Min Woo-Kie, Seo Il, Na Sang-Bong, Choi Young-Seo, Choi Ji-Yeon
Department of Orthopedic Surgery, Kyungpook National University Hospital, Daegu, South Korea.
J Orthop Surg (Hong Kong). 2017 Sep-Dec;25(3):2309499017736562. doi: 10.1177/2309499017736562.
This study aimed to present radiologic analysis of minimal safe distance (MSD) and optimal screw angle (OSA) that enables to fix screws in a lateral mass safely without facet joint violation in open-door laminoplasty using a plate.
A retrospective analysis was made of 22 patients (male: 17; female: 5), average age 62 years. Seventy-nine lateral mass screws were fixed among a total of 158 screws. MSD that doesn't allow 5-mm screws to violate a facet joint was measured for C3-C7 and a comparative analysis was performed. If the MSD is not secured, the OSA to be given to the cephalad direction is calculated to avoid violation of the facet joint.
The screws violating inferior facet joints accounted for 34.1% of the screws fixed in inferior lateral mass. Joint surface to distal mini-screw distances were 3.18 ± 1.46 mm and 4.75 ± 1.71 mm in groups of facet joint violation and non-facet violation (FV), respectively ( p = 0.001). When 5-mm screws were inserted into a lateral mass, MSD was 4.39 ± 0.83 mm. The average MSD of C3, C4, and C5 was 4.05 ± 0.78 mm, 4.10 ± 0.70 mm, and 4.26 ± 0.74 mm, respectively. There was no significant differences among levels ( p > 0.05). The average MSD of C6 and C7 was 4.92 ± 0.81 mm and 4.80 ± 0.96 mm, respectively, showing significant differences from those of C3, C4, and C5 ( p < 0.05). If 6 mm of the MSD isn't secured, OSA showed in the cephalad direction of 11.5° for 5 mm and 22° for 4 mm approximately.
We suggest that mini-screw on lateral mass can be fixed safely without FV, if they are fixed at MSD of 6 mm from a joint surface. Facet joint violation doesn't occur if an OSA is given in the cephalad direction in case of not enough MSD for mini-screws.
本研究旨在对最小安全距离（MSD）和最佳螺钉角度（OSA）进行影像学分析，以便在使用钢板的开门式椎板成形术中安全地将螺钉固定于侧块，而不侵犯小关节。
对22例患者（男性17例，女性5例）进行回顾性分析，平均年龄62岁。总共158枚螺钉中，有79枚侧块螺钉被固定。测量C3-C7不允许5毫米螺钉侵犯小关节的最小安全距离，并进行对比分析。如果最小安全距离未得到保证，则计算向头侧方向给予的最佳螺钉角度，以避免侵犯小关节。
侵犯下小关节的螺钉占下侧块固定螺钉的34.1%。小关节侵犯组和未侵犯组（FV）的关节面至远端微型螺钉距离分别为3.18±1.46毫米和4.75±1.71毫米（p = 0.001）。当将5毫米螺钉插入侧块时，最小安全距离为4.39±0.83毫米。C3、C4和C5的平均最小安全距离分别为4.05±0.78毫米、4.10±0.70毫米和4.26±0.74毫米。各节段之间无显著差异（p>0.05）。C6和C7的平均最小安全距离分别为4.92±0.81毫米和4.80±0.96毫米，与C3、C4和C5相比有显著差异（p<0.05）。如果最小安全距离未达到6毫米，则向头侧方向的最佳螺钉角度对于5毫米螺钉约为11.5°，对于4毫米螺钉约为22°。
我们建议，如果将微型螺钉固定在距关节面6毫米的最小安全距离处，则可以安全地固定在侧块上而不侵犯小关节。在微型螺钉的最小安全距离不足的情况下，如果向头侧方向给予最佳螺钉角度，则不会发生小关节侵犯。
