Unicompartmental Replacement
Oxford Prosthesis in Unicompartmental Knee Arthroplasty Provides Consistent Mechanical Limb Alignment
The use of unicompartmental knee arthroplasty, or partial knee replacement, is still being studied in terms of effectiveness of result compared with total athroplasties. As surgeons become more familiar with the techniques and as techniques and prosthetic designs improve, implant success grows.
One of the issues with partial replacements is the actual design of the implant to improve the range of motion of the joint. The authors of this study wanted to examine the alignment of the knee after surgery and insertion of the medial compartment Oxford implant (introduced in 1987 as a phase 2 implant), how well the implant survives, and how and when the implant did fail.
The researchers reviewed the records of 55 implants performed in 51 patients - 4 of whom had bilateral or double knee replacements. The patients' average age was 64 years old and the average weight was 78.1 kg. The patients were assessed through the use of x-rays of the knees and the Knee Society clinical scoring instrument. The two scales, a knee score and a function score, are based on a score of 100 and the higher the number, the better the score. Before surgery, the 55 knees were scored on average of 43 for the knee score and 56 for the function score. After surgery, the average scores were 75 and 90, respectively.
The alignment of the joint was also assessed before surgery. The researchers found that the overall alignment was restored to neutral.
Failure of the joint was limited to seven knees, six of which went on to have total knee replacements. The main reason for the failure was progression of arthritis and not the implant itself (five knees). One knee had loosening, which occurred over three years after surgery. No failures were due to wear and tear of the polyethylene make-up of the implant.
The authors conclude that any failure of this particular implant was due to the progression of arthritis and not the implant itself.
Reference:
Roger H. Emerson, Jr., MD, and Linda L. Higgins, PhD. Unicompartmental Knee Arthroplasty with the Oxford Prosthesis in Patients with Medial Compartment Arthritis. In The Journal of Bone and Joint Surgery. January 2008. Vol. 90-A. No. 1. Pp. 118-122.'
