A Move Forward in Mobile Bearing Design

The Zimmer NexGen LPS-Flex Mobile and LPS-Mobile Bearing Knees provide an anteriorly positioned pivot near the entry point of the anterior cruciate ligament (ACL).

• An anterior pivot at the ACL site replicates the anatomic center of rotation^1,2
• Anterior pivot design leads to lower patellofemoral forces that lead to anterior knee pain, patellar subluxation and dislocation, component wear, damage, and loosening^3,4
• An anterior stop on the tibial plate prevents bearing spin-out and allows 25 degrees of unimpeded internal/external rotation

The LPS-Flex Mobile Bearing Knee Femoral Component has an enhanced cam/spine mechanism that is designed to provide stability at up to 155 degrees of active flexion.

• Deepened patellar groove delivers smooth patellar tracking, relieves pressure on the patella, and reduces forces that may cause patella clunk, pain, and premature wear
• Subluxation resistance increases at deep flexion angles as the cam moves down the spine
• Extended posterior flanges safely accommodate tibio-femoral contact during deep flexion

Wear

• Increased contact area/lower contact stresses
• Frontal plane conformity ratio

• Sagittal plane conformity ratio at extension and low angles of flexion⁵

• Femoral radii are matched to size-specific articular surfaces
• Allowing only unidirectional rotational motion potentially reduces cross-shear and consequent wear⁶

Successful Clinical History

The LPS-Flex Mobile Bearing Knee is supported by both clinical history and published study results.

• Ten years of successful clinical history in the European Union and Japan
• A study published in The Journal of Arthroplasty in 2010 reports a higher degree of postoperative flexion with the LPS-Flex Mobile Bearing Knee than with comparable mobile bearing designs reported in the literature⁷
• A study published in Clinical Orthopaedics and Related Research in 2004 reports patients with LPS-Flex Mobile Bearing Knee had similar kinematics patterns to the control patients with a healthy knee⁸
• A study published in the Journal of Biomechanics in 2005 reports implanted patella experienced similar kinematics to the non-implanted healthy knee⁹  

References

1. Argenson JN, Scuderi GR, Komistek RD, Scott WN, Kelly MA, Aubaniac JM. In vivo kinematic evaluation and design considerations related to high flexion in total knee arthroplasty. J Biomech. 2005;38(2):277-284.
2. Hollister AM, Jatana S, Singh AK, Sullivan WW, Lupichuk AG. The axes of rotation of the knee. Clin Orthop Relat Res. 1993;290:259-268.
3. Smith AJ, Lloyd DG, Wood DJ. Pre-surgery knee joint loading patterns during walking predict the presence and severity of anterior knee pain after total knee arthroplasty. J Orthop Res. 2004;22(2):260-266.
4. Browne C, Hermida JC, Bergula A, Colwell CW Jr, D’Lima DD. Patellofemoral forces after total knee arthroplasty: effect of extensor moment arm. Knee. 2005;12(2):81-88.
5. Gsell R, Yao JQ, Laurent MP, Crowninshield RD: Improved oxidation resistance of highly crosslinked UHMWPE for total knee arthroplasty. Society for Biomaterials 28th Annual Meeting Transactions, 542, 2002.
6. ZRR_WA_1577_06
7. Jones, V.C. et al. An experimental model of tibial counterface polyethylene wear in mobile bearing knees: The influence of design and kinematics. Bio-medical Materials & Related Research, 1999;9:189-196.
8. Tarabichi, S. et al. Achieving Deep Flexion After Primary Total Knee Arthroplasty. Journal of Arthroplasty. 2010; Vol.25,No.2,219-224.
9. Scuderi G.R. et al. In vivo kinematic evaluation and design considerations related to high flexion in total knee arthroplasty. Journal of Biomechanics. Number 38, pp 277-284. 2005.
10. Ranawat, C.S. “Design features of mobile-bearing knee implants”, Orthopedics Today, Technical Monograph to the Dec. 2000 issue, 10-122, 2000