The Role of Unicompartmental Knee Replacement

7/31/2019 The Role of Unicompartmental Knee Replacement

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Yunus

Orthopedi & Traumatologi

RSU-Dr Soetomo FK UNAIR


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When considering which to offer one mustconsider

the outcome, in terms of symptomatic relief and

function, the survival rate and the difficulty of revision in the

event of failure of each method.


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Until recently UKA has remained aprocedure for the enthusiast because ofthree perceived problems: 1. Inferior survival rates toTKR.

2. Limited indications and therefore a techniqueappropriate for only small numbers of patients.

3. Technical difficulty of the procedure.


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articular cartilage degeneration in the kneeprobably results from high impulse loadingoccurring at heel strike

area of contact in the knee at this phase of thegait cycle is in the anteromedial tibiofemoralcompartment.

Radiological studies in the1960s and1970s

demonstrated that about 90% of patients withosteoarthritis of the knee showed initial wear inthe medial compartment and that progressionto the lateral compartment was uncommon


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Most arthritic knees have a varus deformityand predominantly medial tibiofemoralarthritis

In 1999, it was shown that progression ofosteoarthritis to the lateral compartment isusually associated with rupture of the anteriorcruciate ligament (ACL), probably due to

impingement of osteophytes in theintercondylar space which abrade the synovialcovering of the anterior cruciate ligament


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Rupture of the ACL is also associated with thedevelopment of a fixed varus deformity

Before rupture occurs the posterior parts of the

medial tibial and femoral articular surfacesremain intact so that in flexion the medialcollateral ligament is stretched to its normallength

Once the ACL has ruptured the contact point inextension moves posteriorly causing damage tohitherto normal cartilage.


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The resulting loss of joint height in flexionallows the medial collateral ligament to remainshortened throughout the full range of kneemovement and permanent contracture of theligament then develops.

In order to choose the best treatment for apatient with medial compartment osteoarthritisa comparison of the available options has to bemade.This must compare their efficacy, long-term survival and options for revision in theevent of failure.


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High tibial valgus osteotomy has long been anaccepted treatment for medial osteoarthritis,particularly in young activemen.

few good comparisons to be found in theliterature

di!erent patient groups have been studied

varied outcome measures used


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One comparative study did use a validatedpatient-based outcome measure (the Oxford kneescore) compare two cohorts

One treated by Oxford UKA and the other by HTO 6 years : average score in the HTO group was 26.6 and in the UKA group it was 38.1

The 10 -year survival :

HTO with revision as the end point was 63%, and for the UKA, it was 98%.

In this comparison, the average age of the HTOgroup was younger than the UKA group These differences were maintained.


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In terms of function and survival, HTO performsignificantly worse than UKA in all patient groupsthat have been compared

Is there still an indication for HTO? Primary tibia vara with early secondary medial arthritis

and perhaps it has a place in treating young, active menwho perform heavy labour

Delaying the requirement for prosthetic surgery is now

the primary justification for performing HTO. The question is, which procedure will give the

longest total lifetime of the knee? At present theevidence favours UKA over HTO in most cases.


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Comparisons between TKR and UKA are difficultbecause of the different populations undergoing eachprocedure

Patients undergoing TKR are likely to be older and

have more advanced osteoarthritis in most historicalseries

Functional outcome following UKA is superior thanTKR

In an historical prospective study comparing UKA andTKR, Rugr, et al, found that therewas no statisticallysignificant difference in aseptic loosening between twogroups of patients. However, UKA was associated witha better range of movement and ambulatory function


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In a bilateral study of patients undergoing a UKAon one side and a TKR on the other, it wasdemonstrated that in terms of pain, stability, feeland stair climbing ability, UKA performed better

than the TKR In a randomized controlled trial in Bristol, it wasfound that UKA had less perioperative morbidity,faster rehabilitation and shorter length of staythanTKA

The retention of the ACL in UKA provides normalkinematics with normal patellofemoral jointforces.20 This results in an improved range ofmovement and function especially withdemanding activities such as stairs


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Inferior survival rates of UKA compared to TKRreported in the 1980s and early 1990s

These failures were due to inappropriate patientselection, less refined surgical techniques compared toTKR and polyethylene wear in the original round onflat implant design.

With improvement in all of these areas survival ratesfor both fixed and mobile bearing designs are nowequal to those of the best TKR

It is clear also that surgical technique plays a large partin the success of UKA

Poor results for the Oxford mobile bearing design inthe Swedish knee register were almost entirely due tocatastrophic early failure at 1 centre


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Survival rates for UKA equal to those for thebest TKR can be achieved with strict criteria forpatient selection, adherence to a learnt

technique and the use of a design proven tohave minimal polyethylene wear.

Increasing numbers of groups are nowdemonstrating this to be the case


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The revision of UKA has already beendiscussed.

Revision of TKR is a challenging exercise with

well-recognized technical difficulties exposure,

flexion and extension gap matching,

soft tissue balancing and implant stability

The results of UKA revision equals those ofprimary TKR and are superior to those ofrevision TKR.


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There is little doubt that UKA has significantadvantages over TKR in the short and mediumterm

Using data from the Swedish register,Robertsson estimated that the cost of UKA was57% of that of TKR with lower complicationrates and length of hospital stay.

Revising UKA provides results similar toprimary TKR.


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The success of medial unicompartmental kneereplacements is dependent upon strictadherence to the indications

extending these indications is likely to lead toinferior results.


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The accepted indications formedial compartmentUKA are: 1. Medial compartment arthritiswith symptoms sufficient

to warrant TKR.

2. An intact ACL. 3. An intact lateral tibiofemoral compartment.

4. Correctable varus deformity.

5. Less than101 of fixed flexion deformity.

6. Flexion beyond 100

If these indications are accepted then asmany as 1in 4 osteoarthritic knees will be appropriate forUKA


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The absolute contraindications are: 1. Inflammatory arthropathy. 2. Previous high tibial osteotomy. 3. Sepsis.

However, suggested contraindications haveincluded : patellofemoral joint osteoarthritis, chondrocalcinosis,

obesity, young age and high levels of activity

If these suggested CI are accepted as restrictions to

the use of UKA then less than 1 in 20 knees wouldbe suitable It is important to have good evidence to refute

these contraindications.


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Patellofemoral joint osteoarthritis It is very common in knees with symptomatic

osteoarthritis The arguments against its inclusion as a

contraindication are similar to those againstresurfacing in TKR Correct mechanical alignment, good quadriceps

function and normal knee kinematics are probablymore important in eliminating pain from the

patellofemoral joint than the quality of the articularsurface UKA corrects the mechanical axis and allows normal

kinematics and rapid quadriceps rehabilitation


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Progression of osteoarthritis in thepatellofemoral joint is very rare following UKAand,

in the Swedish register there have been norevisions of UKA for patellofemoral jointosteoarthritis.

The state of the patellofemoral joint, therefore,does not seem to influence the outcomefollowing UKA and should not be considered acontraindication


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Age

Older patients do very well with TKR withexcellent long-term implant survival. Interestingly,

function is usually considered a requirementreserved for young patients.

Elderly patients, particularly those withunderlying medical pathology, run the risk of

significant morbidity and mortality following TKR. With the opportunity for minimally invasive

surgery and the reduction of this risk thesepatients are ideal for UKA.


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Young patients with UKA have the samesurvival as the older patients

there is no evidence that in the age groups

currently undergoing TKR there should be anyrestrictions to the use of UKA because of age


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Obesity Obesepatients present three potential difficulties :

technical, increased risk of complications and

theoretical risk of early failure exposure in the obese knee for a total knee

replacement can be awkward The minimally invasive technique for UKA allows

Straight forward exposure because there is norequirement to dislocate the patella

There is also no correlation between obesity andwear in UKA


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Chondrocalcinosis

Chondrocalcinosis falls into two clinical groups

There are patients with generalized

chondrocalcinosis with synovitis andeffectively an inflammatory condition withinthe knee These should be treated as any otherinflammatory condition

Chondrocalcinosis seen on the X-ray with somecalcification in themeniscus butwith nogeneralized inflammatory signs should not beconsidered a contraindication for UKA


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Lateral compartment UKA is a moredemanding procedure and has produced asmaller quantity of less reliable data than the

medial compartment UKA. Bicompartmental UKA should not be used in

place of TKR.


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Radiographic confirmation of the indications isimportant but straightforward.Three films arerequired: 1. AP standing

2. Lateral 3. Valgus stress view

The standing view demonstrates the typical medialcompartment arthritis (Ahlbach grades 2 and 3 areusually suitable for unicompartmental replacement)

The lateral X-ray demonstrates that the tibial boneerosion is confined to the anterior and mid parts of themedial tibial plateau and does not extend to theposterior margins correlates with an intact ACL


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UKA has been demonstrated that the small implantsmay be inserted through a short parapatellar incisionwithout dislocation of the patella.

The minimally invasive technique has the potential

further to reduce the morbidity, complications andlength of hospital stay in UKA

Early functional recovery has been assessed by the timetaken to achieve independence on stairs, a straight legraise and flexion to 70

Patients undergoing a minimally invasive techniqueachieved these in approximately half the time taken forthose undergoing an open procedure and a third of thetime for patients receiving a total knee replacement


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In bilateral procedures this effect wasmaintained. The medium-term results haveshown no difference in the final range of

movement and knee score between theminimally invasive and the open techniques

Patients are now able to return home within 2-3days and in some centres the surgery is now

performed as a day case.


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UKA is a good alternative for most knees currentlytreated by HTO and for 25-30% of osteoarthritic kneescurrently receiving a TKR

UKA gives better results in terms of function, painrelief, morbidity and patient satisfaction than HTO or

TKR and its long-term survival is significantly betterthan HTO and as good as TKR

The use of a minimally invasive approach withspecifically designed instruments offers further benefit

to the patient from decreased morbidity, fasterrehabilitation and reduced length of hospital stay

UKA should be the preferred procedure for patientsfulfilling the indications if the appropriate surgical

expertise is available


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The Role of Unicompartmental Knee Replacement