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Bioabsorbable Screws
Bioabsorbable implants are made of materials that are first reabsorbed and then replaced by the body with natural material. This topic relates to an objective from Unit 4: Know the stages of bone development and repair. These implants are being used more due to their benefits over certain traditional metal options. The ability to use MRI is invaluable before and after a serious procedure and resorbable materials are often more compatible with the body. In addition, patients often find these implants more convenient for things like airports and metal detectors in the long term.
My project, a drawing, depicts a skeleton of someone having undergone an ACL surgery in which resorbable screws were used to reattach a new ACL. In these surgeries the new ACL is generally a repurposed tendon from either the patient or a cadaver and the screws are made of natural and synthetic polymers. That being said, there are certain bioceramics and metals that are also resorbable and also in use. Depending on the time frame needed there are many options available to choose from with degradation times for a certain implant ranging from a few months to a few years (Huang 2024). This is extremely helpful as extra flexibility is never a bad thing in the medical world. The shape and texture of these implants is also extremely important. Bone growth excels in a stable porous environment and so designs must take this into account. As such most designs now in use display a selection of styles maximizing for immobility and a porous environment ideal for bone ingrowth. A good example is the PEEK interface screw, which is literally just a porous, hollow, spiral holding the ACL firmly and allowing ample space for bone ingrowth (Lind 2020).
As bone growth takes time, it’s paramount that growth goes quickly and before reabsorption occurs. These implants work as a framework for future bone growth (Liu 2014). The process in which bone grows into an implant like this is called osteoconduction and largely consists of the bone developmental steps we learned in class. Osteoblasts are essential here as they deposit new bone matrices leading to the eventual formation of new bone. This growth is especially spurred on by growth factors released from blood clotting. Within six months of surgery, a patient receiving a resorbable screw for an ACL surgery should see bone ingrowth, and within two years the space should be mostly bone (Lind 2020).
Reabsorption of these implants allows for bone growth and is what sets resorbable implants apart from alternatives. The process of these implants breaking down is mainly caused by hydrolysis, which is water reacting with the polymer bonds in our implants to produce multiple smaller molecules (Timo Järvelä 2017). The by-products of this breakdown, including lactic acid, are generally absorbed by the body without complications. The breakdown is constant and consistent, and the space is eventually filled in by further bone growth. In this way a bioabsorbable implant, in this case a screw used in an ACL surgery, is fully and completely replaced by natural bone.
References
Huang, B., Yang, M., Kou, Y., & Jiang, B. (2024). Absorbable implants in sport medicine and arthroscopic surgery: A narrative review of recent development. Bioactive Materials, 31, 272–283. https://doi.org/10.1016/j.bioactmat.2023.08.015
Lind, M., Nielsen, T. O., Ole Henning Sørensen, Bjarne Mygind-Klavsen, Faunø, P., & Leake-Gardner, S. (2020). Bone ingrowth into open architecture PEEK interference screw after ACL reconstruction. 7(1). https://doi.org/10.1186/s40634-020-00285-z
Liu, J., & Kerns, D. G. (2014). Mechanisms of Guided Bone Regeneration: A Review. The Open Dentistry Journal, 8(1), 56–65. https://doi.org/10.2174/1874210601408010056
Timo Järvelä, & Nurmi, J. T. (2017). Improving Biodegradable Interference Screw Properties by Combining Polymers. Elsevier EBooks, 302-306.e2. https://doi.org/10.1016/b978-0-323-38962-4.00077-1
The use of biodegradable screws in bone regrowth and repair appears to be a revolutionary and relatively new technique that can allow for faster healing times and lead to a more comfortable recovery. Traditional metal implants’ main downside as compared to these new biodegradable materials are that they are non-absorbable and can irritate the soft tissues. This leads to increased discomfort the longer they remain in the body. The traditional metal implants are created with titanium alloy and stainless steel while these new biodegradable methods consist of polyethylene, polyurethane, and polyether ether ketone. They allow for osteoblasts to deposit new bone matrices while the implant provides the framework. There is also an added convenience that with a biodegradable implant revision surgeries are uncommon. It increases the biocompatibility of the implant and unknown but seemingly low toxicity rate to soft tissues. Patients that have received biodegradable implant treatments are not subject to metal detectors and are able to use MRI machines without added risk that a metal implant encounters.
The piece is a drawing that highlights the use of these biodegradable screws in application of ACL repair. The screws are connected to both the tibia and femur allowing for ACL reattachment. The subject is portrayed as skiing which in turn highlights the importance of biodegradable implants for use in athletic injuries. In athletics, quick recovery and the convenience of not having revisionary surgeries are most important and driving the entrepreneurial companies to continue investment into this new technology.