The risks of pedicle wall breech with larger screws after undertapping

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• 作者：Kingsley R. Chin ; Brett Gibson
• 关键词：Pedicle ; Screw ; Pullout ; Tapping ; Torque ; Breech
• 刊名：The Spine Journal
• 出版年：2007
• 期刊代码：243_15299430
• 类别：med
• 出版时间：September-October 2007
• 卷：7
• 期：5
• 页码：570-574
• 文件大小：216 K

摘要

A linear relation exists between the insertional torque when placing a screw and the ultimate screw pullout strength; therefore, undertapping of the pedicle followed by insertion of a larger screw may enhance the pullout strength of the screw.

Purpose

To report the risk of pedicle wall breech with placement of 6.2-mm pedicle screws after undertapping with a 5.2-mm tap and to evaluate the effectiveness of direct visualization to identify these breeches.

Study design/settings

Prospective evaluation of risks of pedicle wall breech with undertapping for a larger screw and the utility of directly visualizing pedicle walls during access and placement of pedicle screws for evidence of breech.

Patient sample

Sixty-five consecutive patients.

Outcome measures

Intraoperative direct visualization of pedicle wall breech. Postoperative radicular leg symptoms.

Methods

We prospectively analyzed placement of pedicle screws in sixty-five consecutive patients during lumbar-instrumented fusions after laminectomies performed by a single spine surgeon. Forty-four patients were primary fusions, and 21 were revisions. Twenty-seven were male, and 38 were female, with a mean age of 54.7 years (range, 15–85 years). Four hundred twenty-eight total pedicle screws were placed for an average of 6.6 screws per patient (range, 2–12 screws).

Results

The incidence of pedicle wall breech during access was 0.7%(3/428) and 1.6%(7/428) after screw placement. 71%(5/7) of the screw breeches were noted with direct inspection of the pedicles intraoperatively, and 29%(2/7) were identified on postoperative X-ray films as lateral breakthroughs that were missed on intraoperative fluoroscopy and direct visualization. Therefore, 100%of misplaced screws potentially harmful to nerve roots were identified on direct visualization. Eighty percent occurred from L2–4.

Conclusions

This study provides evidence that undertapping of pedicles followed by placement of a larger diameter pedicle screw may breech the pedicle cortices. Although the risk is low, the authors recommend direct visualization of the pedicle walls during screw placement to identify caudad, medial, and cephalad breeches. This technique is for open laminectomies and should be added to the armamentarium of other techniques and not as a replacement.