COMPONENTS OF TOTAL KNEE REPLACEMENT

TOTAL KNEE REPLACEMENT

PARTS OF KNEE REPLACEMENT PROSTHESIS

Introduction:

Total knee replacement is surgical procedure in which the damaged cartilage lining of bone is replaced with artificial components, thereby eliminating the pain caused by diseased joint.

The most common indication is completely worn out knee joint by osteoarthritis. Knee replacement is also considered in certain arthritic conditions like Rheumatoid arthritis.

Parts of Artificial knee implant:

The components of artificial knee replicate the shape of joint surface so as to allow smooth rolling and gliding movement. Structure and shape of knee joint varies from person to person and also across the genders. In order to address this, the implant companies manufacture artificial joints in different sizes so that the operating surgeon can choose the best fit.

There are also several designs of implant based on patient’s age, gender and lifestyle.  It is the surgeon who can choose and suggest the best design and brand that best suits your need.

There are three main parts

-         Femoral (thigh bone) component

-         Tibial (Shin bone) component

-         Plastic (Cushion) component

-         Patellar component

Femoral (Thigh bone) component:

The lower end of femur in knee joint is a curved surface with central groove allowing movement of knee cap. The prosthesis component is made up metal and is curved with central groove mimicking the natural surface of femur. Femoral component is made up Chrome cobalt alloy or Zirconium alloy or Oxinium .

Tibial (Shin bone) component:

The upper end of shin bone is replaced with flat metal platform which can accommodate Plastic (cushion). Tibial component is made of Titanium alloy or Chrome-cobalt alloy.

Plastic (Cushion):

The plastic (Cushion) is also called as insert accommodates into the tibial metal platform. The plastic component has inbuilt curvature to accept the curvature of femoral component. If surgeon prefers to do a ligament sparing surgery the plastic has notch to accommodate the cruciate ligaments. In case cruciate ligaments are removed it has cam to take over the function. The material used in the manufacturing of plastic is High Molecular Weight Polyethylene (HMWP).

Patellar component:

The back side of knee cap is also replaced by removing damaged cartilage with polyethylene button. Some absolute indications warrant’s patella replacement whereas in some cases its surgeons preference.

TYPES OF TOTAL KNEE PROSTHESIS DESIGN

TYPES OF KNEE PROSTHESIS

1.     Fixed bearing :

This is the most common implant design used. As the name implies the Plastic (polyethylene) insert is fixed firmly on the metal platform of tibia. The femoral component of the prosthesis rolls over this plastic (polyethylene) insert. This design provides motion of knee joint in one plane i.e. bending and straightening of knee.

2.     Mobile bearing implants (rotating platform)

In mobile bearing knee the plastic insert (polyethylene) can rotate short distances on the metal platform of tibia. This design allows few degrees of sideways rotation of knee. The mobile bearing implants needs good ligament support as it allows sideways rotation of knee. They are not indicated in cases where the ligaments are lax or loose. These knee designs are slightly costlier than fixed bearing designs.

3.     Medial pivot implants: 

A normal knee has a component of pivoting motion during bending of knee. This design replicates bending, twisting and rotating of your natural knee.

4.     Personalized implants:

The shape and size of bones in knee joint varies from person to person. During routine total knee replacement surgery, knee implants are available in 6 to 10 different sizes. The surgeon then selects the implant that closely matches with patient size and shape of bones and some minor adjustments are done to fix the implant to the bone. This technique sometimes compromises the precession fit of the implant to the bone. In few cases and instances, such minor adjustments are acceptable, but in few gross adjustments are disaster can result in early failure of knee implant.

To overcome such problem the knee implant companies came up with idea and devised

-         Customized implants ( implant design for a given patient)

-          Personalized implants (Gender specific)

Customized implants:

In order to create customized implant for a particular patient, surgeon gets MRI or CT scan and gets 3D images of the knee joint. This data is collected by the implant design companies to create patient specific instrumentation to make cuts in the bone. They also create patient specific knee implant which actually matches the natural knee.

Personalized implants: Gender specific:

Research studies have shown that there is mismatch in shape and size of bones of knee joint in males and females.  Due to such differences surgeons make some adjustments in the routine knee replacement surgery in order to fix the available implants especially in women.

The main difference in male and female knees is the shape of the lower end of thigh bone. In females lower end of thigh bone is smaller from side to side than front to back. To accommodate this change some implant companies have devised extra set of knee designs to fit female knees.

The choice of selecting customized or personalized implant design is a surgeon preference and changes from patient to patient.   

Posterior cruciate ligament (PCL) Retaining or Substituting implants:

Posterior cruciate ligament is one of the major ligaments in the knee. It prevents roll back of femur over the tibia when bending the knee. During knee replacement surgery this ligament can be preserved or removed based on surgeons choice, type of implant used and during surgical balancing of knee.

Posterior cruciate ligament (PCL) retaining:

In this surgical technique ligament is preserved which also gives additional stability. Femoral and tibial components have notches to accommodate the ligament and plastic insert is flat.

Posterior cruciate ligament (PCL) substituting:

In this surgical technique ligament is removed. In order to compensate the function of ligament the plastic insert has raised slope in front and post in the back. The femoral component has notch to accommodate the post which gives additional stability to that of lost ligament.

The choice of using the specific design and brand of implant is upon the surgeon. There are various factors in choosing the implant which could related to patient or surgeon himself.  Surgeon can choose a particular brand and design with which he is familiar and is best suited for the patient.  

Dr.A.Mohan Krishna
Consultant Orthopedic surgeon
Apollo hospital
Hyderabad,
Appointments :9247258989
                       9441184590
bonesandjointsclinic@gmail.com
www.drmohankrishna.com
www.bonesandjointsclinic.com

Total Joint replacement and Deep vein thrombosis (DVT)

What is a hip or knee replacement surgery?

Hip or knee replacement surgery involves replacing damaged joint lining of  hip or knee joint with metallic or plastic  implant, to repair the damaged surfaces that are causing pain.

Why would you need a hip or knee joint replacement surgery?

-         

     When your hip or knee joint has been damaged by arthritis, a fracture or other conditions due to which common activities such as walking or getting in and out of a chair become painful and difficult may require a joint replacement surgery.

-         In such cases the damaged joint may be so stiff and immovable that even simple activities like putting on your shoes and socks or climbing a few stairs is impossible.

-         You may feel uncomfortable while resting and the pain even continues during rest.

-         There is inadequate pain relief in spite of taking proper anti-inflammatory drugs, physical therapy, or walking supports.

     

      How does your surgeon (Doctor) decide whether you are fit for surgery?

-         

      Your orthopedic surgeon will enquire about your general health and ask questions about the extent of your joint pain and how it affects your ability to perform everyday activities.

-         The surgeon will assess the mobility, strength and alignment of the affected joint.

-         The surgeon will require X-rays to help him determine the extent of damage or deformity in your joint.

-         You may need opinion from cardiologist, general physician and anesthetist before proceeding to surgery.

     

      What happens during surgery?

      

      Your orthopedic surgeon will remove the damaged cartilage and bone and then position the new metallic implants to restore the alignment and function of your joint.

     

      What care should be taken post – surgery?

-         

       There will be some pain after the surgery but your surgeon will provide you necessary medication which should be taken in timely manner.

-         Though there is pain, the movement at the replaced joint should start soon after the surgery.

-         There will also be some antibiotics that you may need to take to  prevent infection.

-         Light exercises like walking are essential parts of recovery. If you do not move as early as possible some postoperative complications become likely.

     

      What is the significance of recommended medication?

-         

      You should continue to take the prescribed medications.

-         You will be recommended to take antibiotics before, during and after the surgical procedure to prevent any infection at the operated site.

-         After the surgery, many of the patients develop blood clots, hence blood thinners such as anticoagulants are recommended.

-         You should follow your doctor’s recommendations for the prescribed duration when blood thinning medications are given.

     

      What are the alert signs after surgery?

-         

       Do report to your doctor in case you observe any of the below

1.     Warmth and redness at the incision site.

2.     Unusual pain or tenderness at the incision site.

3.     Pain or warmth in the calf muscles.

4.     Development of an odor or strong smell.

What are the possible complications of the surgery?

Some possible complications of the surgery include:

1.     Infection that may or may not be limited to the skin of the wound.

2.     Leg-length inequality after hip replacement surgery.

3.     Blood clot formation or deep vein thrombosis (DVT)

What is Deep Vein Thrombosis (DVT)?

-         

     Blood clot formation is the most common complication of replacement surgery which may develop during first several weeks of your recovery.

-         The blood clots generally develop in the leg veins or pelvis.

-         These clots can be life threatening if they break free and travel to your lungs.

-         You should immediately visit your doctor of you develop any of the following warning signs:

1.     Increasing pain in your calf.

2.     Tenderness or redness above or below your knee.

3.     Increasing swelling in your calf, ankle and foot.

How can you prevent DVT?

-        

     Post-surgery, your doctor will outline a prevention program which will be helpful to reduce possibilities of a DVT event.

-         This may include blood thinning medications, inflatable leg coverings, ankle pump exercises and early mobilization.

OXINIUM KNEE

OXINIUM KNEE

Total knee replacement is a surgical procedure in which damaged cartilage of knee joint is replaced with metal lining and plastic cushion. This procedure provides pain free and functional knee joint to the patient.

Traditionally knee prosthesis is being manufactured from the cobalt-chrome alloys because of their strength and relative hardness. When the prosthesis is implanted, it undergoes cyclical loading and stress during usage of knee for daily activities. Over a period of time surface of cobalt – chrome implants gets roughened. When this roughened surface rubs over the plastic bearing surface the plastic wears out. The plastic wear debris secondarily reduces the prosthetic joint life and may warrant for revision surgery.

What is Oxinium:

Oxinium is patented metal alloy produced by SMITH & NEPHEW for the manufacture of knee and hip implants.

Oxinium is an oxidized Zirconium. The zirconium metal alloy is oxidized through a patented process, which then turns metal surface into ceramic. Oxinium implants have ceramic like surface and metal like structure.

This metal alloy has a combination of hardness, smoothness and scratch resistance. The ceramic surface of Oxinium metal alloy is two times harder and twice scratch resistance than cobalt-chrome alloys.  These additional properties produce less wear than cobalt-chrome alloy prosthesis.

Some facts about Oxinium:

·         Surface hardness of Oxinium is double that of cobalt – chrome

·         Research studies in labs have shown that prosthesis made from OXINIUM reduces wear by 50%.

·         OXINIUM material is less brittle as compared with ceramic there by can reduce risk of brittle fractures.

·         Nickle content in Oxinium is minimal there by reducing the problems of metal sensitivities in certain patients.

OXINIUM KNEE:

In the Oxinium knee the femoral component (Thigh component) is made up of Oxinium.  

TOTAL KNEE REPLACEMENT

Knee joint: Basic structure

A.Healthy knee joint:

-Knee joint is formed by the thigh bone (Femur) and shin bone (tibia).
-Knee cap (Patella) lies in front of the knee joint.
-Knee joint is lined by tissue called Synovium which secretes fluid called Synovial fluid. It aids in lubrication of joint.
-The ends of thigh bone and shin bone are covered by Cartilage which provides a cushion for smooth movement of knee joint.
-Joint capsule and ligaments around the knee joint provide stability and strength.

B.Arthritic knee / damaged Knee:

When the cartilage lining of normal joint wears or gets worn out it may result in pain and stiffness in the knee. The cartilage may be damaged by
-Ageing: a result of natural wear and tear which is termed as Osteoarthritis of knee.
-Injury / fractures around knee joint.
-Diseases like Rheumatoid arthritis, gout etc
-In some individuals genetic factors may also predispose to early damage to cartilage.

How will Total Knee replacement help you?

1. Improvement of quality of life
   
2. Improve range of motion
   
3. Improve range of motion
   

Getting ready for Knee replacement surgery:
A.Medical evaluation:
You will be asked to undergo complete health check up. They will help you to indentify the conditions that would interfere with your knee surgery.
B.Cardiac evaluation:
Cardiologist will evaluate you by checking blood pressure, getting ECG and 2D echo. He may order special tests like Dobutamine stress echo or Stress thalium if necessary to know the status of heart.
C.Tests:
Lab tests include Blood, urine and cardiac tests.
D.Preparing your knee:
Surgeon examines your knee prior to the surgery. There should be no skin infection, wounds around the knee and skin should be clean.
E.Others:
You should be in good general condition prior to planned date of surgery. There should not be any fever, generalized weakness etc.You should inform doctor about any blood thinning drugs like Ecospirin, Clopidrogrel if any prior so that you will be advised to stop them at least week before the surgery. You should also inform about any procedures on tooth, urinary tract, eyes that are scheduled during perioperative period.
F.Anaesthtic evaluation:
After getting all the blood tests and cardiologist opinion you will be examined by anaesthetist. He will evaluate you and gives you fitness for giving anaesthesia and advices different modalities of pain relief during postoperative period.

SURGERY:

On the day before surgery:
-You will be admitted in the hospital or asked to come directly to the hospital on the planned day of surgery.
-You need to take the medications for you blood pressure and diabetes.
-You should have light dinner without much oil and spices and plenty of water. You should start fasting from 11PM on the day before surgery till further advice.
-You should give consent and sign an informed consent.
-Follow you anaesthetist and surgeons orders if any given to you in writing.-Have a neat shower.
On the day of surgery:
-You should be on fasting, take your regular blood pressure and thyroid medications if any with sips of water at around 6 AM.
-You can have a plain shower bath
-Limb to be operated will be marked by the surgeon.
-You will be shifted to operation theater half hour prior to surgery.
-Anaesthetist will evaluate once again and prepares you for giving you anaesthesia.
Anaesthesia:
Most of the knee replacement surgeries are carried under spinal anaesthesia. In rare cases when a patient is not fit for spinal anaesthesia, Knee replacement is performed under general anaestheisa.
Postoperative pain relief is achieved by continuous Lumbar epidural pump or continues Femoral block pump.

TOTAL KNEE REPLACEMENT SURGERY:

It is a surgical procedure in which the damaged lining of the knee joint is replaced with metallic lining and plastic cushion to aid smooth movement.

Surgical procedure:

                                                

-The damaged cartilage and bone of lower end of thigh bone (Femur) is replaced by similarly shaped metal shell.
- Similarly damaged cartilage and bone of upper end of shin bone (Tibia) is replaced by metal plate with plastic cushion.
-These metallic surfaces are fixed to bones with the help of bone cement.
-In some conditions when the lining of the knee cap is also damaged it may also be replaced with plastic button.
RECOVERY IN HOSPITAL: POSTOPERATIVE PERIOD
A.First 24 hours:
-Immediately after knee surgery you would be shifted to ICU (intensive care unit) and observed for at least for 24 hours.
-After a day you will be shifted to ward of your choice.
B.First postoperative day:
-On the bed you are advised to perform deep breathing exercises.
-Ankle pump and static quadriceps exercises on the bed.
-Gentle mobilization on bed with legs hanging down the bed and knee movement exercises.
-If you are strong enough you would be made to stand and even walk with the help of walker.
-You will be shifted to ward.
C.Second Postoperative day:
-To continue the exercises on bed and walking with help of walker.
-Drain tubes urinary catheter will be removed on the second day.
-You need to take plenty of fluids and regular diet.
D.Third Postoperative day:
-Depending on speed of your recovery discharge would be planned.
-The bulky dressing on the knee is changed to simple dressing.
-You are advised to continue exercises and walking, gradually increasing the pace.
E.Fourth postoperative day:
-Some patients with slow recovery are discharged on 4^th postoperative day.
Before you are discharged from the hospital, you will be helped to achieve:
-Getting in and out of the bed independently.
-A good progress in bending your knee or to achieve approximately 90 degrees.
-Straightening your knee completely.
-Walking with the help of walker and climbing up and down the stairs.

DISCHARGE ADVICE:

RECOVERY AT HOME
You should continue to stay active when you are at home for full recovery. However remember not to overdo it. You will observe gradual improvement and increased endurance over the next 6 to 12 months.
Tips to make you return home comfortable:
1.Planning your work:
You will be able to walk on crutches or a walker soon after surgery. But you will need help for many weeks with tasks like cooking, shopping, bathing and doing laundry. Make advance arrangements to have someone assist at home.
2.Home planning:
Before going for surgery, follow the steps given below to make your recovery at home easier.
-Fix safety bars in your shower or bathroom.
-Secure your stairways for support and safety.
-Keep a stable chair, for your early recovery period, with firm cushion, firm back, two arm, and footstool for leg elevation.
-If you have low toilet seat, fix a seat raiser with arms.
-Walking up or down the stairs within you pain limits and depending on your recovery.

DO’S AND DONT’S DURING YOUR RECOVERY

DO’S
-Keep the wound area clean.
-If your wound appears red or begins to drain, inform your doctor.
-Check temperature regularly and inform your doctor if it exceeds above normal
-If you observe swelling, elevate your leg slightly with support and apply ice- packs over the swelling intermittently.
-Inform your doctor immediately if you have calf pain, chest pain, or shortness of breath.
-Do mild exercises (physical therapy)
-Practice / initiate regular walking using crutches or walker.
-Perform exercises to strengthen calf and thigh muscles.
DONT’S
-Do not play high impact sports.
-Do not jog, run or jump.
-Avoid gaining weight as it can hasten wear and tear of the implant.
-Do not shower or bath until the sutures are removed.

EXERCISES AFTER KNEE SURGERY:
Physical therapy exercise :Continue to exercise as instructed by your physiotherapist or doctor for at least 2 months after surgery.

1.Static quadriceps: Sit with your legs straight and keep a rolled towel under your knee. Press the knee against the towel while tightening the thigh muscles. Hold this for a count of 5 to 10.




2.Heel slides: Sit or lie on your back and gradually bend your knee by sliding the heel on the bed.





3.Knee straightening exercises: place a small rolled towel just above your heel. Tighten your thigh. Try to fully straighten your knee such that the back of your knee touches the bed. Hold for 5 to10 seconds.





4.Knee bending: Sit on your bed side or chair with your thigh supported. Gradually allow your leg to fall down gently on its own weight. Now gently try to push your leg backwards till the back of the leg touches the chair or cot edge. Hold your knee in this position for 5 to 10 second. Gradually try to lift the leg upwards initially with support of other leg or physiotherapist. When the leg becomes straight maintain it for 5 to 10 seconds.


   5.Weight bearing: Full weight bearing on the operated leg with help of walker for initial 4 to 6 weeks. Single elbow crutch walking next 3 to 4 weeks with crutch on the operated side. Independent walking without any aid can be started depending on the patient’s
recovery and confidence 4 weeks after surgery.

DIET AND PRECAUTIONS AFTER KNEE SURGERY:

-While you are recovering in the hospital you will begin to eat normal diet.
-Your doctors may recommend you to take iron and vitamin supplements.
-Drink plenty of fluids.
-Try to avoid alcohol and smoking.
-Try to maintain ideal weight and weight conscious to avoid putting more stress on the replaced joint.

Daily activities:

1.Driving: avoid driving till you recover fully. Avoid driving at least for 6 to 8 weeks. The reason behind that is that your reflexes may not be as brisk as those before surgery.
2.Metal detectors: It is better to carry a medical alert card or doctors certificate indicating that your joint is replaced with metal prosthesis.
3.Sleeping positions: you can safely sleep on your back, on either side or on your stomach.
4.Return to work: depending on the type of activities you perform, it may be 6 to 8 weeks before return to work.
5.Other activities: Avoid activities that put stress on the knee. These activities including playing tennis, badminton, football, baseball, jumping, squats, skiing and jogging. Do not lift anything heavy.

Recommended medications:

-You should continue taking prescribed medications.
-Antibiotics to be taken during and after surgery for a period of 5-7 days to week to prevent infection.
-Pain medications during recovery and post-operative period will help you to control pain and aid to do physiotherapy comfortably.
-Blood thinning drugs: Following major surgeries in lower limbs, patients are prone to develop blood clots in the veins. This condition is called as DEEP VEIN THROMBOSIS. These clots can dislodge and can reach lungs resulting thromboembolism which is a life threating condition. Hence doctors prescribe Blood thinning drugs called anticoagulation medications. These drugs should be taken for a period of 2 to 4 weeks post-surgery.
-Continue your hypertensive and diabetic medications as advised by physician.

Warning signs after surgery:

-Consult your surgeon immediately if you notice any of the following
1.Redness and warmth around surgical site.
2.Abnormal pain at the surgical site and knee joint.
3.Swelling of the knee joint.
4.All of the complaints with associated fever.

Dr.A.Mohan Krishna
Consultant Orthopedic surgeon
Apollo hospital
Hyderabad,
Appointments :9247258989
                       9441184590
bonesandjointsclinic@gmail.com
www.drmohankrishna.com
www.bonesandjointsclinic.com