Reconstructive implants are grouped into four broad categories: primary (total) replacement, partial replacement, resurfacing and revision.
Total joint replacement (TJR) involves replacing both sides of the natural joint. These devices are the most frequently used reconstructive procedures in the United States.
Partial joint replacements restore one side or a portion of the joint. These procedures have the advantage of preserving more bone and soft tissue but have historically been prone to a higher complication rate than total joint replacements. Partial replacement, also known as hemiarthroplasty, provides an alternative to joint fixation, or arthrodesis, in some instances of skeletal trauma.
Joint resurfacing attempts to preserve as much of the original bone stock as possible by placing a cap over the diseased joint surfaces. The cap is anchored by a short stem within the bone. These procedures are performed more frequently in younger patients, as the preservation of bone stock allows for better outcomes when the implant is eventually replaced later in life.
Revision implants are not a specific product type but refer to the replacement of implanted devices that have either reached the end of their useable lifespan or have become loosened through trauma or pathology. This may entail either the replacement of part of the implant or the entire implant. In general, revision implants require longer stems to anchor in the bone. Conservative estimates indicate that 15 years is an appropriate lifespan to expect from an implant regardless of its construction or method of fixation; however, newer devices are likely to exceed that time frame.
If anything, the trend towards younger patients has meant that the market has been even more mindful of preparing for the eventuality of revision because of the increased average lifespan for these surgical candidates.
Implants are subject to their own wear issues. Regardless of the type of construction, there are some basic safety concerns. Like the cartilage that it replaces, the articulating material is subject to wear. The concern remains with debris generation. While the material itself is inert, the body’s immune response to stray fragments creates the potential for osteolysis, the destruction of bone. There are similar concerns with devices using hard-on-hard articulating surfaces, as early ceramic materials were prone to chipping.