Cortical bone healing following laser osteotomy using 6.1 μm wavelength*

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Abstract
Background and Objective Use of laser wavelengths in the 6.1 μm (amide I) to 6.45 μm (amide II) regions and a macropulse width of 4.0 microseconds delivered by a computer‐controlled delivery system have produced clean, deep cortical bone ablations with minimal collateral thermal injury and no char formation. The purpose of this study was to evaluate the healing of cortical bone following 6.1 μm wavelength laser osteotomy using a 4.0 microsecond pulse, and compare that response to the response of similar osteotomies made with a standard pneumatic surgical bone saw. Study Design/Materials and Methods Sixteen mature rabbits were divided equally into 2, 4, 6 and 8‐week post‐surgical survival groups. A nitrogen driven sagittal bone saw and an FEL generating 6.1 μm wavelength in 4.0 microsecond macropulses of 22.5 ± 2.5 mJ/pulse directed into a 200 μm diameter spot were used to make 6.6 mm linear cuts into rabbit tibial cortex, and the healing response over time was monitored. Bone saw cuts were made halfway through the thickness of the cortex. Laser cuts were directed by a computer‐controlled delivery system, and were either partial or full thickness cortical cuts. Location of the cortical bone cuts (saw or laser, partial or full thickness cut, proximal or distal, medial right or medial left tibia) were randomly assigned. At each predetermined post‐surgical time point, rabbits of the appropriate group were euthanized, and the tibias of each subject collected, processed for histologic evaluation, and analyzed by light microscopy. Results At 2 weeks post‐surgery, bone saw cuts showed no evidence of a healing response, while both the partial and full laser cut sites were filled with trabecular bone and primitive bone marrow. By 4 weeks post‐surgery, the bone saw cuts showed filling of the defect with trabecular bone and primitive marrow, and an intense osteonal remodeling of the original cortex adjacent to the cuts was evident. All laser cut defects were filled, reactive periosteal bone was being converted to osteons and consolidating, and secondary osteons were appearing in the original cortex. At 6 weeks following surgery, the bone saw defects were filed with a mixture of woven and lamellar bone. All laser defects were filled with lamellar osteons and woven bone, the osteons were remodeling from primary to secondary osteons. By 8 weeks following the surgery, all bone saw and laser cut specimens revealed complete healing. Conclusions Histologic evaluation of osteotomy sites made in skeletally mature rabbit tibia using the 6.1 μm wavelength, 4.0 microsecond macropulse FEL, delivered at 6 Hz at the osteotomy site, reveals a healing response which is at least as good as the healing of bone saw osteotomies, and appears to proceed at a faster rate during the first 2–4 weeks following surgery. Lasers Surg. Med. 29:38–43, 2001.