Zhou Jinsong, Espinoza Orías Alejandro A, Kang Xia, He Jade, Zhang Zhihai, Inoue Nozomu, An Howard S
Department of Orthopaedic Surgery, Rush University Medical Center, Chicago, Illinois.
Department of Orthopaedic Surgery, Chengdu Military General Hospital, Chengdu, Sichuan; and.
J Neurosurg Spine. 2016 Nov;25(5):572-579. doi: 10.3171/2016.4.SPINE151431. Epub 2016 Jun 24.
OBJECTIVE The segmental occipital condyle screw (OCS) is an alternative fixation technique in occipitocervical fusion. A thorough morphological study of the occipital condyle (OC) is critical for OCS placement. The authors set out to introduce a more precise CT-based method for morphometric analysis of the OC as it pertains to the placement of the segmental OCS, and they describe a novel preoperative simulation method for screw placement. Two new clinically relevant parameters, the height available for the OCS and the warning depth, are proposed. METHODS CT data sets from 27 fresh-frozen human cadaveric occipitocervical spines were used. All measurements were performed using a commercially available 3D reconstruction software package. The length, width, and sagittal angle of the condyle were measured in the axial plane at the base of the OC. The height of the OC and the height available for the segmental OCS were measured in the reconstructed oblique sagittal plane, fitting the ideal trajectory of the OCS recommended in the literature. The placement of a 3.5-mm-diameter screw that had the longest length of bicortical purchase was simulated into the OC in the oblique sagittal plane, with the screw path not being blocked by the occiput and not violating the hypoglossal canal cranially or the atlantooccipital joint caudally. The length of the simulated screw was recorded. The warning depth was measured as the shortest distance from the entry point of the screw to the posterior border of the hypoglossal canal. RESULTS The mean length and width of the OC were found to be larger in males: 22.2 ± 1.7 mm and 12.1 ± 1.0 mm, respectively, overall (p < 0.0001 for both). The mean sagittal angle was 28.0° ± 4.9°. The height available for the OCS was significantly less than the height of the OC (6.2 ± 1.3 mm vs 9.4 ± 1.5 mm, p < 0.0001). The mean screw length (19.3 ± 1.9 mm) also presented significant sex-related differences: male greater than female (p = 0.0002). The mean warning depth was 7.5 ± 1.7 mm. In 7.4% of the samples, although the height of the OC was viable, the height available for the OCS was less than 4.5 mm, thus making screw placement impractical. For these cases, a new preoperative simulation method of the OCS placement was proposed. In 92.6% of the samples that could accommodate a 3.5-mm-diameter screw, 24.0% showed that the entry point of the simulated screw was covered by a small part of the C-1 posterosuperior joint rim. CONCLUSIONS The placement of the segmental OCS is feasible in most cases, but a thorough preoperative radiological analysis is essential and cannot be understated. The height available for the OCS is a more clinically relevant and precise parameter than the height of the OC to enable proper screw placement. The warning depth may be helpful for the placement of the OCS.
目的 节段性枕髁螺钉(OCS)是枕颈融合术中一种可供选择的固定技术。对枕髁(OC)进行全面的形态学研究对于OCS的置入至关重要。作者着手引入一种基于CT的更精确方法,用于对与节段性OCS置入相关的枕髁进行形态学分析,并描述一种用于螺钉置入的新型术前模拟方法。提出了两个新的临床相关参数,即OCS可用高度和警示深度。方法 使用来自27例新鲜冷冻人尸体枕颈脊柱的CT数据集。所有测量均使用市售的三维重建软件包进行。在枕髁基部的轴平面上测量髁的长度、宽度和矢状角。在重建的斜矢状平面上测量枕髁的高度和节段性OCS可用高度,该平面符合文献中推荐的OCS理想轨迹。在斜矢状平面上模拟将具有最长双皮质固定长度的3.5毫米直径螺钉置入枕髁,螺钉路径不被枕骨阻挡,且在颅侧不侵犯舌下神经管,在尾侧不侵犯寰枕关节。记录模拟螺钉的长度。警示深度测量为螺钉进入点到舌下神经管后缘的最短距离。结果 发现男性枕髁的平均长度和宽度更大:总体上分别为22.2±1.7毫米和12.1±1.0毫米(两者p<0.0001)。平均矢状角为28.0°±4.9°。OCS可用高度明显小于枕髁高度(6.2±1.3毫米对9.4±1.5毫米,p<0.0001)。平均螺钉长度(19.3±1.9毫米)也存在显著的性别差异:男性大于女性(p = 0.0002)。平均警示深度为7.5±1.7毫米。在7.4%的样本中,尽管枕髁高度可行,但OCS可用高度小于4.5毫米,因此螺钉置入不切实际。对于这些病例,提出了一种新的OCS置入术前模拟方法。在92.6%能够容纳3.5毫米直径螺钉的样本中,24.0%显示模拟螺钉的进入点被C-1后上关节边缘的一小部分覆盖。结论 在大多数情况下,节段性OCS的置入是可行的,但术前进行全面的放射学分析至关重要,不可轻视。OCS可用高度是比枕髁高度更具临床相关性和精确性的参数,有助于正确的螺钉置入。警示深度可能有助于OCS的置入。