Knee replacement was first performed in 1968. As joints do not regenerate readily, total replacement is an eventuality when discomfort and decrease in mobility become serious enough issues for prospective patients. The three major segments of the knee replacement market are total joint replacement, partial joint replacement and knee revision.
Total Knee Replacement
Total knee replacement involves replacing the entire joint—both the tibial and femoral sides. As with other areas of reconstructive surgery, total knee replacements are more popular than partial joint replacements.
Partial Knee Replacement
Unicondylar joint replacement provides an alternative to total knee replacement when only part of the knee is affected by wear or disease. This allows for less tissue displacement and a smaller incision. However, the disadvantage to partial replacement is that a total joint replacement may become an eventual necessity. That is to say, the conditions that lead to wear for one side of the joint may continue to affect the healthier side.
Patellofemoral replacement is infrequently used to replace the cartilage surface of the patella. These devices are used for a limited group of patients, as the majority of doctors in the U.S. prefer to use total joint implants rather than partial implants that may need to be revised to total joint replacements at a later date.
Interpositional Knee Implants
Interpositional knee implants are a form of partial knee implant and are somewhat analogous to resurfacing devices in other reconstructive areas. These devices are disc shaped and are used to replace worn cartilage. The devices were sold by Zimmer under the UniSpacer™ brand, ConforMIS under the iForma™ brand and Advanced Bio-Surfaces under the OrthoGlide™ brand; however, in 2011 most of these brands were no longer sold. The procedure time was an hour or less, which is less time than a traditional partial knee implant, and the purpose of these devices was to delay the need for a partial or total joint procedure. However, problems associated with the products dislocating in the knee compartment led to poor patient outcomes and eventually led to the discontinuation of many of these devices by 2011.
Knee revision procedures involve replacing worn implanted joints with new hardware. To be precise, it is not the implant itself that is worn but the quality of its adhesion to the patient’s existing bone. Conservative estimates of implant longevity are around 15 to 20 years, with many implants lasting longer than this period. The rate of revision is expected to climb as the number of primary implanted devices increases.