Autograft Chondrocyte Implantation of the Knee

Introduction

For autograft chondrocyte implantations, this information is intended to provide details regarding surgery. It will include a brief explanation of what is meant by a chondral or osteochondral lesion, a description of the surgical procedure called autograft chondrocyte implantation and what will happen post-operatively and through rehabilitation.

What are chondral and osteochondral lesions?

Articular cartilage is the covering of the bones in the knee, and should not be confused with the meniscal form of "cartilage", which are the "shock absorbers" of the knee. It is glossy white in appearance with a firm consistency and some elasticity. Articular cartilage serves as the load bearing material of joints with excellent friction, lubrication and wear characteristics. It allows smooth movement and can adapt to variable loads and impact. Although it is only a few millimetres thick it can be extremely resilient to force.

Mechanical injuries to articular cartilage occur with either repetitive and prolonged joint overloading or sudden impact, producing high forces through the tissue to the junction of the deeper underlying bone.

"Chondral" means cartilage and "osteo" means bone. A chondral lesion is thus a defect of cartilage alone whereas an osteochondral lesion is a defect involving the underlying bone as well as cartilage.

It is known that articular cartilage has a very limited ability to repair itself and therefore many techniques have been devised to help stimulate repair from the deeper underlying bone and prevent further degeneration, or alternatively to provide replacement forms of articular cartilage.

Chondral and osteochondral lesions do not always cause pain and this is why an accurate diagnosis is necessary. Exactly the same lesion can be completely painless in one patient whilst very painful in another.

Diagnosis of articular cartilage lesions can be difficult as clinical examination, x-ray and MRI have in general a low sensitivity for these problems. Arthroscopy ("keyhole surgery") is the most accurate diagnostic tool as this allows the surgeon to visualise directly and probe the articular cartilage which can be very soft or has become semi-detached from the underlying bone.

Autograft chondrocyte implantation

Autograft chondrocyte implantation is one of the available methods of treating symptomatic (i.e. painful) chondral and osteochondral lesions. It is a technique whereby a small biopsy is taken from your articular surface through "key-hole" (arthroscopic surgery) surgery. The biopsy is then sent to specialist labs which grow the chondrocytes within the biopsy. Chondrocytes are the cells that form articular cartilage but they are found in such small numbers that they cannot heal a defect in the articular surface. The labs grow a super concentrate of your cells which are then re-implanted in your knee four weeks later through a small incision.

There are two techniques for implantation. In the first the articular surface defect is covered with a water-tight membrane and the cells are injected in a super concentrated solution beneath the membrane to fill the defect. In the second the cells are delivered on an absorbable membrane and this membrane is then shaped to fit the defect in your knee and glued into place using special bio-compatible fibrin glue.

The surface of the knee is protected with a careful rehabilitation programme to allow the cells to heal the articular surface defect. This technique was developed in the early 1990's and now shows good longer term results in the treatment of chondral and osteochondral lesions.

Requirements for Surgery

Autograft chondrocyte implantation is appropriate for relatively large defects, greater than 2cm in area. It is also used for smaller defects which have failed with more conservative treatment such as microfracture. It is not appropriate for large areas of degenerative arthritis. You will need to have a full range of motion in the knee and good quadriceps (thigh muscle) tone prior to surgery. In the run up to surgery, try to avoid any stressful activities which involve twisting or pivoting on your knee as this may cause your knee to become swollen. If your knee is swollen at time of operation or does not have full range of movement it may lead to a poorer outcome.

The day of surgery

As explained earlier, the surgery is done in two stages. The first is a simple arthroscopic day-case procedure and the second stage, the implantation of the cells, requires an overnight stay. The pre-operative procedure is the same for both stages.

You will be admitted on the day of your surgery. You will be advised as to what time to stop eating or drinking, usually about 6-12 hours prior to the operation. After admission but prior to your surgery, nursing and physiotherapy staff will explain the post-operative procedure and measure you for crutches and back splint (only used after the second stage).

Your surgeon will always see you on the day of your operation and answer any last minute questions you may have. At this stage he/she will ask you to sign a formal consent form and also draw an arrow on the leg to be operated on.

The anaesthetist will also visit you on the day of surgery to explain the anaesthetic and any post-operative pain control and answer any questions you may have.

When you wake up from your operation in recovery (the area of the operating theatre which allows you to recover from an anaesthetic safely) there will be a tight bandage on your operated knee. You will also have a blue Cryocuff sleeve which contains ice cold water. This helps to minimise swelling in the early post-operative phase. After the second stage, your leg will also be placed in a back splint to prevent bending the knee. This must be worn for two weeks to protect the knee.

After the first stage of surgery you will be discharged with just a tubigrip bandage support and crutches are rarely required. You will then be seen at two weeks post surgery to check your progress and confirm the date for the second stage of surgery.

First post-operative day after second stage

Your dressing will be reduced to a smaller dressing to allow you to start your exercises. Any other attachments such as patient controlled analgesia will also be removed at this time. A physiotherapist will visit you and commence static exercises to help increase quadriceps strength. You will be assisted out of bed and start mobilising with a pair of elbow crutches partial weight bearing. Your splint can be removed at two weeks but you will need to remain partial weight bearing for eight weeks.

You will normally be discharged from hospital one day after surgery when you are safe on crutches and your Consultant is happy with your muscle strength. You will be able to negotiate stairs on crutches before you go home.

After discharge from hospital

You will need to return to the outpatient clinic for removal of any sutures or clips approximately 14 days after surgery. At this time you will be assessed by your Consultant and physiotherapy is started formally at this stage. For the first 14 days or so you will not normally need to see a physiotherapist, but will need to do the exercises demonstrated to you in hospital.

You should be able to return to driving 8-10 weeks after surgery (if you drive an automatic car and the surgery is on the left knee then you may be able to drive once the splint is removed at two weeks).

Most patients in sedentary occupations take 2-6 weeks from work, the time taken largely depending upon the mode of transport to work. In manual occupations the period of time from work will need to be longer.

It will take approximately twelve months to fully recover from the operation. This does not mean that you will be significantly inconvenienced for this long but swelling from the operation itself may take some time to settle down. Very few operations on the lower limb settle within six months, except perhaps relatively minor arthroscopic surgery, which itself takes three months.

Physiotherapy and rehabilitation

Initially on discharge from hospital you will need to continue with the quadriceps exercises you were taught in hospital.

When you are referred to outpatient physiotherapy the protocol that is related to this information sheet is a guide to your full rehabilitation period. Please ask your Consultant or physiotherapist if you have any specific queries relating to your rehabilitation.

Possible complications

There is no surgical procedure in existence that is free from complications. Although autograft chondrocyte implantation has a good record, complications can occur.

Complications include;

• Stiffness of the knee. The knee may have difficulty in achieving full extension or flexion. This is minimised by early physiotherapy, and to some extent requires a degree of effort on your part to do your exercises. In some patients, a manipulation under anaesthetic or an arthroscopy may be required if the knee becomes stiff.
• Persistent pain in the knee over the area of surgery especially on weight bearing activities. There may be persistent numbness around the area of the incision.
• Persistent swelling of the knee, again mainly after weight bearing activities.
• Venous thrombosis ("blood clots in the veins"). Every attempt is made to minimise this complication, although heparin is not routinely given. It is advised that patients should not be taking the oral contraceptive pill for six weeks prior to surgery. Finish your current packet and take other contraceptive precautions until after your operation. It is also advisable not be taking hormone replacement therapy (HRT) at the time of surgery. Please ask for advice if necessary.
• Infection of the knee - this is a rare but serious complication. Antibiotics are given during and shortly after the operation to minimise this risk.

Please contact the hospital at which you underwent surgery if you are at all concerned that there is a problem. In particular, act immediately if you develop a fever, severe pain or significant wound problems. You do not need to contact your GP (unless you wish to do so); please telephone your Consultant, or if it is outside of office hours please contact the hospital in which you had your surgery and they will be able to contact him for you.

How successful is the operation?

Whilst not a complication in itself, in a number of patients the operation does not fully relieve the symptoms that were present prior to surgery. The pain may not be relieved or may only partially be relieved. Unless there is a specific complication as described above, even with failure the knee should be no worse after surgery than before.

In many ways the success rate of the surgery depends upon how bad the defects or lesions were before the operation. However in general terms the success rate for the "average" isolated 2cm by 2cm lesion is an 85% improvement in symptoms.

We hope that this guide has been of use to you.  You will have been recommended surgery only if the potential benefits of the operation outweigh the risks.  If you have any questions relating to to this please ask your consultant.