Strategies of enhancing bone regenerate formation in distraction osteogenesis.

Distraction osteogenesis (DO) is a commonly used technique in multiple orthopedic sub-specialties, including trauma, oncology and pediatrics. This technique aims to produce new bone formation in the distraction gap in a controlled manner. The issue with this technique has been the high risk of complications, one of which is poor regenerate formation during the distraction process. Although several factors (including patient and operative factors) and techniques (including surgical, mechanical and pharmacological) have been described to ensure successful regenerate formation during the process of DO, these factors are sometimes difficult to control clinically. Our aim from this review is to highlight the different factors that affect DO, modalities to assess the regenerate and review treatment options for poor regenerate in the distraction gap. In addition, we propose a management protocol derived from the available literature that can be used to facilitate the management of inadequate regenerate formation.

Osteotomy Healing in Children With Osteogenesis Imperfecta Receiving Bisphosphonate Treatment.

A decade ago our group had reported that osteotomy healing was commonly delayed in children with moderate to severe osteogenesis imperfecta (OI) who were treated with intravenous pamidronate infusions. We subsequently maintained a bisphosphonate infusion-free interval of 4 months after osteotomy and changed the surgical approach (use of an osteotome instead of a power saw). In addition, zoledronic acid has become the standard intravenous bisphosphonate for treatment of OI at our institution. In the present study, we compared osteotomy healing before and after these changes were instituted. We evaluated bone healing post-osteotomy on standard radiographs after 261 intramedullary rodding procedures involving osteotomies (139 femur, 112 tibia) in 110 patients (age at surgery 1.2 to 20.4 years). Delayed healing was diagnosed when the osteotomy line was visible 12 months after the event. We observed delayed bone healing after 48 of the 114 osteotomies (42%) performed with the new approach, and in 106 of the 147 osteotomies (72%) using the previous approach (p = 0.001). The odds for delayed osteotomy healing were significantly lower with the new approach even after adjustment for age, sex, height Z-score, weight Z-score, OI type, and bone involved (odds ratio = 0.17; 95% confidence interval 0.16-0.47). Thus, delayed osteotomy healing occurred less frequently in the past 10 years than in the decade before that. It is likely that this improved result is attributable to the implemented changes in both medical and surgical management.

The effect of altering the mechanical loading environment on the expression of bone regenerating molecules in cases of distraction osteogenesis.

Distraction osteogenesis (DO) is a surgical technique where gradual and controlled separation of two bony fragments following an osteotomy leads to the induction of new bone formation in the distracted gap. DO is used for limb lengthening, correction of bony deformities, and the replacement of bone loss secondary to infection, trauma, and tumors. Although DO gives satisfactory results in most cases, one major drawback of this technique is the prolonged period of time the external fixator has to be kept on until the newly formed bone consolidates thus leading to numerous complications. Numerous attempts at accelerating bone formation during DO have been reported. One specific approach is manipulation of the mechanical environment during DO by applying changes in the standard protocol of distraction. Attempts at changing this mechanical environment led to mixed results. Increasing the rate or applying acute distraction, led to poor bone formation in the distracted zone. On the other hand, the addition of compressive forces (such as weight bearing, alternating distraction with compression or by over-lengthening, and then shortening) has been reported to increase bone formation. It still remains unclear why these alterations may lead to changes in bone formation. While the cellular and molecular changes occurring during the standard DO protocol, specifically increased expression of transforming growth factor-ß1, platelet-derived growth factor, insulin-like growth factor, basic fibroblast growth factor, vascular endothelial growth factor, and bone morphogenic proteins have been extensively investigated, the literature is sparse on the changes occurring when this protocol is altered. It is the purpose of this article to review the pertinent literature on the changes in the expression of various proteins and molecules as a result of changes in the mechanical loading technique in DO and try to define potential future research directions.