Zheng Zhao-Min, Zhang Kui-Bo, Zhang Jia-Fang, Yu Bin-Sheng, Liu Hui, Zhuang Xin-Ming
Department of Spine Surgery, the First Affiliated Hospital of Sun Yat-sen University, Guangzhou 510080, China.
J Spinal Disord Tech. 2009 Dec;22(8):545-50. doi: 10.1097/BSD.0b013e3181929e0c.
Comparison of the biomechanical fixation strengths offered by 3 iliac screw fixation techniques: short screw, short screw augmented with cement, and long screw.
Evaluate the effect of screw length and bone cement augmentation on the fixation strength of iliac screw upon fatigue loading.
Iliac screws have been used in treating spinal disorders such as spinal deformity, spondylolisthesis, and sacral tumor. In clinical practices, both short screws and long screws are being used. It has been reported that short iliac screws have a higher rate of loosening. Therefore, short iliac screws are being used with bone cement augmentation to improve fixation. To date, no biomechanical study has compared the strengths of these 3 different iliac screw fixation techniques.
Fresh, frozen human cadaveric pelvis specimens (n = 18, 12 males, 6 females, average age 61 y) were used. Bone density was measured to characterize bone quality. The specimens were randomly divided into 2 groups. In group 1 (n = 8), short screws of 7.0-mm diameter and 70 + or - 4 mm length (as the length of exceeding over ischial notch) and long screw of 7.0-mm diameter and 120 + or - 4 mm length were placed on either side of the pelvis (left and right). In group 2 (n = 10), short iliac screws were placed after augmentation with polymethyl methacrylate bone cement on 1 side of the pelvis and long iliac screw were placed on the other side (left and right). Cyclic loading ranging from 20 to 200 N was applied to each screw at a frequency of 2 Hz up to 5000 cycles. Pullout tests were then conducted at the rate of 5 mm/min after the fatigue test, and the maximum pullout strength for each screw was recorded and analyzed.
The maximum pullout strength of the long screw and short screw groups after fatigue conditioning were 2386 + or - 1470 and 833 + or - 681 N respectively. Significant difference was found between the 2 groups (P < 0.05). The short iliac screw had a higher loosening rate. The pullout force of the short screw fixation with augmentation and the long screw fixation after cyclic loading were 2436 + or - 915 and 2529 + or - 1055 N, respectively. No significant difference was found between the 2 groups (P > 0.05).
Short iliac screws are susceptible to loosening after cyclic loading. Bone cement augmentation of short screws has demonstrated a significant increase in the fixation strength of short screws to an extent similar to that of long iliac screws. Thus, short iliac screw fixation after augmentation with bone cement will be a viable clinical option for spino-pelvic reconstruction.
比较三种髂骨螺钉固定技术（短螺钉、骨水泥增强短螺钉和长螺钉）提供的生物力学固定强度。
评估螺钉长度和骨水泥增强对髂骨螺钉在疲劳加载时固定强度的影响。
髂骨螺钉已用于治疗脊柱疾病，如脊柱畸形、椎体滑脱和骶骨肿瘤。在临床实践中，短螺钉和长螺钉都在使用。据报道，短髂骨螺钉松动率较高。因此，短髂骨螺钉与骨水泥增强联合使用以改善固定。迄今为止，尚无生物力学研究比较这三种不同髂骨螺钉固定技术的强度。
使用新鲜冷冻的人体尸体骨盆标本（n = 18，男性12例，女性6例，平均年龄61岁）。测量骨密度以表征骨质。标本随机分为两组。在第1组（n = 8）中，将直径7.0 mm、长度70 ± 4 mm（超过坐骨切迹的长度）的短螺钉和直径7.0 mm、长度120 ± 4 mm的长螺钉放置在骨盆两侧（左右）。在第2组（n = 10）中，在骨盆一侧用聚甲基丙烯酸甲酯骨水泥增强后放置短髂骨螺钉，在另一侧（左右）放置长髂骨螺钉。以2 Hz的频率对每个螺钉施加20至200 N的循环载荷，直至5000次循环。疲劳试验后，以5 mm/min的速率进行拔出试验，记录并分析每个螺钉 的最大拔出强度。
疲劳处理后，长螺钉组和短螺钉组的最大拔出强度分别为2386 ± 1470 N和833 ± 681 N。两组间差异有统计学意义（P < 0.05）。短髂骨螺钉松动率较高。循环加载后，骨水泥增强短螺钉固定和长螺钉固定的拔出力分别为2436 ± 915 N和2529 ± 1055 N。两组间差异无统计学意义（P > 0.05）。
短髂骨螺钉在循环加载后易松动。短螺钉的骨水泥增强已证明短螺钉的固定强度显著增加，达到与长髂骨螺钉相似的程度。因此，骨水泥增强后的短髂骨螺钉固定将是脊柱骨盆重建的一种可行临床选择。
