Long-term in vivo Degradation of Poly-L-lactide (PLLA) in Bone
Mark Walton1*
Nicholas J. Cotton2
1 Department of Orthopedic Surgery, University of Otago, Dunedin School
of Medicine, Dunedin, Otago, New Zealand
2 Smith and Nephew Inc., 130 Forbes Boulevard, Mansfield, MA 02048, USA
* To whom correspondence should be addressed.
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Abstract |
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The use of absorbable orthopedic implants has increased substantially during the
last decade. Currently, most of them are fabricated from poly-L-lactide (PLLA),
its co-polymers, or mixtures with other constituents. In vivo, PLLA persists
for years after its surgical role has ended, which is confirmed by a long-term
histological study of PLLA implanted in sheep either as functional interference screws
or nonfunctional rods. The first tissue reaction is the sequestration of the implant
within new bone during the initial 3 months. After a nonreactive period, a second tissue
reaction is associated with the early signs of structural disintegration of the PLLA at
1 year. Subsequently, as the polymer mass reduces, it is replaced by a relatively
avascular fibrous tissue containing macrophages and having an occasional multinucleated
giant cell on the implant surface. After 3 years much of the polymer is still present,
although as isolated fragments. The tissue reactions can be explained in terms of the
physical chemistry of PLLA degradation. Though biocompatible, the excessive longevity of
PLLA and the absence of its replacement by bone, indicates that despite being
satisfactory clinically, it is not an ideal implant material, and that improved
absorbable materials need to be developed.
Key Words:
bone, polymer degradation,
in vivo
, poly-L-lactide
