Introduction: Although distraction osteogenesis techniques have been used clinically for the treatment of many skeletal conditions with great success over the last 2 decades, one-step larger extent tibial lengthening (> 5 cm) still remains a clinical challenge. In which tension unbalance of bone and soft-tissue may occur, and complications such as foot drop, ankle and knee dysfunction, cartilage injure and secondary osteoarthritis were common. We have designed and manufactured a new lengthener, which allows bone and soft tissue to be lengthened in synchronism, and ankle joint remain in functional position and may move freely during lengthening.

Methods: A dynamic cross joint apparatus at ankle level was added to a classic Ilizarov circular four-ring lengthener, the apparatus is consisted of a half ring, two dynamic junctions and an elastic (spring) device. In application pins were inserted into distant and proximal segment of the tibia, also through calcanues, the external fixator with the trans-joint device was then applied. Total 296 patients (age 6–46, average 21), 466 legs, were treated with this new lengthener, among them were 55 cases of infantile paralysis, 38 cases of post-trauma bone defects, 33 cases with congenital dysplasia and 170 cases of chordrodysplasia, rickets, dwarf and short stature (height < 148cm). Unilateral tibia lengthening was performed in 126 legs and bilateral tibia lengthening was performed in 340 legs.

Results: Average lengthening for lower limb discrepancy cases was 6.8 cm (2–8cm), and 8.8 cm (8–18cm) for dwarf and short stature. Patients can stand straight and walk during the lengthening. Average movement of ankle joint remained at 10 degree in all cases and x-ray confirmed that average ankle joint space was 2.2 mm (1–4mm). There was no foot drop and ankle joint deformity seen, and in 98% cases ankle joint function fully recovered within 1.5 years after lengthening (6–8 months). Common complications were pinhole infection (25 cases) and broken pin (8 cases). If total lengthening was over 10cm, 70% cases developed slight ankle joint stiffness that would gradually recover after physiotherapy. Severe complications occurred in 5 cases (1%), including nonunion 1 case, mal-union 1 case, bone deformity 1 case and re-fracture 2 cases. All of those cases were cured with satisfactory clinical outcome.

Discussion: The challenge of larger range tibial lengthening is mainly the soft tissue complications, such as foot drop, varus and valgus deformity of ankle joint and loss of ankle function. Prolonged soft tissue traction around the ankle joint may lead to increasing cartilage compression, cartilage damage and partial or permanent loss of joint function. Our dynamic lengthener would allow synchronized lengthening of triceps, Achilles tendon and prosterior tibia muscle with tibia, maintain ankle joint space and free ankle movement. This device was simple and easy to apply, with no need of additional Achilles tendon lengthening. Our clinical study has demonstrated that this device drastically reduced the rate of soft tissue complication. This device makes larger extent tibial lengthening (> 5cm) safer and realistic in clinical practice.

Introduction Experimental heterotopic bone formation in the canine urinary bladder has been observed for more than seventy years without revealing the origin of the osteoinductive signals. In 1931, Huggins demonstrated bone formation in a fascial transplant to the urinary bladder. Through an elaborate set of experiments, it was found that proliferating canine transitional epithelial cells from the urinary system act as a source of osteoinduction.

Urist performed a similar series of experiments in guinea pigs as Huggins did in his canine model. After two weeks, mesenchymal cells condensed against the columnar epithelium and membranous bone with haversian systems and marrow began to form juxtapose the basement membrane. At no time was cartilage formation noted, only direct membranous bone formation. They also demonstrated the expression of BMP’s in migrating epithelium and suggested that BMP is the osteoinductive factor in heterotopic bone formation.

Method This study was approved by Institutional Animal Ethics Committee. Six dogs underwent a mid-line laparotomy incision followed by mobilisation of a right sided myoperitioneal vascularised flap based on an inferior epigastric artery pedicle. A sagittal cystotomy is made in the dome of the bladder and the vascularised flap was sutured in place with acryl absorbable, continuous suture. The animals were sacrificed at 6 weeks. The bladder samples were removed and assessed by histology and immunohistochemistry. Sections were incubated with optimal dilution of primary antibody for type I collagen, type III collagen, alkaline phosphatase (ALP), bone morphogenetic protein (BMP)-2 and –4, osteocalcin (OCN), osteopontin (OPN), bone sialoprotein (BSP).

Results The mechanism for bone formation induced by the epithelial-mesenchymal cell interactions is not clear. We were able to demonstrate mature lamellar bone formation 6 weeks after transplanting a portion of the abdominal smooth muscle into the bladder wall. The bone formed immediately adjacent to the proliferating transitional uroepithelium, a prerequisite for bone formation in Huggins’ model. Here we report evidence of cartilage formation and therefore endochondral ossification as well as membranous bone formation. This is very similar histologically to the process of endochondral ossification at the growth plate in the growing skeleton. We propose a mechanism for the expression of BMP by epithelial cells.

Discussion This study demonstrates transitional epithelium induced formation of chondrocytes and osteoblasts in muscle tissue. The sequential expression of bone matrix proteins was related to cell proliferation, differentiation and formation of endochondral and membranous bone. Further information regarding the molecular mechanism of bone formation induced by epithelial-mesenchymal cell interactions will improve understanding of cell differentiation during osteogenesis.