The Journal of Bone and Joint Surgery, Vol 77, Issue 1 97-110, Copyright © 1995 by Journal of Bone and Joint Surgery, Inc
The effect of operative fit and hydroxyapatite coating on the mechanical and biological response to porous implants
JE Dalton, SD Cook, KA Thomas and JF Kay
Department of Orthopaedic Surgery, Tulane University School of Medicine, New Orleans, Louisiana 70112.
Femoral intramedullary implants were constructed by threading
4.0-millimeter-thick disks with a titanium-alloy (Ti-6Al-4V) porous bead
coating onto a two-millimeter-diameter threaded rod. Each porous-coated
disk, which was 6.0, 8.0, 9.0, or 10.0 millimeters in diameter, was
separated by a two-millimeter-thick acrylic disk with a diameter of ten
millimeters. Implants with and without a hydroxyapatite coating of
twenty-five micrometers were inserted into fifteen skeletally mature adult
mongrel dogs. The femoral canal was sequentially reamed bilaterally to a
ten-millimeter diameter, resulting in uniform initial implant-bone
interface gaps of 0.0, 0.5, 1.0, and 2.0 millimeters. Each animal received
paired hydroxyapatite-coated and uncoated implants. Three animals each were
killed at four, eight, twelve, twenty-four, and fifty-two weeks after the
implantation. The harvested femora were sectioned through the acrylic
spacers, transverse to the long axis, to produce individual push-out test
specimens for mechanical testing. Characteristics of interface attachment
were determined with test fixtures that supported the surrounding bone to
within 150 micrometers of the interface. Histological sections were
prepared, and the amount of bone within the porous structure and the amount
of the original gap that was filled with new bone were quantified with a
computerized video image-analysis system. Mechanical attachment strength
and bone ingrowth were found to increase with the time after implantation
and with a decrease in the size of the gap. Placement of the implant in
proximal (cancellous) compared with distal (cortical) locations had no
significant effect on the strength of attachment, bone ingrowth, or
gap-filling. However, implants with a large initial gap (1.0 or 2.0
millimeters) demonstrated greater attachment strength in cancellous bone
than in cortical bone. With a few exceptions, hydroxyapatite-coated
implants with an initial gap of 1.0 millimeter or less demonstrated
significantly increased mechanical attachment strength and bone ingrowth at
all time-periods. Interface attachment strengths were positively correlated
with bone ingrowth, the time after implantation, the use of a
hydroxyapatite coating, and decreasing initial gap size. CLINICAL
RELEVANCE: Initial implant-bone apposition is thought to be a prerequisite
for good biological fixation. This apposition is often not achieved because
of the design of the implant or instruments and the operative technique.
Poor initial fit during the operation may decrease the longevity of the
implant. The results of the present study indicate that attachment strength
and bone ingrowth are significantly affected by gaps in the interface,
particularly those of more than 1.0 millimeter.(ABSTRACT TRUNCATED AT 400
WORDS)
CiteULike 
Connotea 
Del.icio.us 
Technorati What's this?
