Assessment of fracture healing in the tibia using the impulse response method.

The resonant frequency of a long bone as measured using the impulse response method (IRM) can reflect the bending rigidity of the bone. A study was performed using IRM to quantitatively assess fracture healing in 67 tibial fractures. A temporary decrease in resonant frequency early in the treatment course was found in 55.6% of tibias, most frequently in the cases treated by external fixation (83.3%) and the AO plate (80%). The resonant frequency also decreased temporarily following the removal of the fixation devices in 76% of the tibias where they were removed. The resonant frequency of the fractured tibia at the final follow-up exceeded that of the contralateral side in 18% of tibias, approached within 20 Hz in 11.5%, and did not reach within 20 Hz in 70.5%. A questionnaire on the effectiveness of the IRM examination in the treatment of the tibia fractures was completed by the treating orthopaedic surgeons. The IRM examinations were found to be very useful in 58.2% of cases, useful in 31.3%, and useless in 10.4%. Thus, IRM examinations are most helpful when they are able to detect the change in bending rigidity early in the treatment of tibia fractures.