COMPARISON OF POLY-L-LACTIDE AND POLY LACTIDE CARBONATE SUTURE ANCHORS ON THE HEALING OF THE OVINE PATELLAR TENDON-TIBIAL ENTHESIS

Abstract

Sutures from intraosseous anchors are used to secure soft tissue down onto bone during healing. Increasingly anchors are made from absorbable materials. Poly lactide carbonate (PLC - poly lactide with calcium carbonate) is an absorbable formulation with osteoconductive properties that should enhance both tissue healing and its own replacement by bone over time. An animal model of soft-tissue-to-bone healing was used to assess the efficacy of PLC Bioraptor™ anchors in comparison to anchors of non-osteoconductive poly lactide (PLLA).

Forty-seven ewes were used in two groups of PLC or PLLA anchors, surviving to either four or 12 weeks. The patellar tendon was pared off the tibia, the footprint decorticated then the tendon re-attached. An external fixator protected the tendon from load bearing for three weeks. At post mortem the patella/patellar tendon/tibia complex was either prepared for histological examination or stored deep frozen for later measurement of peak load at failure.

Non-operated specimens failed within the tendon mid substance; the failure site of healing specimens was dependent on their strength, with the weakest through interpositional granulation tissue, stronger specimens through fibres at various distances from the bone and the strongest, by partial bone avulsion.

Active healing of the enthesis consisted of merging regions of

1. a) re-established cortical bone plate;

2. b) advancing mineralization of new, oriented collagen;

3. c) dense, cellular collagen parallel to the tendon axis.

4. Thin new bone was present around both PLLA and PLC anchors.

Healing tissues held by PLC suture anchors, were significantly stronger by 12 weeks than those held by PLLA anchors, possibly due to the calcium carbonate in the PLC anchor. However, the macroscopic and microscopic appearances of the healing tissues seemed little different between the two groups. This study indicates that PLC is a suitable replacement for PLLA in the fabrication of suture anchors. As well as its ability to produce stronger healing tissues, PLC has a shorter longevity in vivo and longer term is replaced by bone.