Mobile bearing knees use a plastic insert which is allowed to move within the artificial knee joint, allowing a more natural movement of the knee, and reducing wear of the plastic insert in higher demand patients. These devices are thus designed for use in the younger, more active patient. The design of the Rotaglide Mobile Bearing Knee allows the plastic insert to both rotate and to move backwards and forwards. Introduced in 1988, it has the longest clinical history of this type of knee and may be considered as a fourth generation knee replacement. It is specifically intended to provide more normal movement for a replaced knee than the older, fixed bearing designs and offers the more active patient the possibility of a long lasting, high demand knee replacement. Mobile bearing knee replacements are becoming increasingly widely used as the surgical community accepts the benefits that these devices are likely to provide. Virtually every orthopaedic device manufacturer has introduced a mobile bearing knee within the last five years, recognising the need to be able to offer younger patients a long-term solution for their joint disease. Knee replacements in the 21st century will increasingly be of the mobile bearing type and the Rotaglide Knee is a clinically proven and extensively tested design, which has been shown to have excellent mid-term results, with 99% survivorship at up to 12 years.
More on Mobile Bearing Knees
The outcomes of total knee arthroplasty (TKA) have improved over the last few decades due to a better understanding of design components and surgical techniques. Despite this improvement, a small percentage of these implants continue to fail. The major causes of failure aside from infection are mechanical in nature and depend on wear, fixation, and kinematics. The issue of fixation has received sufficient attention. To further improve longevity and function in contemporary TKA, surgeons must focus on problems of knee kinematics and polyethylene wear. A symposium held at the Knee Society Specialty Day examined the use of mobile bearing design in TKA.
Since the late 1970s, there have been a steady stream of studies examining total knee implants using the concept of the mobile bearing. The first mobile-bearing design was the Oxford Knee and was introduced by Goodfellow and O’Connor in the United Kingdom. Buechel and Pappas introduced the initial mobile-bearing total knee design in North America. They used free meniscal bearings to address the issues of wear and kinematics and developed the Low Contact Stress (LCS) knee system.
Mobile-bearing total knee designs can be categorized as meniscal-bearing or rotating platform designs. The meniscal bearings require that patients have cruciate ligament integrity and balance for functional purposes. The rotating platform, however, is designed for the cruciate-deficient scenario. Currently, numerous variations of the mobile-bearing concept are being evaluated in Europe and most are pending Food and Drug Administration (FDA) down-classification before widespread release in the United States.
Approximation of Normal Knee Mechanism
Mobile-bearing designs in TKA implant systems are designed to reduce contact stresses transferred to the polyethylene and bone-prosthesis interface via increased conformity of the femoro-tibial articulation and moveable tibial polyethylene inserts. Compared with conventional fixed-bearing designs, the resultant in vitro improved kinematics of mobile bearing designs has been hypothesized to produce a closer approximation of the normal knee mechanics. It is guided by the soft-tissue envelope at appropriate tension, especially the anterior and posterior cruciate ligaments with the meniscal bearing variety.