Chrondral Grafting: Overview
Surface cartilage in the knee joint is avascular and consequently has very little capacity to heal. Often, partial- and full-thickness cartilage defects progress into degenerative pathologies, as existing lesions expand and affect the mechanical and nutritional characteristics of the articular surface, thus predisposing the joint to further degradation and subjecting the patient to more severe symptoms. Therefore, interest in repairing surface cartilage has peaked, particularly if sub-chondral pain and joint degeneration can be alleviated. Articular cartilage surface grafting, or chondral grafting, is used to transplant cartilage from a nonessential region from the same knee or opposite knee to plug the cartilage defect and hopefully return the patient to near-normal functioning.
Mosaicplasty, a form of chondral grafting, is a therapy designed to stimulate growth of articular cartilage on the surface of the knee joint that has been damaged by trauma or arthritis by implanting osteochondral plugs. Often, it involves harvesting the patients own cartilage for transplant to the defective area, known as autologous transplantation. Occasionally, a significant amount of replacement cartilage is needed which would be inconvenient and likely damaging to remove entirely from the suffering individual. Specifically, there are reports of l esions of the femoral condyle up to 8.5 cm 2 that have been filled by up to 19 cylindrical osteochondral plugs (Figure 3). Therefore, if available, allogenic (cadaver) cartilage is sometimes used, which has been demonstrated to have a comparable survival rate to autologous cartilage. Additionally, allogenic plugs may be harvested from areas similar to the recipient site (for example, allogenic femoral condylar grafts for a lesion on the patient’s femoral condyle), which would exhibit material properties most similar to those of the defective or cartilage.
Giant lesion treated by mosaicplasty
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Articular cartilage paste grafting is also a form of chondral grafting, which includes morselizing the osteochondral plugs and mixing with a paste, typically hydroxyapatite, to more adequately fill the cartilage defect.
Active individuals and those with localized areas of osteoarthritis are typical candidates for cartilage transplantation therapy. For patients with global arthritis, which occurs throughout the joint and is accompanied by secondary changes such as the presence of osteophytes and joint space narrowing, the efficacy of the procedure is thought to be decreased. These patients are better suited for total joint replacement, although younger patients have higher rates of failure with joint replacement therapies. Therefore, particularly for younger individuals, in instances with localized arthritis it would be advantageous to resurface symptomatic chondral defects to relieve the pain of lesions, halt continued degeneration, and to avoid total joint replacement.
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Typically, most chondral graft patients are within the 15-55 age range, although age should not be the only factor considered in determining the appropriateness of chondral graft therapy. For example, a 40-year-old patient with global arthritis would be a less desirable candidate than a 60-year-old patient with a symptomatic, small, focal traumatic lesion. Therefore, as long as the desirable healing response can be expected, a wide range of ages are acceptable for the procedure.
Typical relative defect size.
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Though there is no defect size restriction for this therapy, a small chondral lesion (<1 cm 2) is a reasonable target, particularly if the apparent cause of the patient’s symptoms has not been removed by other therapies. The upper limit for lesions in which reasonable results can be expected seems to be 4 cm 2. Additionally, the depth of the defect should be considered in selection of therapy candidates. Because the technique involves press fitting osteochondral cylindrical plugs into defects, only up to a specific lesion depth can there be sufficient stability for the cancellous bone plug. Defects deeper than 10 mm appear to compromise stability, however there has not been significant research to support this data limit.
The majority of cartilage repair procedures are performed for lesions of the femur and the patello-femoral articulation. Patients with damage to the tibia are rarely recipients of this procedure due to the inaccessibility of the tibia and the relative infrequency of traumatic tibia cartilage lesions. Tibia repair is generally limited to the microfracture technique.
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Finally, to maximize the long-term success of chondral grafting, joint malalignment and instability should be eliminated. Tumors, synovial disease, or other factors may also indicate that a patient is a poor candidate for the complicated surgery.
