Failure strength of bioabsorbable interference screws: effects of in vivo degradation for 12�weeks

Abstract

We investigated the effect of in vivo degradation for 6-12 weeks on the fixation strength of polylactide bioabsorbable interference screws. Ten bioabsorbable interference screws were used to fix the patellar tendon autograft in ten live sheep knees, which were equally divided into two groups and killed in the 6th or 12th week. The control group consisted of four cadaveric knees. Following the killing of the animals the screws were retrieved and reused to fix patellar tendon grafts in cadaveric sheep knees. Tendon pull-out tests were performed for the partially degraded screws, for the control group, and for the reused screws of the control group. Macroscopic and microscopic examinations of the 6- and 12-week specimens were performed. Tendons pulled-out with an average force of 357+/-30 N in the cadaveric control group on the first use and with 465+/-118 N on the second use. The partially degraded screws failed with a mean load of 399+/-119 N in the 6-week group, and 12-week screws at 447+/-72 N. No macroscopic sign of degradation was observed on the retrieved screws. Histological examination of the 6 week specimens showed necrotic changes in the tendon around screw contact areas. Healing with granulation tissue was present in the same area in the 12th week. Foreign body reaction or an excessive inflammatory reaction was not observed. In vivo degradation of poly- l-lactide interference screws for 12 weeks thus causes neither a loss in the fixation strength of the screws nor an obvious inflammatory reaction.

How four and twelve weeks of implantation affect the strength and stiffness of a tendon graft securely fixed in a bone tunnel: a study of Evolgate fixation in an extra-articular model ovine model

“…They found a dramatic reduction in strength of the complex at both 6 and 12 weeks, mainly due to rupture of the patellar tendon. A significant decrease of the strength of the graft, as reported by Kilicoglu et al [7] and by others [15] in previous animal studies, as a result of graft revascularization or maturation, was not observed in the present study.…”

“…We also speculate that at that time the Sharpey's fibers contributed sig-nificantly to the stability of the implant. On the contrary, using a bioabsorbable interference screw fixation, Kilicoglu et al [7] did not find Sharpey-like fibers at either 6 or 12 weeks; instead, the bone tendon interface was formed of three layers: a superficial band of necrotic cellular debris and active granulation tissue, a middle layer of residual tendon, and the deepest new fibrous tissue formation merging with medullary bone tissue.…”

“…Kilicoglu et al [7], using an ovine patellar tendon, attempted to determine changes in the fixation strength of a poly-L-lactide bioabsorbale interference screw 6 and 12 weeks after impantation. They found a dramatic reduction in strength of the complex at both 6 and 12 weeks, mainly due to rupture of the patellar tendon.…”

“…Moreover, a labora-which is still considered the weak point of this technique. Although several studies [5] investigated the biomechanics of the initial strength and stiffness of various devices for tibial fixation of hamstring grafts, very few in vivo studies [4,[6][7][8][9] dealt with the effect of a fixation device on healing of a tendon graft to the bone tunnel and how strength and stiffness of the complex (tendon-devicebone) change after implantation.…”

Time-Dependent Changes in Failure Loads of 3 Biceps Tenodesis Techniques

“…Recently, an increase in the fixation strength of PLLA interference screws after intra-articular tenodesis was reported in an experimental study. 11 This increase was not accompanied by an increase in the screw diameter. The authors explained these findings with the observations of Mainil-Varlet et al, who found an acute water uptake by an increase in the crystallinity of the PLLA rods, without an increase in rod diameter.…”