Smith & Nephew | GENESIS II Total Knee System | Which Medical Device

Description

From Which Medical Device

The Genesis II Total Knee System is a cemented primary and revision knee replacement system from Smith and Nephew, implanted since the 1990s. The features of this device include a deeper and more lateralized trochlear groove than earlier designs, an externally rotated femoral component (meaning the femoral cuts are performed in neutral rotation relative to the epicondylar axis, but the implant has a thicker posterolateral femoral condyle to compensate) and an anatomic asymmetrical tibia. The system is said to allow compatibility between a femoral component of a given size and up to four sizes of tibia.

Available versions include cruciate retaining, posterior stabilized, and constrained arthroplasties. Components can be porous or non-porous. High flexion knee and deep-dished tibial inserts are available, as is an all-polyethylene tibia in cruciate retaining or posterior stabilized versions. Recent studies have suggested the deep flexion tibial insert (with a lower posterior margin to facilitate rollback) was associated with higher flexion than standard inserts (around 7 degrees more)(Crow 2010), but factors including BMI and preoperative flexion are likely to be more important (Harato 2008, McCalden 2009, 2010, Zeh 2010).

The standard femoral implant is manufactured in cobalt chrome - the tibial tray is polished titanium, and the polyethylene locks using a dovetail mechanism. There are standard and minimal access instruments available.

The Genesis II knee is also available in Oxinium ™, which is zirconium, oxidised in such a way that the surface becomes a ceramic, is therefore smoother and is associated with lower in vitro wear rates. This device has found favour with patients who have a known nickel sensitivity as the nickel content is very low.

In the 7^th UK National Joint Registry report, the Genesis 2 had 7% of the primary knee replacement and 5% of the revision market, and was growing in popularity. The revision rate in this report was 2.4% at 5 years (2.0 to 2.9%).

References:

• Crow BD, McCauley JC, Ezzet KA. Can high-flexion tibial inserts improve range of motion after posterior cruciate-retaining total knee arthroplasty? Orthopedics. 2010 Sep 7;33(9):667. doi: 10.3928/01477447-20100722-03.
   
• Harato K, Bourne RB, Victor J, Snyder M, Hart J, Ries MD. Midterm comparison of posterior cruciate-retaining versus -substituting total knee arthroplasty using the Genesis II prosthesis. A multicenter prospective randomized clinical trial. Knee. 2008 Jun;15(3):217-21. Epub 2008 Mar 5.
  
• McCalden RW, MacDonald SJ, Charron KD, Bourne RB, Naudie DD. The role of polyethylene design on postoperative TKA flexion: an analysis of 1534 cases. Clin Orthop Relat Res. 2010 Jan;468(1):108-14.
   
• McCalden RW, MacDonald SJ, Bourne RB, Marr JT. A randomized controlled trial comparing "high-flex" vs "standard" posterior cruciate substituting polyethylene tibial inserts in total knee arthroplasty. J Arthroplasty. 2009 Sep;24(6 Suppl):33-8. Epub 2009 May 15.
   
• Zeh A, Davis J, Laskin R, Klima S, Wohlrab D. Early results with the Genesis II Posterior Stabilized High Flexion knee prosthesis. A one year follow-up study. Acta Orthop Belg. 2009 Dec;75(6):792-800.

Which Medical Device of the Year 2011

Runner-up: Orthopaedics

"We make this award in recognition of the high-flexion variation which may be of benefit for patients, particularly those who need to kneel. Although there is some debate about this, the GENESIS II is our runner-up because of the proven impact it has had on the lives of many patients, with over 5,000 implantations in the England and Wales National Joint Registry in 2011." - Mr Craig Gerrand, Editor-in-Chief. Read more