A PEEK implant, or Polyetheretherketone, is a high-performance thermoplastic polymer increasingly utilized in surgical procedures to replace or support damaged biological structures. It offers an alternative to traditional metallic implants, such as titanium or stainless steel, in various anatomical locations.
Material Properties of PEEK
PEEK’s unique characteristics make it suitable for implantation within the human body. Its radiolucency, meaning it is transparent to X-rays and computed tomography (CT) scans, allows medical professionals to clearly visualize the surgical site and assess bone healing or fusion around the implant without obstruction. Metal implants often create imaging artifacts that can obscure the surrounding tissues.
The modulus of elasticity, which describes a material’s stiffness, is another defining feature of PEEK. PEEK’s modulus is remarkably similar to that of human cortical bone, typically ranging from 3 to 4 GPa. This similarity helps to mitigate stress shielding, where a much stiffer implant absorbs most of the mechanical load, leading to the weakening or resorption of the adjacent bone tissue. By sharing the load more naturally, PEEK implants encourage the surrounding bone to maintain its density and strength.
Beyond its flexibility, PEEK exhibits considerable strength and durability, making it appropriate for numerous load-bearing applications. It maintains a relatively low density, contributing to lighter implant designs compared to their metallic counterparts. The material is also chemically inert, meaning it does not react with bodily fluids and resists corrosion within the physiological environment. This minimizes the risk of adverse tissue reactions and ensures long-term stability of the implant.
Common Surgical Applications
PEEK implants find widespread use across various surgical specialties due to their favorable properties. Spinal surgery represents the most prominent application, particularly in the form of interbody fusion cages. These cages are designed to be inserted between vertebrae after a disc removal, helping to restore disc height, decompress nerve roots, and create a stable environment for bone fusion to occur, often packed with bone graft material. Their radiolucency allows monitoring of bone fusion post-operatively.
Within orthopedics, PEEK is employed in several capacities. It is used in certain joint replacement components, particularly in finger or toe joints, where its modulus of elasticity benefits load distribution. Suture anchors, small devices used to reattach tendons or ligaments to bone, also frequently incorporate PEEK. Furthermore, PEEK plates and screws are utilized for internal fixation of fractures, especially where imaging clarity is important.
Craniomaxillofacial surgery benefits from PEEK’s ability to be precisely molded for custom applications. Surgeons use PEEK to create custom plates and meshes for reconstructing parts of the skull or facial bones following trauma, tumor removal, or congenital defects. Its inertness and ability to be sterilized make it suitable for these reconstructions. In the field of dentistry, PEEK serves as a framework material for certain dental prosthetics, including fixed and removable dentures, offering a lightweight and biocompatible option.
Biocompatibility and Osseointegration
Biocompatibility refers to a material’s ability to exist within the body without eliciting an adverse biological response. PEEK is highly biocompatible, meaning the body generally accepts it without triggering significant immune rejection or inflammatory reactions. This acceptance is due to its inert nature, which prevents the release of substances that could provoke a biological response.
However, PEEK in its unmodified form is considered bioinert, meaning it does not actively promote bone growth onto its surface. For an implant to achieve direct bonding with surrounding bone, osseointegration is important. Osseointegration is the direct structural and functional connection between living bone and the surface of a load-carrying implant. While PEEK does not naturally osseointegrate, advancements in material science have addressed this.
Many contemporary PEEK implants are engineered with surface modifications or coatings to enhance interaction with bone. These enhancements often involve applying thin layers of osteoconductive materials, such as titanium plasma spray or hydroxyapatite, to the PEEK surface. Hydroxyapatite is a calcium phosphate compound that mimics the mineral component of natural bone, encouraging bone cells to attach and grow onto the implant surface, promoting robust osseointegration and long-term implant stability.