Patients most likely to receive a unicompartmental knee replacement have osteoarthritis that is painful and severe affecting the front and inner half (side closest to the other knee). This would be labeled end-stage osteoarthritis.
Diagnostic examination of the knee joint would show full-thickness loss of cartilage in the medial compartment but full thickness cartilage in the lateral compartment. The lateral compartment is the section of the joint on the side away from the other knee.
Other criteria for unicompartmental knee replacement include: 1) the patient has an intact and fully functioning anterior cruciate ligament (ACL) and 2) medial collateral ligament (also along the inside of the knee joint). These two ligaments provide stability while still allowing smooth motion of the joint.
There is evidence that cementless unicompartmental knee replacements are as good (if not better) than cemented implants of the same type. 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 addressed in a study from the United Kingdom.
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).
Results showed that after five years, 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 pointed out these advantages of the cementless device: 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 surgeons to use cementless fixation for unicompartmental knee replacements.