Surgical options for early arthritis in young persons and athletes: the role of meniscus transplants, microfracture, Osteoarticular Transplants (OATs), Autologous Chondrocyte Implantation (ACI) and osteotomy

About the procedure

Technical details

Cartilage-restoration procedures are extremely complex; each step plays a critical role in the outcome. The procedures can be performed in the elbow, shoulder, hip, knee, and ankle.  For the purposes of this explanation, procedures on the knee (the most commonly involved joint) will be discussed here.

After the patient is comfortably positioned on the operating table and anaesthetic has been administered, the knee is washed and draped.  The surgeon begins by examining the knee while the patient is asleep; during this time the knee muscles are relaxed so the surgeon can assess the relative stability of the joint, the range of motion, and feel for any abnormal grinding or catching of the joint. 

Next, two or three very small (1cm) incisions, or “portals” are made, at the front of the knee.  Through these small portals, hollow instruments called “canulas” are placed that irrigate the inside of the knee joint with sterile saline and “inflate” the joint with clear fluid.  The canulas allow the placement of an arthroscopic camera and specially designed instruments within the knee joint.

The surgeon maneuvers the camera around the joint while he or she watches a video monitor of what the camera “sees”.  A highly-skilled surgeon can evaluate all of the important structures within the joint, test their stability and integrity, and look for signs of ligament injuries, cartilage wear (or arthritis), and bony injuries that can be caused by or lead to knee instability or mechanical grinding.  (Video 1)  Most often, the surgeon will take photographs of the interior of the joint to help explain to the patient what was found, and how it was corrected.  This portion of the surgery is called a “diagnostic arthroscopy” and, in conjunction with a pre-surgical MRI, is absolutely necessary to assure the success of any surgical procedure for knee instability or cartilage deterioration. 

Once the surgeon understands the nature of the cartilage problem, he or she will choose the best possible surgical approach to treat it.  Brief descriptions of the different procedures follow.

A microfacture technique is employed to create a scar tissue “cap” over a region of diseased cartilage.  The concept takes advantage of the body’s own healing potential.  A lesion in the cartilage is prepared so that the “shoulder” or edge of the lesion is surrounded by healthy cartilage.  Then, the base of the lesion is stripped of all remnants of unhealthy cartilage debris, to a bare bone end.  Next, specially-designed instruments, called “microfracture picks” are used to create small holes/channels in the base of the prepared bone.  These channels enter the bone’s marrow cavity, which is filled with blood and special cells that can differentiate into cartilage-like cells (fibro-chondrocytes).  After the procedure, the defect fills with a fibrous clot of blood, platelets, and fibrocytes.  With the correct post-operative regimen, the clot can be “trained” to become even more like regular cartilage.  Microfracture procedures are almost always done arthroscopically.  (Figure 10a, Figure 10b, Video 2: microfracture)

During an OATs procedure, the diseased region of cartilage and its underlying bone are outlined and will be removed and replaced with donor cartilage and bone.  For small lesions, (< 1cubic centimeter), the diseased cartilage is removed in a cylindrical core (called the “recipient site”) and replaced with a healthy cartilage-bone core from elsewhere in the knee (called the “donor site”).  When lesions are large, a single core large enough to fill the recipient site cannot be safely harvested from elsewhere in the knee.  There are two ways to address larger lesions:

• One method is called “mosaicplasty”.  During mosaicplasty, the diseased recipient site is prepared by the removal of several small cylinders (<1 cubic centimeter) and each of the smaller cylindrical defects is filled with a donor plug from elsewhere in the knee.  The small spaces between the adjacent plugs fills with fibrocartilage, similar to the microfracture procedure.
• Another method is called “allograft OATs” or “massive OATs”.  During this procedure, a size-matched, fresh-refrigerated or fresh-frozen donor graft (allograft) must be obtained.  The diseased cartilage is mapped, and a single, large cylinder of the poor cartilage and underlying bone is removed.  This leaves a recipient site that has normal surrounding cartilage and a healthy bone socket.  The allograft donor cylinder, or plug, is taken from the identical region of the donor bone.  This is then inserted into the socket, restoring a normal joint contour.  Unlike kidney, heart, lung, or liver transplants, allografts have relatively few viable cells, so there is rarely an immune response to them.  No immuno-suppressive medications are required. 

Once the bony plug of the OATs, mosaicplasty, or allgograft OATs heals in the socket (like healing a fracture), the overlying cartilage will transmit force more normally.  Very small OATs plugs can be harvested and implanted arthroscopically, but larger lesions usually require a small incision. (Figure 11a, Figure 11b)

Autologous Chondrocyte Implantation:  ACI

ACI is used to fill a defect that has normal underlying bone with cartilage-like cells.  ACI requires two procedures.  The first procedure is a diagnostic arthroscopy in which several (5 or 6) small rice-sized pieces of cartilage are removed from the knee.  These are sent to a laboratory where the cells are cultured to become the precursor cells of cartilage tissues, called “chondrocytes”.  These cells are then sent back to the surgeon in a small vial.

The second procedure is done using open incisions.  Like microfracture, the defect is prepared so that the surrounding shoulder of cartilage is normal—like a pothole in the road.  Next, a flap of tissue removed from the nearby bone (called “periosteum”) is sewn directly over the recipient site to enclose the defect (like Saran wrap over a bowl).  The grown chondrocytes are then injected beneath this cover or flap, where they will grow and mature into cartilage-like cells. 

The flapped, filled defect must be protected from trauma while the cells mature.

A meniscus is a c-shaped structure in the knee that is attached to the bone of the tibia at the front and back, and to the surrounding knee-joint capsule around the edge.  This structure is critical to the function of the meniscus, so the bony attachments and soft-tissue attachments must be duplicated during replacement.  During meniscal transplantation, the damaged remnants of the original meniscus are removed back to the attachment of the meniscus to the inside edge of the joint (called the capsule), and the front and back attachments are removed from the bone.

A donor meniscus is used, and prepared in such a way that the donor’s bony attachments are preserved.  These are left separate plugs (for medial meniscus transplants) or a dovetailed block.  A matching dovetailed slot is created in the patient’s tibia, where the donor block will be inserted.  In addition, the meniscus is sewn to the prepared capsule at its edges, re-establishing the bony and soft-tissue connections.  Some time is required for the bone and soft-tissue to heal before the meniscus can be expected to function normally—during this time, the transplant must be protected.

Unlike kidney, heart, lung, or liver transplants, allografts have relatively few viable cells, so there is rarely an immune response to them.  No immuno-suppressive medications are required.

Osteotomy procedures are designed to correct abnormalities in the weight-bearing axis of bone.  In general, the procedures involve taking or making a “wedge” out of the bone to re-align the extremity.  This is like making a very controlled fracture of bone. These osteotomies can be made in the upper tibia (“high tibial osteotomy” or HTO) or at the far end of the femur (“distal femoral osteotomy”).  The bone is held in the new alignment with plates and/or screws during the healing process.  When the bone is healed, it will be in a position that changes the regions where force is concentrated within the joint. 

Another type of osteotomy can be made to change the direction of pull and force that the joint experiences between the patella and the femur.  The indications for each type of osteotomy are beyond the scope of this review, and should be discussed with your surgeon.

Anesthetic

Length of microfracture, meniscal transplantation, osteoarticular allograft/autograft transplants (oats), autologous chondrocyte implantation (aci) and ostotomy for arthritis in the athlete.

Surgery for Arthritis, osteochondral defects (OCD lesions), meniscus transplantation and cartilage loss in the knee. at the University of Washington, Department of Orthopaedics and Sports Medicine, Seattle, Washington

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