Surgical intervention is warranted in the fixation of finger fractures only if it results in high mechanical stability. This allows early motion and avoids loss of range of motion and stiffness often associated with immobilization. To facilitate the rational design of finger fracture fixation devices an analytical and experimental program is presented to establish appropriate design criteria. The analytical scheme uses composite beam theory treating the device and bone as components of a system contributing to the strength and rigidity of fixation. The experimental program uses the pig metacarpal as an animal model for the proximal phalanx. K-wire fixation and intramedullary fixation with a polylactic acid polymer (PLA)-carbon fiber composite device are considered. Fixation rigidity is found to be limited by device slippage and device-bone hardness mismatch. However, both techniques are shown to be capable of sustaining the bending moments expected in normal pinch hand function. A method of fixation using four 0.712-mm ( 28 1000-in.) wires is shown to increase the maximum bending moment by 170% and bending rigidity by 300% over the conventional two crossed K-wire method. Its maximum bending moment capability provides a safety factor of 2.01 over expected tip pinch moments. A method using a 3.5-mm square cross-section PLA-carbon intramedullary (IM) device is shown to increase the maximum bending moment by 240% and bending rigidity by 297% over the two-wire method with a maximum bending moment safety factor of 2.53.
All Science Journal Classification (ASJC) codes
- Orthopedics and Sports Medicine
- Biomedical Engineering