Our study focuses on reducing the use of CT (Computer Tomography) for pedicle screw instrumentation, replacing CT with X-ray. We are writing a program to measure the position on X-ray seeing whether the position meets that on CT after operation. In the future,our method can be used in fluoroscopy, helping us detecting screw malposition efficiently during the surgeries, and hoping reduce complications.

Most of the spine surgeries are decompression, fusion, with instrumentation.Instrumentation needs screws. Pedicle screws are often used. If the pedicle screws are mal-located, that is breaking the pedicle wall; the consequence may be injury of the spinal cord, or nerve root. Some lucky patients may have no symptom; however, broken pedicle will reduce the fixation strength which may reduce fusion rate.

Detecting malposition screws, currently we use CT (computer tomography) method. The surgeon carefully read the CT slice by slice, looking for clues of screws malposition. However, CT is costly both price and radiation dose.We invented a plain radiograph method which has been pilot tested in one patient with good correction rate. The purpose of this study is to solve the following two clinical problems:

1. What are the inter-observer and intra-observer reliabilities of CT method?
2. The radiation dose for CT method is too high. Does our plain radiograph method has the same correction rate? Materials and methods We planned to collect about 100 patients received spinal fusion and instrumentation who has preoperative CT(or MRI) and postoperative plain radiographs and CT. We will firstly verify CT method's reproducibility by interobserver and intra-observer reliability test. With the same databank, we will use our plain radiograph method again, and test if the two methods' results are the same by Chi-square test.

Conclusion:

We hope our study can reduce some unnecessary CT examination. In the future,our method can be used in fluoroscopy, helping us detecting screw malposition efficiently during the surgeries, and hoping reduce complications.

Inclusion Criteria:

• s/p pedicle screw insertion surgery
• good quality postoperative plain radiograph
• good quality postoperative CT

Exclusion Criteria:

• poor quality postoperative plain radiograph
• poor quality postoperative CT

Patients from Shuang Ho Hospital