Automated Continuous Distraction Osteogenesis Allows for Faster Rates of Distraction

Distraction osteogenesis (DO) is a method of skeletal expansion that exploits the body’s natural healing capacity to form new bone.  Distraction of the mandible at a rate of 1 mm/day and rhythm of 1-4 times per day has been shown to produce adequate bone formation and clinical union; faster rates have resulted in inadequate bone formation and non-union.^{1, 2} We hypothesize that continuous distraction will allow for osseous union of the distraction gap at rates faster than 1 mm/day. The purpose of this study was to assess whether continuous DO at rates greater than 1 mm per day would result in adequate bone formation in the distraction gap and clinical union in a standardized mini-pig model.

An automated, continuous distraction device has been developed and evaluated by the Massachusetts General Hospital Department of Oral and Maxillofacial Surgery and Physical Sciences Incorporated® (Andover, MA). The device uses hydraulic pressure to open and senses position using an induction sensor with closed-loop control.  The automated distraction device was placed across a mandibular osteotomy 1 cm in front of the mandibular angle in 10 Yucatan immature mini-pigs. No latency period was used and the devices were continuously opened to 12 mm followed by a consolidation period of 24 days. The predictor variables were rates of distraction:  Group 1: 1.5 mm/day and Group 2: 3 mm/day.  The outcome variables were clinical stability of the distraction gap (a 4 point semi-quantitative scale; 3=no mobility, 2, 1=mobility in 1 or 2 anatomical planes respectively, 0=mobility in 3 dimensions); clinical appearance of the mandible (3 = osteotomy not visible, 2= <50% visible, 1= >50% visible, 0= clearly visible); and radiographic density of distraction gap (3= entire gap opaque, 2= >50% opacity, 1= <50% opacity, or 0= completely radiolucent.  A previous study using the same mini-pig model using discontinuous distraction at rates of 1, 2, and 4 mm day was used as control groups. The curvilinear vector (5 cm radius of curvature) of distraction allowed for assessment of differential distraction rate with the superior aspect distracting slower than the inferior aspect.  With a 1.5 mm/day distraction rate at the center the mandible, the superior portion opened 1 mm/day while the inferior border opened at 2 mm/day.   The 3 mm distraction rate opened the superior portion 2 mm/day and the inferior portion 4 mm/day.

All mini-pigs survived the operation, distraction, and consolidation periods. Group 1 (n=5) averaged 1.4 mm/day of distraction and 25 days of fixation. Mean scores for stability, clinical bone fill and radiographic densities were 2.4, 2.6 and 2.6, respectively.  Group 2 (n=5) averaged 2.4 mm/day of distraction and 28 days of fixation. Mean scores for stability, clinical bone fill and radiographic densities were respectively 3, 2.6, and 2.6.  The historical control groups using discontinuous distraction rates of 1, 2 and 4mm/day had mean stability scores of: 3, 1.5 and 1.5, respectively, clinical bone fill: 3, 2, and 2 and for radiographic bone fill 3, 2, and 1.5.

Results of this study validate a novel automated device for DO and demonstrate that continuous distraction allows bone fill at faster rates than discontinuous DO.  Continuous distraction rates up to 4 mm/day allowed for stability, clinical and radiographic bone fill.  This device and technique has the potential to shorten treatment time in the management of craniofacial deformities. 

References:

1. Glowacki J, Shusterman EM, Troulis M et al. Distraction osteogenesis of the porcine mandible: histomorphometric evaluation of bone. Plast Reconstr Surg:566-73, 2004

2. Troulis MJ, Glowacki J, Perrott DH et al. Effects of latency and rate on bone formation in a porcine mandibular distraction model. J Oral Maxillofac Surg58:507-13, 2000