K. Jukkala-partio et al., Biodegradation and strength retention of poly-L-lactide screws in vivo. Anexperimental long-term study in sheep, ANN CHIR GY, 90(3), 2001, pp. 219-224
Background and Aims: Poly-L-lactide implants have gained popularity in the
fixation of fractures and osteotomies in the past decade. The aim of the pr
esent experimental longterm study was to examine the degradation and streng
th retention of self-reinforced poly-L-lactide (SR-PLLA) lag-screws and the
bone tissue response.
Material and Methods: A total of 27 young adult sheep were used. Self-reinf
orced poly-L-lactide (SR-PLLA) lag-screws of 6.3 mm were implanted in the l
eft proximal femur of nine sheep. At two, three and five years three of the
sheep were sacrificed and the degradation was studied radiologically, micr
oradiographically and histologically. For the strength retention measuremen
ts five SR-PLLA lag-screws of 6.3 mm and five lag-screws of 4.5 mm were imp
lanted in the subcutaneous tissue of the five sheep and lag-screws of 6.3 m
m for the pull-out test in the left proximal femur of 20 sheep. At 0, 12, 1
8, 24, 32, and 36 weeks bending and shear strength, molecular weight and pu
ll-out measurements were performed.
Results: At five years no SR-PLLA material could be seen. The implant area
was surrounded by high density bone with bone ingrowth in the screw area. A
t 36 weeks the bending strength of the 6.3 mm screws had decreased from 257
.9 MPa to 36.4 MPa and the shear strength from 131.8 MPa to 19.8 Wa. The pu
ll-out strength of the lag-screws of 6.3 mm in diameter decreased from 1507
N to 331 N in 24 weeks.
Conclusions: SR-PLLA lag-screws showed high initial values, a controlled st
rength retention and gradual degradation process making the use of them saf
e also in demanding fixations.