Fox Valley Orthopedics

Ion reflections at the quadrupole pre-filter/mass filter boundary lead to the trapping of ions within the pre-filter. The trapped ions lead to space charge effects on the transmission of ions through this region which become more of an issue with the development of high sensitivity mass spectrometers which have bright ions beams. Simulations were carried out matching the effective potentials at the pre-filter/mass filter boundary to reduce the field gradients across the boundary by reducing the field radius of the pre-filter. A further rotation of the pre-filter relative to the mass filter was incorporated into the model. Experiments were carried out to reproduce the conditions of the simulations. Simulations show that matching the effective potentials at the pre-filter/mass filter boundary and rotating the pre-filter by 45° reduced the number of reflected ion trajectories when the mass filter was operated in either the radiofrequency (RF)-only mode or in mass resolving mode. Experiments confirmed the reduced effects of space charge on the transmission of ions through the pre-filter through the measurement of pre-filter transmission profiles with and without the use of an empty step to remove any trapped ions. These results showed significant improvement over the typical pre-filter/mass filter set-up. Matching the effective potentials at the quadrupole pre-filter/mass filter boundary and rotating the pre-filter result in a pre-filter/mass filter set-up that does not lead to ions that are reflected at the boundary. The modified set-up does not result in the presence of unwanted trapped ions in the quadrupole pre-filter.

This study compared the revision rates after autograft and allograft bone-patella tendon-bone anterior cruciate ligament (ACL) reconstruction. All bone-patella tendon-bone ACL reconstructions performed by a single surgeon between January 2000 and December 2006 were identified by retrospective chart review. Two hundred twenty-three patients met the inclusion criteria and 173 patients were available for follow-up. One hundred forty-two patients underwent bone-patella tendon-bone autograft reconstruction, and 31 patients underwent bone-patella tendon-bone allograft reconstruction. At a mean follow-up of 49 months (range, 11-91 months), revision rates were 0.7% (1/142) in the bone-patella tendon-bone autograft group versus 9.7% (3/31) in the bone-patella tendon-bone allograft group (P=.02). Subjective International Knee Documentation Committee (IKDC) scores of nonrevised (surviving) grafts in the bone-patella tendon-bone autograft group were 98.3 versus 95.2 in the bone-patella tendon-bone-allograft group (P=.0006). Tegner scores of nonrevised grafts in the bone-patella tendon-bone-autograft group were 6.2 vs 6.5 in the bone-patella tendon-bone-allograft group (P=.03). Fourteen of the 31 (45%) allografts were irradiated and all failures occurred in irradiated grafts. When irradiated grafts were excluded, no difference in revision rates was found. Anterior cruciate ligament reconstruction with the use of bone-patella tendon-bone allografts is associated with a higher revision rate when compared to bone-patella tendon autograft reconstruction. In addition, when comparing surviving grafts, the subjective IKDC scores are higher in the autograft group. When irradiated grafts are excluded, no difference in revision rates was found. Surgeons should be aware of the higher revision rate associated with allograft ACL reconstruction when counseling patients on graft options.