Mechanical comparison of a distal femoral side plate and a retrograde intramedullary nail.

OBJECTIVE: To compare quantitatively the axial and torsional stiffness of a retrograde intramedullary nail and a fixed angle screw side plate in treating a supracondylar femur fracture in osteopenic femora. To determine the modes of failure of an intramedullary nail and a side plate under axial loading. DESIGN: Matched pair cadaveric study. SETTING: Orthopaedic biomechanics laboratory. PATIENTS AND OTHER PARTICIPANTS: Eleven matched pairs of preserved human femora were selected. The cadaveric specimens were harvested from relatively elderly donors with an average age of 75.6 years, which represents the principal population at risk for poor fracture fixation. INTERVENTION: The eleven matched pairs were osteotomized to simulate segmental structural defects in the supracondylar region. One femur of each matched pair was fixed with an intramedullary nail, and the contralateral femur was fixed with a side plate. MAIN OUTCOME MEASURES: Axial and torsional stiffness values. Axial modes of failure. RESULTS: The intramedullary nail axial stiffness was 14 percent (p = 0.04) less and torsional stiffness was 17 percent (p = 0.05) less than that provided by the side plate. The axial failure of the intramedullary nail occurred distally, allowing the hardware to protrude into the articular space. The side plate also failed distally by displacing the condylar screw into a varus angulation. CONCLUSION: The mechanical advantages favor the use of the side plate if fixation stiffness is essential. The axial mode of failure occurs distally for both fixation devices.

Effect of nicotine on the rate and strength of long bone fracture healing.

Empirical clinical observation suggests that cigarette smoking had an inhibitory effect on long bone fracture healing, but this has not been proven scientifically. Forty female New Zealand White rabbits had midshaft tibial osteotomies performed and plated. These were divided randomly into two groups receiving either systemic nicotine or saline (placebo). Lateral radiographs were taken at 4, 6, and 8 weeks that showed a 17.2% average difference in callus formation between the two groups and a significant lag in formation of cortical continuity in the nicotine group. The rabbits were sacrificed 8 weeks after fracture, and healing was compared biomechanically. Three (13%) fractures showed no clinical evidence of union in the nicotine group, whereas all fractures in the control group healed. Biomechanical testing showed the nicotine exposed bones to be 26% weaker in three-point bending than were those exposed to placebo.