The orthopedic industry is a lucrative and growing one. The US population age 50 and over is increasing[i]; this is exactly the age at which osteoarthritis[ii] (often requiring knee implants) and spinal stenosis[iii] (often requiring spinal implants), for instance, become markedly more common. Therefore, new orthopedic and other bone implants are a promising sector for any device manufacturer.
Bone implants are Class II or above devices for the FDA, and are similarly classified by other regulatory authorities. Thus, a regulatory package should be developed with care; and a key part of that package is a bone implantation study. The FDA guidance for some devices specifically requires it (for example, metallic orthopedic implants with surface treatments[iv]); for others, the necessity appears in demonstrating safety and efficacy in the most clinically-relevant manner.
A bone implant can serve several purposes:
Safety. Does your product cause inflammation or necrosis in the bone or surrounding tissue? How does it compare to a negative control, an untreated defect, or a marketed predicate device? This information is important for evaluating whether a device can be used in humans and under what circumstances.
For this purpose, a muscle implantation study can also be useful, but it does not provide the direct evidence of cellular reaction that an actual bone implant does. ISO 10993-6:2007 states “The test sample shall be implanted into the tissues most relevant to the intended clinical use of the material.” Implanting your material directly in the cortical or cancellous bone, as is most appropriate, will give the best evaluation of what will happen when it is implanted in humans.
Resorption. For devices meant to degrade or resorb (for example, bone void fillers or dental grafts), bone implantation can demonstrate how long the material remains at the site and how the response of the surrounding cells evolves—when inflammation develops, how long it lasts, and whether it is significantly different from similar marketed products. This also goes hand-in-hand with functionality when resorption is a vital part of the purpose of the device. Resorption can be measured quantitatively, semiquantitatively, or qualitatively; any of these options provides a picture of what happens to the device and the implantation site as time goes on.
Functionality. A bone implant device may induce several different effects, including:
- Osteointegration: the growth of surrounding tissue into the implant. Examples: prostheses, hearing aid implants.
- Osteoconductivity: the ability of the device to act as a scaffold, supporting osteogenic cells. Examples: spinal plates, bone void grafts and fillers.
- Osteoinduction: encouraging bone formation at sites where bone does not normally form (for example, in subcutaneous or muscle tissue). Examples: bone grafts and fillers.
- Osteogenic potential: the ability of osteogenic stem cells and progenitors to create new bone through homing, activation, proliferation, migration, differentiation and survival. Examples: hip and other joint implant coatings.[v]
When your device is intended to support bone formation or speed new growth, having data supporting that it does in fact do so is important for both regulatory and marketing purposes. A bone implantation study can cover many of the endpoints above in a single study, combining local toxicity with efficacy; multiple studies can also determine how effects, and the device itself, change over time.
Proper prior planning and design of a bone implantation study is important to ensure that your data is useful, valid, and complete. This is covered in the second part of this series, Designing an Effective Bone Implantation Study.
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