hutt et al. BMC Musculoskeletal Disorders (2018) 19:172 Page 4 of 6
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of the errant cement. The second dislocation occurred for
no clear reason and was revised to a bearing 1 mm thicker;
this patient is currently functioning extremely well (2-year
OKS 48). The dislocation rate of 1% is in line with other
published rates in the literature and remains a potential
complication of any mobile bearing UKA design.
Two cases went on to have further compartments re-
placed one patellofemoral at 40 months and one lat-
eral at 32 months after UKA. If anything, this represents
a failure of patient selection, necessitating a further op-
eration a moderate time after the primary surgery with a
rate of 1%. Patient selection and indeed implant selec-
tion in any orthopaedic surgery is complex and often dif-
ficult, and no selection process will be perfect. By
narrowing the inclusion criteria for UKA this 1% failure
rate could be lowered, but perhaps not eradicated due to
natural variances. There were no deep infections in this
series, and this is consistent with other reports of low in-
fection rates for UKA in comparison with TKA [2729].
For any new orthopaedic implant, favourable results
would be expected from developing centres, and whilst
it might be rational to assume that similar outcomes will
not be achieved by the wider surgical community, our
series forms part of a growing number of independent
reports of good results and favourable revision rates [6,
7,9,10]. There are also reports from other units with
less success [1114], but the main contrast comes from
concerns raised primarily by registry data [30]. Inevitably
the performance of an implant is dependent on the tech-
nique used to implant it, and studies have demonstrated
the effect of a significant learning curve for UKA [31
34] with some authors advocating minimum numbers to
be undertaken in order to maintain competence [7].
Strengths of the study that should be noted are the
series does not include the learning curve of the senior
author, with more than 50 procedures being carried out
as a registrar and fellow, but all cases carried out as a
consultant are included with a usage of 30% as recom-
mended for optimal results.
Limitations include the difficulty to quantify the effect
of a single surgeons ability to master a new technique.
Undoubtedly many surgeons never get over this learning
curve before abandoning the technique in favour of ei-
ther osteotomy or total knee arthroplasty, which will
affect global outcomes. Ultimately, the fate of UKA may
depend on whether there is any clinical benefit for the
patients. Level one evidence on this issue is on the way
[30].
Conclusions
In conclusion, we have shown comparable clinical out-
comes and survivorship of the medial Oxford UKA
when used with wider indications in a large cohort of
patients. Our all cause revision survivorship rate of 93%
at 7 years is similar to figures reported from systematic
reviews of registry data which show an all cause revision
rate for total knee replacement of 6% at 5 years and 12%
at 10 years [35]. In addition, the use of extended indica-
tions in this series has not had a detrimental effect on
post-operative outcomes or re-operation or revision
rates. We believe this data justifies the continued use of
UKA at our institution within our current indications
and serves to highlight the importance of practice ana-
lysis by individual surgeons of techniques that might be
controversial in the wider orthopaedic literature.
Additional file
Additional file 1: Outcome life tables. (TIFF 3853 kb)
Funding
No funding was received for this study.
Availability of data and materials
The datasets generated and/or analysed during the current study are
available in the figshare repository, https://figshare.com/s/
7efe5c493ce1235091c9
Authorscontributions
JH was involved in data analysis and drafting the manuscript. AR and HS
were involved in data acquisition. AS was involved in data acquisition and
preparation for submission. MR was the operating surgeon and was involved
in the acquisition and interpretation of the data. All authors read and
approved the final manuscript.
Ethics approval and consent to participate
As the manuscript contains outcome data collected as part of standard
routine care, the ethics department at St Georges Hospital determined that
formal ethics approval was not required. However, all procedures performed
in studies involving human participants were in accordance with the ethical
standards of the Clinical Research Facility of St Georges Hospital. All patients
provided written informed consent to their data being part of this study as
part of their surgical consent.
Competing interests
The authors declare that they have no competing interests.
PublishersNote
Springer Nature remains neutral with regard to jurisdictional claims in
published maps and institutional affiliations.
Author details
1
Department of Trauma and Orthopaedics, St Georges University Hospitals
NHS Foundation Trust, London, UK.
2
Department of Orthopaedics and
Trauma, The University of Adelaide and Royal Adelaide Hospital, Adelaide,
Australia.
Received: 15 July 2017 Accepted: 17 May 2018
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Supplementary resource (1)

Article
Full-text available
Background Mobile-bearing unicompartmental knee arthroplasty (MB-UKA) is a proven implant that has reliably delivered excellent results for decades. Based on the constrained implant design in MB-UKA, the occasional occurrence of anterior impingement should be expected. However, surprisingly, there are no clinical reports. Methods From 2016 to 2020, 14 patients with anterior medial knee pain were admitted to our arthroplasty center after MB-UKA implantation elsewhere. After taking the medical history and clinical examination, radiological imaging of the implant in at least 2 planes, including a whole-leg anteroposterior view, was performed. The “Knee Society Score (KSS)” and the “Knee Injury and Osteoarthritis Outcome Score (KOOS)” were recorded. Anterior impingement was diagnosed by reviewing the typical findings and specific exclusion of other diagnoses. Results The 14 patients showed a KSS of 46.6 and a KOOS of 51.5. The average pain level on the “Visual Analog Scale” was 7.8. The positioning of the implants showed consistently noticeable deviations from the standard recommendations. All 14 patients were treated by removing the MB-UKA and changing to a complete TKA. At the 12-month follow-up, the average Visual Analog Scale score was 1.8, and KOOS and KSS were 86 and 82, respectively. Conclusions The potential risk of anterior impingement in MB-UKA can be assumed. Diagnosis requires a detailed collection of medical history and clinical details combined with accurate radiological imaging. The cause of anterior impingement in MB-UKA is multifactorial and refers in our small group to the sum of minor deviations in implant positioning compared to the general recommendations.
Article
Full-text available
Purpose Surgeons with higher medial unicompartmental knee arthroplasty (UKA) usage have lower UKA revision rates. However, an increase in UKA usage may cause a decrease of total knee arthroplasty (TKA) usage. The purpose of this study was to investigate the influence of UKA usage on revision rates and patient-reported outcomes (PROMs) of UKA, TKA, and combined UKA + TKA results. Methods Using the New Zealand Registry Database, surgeons were divided into six groups based on their medial UKA usage: < 1%, 1–5%, 5–10%, 10–20%, 20–30% and > 30%. A comparison of UKA, TKA and UKA + TKA revision rates and PROMs using the Oxford Knee Score (OKS) was performed. Results A total of 91,895 knee arthroplasties were identified, of which 8,271 were UKA (9.0%). Surgeons with higher UKA usage had lower UKA revision rates, but higher TKA revision rates. The lowest TKA and combined UKA + TKA revision rates were observed for surgeons performing 1–5% UKA, compared to the highest TKA and UKA + TKA revision rates which were seen for surgeons using > 30% UKA ( p < 0.001 TKA; p < 0.001 UKA + TKA). No clinically important differences in UKA + TKA OKS scores were seen between UKA usage groups at 6 months, 5 years, or 10 years. Conclusion Surgeons with higher medial UKA usage have lower UKA revision rates; however, this comes at the cost of a higher combined UKA + TKA revision rate that is proportionate to the UKA usage. There was no difference in TKA + UKA OKS scores between UKA usage groups. A small increase in TKA revision rate was observed for high-volume UKA users (> 30%), when compared to other UKA usage clusters. A significant decrease in UKA revision rate observed in high-volume UKA surgeons offsets the slight increase in TKA revision rate, suggesting that UKA should be performed by specialist UKA surgeons. Level of evidence III, Retrospective therapeutic study.
Article
We aimed to compare postoperative pain, functional recovery, and patient satisfaction among patients receiving one-stage medial bilateral or unilateral medial UKA. Our main hypothesis was that during the first 72 postoperative hours, patients who underwent medial bilateral UKA did not consume more analgesics than those who underwent medial unilateral UKA. Patients and methods A prospective case-control study was undertaken involving 148 patients (74 one-stage medial bilateral versus 74 medial unilateral Oxford UKA). The primary outcome was evaluation of the postoperative total consumption of analgesics from 0 to 72 h. Next, the postoperative evolution of pain scores and functional recovery were assessed. Oxford knee scores (OKS) were assessed preoperatively at 6 and 12 months with the occurrence of clinical or radiological complications. Finally, patient satisfaction was evaluated at the final follow-up. Results The cumulative sums of analgesic consumption (0–72 h) calculated in the morphine equivalent dose were 21.61 ±3.70 mg and 19.11 ±3.12 mg in the patient and control groups, respectively (p=0.30). Moreover, there were no significant differences in terms of pain scores (p=0.45), functional recovery (p=0.59, 0.34), length of stay (p=0.18), OKS scores (p=0.68, 0.60), complications (p=0.50), patient satisfaction (p=0.66), or recommendations for intervention (p=0.64). Conclusion Patients who undergo one-stage medial bilateral UKA do not experience more pain and do not consume more analgesics than those who undergo medial unilateral UKA. A bilateral procedure is not associated with a lower recovery or a higher rate of complications, as functional outcomes at 6 and 12 months are similar to those of unilateral management.
Article
Background An intact anterior cruciate ligament (ACL) is thought to be prerequisite for successful unicompartmental knee arthroplasty (UKA), but recent studies reported successful midterm results of UKA in ACL-deficient (ACLD) knees. We hypothesized that ACLD is not always a contraindication for medial UKA when preoperative radiographs showed typical anteromedial knee patterns. Methods From April 2012 to March 2016, 401 Oxford mobile-bearing UKAs in 282 patients were retrospectively identified from our database. Patients whose ACL was severely damaged, but preoperative X-rays showed typical anteromedial osteoarthritis (OA) patterns, were categorized into the ACLD group. From intraoperative data, those whose ACL was intact were categorized into the ACL functional (ACLF) group. There were 32 and 369 knees in the ACLD and ACLF groups, respectively, and mean follow-up periods were 66.1 and 63.8 months for the ACLD and ACLF groups, respectively. We compared the postoperative clinical outcome and component survivorship, with an endpoint of component revision, between ACLD groups and ACLF groups. Results In both groups, the Oxford knee score, Knee Society score, Tegner activity score, and knee range of motion in extension were improved after surgery. The UKA component survival rate at five years was 100% in the ACLD group and 98.9% in the ACLF group. There were no significant differences between the groups. Conclusion Mid-term clinical outcomes of Oxford mobile-bearing UKA in ACLD knees were similar to those in ACLF knees. ACL deficiency is not always a contraindication for medial unicompartmental knee arthroplasty in patients with typical anteromedial osteoarthritis radiographs.
Article
Full-text available
In this literature review, a systematic analysis of modern data on the study of complications of unicompartmental arthroplasty of the knee, their prevalence, the main methods of treatment and prevention. Instability of the components of the endoprosthesis, wear of the polyethylene and progression of the degenerative process in the contralateral joint were found to have the highest frequency in the structure of complications. Additional factors for the development of negative effects of unicompartimental arthroplasty of the knee are local osteoporosis of the femur and tibia, periprosthetic fractures, infectious complications and pain syndrome.
Chapter
The best indication for UKA is painful osteoarthritis in an isolated tibiofemoral compartment (medial or lateral). An age younger than 60 years, a weight of 180 lb. (82 kg) or more, performing heavy work, having chondrocalcinosis, and having an exposed bone in the patellofemoral (PF) joint are not contraindications for unicompartmental knee arthroplasty (UKA). Severe impairment of the lateral facet of the PF joint with bone loss and grooving is a contraindication for UKA. Medial UKA should only be performed in cases of severe osteoarthritis (OA) as shown in preoperative X-rays, with medial bone-on-bone contact and a medial/lateral ratio of <20%. The postoperative results of UKA are generally good. Medium-term and long-term studies have reported acceptable results at 10 years, with implant survival >95% for UKAs performed for medial OA or osteonecrosis and for lateral UKA, especially when fixed-bearing implants are used. When all implant-related reoperations are considered failures, the 10-year survival rate is 94% and the 15-year survival rate is 91%. Aseptic loosening is the principal failure mechanism in the first few years and in mobile-bearing implants, whereas OA progression causes most failures in later years and in fixed-bearing implants. The comprehensive complication rate and the comprehensive reoperation rate are comparable between mobile bearings and fixed bearings. The survival likelihood of the all-polyethylene UKA implant is similar to that of metal-backed modular designs for UKA. Notable cost savings of approximately 50% can be achieved with an outpatient UKA surgery protocol. Outpatient surgery for UKA is efficacious and safe, with satisfactory clinical results.
Article
Background To evaluate and compare the clinical and radiological outcomes of patients subjected to medial unicompartmental knee arthroplasty (UKA). Methods The study included 146 knees of 115 consecutive medial UKAs patients with a minimum five-year follow-up. Pre- and postoperative functional and clinical outcomes were measured using the Visual Analog Scale (VAS), Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC), Oxford Knee Score (OKS), American Knee Society Score (AKSS-O), knee range of motion (ROM), and Short-Form Health Survey (SF-36). The Kellgren–Lawrence osteoarthritis (OA) grading system was used for the evaluation of the OA status. The joint line convergence angle (JLCA) of the operated and contralateral knee, the tibiofemoral coronal angle (TFCA), and the tibial slope angle were used in the radiological evaluation. Results The mean age of patients was 58.8 ± 7.0 years. The mean follow-up period was 7.41 ± 1.54 years. Good to excellent functional outcomes were obtained according to VAS, WOMAC, OKS, AKSS-O, and SF-36 scores. Insert dislocation was the main reason for revision surgery (nine patients, 90%). Preoperative body mass index (BMI), postoperative BMI, American Society of Anesthesiologists (ASA) Score, postoperative knee flexion contracture, mean increase in postoperative medial joint space (PMJS) height, and OA progression were found to affect the revision status. Conclusions Good to excellent functional, clinical, and radiological outcomes were obtained with medial UKA at a minimum follow-up of five years. Differences in preoperative and postoperative radiological parameters except an increase in PMJS height had no impact on revision status.
Article
Full-text available
Unicompartmental knee arthroplasty (UKA) has advantages over total knee arthroplasty but national joint registries report a significantly higher revision rate for UKA. As a result, most surgeons are highly selective, offering UKA only to a small proportion (up to 5%) of patients requiring arthroplasty of the knee, and consequently performing few each year. However, surgeons with large UKA practices have the lowest rates of revision. The overall size of the practice is often beyond the surgeon’s control, therefore case volume may only be increased by broadening the indications for surgery, and offering UKA to a greater proportion of patients requiring arthroplasty of the knee. The aim of this study was to determine the optimal UKA usage (defined as the percentage of knee arthroplasty practice comprised by UKA) to minimise the rate of revision in a sample of 41 986 records from the for National Joint Registry for England and Wales (NJR). UKA usage has a complex, non-linear relationship with the rate of revision. Acceptable results are achieved with the use of 20% or more. Optimal results are achieved with usage between 40% and 60%. Surgeons with the lowest usage (up to 5%) have the highest rates of revision. With optimal usage, using the most commonly used implant, five-year survival is 96% (95% confidence interval (CI) 94.9 to 96.0), compared with 90% (95% CI 88.4 to 91.6) with low usage (5%) previously considered ideal. The rate of revision of UKA is highest with low usage, implying the use of narrow, and perhaps inappropriate, indications. The widespread use of broad indications, using appropriate implants, would give patients the advantages of UKA, without the high rate of revision. Cite this article: Bone Joint J 2015;97-B:1506–11.
Article
Full-text available
Background and purpose Some studies have found high complication rates and others have found low complication rates after unicompartmental knee arthroplasty (UKA). We evaluated whether hospital procedure volume influences the risk of revision using data from the Norwegian Arthroplasty Register (NAR). Materials and methods 5,791 UKAs have been registered in the Norwegian Arthroplasty Register. We analyzed the 4,460 cemented medial Oxford III implants that were used from 1999 to 2012; this is the most commonly used UKA implant in Norway. Cox regression (adjusted for age, sex, and diagnosis) was used to estimate risk ratios (RRs) for revision. 4 different volume groups were compared: 1–10, 11–20, 21–40, and > 40 UKA procedures annually per hospital. We also analyzed the reasons for revision. Results and interpretation We found a lower risk of revision in hospitals performing more than 40 procedures a year than in those with less than 10 UKAs a year, with an unadjusted RR of 0.53 (95% CI: 0.35–0.81) and adjusted RR of 0.59 (95% CI: 0.39–0.90). Low-volume hospitals appeared to have a higher risk of revision due to dislocation, instability, malalignment, and fracture than high-volume hospitals.
Article
Background: Outcomes after unicompartmental knee arthroplasty (UKA) are variable and influenced by caseload (UKA/y) and usage (percentage of knee arthroplasty that are UKA), which relates to indications. This meta-analysis assesses the relative importance of these factors. Methods: MEDLINE (Ovid), Embase (Ovid), and Web of Science (ISI) were searched for consecutive series of cemented Phase 3 Oxford medial UKA. The primary outcome was revision rate/100 observed component years (% pa) with subgroup analysis based on caseload and usage. Results: Forty-six studies (12,520 knees) with an annual revision-rate ranging from 0% to 4.35% pa, mean 1.21% pa (95% confidence interval [CI], 0.97-1.47), were identified. In series with mean follow-up of 10-years, the revision-rate was 0.63% pa (95% CI, 0.46-0.83), equating to a 94% (95% CI, 92%-95%) 10-year survival. Aseptic loosening, lateral arthritis, bearing dislocation, and unexplained pain were the predominant failure mechanisms with revision for patellofemoral problems and polyethylene wear exceedingly rare. The lowest revision-rates were achieved with caseload >24 UKA/y (0.88% pa; 95% CI, 0.63-1.61) and usage >30% (0.69% pa; 95% CI, 0.50-0.90). Usage was more important than caseload; with high usage (≥20%), the revision-rate was low, whether the caseload was high (>12 UKA/y) or low (≤12 UKA/y; (0.94% pa; 95% CI, 0.69-1.23 and 0.85% pa; 95% CI, 0.65-1.08), respectively); with low usage (<20%), the revision-rate was high, whether the caseload was high or low (1.58% pa; 95% CI, 0.57-3.05 and 1.76% pa; 95% CI, 1.21-2.41, respectively). Conclusion: To achieve optimum results, surgeons, whether high or low caseload, should adhere to the recommended indications such that ≥20%, or ideally >30% of their knee arthroplasties are UKA. If they do this, then they can expect to achieve results similar to those of the long-term series, which all had high usage (>20%) and an average 10-year survival of 94%.
Article
Aims Approved by the Food and Drug Administration in 2004, the Phase Ill Oxford Medial Partial Knee is used to treat anteromedial osteoarthritis (AMOA) in patients with an intact anterior cruciate ligament. This unicompartmental knee arthroplasty (UKA) is relatively new in the United States, and therefore long-term American results are lacking. Patients and Methods This is a single surgeon, retrospective study based on prospectively collected data, analysing a consecutive series of primary UKAs using the Phase Ill mobile-bearing Oxford Knee and Phase Ill instrumentation. Between July 2004 and December 2006, the senior author (RHE) carried out a medial UKA in 173 patients (213 knees) for anteromedial osteoarthritis or avascular necrosis (AVN). A total of 95 patients were men and 78 were women. Their mean age at surgery was 67 years (38 to 89) and mean body mass index 29.87 kg/m2 (17 to 62). The mean follow-up was ten years (4 to 11). Results Survivorship of the Oxford UKA at ten years was 88%, using life table analysis. Implant survivorship at ten years was 95%. The most common cause for revision was the progression of osteoarthritis in the lateral compartment. The mean knee score element of the American Knee Society Score (AKSS) was 50 pre-operatively and increased to 93 post-operatively. The mean AKSS function score was 56 pre-operatively rising to 78 post-operatively Conclusion This ten-year follow-up study of the Oxford UKA undertaken in the United States shows good survivorship and excellent function in a wide selection of patients with AMOA and AVN.
Article
Aims Approved by the Food and Drug Administration in 2004, the Phase III Oxford Medial Partial Knee is used to treat anteromedial osteoarthritis (AMOA) in patients with an intact anterior cruciate ligament. This unicompartmental knee arthroplasty (UKA) is relatively new in the United States, and therefore long-term American results are lacking. Patients and Methods This is a single surgeon, retrospective study based on prospectively collected data, analysing a consecutive series of primary UKAs using the Phase III mobile-bearing Oxford Knee and Phase III instrumentation. Between July 2004 and December 2006, the senior author (RHE) carried out a medial UKA in 173 patients (213 knees) for anteromedial osteoarthritis or avascular necrosis (AVN). A total of 95 patients were men and 78 were women. Their mean age at surgery was 67 years (38 to 89) and mean body mass index 29.87 kg/m2 (17 to 62). The mean follow-up was ten years (4 to 11). Results Survivorship of the Oxford UKA at ten years was 88%, using life table analysis. Implant survivorship at ten years was 95%. The most common cause for revision was the progression of osteoarthritis in the lateral compartment. The mean knee score element of the American Knee Society Score (AKSS) was 50 pre-operatively and increased to 93 post-operatively. The mean AKSS function score was 56 pre-operatively rising to 78 post-operatively Conclusion This ten-year follow-up study of the Oxford UKA undertaken in the United States shows good survivorship and excellent function in a wide selection of patients with AMOA and AVN. Cite this article: Bone Joint J 2016;98-B(10 Suppl B):34–40.
Article
Background: High-volume surgeons attain the best results following unicompartmental knee replacement (UKR), but the exact relationship between caseload and outcome is not clear. It is not known whether this effect is due to patient selection or surgical skill nor whether a similar effect is seen in total knee replacement (TKR). The aim of this study was to quantify the effect of surgical caseload on survival of both TKR and UKR. Methods: This study was based on 459,280 patient records (422,149 TKRs and 37,131 UKRs) from the National Joint Registry for England and Wales. The caseload-outcome relationship was characterized graphically and quantified using regression techniques. Patient selection was compared among high, medium, and low-volume surgeons. Prosthetic survival was compared between UKRs (performed by high, medium, and low-volume surgeons) and matched TKRs. Results: Caseload affected survival of TKR and, more strongly, of UKR. The revision rate following UKR dropped steeply until the volume reached ten cases per year, plateauing at thirty cases. For surgeons performing fewer than ten UKRs per year, the mean eight-year rate of survival of the UKRs was 87.9% (95% confidence interval [CI] = 86.9% to 88.8%) compared with 92.4% (95% CI = 90.9% to 93.6%) for those who performed thirty UKRs or more per year. Analysis of the TKRs showed a linear decrease in revision rate as caseload increased (hazard ratio [HR] for revision = 0.99 [95% CI = 0.98 to 0.99] for every five-case increase in caseload). Surgeons who performed a lower volume of UKRs tended to operate on younger and healthier patients and were more likely to perform revisions to treat loosening and pain. After matching of patients who had undergone UKR with those who had undergone TKR, the surgeons who performed a high volume of UKRs were found to have an eight-year revision/revision rate similar to that seen after TKR (HR for revision or reoperation = 1.10 [95% CI = 0.99 to 1.22] favoring TKR). Conclusions: This study confirmed the importance of surgical caseload in determining the survival of UKR and, to a lesser extent, TKR. The reasons for this effect are complex and not fully explained by variables recorded in the National Joint Registry; however, the patient selection and revision threshold of lower-volume surgeons may be a factor. Examination of matched patients in this study demonstrated that high-volume surgeons can achieve revision/reoperation rates similar to those observed following TKR.
Article
This prospective study reports the 15-year survival and ten-year functional outcome of a consecutive series of 1000 minimally invasive Phase 3 Oxford medial UKAs (818 patients, 393 men, 48%, 425 women, 52%, mean age 66 years; 32 to 88). These were implanted by two surgeons involved with the design of the prosthesis to treat anteromedial osteoarthritis and spontaneous osteonecrosis of the knee, which are recommended indications. Patients were prospectively identified and followed up independently for a mean of 10.3 years (5.3 to 16.6). At ten years, the mean Oxford Knee Score was 40 (standard deviation (sd) 9; 2 to 48): 79% of knees (349) had an excellent or good outcome. There were 52 implant-related re-operations at a mean of 5.5 years (0.2 to 14.7). The most common reasons for re-operation were arthritis in the lateral compartment (2.5%, 25 knees), bearing dislocation (0.7%, seven knees) and unexplained pain (0.7%, seven knees). When all implant-related re-operations were considered as failures, the ten-year rate of survival was 94% (95% confidence interval (CI) 92 to 96) and the 15-year survival rate 91% (CI 83 to 98). When failure of the implant was the endpoint the 15-year survival was 99% (CI 96 to 100). This is the only large series of minimally invasive UKAs with 15-year survival data. The results support the continued use of minimally invasive UKA for the recommended indications. Cite this article: Bone Joint J 2015;97-B:1493–99.
Article
There are few reports of the Oxford unicompartmental knee arthroplasty (UKA) survival rate in Asia. This study describes outcomes of 1279 Oxford UKAs for Japanese patients. The mean follow-up was 5.2 years. We divided patients into two groups based on preoperative indications (extended indications group and strict indications group). The Oxford knee score improved from 22.3 to 40.8 (P = 0.041). The 10-year survival rate using revision was 95%. A total of 25 UKAs (2.0%) required revision. The most common reason was subsidence of tibial component. The 5-year cumulative survival rate of the strict indications group was significantly higher than that of the extended indications group (99.1% vs. 93.8%, P < 0.001). When we followed inclusion criteria strictly, good clinical results were achieved in Asia.
Article
Mobile-bearing unicompartmental knee replacements (UKRs) with a flat tibial plateau have not performed well in the lateral compartment, owing to a high dislocation rate. This led to the development of the Domed Lateral Oxford UKR (Domed OUKR) with a biconcave bearing. The aim of this study was to assess the survival and clinical outcomes of the Domed OUKR in a large patient cohort in the medium term. We prospectively evaluated 265 consecutive knees with isolated disease of the lateral compartment and a mean age at surgery of 64 years (32 to 90). At a mean follow-up of four years (sd 2.2, (0.5 to 8.3)) the mean Oxford knee score was 40 out of 48 (sd 7.4). A total of 12 knees (4.5%) had re-operations, of which four (1.5%) were for dislocation. All dislocations occurred in the first two years. Two (0.8%) were secondary to significant trauma that resulted in ruptured ligaments, and two (0.8%) were spontaneous. In four patients (1.5%) the UKR was converted to a primary TKR. Survival at eight years, with failure defined as any revision, was 92.1% (95% confidence interval 81.3 to 100). The Domed Lateral OUKR gives good clinical outcomes, low re-operation and revision rates and a low dislocation rate in patients with isolated lateral compartmental disease, in the hands of the designer surgeons. Cite this article: Bone Joint J 2014;96-B:59–64.