Design Review & Preliminary Testing for a Biomimetic Absorbable Ligament Anchor

Abstract

Review of current Anterior Cruciate Ligament (ACL) anchor technologies indicates that many devices facilitate osteointegration but not soft tissue in-growth. The design and preliminary testing of a novel biomimetic in-situ dilating bioabsorbable ACL anchor for simultaneous soft and hard tissue attachment is the subject of this study. The anchor method for this concept has been developed to mimic the mechanical-key configuration observed in a hair root. Reviewed anchor devices are typically interference screw-based. Screw anchors can lead to unnecessary ligament pre-stress, tearing during deployment and poor graft-bone contact. This work demonstrates a new fixation concept specifically developed for use with devices consisting of temperature-sensitive glass-reinforced-glass (GRG) soft tissue conductive biomaterial. Ligament anchorage is accomplished by dilation of the device into the base of a hair-root shaped osteotomy where a ligament with a collar and self tightening knot is inserted beforehand. This method facilitates full ligament-to-bone contact at the osteotomy zone where critical physiological ligament anchorage develops. Ligament pull-out loads equivalent to published results for conventional anchors were achieved using graft analogue. Testing with porcine ligaments resulted in a substantial reduction in ligament pull-out loads. Tibia bone sample constraints combined with the unraveling of the ligament knot were identified as primary factors for low pull-out loads for the porcine ligament tests. Subsequent design iterations will employ a reduction in prototype dimensions in addition to the use of a suture to lock the ligament knot. The hair-root shaped osteotomy and ligament anchor knot elements of this approach may be translated to other fixation systems and methods. By improving macro-mechanical-key interaction between the anchor, bone and ligament, further increase in pull-out forces may be achieved without unnecessary ligament pre-stress and tear damage caused by conventional interference screw threads.

Development of a Bioabsorbable Glass-Reinforced-Glass Intra-Osseous Scaffold for Fracture Healing

“…Carbohydrate based materials play an important role in tissue engineering and drug delivery [24][25][26][27][28]. Carbohydrates are more readily metabolized by the body than naturally derived proteins, biodegradable polymers or biodegradable metals.…”

“…Extremes in acidity or alkalinity due to byproducts are avoided. A bioabsorbable ligament anchor has been developed using carbohydrate glass composite [28]. Glass-reinforced glass (GRG) composite consists of enveloped carbohydrate glass matrix reinforced with resorbable silicate glass fibre [28].…”

“…A bioabsorbable ligament anchor has been developed using carbohydrate glass composite [28]. Glass-reinforced glass (GRG) composite consists of enveloped carbohydrate glass matrix reinforced with resorbable silicate glass fibre [28]. The glass fibre component becomes a scaffold for soft and hard tissue while carbohydrate glass matrix is absorbed as nutrients.…”

“…To reduce morbidity caused by cross pinning or canal reaming alternative fixation approaches have employed a dilation mechanism in situ [31][32]. A GRG composite ligament anchor prototype exploits a similar dilation approach to engage with bone [28]. Temperature sensitive GRG can be plastically deformed when warmed above the glass transition range.…”