Biomedical Engineering Reference
In-Depth Information
design improvement, probably will come from the development of new materials
rather than new design concepts.
During the last quarter century, after the development of mobile bearing knees,
there has been little improvement is knee joint replacement design. The Oxford
knee is basically the same as it was a quarter century ago. The B-P design variants
are only slightly improved in that time. Posterior stabilization seems unsound
based on engineering principles and clinical experience.
The primary improvements have come from the introduction of ceramic coated
titanium alloys and the possible improvement of UHMWPe. Even here the
advantages of these materials are somewhat controversial and time is needed to
more fully evaluate their benefits.
Probably the greatest impact may come in surgical technique, rather than
implant design. The application of computer technology to surgery, although in its
infancy, has great potential in producing greatly improved prosthetic alignment, an
important, if not critical, need for improved knee joint replacement performance.
This is particularly true for mobile bearing unicondylar knee replacement where
accurate positioning is more important since all the ligaments are retained. The
shape and location of the implants must be such that the functioning of these
ligaments is not excessively degraded.
6.9 Conclusion
Analysis, experimentation and clinical results clearly show that two piece,
incongruent knees do not provide the stability, mobility and wear resistance of
mobile bearing knees. Further, analysis and clinical experience has shown a
fundamental flaw in widely used posterior stabilized designs introduced to attempt
to solve stability problems with the fixed bearing designs. Only mobile bearing
designs have provided needed stability, mobility and long-term wear resistance
and survivability that should be expected of well designed implants.
The mobile bearing Mark V B-P Total Knee Replacement is the culmination of
more than thirty years of development. It fully exploits the mobile bearing concept
by maintaining full congruity in the highly loaded phases of walking motion and
fully line contact in the remaining phases and high flexion activities. Further, it
provides nearly normal knee motion and stability along with this congruity. The
low wear ceramic coating of superior biocompatibility along with its porous
coated ingrowth fixation geometry, provide a realistic expectation for a long life
and perhaps a lifetime joint replacement.
References
[1]
Nakagawa, S., et al.: Tibial-Femoral Movement 3: Full Flexion in the Living Knee
Studied by MRI. JBJS 82B(8), 1199-1203 (2000)
[2]
Townsend, M.A., Izak, M.: Jackson RW, Total knee motion goniometry. Journal of
Biomechanics 10, 183-193 (1977)
[3]
Tria, A.J., Klein, K.S., Li, R.-Z.: An Illustrated Guide to the Knee, Ch. 6. Churchill
Livingstone, New York (1992)
