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Editorial
Understanding Implants in
Knee and Hip Replacement
An interview with
Douglas E. Padgett, MD
Chief of the Adult Reconstruction and Joint
Replacement Division, Orthopedic Surgeon,
Hospital for Special Surgery
Information about knee and hip
replacements is more easily available
than ever before. But direct-toconsumer
advertising, online articles and
other reports in the media may make
it more difficult for people considering
these surgeries to understand their
options. Becoming familiar with the key
considerations that go into selection of
the implant that is used to replace the
injured or damaged joint can make the
process easier.
I
Russell E. Windsor, MD, PC
Orthopaedic Surgeon, Hospital for Special Surgery
Figures 2a and b: Picture of Implant in Knee
Figure 2c: X-ray
of a Total Knee
Arthroplasty
Types of Knee Replacement
In the majority of total knee
Figure 1: Anatomy of the Knee Joint
replacements, the surgeon places
components of the implant (also called a
prosthesis) on the joint surfaces of three bones that make up the knee joint: the femur,
the long bone in the thigh, the tibia, the larger of the two bones in the lower leg and a
patellar (kneecap) component, which glides on the femur, the bone that you feel at the
front of the knee. The patellar component is sometimes not needed.
Although there are now many different models of knee implants available from
a number of different manufacturers, there are
two primary types - one that substitutes for the
posterior cruciate ligament (PCL), a central ligament
that stabilizes the knee joint, and one that spares it.
[Figure 1]
“The choice between these two implants usually
comes down to surgeon preference,” explains
Russell E. Windsor, MD, Orthopedic Surgeon at
the Hospital for Special Surgery (HSS). “At HSS, the
majority of surgeons prefer an implant that replaces
the PCL.”
In part, this preference is based on the
pioneering work done at HSS by John Insall, MD,
Chit Ranawat, MD and Peter Walker in 1973, the
orthopedists and bioengineer who developed the total condylar prosthesis, designed
to closely replicate the anatomy and functional characteristics of the knee joint.
“This really marked the beginning of successful modern knee replacement,” says Dr.
Windsor. Since that time thousands of successful surgeries have been completed using
more modern, refined versions of this implant. But research also suggests that equally
successful outcomes are achieved with implants that spare the PCL.
“Prospective patients may also read or hear about fixed-bearing implants versus
rotating platform implants, and wonder which one is preferable,” Dr. Windsor notes.
These terms refer to the portion of the replacement that is attached to the tibia.
When fixed-bearing implants are used, a metal component is inserted into the
tibia and a polyethylene (plastic) tray is locked into place on top of it. [Figures 2a,b,c]
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