Bone Mineral Density Changes Under Two Tibial Components in Total Knee Arthroplasty

Randomized Clinical Evaluation of Bone Mineral Density Changes Under Non-cemented Trabecular Metal Tibial Component and Cemented Titanium Controls.

Osteoarthritis is a progressive disease afflicting to two thirds of Americans. Today, an estimated 43 million individuals have arthritis. By 2020, more than 59.4 million Americans will be affected by the disease. Despite the relative good track record of total knee replacement, it remains a biomedical device that can fail over time. A recent study looking at the current mechanisms of total knee replacement failures, listed polyethylene wear and osteolysis around implants. The material used for polyethylene insert as well as the conformity of articular surface of implants has been modified to decrease wear. While introducing modularity, the usage of metal backing in tibial base plates became obvious as it offered better stress distribution to the proximal tibial bone. However, it introduced other modes of failures. Micromotion has been demonstrated between the metal backing and the tibial liner, and produced backside polyethylene wear in 44% of implants at retrieval for revision. Factor influencing the surgeon's choice of implant include: reproductibility and longevity of results, technical difficulty of implantation, cost, and impact on bone stock. The modulus of elasticity of the tibial base plate has a direct effect on periprosthetic bone biology. Studies have described a significant decrease in postoperative Bone mineral density (BMD), adjacent to the implants, after total knee replacement. No study, to our knowledge, has looked at BMD in vivo after total knee replacement comparing different tibial base plate designs. Direct effect of changes in design on overall implant survival can be studied with randomized clinical trials isolating specific variables. No randomized clinical trial has looked at tibial insert stiffness and modularity, and it effect on bone density changes, synovitis, osteolysis or survivorship. In order to isolate stiffness and modularity as study variables, one would aim at randomizing an homogenous patient population undergoing total knee arthroplasty with implants of similar articular geometry designs with different tibial insert modularity and stiffness.

NexGen LPS Monobloc (Trabecular Metal) tibia (Zimmer), NexGen Option Stemmed (Titanium) modular tibia (Zimmer).

Evaluation of Bone Mineral Density using dual energy x-ray absorptiometry (DEXA) scan under tibial base plate implant after Total knee arthroplasty.

Radiological evaluation of implant loosening according to Radiographic Knee Society Score at follow-up after total knee arthroplasty.

Inclusion Criteria: Tri-compartmental knee arthrosis 55 to 75 years of age Stable health condition Exclusion Criteria: Inflammatory arthritis Osteonecrosis Infection Amputation (AK or BK) Biphosphonates Metal in the proximal tibia (25cm) History of fracture or osteotomy Ligament instability