The diagnostic value of subtraction radiography in the assessment of granular hydroxylapatite implants.

Although histologic analysis of osseous changes around hydroxylapatite (HA) implants can be highly accurate, it is of limited use in human beings. Digital subtraction radiography may provide a noninvasive alternative. Ten patients with bony lesions were operated on and nine of the iatrogenic defects were filled with granulated HA. In one patient, the defect was left unfilled for reference. Customized film holders provided standardized radiography. Follow-up images after 4 to 6 months were subtracted from immediately obtained postoperative images, and changes around the implants were noted. From ten pairs of radiographs, eight could be successfully subtracted, whereas two pairs required corrective image transformation before subtraction. Although no bone loss was observed in any of the patients, the implants did not appear to enhance physiologic bone regeneration either. Hence, subtraction radiography holds the potential of clinical utility for the follow-up of HA implants. However, technical improvements are necessary to yield quantitative data.