Partial- and full-thickness cartilage injuries, as well as osteochondral pathology in weightbearing joints, have produced deleterious effects in knees in both the short and long term. The decreased capacity of damaged articular cartilage to heal or regenerate has contributed measurably to these effects. Surgeons, therefore, are challenged to search for ways to overcome this inadequacy in order to reestablish normal joint function in the face of trauma or disease. [1, 2, 3, 4, 5]
Lesions can be traumatic or degenerative (arthritic). Whether a lesion is traumatic or degenerative is called into question more often with large lesions. It is an issue of relevance, as all of the techniques discussed are recommended for posttraumatic lesions. Obviously, many of the procedures are performed for degenerative lesions.
Peripheral containment of the lesion is another factor when subchondral bone is markedly involved. Ideally, the periphery of the defect should be rigid enough to contain the outermost grafts. This is intuitive and important from a mechanical stability standpoint; without adequate press fit, unconstrained grafts may loosen in the early postoperative period when range of motion is started, even without weightbearing.
In the past, articular cartilage lesions have been treated by subchondral bone abrasions or drilling at the site of focal damage with procedures popularized by Pridie and Johnson. [6, 7] For osteochondral lesions, bulk autografts and allografts [8, 9] have been used. However, these generally are reserved for massive (>10 cm2) lesions.  These procedures have evolved to modern-day techniques, but to date, no single procedure has gained universal acceptance. Both small and large articular surface lesions continue to pose challenges to surgeons.
Attempts to restore weightbearing hyaline cartilage via clinical techniques of joint resurfacing have been described. Although elderly patients can benefit from total joint replacement surgery when singular lesions or global arthrosis has affected the joint, younger patients have higher rates of failure with these procedures. Therefore, it would be advantageous to resurface symptomatic chondral and osteochondral defects to relieve the pain of those lesions and halt the progression of degenerative arthrosis. With the available reports, it appears that osteochondral grafting is an efficacious procedure to restore weightbearing joints. 
Although biologic resurfacing may not be an appropriate first-choice procedure for patients with these problems, a large population of patients with articular surface lesions exists in whom simple debridement has failed to alleviate symptoms. Within this population, many patients are too young to consider a total joint replacement. Others simply refuse total joint replacement (regardless of age), though joint surface incongruity and/or defects due to cartilage lesions have left them handicapped. With disability derived solely from articular disorders of the patellofemoral joint, trochlear replacement systems may be an option in a limited number of instances. [3, 12, 13, 14]
When an unexpected chondral or osteochondral lesion is found during surgery or when simple debridement of damaged tissue does not suffice, a limited number of procedures appear to be available. Techniques such as microfracture,  popularized by Steadman, [16, 17] and autologous chondrocyte transplantation have shown some promise. However, the former actually does not recreate a hyaline cartilage surface. The latter requires two procedures, is dependent upon an outside lab, is very expensive, and requires an arthrotomy. Thus, transplants of autogenous or allogeneic osteochondral plugs have become popular for the following reasons:
They offer the chance at true hyaline cartilage resurfacing
They can be performed in a single procedure
They are performed with reusable equipment
They do not require outside laboratory assistance
However, unlike microfracture, osteochondral grafts are not always amenable to arthroscopic technique and may require an arthrotomy. 
Hangody helped promote the use of small-diameter osteochondral cylinders to resurface damaged chondral surfaces. [19, 20, 21, 22, 23, 24] His inspiration came from the noted longevity of the wooden mosaic walkways on the shores of Lake Balaton in Hungary. In Japan, Matsusue began using multiple autogenous osteochondral pegs, expanding on the work of Yamashita, who used autogenous shell autografts obtained from the noncontact areas of the femoral condyles. [25, 26]
Clinical trials began in 1992 in Hungary with instrumentation created for procurement and insertion of grafts after years of study in horses and dogs. Originally, procedures involved an open technique, with subsequent modifications to include equipment for arthroscopic techniques.
The technique and science for osteochondral grafting continues to evolve, as do the indications for its use. Hangody made early suggestions for patient selection in order to maximize the chance for success. This included limiting surgery to focal lesions and patients younger than 45 years who are in good physical condition. In addition, preeducation regarding science of the grafts, informed consent on the possibility of finding an unknown lesion intraoperatively, and postoperative protocols were stressed.
Although an absolute age cutoff might seem reasonable, especially in social healthcare systems that challenge quality-of-life disabilities, other factors should be considered. Certainly, a 40-year-old patient with global arthrosis is less of a candidate than is a 60-year-old patient with a symptomatic small focal traumatic lesion. Therefore, as long as a bony healing response can be expected, a wide age range is acceptable for surgical indication.
In theory, this technique could be used for any joint surface. However, practical considerations have limited its early use to a small number of joint surfaces. The talus of the ankle has been approached in an open fashion, both with and without malleolar osteotomies. In addition, resurfacing of the shoulder and elbow has been reported.
The knee joint, because of its size and varied pathology, is the most readily approached with this technique.  Femoral condyles can be approached by an open or an arthroscopic technique. The retropatellar area and trochlea groove necessitate an open approach because perpendicular access to the patella usually can be obtained arthroscopically. An exception may be the knee with a patella that is sufficiently lax to allow displacement and eversion with a smaller incision. Retrograde techniques currently are being examined in various laboratories.
As already indicated, the tibia presents a unique difficulty. Because direct perpendicular access is not possible with either an open or an arthroscopic approach, an indirect retrograde method can be used. Care must be taken to obtain oblique donor grafts that match the angle of the recipient tunnel surface angle. This is a very technically demanding approach to the problem. Retrograde fill of the defect with plug(s) and elevation of the ipsilateral collateral ligament with a piece of bone are options to enable tibial access for graft transplantation.
The most obvious contraindication is global arthrosis. This does not necessarily mean chondral disease in two or three compartments; focal lesions in two or more areas of the knee may be amenable to the technique. However, where secondary changes exist (eg, osteophytes, joint space narrowing), the efficacy of the procedure is thought to be decreased.
Certainly, it is not appropriate to address the articular surface abnormality in a vacuum. Associated mechanical malalignment or instability must be addressed to maximize the long-term success of this procedure. Osteotomy for malalignment and/or ligament reconstruction for instability optimizes the mechanical milieu in which any cartilage transfer takes place. In situations where mechanical issues cannot be addressed, this must be thought of as a contraindication. Finally, tumor, synovial disease, and any other factor that would make a patient a poor candidate for delicate and complicated surgery should be strongly considered before the decision is made to proceed with this procedure.
The anatomy of the knee is reflective of its function in ambulation. Knee stability and pain-free range of motion are important in maintaining daily function. Most commonly, overuse, age, and traumatic injuries cause structural damage to the knee that may limit its function. Therefore, a thorough understanding of the anatomy of the knee is essential to properly diagnosing and treating knee pathology.
The femur is the longest and strongest bone in the human body. The proximal end forms the head of the femur, which projects anterosuperomedially to articulate with the acetabulum. The distal end is wider and forms a double condyle that articulates with the tibia and patella. The tibia articulates with the distal lateral and medial femoral condyles. The patella articulates anteriorly to the femoral condyles in the region of the intercondylar fossa (trochlear groove).
The tibia lies distal to the femur and medial to the fibula. The proximal end consists of medial and lateral condyles, an intercondylar area, and the tibial tuberosity that articulates with the medial and lateral condyles of the femur. Distally, the tibia articulates with the ankle. The distal and proximal ends of the tibia articulate with the fibula. In addition, the shaft of the tibia and fibula are connected with an interosseous membrane to form a syndesmosis joint.
The fibula does not articulate with the femur or patella. Furthermore, the fibula is not directly involved in weight transmission.
The patella is the largest sesamoid bone in the human body. This bone is flat, proximally curved, and distally tapered; however, the shape can vary. The posterior patella articulates with the femur, but the apex sits proximal to the line of the knee joint. The tendon of the quadriceps femoris completely encompasses the patella.
For more information about the relevant anatomy, see Knee Joint Anatomy, as well as Technique.
Both partial- and full-thickness hyaline cartilage defects have well-documented progressions of degenerative pathology. Cartilage is avascular and therefore has virtually no potential to heal. Existing lesions tend to progress in severity, altering the biomechanics, rheostosis, and nutrition of the articular surfaces. These can predispose the joint to further degeneration and progressive symptomatology.
For these reasons, interest and activity have increased in replenishing articular surfaces on the basis of the hypothesis that subchondral pain and joint degeneration will be thwarted. Even today, it is clear that symptoms derived from some lesions can be eradicated by techniques discussed herein. Whether or not these procedures influence future degenerative change is not clear. This raises the issue of whether lesions not known to cause symptoms should be considered for treatment. If chondral repair is needed to reduce pain, why does debridement of chondral lesions often result in pain abatement? Should the type, depth, dimensions, or other specific lesion attributes determine the surgical action?
Provided that an answer of sorts is available for focal chondral defects, what lesions can be addressed and fixed? Certainly, global compartment arthrosis (severe joint space narrowing or collapse, osteophyte formation, and/or subchondral cyst formation) is not amenable to cartilage resurfacing at this time. Conversely, a small (<1 cm2) chondral lesion is a reasonable target for a chondral repair operative technique, especially if the apparent cause of significant symptoms has not been relieved by lesser therapies. The primary dilemmas are larger lesions: Should they be operated upon, and which of the available procedures should be used?
Steadman claimed success with the microfracture technique on lesions having a diameter of up to 3 cm. [16, 17] Pedersen similarly reported success with lesions of this large dimension using chondrocyte transplantation techniques. With respect to osteochondral grafting methods (eg, mosaicplasty, osteoarticular transfer surgery), large lesions indeed are a dilemma.
The amount of tissue available for transfer is the only limitation for chondral lesions with minimal subchondral bone loss. Lesions of the femoral condyle up to 8.5 cm2 have been filled by up to 19 cylindrical osteochondral plugs, measuring 4.5-6.5 mm in diameter (see the image below). However, 4 cm2 appears to be the upper limit for lesions in which reasonable results can be expected. Hangody considers lesions larger than this to be salvage situations.
For osteochondral defects, a limit may be approached relative to width and length of lesions. Additionally, depth of bony involvement becomes a factor. Because the technique involves placing osteochondral cylindrical plugs into recipient holes on the basis of a press fit, a finite depth of lesion crater can offer sufficient stability for the cancellous bone plug. Defects deeper than 10 mm appear to compromise this stability. In these situations, a primary procedure of bone grafting may provide a secondary osteochondral grafting with a better chance at mechanical survival. No data support this depth limit at present.
Apart from the contentious issue of whether donor sites contribute morbidity and/or degenerative progression of the knee, there are the not insignificant issues of how to gain enough harvest to fill the defect and, further, to fill the defect with reasonable congruence. The more Herculean efforts demanded by chondrocyte transplantation and mosaicplasty-type procedures are justified, in theory, by their potential for restoring a surface with hyaline cartilage.  The microfracture technique results in a fibrocartilage surface but has reported efficacy in symptom relief, with longevity of maintained relief for nearly a decade in some instances.
Possibly, some of the drawbacks in the use of osteocartilaginous grafts for large lesions, especially donor site morbidity and scarcity of available graft, might be alleviated with the use of allograft osteocartilaginous plugs. A respectable survival rate of chondrocytes has been demonstrated. Furthermore, plugs may be harvested from areas similar to the recipient sites (eg, femoral condylar grafts for the femoral condyle).
The vast majority of cartilage repair procedures are performed for lesions of the femur and the patellofemoral articulation. The tibia rarely is the recipient of these procedures, predominantly because of its inaccessibility and the relative infrequency of obviously traumatic lesions on the plateau. The tibia is inaccessible to all but the microfracture technique; osteocartilaginous grafts would require an oblique insertion (with an oblique harvest). Hangody has performed such procedures, but they are extraordinarily labor-intensive. [19, 20, 21, 22, 23, 24] Oblique allografts might lessen the burden.
Technically, a chondrocyte transplantation procedure upon the tibia would be very difficult to perform. The development of matrices, laden with chondrocyte, growth factors, and cytokines, representing induction, conduction, and a vehicle may threaten current techniques of cartilage repair. [28, 29]