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Comparative Study
. 2002 Apr 1;27(7):682-8.
doi: 10.1097/00007632-200204010-00003.

The effect of cage stiffness on the rate of lumbar interbody fusion: an in vivo model using poly(l-lactic Acid) and titanium cages

Martijn van Dijk  1 , Theo H Smit, S Sugihara, Elisabeth H Burger, Paul I Wuisman
Affiliations
Comparative Study

The effect of cage stiffness on the rate of lumbar interbody fusion: an in vivo model using poly(l-lactic Acid) and titanium cages

Martijn van Dijk et al. Spine (Phila Pa 1976). .

Abstract

Study design: A goat interbody fusion model using poly-(L-lactic acid) and titanium cages was designed to evaluate the effect of cage stiffness on lumbar interbody fusion.

Objective: To investigate the effect of cage stiffness on the rate of interbody fusion.

Summary of background data: Various types of cages considerably exceed the stiffness of vertebral bone, which ultimately may lead to postoperative complications. To avoid these complications, poly-(L-lactic acid) cages with limited stiffness have been designed. The mechanical integrity of the cages remains intact for at least 6 months.

Methods: Interbody fusions were performed at L3-L4 of 15 Dutch milk goats, and one of three cages was randomly implanted: 1) a titanium cage (n = 3), 2) a stiff poly-(L-lactic acid) cage (n = 6), or 3) a flexible poly-(L-lactic acid) cage (n = 6). Interbody fusion was assessed radiographically by three independent observers 3 and 6 months after surgery.

Results: At 3 months, all the poly-(L-lactic acid) specimens showed ingrowth of new bone, but with radiolucency in the fusion mass. At 6 months, solid arthrodesis was observed in four of six poly-(L-lactic acid) specimens, advanced ingrowth in one specimen, and infection in one specimen. Titanium cages showed ingrowth of bone, but with radiolucency in the fusion mass. Interbody fusion using poly-(L-lactic acid) cages showed a significantly higher rate statistically (P = 0.016) and more complete fusion than titanium cages of the same design.

Conclusions: The reduced stiffness of poly-(L-lactic acid) cages showed enhanced interbody fusion, as compared with titanium cages after 6 months. Bioabsorbable poly-(L-lactic acid) cages thus may be a viable alternative to current interbody cage devices, thereby avoiding the concomitant problems related to their excessive stiffness. However, the bioabsorbability of the poly-(L-lactic acid) cages awaits investigation in a long-term study currently underway.

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