Effects of low-intensity pulsed ultrasound stimulation on porous hydroxyapatite blocks for posterolateral fusion of lumbar spine in rabbits

The effects of porous hydroxyapatite blocks (PHABs) and an adjunct low-intensity pulsed ultrasound stimulation (LIPUS) on the fusion rate in a rabbit spinal posterolateral fusion (PLF) model were evaluated. Twenty rabbits underwent PLF with autograft and PHABs were randomly assigned to two groups: treated group with 20 min LIPUS daily and untreated control group for 4 weeks until euthanasia. The fused motion segments were subjected to manual palpation, gross observation, and radiographic investigation before histomorphologic and scanning electron microscopic analyses. Statistical differences between the LIPUS group and the control group are found in the fusion rate, bone density gray scale, trabecular bone formation, osteoblast-like cells, chondrocytes and positive expression of BMP-2 and TGF-β1 in the junction zone (significance level p<0.05). The results suggest that LIPUS can increase fusion rates and accelerate bone in-growth into PHAB. Hence, PHAB and LIPUS may be used together to increase fusion rates in a rabbit spinal fusion model with a promising extension to human application.