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Is Type of Fixation with Knee Replacements Linked with Blood Loss?

Blood loss is a fact of life when surgery is done on any body part. Total knee replacements require cutting into the bone and that's 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. Is it the patient's age? The way the tourniquet is applied to the leg? The patient's sex (male versus female)?

In this study, surgeons from France take a look at fixation methods as a potential risk factor for bleeding. Fixation refers to the way in which the implant is placed and held in the bone. Some implants can be put in place without cement to hold them there. This method is called a press-fit fixation. The bone is cut and the implant pressed into the bone in such a way that it holds without cement.

The other most common fixation method is with cement. There's been some suggestion that blood loss is more likely with cementless implants. That's because once the bone is cut, there is quite a bit of bleeding and nothing to stop it.

The exact mechanism by which cemented implants might reduce bleeding isn't completely clear. Some experts suggest that when cement is used to hold the implant against the bone, the cement itself 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 hybrid implant refers to a joint replacement that has one side cemented (the tibial component) and one side that is uncemented (femoral component). 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 exactly 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 also done to measure two important values: hematocrit and hemoglobin. These two measures are another 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.

References: Guillaume Demey, MD, et al. The Influence of Femoral Cementing on Perioperative Blood Loss in Total Knee Arthroplasty. In The Journal of Bone and Joint Surgery. March 2010. Vol. 92-A. No. 3. Pp. 536-541.

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