Cementless Unicompartmental Knee Replacement: Good or Better Than Cemented

Orthopedic surgeons from the United Kingdom have proven for themselves that cementless unicompartmental knee replacements are as good (if not better) than cemented implants of the same type. They conducted this preliminary study using the Oxford unicompartmental knee replacement. The study was partially funded by the company (Biomet) that makes these implants.

The results were so positive for the cementless version, they say that they only use this type of implant now when unicompartmental replacement is needed. In fact, they have already studied 1,000 patients for a year who received the Oxford cementless unicompartmental knee replacement. Results of that study will be published in the near future.

What makes the cementless implant better than the cemented device? And how do we know this is true? These are the two questions the researchers answered in this article. They compared two groups of patients: 32 who received the cemented Oxford unicompartmental knee replacement and 30 others who were implanted with the cementless Oxford device. All of the procedures were done using a minimally invasive surgical technique.

Participants in the study were followed for five years using fluoroscopic (real-time) X-rays. The advantage of this type of imaging study is that the X-ray beam can be focused on the underside of the implant. This gives the surgeon a better view of the bone-to-implant interface (where the implant sits against the bone). This type of imaging study is helpful since the most common cause of revision surgery after unicompartmental knee replacement is loosening of the implant without infection (called aseptic loosening).

Other measures of outcome included functional and activity scores on three valid, reliable tools: the Oxford Knee Score, the Tegner Activity Score, and the Knee Society Scores. These questionnaires are filled out by the patient providing information about symptoms (pain, swelling, clicking, locking, knee giving out), function (ability to kneel, squat, stand up from a chair, go up and down stairs), and activities of daily living (shopping, cooking, bathing, driving).

Results showed that after five years, there was no significant difference between the two groups based on most of the functional outcome measures. The one exception was the Knee Society Functional Score, which was significantly better for the cementless group. Overall, everyone in both groups improved significantly from before surgery to after surgery.

The major difference of note was seen in the X-rays. The cementless group had better fixation with fewer cases of aseptic (without infection) loosening. The end-result was fewer revision surgeries for the cementless group. In fact, even the cementless implants that were not placed with perfect alignment were still in place and working well without symptoms or problems for the affected patients.

The authors concluded that the use of the cementless unicompartmental knee replacement has a lower failure rate compared with the cemented version of this implant. They point out the advantages of the cementless device as: 1) shorter surgical time, 2) simpler surgical procedure, 3) more forgiving when a less than optimal position of the implant is achieved, and 4) no complications caused by cement.

Problems associated with cemented implants (from the cement itself) include tightening tissues from excess cement oozing into the nearby soft tissue structures, loose fragments of cement causing pain and mechanical problems, and excess wear and failure of components requiring additional surgery. These observations and the better results for the cementless group provide the evidence needed for these surgeons to shift to the exclusive use of cementless fixation for unicompartmental knee replacements.