POTENTIAL COMPLICATIONS OF KNEE REPLACEMENT
Deep Venous Thrombosis(DVT)
All major lower limb and pelvic surgery is associated with a risk of deep venous thrombosis. A thrombosis is a clot within the deep veins of the calf, thigh or pelvis of the patient
Measures we employ to reduce this risk are the use of surgical stockings which compress the deep veins emptying them of blood during stocking use.
We also utilise a low molecular weight heparin. This reduces the ability of the blood to clot by a small amount.
During surgery we utilise a pneumatic compression device which massages the calf of the patient and reduces the risks of clot formation.
On discharge from hospital we perscribe an oral anticoagulant -Rivoroxaban - to further reduce the risk of DVT.
Despite measures employed to reduce the risk it is never completely eradicated.
Pulmonary Embolus (PE)
The formation of small clots within the deep veins of the calf, thigh and pelvis can be associated with a pulmonary embolus. Portions of the deep venous clots become detached and circulate through the venous system back to the heart and then on to the lungs.
Here they block vessels and prevent the lung from delivering oxygen to the blood on its return to the heart.
Again the combination of surgical stockings and a low molecular weight heparin are both used to reduce the risk of this occurring.
There is a lot of speculation to the true rate of both DVT and pulmonary embolus following major lower limb surgery during hip and knee replacement.
Treatment for either DVT or PE requires the use of a medicine to reduce the bloods ability to clot and to help dissolve the existing clot. This medicine is Warfarin and it is used typically for 6 months.
Fatal Pulmonary Embolus (PE)
In a very low proportion of cases a pulmonary embolus may be large enough to be fatal. The incidence of this has been reported as being in the order of 0.34%.
Despite all the techniques employed in modern day joint replacement there remains a risk of infection with all modern day joint replacement.
This risk is low and the risk of a deep infection is generally quoted as being one (1) percent i.e. 1 in 100 cases.
This remains constant for all hospitals.
Hemorrhage and Haematoma
All surgical procedures result in bleeding (hemorrhage). At the end of the surgical procedure we use a drain to collect the blood which accumulates following surgery.
This drain appears as a small plastic tube exiting through the skin at the end of the operation. This will usually remain in place for 24 hours following the operation.
The drains we use are designed in such a way that the blood they collect can be returned to the patient to improve their post-operative recovery and reduce the requirement for a blood transfusion. Very rarely, less than 1 percent of cases, the drain will fail to collect all the blood from the deep tissues.
A collection of blood in the deep tissue is known as a haematoma. In the majority of cases this will be small and will drain on its own typically via the vacant drain site. In very rare instances a haematoma would be large enough to require drainage with surgery.
The knee has both blood vessels and nerves around it. During knee replacement instruments are placed to retract the soft tissues and saws are used to fashion the bone to take the knee replacement.
Whilst great care is taken to protect the tissues there is always a risk to both the blood vessels and nerves. This is thankfully very low.
Whilst some of the ligaments within the knee are removed the broad ligaments along the inner and outer aspects of the knee are preserved during surgery.
Great care is taken to protect these during surgery.
However since surgery involves the use of sharp instruments to remove soft tissue and saws to remove bone there remains a risk of injury to these ligaments.
The risk is exceptionally low.
Post-operative recovery from knee replacement requires a great amount of hard work from the patient with the physiotherapist.
Despite this some patients never achieve a satisfactory range of movement. Very rarely this will require a further manipulation of the knee.
The components inserted during knee replacement are inserted with a hammer and stuck to the bone with “cement” which acts like a grout.
Very rarely pre-existing weakness in the bone or the fact that it has been shaped to receive the knee components will lead to fracture.
This would be repaired at the time of surgery if realised.
Extreemely rarely a fracture may only become visible after a post operative radiograph. In such a case a period of non weight bearing may be required.
Loosening and Revision
The knee components are stuck to the bone using “cement”. This acts like a grout to hold the components to the bone.
The knee replacement consists of two metal components one on each bone with a plastic (polyethylene) component in between.
During the normal lifetime of the knee the polyethylene wears, generating wear debris.
Over many years this will lead to loosening of the knee replacement at the join between the cement and the bone.
Typically the average lifespan of the knee replacement is 15-20 years.
As it becomes loose it will lead to new symptoms and ultimately the knee replacement will require revision knee replacement.