Bone healing of the sheep tibia shaft after carbon dioxide laser osteotomy: histological results

The aim of the study was to compare the histological results after complete osteotomies of the sheep tibia using either the prototype carbon dioxide (CO₂) laser osteotome ‘OsteoLAS’ (n = 12) or an oscillating saw (n = 12). The laser parameters were as follows: wavelength 10.6 µm; energy of laser pulses 75–85 mJ; pulse duration 80 μs; pulse repetition rate 200 Hz; spot diameter 460 μm (1/e² level); radiant exposure 45–51 J/cm²; peak irradiance 0.56–0.64 MW/cm². Both groups were divided into two subgroups (n = 6), and the animals were killed after 4 weeks or 12 weeks, respectively. Light and fluorescence microscopy with semiquantitative analysis and histomorphometry were performed to compare bone healing. Charring-free laser osteotomies were possible up to a depth of 20 mm with the short-pulsed CO₂ laser. The laser, however, required a significantly longer time to perform, and a wedge-shaped gap was present on the cis-cortex. After 4 weeks the osteotomy gaps were almost unchanged in both groups and filled with connective tissue. After 12 weeks the gaps were filled with newly formed bone in both groups. Primary gap healing was predominant in the laser group and longitudinal cortical remodelling in the control group. On a cellular level, no fundamental differences were observed for early and late stages of bone healing. Further research has to be focussed on improving the CO₂ laser ostetome in order to reduce the long duration of the laser osteotomy and the necessity of creating a wedge-shaped cut in thick bones.