Distraction osteogenesis of the porcine mandible: histomorphometric evaluation of bone.

Distraction osteogenesis is a technique for skeletal lengthening that exploits the body's innate capacity for bone formation in response to tension forces on the repair callus. The authors developed a distraction osteogenesis model with a semiburied device in the Yucatan minipig mandible because of similarities between human and porcine mandibular anatomy, temporomandibular function, chewing patterns, and bone turnover rates. The purpose of this study was to measure histomorphometric bone fill after different latency periods, rates of distraction, and duration of neutral fixation in the minipig mandible. In addition, the relationship between histomorphometric bone fill and clinical stability was investigated. Mandibular osteotomies in 20 female Yucatan minipigs weighing 25 to 30 kg were distracted with modified semiburied distraction devices. Variables included 0-day or 4-day latency; 1-mm, 2-mm, or 4-mm daily distraction rates; gap size of 7 or 12 mm; and evaluation after neutral fixation for various lengths of time. Specimens were fixed in 2% paraformaldehyde, pH 7.4, before being embedded in methylmethacrylate. Sections were prepared from the region just below the inferior alveolar canal. The area of new bone formation within the gap was measured and expressed as a percentage of the total area of the distraction gap. Bone fill ranged from 0 to 100 percent. A pilot study with 7-mm advancements showed similar bone fill with 0-day or 4-day latency, but with poor reproducibility. Mandibles that were distracted to 12 mm at 1 mm per day exhibited nearly complete bone fill, either with 0-day latency (average, 93 percent) or 4-day latency (average, 100 percent). Mandibles that had been distracted for 3 days at 4 mm per day showed moderate osteogenesis and clinical stability with increasing time of neutral fixation. Bone fill was significantly correlated with clinical stability (Spearman r = 0.801, p = 0.001). Histological examination showed exuberant periosteal osteogenesis in distracted mandibles, even in those that showed poor bone fill and clinical stability. Thus, the periosteum appears to be a major source of new bone formation. These results show that osteogenesis was nearly complete with 1 mm per day and 0-day or 4-day latency. These results are consistent with the authors' previously reported clinical and radiographic observations that a latency period is not necessary for successful healing of the mandibular distraction osteogenesis wound.