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Wednesday, March 10, 2004

Late radiotherapy inhibits heterotopic ossification

By Carolyn Rogers Late radiotherapy can significantly inhibit the progression of heterotopic ossification (HO) both in terms of total amount of bone formation, as well as the time required for HO to stop progressing, according to investigators for Poster Exhibit P082.

Immediate postoperative prophylactic radiotherapy has been shown to be effective for the prevention of HO. However, it treats all patients at risk, and therefore overtreats patients who may not actually develop HO. Late radiotherapy would treat only those known to have developed HO and, therefore, avoids overtreating patients and putting them at risk of complication.

The natural history suggests that, left untreated, HO will progress. Treatment to prevent its progression into clinically advanced stages would therefore also be desirable. To that end, the researchers sought to determine if late radiotherapy could halt the progression of heterotopic bone formed following cementless total hip arthroplasty.

For this study, eight hips that developed HO six weeks or three months following total hip arthroplasty were treated with 700 rads. All patients were followed clinically and radiographically for two years postoperatively. HO was evaluated using the Brooker classification. In addition, all X-rays were digitized and a computer analysis was done to determine the amount of bone that formed. A non-radiated control group of nine identical cementless hips, all of which had developed HO by six weeks postoperatively, was used for comparison.

Five of the eight radiated hips and four of the nontreated control hips showed no progression in Brooker class over this two-year time period. Digital X-ray analysis revealed some progression occurred in all hips but averaged only 32 percent in the radiated group, compared to 86 percent in the untreated controls (p<0.05).

This was most evident in hips with Brooker class II HO (18 percent increase in the radiated group vs. 91 percent increase in the controls).

The untreated control hips continued to develop additional HO over the entire 2 year study period, while the radiation-treated hips showed no further bone formation after the intital six months, postoperatively (p<0.05).

Stephen R Kantor, MD, of La Jolla, Calif., authored the study. Other members of the research team were Michael Tanzer, MD, Louis Souhami, MD, and Gyorgy Hegyi, PhD, all of Montreal, Quebec, Canada.

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Last modified 01/March/2004