Pedicle screw fixation of the C7 vertebra using an anteroposterior fluoroscopic imaging technique.

Cervical pedicle screws have been reported to be biomechanically superior to lateral mass screws. However, placement of these implants is a technical challenge. The purpose of this investigation was to use an anatomic and a clinical study to evaluate a technique for placement of the pedicle screws in the C7 vertebra using fluoroscopic imaging in only the anteroposterior (A/P) plane. Ten adult cadaver C7 vertebrae were used to record the pedicle width, inclination and a suitable entry point for placement of pedicle screws. A prospective study of 28 patients undergoing posterior instrumentation of the cervical spine with C7 pedicle screw placement was also performed. A total of 55 C7 pedicle screws were placed using imaging only in the A/P plane with screw trajectory values obtained by the anatomic study. Radiographs and CT scans were performed post-operatively. The average posterior pedicle diameter of C7 vertebra was 9.5 ± 1.2 mm in this study. The average middle pedicle diameter was 7.1 mm and the average anterior pedicle diameter was 9.2 mm. The average transverse pedicle angle was 26.8 on the right and 27.3 on the left. CT scans were obtained on 20 of 28 patients which showed two asymptomatic cortical wall perforations. One screw penetrated the lateral wall of the pedicle and another displayed an anterior vertebral penetration. There were no medial wall perforations. The preliminary results suggest that this technique is safe and suitable for pedicle screw placement in the C7 vertebra.

Hip dislocation after modular unipolar hemiarthroplasty.

An institutional review board-approved retrospective review of hip fractures in elderly patients treated with a modular unipolar implant was carried out to identify factors predisposing to dislocation of a hemiarthroplasty. The main outcome measure evaluated was dislocation vs nondislocation. Two hundred seventeen patients underwent the surgery, and 174 were available for review at 6 weeks and 144 at 1 year. The incidence of dislocation was 6%. The average time of dislocation after surgery was 19.3 days. Clinical factors significant for dislocation were male sex and mental disease. Radiographic factors in dislocated hips included a smaller femoral neck and contralateral femoral neck offset. The center edge angle was also smaller in the dislocated patients. These patients had a higher mortality rate.