Autologous Chondrocyte Implantation

Overview
Autologous Chondrocyte Implantation (ACI) is a technique that aims to repair damaged cartilage in a joint. The knee joint is most commonly treated with this technique. Cartilage Cells (chondrocytes) are taken from the knee and multiplied in culture to increase the number of cells. When there are enough cells available, these cells are implanted back into the knee to repair the area of cartilage damage.

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Stage I (Cell Harvest)
The first procedure is usually an arthroscopy, (key-hole surgery) to
collect cartilage, which is then sent to the laboratory for the
cartilage cells (chondrocytes) to be prepared. (see cell culture )
Some blood is taken from you, and from this sample serum is prepared.
The serum contains nutrients and growth factors, which helps the cells
to grow.

Stage II (Cell implantation)
Stage II involves a more major operation.
Knee - defects of cartilage only
The joint is opened through an incision at the front of the knee. The
cartilage defect is debrided (tidied up) and all loose bits of tissue
are removed. A patch of periosteum is usually taken through a separate
incision on the shin. The periosteum is the outer lining of the bone
and is used to make a patch that is fixed to the defect. Very fine
stitches are used to hold the periosteum to the defect and tissue
"glue" may be used to make the patch watertight. The cells are then
injected under the patch.
An alternative to periosteum is to use chondrgide or a similar
collagen membrane - this has some advantages in the short term but
these have yet to be proved in the long term.

Knee - defects of cartilage and bone - osteochondral or OCD or
osteochondritis dissecans
Again the knee is approached through an open incision as the bone
defect is a large part of the pain source and needs to be drilled out.
THis can be as large as 25mm in diameter. A new technique developed at
Oswestry is the OsPlug operation. The defect is filled with a plug of
bone the same size taken from the side of the knee. This is a secure
and stable graft of your own bone. Care is take to contour this o the
right shape and then a patch of collagen membrane sutured over the
surface using a 'top down' method. Water tightness is tested using some
spare serum (saline is harmful to cells) and then your cultured cells
inserted over the bone plug.

Patella and trochlea
The knee cap has a joint that forms part of the knee and has to be
carefully assessed for alignment. If condrocyte implantation is
undertaken with bad alignment then the new cartilage will wear as fast
as the old. Various techniques are used depending on what is needed.
The patellar tendon may need to be moved, or the medial
patello-femoral ligament reconstructed. A new method of reconstructing
the medial ligament developed at Oswestry appears to be very
effective.

In all methods the incisions are closed and a splint applied for 6 hours.

Ankle
Good exposure is key to success in the ankle and either the bone on
the inside or the outside of the ankle is divided to allow access.
Bone loss is common and is debrided and plugged with a piece of your own
bone. A layer of periosteum or chondrogide is then used to repair the
defect.
Another option preferred by some surgeons at Oswestry is to treat the
defect by keyhole surgery. After careful debridemet of cartilage and
bone as necessary, air is put in the joint. Chondrocytes are added to
a collagen membrane and inserted with a fibrin sealant.

Hip
An anterior approach to the hip allows the femoral head to be
dislocated carefully. Similar steps to the knee then are used either
to remove unstable cartilage and debride the base of the cartilage
base. If there is an area of avascular necrosis or dead bone then this
is best drilled out and plugged in the OsPlug procedure. Again a
membrane is stitched over, tested for cell leakage and cells inserted.
The hip is reduced into the socket and the muscle sutured back in
place.