– A New Application for an Existing Technology 

By Scott Grabill, DO

Historically, surgeons have used cement to hold the components in place in total joint replacements. Over the last decade, we’ve seen improved porous metals designed to mimic cancellous bone of the human body. Recently, we have newer implants with this porous metal that can be press-fit directly against the bone, which then grows onto those implants. That’s been the gold standard for hip replacements for many years, but has not been refined for use in total knee replacements until recently.

Although there have been versions of cementless prostheses with reliable ingrowth of the patient’s bone to the femoral component for knee replacements, most older versions have shown higher failure rates with the tibial component fixation.

Press-fit fixation is now feasible in an increasing number of knee replacement cases.  As in the hip, the press-fit prosthesis gives us the potential of a permanent fixation: it becomes part of the patient’s bone because it’s directly attached; there’s no interface holding it in place that could break down or become loose over time. With these newer metals, we have a better likelihood of long-term ingrowth on the tibial component. Among the benefits of the press-fit technology is that it can be applied using either conventional or robotic assisted surgical techniques.

Physicians and surgeons are seeing younger and younger patients presenting with arthritis, whose active lifestyles makes them candidates for total knee replacement at a much earlier age. For these patients, press-fit knee replacement offers a more permanent method of fixation of their components, which we believe will demonstrate a lower incidence of loosening or failure requiring revision surgery.

Press-fit fixation is appropriate for most patients who are active, healthy, and without multiple comorbidities, and who have healthy bone in the knee. It may not be ideal for patients with osteoporosis or low bone mineral density, because when we press-fit the prosthesis, there is a risk of fracture, or subsiding into the bone. As people maintain more active lifestyles later into life, bone density improvements may allow this technology to be performed successfully in much older patients.

The decision to press fit can be easily and quickly made intra-operatively; that is, we anticipate what we’ll find based on a comprehensive pre-op history and physical exam, but sometimes find a different scenario when we actually examine the bone with our own eyes and hands. If the bone is healthy, we have the option of press-fitting the prosthesis, and if we find poorer bone quality, we can cement it. This decision can be made easily without having to shift gears in the OR.

The key, as always, is proper patient selection and patient education. It’s vital to talk to patients before the procedure, so they understand the potential long-term benefit of press fit biologic fixation, as well as the reliability of a traditional cemented knee arthroplasty.

CDR Scott Grabill, DO, has served on active duty in the US Navy for 13 years.  He completed his orthopaedic surgery residency at Portsmouth Naval Medical Center, and a fellowship in orthopaedic total joint reconstruction at the Cleveland Clinic.  He is currently employed by Sports Medicine and Orthopaedic Center and will join the practice full-time upon leaving the Navy in 2016. smoc-pt.com