Purpose: Vascular Endothelial Growth Factor (VEGF) is vital for both angiogenesis and osteogenesis. The aim of this study was to investigate the effect of cell based VEGF gene delivery on the proliferation and mineralization of rabbit osteoblasts in vitro.

Method: Primary cultured rabbit osteoblasts were divided into four groups (each n=6). In Group I, osteoblasts were transfected with pcDNA3.1-VEGF; in Group II, osteoblasts were transfected with pcDNA-Efficiency Green Fluorescent Protein (EGFP); in Group III, osteoblasts were treated with the supernatant of fibroblasts that were transfected with VEGF genes; and in Group IV, osteoblasts were treated with the supernatant of fibroblasts that were transfected with EGFP. The cells were cultured in a-EME with 10% FBS, 2% penicillin/streptomycin with or without 10-^7 M dexamethasone and 50μg/ml L-ascorbic acid for 28 days. In the last 4 days, the cells were stimulated to initiate calcium mineralized nodule formation by adding 10 mM B-glycerophosphate. They were stained by the Von Kossa technique so that the number and the area of the nodules could be assessed by an imaging analysis system.

Results: The cells transfected by VEGF were indicated by the EGFP marked cells under a fluorescent microscope. There was a significant difference in the total nodule area (mean 18.38 mm² SE 3.73 and 5.07 mm² SE 0.55, p< 0.05) and count (mean 18.67 SE 3.22 and 2.17 SE 0.40, p< 0.001) between Group I and Group II (ANOVA, SPSS). More unmineralized and smaller nodules were found in Group III and Group IV. However, the nodules in Group III covered greater areas with dark brown staining in the cell culture dishes when compared with Group IV.

Conclusion: The observations indicate that cell based VEGF gene delivery has a positive effect on the proliferation and mineralization of osteoblasts. The greatest effect is seen with direct transfection of osteoblast cells. Cell-based VEGF gene therapy may be used to promote fracture healing.

We have investigated the accuracy of placement of the femoral component using imageless navigation in 100 consecutive Birmingham Hip Resurfacings. Pre-operative templating determined the native neck-shaft angle and planned stem-shaft angle of the implant. The latter were verified post-operatively using digital anteroposterior unilateral radiographs of the hip.

The mean neck-shaft angle determined before operation was 132.7° (118° to 160°). The mean planned stem-shaft angle was a relative valgus alignment of 9.7° (sd 2.6). The stem-shaft angle after operation differed from that planned by a mean of 2.8° (sd 2.0) and in 86% of cases the final angle measured within ± 5° of that planned. We had no instances of notching of the neck or varus alignment of the implant in our series. A learning curve was observed in the time taken for navigation, but not for accurate placement of the implant.

Navigation in hip resurfacing may afford the surgeon a reliable and accurate method of placement of the femoral component.

A total of 20 pairs of fresh-frozen cadaver femurs were assigned to four alignment groups consisting of relative varus (10° and 20°) and relative valgus (10° and 20°), 75 composite femurs of two neck geometries were also used. In both the cadaver and the composite femurs, placing the component in 20° of valgus resulted in a significant increase in load to failure. Placing the component in 10° of valgus had no appreciable effect on increasing the load to failure except in the composite femurs with varus native femoral necks. Specimens in 10° of varus were significantly weaker than the neutrally-aligned specimens.

The results suggest that retention of the intact proximal femoral strength occurs at an implant angulation of ≥ 142°. However, the benefit of extreme valgus alignment may be outweighed in clinical practice by the risk of superior femoral neck notching, which was avoided in this study.

A cadaver study using six pairs of lower limbs was conducted to investigate the accuracy of computer navigation and standard instrumentation for the placement of the Birmingham Hip Resurfacing femoral component. The aim was to place all the femoral components with a stem-shaft angle of 135°.

The mean stem-shaft angle obtained in the standard instrumentation group was 127.7° (120° to 132°), compared with 133.3° (131° to 139°) in the computer navigation group (p = 0.03). The scatter obtained with computer-assisted navigation was approximately half that found using the conventional jig.

Computer navigation was more accurate and more consistent in its placement of the femoral component than standard instrumentation. We suggest that image-free computer-assisted navigation may have an application in aligning the femoral component during hip resurfacing.

1. Thirty-seven cases of fracture of the dens have been studied.

2. The incidence of non-union was high: 64 per cent after apparently adequate closed treatment.

3. Possible causes of the high incidence of non-union have been studied : attention is drawn to the effect of displacement and to that of posterior displacement in particular.

4. Non-union of the dens with potential instability at the atlanto-axial joint is not acceptable in a patient who expects to lead a normal active life.

5. Atlanto-axial fusion is the method of choice in the treatment of instability ; once that has been secured, pseudarthrosis of the dens is no longer significant.