The Utilisation of Osteochondral Autografts
in the Treatment of Articular Cartilage Lesions (Part 2 of 3)

Vladimir Bobic, M.D.
Consultant Orthopaedic Knee Surgeon
The Royal Liverpool University Hospitals, Broadgreen Hospital Knee Service, Liverpool, The Grosvenor Nuffield Hospital Knee Clinic, Chester, United Kingdom

OATS Surgical Technique: Step-by-Step Guide

Step 1: Selection of Donor Site

The potential donor sites lie in an area along the outer edge of the lateral femoral condyle, above the sulcus terminalis. This area has a convex articular surface similar to that of the central weight-bearing areas of both femoral condyles. Access to this donor area is made through a standard lateral portal with the knee flexed only about 30 degrees.

An alternative donor sites are directly adjacent to the superolateral margin of the intercondylar notch (notchplasty and roofplasty area in ACL reconstruction).

The decision to transplant single or multiple osteochondral grafts should be based on the size and location of the lesion, harvest site accessibility and the convex/concave relationships of donor and recipient sites.

Chondro-osteophyte in chronic ACL deficiency: this site is a usable alternative to regular donor sites, for multiple small grafts. However, in chronic ACL deficiency the peripheral area may contain a high percentage of fibrocartilage.

Step 2: Chondral defect size determination and surgical planning

The chondral defect is inspected arthroscopically and the size of the lesion is measured using a range of appropriate colour-coded sizers. These instruments are also used to evaluate potential donor sites. The appropriately sized donor graft harvester is introduced into the joint and placed over the selected hyaline cartilage harvest site. It is essential that the harvester is perpendicular to donor articular cartilage area.

The T mark and the depth markings on the barrel of the harvester should be clearly visible, and should be carefully observed during the impaction. Using a mallet the tubular harvester is driven into subchondral bone to a depth of approximately 15 mm. Care should be taken not to change the angle or to rotate the tube harvester during impaction.

It is very important to insert the harvester at 90-degree angle in order to obtain circular graft. If this is not done properly the graft may not fit the recipient area and transplanted cartilage may not be flush with the recipient cartilage (far right picture below).

Step 3: Donor core harvesting

Once the selected depth has been attained, remove the tubular harvester containing the graft, by rotating the driver/extractor 90 degrees clockwise and counter-clockwise. The handle of the driver/extractor should be rocked gently superior and inferior, to fracture the cancellous base of the bone core for removal. Once removed, the donor core length and hyaline cartilage thickness can be seen through the slots in the harvester, and measured for overall length with a calibrated alignment stick.

Step 4: Recipient socket creation

Tubular harvester vs. drilling: laboratory cadaver trials clearly demonstrate that drilling of the recipient area, even at slow speeds, causes thermal damage, circular necrosis, it does not provide press-fit graft fixation, and produces tissue debris (picture opposite). Tubular harvesters, with specially designed "atraumatic" cutting edge uniformly provide precise recipient site and cut sharp recipient cartilage edges, with minimal peripheral trauma (pictures below).

If a single core transfer has been selected to repair the defect, the recipient tube harvester is positioned to cover the entire defect and is driven into the subchondral bone to depth of approximately 13 mm. During socket creation attention to maintaining the harvester at a 90-degree angle to the articular cartilage in both the sagittal and coronal planes is very important to achieve a flush transfer. Prior to harvesting rotate the barrel of the tube harvester until the depth markings can be clearly seen. Care must be taken to adjust the insertion and knee flexion angle to ensure that the end of the tube harvester is flush with the chondral surface prior to impaction. Using a sturdy mallet, the tube harvester is then driven into subchondral bone. Care should be taken not to change the angle of insertion or to rotate the tube harvester during impaction.

Once the selected depth has been attained, the tube harvester containing the captured bone should be rotated 90 degrees clockwise and counter-clockwise, and pulled out.

Step 5: Use of alignment sticks

A calibrated alignment stick of the appropriate diameter may be used to measure the recipient socket depth and to correctly align the angle of the recipient socket in relation to the position of the insertion portal when using an arthroscopic approach. The alignment stick may be used as an impactor to "fine tune" recipient socket length, to match the length of the donor core.

Step 6: Donor core insertion

The donor tube harvester containing the collared pin and autograft core to be transferred are reinserted into the driver/extractor, the impaction cap is unscrewed and the T-handled mid section removed. This exposes the end of the collared pin which is used to advance the graft into the recipient socket. A flat pin calibrator is inserted over the guide pin and pressed onto the open back end of the driver/extractor.

Step 7: Final donor core seating

The donor tube harvester's bevelled edge is inserted fully into the recipient socket. This stabilises the harvester during autograft impaction and correctly seats the harvester for proper insertion depth control. A mallet is used to lightly tap the end of collared pin and drive the graft into recipient socket. The collared pin should be gently advanced until the end of the pin is flush with the pin calibrator. This provides exact mechanical control to assure proper graft insertion. The pre-determined length of the collared pin is designed to advance the graft so that 1 mm of the graft will be exposed.

A sizer, measuring at least 1 mm in diameter larger than the diameter of the graft, is positioned over the graft core.

Final seating of the graft is achieved by tapping the tamp lightly, until the articular cartilage is flush with the recipient cartilage.

Multiple osteochondral transfers. When multiple cores of various diameters are elected to be harvested and transferred into specific areas of the defect, each core transfer should be completed prior to creation of the further recipient socket. This prevents potential recipient tunnel wall fracture and allows subsequent cores to be placed directly adjacent to previously inserted bone cores.

Donor sockets are routinely left open after harvesting and have been shown to fill in with cancellous bone and fibrocartilage within 12 weeks (left picture below). At one year the donor site is filled with fibrocartilage, which is usually level with the surrounding cartilage (right picture below). Cancellous bone removed from the recipient area may be inserted into donor sites and should be impacted firmly into the donor site with an alignment stick to compress and widen the cancellous bone. Alternatively, porous hydroxyapatite (HA) rods can be used for this purpose.

Complications: Hemarthrosis, effusion, pain, donor site pain, graft fracture, potential for condylar fracture and avascular necrosis (if a large number of small grafts is harvested from the same area), loose bodies.

Rehabilitation: If the surgical technique is correct there is no need for restrictions or immobilisation: early movement and weight-bearing are essential for normal joint function. This is not a fracture situation, as the graft is press-fitted into a compacted half-tunnel (similar to patella tendon bone block in ACL reconstruction) of the same size. In trochlear grafting, the knee is kept at 300 of flexion, to keep patella pressure on the graft, which tends to be shorter because of the hard subchondral bone in this area. Hemarthrosis, effusion and pain tend to slow rehabilitation down during initial 2-4 weeks. Pre-emptive pain management and swelling control are essential.

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