By: 25 October 2011

Guillaume Demey, MD, et al.
The Journal of Bone and Joint Surgery. March 2010. Vol. 92-A. No. 3. Pp. 536-541.

Total knee replacements require cutting into the bone which is a major cause of blood loss. In an effort to reduce this problem, surgeons are studying what patient factors might be contributing to the bleeding.

In this study, surgeons from France take a look at fixation methods as a potential risk factor for bleeding. Press-fit fixation implants can be put in place without cement to hold them there. Or the most common fixation method is with cement. There’s been some suggestion that blood loss is more likely with cementless implants, as once the bone is cut, nothing can stop the bleeding.

The exact mechanism by which cemented implants might reduce bleeding isn’t completely clear. Some experts suggest that when cement is used it may plug some of the bleeding vessels. Others propose that heat released by the cement coming in contact with the bone might cauterize bleeding blood vessels.

There are very few studies comparing blood loss between cemented and hybrid implants. That makes the results of this study of great interest. A total of 130 patients formed two groups based on fixation type (Group 1: cemented hybrid and Group 2: uncemented). The implants used in all 130 patients were the same size and shape and put in place by the same two surgeons.

Measuring blood loss isn’t easy. Drains are used to catch any fluid loss (including blood) during the procedure and for several days afterwards. But the drains can’t collect all blood lost during this time. A special formula is used to calculate total amount of blood lost given all the required variables.

Blood tests are done to measure two important values: hematocrit and hemoglobin. These two measures are an indication of how much blood loss has occurred. When the hemoglobin levels drop down too far (less than eight g/dL in this study), then a blood transfusion is ordered.

The results did not show a difference in blood loss between the two groups. The cemented implants did not produce a smaller volume of blood or lower levels of hemoglobin/hematocrit. An equal number of patients in both groups ended up needing a blood transfusion.

Based on the results from this study, the authors suggest that cementing the femoral side of the implant in place does not influence how much blood is lost during a total knee replacement. Surgeons still have to plan for blood transfusions in patients having a total knee replacement, but it won’t be because of the type of fixation used. Some other factor may yet need to be discovered.