Methods: Seventeen patients undergoing distraction of the mandible or cranial vault with a semi-buried KLS-Martin (KLS-Martin, Tuttlingen, Germany) distractor, were included in this prospective study. Subjects’ distractors were activated each day by study personnel, using a digital torque-measuring screwdriver. Torque measurements were then converted into generalizable force values and associated with patient outcomes.
Results: Cranial vault distraction (CVDO) was performed on 7 subjects (41.2%), and mandibular distraction (MDO) on 10 subjects (58.8%). Across the entire cohort, the maximum force per activation was 27.023.5 N, and the elastic force (the rise in force over a single activation) was 10.714.1 N. Maximum force (CVDO:52.920.2 N vs. MDO: 12.98.5 N; p<0.0001), and elastic force (CVDO: 22.015.6 N vs. MDO: 4.58.2 N; p<0.0001) were significantly higher in the CVDO sub-group than in the MDO cohort. On multivariate regression analysis, statistically significant associations were seen between maximum activation force and the following independent variables: active DO day number (beta-coefficient: 1.1; P<0.001), DO rate (mm/day) (beta-coefficient: 8.9; P=0.016), CVDO (relative to MDO) (beta-coefficient: 41.4; P<0.001), and device failure (beta-coefficient: 10.3; P=0.004).
Conclusion: In CMF DO, both the magnitude of, and the trend in forces are relatively predictable, and correlate significantly with easily discernable factors such as DO-modality (MDO vs. CVDO), DO rate, and other factors. Deviations from these predictable force magnitudes and trends are correlated with systems failures. A more thorough understanding of the normal and abnormal states, as they relate to force measurements, may allow for novel diagnostic and prognostic tools, and a better heuristic with which clinicians can optimize DO protocols for the patients.