cadera / hip - Active Congress.......

MARTES / TUESDAY
76
The information suggests that excellent
long-term results can be achieved with a
well-conceived design and good surgical
technique.
OSSEOINTEGRATION IN
PRIMARY CEMENTLESS
HIP FIXATION
J. D. Blaha, M.D.
University of Michigan. Medical
School, USA
Osseointegration implies the formation of a
“single” (i.e., integrated unit) between bone
and, in the case of a joint replacement arthroplasty,
a prosthetic component. Although it
has not always been such in common usage,
osseointegration and fi xation are synonymous
terms. Fixation, for total joint replacement,
implies that a prosthesis is bonded
to the bone in such a way that there is no
relative motion at the interface between the
prosthesis and the bone. Osseointegration is
a term that describes the histological features
by which this fi xation is achieved and implies
the mechanical features of a fi xed implant.
Many total joint prostheses have been successful
at the hip. There are numerous
shapes and sizes of implants that have associated
with successful clinical outcomes.
The clinician is presented with a plethora
of seemingly contradicting claims regarding
the need for certain design features of
implants in order to achieve a successful
result. (E.g., “maximum fi t and fi ll”, porous
coating, hydroxylapetite coating, “scratch fi t”
grit-blasting etc.)
This presentation suggests a unifying explanation
for the success of implants. This
explanation is based on dividing the time after
implantation into four periods: primary stability,
intermediate stability, secondary stability
and long-term remodeling.
Primary stability: For a cementless implant
this period would be during the operative
intervention when the prosthesis is inserted
into the bone. The interference of the implant
in the bone leads to a “press-fi t” that will hold
the implant stable.
Intermediate stability: For a cementless implant
this period begins after primary stability
is achieved in the OR and ends when bone
apposition to the implant leads to secondary
stability and osseointegration.
Secondary stability: When bone apposition
to the implant has progressed so that
the implant has been “fi xed” (i.e., no relative
motion at the interface of the implant to the
bone) secondary stability has occurred. The
time required to achieve this is not certain
but bone healing is generally thought to take
between 6 and 12 weeks.
Long-term remodeling: The progressive
change of bone at the interface to hypertrophy
in areas of increased load and atrophy
in areas of no load (i.e., the expression of
Wolf’s law of bone) leads to this long-term
remodeling. Other conditions at the interface
(e.g., fracture, infection, debris induced bone
resorption etc.) can lead to dissolution of the
bone and loosening of the implant.
In fact, this same concept can be applied to
cemented arthroplasty as the ultimate fi xation
of a cemented joint must be against live bone
and the term osseointegration is appropriate
for the cemented joint as well.