Critical size bone defects pose a serious clinical problem, as the intrinsic healing capacity of bone fails due to the size of the defect. Bone healing might be aided by addition of 1,25(OH)2 vitamin D3 (vitD3) to bone tissue engineering scaffolds. VitD3can promote osteogenic differentiation of human stem cells such as adipose stem cells (hASCs), which is a clinical-relevant source of mesenchymal stem cells. However, it is unknown which release kinetics of vitD3, i.e. short or sustained release from scaffolds, leads to the most optimal osteogenic differentiation of hASCs. We hypothesized that sustained release of vitD3 leads to more osteogenic differentiation of hASCs than shorter applications.

hASCs (1×105, passage 3–4) were seeded on 20 ± 1 mg of calcium phosphate particles (day 0), cultured for 20 days, and treated with a total amount of 124 ng vitD3. This treatment was provided either during 30 min before seeding (pre-incubation, short stimulation: [200 nM]), after seeding, over the first 2 days (burst- release high: [100 nM]), or over the total culture period of 20 days (sustained-release: [10 nM]). In the extra condition: burst-release low the hASCs were treated for 2 days after seeding with 6.2 ng vitD3 ([10 nM]) per day.

Live/dead staining followed by fluorescent microscopy showed that hASCs attached to the calcium phosphate particles and were mostly viable (±75 %) at day 2. VitD3 applied for any duration did not affect the proliferation of hASCs at day 7 and day 20, measured with an alamar blue assay. At day 7, sustained-release increased the release of active alkaline phosphatase on average by 3.5-fold, compared to all the other conditions. At day 20, this was increased 4.3-fold. At both day 7 and day 20 total protein levels were similar in all conditions.

Our results suggest that sustained release of VitD3 from bone tissue engineered scaffolds may be beneficial for the osteogenic differentiation of human stem cells for the treatment of critical bone size defects.

Radiographs of the scaphoid after injury are difficult to interpret, and bone scintigraphy is widely used to increase the accuracy of diagnosis, though many fractures suspected on scintigraphy cannot be confirmed radiologically. We have reviewed the clinical consequences, after one year, of managing suspected scaphoid fractures according to the bone-scan results. We studied 160 patients, 35 of whom had initially positive radiographs and were treated in a cast for 12 weeks. The other 125 had bone scintigraphy and were managed according to the result. After a minimum of one year 119 patients were reviewed. Scintigraphically suspected scaphoid fracture could not be confirmed radiologically in 25%. There were no cases of nonunion. The long period of immobilisation in patients with positive radiographs or positive bone scans did not influence the frequency or severity of late symptoms compared with those with a normal bone scan.