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Comparison of Free Fibular Flaps to Reamer-Irrigator-Aspirator (RIA) Putty for Reconstruction of Critical Sized Porcine Mandibular Defects
Raja Mohan, MD, Gerhard S. Mundinger, MD, Emile N. Brown, MD, John A. Kelamis, MD, Branko Bojovic, MD, Michael R. Christy, MD, Amir H. Dorafshar, MbCHb, Eduardo Rodriguez, MD DDS.
University of Maryland/Shock Trauma Center, Baltimore, MD, USA.

PURPOSE:
Vascularized bone flaps are the gold standard for reconstructing mandibular defects ≥ 6cm. However, this technique can result in significant donor site morbidity and requires microsurgical expertise. Reamer irrigator aspirator (RIA, Synthes, Westchester, Pennsylvania) was recently developed to reduce the risk of fat embolization associated with reaming a femur prior to intramedullary rod fixation and is well characterized for a sizable medullary bone harvest. We sought to compare the RIA putty to osseous free fibular flaps in reconstructing porcine critical sized mandibular defects.
METHODS:
Nine 3-month old Yorkshire pigs underwent 6cm full-thickness resection of the left mandible. The right mandible served as a control. A reconstruction plate was placed at the inferior border of the mandible prior to osteotomies and secured in place. For the free fibular group (four pigs), an 8-10cm osseous free fibula flap from the left leg was harvested through a 15cm lateral incision. The artery to the fibula, a branch of the cranial tibial artery provided a pedicle length of approximately 2.5cm. The free fibula flap was inset and secured in place with the reconstruction plate. Microsurgical anastomosis between the proximal cranial tibial artery and facial artery was performed. For the RIA group (five pigs), a four-centimeter internal parapatellar approach was used to expose the distal third of the femur and the proximal third of the tibia. After exposure, a drill-bit was inserted through the intercondylar surface and reaming was begun in 1 mm increments for approximately 15 minutes.(Figure 1) RIA putty(Figure 2) containing medullary bone marrow contents was obtained and placed in the mandibular defect and secured with a reconstruction plate.(Figure 3) Animals were followed with serial radiographs and clinical evaluations for a six-month time period. Volumetric and biomechanical analysis of the mandibular reconstruction sites was performed on necropsy samples.
RESULTS:
The reconstruction of the defect was successfully performed in both experimental groups. There was a significant difference in average operative times (RIA-144.4min, fibula 353.3min, p<0.05). There were no immediate infections; all the animals ambulated well and gained weight normally. There was no significant difference in average maximum stress load sustained (RIA-468N, fibula-689N, p=0.11). The average ratio (experimental/control) of biomechanical load was 0.88 (fibula) and 0.74 (RIA) (p = 0.46). The average volume ratio (experimental/control) of bone growth at the reconstructed sites was obtained using three-dimensional CT scans and was not significant (RIA-71%, fibula-72%, p=0.60).
CONCLUSION:
RIA is a quick, facile technique that is comparable to free fibular flaps in reconstructing porcine critical size bone defects. Future directions include histologic assessment of the reconstructed sites in both groups.


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