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Thursday, March 19, 1998

Greater risk of fat embolization in cemented fixation

Clinically significant fat embolization is likely to occur during cemented total hip arthroplasty due to the high intramedullary pressure generated by femoral component insertion, study co-author Tatsuro Inadome, MD, concluded in scientific exhibit 48.

"This high, prolonged intramedullary pressure was associated with escape of a large amount of fat from the bone surface," said Dr. Inadome, research fellow, Biomechanical Research Laboratory, St. Louis, Mo.

In contrast, fat embolization is unlikely to occur during cementless fixation because neither broaching nor insertion raises the pressure for long. "There is, however, a risk during initial femoral reaming," he said.

Dr. Inadome and colleagues compared the effects of cemented and cementless techniques on intramedullary pressure and the amount of fluid forced from the medullary cavity into the venous circulation.

Five unpaired, fresh-frozen femurs were used for each method of fixation. After the soft tissue was removed, two calibrated pressure transducers were fixed in 6.4-millimeter diameter holes through a pipe connector on the lateral aspect of the femur.

"One transducer was placed one centimeter distal to the stem tip and the second was placed eight centimeters distal to the first transducer," said Dr. Inadome, "so that pressures could be recorded proximally and distally to the cement plug in cemented specimens." Only proximal pressure measurements were used from the cemented specimens for comparison because of the plug, he noted. The temperature in the medullary canal was maintained at 37 C.

As each procedure was performed, the intramedullary pressure was measured. "The fluid forced from the medullary canal to the bone surface was collected with a pre-weighed cloth," said Dr. Inadome. "This served as an indicator of the volume of material forced into the venous system."

According to Dr. Inadome, transesophageal echocardiographic examinations have shown greater embolization (amount, size, duration) after insertion of cemented prostheses than of cementless prostheses. "Our new study shows markedly higher intramedullary pressure for a longer duration was generated with the cemented technique," he said. "The maximum pressure reached more than 5,800 millimeters/mercury (mm Hg) during insertion of the femoral component. The duration that intramedullary pressure exceeded 30 mm Hg (capillary pressure) reached two-and-one-half minutes in two specimens. The average amount of fluid captured in the cloth was approximately two grams.

"In the cementless fixation group, initial reaming generated mild increases in intramedullary pressure," Dr. Inadome said. "The pressure exceeded 30 mm Hg for an average duration of 11.5 seconds. The average weight of captured fluid was 0.3 gram."

Co-authors of the study with Dr. Inadome are Michael C. Wall, RN, research technician; Clyde L. Smith, BS, engineer; and Leo A. Whiteside, MD, director, Biomechanical Research Laboratory.

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Last modified 04/March/1998