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Osteoarthritis commonly affects the knee joint, resulting in joint space narrowing and development of osteophytes and sclerosis of the underlying subchondral bone. Total knee arthroplasty is now considered the surgical treatment of choice for osteoarthritis of the knee. It is indicated in patients over age 65 with degenerative arthritis in two or three compartments of the knee (Figure 1). However, osteoarthritis may involve only one compartment of the knee joint. Unicompartmental osteoarthritis of the knee occurs in the medial compartment in about one-third of patients and in the lateral compartment in about 3% of patients . The optimal treatment for osteoarthritis of the medial compartment or lateral compartment of the knee joint is still controversial. In patients with involvement of the medial or lateral compartment of the knee there are various surgical options, Including arthroscopy and joint debridement, high tibial osteotomy, unicompartmental.
Knee arthroplasty or total knee arthroplasty. Unicompartmental knee arthroplasty is indicated in patients under age 65 with involvement of either the medial or lateral compartment (Figure2). Total knee arthroplasty (TKA) is a proven procedure for the treatment of advanced knee arthrosis. However, as much as 20% of these patients have isolated unicompartmental osteoarthritis amenable for a unicompartmental replacement . Unicompartmental knee arthroplasty (UKA) has been performed since the 1970s for these patients with an aim of replacing only the diseased compartment of the knee joint and preserving the bone stock. The initial results
of UKA were very encouraging but later proved disappointing
and many surgeons abandoned the procedure. The causes of
the early failures are multi-factorial and include poor patient
selection and surgical technique , inadequate implant design
, polyethylene wear , inaccurate instrumentation , poor
understanding of the knee kinematics
Is an established procedure but has been controversial
for three decades. Initial results in the early 1970’s were
discouraging, however, Introduction of newer techniques of
exposure and design Improvements have made this procedure
quite popular in recent years. UKA is now being performed with
increasing frequency in younger patients .
Patients with inflammatory types of arthritis, such as
rheumatoid arthritis, are not regarded as good candidates
for partial knee replacement. With inflammatory arthritis,
more than one compartment is usually involved.
Previous HTO with overcorrection
Cruciate ligament lesion
Medial or lateral subluxation (usually associated with a
torn ACL) 6-Tibial or femoral shaft deformity
Flexion contracture greater than 15°
Varus deformity greater than 15° (medial
unicompartmental knee arthroplasty) 9-Valgus deformity
greater than 20° (lateral unicompartmental knee
arthroplasty) 10Flexion less than 110° .
Patellofemoral joint arthritis
Progression of osteoarthritis in the patellofemoral joint
after unicompartmental knee arthroplasty is rare, according to
some studies. In the Swedish Registry, no unicompartmental
knee arthroplasties have required revision for patellofemoral
Murray et al. [10-12] reported that residual postoperative
pain was independent of the state of the patellofemoral joint, and
no knee surgery was revised because of patellofemoral problems.
Unicompartmental arthroplasty improves the mechanical axis
and patellar tracking and allows more normal kinematics and
rapid quadriceps rehabilitation. For these reasons, osteoarthritis
of the patellofemoral joint may not be considered an absolute
contraindication. However, other investigators and surgeons
have reached the opposite conclusion; thus, many consider
patellofemoral disease to be an absolute contraindication for
unicompartmental knee replacement. For more information.
There are benefits to having a partial knee replacement.
With this surgical procedure, there is:
less bone and soft tissue dissection
less blood loss
Faster recovery of range of motion.
better range of motion overall
There are also risks associated with partial knee replacement.
The risks include:
A higher revision (repeat or re-do) rate for partial knee
replacement than total knee replacement 2-potentially worse
function after revision of partial knee replacement than total
knee replacement 3-revisions can be more complicated than
primary surgeries .
The complications after a unicondylar knee replacement are
similar to a total knee replacement. These complications include
inadequate pain relief, deep venous thrombosis in 1% to 5% of
patients, infection in less than 1% of patients, and unexplained
pain about the knee. Late complications include loosening of a
component, subsidence of the component, degeneration of the
other compartment resulting in pain, infection, polyethylene
wear, and possible dislocation of the polyethylene component in a
mobile-bearing knee replacement. The main concern associated
with partial knee replacement is a possible need to have surgery
again if another compartment becomes affected. In this case, the
patient would have their partial knee prosthesis removed, and it
would be replaced with total knee prosthesis .
While UKA may have advantages as a surgical option
for selected patients who meet the operative criteria
detailed previously, TKA remains a popular operation for
unicompartmental pathology. The widespread performance of UKA has been limited by the technical difficulty of performing the
procedure. In particular, UKA has less tolerance for acceptable
component positioning when compared to TKA, as improper
component positioning, by as little as 2o, can result in UKA
failure (Figure 3) [15-19]. Failures of UKA occur when there is
medial-lateral mismatch, inadequate stability of the components,
heterogeneous polyethylene wear, improper patient selection
(such as performing UKA for bilateral osteoarthritis), aseptic
loosening, and tibial Subsidence (Figure 4) [20,21].
Although results can be optimized with careful patient
selection and use of a sound implant design, the most important
determinant of success of UKA is component alignment. Studies
have shown that component malalignment by as little as 2° may
predispose to implant failure after UKA. Robot-assisted UKA has
been projected to address this issue, which combines patient
specificity and navigation. Short-term results for robot-assisted
UKA are promising, although long-term results are awaited to
determine implant survivorship and functional outcome .
Osteoarthritic destruction of the knee is the
commonest reason for total knee replacement. This is a disease of synovial joints characterized by degenerative and
reparative processes and is seen in 40 percent of 40- yearold’s
on radiographic examination. However only 50 percent
of these will be symptomatic. Osteoarthritis may be primary
Mechanical derangement such as previous meniscal or
cruciate ligament damage, pyogenic infection, ligamentous
instability, and fracture into a joint are among the common
causes of the secondary type.
Other causes of cartilage destruction include
rheumatoid arthritis, haemophilia, the seronegative
arthritis, crystal deposition diseases, pigmented villonodular
synovitis, avascular necrosis and the rare bone dysplasia.
Contraindications:Absolute contraindications to total knee
Knee sepsis including previous osteomyelitis, a remote
source of ongoing infection
Extensor mechanism dysfunction,
Severe vascular disease,
Recurvatum deformity secondary to muscular
weakness, and 5-the presence of a well-functioning knee
Relative contraindications include
medical conditions that preclude safe anaesthesia ,the
demands of surgery and rehabilitation
skin conditions within the field of surgery e.g psoriasis,
a neuropathic joint and obesity
Thromboembolism: This includes deep vein thrombosis
(DVT), with subsequent life-threatening pulmonary
Infection: Factors relating to a higher rate of infection
after TKA include rheumatoid arthritis, skin.
Patellofemoral complication: Patellofemoral
complications include patellofemoral instability, patellar
fracture, patellar component failure, patellar clunk
syndrome, and extensor mechanism tendon rupture. All have
been cited as the common reasons for re-operation. These
can be avoided by attention to detail, meticulous technique
and the avoidance of component malposition.
Neurovascular complication: Arterial thrombosis after
total knee replacement is a rare (0.03-0.17%) but devastating
complication, frequently resulting in amputation. Several
authors have recommended performing TKA without the
use of a tourniquet in patients with significant vascular
disease. Such patients should undergo a vascular surgery
consultation prior to their knee replacement.
Peroneal nerve palsy is the commonly reported nerve
palsy after total knee replacement. It usually occurs in the
correction of combined fixed valgus and flexion deformities,
as are often seen in patients with rheumatoid arthritis. 50%
undergo spontaneous recovery and 50% undergo partial
recovery with conservative treatment. Some good results
have been obtained with surgical decompression.
Peri prosthetic fractures: Supracondylar fractures of
the femur are not common after total knee replacement
(0.2% to 1%) They are seen if the anterior femoral cortex is
notched and weakened during surgery and in patients with
osteoporosis, rheumatoid arthritis, poor flexion, revision
arthroplasty, and in neurological disorders. Treatment is
with internal fixation or revision total knee arthroplasty.
Tibial fractures are uncommon.
Most patients seem satisfied with their knee replacements
and if relief of pain is the main indication for surgery then this
should indeed be the case. Satisfactory knee function is usually
restored after total knee replacement and the majority is able to
return to low impact sporting activity . Long term studies
confirm satisfactory functional scores and show 91% to 96%
prosthesis survival at 14- to 15-year follow-up. There does not
appear to be any difference between PCL-retaining and PCLsubstituting
designs. Cement less designs do not have the same
length of follow up but studies showing 10-12 years report 95%
prosthesis survival [23,24].
The total knee replacement and the partial knee replacement
are both surgeries that can change the lifestyle of a person
living with osteoarthritis or another knee condition that causes
continuous pain. While there are many risks involved with this
surgery and a long recovery process, the outcome is worth
the work in most cases. The total knee replacement is a more
invasive surgery where the bone is cut away and the entire
joint is replaced with prosthesis. Recovery is difficult, and
usually takes six to eight weeks of intense physical therapy. A
partial knee replacement is slightly less invasive, because only
one compartment of the knee is cut and replaced, which allows
for a quicker recovery and decreased risks. Because only one
compartment is replaced, it is less common than a total knee
replacement since many patients have injury in more than one
compartment and are not eligible for this surgery. The patient
still needs physical therapy, but should be able to walk without
assistive devices sooner. Both surgeries have their limitations,
as full range of motion may never be reached and the patient
should refrain from participating in high impact sports such as
running. This is because the large amount of force on the knee
can degrade the prosthesis more quickly, causing a need to have
it replaced sooner .
The total knee replacement and the partial knee replacement
are both effective at reducing pain in the knee. However, both
surgeries are useful for different populations. There is more
information about the total knee replacement because it is more
common, and generally this would be beneficial to the patient
and their wellbeing.