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The Immune System Blamed for Loosening of Hip Implant

Elvis Presley was often accused of having loose hips. That's okay for someone in the world of rock and roll. But adults who have a total hip replacement (THR) need a stable implant. There are many reasons why hip implants come loose. The authors of this study think one cause may be the immune system. Some patients may react to the materials in the implant, which leads to loose hip joints.

The authors studied 90 replacement hips and divided them into two groups. The first group had loosening before 15 years. The second group had loosening after 15 years. All patients had a blood test and X-rays.

Many different human leukocyte antigens (HLAs) were measured in these two groups. HLAs are part of the immune system. They are numbered to keep track of them. Each person has HLAs as unique as fingerprints. They tell the immune system, "It's me!" When the immune system sees the HLA, it recognizes it as part of its body and leaves it alone. HLAs are inherited. Some can increase a person's chances of getting certain diseases.

In this study, patients who tested positive for HLA-A31(19) had three times as many loose hips as those who tested negative. The number of hips with a positive test was greatest in the group with loosening before 15 years. There were some patients with a lot of wear in the socket but no loosening. They didn't have the A31(19) antigen.

The authors of this study conclude that a patient's immune response to implant particles, together with HLAs, may be a risk for loosening is certain implants.

References: Satoshi Takayanagi, MD, et al. Human Leukocyte Antigen and Aseptic Loosening in Charnley Total Hip Arthroplasty. In Clinical Orthopaedics and Related Research. August 2003. Vol. 413. Pp. 183-191.

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