Development of quantitative measures for bone comminution severity.

摘要

Bone and joint injuries with comminution (multiple small fragments) challenge orthopaedic traumatologists. Furthermore, the presence of many fragments makes it hard to classify such injuries into clinically meaningful groups. In order to improve treatments for patients who suffer these injuries, it is imperative that outcome evaluations occur in a manner that objectively separates the effect of injury severity from the effect of treatment. This thesis will show that a rigorous, biomechanically-based, quantitative measure can provide an objective gauge of bone comminution severity. Such a measure, based on fracture energy absorption, was developed utilizing controlled laboratory models.; The quantitative estimate of fracture energy here employed is predicated on fracture mechanics theory, in which the liberated fracture surface area is directly proportional to the energy absorbed in the crack propagating process. In systematic investigations, the feasibility of this approach with CT-based area assessments from a custom-designed digital image analysis algorithm was demonstrated. Laboratory impact drop tower tests were first conducted in a specially-developed bone surrogate material. The dense polyetherurethane surrogate produced a spectrum of fragmentation patterns comparable to that present clinically in distal tibial pilon fractures. CT-based surface area measurements of the shattered surrogate, which was rendered radiographically similar to human cortical bone, were directly proportional to input energy. In addition, the principles of comminution phenomena that govern the theoretically-expected fragment size distribution, and that have been observed in other materials, were applicable to the surrogate.; In the next phase of the study, a more complex model was explored. In these impacted, excised cortical bovine bone segments, area measurements incorporated the local apparent density of the fragments. Bone impact fracture indices also were compared to corresponding quasi-static fracture toughness parameters. (These parameters were derived from a thin-ring technique, newly applied to bone as a part of this research). Again, a statistically significant linear regression was apparent in de novo surface-versus-energy absorption data. Although further image analysis algorithm development is still warranted to speed processing time and increase automation, the surface measurement techniques have also successfully been applied to an actual clinical dataset from a pilon fracture patient.