The spine journal : official journal of the North American Spine Society
-
Public interest, monetary pressures and improving diagnostic techniques have placed an increasing emphasis on minimalism in lumbar disc excision. Current techniques include microlumbar discectomy and minimally invasive spinal surgery. Both are good techniques but may be painful, require a hospital stay and/or are not widely used because of difficulty acquiring the necessary skills. The author therefore developed a less invasive microscopic technique that may be performed on a consistent outpatient basis with easily acquired skills. ⋯ The author has described a minimally invasive technique for excising herniated discs that is applicable to all types of lumbar herniations, except for those residing in the canal at L5-S1. Clinical outcomes are comparable to those of other forms of discectomy.
-
Posterolateral fusions of the lumbar spine have nonunion rates as high as 35%. The availability of autologous bone to promote fusion is limited, particularly for multilevel fusions. Bone substitutes have been proposed to augment or replace autologous bone for spinal surgery. Calcium sulfate offers high porosity, osteoconductivity, and high resorption rate. This material has been used successfully for treatment of long bone defects but has not been investigated as a bone graft substitute for spinal fusions. ⋯ This study found that calcium sulfate as a bone graft substitute was unsuccessful in promoting spine fusion in a rabbit model. There was radiographic evidence of rapid resorption of the calcium sulfate within 4 weeks after surgery. The use of electrical stimulation created a dose-dependent increase in mechanical competence of the bony mass. However, the addition of direct current (DC) current did not significantly alter fusion rates with calcium sulfate used as the bone graft substitute in this model.
-
Biomechanical studies show that bone-mineral density, pedicle morphology, and screw thread area affect pedicle screw pullout failure. The current literature is based on studies of cylindrical pedicle screw designs. Conical screws have been introduced that may provide better "fit and fill" of the dorsal pedicle as well as improved resistance to screw bending failure. However, there is concern about loss of fixation if conical screws must be backed out after insertion. ⋯ Conical screws offer improved initial fixation strength compared with cylindrical screws of the same size and thread design. Our results suggest that appropriately designed conical screws can be backed out 180 to 360 degrees for intraoperative adjustment without loss of pullout strength, stiffness or work to failure. Intraoperative adjustments of these specific conical screws less than 360 degrees should not affect initial fixation strength. These results may not hold true for screws with a smaller thread area or larger minor diameter.