Spivak J M, Neuwirth M G, Labiak J J, Kummer F J, Ricci J L
Department of Orthopaedics, Hospital for Joint Diseases Orthopaedic Institute, New York, New York.
Spine (Phila Pa 1976). 1994 Apr 15;19(8):955-64. doi: 10.1097/00007632-199404150-00015.
The ability of hydroxyapatite (HA) materials to enhance the fixation strength of posterior spinal instrumentation was examined in 19 adult mongrel dogs.
Sixteen dogs underwent bilateral placement of lumbar transpedicular screws from L1 to L6, sacral alar screws, and posterior iliac rods. The six transpedicular screw test groups included standard and plasma-sprayed HA-coated screws with the recommended insertion technique, standard and HA-coated screws with a poor initial fit insertion technique using an oversized pilot hole, and HA-grout augmentation of standard and HA-coated screws with a poor initial fit. The sacral alar screws and posterior iliac rods were either uncoated or HA-coated. Six dogs were killed immediately; ten dogs were killed at 6 weeks, and the fixation elements were mechanically tested or histologically examined. Three additional dogs and synthetic bone material were used for additional baseline mechanical testing.
The strength of standard screws with recommended insertion did not change after 6 weeks in vivo. HA-coated screws were initially 13% less resistant to pull out than standard screws, but this difference was not significant at 6 weeks. Screws inserted with a poor initial fit technique were significantly weaker initially; at 6 weeks, pull-out strength was similar to the standard screws properly inserted. The HA-grout material significantly enhanced pull-out strength for both screw types at 6 weeks. Sacral alar screw pull-out strength was not significantly different between standard and HA-coated screws initially or at 6 weeks. HA-coated rods were initially twice as resistant to pull out than standard rods and became stronger after 6 weeks in vivo, whereas standard rods became significantly weaker. Histologically, the quantity and morphology of bone around all implants was similar, with HA-coated rods and screws demonstrating regions of direct attachment to bone. An osteoconductive response and new bone formation was observed within the HA-grout material. Scanning electron microscopic observation of mechanically tested implants revealed a shear failure of surrounding bone (and HA if present) at the screw outer thread margin or at the bone-metal or HA-metal interfaces for the posterior iliac rods.
The strength of poorly inserted transpedicular screws was significantly enhanced in vivo by the resorbable HA-grout material. The lower strength of HA-coated screws was attributed to screw geometry changes resulting from the coating process, and modifications of screw coating are recommended.
在19只成年杂种犬中检测了羟基磷灰石（HA）材料增强后路脊柱内固定强度的能力。
16只犬接受了从L1至L6的双侧腰椎椎弓根螺钉、骶骨翼螺钉和髂后棒置入。六个椎弓根螺钉测试组包括采用推荐置入技术的标准螺钉和等离子喷涂HA涂层螺钉、采用超大导向孔的初始配合不佳置入技术的标准螺钉和HA涂层螺钉，以及对初始配合不佳的标准螺钉和HA涂层螺钉进行HA骨水泥增强。骶骨翼螺钉和髂后棒要么未涂层，要么为HA涂层。6只犬立即处死；10只犬在6周时处死，对固定元件进行力学测试或组织学检查。另外使用3只犬和合成骨材料进行额外的基线力学测试。
采用推荐置入的标准螺钉在体内6周后强度未改变。HA涂层螺钉最初的拔出阻力比标准螺钉低13%，但在6周时这种差异不显著。采用初始配合不佳置入技术置入的螺钉最初明显较弱；在6周时，拔出强度与正确置入的标准螺钉相似。HA骨水泥材料在6周时显著增强了两种螺钉类型的拔出强度。标准螺钉和HA涂层螺钉在骶骨翼螺钉的初始和6周时的拔出强度无显著差异。HA涂层棒最初的拔出阻力是标准棒的两倍，在体内6周后变强，而标准棒则显著变弱。组织学上，所有植入物周围骨的数量和形态相似，HA涂层棒和螺钉显示出与骨直接附着的区域。在HA骨水泥材料内观察到骨传导反应和新骨形成。对力学测试后的植入物进行扫描电子显微镜观察发现，在后路髂棒的螺钉外螺纹边缘或骨-金属或HA-金属界面处，周围骨（以及如有HA）发生剪切破坏。
可吸收的HA骨水泥材料在体内显著增强了置入不佳的椎弓根螺钉的强度。HA涂层螺钉强度较低归因于涂层过程导致的螺钉几何形状改变，建议对螺钉涂层进行改进。
