Treatment of full-thickness defects of the weight-bearing gliding surfaces is a frequent problem in orthopaedic practice. Focal chondral and osteochondral defects of loading surfaces often cause several problems for the patient, such as pain, swelling, clicking, and instability, and may lead to early degenerative changes. Several treatment options involving surgical resurfacing are available to treat such defects, but the clinical outcomes of these procedures are controversial and none represents a long-term solution.
Outline of the Technique
In the last decade of the 20th century, several series of animal and cadaveric studies were carried out to develop the mosaicplasty resurfacing technique. According to the basic thesis, mosaic-like transplantation of multiple, small-sized, cylindrical osteochondral grafts harvested from the relatively less–weight-bearing periphery of the patellofemoral joint might provide a congruent resurfaced area . The transplanted hyaline cartilage survives the procedure and results in a more durable surface than that provided by fibrous repair tissue. Donor-site repair by natural healing processes should result in filling of the tunnels with cancellous bone and coverage of the surface with reparative fibrocartilage .
Autologous osteochondral mosaicplasty involves obtaining small-size cylindrical osteochondral grafts (2.7, 3.5, 4.5, 6.5, and 8.5 mm in diameter) from the minimal weight-bearing periphery of the femoral condyles at the level of the patellofemoral joint and transplanting them to prepared defect sites on the weight-bearing surfaces. Combinations of different graft sizes allow a 90% to 100% filling rate. Fibrocartilage grouting, stimulated by abrasion arthroplasty or sharp curettage at the base of the defect, is expected to complete forming the new surface.
Autologous osteochondral mosaicplasty can be done as an open procedure, through a mini-arthrotomy, or arthroscopically. The essence of these surgical procedures is similar. There are only small technical differences at certain steps of each operation. Cartilaginous lesions are usually determined with arthroscopy. If the preoperative differential diagnosis includes such a lesion, the patient should be advised of the possibility of a mosaicplasty. The patient should then be prepared and have provided consent to an open procedure, as the site may be inaccessible because of its location posteriorly or because of the inability to flex the knee sufficiently. General or regional anaesthesia with tourniquet control is recommended for this procedure, and prophylactic antibiotics are routinely used. The patient is positioned supine with the knee free to flex to 120°. The contralateral extremity is placed in a stirrup. After the defect is identified, its edges are debrided to healthy hyaline cartilage with curettes, a knife blade, or an arthroscopic resector blade. The base of the lesion is abraded or curetted down to viable subchondral bone. At this point, a drill guide is used to determine the number of grafts that are needed. By tapping the drill guide down to viable subchondral bone, optimal filling of the defect can be projected. During an open procedure, the periphery of both femoral condyles at the level of the patellofemoral joint can serve as donor sites). During the arthroscopic approach, the medial border of the medial femoral condyle is recommended as a primary donor site because distension pushes the patella laterally, allowing perpendicular access to the medial femoral condyle. If necessary, the lateral border can also be used as a secondary harvest site. A properly sized tubular chisel is introduced perpendicular to the donor site. This harvester device is then tapped into the donor site. A depth of 15 mm is usually recommended for resurfacing of pure cartilage defects and a depth of 25 mm is appropriate for osteochondral defects because in the latter case, the grafts should fill the bone loss as well. After tapping and toggling, the chisel is removed and the graft is delivered from the harvester with use of a chisel guard. It is very important to push out the grafts from the osseous end to avoid damaging the hyaline cartilage cap. Insertion of the grafts is done through the universal guide. As a first step in the implantation, the 3-mm-long cutting edge is introduced and tapped into the osseous base of the defect to help define perpendicular access to the defect. With the assistance of this universal guide, a recipient tunnel is created with a drill bit of appropriate size. A dilator is used to create a conical shaped recipient tunnel for easy insertion of the transplanted graft. Finally, insertion of the graft is done with an adjustable plunger to match the surface of the graft to the surrounding articular surface. With the use of this step-by-step sequence (drilling, dilating, and delivering), all of the grafts are inserted. In uncontained or marginal lesions, the grafts are implanted in a perpendicular fashion. When all of the holes are filled, the knee is put through a range of motion with varus and valgus stress to seat the grafts fully and to ensure their press-fit stability. The portals are closed, and the joint is drained. After surgery, an elastic bandage is used to minimize bleeding from the donor sites.