Total Knee Replacement(TKR) the name inspires both awe as well as fear.Awe because of the wonderful results of the surgery in patients successfully operated and fear because of lack of knowledge and information regarding the procedure. The knee replacement as we today is the work of number of stalwarts like Dr Ranawat, Dr Insall ,Dr Freeman and Dr. Laskin to name a few.
TKR started as a hinge joint and has evolved into as some people say invention of the century
What is Total Knee Replacement?
In Total knee replacement Surgery, the parts of the bones that rub together are resurfaced with metal and plastic implants. Using special, precision instruments, the damaged surfaces of the bones are removed and replacement surfaces fixed into place.
The surface of the femur is replaced with a rounded metal comonent that comes very close to matching the curve of your natural bone. The surface of the tibio/leg bone is replaced with a smooth plastic component. This flat mental component holds a smooth plastic piece made of ultra-high-molecular-weight polyethlene plastic that serves as the cartilage. The undersurface of the kneecap may also be replaced with an implant made of the same polyethylene plastic.
Condition Where TKR is Useul?
The most common indications are osteoarthritis(O.A) and Rheumatoid arthritis(R.A). Osteoarthritis(O.A) is a wear and tear disease where either medial or lateral side of the knee wears down resulting in gradual thinning of cartilage.This thinning of cartilage can be seen on an Xray as reduced Joint space.
The symptoms of O.A are gradual reduction in the distance that a person can walk over the years due to increasing pain.Whenever I enquire "how much can you walk” most Indian patients answer it as- saare din ghar ghar mein chalti hoon.When enquired deeply they will confess that-Bahar to 100-150 metre chalne ke baad dard ki wajah se mujhe rukna padta hai.These people are classified as home ambulators.One category better than wheel chair bound.How long can you stand – people will usually answer it as 20 min 30 min before it forces them to find a chair to sit.Can you climb stairs-usually answered as yes or no. If yes than usually it is with difficulty or with support.
What are the type of Implants?
Broadly there are two basic types of implants
A.Unicondylar or Partial knee replacement where only half of the knee usually medial is replaced.
B.Total knee replacement - Here the total knee surface is resurfaced The total knee implants can be anatomic like natural joint or non anatomic which is more common. Based on how the implants are fixed to the bone they can also be classified as cemented or cementless. Most of the successful designs today are cemented
What is fixed and mobile bearing?
he original designs developed simultaneously
Fixed bearing refers to the tibial insert is fixed and does not allow any rotation or swivel action between insert and tibial base plate
Mobile bearing Here the tibial insert is put on a highly polished tibial tray and swivels over it mimicking natural knee movement of internal and external rotation.Theoretically this should lead to reduced wear and longer life of implants.
What is hiflex design?
Dr. Answer : Most of the Hiflex design makers say that these designs give more flexion(bending at the knee).But we can find a number of articles in the medical literature vying for both-“ that they do and don’t allow more flexion” depending on which side you are on.In my practice I have found no significant difference .
Most of these designs cut more bone posteriorly from femur meaning more difficult revisions in future. Secondly some hiflex designs are also assosciated with more anterior knee pain. Although the designers say that you can sit crosslegged on ground ,perform namaz and squatt as well most of the surgeons in India as well abroad advice against these activities it as it accelarates wear due to pressure.May be the coming decade will make it more clear when the survival results of these implants when used with these activities become available.
In my practice patients who can sit crosslegged are allowed to sit crosslegged only on bed or a higher platform and to avoid squatting and sitting crosslegged on ground.
What about the knee for females?
Dr. Answer : Most of the patients undergoing TKR are females. Most of the knees are designed as an average of male and female knees.Anatomically the female knees are narrower than male knees. The knee designed for females is slightly narrower and the patellar groove is slightly more lateral. In my practice most of the knees can be done easily with standard knees but having the female specific knee is occsionally helpful in the operation room. The cost of this female specific knee is slightly higher
What about Custom jigs
Recently a company has introduced customized jigs for the surgery in India. The patient’s MRI of the knee is taken and sent to the company centre. There the company designs a jig specifically for the patient . This allows ease for the surgeon as a number of steps can be done using the same jig reducing the operative time and ease for the surgeon reducing the blood loss and anaesthesia time.
Are there alternate bearing surfaces for the knee like in hips
Dr. Answer : Yes, the routine femur and tibia are made of modified cobalt chromium molybdenum alloy.Compared to metals ceramics are harder and less likely to develop scratches.This means lower wear and longer life for the knee. Oxidized Zirconia (a form of ceramic)knees have been present for some time and are supposed to prolong implant survivorship.The risk of fractures assosciated earlier has not been noted in these surfaces.Go to Top
What is MIS ?
Dr. Answer : MIS refers to minimally invasive surgery.The idea is to do surgery through small incision minimizing the trauma to to muscles and tissues. This has been a hot topic during recent times. The conventional TKR as we know also has gradually resulted in reduced incisions and less trauma as the companies have designed instrumentation to make it easier for surgeon to operate through smaller incision.
Various approaches such as subvastus and midvastus have been used to reduce the trauma to quadriceps muscle so that patients can recover faster the straight leg raise(ability to raise the leg with knee straight while lying on bed.)
But MIS has been fraught with its own complications as a number of papers have reported improper sizing,bad cementing and higher complications as surgeon struggle to do surgery in improperly selected cases with limited visualization
A landmark japanese paper where they studied the blood levels of tissue injury markers and found no difference.
In my practice I follow mantra of reduced tissue trauma where I carefully select patients where we can do MIS . In rest of the patients surgery is done through comfortable incisions. Using multimodal analgesia in combination we achieve SLR(straight leg raise)in 85 to 90% of patients within 4-6 hours on day of surgery eliminating the phenomenon of quadriceps inhibition.
What is multimodal analgesia ?
Dr. Answer : Multimodal analgesia refers to using a combination of pain relieving agents to achieve best results. In my practice we use a intraarticular injection of cocktail of drugs .The surgeries are done under spinal or combined spinal epidural . The epidural is ususally removed immideately after surgery.This results in achieving SLR(straight leg raise)in 85 to 90% of patients within 4-6 hours on day of surgery eliminating the phenomenon of quadriceps inhibition
How is the implant affixed in the Body.?
Generally, implant systems are affixed in the body by using bone cement. Bone Cement is a special type of acrylic bone cement may be used to secure some or all of the implant components to the bone. Bone cement takes about 15 minutes to set.
When can I stand and go to toilet myself?
Dr. Answer : Most of the patients are mobilized within 12 – 18 hours after surgery. They can go to a western style toilet after 24-48 hrs after surgry and are usually home on 3rd to 4th postoperative day.
When can I climb stairs?
Stair Climbing within 4 week after TKR
Dr. Answer : If you have undergone only one knee than stair climbing is allowed 3rd day after surgery. If both the knees are done than stair climbing is started after 3 to 4 weeks
When can I drive a car/vehicle?
Walking within 4 week after TKR
Dr. Answer : You are allowed to walk as much as you can.Many of my patients who were avid morning walkers routinely walk 3-5 Kms daily.The general medical health of the patients (cardiac and lung status)is the limiting factor not the knee.
How long my knee will last?
Dr. Answer : Metanalysis of survivorship results of TKR have shown the following results
97% at 10 years
94% at 15 years
91% at 20 years.
These are statistical results of a large pool of patients however every patient is a individual in himself.
What are the complications of surgery?
Dr. Answer : Total knee replacement is safe and effective. The vast majority do not experience any complications but some complications that may occur are listed below
2.Deep vein thrombsis and symptomatic pulmonary embolism-(3-5%)
3. Fat embolism rare
5 .Vessel and nerve injury-(0.1%).Common peroneal nerve palsy is more common in valgus knees
6. Fracture – rare
7. Loosening and wear
Any care to be taken after TKR
Dr. Answer : 1. Treat every infection promptly. Any infection in the skin ,chest or even UTI can localize in the artificial kneeso consult with a physician and treat at the earliest
2. Even minor procedures such s dental procedure ,catheterization should be done under prophylactic antibiotic cover