Controversies in Knee Replacement: Implant Designs
Patrick A. Meere, MD
Some of the unhappiest total knee arthroplasty (TKA) patients are the ones who first underwent patellofemoral arthroplasty (PFA), says Patrick A. Meere, MD, from NYU Langone Medical Center – Hospital for Joint Diseases in New York.
The procedure has traditionally had a failure rate of up to 40% with either the first-generation inlay implant designs or the second-generation onlay implant designs. The difference is the time to failure: within 5 years for the inlay designs, but within 16 years for the onlay designs.
Implant designs are improving, Dr. Meere said, as are the indications for PFA and the surgical technique used, which is translating to the greater longevity seen with the onlay implants.
The early inlay designs had serious issues, such as a deeper trochlear groove, more obtuse angle, and limited proximal extension. The newer onlay implants solve these issues with a shallower trochlear groove, optimized distal femoral curvature, and adapted proximal extension.
Click the image above to watch Dr. Meere’s presentation.
Unicondylar Knee Arthroplasty
Ormonde M. Mahoney, MD
Total knee arthroplasty (TKA) is a generally successful procedure, with 95% implant survivorship. It’s a tough construct to beat, says Ormonde M. Mahoney, MD, from Athens Orthopedic Clinic in Athens, Georgia.
So why does he perform unicondylar knee arthroplasty (UKA) in 1 out of 10 of his patients with knee osteoarthritis, particularly given that UKAs fail twice as fast as TKAs? Because up to 20% of TKA patients are unsatisfied with their new knee, usually due to it not feeling “normal.” With UKA, Dr. Mahoney can give carefully selected patients that more normal-feeling knee.
He noted that UKA involves less trauma and imposes a lower biologic load of foreign material because the implants are so much smaller. And, durability is improving – although not yet to the level of TKA – thanks to changes in implant design and technique.
Click the image above to watch Dr. Mahoney’s presentation.
Bicruciate Retaining TKA
Christopher L. Peters, MD
Christopher L. Peters, MD, from the University of Utah in Salt Lake City, agreed with Dr. Mahoney that with conventional total knee arthroplasty (TKA), many of the unsatisfied patients may be unhappy due to abnormal kinematics of the knee.
Fluoroscopic analysis, he noted, has shown that the knee functions better after TKA if the anterior cruciate ligament (ACL) is retained, compared with a knee design that sacrifices this ligament. 
Dr. Peters was one of the surgeons who participated in the design of a new bicruciate knee implant. Because the ACL drives normal knee kinematics, and because more patients than not have an intact ACL at the time of surgery, they hypothesized that retaining an undamaged ACL would create more normal kinematics, which would increase patient satisfaction.
In early results, Dr. Peters has seen a slightly higher risk of revision for patients who received the bicruciate implant, which has raised questions about the cause: Is it the learning curve for the procedure? The patient selection criteria? The surgical technique or the implant design?
Although no answers are clear yet, studies are ongoing.
What Dr. Peters does know is that patients who do well, seem to do extremely well, perhaps even better than conventional TKA patients, with greater improvement at 1 year in physical functioning and pain relief.
Click here to watch Dr. Peters’s presentation.
- Stiehl JB, Komistek RD, Cloutier JM, Dennis DA.The cruciate ligaments in total knee arthroplasty: a kinematic analysis of 2 total knee arthroplasties. J Arthroplasty. 2000 Aug;15(5):545-50