Kwan Mun Keong, Chan Chris Yin Wei, Saw Lim Beng, Rukmanikanthan Shanmugam, Lenke Lawrence G
*Department of Orthopaedic Surgery, Faculty of Medicine, University of Malaya, Kuala Lumpur, Malaysia †Department of Orthopaedic Surgery, Washington University Medical Center, Saint Louis, MO.
Clin Spine Surg. 2017 Apr;30(3):E297-E304. doi: 10.1097/BSD.0b013e3182aab29d.
Cadaveric and biomechanical study.
The aim of this study was to assess the safety and pullout strength of medial, partial nonthreaded thoracic pedicle screws compared with conventional screws.
The perforation rate of the pedicle screws has been reported as high as 41%. Nerve injury and irritation can result from the compression of malpositioned screw on neural structures.
Ten fresh cadavers were studied. Screws, 5.0 and 6.0 mm, were inserted from T1 to T6 and T7 to T12, respectively. Pedicle perforations and fractures were recorded upon screw insertion and final positioning (nonthreaded portion facing medially) after a wide laminectomy. Pullout strength of novel and conventional screws were then tested using an Instron machine in an artificial bone substitute.
A total of 240 thoracic pedicle screws were inserted. Of them, 88.8% (213 screws) were fully contained during screw insertion. There were 5.0% (12 screws) grade 1 medial perforations and 6.2% (15 screws) grade 1 lateral perforations during screw insertion. Upon final positioning, 93.8% (225 screws) were fully contained. All grade 1 medial perforations, which occurred during insertion, were converted to grade 0. No dural or nerve root injuries occurred. Pedicle split fractures were noted in 6.7% (16 screws). The use of medial, partial nonthreaded screws reduced the overall perforation rate from 11.2% to 6.2%. The mean pullout load for the 5 mm fully threaded screw versus medial, partial nonthreaded was 1419.3±106.1 N (1275.8-1538.8 N) and 1336.6±44.2 N (1293.0-1405.1 N) respectively, whereas 6 mm pullout load averaged 2126.0±134.8 N (1986.3-2338.3 N) and 2036.5±210.0 N (1818.4-2355.9 N). The difference was not statistically significant.
The use of medial, partial nonthreaded pedicle screws reduced the medial perforation rate from 5.0% to 0%; however, the pullout strength was not significantly reduced. The use of this novel screw can potentially reduce the incidence of nerve injury or irritation after medial pedicle perforations.
尸体及生物力学研究。
本研究旨在评估与传统螺钉相比，内侧部分无螺纹胸椎椎弓根螺钉的安全性及拔出强度。
据报道，椎弓根螺钉的穿孔率高达41%。位置不当的螺钉对神经结构的压迫可导致神经损伤和刺激。
对10具新鲜尸体进行研究。分别将5.0mm和6.0mm的螺钉从T1至T6以及T7至T12置入。在广泛椎板切除术后，记录螺钉置入时及最终定位（无螺纹部分朝内侧）时的椎弓根穿孔及骨折情况。然后在人工骨替代物中使用英斯特朗材料试验机测试新型螺钉和传统螺钉的拔出强度。
共置入240枚胸椎椎弓根螺钉。其中，88.8%（213枚螺钉）在螺钉置入过程中完全位于椎弓根内。螺钉置入时，有5.0%（12枚螺钉）为1级内侧穿孔，6.2%（15枚螺钉）为1级外侧穿孔。最终定位时，93.8%（225枚螺钉）完全位于椎弓根内。所有在置入过程中发生的1级内侧穿孔均转变为0级。未发生硬脊膜或神经根损伤。观察到6.7%（16枚螺钉）出现椎弓根劈裂骨折。使用内侧部分无螺纹螺钉使总体穿孔率从11.2%降至6.2%。5mm全螺纹螺钉与内侧部分无螺纹螺钉的平均拔出载荷分别为1419.3±106.1N（1275.8 - 1538.8N）和1336.6±44.2N（1293.0 - 1405.1N），而6mm螺钉的拔出载荷平均为2126.0±134.8N（1986.3 - 2338.3N）和2036.5±210.0N（(1818.4 - 2355.9N）。差异无统计学意义。
使用内侧部分无螺纹椎弓根螺钉可使内侧穿孔率从5.0%降至0%；然而，拔出强度并未显著降低。使用这种新型螺钉可能会降低内侧椎弓根穿孔后神经损伤或刺激的发生率。
