EOR | |
DOI: 10.1302/2058-5241.6.200102
www.efortopenreviews.org
Osteoarthritis of the medial compartment, where the lat-
eral compartment and patella-femoral joint are relatively
spared, is a common orthopaedic presentation.
Most frequently, the treatment of choice would be a total
knee replacement, which involves removing healthy joint
surfaces in such patients.
Arthroscopic debridement in the osteoarthritic knee has
fallen out of favour due to poor clinical results.
A trend has developed towards less invasive surgery with
uni-compartmental knee replacement (UKR) and high
tibial osteotomy (HTO) gaining increasing popularity.
Surgeons differ in their relative indications and contraindi-
cations to performing these procedures.
Total knee replacement (TKR) continues to have the low-
est overall revision rate of the available options.
Growing evidence demonstrates more favourable patient-
reported outcome measures in UKR and HTO patients,
compared to TKR.
Knee joint distraction (KJD) has been demonstrated as an
alternative method of treatment in such patients.
Keywords: knee; osteoarthritis
Cite this article: EFORT Open Rev 2021;6:113-117.
DOI: 10.1302/2058-5241.6.200102
Introduction
Many patients present to orthopaedic surgeons with a
painful knee attributed to osteoarthritis of the medial
compartment, where the lateral compartment and
patella-femoral joint are relatively spared. Traditionally,
the treatment of choice would be a total knee arthroplasty;
however, this involves removing healthy joint surfaces.
Arthroscopic debridement in the osteoarthritic knee has
fallen out of favour due to poor clinical results.1 Recently,
a trend has developed towards less invasive surgery with
uni-compartmental knee replacement (UKR) and high tib-
ial osteotomy (HTO) gaining increasing popularity. Recent
research has looked into potential benefits of these options
over total knee arthroplasty. Knee surgeons differ in their
willingness to offer patients such interventions. Those who
do often differ in their relative indications and contraindi-
cations to performing them. In this instructional review
article, we demonstrate the evidence for each option with
particular focus on controversies and unanswered ques-
tions. The aim of the article is to provide an up-to-date
evidence base for the treatment options for such patients.
Options
Ultimately, a patient with knee arthritis can be treated oper-
atively or non-operatively. Non-operative management
may include appropriately titrating oral analgesia, shock-
absorbing footwear, supports to offload the joint and weight-
reduction strategies. An intra-articular injection of either a
corticosteroid, platelet-rich plasma (PRP) or hyaluronic acid
may be considered. Orthotic treatments such as a hinged
offloader brace can also be employed. Operative manage-
ment might involve a total knee replacement (TKR), with
other options being a uni-compartmental knee replacement
(UKR) or high tibial osteotomy (HTO), if the patient and the
disease characteristics allow. The indications and contraindi-
cations for UKR and HTO are open to ongoing debate. More
recently, joint distraction has been employed as a method
of offloading the affected medial compartment, with the
proposed mechanism of cartilage regeneration.
UKR
In 1989, Kozinn and Scott recommended contraindications
for UKR as patient < 60 years of age, weight > 82 kg, chon-
drocalcinosis, exposed bone on the patello-femoral com-
partment and those who are very active or undertake heavy
labour.2 It is widely accepted that these criteria are too strict
and are now directly challenged in many instances. Cur-
rent criteria have suggested the consideration of UKR in sit-
uations of uni-compartmental full-thickness osteoarthritis,
a functionally stable anterior cruciate ligament with stable
collateral ligaments, correctable intra-articular deformity
and the absence of an inflammatory aetiology.3
Medial compartment osteoarthritis of the knee:
a review of surgical options
Daniel J. McCormack
Darren Puttock
Steven P. Godsiff
6.2001EOR0010.1302/2058-5241.6.200102
review-article2021
Knee
114
High activity levels, once thought to be detrimental to
patients undergoing UKR, have since been found to be ben-
eficial in terms of implant survivorship and revision rates.4
Patients also have higher rates of returning to sporting activ-
ities, particularly if low impact, compared to with TKR.5
The Oxford Group found that patients undergoing UKR
with partial-thickness medial compartment cartilage loss
on the femur, tibia or both, had poorer functional out-
comes compared to full-thickness loss from both femur
and tibia.6 The authors suggest UKR should be reserved
for patients with bone-on-bone arthritis, a so called ‘kiss-
ing lesion’. A medial UKR has also been shown to have
excellent long-term results in patients with osteonecrosis
of the medial femoral condyle.7
ACL-deficient knees may still benefit from UKR; how-
ever, the knee should be assessed for evidence of functional
instability which may be considered a contraindication to
a mobile bearing UKR.8 Functional instability is thought to
be more prevalent in primarily ACL-deficient knees, usually
resulting from trauma, compared to those with secondary
ACL deficiency as a result of osteoarthritis, where the knee
may still be functionally stable. A UKR should be avoided
if the knee is expected to be unstable after the procedure.
It must be noted that an ACL-deficient knee is predis-
posed to posterolateral tibial wear, which may mean a
medial UKR is contraindicated as the arthritis may not be
unicompartmental in nature.9
UKR differs from a HTO in approach to deformity
correction. UKR will correct an intra-articular deformity
caused by cartilage loss with the aim of restoring collateral
ligaments to their normal tension.10 An HTO differs in that
the aim of the procedure is to alter the mechanical axis of
the limb.11 For this reason, UKR is contraindicated in large
deformities (> 15 degrees), as they will not be corrected
by the intra-articular procedure.
The decision to offer patients a UKR presents a dilemma
for the surgeon. UK registry data suggests that low-
volume surgeons have a higher revision rate; however, the
traditional contraindications of Kozinn and Scott would
mean only 6% of knees are appropriate.12 Other studies
have suggested that although currently fewer than 10%
of knee arthroplasties are a UKR, up to 47% of patients
requiring a knee replacement have uni-compartmental
disease.13 With this in mind, surgeons must decide indi-
vidually whether they would benefit from adjusting their
own indications for UKR to ensure they are adequately
exposed to the technique, without compromising out-
comes by offering UKR to patients who are unlikely to
benefit. National Joint Registry evidence demonstrates the
revision rate falls sharply until 10 cases are performed a
year, with a levelling off at 30 cases a year.14 The challenge
lies in appropriate patient selection.
The TOPKAT Study Group have concluded that UKR
is a viable option for patients with uni-compartmental
knee arthritis both in terms of clinical and cost effective-
ness after comparing UKR to TKR.15 The inclusion criteria
for this multi-centre randomized controlled trial (RCT)
were isolated full-thickness cartilage loss of the medial
compartment tibia and femur, a functionally intact
ACL, full-thickness lateral cartilage presence and a cor-
rectable intra-articular varus deformity. Only medically fit
patients with an ASA of 2 or less were included. Patients
with inflammatory arthropathy, those requiring revision
surgery, those with spine, hip or foot pathology were
excluded. Patients with a past history of septic arthritis or
previous surgery other than diagnostic arthroscopy were
also excluded. Significant patella-femoral joint damage
and an inability to perform the required clinical tests were
also a contraindication for inclusion within this RCT. Whilst
the trial found no difference in Oxford Knee Scores at five
years between TKR and UKR patients, UKR was superior in
terms of length of stay, overall cost, fewer complications
and improvements in some satisfaction outcomes.15
Although the above study confirms that UKR is both
cost effective and non-inferior to TKR in terms of five-year
outcomes, UK registry data confirms UKR has a higher
overall revision rate of 16.9% at 14 years.16 Time will tell
whether these clinical and cost effectiveness benefits at
five years continue at medium to long term. Progression
of lateral-sided disease is a mode of failure exclusive to
UKR in comparison to TKR.
In the age of consent and shared decision making, it is
important patients understand what to expect with a UKR
as opposed to a TKR. A recent meta-analysis of available
evidence demonstrated a significant reduction in length of
inpatient stay with UKR.17 Post-operative pain was no dif-
ferent between UKR and TKR; however, functional patient-
reported outcome measures (PROMs) favoured UKR.
Five-year revision rates were higher in UKR compared to
TKR in RCTs, cohort studies and registry studies.17 A recent
radiographically matched cohort analysis gives further evi-
dence towards improved PROMs in patients undergoing
UKR, over those having TKR at one-year follow-up.18
When choosing between implants, surgeons must
decide between mobile and fixed bearing UKR. The mode
of failure differs depending on the type of implant, with
mobile bearing UKR being more susceptible to polyethyl-
ene dislocation and fixed bearing being more susceptible
to a combination of polyethylene wear and aseptic loos-
ening.19 A recent meta-analysis showed no difference in
revision rate or complication rate between the two types
of bearing.20 Some surgeons have concerns about poly-
ethylene dislocation with a mobile bearing prosthesis and,
although the above study would suggest that this may not
translate to an overall increased revision rate, a fixed bear-
ing would act to prevent this complication occurring.
To summarize, UKR should be considered in patients
who have isolated, non-inflammatory, medial compartment,
115
Medial coMpartMent osteoarthritis of the knee
bone-on-bone arthritis in a stable knee without significant
deformity. Patients can expect a shorter post-operative
inpatient stay, though equal post-operative pain levels to
those undergoing TKR. Increased activity levels should not
act against a decision to perform a UKR and such patients
may more realistically expect to return to low-demand
sport, and sooner than patients undergoing TKR. Func-
tional outcomes are equivalent at five years; however,
overall revision rates are higher compared to TKR. Sur-
geons should be reluctant to offer UKR if they are unable
to operate on at least 10 appropriate cases a year. If this is
not attainable, patients would be better served by being
referred to a higher-volume surgeon if they wish to con-
sider UKR over TKR.
HTO
High tibial osteotomy is another option for patients with
isolated medial compartment osteoarthritis. The aim of the
procedure is to alter the mechanical axis of the lower limb
to offload the arthritic medial compartment and relatively
increase the load on the unaffected lateral compartment,
thereby reducing pain and improving function. Research-
ers have hypothesized that this may lead to cartilage
regeneration in the affected medial compartment.11 High
tibial osteotomy can be performed by a medial opening
wedge osteotomy, or lateral closing wedge osteotomy, in
cases of the varus mal-aligned knee.
Historically, HTO has been performed for patients
with varus mal-alignment and isolated medial compart-
ment arthritis with a stable knee, and the absence of varus
thrust.21 Osteotomies can also be employed to address
associated instability at the time of the osteotomy. HTO
can address the coronal alignment of the tibia, but can
also alter the posterior tibial slope, which has a direct
effect on anterior tibial translation. Reducing the poste-
rior tibial slope can reduce anterior tibial translation in
the setting of an ACL-deficient knee.22 In patients with
arthritis and instability, correcting the coronal alignment
alone may be insufficient, as the altered knee kinematics
caused by instability may be a key driver in their pattern of
arthritis.9 It is generally accepted that in patients with ACL
instability whose dominant symptom is arthritic pain, a
ligament reconstruction should be avoided.21 Combined/
staged HTO and ACL reconstruction is more often consid-
ered in patients with femoro-tibial mal-alignment whose
main symptom is instability, but who also have medial
compartment pain or signs of medial overload. Lateral/
postero-lateral ligament insufficiency may also prevail in
these circumstances. The HTO is usually performed first
since this alone may give sufficient relief of symptoms,
especially in low-demand patients, but ligament recon-
struction can be considered at the same time as, or later
than, the time of implant removal if necessary.23,24
Few randomized controlled trials have compared HTO to
other interventions. A meta-analysis found no difference in
walking velocity, knee scores, lateral disease progression or
need for further surgery or revision when comparing with
UKR.25 Range of motion was better in HTO patients; how-
ever, UKR performed better in pain scores, functional assess-
ment and number of complications.25 An RCT in Norway
has demonstrated no difference in clinical improvement
when comparing closing or opening wedge osteotomy
for medial compartment osteoarthritis.26 More RCTs have
looked into the different technical aspects of performing an
HTO, rather than its efficacy over other treatment options.
Over the last five years, few RCTs have been performed
comparing HTO to other treatments. HTO has been shown
to be beneficial compared to non-operative management;
however, there was no functional difference when com-
pared to a medial offloading brace.27 Due to poor com-
pliance, an offloading brace is rarely used as a definitive
management of patients with medial knee osteoarthritis.
A trial of an offloading brace (a so called ‘brace-test’) has
been shown to be beneficial in predicting the pain-relieving
effect of a HTO, and thus holds significant clinical value.28
A meta-analysis comparing UKR and HTO concluded nei-
ther procedure was superior, with both procedures giving
good functional outcomes.25 The authors suggest HTO in
younger active patients, with these patients obtaining a
slightly better range of motion.25 An RCT looking at cartilage
regeneration compared HTO to joint distraction, and con-
cludes both procedures have efficacy.29 The HTO patients
had better patient-reported outcome measures; however,
joint space increased more in the joint distraction group.29
Surgeons performing HTO differ in their suggested
post-operative weight-bearing regimen. RCT evidence has
demonstrated improved early functional outcomes with
early full weight bearing, compared to six weeks of partial
weight bearing only.30
A Finnish registry study estimated the survivorship of
HTO to be 89% at five years and 73% at 10 years when
taking conversion to TKR as an end point.31 This is lower
than the equivalent survivorship for both primary TKRs
and UKRs at five and 10 years respectively, suggesting
an increased likelihood of earlier major re-operation in
patients undergoing HTO.
There is much less available evidence for the indications
and contraindications of HTO as opposed to UKR. Less has
also been published regarding the monitoring of outcomes
and survivorship. Much of the high-level evidence com-
pares the specifics of HTO surgery, for instance graft type or
osteotomy location as opposed to its efficacy compared to
UKR or TKR. Although a UK knee osteotomy registry exists,
this is as yet non-compulsory,32 in contrast to the National
Joint Registry of England and Wales.33 Selecting appropriate
patients for an HTO is challenging. It is suggested that HTO is
an option in patients with a significant varus mal-alignment
116
with medial-sided disease. It is often reserved for younger
more active patients and ACL instability is less often seen
as a contraindication. The trend towards offering HTO to
more active patients is interesting, particularly as outcomes
in UKR have been favourable in more active patients com-
pared to more sedentary patients.4 Further high-level stud-
ies are required to determine whether surgeons should be
reluctant to offer UKR for these patients. One barrier to set-
ting up such studies would be to address whether surgeons
feel these two interventions are addressing the same type of
disease, or whether they feel these procedures are address-
ing a heterogonous group of patients. Younger patients
more commonly undergo an HTO than a UKR.34 Unless the
orthopaedic community agrees both options are viable in
the same group of patients, meaningful randomized stud-
ies between the two options will be hard to come by.
In summary, an HTO is an option for patients with iso-
lated medial compartment osteoarthritis. Patients can
expect improvement in clinical outcomes after surgery;
however, no study has proven a significant difference when
compared to UKR or TKR. Younger, more active patients
are generally considered for HTO; however, this does not
currently appear to be based on any high-level evidence.
Knee joint distraction
Knee joint distraction (KJD), with an external fixator, for
a period of 6 to 8 weeks has been proposed as a treat-
ment for patients with end-stage osteoarthritis, to delay
the need for total knee replacement.35 An RCT compar-
ing knee joint distraction to TKR concluded non-inferiority
in outcomes when compared to TKA at one year. Knees
were distracted by 5 mm for a period of six weeks.35 The
trial only included patients below the age of 65 years,
with a BMI of ≤ 35, flexion ≥ 120 degrees and intact knee
ligaments. A high incidence of pin track infections was
reported in knee joint distraction patients (60%), which
may partly account for its low uptake at present. There is
no current evidence to suggest that these patients had an
increased infection risk if subsequently undergoing TKR.36
A further RCT by the same group compared HTO to knee
joint distraction, demonstrating clinical improvement in
both groups, with slightly better PROM data in the HTO
group.29 Although follow-up in this study was short, pre-
vious studies have suggested survival rates of 80% and
65% at five and 10 years respectively, when looking at
conversion to TKR after knee joint distraction.
Knee joint distraction remains in its infancy for the
treatment of osteoarthritis; however, from the studies
performed, it appears to have some efficacy. The proce-
dure avoids arthroplasty, and limb re-alignment, so has
promise in the treatment of younger patients wishing to
avoid these options. Although pin track infection rates are
high, these were all successfully treated with oral antibi-
otics, so may not be of long-term consequence to KJD
patients. There is also currently no evidence to suggest
these patients are more likely to have an infection if subse-
quently treated with TKR. Caution must be taken, as KJD
is the least studied of the three less-invasive methods of
treating medial knee osteoarthritis.
Conclusions
If low revision rate is seen as the key indicator for success,
TKR remains the most successful option for treating medial
compartment osteoarthritis with an estimated revision
rate of 4–5% at 14 years.16 Many patients wish to avoid
TKR. UKR, HTO and KJD are other options which can be
considered. UKR and HTO both have reasonable evidence
demonstrating some benefits over TKR in terms of PROM
data; however, this should be considered at the cost of an
increased revision rate compared to TKR. All three treat-
ments have RCT evidence of their efficacy, although each
comes with its own set of benefits and limitations. Ortho-
paedic surgeons should be aware of the options at their
disposal so they can better inform patients, and ensure
their own practice allows the best possibility of successful
outcomes. It must be noted that surgeons should avoid
such options if they cannot expect to perform them in ade-
quate numbers, and local referral pathways should ensure
there is no compromise of patient choice as a result.
ICMJE CONFLICT OF INTEREST STATEMENT
The authors declare no conict of interest relevant to this work.
FUNDING STATEMENT
No benets in any form have been received or will be received from a commercial
party related directly or indirectly to the subject of this article.
OPEN ACCESS
© 2021 The author(s)
This article is distributed under the terms of the Creative Commons Attribution-Non
Commercial 4.0 International (CC BY-NC 4.0) licence (https://creativecommons.org/
licenses/by-nc/4.0/) which permits non-commercial use, reproduction and distribu-
tion of the work without further permission provided the original work is attributed.
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Author Information
Department of Orthopaedics, University Hospitals of Leicester NHS Trust,
Leicester, UK.
Correspondence should be sent to: Daniel J. McCormack, Department of
Orthopaedics, University Hospitals of Leicester NHS Trust, Gwendolen Road,
Leicester, Leicestershire, LE5 4PW, UK.
Email: daniel.mccormack@gmail.com
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