Bone-Grafting in Polyostotic Fibrous Dysplasia

Abstract

Background: Polyostotic fibrous dysplasia is a skeletal disease that results from somatic activating mutations in the gene GNAS in skeletal stem cells, leading to proliferation of immature osteogenic cells with replacement of normal marrow and bone with fibro-osseous tissue. Lesions may cause bone deformity or fracture. In the surgical care of polyostotic fibrous dysplasia, the role of grafting and the optimal grafting material are not clear. The purpose of this study was to evaluate the long-term survival of bone-grafting procedures in subjects with polyostotic fibrous dysplasia over time.

Methods: The operative reports and radiographs of a cohort of subjects with polyostotic fibrous dysplasia followed in a natural history study were reviewed. Twenty-three subjects (mean age at the time of enrollment, thirteen years [range, two to forty years]) with fifty-two bone-grafting procedures had a mean follow-up time of 19.6 years (range, twenty-nine months to forty-seven years). Kaplan-Meier life table estimates, Cox proportional hazard models, and t tests comparing means were performed to assess various aspects of graft survival.

Results: Kaplan-Meier curves showed a 50% estimate of survival of 14.5 years. Cox proportional hazards models showed no advantage comparing allograft with autograft or structural with nonstructural graft materials. The mean age of the patients was significantly greater (p < 0.001) in the subgroup of subjects in whom grafts were maintained over time (20.9 years) compared with the subgroup of patients whose grafts were resorbed over time (9.8 years).

Conclusions: Bone-grafting, including both allograft and autograft, is of limited value in ablating the lesions of fibrous dysplasia. The expectations of patients and surgeons should include the high probability of graft resorption over time with return of bone characteristics of fibrous dysplasia, particularly in younger patients. This suggests the maintenance of normal bone mechanics with implant support should be the priority of any surgical intervention.

Fig. 1

Graft and implant evolution demonstrating a typical approach to restore the neck-shaft angle in proximal femoral disease using different grafting materials and devices. Grafting materials included allograft and Grafton (Fig. 1-A) and allograft chips (Fig. 1-B). Grafting material was minimally resorbed (Fig. 1-C), and eventually support was attempted with an intramedullary rod (Fig. 1-D).

Fig. 2

Partially resorbed graft. Fig. 2-A The initial approach included curettage and bone-grafting with coral and iliac crest graft. Fig. 2-B Five years later, a hip screw and side plate as well as bone-grafting with an allograft strut and allograft chips were used. Fig. 2-C Eight years later, implant revision alone was performed with the lytic lesion of fibrous dysplasia visible again; the grafting material had been resorbed.

Fig. 3

Graft survival for all materials. The Kaplan-Meier survival curve for the entire population and for all materials is shown. The number of surviving grafts at specific intervals is indicated above the x axis. The time points at which data censoring took place are indicated by the plus signs. 95% CI = 95% confidence interval.

Fig. 4

Graft survival by material. The Kaplan-Meier survival curves were stratified into four groups consisting of nonstructural allograft (solid line), nonstructural autograft (small dashed line), structural allograft (dashed and dotted line), and structural autograft (large dashed line), as indicated. There was no significant difference between any of the curves, indicating no selective advantage of one type of graft over another. The number of each type of graft surviving at fixed intervals is indicated in the lower section of the panel above the x axis. The time points at which data censoring took place are indicated by the plus signs.

Fig. 5

Graft survival by age. Kaplan-Meier survival curves for all grafts grouped according to age at which a graft was used. The length of survival of the grafting material in subjects who received grafting at eighteen years of age or older are shown by the solid line, and survival of the grafting material for those who were younger than eighteen years of age at the time of grafting is shown by the dashed line. Time points at which data censoring took place are indicated by the plus signs.