The road to the Pearl-String Technique: lessons learned from early IMT modifications using RIA autograft and cancellous allograft granules.

BACKGROUND: The induced membrane technique (IMT) is widely used for reconstruction of large bone defects; however, reported outcomes vary considerably among technical modifications. One potential mechanism impairing consolidation is graft sedimentation, particularly when low-density cancellous autograft harvested using the reamer-irrigator-aspirator (RIA) is applied. This study evaluates a standardized modification of the IMT and explores mechanical factors potentially affecting graft consolidation. METHODS: In this retrospective single-center study, 28 patients were treated following eradication of osteomyelitis using a defined modification of the IMT. Mean follow-up was 7.4 years. Defect length ranged from 3.2 to 15.7 cm. During the second stage, RIA-harvested autologous cancellous bone was combined with lyophilized cancellous bone allograft granules. Definitive fixation was achieved using intramedullary nailing or locking plate fixation; one patient was treated with a ring fixator. RESULTS: Primary consolidation was achieved in 57.1% of cases. Aseptic nonunion occurred in 10.7%, with secondary consolidation achieved after revision in all affected patients. Recurrent infection was observed in 35.7%; infection control was achieved in 90% of these cases following additional procedures, and reconstruction was ultimately completed using alternative strategies. Median time to full weight bearing was 35 weeks. Graft sedimentation occurred in 42.9% of cases and was predominantly observed in patients who failed to achieve primary consolidation. CONCLUSIONS: This modification of the IMT allowed bone union in a substantial proportion of patients but was associated with high rates of complications, particularly infection recurrence and nonunion. The findings indicate that insufficient mechanical stability of cancellous composite grafts may promote graft sedimentation and impair consolidation, particularly when extensive allograft expansion and compromised host biology coexist. While the combination of autologous and allogenic cancellous bone within an induced membrane remains conceptually attractive, ensuring adequate mechanical stability of the graft construct appears essential when treating large bone defects.