Mechanical properties of biodegradable poly-l-lactide ligament augmentation device in experimental anterior cruciate ligament reconstruction

Summary

The mechanical properties, including maximum load, elongation, and axial rigidity, of the biodegradable poly-l-lactic acid (PLLA) ligament augmentation device were investigated, 6, 12, 24, and 48 weeks after experimental anterior cruciate ligament (ACL) repair in 32 sheep. In 16 sheep the cut ACL was removed and reconstructed with the fascia lata augmented with a braided PLLA implant 3.2 mm in diameter. In 16 sheep the ACL was cut from its midportion, sutured, and then augmented with a PLLA implant. The contralateral knee served as a control. At 6 weeks the maximum loads of the reconstructed ACL in the fascia lata-PLLA and primary suture-PLLA groups were 9% and 6%, respectively, of the contralateral ACL, but they increased with time and at 48 weeks were 21% and 12%, respectively, of the control. In the fascia lata-PLLA group the increase in maximum load was evident (P < 0.05) during the follow-up period. During the first 12 weeks the axial rigidity (expressing the elasticity of the reconstruction) was poor, especially in the high-stress region corresponding to the tensile load close to the maximum load. Thereafter the axial rigidity increased, being 48% of the control in the fascia lata-PLLA group and 29% in the primary suture-PLLA group at 48 weeks. In the low-stress region between 10 N and 100 N the increase in axial rigidity in the fascia lata-PLLA group was apparent (P < 0.05) throughout the follow-up, with values of 72% of the control in the fascia lata-PLLA and 47% in the primary suture-PLLA group at 48 weeks. Fascia lata augmented with PLLA seemed to yield a better result than primary suture augmented with PLLA, although no statistically significant difference was found. Despite modest mechanical properties in the early postoperative period, good functional recovery with minor radiographic changes and acceptable mechanical properties were achieved by the end of the 1-year follow-up period.