October 18, 2018
2 min read

Heterotopic bone formation may no longer be an issue after THR

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In the 1980s when I started training in orthopaedic surgery, heterotopic bone formation in the soft tissue around a newly implanted total hip replacement was a common event and an occurrence that was regularly observed on radiographs taken as soon as 3 to 6 months after surgery. In fact, at that time, severe bridging Brooker grade IV ossifications were frequently observed in as many as 5% to 10% of cases, which left patients who underwent THR with a permanently significantly reduced hip range of motion. In some cases, patients even had a stiff hip in a flexion contracture, as well as pain during the first 6 to 12 months after the index surgery.

At that time, only sporadic research had been done into prevention of heterotopic bone formation (HBF) after THR. It focused on irradiation of the soft tissue round the hip or systemic treatment with either bisphosphonates or NSAIDs. We decided at my institution, Kolding Hospital in Denmark, to initiate a randomized, placebo-controlled, double-blinded clinical trial to study the difference in HBF 1 year after THR when patients took either 25-mg indomethacin three times daily for 6 weeks or placebo. The study became the first randomized trial to show the effect of postoperative NSAIDs. The outcome was dramatic. NSAIDs were shown to highly significantly reduce the risk for developing significant HBF after THR.

Per Kjaersgaard-Andersen, MD
Per Kjaersgaard-Andersen

Several good studies have since shown the same outcome when a less potent NSAID was given and for a shorter duration of treatment.

Fate of heterotopic bone formation

Now, 30 years later, we regularly discuss at our institution, where more than 800 THRs are performed annually, what happened with the HBF after THR. We wonder if this problem has disappeared because we rarely see any amount of HBF when patients return for a follow-up examination after THR.

The answer is clear to me because in 1989, I had the opportunity to lecture on this topic at the American Academy of Orthopaedic Surgeons Annual Meeting and later at the Mayo Clinic. At the Mayo Clinic, in a discussion with Mark B. Coventry, MD, and he told me HBF after THR was rarely seen at the Mayo Clinic, and in some way, it seemed he questioned the high incidence of HBF (60%) we found in the placebo group. When I asked Coventry about the drugs their patients were given in the postoperative period after THR, he said they gave 1 g aspirin twice daily for some weeks as prophylaxis for deep venous thrombosis. Immediately, we looked at each other and understood why the incidence of HBF was so low at the Mayo Clinic and so high in our placebo group, because aspirin is certainly a potent NSAID.


Effect of NSAIDs on heterotopic bone

Today, and for several years, we use NSAIDs in our multimodal postoperative pain protocol, which by chance, and as a side benefit, prevents HBF after THR to be a significant event.

This story is an eye-opener to the fact that this treatment, and especially medical drug treatment, may impact more than one component of a surgical outcome. We fortunately had a positive outcome as a surprise. However, unknown negative outcomes could also occur. Keep in mind: Science is looking at your data from more than one angle. Science is also doing lateral thinking along with everything else, just as Dr. Edward de Bono mentioned in his little booklets about life.

Disclosure: Kjaersgaard-Andersen reports no relevant financial disclosures.