Lower limb lengthening and deformity correction in polyostotic fibrous dysplasia using external fixation and flexible intramedullary nailing.

The study describes preliminary experience of the use of external fixators for limb lengthening and deformity correction in combination with flexible intramedullary nailing in management of polyostotic fibrous dysplasia.

Patients and methods: The retrospective study included 8 patients (mean age 11.6 ± 3.38 years; range 7-17 years) with polyostotic fibrous dysplasia operated on using external circular frame and flexible intramedullary nailing. Mean follow-up was 2.6 years. Surgical technique consisted of percutaneous osteotomy of a segment and application of circular external frame. The intramedullary nailing was done using two bent nails. Hydroxyapatite-coated nails were applied in three patients; five patients had titanium nails. Amount of lengthening (cm and %), amount of deformity correction, duration of external fixator use, index of external fixation, "nail/medullary canal at narrowest site" ratio, "nail-medullary canal at osteotomy site" ratio were analyzed. Results and complications were assessed according to Lascombes's classification.

Results: The mean amount of lengthening was 4.5 cm (or 13.7 ± 6.0% per segment). This gave a mean external fixation index of 32.5 ± 13.97 days/cm. The mean ratio of IM nail diameter/medullary canal diameter at the narrowest site was 0.22 ± 0.07 (range, 0.125-0.3 mm). No migration of IM nails into medullary canal were noticed. But in one case there was external migration of Ti-nail. In a year after frame removal, the results of treatment were classified as grade I in 7 cases and IIb in one case.At the latest follow-up control, mechanical axis deviation was found within normal limits in six patients. Two patients had excessive MAD of 11 and 28 mm. In the first case a partial varus deformity recurrence occurred at middle shaft site where a large dysplastic zone was presented. In the second case, a specific shepherd's crook deformity developed and caused excessive MAD. Mean lower limb length discrepancy varied from 1 to 15 mm.

Conclusion: There are advantages of using elastic intramedullary nailing and external fixation in the treatment of limb length discrepancy and deformity of long bones in patients with PFD. This strategy ensures reduced external fixation time and high accuracy of alignment. Intramedullary nails left in situ, especially nails with HA-coating, seem to prevent deformity recurrence and stimulate remodeling in dysplastic fibrous zones.