Sacral fixation technique in lumbosacral fusion.

STUDY DESIGN: Servohydraulic load displacement testing was used to study the biomechanical properties of sacral fixation in human cadaveric specimens. OBJECTIVES: To evaluate a modification of standard sacral fixation that uses the first dorsal sacral foramina as an adjunct location for the placement of a sacral hook in addition to S1 pedicle screws. BACKGROUND DATA: The stiffness or rigidity of an instrumentation construct governs the amount of relative movement allowed between motion segments undergoing fusion. This property provides the greatest influence over the mechanical conditions necessary for fusion to occur. METHODS: Sixteen human cadaveric specimens were divided into two groups with similar bone density assessed by quantitative computed tomography scan. All were instrumented with pedicle screws at L4 and S1. One group also had downgoing offset hooks in the first sacral foramina distracted against the S1 pedicle screw. Instron servohydraulic testing was performed in anterior compressive flexion, and load displacement curves were recorded. RESULTS: The bending stiffness of the specimens instrumented with screw and hook was significantly higher than in those instrumented with pedicle screws alone. The ultimate strength and energy absorbed did not differ between the two groups. CONCLUSIONS: The addition of sacral foraminal hooks to standard pedicle screw instrumentation constructs across the lumbosacral junction provides more rigid stabilization of the lumbosacral motion segment in this model.

Pedicle screw instrumentation for unstable thoracolumbar fractures.

We evaluated the results of short-segment pedicle screw instrumentation in 54 patients with unstable thoracolumbar fractures. Follow-up averaged 25 months (range, 11 to 36 months); 42 patients completed the study. Kyphosis was corrected by an average of 7 degrees at surgery and loss of correction averaged 5 degrees at the end of follow-up. On computed tomography, canal compromise averaged 57% preoperatively and 33% postoperatively. Complications included nerve root irritation due to screw penetration (1/42), screw breakage (2/42), and screw bending (6/42). Solid fusion was achieved in all cases at an average of 3 months. Of the 31 patients with normal neurologic function, 24 (77%) were pain-free at follow-up and had returned to previous levels of activity. We conclude that short-segment fixation with posterolateral fusion is effective in the treatment of unstable thoracolumbar fractures; it prevents progression of kyphotic deformity and neurologic deterioration, results in a stable fusion, and preserves uninvolved motion segments above and below the fracture site.

Determination of accuracy of preoperative templating of noncemented femoral prostheses.

The purpose of this study was to determine the accuracy of preoperative templating of primary, noncemented femoral components. A retrospective review of charts and radiographs was performed on 74 hips in 64 patients who had undergone either noncemented total hip arthroplasty (THA) or placement of an endoprosthesis (including bipolar). Preoperative radiographs were templated by a total joint arthroplasty attending surgeon, a senior orthopaedic resident, and a junior resident. The templated size corresponded to the actual femoral implant used in approximately 50% of cases. When femoral prostheses within one size above or below the templated size were included, the accuracy of preoperative templating rose to 88-95%. When implants within two sizes of the templated size were included, the accuracy approached 100%. Factors associated with discrepancies in the size of femoral stem used included placement of an undersized implant, presence of metal hardware that obscured the ability to template accurately, proximal bone deformity, sclerotic bone, acute femoral neck fracture, and inadequate preoperative radiographs. The accuracy of templating increased gradually with the level of training. The most experienced investigator was able to template within one size of the actual implant used in 95% of cases, compared with 88% and 82% for the less experienced investigators. Acute femoral neck fractures and proximal bone deformity were associated with the largest discrepancies in templated sizes.