Page 4 - KNEETA

and retaining soft tissue balance and both cruciate ligaments The 1980s were also a changing time for the orthopaedic
to provide stability. However, this design, although great community. Many orthopaedic companies began designing total
in theory, experienced complications including instability,
prosthetic loosening, and patellofemoral abnormalities. needs. These companies touted complete interchangeability to
These issues and other complications resulted in a revision rate
of 28.5%, naming instability as the major cause. 1| also a major push toward creating instrumentation that aided in
making total knee procedures easily repeatable. There was also an
Due to the complications within the patellofemoral joint,
increasing need to create the most natural-feeling knee possible;
however, little kinematic research had been performed to study
introduced patellofemoral joint replacement options. natural knee motion.
The Total Condylar Knee, developed by Dr. John Insall, was the
In the 1990s, total knee implants were still based on the four-bar
Insall’s device featured a round-on-round geometry in both link theory. Implants designed on this philosophy had J-curved
the coronal and sagittal planes. This design touted partial femoral components, which boasted changing radii on the sagittal
conformity, which aimed at providing mediolateral stability.
Fixation was improved by adding a central stem to the tibial
back. FIGURE 3 Fluoroscopic research was performed that actually
showed the medial pivot side of the knee acted more like a ball-in-
attempt featured an all-polyethylene base, and it was not socket joint, similar to a hip.
until the mid-1970s that a cobalt chromium baseplate was
introduced. Although a design much aheadof its time, axial According to this literature, the condyles, which are actually
compression tests would later show failureof the prosthesis. 2
circular, do not rollback at the same time. In the normal knee,
kinematic analyses showed the tibia rotates about a constant axis
Its designers, Drs. Buechel and Pappas, aimed to design a
mobile-bearing, metal-backed knee system with low constraint distances between this axis and the distal and posterior condylar
forces and low contact stresses which would allow normal surfaces are nearly equal. FIGURE 4 5,6,9,10
joint articulation and loading. The result was the New Jersey
Knee, or as it later became known, the LCS (Low Contact Stress)

been unable to provide mobility while eliminating unnecessary
constraint forces. Buechel and Pappas believed a mobile- R1
bearing prosthesis would eliminate unnecessary constraint
forces and produce low constraint forces and low contact R3
stresses. By doing so, surgical misalignment may be corrected, R2
and both intraoperative adjustment of the joint space and
postoperative replacement of the bearings may be carried FIGURE 3 | J-Curved
3 However, Femoral Component
complications with the LCS Knee included bearing dislocation,
bearing breakage and an increase in polyethylene wear. 4
This data showed that the way in which researchers designed total
Even if all the ligaments are healthy, it may be advantageous
knees was incorrect from a kinematic perspective.
Medial- Pivot Total Knee from wright medical , launched in 1998,
through features of an implant. This approach was originally
introduced to increase the amount of exposure available to
than previously thought.
surfaces. Many femoral components featured sagittal plane
geometry that approximated the shape of the natural condyles
while the tibial plateaus were “dished” to provide constraint in
the anterior-posterior direction. The constraint provided by this

not PCL function, which was a major drawback of the original
Total Condylar device developed in
the early 1970s.

FIGURE 4 | Distal Radius (Rd)
= Posterior Radius (Rp)
FIGURE 2 | Total Condylar Knee KNEETA

SUNTEK KNEETA R
Medical Devices
and Electronic
Products Trade Co. KNEETA® Medial-Pivot Knee System Total Knee system
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