higher than in hips because of watershed nature of the vascular supply and lack of covering muscle.
risk factors
components with more constraint, particularly hinged prostheses
horizontal laminar flow theatres.
prolonged wound drainage.
In 17-50% of patients who go on to have an infection there is prolonged wound drainage.
RA, diabetes, psoriasis, obesity, open skin lesions on the leg, a previous knee operation and a history of previous infection.
Not a risk factor
no different with the use of cement.
Organism
The predominant organisms are S. aureus 50-65% and S.epidermidis 25-30%.
Management of UTI
should see urologist.
If there is a structural reason for the UTI it should be corrected
if there isn’t then life long suppressive antibiotic therapy is necessary and the patient should be told there is an increased risk of infection.
Diagnosis of infection
Painful, warm, stiff, swollen and tender joint.
Differential diagnosis includes RSD, arthrofibrosis and HO.
Keystone of diagnosis is aspiration.
Management of infection
Need to make a decision about the overall goals of treatment
eradication vs suppression
Suppression
This doesn’t eliminate infection
Used in patients in whom operative intervention is too dangerous or is declined.
Success rate is around 20%.
Debridement
Open debridement can be used in patients with an acute infection and well fixed prostheses.
The success rate is around 30%
the best chance of success is when debridement occurs soon after the onset of infection and is caused by a low virulence organism such as S.epidermidis.
Two Stage arthrodesis
A staged arthrodesis with use of an intramedullary nail is associated with a 90% success rate.
External fixateurs have a 65% success rate.
Reimplantation
usually a two stage procedure
A single stage procedure is not as successful as in the hip, with a success rate of around 50-60%.
There are several conditions necessary for staged treatment of infection:
Adequate skin and soft tissue
Adequate bone stock
Intact extensor mechanism if contemplating reimplantation
Competent immune system
Need several antibiotic options to prevent the development of resistance.
Technique
debridement of all cement and the prosthesis, lavage, antibiotic spacer, parenteral IVABs, then 6 weeks off antibiotics with normal ESR/CRP and negative aspirate prior to reimplantation.
A patellectomy and posterior cruciate substituting prosthesis are sometimes useful to help in skin closure in this setting.
Antibiotic cement is routinely used in this setting.
Reported success rate is up to 97%.
Resection arthroplasty
this is an option in older patients with rheumatoid arthritis and limited functional demands.
makes sitting easier but is often unstable and painful.
Usual ROM is around 40 degrees.
Amputation
indicated for life threatening sepsis or local infection combined with massive bone loss.
In one series of infected TKRs amputation was necessary in 6%.
Patients treated with an AKA have only around a 25% chance of remaining ambulant.
Thromboembolic disease
The rate of DVT without prophylaxis is around 70-80%, higher than in THR, but the risk of symptomatic PE is lower than in THR.
Use of epidural anaesthesia decreases this risk.
No conclusive proof about increased rate with tourniquet use.
Wound problems
blood supply
to the anterior skin is completely random and arises from the peripatellar anastomotic arterial ring.
The branches lie in the dermis superior to the subcutaneous fascia.
Any elevation of skin flaps must be deep to the subcutaneous fascia.
Lateral release
There is a higher rate of wound complications with a lateral release because this reduces oxygen tension to the lateral skin.
If a lateral release is performed one should attempt to preserve the superior lateral geniculate artery, which is found at the musculotendinous junction of the vastus lateralis.
Risk factors
obesity,
rheumatoid arthritis,
malnutrition,
nicotine abuse,
diabetes
chemotherapy
CPM
in excess of 40 degrees in the first three days decreases oxygen tension in the flaps and may have a higher rate of wound breakdown.
Continuous wound drainage
without obvious infection
is treated with immobilization and dressings.
If drainage persists for more than 5 days an open debridement should be performed.
Superficial soft tissue necrosis
should be managed with debridement and skin grafting.
Full thickness skin loss
medial head of gastrocnemius myocutaneous flap.
The medial head is preferred because it is longer and doesn’t have to traverse the fibula so there is more effective length.
Neurovascular complications
Peroneal nerve palsy
Rate
0.58% of all knees
Risk factors
valgus deformity (3%) and flexion contracture.
epidural anaesthesia
Epidural anaesthesia is probably not wise in a patient with a valgus knee and or laminectomy.
previous laminectomy.
Not Risk factors
Peroneal nerve palsy is not related to
age,
gender,
type of arthritis
duration of tourniquet use.
Treatment
Initial
As soon as the problem is diagnosed the dressing should be released and the knee flexed 20 degrees, the hip extended, and external rotation of the leg prevented with a soft pillow under the hip.
The area around the head of the fibula should be observed for an expanding haematoma.
Operative
Operative intervention should be considered at 3 months if there is no improvement.
97% improvement rate after neurolysis, with 2/3 of patients making a full recovery.
Only 1/3 of patients made a recovery without a neurolysis.
pre-neurolysis severity did not correlate with the results of neurolysis.
There has been no benefit demonstrated in exploring and prophylactically releasing the nerve in high risk knees.
Prognosis
Complete recovery post palsy is rare.
Arterial injury
Rate of arterial damage is around 0.1%
Prevention
If the pulses are impalpable the procedure should be done without a tourniquet to decrease the risk of thrombosis and plaque fracture in atherosclerotic arteries.
Treatment
If there is any suspicion of a vascular injury the tournique should be released prior to the insertion of components.
urgent on table angiogram
vascular consultation
Prognosis
up to 25% lead to amputation.
Extensor mechanism problems
Rate
Problems with the extensor mechanism are responsible for up to 50% of revisions.
Malpositioning of the components is often the cause of this:
Internal rotation of the femoral component
Medial shift of the femoral component
Internal rotation of the tibial component
Medial shift of tibial component
Lateral placement of the patella button – the button should be placed on the medial border of the patella.
Patella
Assessment of maltracking
patella maltracking can only be assessed after the tourniquet is deflated to free up the quadriceps.
Patella Resection
Patellar resection that leaves less than 15mm of bone substantially increases anterior patellar strain. When the patella is cut only a minimum of bone should be removed from the lateral facet, to create symmetry in the patella with decreased rates of maltracking. Cutting equal amounts of bone from the medial and lateral facets will actually create an asymmetrical patella.
A large central cement plug increases strain compared with peripheral, smaller holes.
Loosening of a cemented patellar component occurs in 2%. Higher rates are found in noncemented components.
Metal backed patellae have had a high failure rate.
This is due to the development of a fibrous nodule at the posterior aspect of the quadriceps tendon and proximal pole of the patella.
Treatment is open or arthroscopic debridement of the nodule.
Tendon rupture
This has a 1% incidence and is treated by an augmented repair e.g. with semitendinosis.
Stiffness
Range of motion usually increases steadily over the first three months and then to a lesser extent over the next nine months.
CPM hasn’t been shown to decrease hospital stay or increase ROM.
Diagnosis
Physical examination to rule out infection
XR to rule out overstuffing or patellar maltracking.
Bone scan if stiffness develops more than a year postoperatively.
Joint aspiration
Treatment
Physiotherapy
should be continued if getting response.
If there is a plateau or no response by three months, and infection has been excluded, then an MUA can be performed.
MUA can be performed at several months post surgery and the results retained to some extent
Complications of MUA
Supracondylar fracture
Patellar tendon avulsion
Myositis ossificans
Wound breakdown
Operative
If MUA is ineffective an arthroscopic debridement can be done but the results are unpredictable, and poor in the setting of arthrofibrosis.
The next step is revision with a PCL substituting prosthesis and increased flexion gaps while all adhesions are removed.
Supracondylar femoral fracture
Rate: 1%.
Risk factors
Increased in patients with osteoporosis e.g. secondary to RA or chronic steroid use.
Notching
Contribution of notching is controversial with some finding an increased rate of supracondylar fracture and others no difference, but it should be avoided, particularly in osteoporotic bone.
If a notch is discovered intraoperatively should consider use of a stemmed prosthesis.
In open treatment, one should have long stemmed revision components as well as an IMN in case the implant is unstable.
IM nailing is simpler, biomechanically more sound and less prone to failure than blade plates.
he results are much better with intramedullary nailing.
