Biodegradable fixation devices made of the polymers polylactide, polyglycolide and their copolymers are used routinely during maxillofacial, craniofacial, and orthopedic reconstructive surgical procedures, thanks to their property of biodegradation that avoid the need for implant removal. In particular, they are used in the treatment of craniosynostosis in pediatric patients affected by Pfeiffer syndrome, where the resorption time of 1 year or less does not interfere with the normal growth of the skull. To study the mechanism how polylactide-polyglycolide (PLPG) acid plates can induce osteoblast differentiation and proliferation in normal osteoblasts and in osteoblasts derived from a patient with Pfeiffer syndrome, the expression levels of bone-related genes were analyzed using real-time reverse transcription-polymerase chain reaction. Osteoblasts grown on the PLPG acid plates resulted in significant upregulation of mRNA expression of many genes related to osteodifferentiation during the treatment, indicating that polylactide, polyglycolide biopolymers enhance proliferation, differentiation, and deposition of matrix in osteoblasts. This study also revealed some differences in gene expression between normal osteoblasts and osteoblasts derived from patients with Pfeiffer syndrome, cultivated on PLPG acid plates.