Cost and time savings
A focal implant replaces a small part of a joint surface with an uncemented prosthesis made of cobalt-chrome, leaving the rest of the joint cartilage functioning as normal.
Focal implants are much smaller than total or partial knee replacements. A focal implant may prevent further damage in a way analogous to a dental filling, providing an alternative to a joint replacement. Results of using a focal implant may be comparable to a biological implant, but there are cost and time savings.
Indications for focal implants
A key indication is for those patients who are in their middle years and who have focal cartilage defect, but who do not yet show any signs of impending arthritis such as joint space narrowing. Patients with such a problem are often relatively young with otherwise healthy joint cartilage.
Younger patients may instead be offered a biological solution such as autologous chondrocyte implantation (ACi) and older patients might be offered a knee replacement, but in between these two age groups a focal implant appears to have a significant role.
Another indication - where younger patients may be considered - is if there is bone oedema associated with the cartilage damage, in which case any biological solution might fail.
"Mini-metal and other focal resurfacing techniques have been developed to tackle the "so-called “treatment-gap” of patients considered too young and active for arthroplasty and either too old for biological procedures, or who have failed previous articular cartilage repair procedures"...However "(c)oncerns about revision rates with such implants remain present..."
Where in the knee are focal implants used?
Focal implants are available for the convex femoral condyles and also for the concave patello-femoral groove where the patella glides. They are appropriate in the middle age group for areas where damage is localised with healthy opposing cartilage surfaces, the mechanical alignment of the joint is good and meniscal function is not seriously compromised.
Other relevant links
Focal cartilage defect, Joint space narrowing, Biological resurfacing, Focal resurfacing