Controversies around UKA are discussed as Ten Enigmas.

1. Unicompartmental Knee
Arthroplasty: An ENIGMA
Dr. Anurag Mittal

2. Introduction
• Ahlback in 1969 discovered, 85% OA knees are actually medial OA.
• It means these patients can be managed with only medial compartment
replacement.
• Doing a total knee replacement will be overkill for these population.
• Revolutionalised knee arthroplasty
• Successful procedure
• Preserves joint proprioception and gait kinematics
• Bone and ligament sparing technique

3. Comparison of bone cuts
Total Knee Replacement Unicompartmental Knee Replacement

4. American Joint Replacement Registry(AJRR) report
0
1
2
3
4
5
6
7
2012 2015 2017
Percentage of UKR
Percentage of UKR
Rate trending down from 6.66% in 2012 to 1.81% in 2017.
10% of orthopedic surgeons worldwide perform UKAs

5. Because of inconclusive evidences and controversies
surrounding UKA
• Should I risk doing UKA in a 50 year old
patient with medial OA?.....
• MRI before UKA……hmm. Is it necessary?
• Should I overcorrect or undercorrect the
deformity………?
• Can I produce better result than TKA…?

6. TEN
ENIGMAS
FOR UKA
UKA or
TKA?
Indications
of UKA?
Need for
preoprative
MRI?
Fad about
minimal
invasive
approach?
Fixed or
mobile
bearing?
Ideal
surgical
prameters?
Cemented
or
cementless
?
ACL
Reconstruct
ion+ UKR. Is
it too
much?
Cost
effective
?
Are we
Future
ready?

7. Presentation template
• Each section of the controversy will first cover the reason “why the
controversy is an Enigma”
• Then we will highlight “literature” specific to the controversy.
• Finally, we will conclude with “our own recommendations” as derived
from the literature.

8. TEN
ENIGMA
FOR UKA
1.UKA or
TKA? Indications
of UKA?
Need for
preoprative
MRI?
Fad about
minimal
invasive
approach?
Fixed or
mobile
bearing?
Ideal
surgical
prameters?
Cemented
or
cementless
?
ACL
Reconstruct
ion+ UKR. Is
it too
much?
Cost
effective
?
Are we
Future
ready?

9. Why is it enigma?
• Despite the obvious advantages, UKA is
not performed widely
• Controversial reports in the literature
• Varied surgeon experiences
• Longer learning curve-Surgeons more comfortable with TKR
• More number of revisions during first two years of starting UKR surgery
• Surgeons reluctant to offer UKR due to reported high revision rate
especially in National Joint Registries-(2-3 times than TKA).
UKA Advantages over TKA (Berend KR.
Orthopedics. 2007)
• Shorter operative time and hospital stay
• Bone stock preservation
• Easier recovery
• Better functional outcome
• Subjective feeling of more natural knee
Can we do UKR instead
of TKR when indicated?

10. What does evidence say?
• UKA provided more patient satisfaction than the TKA in comparative
studies. -Laurencin CT, CORR 1991
• Modern technique and implant design of UKAs leads to less wear.
-Forster-Horváth.Knee.2017
• Higher failure rates of UKA are associated with centres and surgeons
performing low numbers of the procedure. -Liddle and pandit.JBJS.2015
• Expand indication by increasing UKR usage, which can help in
lowering revision rates. -Murray.BJJ.2016

11. TKOS Viewpoint
More the number of cases Less is the revision rate
• UKA usage- If you are doing 100 knee arthroplasty
then at least do 20 UKR for acceptable revision rate.
• Then, UKA can be used as an alternative to TKA when
indicated.

12. TEN
ENIGMAS
FOR UKA
UKA or
TKA? 2.Indications.
Which knee is
the best?
Need for
preoprative
MRI?
Fad about
minimal
invasive
approach?
Fixed or
mobile
bearing?
Ideal
surgical
prameters?
Cemented
or
cementless
?
ACL
Reconstruct
ion+ UKR. Is
it too
much?
Cost
effective
?
Are we
Future
ready?

13. Why is this an enigma?
• No consensus on indication
• Controversy on age of patient, obesity status, presence of lateral
osteophytes, arthritis in patellofemoral joint
• In recent years, there is an increase in life span, an increasingly active
population, and rising obesity rates. So we cannot keep strict
indications.
Traditional contraindications
• High activity level
• Anterior knee pain (PFA)
• Chondrocalcinosis
• Osteophytes in lateral side
• Inflammatory arthritis
Can these traditional indications
and contraindications be modified
with modern prosthesis?
Traditional indications of UKR
• Age >60 years
• Weight <82 kg
• Angular deformity
<15:passively correctable to
neutral
• Flexion contracture <5

14. What does evidence say in young and active patients?
• Germany study examining return to activity in young patients
following UKR, 93% of patients returned to regular activity and the
revision rate was merely 2.5%

15. What does evidence say in obese patients?
• Pandit et al in their prospective study of 1000 patients with oxford
knee reported similar clinical outcomes and survivorship in patients
weighing less than and more than 82 kg.

16. What does evidence say in lateral osteophytes?
• Hamilton et al found that, with presence of lateral osteophytes there
was only one failure with the 15-year survival calculated as 98 %

17. TKOS Viewpoint
• Indications
• Significant symptoms
• Anteromedial osteoarthritis: Bone
on bone
• Full-thickness cartilage in the lateral
side
• Contraindications
• Inflammatory disease
• Ligamentous instability
• Uncorrectable varus
deformity
• Severe (grade 3)
patellofemoral arthritis

18. TKOS Viewpoint: Specific population
• Younger patients: should be counseled preoperatively about their pot
ential risk for higher revision rates, as reported in the literature, for bo
th UKA and TKA.
• Patients with high BMI: should be counseled on the preoperative risk
s and the conflicting evidence regarding implant survivorship and be e
ncouraged to lose weight to help improve this modifiable risk factor.
• Lateral osteophytes: avoid in grade 3 large osteophytes-impingement
• Patellofemoral joint osteoarthritis: not a contraindication if patient is
asymptomatic.

19. Additional Benefit: UKR usage increases from
6- ~50%- less revision rate
0%
10%
20%
30%
40%
50%
60%
Traditional indication Modern indication
UKR usage
UKR usage

20. TEN
ENIGMAS
FOR UKA
UKA or
TKA?
Indications
of UKA?
3. Need for
preoperative
MRI?
Fad about
minimal
invasive
approach?
Fixed or
mobile
bearing?
Ideal
surgical
prameters?
Cemented
or
cementless
?
ACL
Reconstruct
ion+ UKR. Is
it too
much?
Cost
effective
?
Are we
Future
ready?

22. Why is it an enigma?
• Meticulous preoperative evaluation is critical to determine
appropriate candidates for successful UKA, and to minimize the
potential risk for conversion to TKA.
• Hence, some surgeons prefer MRI.
• But, role of pre-operative MRI is still debatable
• Some studies suggest that it over-estimates the degree of knee
pathology- thereby decreasing UKR ‘usage’
So, should an MRI be done before
selecting patients for UKR?

23. What does evidence say
• Nearly two thirds of all routine knee MRIs demonstrated articular
cartilage damage of uncertain clinical significance. – Disler. Radiology.2005
• Abnormal preoperative MRI findings do not have an influence on the
outcome of UKA when modern radiographic and clinical criteria (also
intraoperative assessment) are met. -Hurst et al.JBJS.2014
• MRI is too sensitive to be of “any practical value” in evaluating the
ACL because its structure and function in osteoarthritis is highly
variable. -Sharpe et al. International orthopaedics.2011
• Expenditure of our already limited healthcare resources

24. TKOS Viewpoint
• Avoid routine preoperative MRI scan, instead do
• Complete ligamentous exam (ACL/MCL status)
• Radiographic study including valgus stress views (lateral compartment
cartilage thickness)
• Complete intraoperative assessment (confirm the preoperative findings)
• However, when the clinical presentation is not clear, an MRI can be
very useful in assessing other conditions such as avascular necrosis
and neoplasm which otherwise might have gone undetected

25. TEN ENIGMAS
FOR UKA
UKA or
TKA?
Indications
of UKA?
Need for
preoprative
MRI?
4. Fad about
minimal
invasive
approach?
Fixed or
mobile
bearing?
Ideal
surgical
prameters?
Cemented
or
cementless
?
ACL
Reconstruct
ion+ UKR. Is
it too
much?
Cost
effective
?
Are we
Future
ready?

26. Why is it an enigma?
• The minimal invasive approach for UKA avoids patellar eversion and
quadriceps muscle violation.- early rehab.
• The potential benefits of minimal incision surgery include less surgical
dissection, less blood loss and pain, earlier return to function, a
smaller scar, and subsequent lower costs.
• However, there are concerns about loss of accuracy with minimally
invasive techniques
Should it be minimal or
optimal?

27. What does evidence say?
• Muller et al comparing the standard and MIS in UKR surgery found
superior functional outcomes but implants were suboptimally
positioned with MIS.
• Berend and colleagues reported 20% failure rate in short incision UKR
after a follow up of 3 years.
• Dalary and Dennis showed that significant number of patients had
tibial component varus malalignment in mini open UKR

28. TKOS Viewpoint
• Choice of incision should depend on surgeon preference
• Size is individual’s perspective.
• Identification of proper landmarks for bony cuts, complete evaluation
of ACL sufficiency and the other compartment arthritis should be
easily done
• There should be no struggle during surgery in any step as soft tissue
manhandling may inadvertently lead to poor results and thereby
defeating the very purpose of MIS.
Which vision you want, tunnel or wide?
Incision should be optimal not minimal.

29. TEN
ENIGMAS
FOR UKA
UKA or
TKA?
Indications
of UKA?
Need for
preoprative
MRI?
Fad about
minimal
invasive
approach?
5. Fixed or
mobile
bearing?
Ideal
surgical
prameters?
Cemented
or
cementless
?
ACL
Reconstruct
ion+ UKR. Is
it too
much?
Cost
effective
?
Are we
Future
ready?
Two fundamentally different
design concepts for UKA

30. Mobile Bearing (MB) UKA
• More natural joint mechanics
• Higher conformity
• Reduce contact stresses
• Less wear
Fixed Bearing (FB) UKA
• Less conformity
• Higher point contact stresses
• Increased wear
• No bearing dislocation

31. Why is it an enigma?
• Both mobile bearing and fixed bearing have some advantages as well
as disadvantages.
• Thus, it becomes difficult for surgeons to choose between them.
• Studies are also contradicting, further making the situation worse.
MOBILE UKA FIXED UKA Which road to
travel?

32. What does evidence say about MB implants?
• Bearing dislocation is a unique complication of MB, which may be the
reason why MB-UKA tends to occur earlier in failure.
-Goodfellow et al.Knee.2012
• Less tolerant to errors: Precise alignment and ligamentous balancing
is essential to prevent MB dislocation
• If undercorrection - stress on the medial side- bearing dislocation and aseptic
loosening
• If valgus overcorrection- stress on lateral compartment- further degeneration
• Similar survivorship or clinical and functional outcomes b/w FB and
MB UKA

33. What does evidence say about FB implants?
• More tolerant to surgical errors
• Not prone to bearing dislocation and instability (ACL and MCL
rupture)
• FB-UKA tend to fail late, due to polyethylene wear.
- Burton et al. Knee. 2009
• Less requirement of tibial augments during revision compared to MB.
- Bloom et al. J Arthroplast.2014
• Revision rates of FB and MB designs are equal.
-Van der List et al.CORR.2009

34. TKOS Viewpoint
• FB-UKA shows more promising results with newer prosthesis.
• FB is not associated with bearing dislocation.
• Moreover, combined wear(surface+backside) is higher in MB-UKA.
• Fixed bearing can also be used in ACL deficient knees.
• MB prosthesis has higher technical requirements and longer learning
curve for the surgeon.
• However, surgeons should still use their personal experience when
deciding between these options.

35. TEN
ENIGMAS
FOR UKA
UKA or
TKA?
Indications
of UKA?
Need for
preoprative
MRI?
Fad about
minimal
invasive
approach?
Fixed or
mobile
bearing?
Ideal
surgical
prameters?
6. Cemented
or
cementless?
ACL
Reconstruct
ion+ UKR. Is
it too
much?
Cost
effective
?
Are we
Future
ready?

36. Why is it an enigma?
• There has been a growing interest in cementless fixation for UKA due to ease of revision.
• But, conventional training of surgeons is with cemented implants.
• And, also the cementless concept in UKA is new.
Advantages of cementless implant
• No errors associated with
cementation
• Less impingement
• No third body particle wear
• Shorter operative time
• Induces bone growth
Should we shift to
cementless UKR?

37. What does evidence say?
• Reported high failure rates by study of Lindstrand in initial use of
cementless UKA – less to less interest initially
• In recent studies, clinical outcome, failures, reoperation rate, and
survival were comparable to that reported in similar studies on
cemented UKAs
• Daniilidis et al showed less radiolucent lines thus less
misinterpretation for loosening.

38. • And, UKAs are more suitable for cementless fixation than TKA
because of mechanical advantage of UKA at bone-implant interface.
• There are mainly compressive loads both when the knee is centrally or eccentrically loaded
Native tight ligaments
Compressive loads
Shearing force
Compressive loads only
more
osseous
ingrowth
TKR UKR

39. TKOS Viewpoint
• Based on the most recent literature,
cementless designs may offer a very slight
edge over cemented prostheses in terms of
shorter operative times and long-term
implant survivorship.
• However, we need large RCTs and longer
follow up comparing cemented and
cementless UKA components for reaching
on a conclusive decision as it is newer
concept for UKR.

40. TEN
ENIGMAS
FOR UKA
UKA or
TKA?
Indications
of UKA?
Need for
preoprative
MRI?
Fad about
minimal
invasive
approach?
Fixed or
mobile
bearing?
7. Ideal
surgical
prameters?
Cemented
or
cementless
?
ACL
Reconstruct
ion+ UKR. Is
it too
much?
Cost
effective
?
Are we
Future
ready?

41. Limb alignment: Angle between
mechanical axis of femur and tibia

42. Tibial slope and femoral flexion and extension

43. Divergence angle: Angle formed by the longitudinal axis of femoral
component and a line perpendicular to tangent of the tibial component

44. Varus/ valgus of components

45. Depth of tibial component/ joint line: Distance between elongated lines
on the lateral tibial plateau and the tibial component.

46. Why is it an enigma?
• UKA must restore the pre-osteoarthritic femoro-tibial geometry
• Parameters have shown to influence the outcome of UKR and its long
evity.
• However, the ranges for an adequate lower limb alignment and other
surgical variables after medial UKA are still debated.
• What are the ideal surgical
parameters which can result in best
outcomes and increase the longevity?

47. What does evidence say?
• Hernigou and Deschamps found that
• severe undercorrection of varus deformity can lead to accelerated
polyethylene wear with early implant loosening and
• overcorrection into valgus result in rapid degeneration in lateral
compartment.
• Zuiderbaan et al suggested that post-operative varus angle of 1- 4
degrees should be persued when performing medial UKA to optimize
subjective results
• A study showed that when the medial joint space is >2 mm thickness
of the lateral joint space preoperatively, the reoperation rate after
medial UKA was 6 times higher.

48. TKOS Viewpoint
Limb alignment
Tibial side
parameters
Coronal-
varus/valgus
Sagittal- posterior
slope
change in joint
space height
Sizing
Intraprosthetic
divergence
Femoral side
parameters
Varus/ valgus
angulation
Flexion/extension
1-4 mm
varus
5 deg slope or a
change in slope <2
deg
<2 mm
<3 mm
overhang
< 6
degree
<6
degree
+/-10
degree
+/- 10
degree

49. Some poorly performed UKA

50. TEN
ENIGMAS
FOR UKA
UKA or
TKA?
Indications
of UKA?
Need for
preoprative
MRI?
Fad about
minimal
invasive
approach?
Fixed or
mobile
bearing?
Ideal
surgical
prameters?
Cemented
or
cementless
?
8. ACL
Reconstruction+
UKR. Is it too
much?
Cost
effective
?
Are we
Future
ready?

51. Why is it an enigma?
• ACL deficiency in UKR patients can lead to
higher incidence of complication such as
bearing dislocation, polyethylene wear and
tibial loosening resulting in early implant
failure
• Some authors suggest combined UKA with
ACL reconstruction.
• But most of the surgeons are reluctant to do
two surgery simultaneously in the same knee.
Should we attempt to
reconstruct ACL simultaneously
with UKR?

52. What does evidence say?
• A review by Weston-Simons reports 93% implant survival at five years
for 52 patients with a mean age of 51 years who underwent staged or
simultaneous ACL reconstruction and Oxford UKR.
• Clinical results are good, with patients achieving a high level of
function. -Boissonneault et al. JBJS.2015
• Sagittal plane kinematics are nearly normal after combined ACL
reconstruction and UKR. -George et al.Knee.2017
• However, some authors report difficulty in tunnel position and early
graft failure.

53. TKOS Viewpoint
• Doing simultaneous ACL reconstruction with UKR in young patients is
cumbersome, require expertise and results in less optimal outcomes
with his own complications.
• Long term RCTs are needed to reach to a conclusive evidence

54. TEN
ENIGMAS
FOR UKA
UKA or
TKA?
Indications
of UKA?
Need for
preoprative
MRI?
Fad about
minimal
invasive
approach?
Fixed or
mobile
bearing?
Ideal
surgical
prameters?
Cemented
or
cementless
?
ACL
Reconstruct
ion+ UKR. Is
it too
much?
9. Cost
effective?
Are we
Future
ready?

55. Why is it an enigma?
• Because of reported high revision rate, it is thought that UKR is not
cost effective.
• But if its advantages of shorter hospital stay and quicker rehabilitation
are taken into account, the scenario may change.
• Moreover, recent studies have reported similar revision rate between
UKR and TKR.
• However, trade-offs between upfront benefits and later risk of
revision of unicompartmental knee arthroplasty compared with those
of total knee arthroplasty are poorly understood.
TKR
UKR
Which is more cost heavy?

56. What does evidence say?
• Konopka and his colleagues in 2008 followed up 50,493 knee
replacement patients identified from Finnish arthroplasty register and
straightway recommended discontinuation of UKR in
unicompartmental OA on the basis of low-cost effectiveness owing to
high revision rates
• In contrast recent literature without any uncertainty reports that the
UKR is a cost-effective procedure and should be contemplated when
indicated. -Burn and Liddle. J Arthroplasty.2015
• When UKR was performed by surgeons with a usage above 10%, UKR
was found to be unequivocally cost-saving and health improving
compared with TKR. -Collier et al.Knee.2014

57. TKOS Viewpoint
• Decreased operating time
• Shorter length of hospital stays
• Reduced occurrence for transfusions
• Lower component cost
• Advice: Increase UKA usage by broadening their indication to make it
more cost effective.
Makes UKA the more cost-
effective option for both
the patient and surgeon.

58. TEN
ENIGMAS
FOR UKA
UKA or
TKA?
Indications
of UKA?
Need for
preoprative
MRI?
Fad about
minimal
invasive
approach?
Fixed or
mobile
bearing?
Ideal
surgical
prameters?
Cemented
or
cementless
?
ACL
Reconstruct
ion+ UKR. Is
it too
much?
Cost
effective
?
10. Are we
Future ready?
• PSI/ 3D printing
• Computer navigated
• Robotic-arm-assisted
• Virtual rehabilitation

59. Why is it an enigma?
• Chatellard et al observed that high level of accuracy is required for
optimal position of implant and even minute change in the position
lead to revision of UKR
• Assistive technologies have been developed which has the potential
to improve the accuracy of implant positioning and limb alignment by
minimizing surgeon controlled errors using smart tools• But are these cost effective?
• Are we trained enough for
advanced technology?
• Does experienced surgeon
need it who does TKR in ~20
minutes and with precision?

60. What does evidence say?
• Bell et al showed that components implanted with robotic assistance
have been found to be positioned within 1° of error
• But does it really matter? What if error is 2 or 3 °?
• Konyves et al revealed better implant positioning, less contact
stresses in navigated UKA and no difference in survivorship at 9 years
compared to conventional manual technique
• Ollivier et al cautioned that claiming assistive technologies improves
alignment, pain or function cannot be used ‘to justify the extra cost
and uncertainty related to these technique’

61. TKOS Viewpoint
• Functional benefits and effect on the longevity of components are
currently being investigated.
• Evidence may be market driven and sponsored by the companies.
• Keep in mind-New is not always better.
• However, assistive technique could provide precious assistance to less
experienced surgeons performing this surgery.

63. Conclusion
• As UKA enters the modern era of surgery centers, less invasive
surgical techniques, and rapid recovery protocols, many surgeons
have again considered this procedure, leading to a resurgence in its
popularity
• With careful and stringent patient selection criteria and meticulous
surgical technique, surgeons are seeing higher patient satisfaction,
greater overall success rate, and increasing implant survivorship.
• As the orthopedic community continues to debate on the broad
implementation of this procedure, additional questions will
undoubtedly arise as surgical technology advances.

64. Summary
Controversy Conclusion
1 UKA or TKA UKA
2 Indications Keep them wide to increase UKR usage
3 Need for preoperative MRI No (thorough clinical and radiological examination with intraoperative assessment)
4 Minimally invasive surgery Not required (optimal incision)
5 Fixed or mobile bearing Fixed bearing
6 Cemented or uncemented Cemented as of now, further research needed
7 Ideal limb alignment 1-4 degree varus
8 ACL + UKR Surgeon expertise
9 Cost effective Yes
10 Are we future ready? Not yet, stick to conventional technique (especially experienced surgeon)