We use the Arthrex (Naples, FL) OAT system including the single-use OAT set and OAT sizer/tamp instrumentation set. Description of the technique will be based on this system.

Preoperatively, the size of the lesion can be estimated (Fig. 26.1). However, the true size of the lesion and/or OAT plug(s) needed is often underestimated and cannot be fully determined until the lesion is débrided and prepared for implantation.¹⁹ General anesthesia with a regional single-shot block of the femoral and sciatic nerve is performed by the anesthesia team. The operative limb is then examined under anesthesia for range of motion and ligamentous stability. Block to full range of motion under anesthesia suggests a large loose body within the knee. A nonsterile tourniquet is applied to the upper thigh and generally set to 250 mm Hg. After sterile preparation and draping, a standard diagnostic arthroscopy using two anterior portals with or without a superior outflow portal is performed. Following careful inspection of the joint for loose bodies, identifying the location of the OCD lesion, and defining any other intra-articular pathology, the surgeon can begin to prepare the bed of the lesion.

Any loose, fibrillated, or unstable full-thickness articular cartilage defect should be removed from the bed of the lesion
using a curette, ring curette, and motorized shaver (Fig. 26.2). Take care to remove large fragments of cartilage from the joint as they are removed from the lesion to prevent loose bodies. The edges of the lesion should be débrided to have vertical smooth walls to circumferentially contain the OAT plug(s) using a scalpel or small curette (Fig. 26.3). When the lesion is completely prepared, the total diameter can be sized with a plastic sizing tamp (Fig. 26.4). If multiple donor plugs will be needed, the surgeon can make an assessment of the appropriate number and sizes of plugs.

If the lesion is located in a more anterior or distal position on the femoral condyle, the remainder of the procedure may be performed arthroscopically. If the lesion is more posterior on the femoral condyle, an appropriate angle for harvesting the lesion and placing the plug may not be feasible, in which case an arthrotomy should be made. The decision for an arthroscopic or open technique is ultimately at the discretion of the surgeon. (Figures in this section depict the use of an arthrotomy for visualization and perspective in this text.) If an open incision is used, a longitudinal incision is made through the skin from the distal pole of the patella to the tibial plateau. The location of the skin incision can be midline or parapatellar on the side of the lesion at the discretion of the surgeon. Often, it is possible to plan the incisions to incorporate one of the initial anterior arthroscopy portals into the incision for a more cosmetic result. The subcutaneous tissue is divided in line
with this incision down to the paratenon of the patellar tendon. A medial or lateral parapatellar arthrotomy is made adjacent to the patellar tendon depending on the location of the lesion. The skin incision and/or arthrotomy may need to be extended for visualization and should be tailored to the location of the lesion and the comfort of the surgeon. Controlling flexion and extension of the knee is helpful in allowing for a smaller arthrotomy by bringing the lesion into view.

Should the previously described incision allow for access for the donor plug harvest, no further incision is needed. If not, a separate arthroscopy portal, open incision, or extension of the arthrotomy is made. The autograft osteochondral donor plugs are harvested from a non-weight-bearing portion of the femoral condyle. Options for locations of harvest include areas of the femur which are not major load-bearing areas such as the lateral supracondylar ridge, medial supracondylar ridge, posterior femoral condyle, lateral aspect of the lateral femoral condyle just above the sulcus terminalis, medial or lateral portions of the trochlea, and the superior aspect of the intercondylar notch. The size and contour of the recipient site should be taken into account when deciding where to harvest the plug. The distal medial aspect of the trochlea has been shown to have the least load-bearing area during range of motion followed by the intercondylar notch.²⁰ The same study found that the medial and lateral trochlea matched recipient sites on the femoral condyles well, and the central portion of the non-load-bearing trochlea in the notch matched trochlear lesions best.²⁰ Another consideration in the decision for a donor site in the skeletally immature population is the open physis. Harvest of the plug should be performed under fluoroscopic control and as far from the physis as possible to avoid inadvertent damage. The supracondylar ridge is the closest to the physis. The authors’ preferred technique is to harvest the donor graft from the distal medial trochlea in skeletally immature patients to stay farther from the physis and in a non-load-bearing zone.

For implantation of a single OAT donor plug, the harvester size 1 mm larger than the size of the measured lesion is chosen so that upon seating of the donor plug, there will be a press fit. The harvester should be placed perpendicular to the articular surface and the angle should not be changed during harvesting. Using a mallet, the donor plug harvester is impacted to a depth of 15 mm using the numbered laser lines as a guide (Fig. 26.5). Without changing its angle, rotate the harvester clockwise 90 degrees twice and pull the device straight out of the lesion. It is recommended to harvest grafts perpendicular to the articular surface and without any levering during extraction to obtain the most anatomically suited graft for the recipient site.²¹,²² Both arthroscopic and open techniques can yield an appropriate graft with attention to proper harvesting technique.²¹,²² The donor plug will be withdrawn inside the harvester. The actual depth of donor plug that was taken can be measured inside the harvester device through the window and is then used to determine the depth of the recipient plug that will be removed. Leave the donor plug in place within the harvester until needed for implantation.

The recipient site harvester corresponding to the size of the lesion (1 mm smaller than the donor plug) is chosen and placed over the recipient defect perpendicular to the articular surface (Fig. 26.6). The recipient plug depth should be approximately 1 to 2 mm shallower than the donor plug length to avoid countersinking the donor plug. This harvester is then malleted in to this depth using the laser lines etched on the outside of the harvester as a guide. Similar to the harvest of the donor plug, take care not to change the angle of the device during this step. The harvester is again removed with two 90-degree clockwise turns and by pulling straight back on the device. The plug is removed and an alignment rod is inserted into the recipient site to recheck the depth and visualize the angle needed for insertion of the OAT donor plug.

To remove the donor plug, a plastic delivery tube is placed over the donor harvester. The core extruder is placed into the harvester and the donor plug is advanced until it is flush with the edge of the harvester. This complex is placed into the recipient site at the previously determined angle. The core extruder is then used to advance the OAT plug. The plug can
also be seated by removing it from the harvester with the core extruder, placing it over the recipient site at the appropriate angle and using a plastic tamp and mallet to tap the plug into position (Fig. 26.7). Grafts have been shown to incorporate best when they are press fit between 0 and 2 mm of being flush with the surrounding articular surface but not countersunk below the articular surface.²² If impacting the osteochondral dowel, a larger number of less forceful blows has been shown to decrease damage to chondrocytes.¹⁶,²³ If using a mosaicplasty technique, following placement of the first graft, the steps are repeated for subsequent grafts (Fig. 26.8). Once the donor plug is inserted, the knee should be taken through a range of motion to ensure that there is no mechanical block to full motion and the graft is stable.