It's About Time! Mobile-Bearing Knee Is Headed for a Down Classification
BY JOHN CHOPACK, JUNE 7, 2004
On Wednesday of last week, (June 2/2004) an FDA panel recommended to down classify both the tricompartmenal and unicompartmental mobile bearing knee by a vote of 6 to 2 and 5 to 3, respectively. Although this doesn't guarantee that the FDA will reclassify these devices from a Class III classification to a Class II, it is very rare for the FDA to go against a panel decision. Given that most orthopedic manufacturers have been marketing a mobile bearing knee in Europe for years, we are anticipating that most large joint reconstructive companies will be in a position to launch a product in the U.S. within 3-6 months of an FDA approval. We examine what this means for patients, doctors and manufacturers within the sector.
A Little Background
DePuy began marketing both the meniscal bearing and New Jersey Low Contact Stress (LCS) mobile bearing knees in the early 1980's. The meniscal bearing knee fell out of favor, but the LCS has demonstrated significant clinical success rates. A study conducted by Buechel showed a 98% survivorship from 309 LCS implants after a mean follow-up of 12.4 years. The reason for its well documented clinical success is its improvement in patient knee kinematics. The natural knee has two distinct movements - flexion and rotation. Most knee implants, however, only offer movement in only in flexion/extension. The mobile bearing knee moves in both directions. This reduces stresses on both the tibial insert and tibial tray. The reduction in stress limits polyethylene delamination, pitting & cracking as well as loosening of the tibial insert.
Effect on Patients
We believe that the reclassification of the mobile bearing knee will have the most beneficial effect on young and/or more active patients. In fact, it is likely that this type of knee prosthesis will become the component of choice for the aging baby boomer population.
Effect on the Market
We estimate that the mobile bearing knee market accounts for 30% of all knee prosthesis implanted in Europe. In contrast, the mobile bearing knee accounts for approximately 10% of all knee prosthesis in the U.S. It is our belief that over the next couple of years, the penetration rate of the product within the U.S. will reflect that of Europe (i.e. representing 30-35% of the U.S. knee market). Therefore, we estimate that the mobile bearing knee market will grow within the U.S. from $320 million to greater than $900 million over the next three years representing a 22% CAGR.
Effect on Product Mix & DePuy
On the surface, the down classification of the mobile bearing knee is a negative for DePuy, effectively eliminating the monopoly which they have had for 20+ years within the U.S. However, we believe that DePuy may not lose that much business. It is likely that Zimmer, Stryker Corp., Biomet, etc. will convert their respective existing surgeons to a mobile bearing knee rather than going after DePuy surgeons. To date, the mobile bearing knee is priced at a premium to traditional knee prosthesis. We believe that this just offers another way for these companies to benefit from a product mix shift similar to highly cross-linked poly, and cementless vs. cemented components.
