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Proper identification of cells necessary to avoid infection misdiagnosis in THA, study finds

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Cell counters can falsely identify fat marrow cells as leukocytes in cases of advanced osteonecrosis of the femoral head, meaning microscopic confirmation of the cells is necessary to prevent misdiagnosis, according to Korean investigators.

The findings were presented by Tae-young Kim, PhD, at the 2011 Annual Meeting of the American Academy of Orthopaedic Surgeons, in San Diego.

“The purpose of this study was to describe the erroneous leukocytosis of the synovial fluid in femoral head osteonecrosis, and how to distinguish this erroneous leukocytosis from joint infection,” Kim said.

False findings of infection could lead to negative impact upon a patient’s quality of life, Kim noted, and thus it is important to confirm cell identities microscopically with a smear to determine whether they are leukocytes or fat cells.

Between 1997 and 2004, Kim and his team performed primary total hip arthroplasty (THA) for osteonecrotic femoral heads in 486 hips — and found “gushing pus-like fluid” in 7 hips. Preoperative evaluation in these cases reportedly did not reveal any signs of joint infection.

The pus-like fluid was aspirated during surgery, Kim reported with cell counting revealing numbers of leukocytes ranging from 4,500/ml to 18,400/ml with a mean of 8,970/ml. Under the microscope, the team found no leukocytes and confirmed the cells interpreted as leukocytes were actually marrow fat cells. The seven patients underwent THA, and no bacteria were identified in joint fluid smears or cultures in any patients. There were no signs of infection after a minimum 6-year follow-up.

“The presence of lipid material or fat cells can cause erroneous leukocytosis,” Kim said. “Our study shows that the fat cells from the osteonecrotic femoral head can cause a false leukocytosis in automated cell counting. Due to this, an erroneous diagnosis of septic arthritis can be made. Misdiagnosis can lead to significant damage to the patient’s quality of life.”

Reference:

• Kim TY, Ha YC, Lee YK, et al. Accumulation of fatty marrow in the osteonecrotic hip joint mimicking joint infection. Paper #472. Presented at the 2011 Annual Meeting of the American Academy of Orthopaedic Surgeons. Feb. 15-19. San Diego.
• Disclosure: Kim has no relevant financial disclosures.

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