Background Ectopic bone formation has been reported as the complication after hip arthroplasty, at the time of paralysis of extremities and cerebral trauma, and in the presence of congenital diseases such as progressive ostosis. Bisphosphonates have been developed as the agent for improving bone metabolism, and are currently used as 1) a derivative in making a radioisotope diagnosis, 2) an inhibitor of bone resorption, 3) a preventive agent for ossification, and 4) an inhibitor of calculus formation in dentistry.
Objectives We have investigated the therapeutic effects of etidronate disodium (EHDP) as a bisphosphonate on ectopic bone formation developing after hip arthroplasty and the indications for administration of EHDP. The patients who had received implant arthroplasty 8 years ago were clinically evaluated, and the influence of EHDP on the prostheses was investigated.
Methods The subjects were the patients who had undergone total hip replacement or hip prosthesis replacement. They consisted of 40 women, and the ages at the time of operation ranged from 50 to 82 years, with a mean of 63.9. Twenty (mean age at operation, 62.6 years) of them were administered EHDP, and the rest 20 (mean age at operation, 65.1 years) were not administered the agent. The administration was initiated within 2 weeks postoperatively at a daily dose of 600–1000 mg, and continued for 12 weeks. The patients were clinically evaluated 4, 8, 12, 24, and 96 weeks and 8 years after the start of administration. The Finermann’s classification was used for radiological evaluation of ectopic bone formation.
Results The incidences of ectopic bone formation 24, 96 weeks and 8 years after the start of administration in the group administered EHDP (EHDP group) were 15%, 25%, and 30%, respectively, while the corresponding values in the non-administration (control) group were 30%, 40%, and 45%, respectively. Within 12 weeks after operation, the ectopic bone formation occurred in 33% of all patients with the ectopic bone formation and 17% of the patients administered EHDP. According to the Finermann’s classification, grade 1 was observed in 67%, grade 2 in 22%, and grade 3 in 11% of all patients with the ectopic bone formation 24 weeks postoperatively, while grade 1 was observed in 73% and grade 2 in 13% grade 3 in 14% 8 years postoperatively.
Conclusion The incidence of ectopic bone formation has been reported to range from 15% to 90% in Western countries. In contrast, the incidence in Japan is 15.7–38.5%, being lower than in Western countries. The severity has also been reported to be mild in Japan, as compared to cases in Western countries. In our data, the incidences were 20% and 30% in the control and EHDP groups, respectively, 24 weeks postoperatively, and the mildest grade 1 accounted for 67%. The ectopic bone formation manifested within 12 weeks after operation in 13% of the patients who had the condition, showing that the occurrence was suppressed during this period. These results suggest that the administration is efficacious for postoperatively early prevention of ectopic bone formation and that the indications for the administration must be taken into much consideration.
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