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Total Knee Replacement
S H PALMER, M CROSS
Figure1: Total Knee Replacement before implantation
Introduction
Total knee replacement in some form has been around for
over 50 years. The complexities of the knee joint
only began to be understood 30 years ago and because of
this total knee replacement was initially not as successful
as Sir John Charnley's artificial hip. However over
the last twenty years there have been dramatic advancements
in knowledge of knee mechanics that have led to modifications
of design which appear to be durable. As with most
techniques in modern medicine the envelope is constantly
expanding so that more and more patients are receiving the
benefits of total knee arthroplasty.
History
In the 1860’s Fergusson reported
performing a resection arthroplasty of the knee for arthritis
and Verneuil is thought to have performed the first interposition
arthroplasty using joint capsule. Other substances were
subsequently tried including skin, muscle, fascia, fat,
and even pig bladder!
The first artificial
implants were tried in the 1940s as molds fitted to the
femoral condyles following similar designs in the hip. In
the next decade tibial replacement also was attempted but
both designs had problems with loosening and persistent
pain. Combined femoral and tibial articular surface replacements
appeared in the 1950s as simple hinges. These implants
Failed to account
for the complexities of knee motion and consequently had
high failure rates.
In 1971 Gunston importantly
recognized that the knee does not rotate on a single axis
like a hinge but rather the femoral condyles roll and glide
on the tibia with multiple instant centres of rotation.
His poycentric knee replacement had early success with its
improved kinematics
over hinged implants
but failed because of inadequate fixation of the prosthesis
to bone.
The highly conforming
and constrained Geomedic knee arthroplasty introduced in
1973 at the Mayo Clinic ignored Gunston’s work and a “kinematic
conflict” arose. Other designs followed, either following
Gunston’s principle in attempting to reproduce normal knee
kinematics or allowing a conforming articulation to govern
knee motion.
The Total Condylar
prosthesis was designed by Insall at the Hospital for Special
Surgery in 1973. This prosthesis concentrated on mechanics
and did not try and reproduce normal knee motion. Ranawat
et al. reported a survivorship of 94% at 15-year follow-up
which is the most impressive reported to date (1). The component
was subsequently altered to artificially introduce normal
kinematics to improve range of motion of the component.
At the same time a prosthesis with more natural kinematics
was developed at the Hospital for Special Surgery relying
on the retained cruciates to provide knee motion.
The argument as to
whether knee ligaments should be preserved or sacrificed
goes on to this day. Long term follow up studies do not
show any significant differences although gait appears to
more normal if ligaments are preserved, especially when
walking up and down stairs. One theoretical way of incorporating
normal kinematics and maximal conformity is with mobile
tibial bearings. Current mid-term follow up studies of these
prostheses have so far shown encouraging results.
Definition of problem
Patients with painful, deformed and unstable knees secondary
to degenerative or inflammatory conditions need a prosthesis
that will provide reproducible relief of pain and improvement
in function. The morbidity and complications from
the procedure should be minimal. The complexities
of a normal knee joint however are not reproducible with
modern techniques and the patient should understand that
they will not have a “normal knee”. The prosthesis should
be durable requiring the patient to undergo one definitive
procedure in their lifetime although in the younger patient
this may simply be unrealistic.
Frequency
Approximately 130,000 knee replacements are performed every
year in the United States of America.
Etiology
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-year-old's on
radiographic examination. However only 50 percent
of these will be symptomatic. Osteoarthritis may be primary
or secondary. 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 arthritides, crystal deposition diseases, pigmented
villonodular synovitis, avascular necrosis and the rare
bone dysplasias.
Figure 2: X-ray demonstrating
post-traumatic osteoarthritis
Recent studies into
risk factors for severe osteoarthritis of the hip and knee
have revealed that siblings of individuals undergoing joint
replacement are between 3 and 5 times likely to require
similar surgery as an age matched control (2). This means
that genes contribute around 30% of the overall risk for
severe OA. Laboratory based studies have shown that chromosome
11 is linked to severe OA of the hip and chromosome 2 to
severe OA of the knee. The precise genes involved are as
yet unknown.
Pathophysiology
The exact cause of the degenerative process in primary
osteoarthritis is unknown. It may represent a defect in
cellular (chondrocyte) repair processes. Osteoarthritic
cartilage contains increased amounts of water, alterations
in the type of proteoglycan, type 2 collagen abnormalities
and increased levels of the cathepsins, metalloproteinases,
interleukin 1 and others as a complex cascade of enzymatic
process. Changes in the synovium include synoviocyte hyperplasia,
an increased leukocyte population in the membrane and fluid,
occasional giant cells, neovascularisation with increased
vessel permeability and altered matrix and cellular cytokine
formation.
Clinical Presentation
The clinical history in a patient with arthritis of the
knee is dominated by pain. This predominantly occurs on
weight-bearing but in the end stages may be constant and
unrelieved by rest. Night pain is a particularly disabling
symptom that demands urgent attention. The pain may be localised
to one compartment or maybe diffuse. Other symptoms include
stiffness, swelling, locking and giving way. It is useful
to try and quantify the level of pain on a simple scale
( e.g mild, moderate, severe or a numerical scale of 1 to
10) and to assess how the patient’s activities of daily
living (ADL) are affected. The patient should be asked questions
on maximum walking distance, recreational sporting ability
and aspirations, stair climbing (which often gives clues
about patellofemoral disease), the need for walking aids,
the ability to dress and perform self-care and the ability
to perform activities that require knee flexion. Some patients
may have considerable interference with social interaction,
sexual function and sleep deprivation and may experience
exhaustion and even depression from their disease.
Various structured
outcomes evaluation can be used to try and quantify disability
from dysfunction of the knee and are useful as research
tools in follow-up studies of total knee replacement. These
include general health status measures such as the Medical
Outcomes Short Form 36 (SF 36) or specific knee scoring
systems such as that used by the Knee Society (3, 4).
The mortality from
a total knee replacement is overall less than than 1% but
this figure increases with age, male gender and the number
of pre-existing medical conditions. Identification and optimisation
of such conditions prior to surgery is important to reduce
peri-operative complications.
An assessment of the
patient’s social circumstances is important for organisation
of post-operative rehabilitation and placement.
Examination should
include assessment of scars or soft tissue defects around
the knee. Plastic surgical consultation should be obtained
if wound healing is predicted to be a problem. Similarly
an accurate assessment of vascular status to the limb should
be performed. Chronic local or systemic infection should
be identified and treated.
Deficiency of the
quadriceps musculature and extensor mechanism should be
identified and treated by rehabilitation as this may improve
mechanical pain and facilitate post-operative recovery.
Range of motion, including fixed flexion deformity, should
be measured with a goniometer and recorded. The best predictor
of range of motion after total knee replacement is the pre-operative
range of motion. This is an important factor when
obtaining consent from the patient for surgery.
Figure 3: Patient
demonstrating varus deformity of right knee and a valgus
deformity of left knee
Integrity of the ligaments
should be established as deficiency may require use of a
special prosthesis with intrinsic stability.
Other sources of knee
and leg pain must be sought and systematically excluded.
These
include root pain
from spinal disease, referred pain from the ipsilateral
hip, peripheral vascular disease, meniscal pathology, and
bursitis of the knee.
Roentgenographic findings
must correlate with a clear clinical impression of knee
arthritis
Knee roentgenograms
should include a standing anteroposterior view, a lateral
view, and a skyline view of the patella. Loss of joint space,
cysts, subchondral sclerosis and osteophytes confirm the
diagnosis of osteoarthritis.
Figure 4: X-ray of
the same patient demonstrating the features of osteoarthritis
Indications
The primary indication for total knee arthroplasty is to
relieve pain caused by severe arthritis. The pain should
be significant and disabling. Night pain is particularly
distressing and significant. If dysfunction of the knee
is causing significant reduction in the patient’s quality
of life then this should be taken into account. Correction
of significant deformity is an important indication but
is rarely used as the primary indication for surgery. Roentgenographic
findings must correlate with a clear clinical impression
of knee arthritis. Patients who do not have significant
loss of joint space tend to be less satisfied with their
clinical result after total knee arthroplasty. Before surgery
is considered all conservative treatment measures should
have been exhausted.
Knee replacement has
a finite expected survival that is adversely effected by
activity level. It
generally is indicated
in older patients with more modest activities . It is also
is clearly indicated in younger patients who have limited
function because of systemic arthritis with multiple joint
involvement. Young patients requesting knee replacement,
especially those with post-traumatic arthritis, are not
excluded by age but must be significantly disabled and must
understand the inherent longevity of joint replacement.
Rarely, severe patello-femoral arthritis may
justify arthroplasty
because the expected outcome of arthroplasty is superior
to patellectomy. Isolated patellofemoral replacement is
still undergoing clinical investigation.
Figure 5: Lateral
x-ray demonstrating severe patello-femoral osteoarthritis
Deformity can sometimes
become the principal indication for knee replacement in
patients with moderate arthritis when flexion contracture
or varus or valgus laxity is significant. In such cases
often a more constrained prosthesis is required leading
to greater technical difficulty at operation more uncertain
long-term survival.
Contraindications
Absolute contraindications to total knee replacement include,
knee sepsis including previous osteomyelitis, a remote source
of ongoing infection, extensor mechanism dysfunction, severe
vascular disease, recurvatum deformity secondary to muscular
weakness, and the presence of a well functioning knee arthrodesis.
Relative contraindications include medical conditions that
preclude safe anesthesia,the demands of surgery and rehabilitation.
Other relative contraindications include skin conditions
within the field of surgery e.g psoriasis, a neuropathic
joint and obesity.
Relevant Anatomy
.
Movement of the knee joint can be classified as having six
degrees of freedom—three translations: anterior/posterior,
medial/lateral, and inferior/superior and three rotations:
flexion/extension, internal/external, and abduction/adduction.
The movements of the knee joint are determined by the shape
of the articulating surfaces of the tibia and femur and
the orientation of the four major ligaments of the knee
joint: the anterior and posterior cruciate ligaments and
the medial and lateral collateral ligaments as a four bar
linkage system.
Figure 6: Saggital
MRI scan showing the anterior and posterior cruciate ligaments
Knee flexion/extension
involves a combination of rolling and sliding called “femoral
roll back” which is an ingenious way of allowing increased
ranges of flexion. Because of asymmetry between the lateral
and medial femoral condyles the lateral condyle it rolls
a greater distance than the medial condyle during 20 degrees
of knee flexion. This causes coupled external rotation
of the tibia which has been described as the screw-home
mechanism of the knee which locks the knee into extension.
The primary function
of the medial collateral ligament is to restrain valgus
rotation of the
knee joint with its
secondary function being control of external rotation. The
lateral collateral ligament restrains against varus rotation
as well as resisting internal rotation.
The primary function
of the anterior cruciate ligament (ACL) is to resist anterior
displacement of the tibia on the femur when the knee is
flexed and control the screw home mechanism of the tibia
in terminal extension of the knee. A secondary function
of the ACL is to resist varus or valgus rotation of the
tibia, especially in the absence of the collateral ligaments.
The ACL also resists internal rotation of the tibia.
The main function
of the posterior cruciate ligament (PCL) is to allow femoral
rollback in flexion and resist posterior translation of
the tibia relative to the femur. The PCL also controls external
rotation of the tibia with increasing knee flexion. Retention
of the PCL in total knee replacement has been shown biomechanically
to provide normal kinematic rollback of the femur on the
tibia. This is also important for improving the lever arm
of the quadriceps mechanism with flexion of the knee.
The movement of the
patellofemoral joint can be characterized as gliding and
sliding. During flexion of the knee the patella moves distally
on the femur. This movement is governed by its attachments
to the quadriceps tendon, ligamentum patellae and the anterior
aspects of the femoral condyles. The muscles and ligaments
of the patellofemoral joint are responsible for producing
extension of the knee. The patella acts as a pulley in transmitting
the force developed by the quadriceps muscles to the femur
and the patellar ligament. It also increases the mechanical
advantage of the quadriceps muscle relative to the instant
center of rotation of the knee.
The mechanical axis
of the lower limb is an imaginary line through which the
weight of the body passes. It runs from the centre of the
hip to the centre of the ankle through the middle of the
knee. This is altered in the presence of deformity
and must be reconstituted at surgery This allows normalisation
of gait and protects the prosthesis from eccentric loading
and early failure.
Work up
A thorough preoperative
medical evaluation of patients undergoing total knee arthroplasty
is important to prevent potential complications in the perioperative
period. This should be completed in an elective preadmission
clinic well before the date for surgery. This allows
a careful and unhurried assessment to be performed
with adequate time for investigations, specialist
anaesthetic and medical opinion and consent. This also allows
operating schedules to be reorganised if patients are deferred
from surgery.
Most patients who
have total knee arthroplasty are elderly with comorbid diseases.
Patients must have good cardiopulmonary function to withstand
anesthesia and to withstand a blood loss of 1000 to 1500
ml over the perioperative period. A routine preoperative
electrocardiogram should be performed in the elderly patient
and those patients with ischaemic heart disease, congestive
heart failure and chronic obstructive airways disease should
be seen by a medical specialist or anaesthetist. Patients
with significant peripheral vascular disease should be seen
by a vascular surgeon.
A. Lab Studies
Routine preoperative laboratory evaluation should include
a full blood count and white cell differential, urea, electrolytes,
creatinine and urinalysis to exclude occult urinary tract
infection. The routine use of a chest roentgenogram is not
usually recommended as a screening tool. However it is indicated
in patients with cardiopulmonary disease or in patients
with clinical signs identified in the preadmission clinic.
Similarly, routine preoperative evaluation of coagulation
studies is not necessary except in patients with a history
of bleeding or previous liver disease.
B. Imaging Studies
Radiographic views for the assessment of the patient with
knee arthritis include the standing anteroposterior (AP)
view, the lateral radiograph and the patellofemoral (skyline)
view. Long leg films to assess malalignment are helpful
for preoperative plannning. Standing AP radiographs with
the knee in extension or 45 degrees of flexion
can improve the sensitivity of detection of cartilage degeneration.
Figure 7: “skyline”
view of the patello-femoral joint demonstrating lateral
and medial osteophytes and lateral subluxation of the patella
C. Other Tests
More sophisticated imaging modalities in the investigation
of knee arthritis are of occasional benefit and include
indium white blood cell scanning, computed tomography scanning
and magnetic resonance imaging scanning for the assessment
of significant bone loss or bone infection.
Procedures
There are a number of operative procedures that should be
considered in patients with degenerative disease of the
knee. Arthroscopic debridement is sometimes indicated
in mild degenerative joint disease with mechanical symptoms
and recurrent persistent effusions. Proximal tibial
valgus osteotomy should be reserved for patients with medial
tibiofemoral compartment disease, stable collateral ligaments,
and a correctable varus deformity of the knee joint.
Figure 8: X-ray demonstrating
a proximal tibial valgus osteotomy created to off-load the
medial compartment of the knee.
Similarly a distal
femoral varus osteotomy can be considered for patients with
lateral tibiofemoral compartment disease, stable collateral
ligaments, and a valgus deformity of the knee joint.
Figure 9:
X-ray demonstrating a distal femoral varus osteotomy.
These procedures restore
the mechanical axis of the lower limb and off-load the diseased
compartment. They are generally reserved for young,
high-demand patients because of concerns with the durability
of total knee replacement in this patient group. Unicompartmental
knee replacement or hemiarthroplasty can be used in low-demand
younger patients with unicompartmental disease or in elderly,
nonobese patients with unicompartmental disease of the knee
joint.
Figure 10:
X-ray demonstrating a medial unicompartmental replacement.
Note relative preservation of lateral joint compartment.
Arthrodesis or fusion
of the knee is rarely performed but should be considered
in patients with chronic sepsis, younger patients with tricompartmental
disease (e.g following trauma) who require stability and
durability and in patients with a deficient extensor mechanism.
Total knee arthroplasty is performed in patients with symptomatic
advanced degenerative changes in one or more compartments
of the knee joint.
Histology
Macroscopic examination shows a spectrum of changes in the articular
cartilage from softening and fibrillation through to complete cartilage
destruction, subchondral bone thickening, cysts and osteophytes.
Microscopic examination shows chondrocyte proliferation into embryonic
and dedifferentiated forms in the deeper zones, fibrocartilage formation
with capillary infiltration, loss of proteoglycan ground substance with
altered staining characteristics, chondrocalcinosis and synovial hyperplasia
Treatment.
Medical therapy
Initial management of most patients with osteoarthritis
should be non-operative and may include non-steroidal anti-inflammatory
medications, analgesics, bracing, orthoses, shoe modifications,
weight loss and ambulatory aids such as a walking stick
(held in the opposite hand). Activity modification also
may be necessary. Home health care-assistive devices for
daily living (e.g. toilet extenders, safety rails, bath
seats) may help the patient cope with their disability and
should be prescribed after consultation with an occupational
therapist. Knee rehabilitation under the supervision of
a physiotherapist should include strengthening and range-of-motion
exercises, gait training and patient education.
Joint aspiration and
intra-articular steroid injection may be used to improve
synovitis. Osteoarthritis in the knee usually progresses
slowly thus affording opportunities for non-operative treatment.
Responses to non-operative treatment, however, are varied
and unpredictable
because none of the treatment is specific for the disease.
Because of the progressive
nature of the disease, many patients with osteoarthritis
of the
knee eventually require
operative treatment
Surgical therapy
The aim of total knee replacement is to resurface
the deficient and damaged tibiofemoral joint surfaces with
metal components and provide a low-friction articulation
with a polyethylene bearing. If significant patellofemoral
disease is present then this joint can also be resurfaced
although the need for this is rather variable. The mechanical
alignment and soft tissue balance around the knee should
be anatomically restored for optimum function and longevity
of the knee replacement.
Preoperative details
The patient should have completed an informed consent
for surgery and fully understand the risks and possible
complications of the procedure. They should have had all
medical conditions optimised before surgery and be free
of intercurrent infections. Two units of blood should be
available for perioperative transfusion either from the
blood bank or preferably as pre-donated blood. Full medical
and surgical back-up must be available in case unforseen
complications occur.
The selection of regional
or general anesthesia is decided following discussion preoperatively
between the anaesthetist and the patient with some input
from the surgical team. This decision is affected partly
by the medical condition of the patient although cardiovascular
outcomes, cognitive function and mortality rates of regional
and general anesthesia have not been proved to be significantly
different. Patients who have epidural anesthesia have been
shown develop fewer perioperative deep vein thromboses.
Whether this has any overall positive benefit to the patient
is not known. Another benefit of epidural anesthesia is
the presence of an indwelling catheter for 48 to 72 hours
postoperatively for pain control thus avoiding the need
for excessive amounts of centrally acting analgesics. Side
effects of continuous postoperative epidural analgesia include
pruritis, urinary retention, nausea, vomiting, and rarely
the formation of an epidural hematoma.
Antibiotics and anti-thrombotic
prophylaxis are given approximately 30 minutes before the
incision is made and mechanical anti-thromboembolic devices
(e.g stockings, foot pumps) are used intra-operatively.
The patient is set up on the operating table in a supine
position after preoperative cleaning of the leg.
Figure 11:
A patient on the operating table before sugery.
A thigh tourniquet
is generally used to aid surgical exposure although should
be avoided in patients with a history of previous deep vein
thrombosis or significant vascular disease. The operation
should be performed in a laminar flow operating theatre
with meticulous attention to detail to prevent contamination
of the operation site.
Intraoperative
details
The knee joint
is usually approached anteriorly through a medial parapatellar
approach although a lateral or subvastus approach is used
by some surgeons. Osteophytes and intra-articular soft-tissues
are then cleared. Bone cuts in the distal femur are made
perpendicular to the mechanical axis usually using an intramedullary
alignment system which is then checked against the centre
of the hip. The proximal tibia is cut perpendicular to the
mechanical axis of the tibia using either intra or extramedullary
alignment rods. Restoration of mechanical alignment is important
to allow optimum load sharing and prevent eccentric loading
though the prosthesis. Sufficient bone is removed so that
the prosthesis will recreate the level of the joint line.
This allows the ligaments around the knee to be balanced
accurately and prevents alteration in patella height
which can have a deleterious effect on patellofemoral mechanics.
Because of preoperative deformity some ligaments around
the knee will have become contracted These are carefully
released in a step-wise fashion to balance the soft-tissues
around the knee and allow optimum knee kinematics.
Figure 11: An intraoperative
photograph showing the trial components with the patella
everted.
Patello-femoral tracking
is assessed with trial components in situ and balanced if
necessary with a lateral release or medial reefing procedure.
If the patellofemoral joint is significantly diseased then
this can be resurfaced with a polyethylene button.
It is essential that the original width of the patella is
recreated.
Once the definitive
components have been selected they are cemented into place
with poly-methylmethacrylate cement. If an uncemented system
is being used, press-fit and bony ingrowth provides the
short and long term fixation of the component. The tourniquet
should be deflated prior to closure to allow accurate haemostasis
and the knee joint is usually drained and dressed in extension.
The foot pulses are checked at the end of the procedure.
Figure 12:
The definitive components in situ.
Postoperative details
The patient is recovered and usually observed for a 24 hour
period in a high dependancy ward. Adequate hydration and
analgesia are essential in this time of high physical stress.
Analgesia is provided by continuation of the intra-operative
epidural, patient controlled intravenous analgesia or oral
analgesia. The patient begins knee movement and exercises
at this early stage which are continued back on the ward
until discharge. The drains are usually removed within 24
hours and the patient is encouraged to walk on the second
post-operative day. Continual improvement is usually
seen and discharge occurs between seven and 14 days. This
is only recommended once wound healing is satisfactory,
knee flexion of 90 degrees has been achieved, the patient
is considered to be safe and supported in their home environment
and there are no complications. Thromboprophylaxis is often
continued at home for a period of time. The first outpatient
review is usually between six weeks and three months.
Figure 13:
Satisfactory knee flexion 6 weeks postoperatively.
Follow up
Follow up depends on the surgeon, the patient and the health-care
system. A typical example would be a surgical follow-up
appointment at six weeks, three months, six months, one
year, two years, five years, 10 years and thereafter as
appropriate. This is modified for each patient according
to their age, degree of activity and the presence of complications.
Complications
THROMBOEMBOLISM
This includes deep
vein thrombosis (DVT), with subsequent life-threatening
pulmonary embolism (PE). Predisposing factors for an increased
risk of DVT include age over 40 years, female sex, obesity,
varicose veins, smoking, past history of DVT, diabetes mellitus,
and coronary artery disease. The overall incidence of DVT
after total knee replacement without any prophylaxis has
been reported to range from 40% to 88%. Most of these are
calf thromboses. The risk of fatal PE however is the important
figure and varies between 0.1% and 1%. Many current methods
of DVT prophylaxis are available and are used, including
mechanical compression stockings or foot pumps and pharmaceutical
agents including low-dose warfarin, low-molecular-weight
heparin, and aspirin. Many studies show evidence of reduction
of rates of DVT but how this affects overall death
rates from PE is unclear at this time, with many of the
current studies concluding after only 10 days. It is probably
prudent to use a multifactorial approach to prevention of
DVT to include intraoperative foot pumps, an epidural, a
pharmaceutical agent, antithromboembolic stockings, adequate
hydration, early mobilisation of the patient and regular
postoperative surveillance.
INFECTION
Prevention of infection
in total knee replacement begins in the preoperative examination
of the patient in order to exclude intercurrent infection.
In the operating room, personnel should be kept to the smallest
number and traffic in and out of the room should be kept
to a minimum. The use of vertical laminar flow in operating
theatres, the use of prophylactic antibiotics, ultraviolet
light, body exhaust systems to prevent bacterial shedding
and meticulous and expeditious surgery all help to reduce
infection to less than 1% of operations.
Factors relating to
a higher rate of infection after TKA include rheumatoid
arthritis, skin
breakdown, prolonged
wound drainage (more than 6 days), previous knee surgery,
use of a hinged knee prosthesis, obesity, concomitant urinary
tract infection, steroid use, renal failure, diabetes mellitus,
malignant disease, and psoriasis.
Treatment of the infected
total knee replacement is often laborious and time consuming
and a disaster for the patient. The risk is minimised by
a theatre team obsessed with detail on a day-to --day basis
backed up by good nursing skills on the ward and vigilance
by the surgeon in the post-operative period.
PATELLOFEMORAL COMPLICATIONS
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.
Figure 14:
Skyline views of both knees showing lateral patella tilt
and subluxation in both knees. This patient required a patello-femoral
resurfacing procedure and realignment because of persistent
anterior knee pain in the post-operative period.
NEUROVASCULAR COMPLICATIONS
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
PERIPROSTHETIC 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 .
Outcome and Prognosis
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
(7). Long term studies confirm satisfactory functional scores
and show 91% to 96% prosthesis survival at 14- to 15-year
follow-up (1,5,6). There does not appear to be any difference
between PCL-retaining and PCL-substituting designs. Cementless
designs do not have the same length of follow up but studies
showing 10-12 years report 95% prosthesis survival (8).
Future and Controversies
Cemented total knee replacements will remain the gold standard
for total knee replacement but the use of uncemented designs
with bioactive surfaces such as hydroxyapatite are showing
promising midterm results.
Figure 15:
Top picture is an electromicrgraph showing incorporation
of bone (red) onto the surface of the hydroxyapatite. Bottom
picture shows an x-ray of an uncemented, hydroxyapatite
coated total knee replacement. There are no gaps in the
bone-prosthesis junction indicating incorporation of the
bone onto the prosthesis.
Research into mobile
bearing knee replacements continues. Such prostheses
appear to demonstrate an attractive way of overcoming the
constraint versus conformity conflict inherent in any artificial
knee replacement.
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