Upasani Vidyadhar V, Farnsworth Christine L, Tomlinson Tucker, Chambers Reid C, Tsutsui Shunji, Slivka Michael A, Mahar Andrew T, Newton Peter O
Department of Orthopedic Surgery, University of California San Diego, San Diego, CA, USA.
Spine (Phila Pa 1976). 2009 Feb 15;34(4):335-43. doi: 10.1097/BRS.0b013e318194878d.
Biomechanical and histologic analysis.
To compare the strength of the bone-screw interface of standard uncoated pedicle screws with screws treated with hydroxyapatite (HA), titanium plasma spray (TPS), and a composite HA-TPS coating.
Transpedicular screw fixation has become the gold standard in the treatment of various thoracolumbar spinal conditions. Pedicle screw loosening, however, has been reported, especially in mechanically demanding constructs or in vertebrae with low bone mineral density.
Six mature porcine were instrumented with 4 types of titanium monoaxial pedicle screws (uncoated, HA-only coated, TPS-only coated, and HA-TPS composite coated) in a systematically varied, single-blinded fashion. After a 3-month survival period, the spines were harvested en-bloc and "time zero" control screws were instrumented in adjacent vertebrae. Screw placement and bone mineral density were evaluated with a postharvest computed tomography, and the strength of the tissue-implant interface was evaluated with a torsional screw extraction analysis (60 screws) and a nondecalcified histologic analysis (16 screws).
At 3 months postoperative, peak torque increased for all 3 types of coated screws (increased fixation) and decreased significantly for the uncoated screws (P < 0.001). Although 3-month peak torque was not statistically different between the 3 screw coatings, 4 of 10 TPS-only coated screws had a peak torque that was nearly 0 (<0.1 N m) versus only 1 of 10 HA-only screws and 0 of 10 HA-TPS composite screws. Histologic analysis confirmed the biomechanical findings with improved osseointegration in the HA-only and HA-TPS composite screws.
Pedicle screw coatings that promote mechanical interlocking, TPS, or direct osteoblast bonding(HA) increased screw fixation in this nonfusion model. More non-HA coated screws, however, were thought to be "loose" with a nearly zero peak extraction torque and fibrous encapsulation. Increased osseointegration with HA may result in a decreased incidence of screw loosening and improved outcomes of transpedicular spinal instrumentation in nonfusion procedures.
生物力学和组织学分析。
比较标准无涂层椎弓根螺钉与经羟基磷灰石（HA）、钛等离子喷涂（TPS）及HA-TPS复合涂层处理的螺钉的骨-螺钉界面强度。
椎弓根螺钉固定已成为治疗各种胸腰椎脊柱疾病的金标准。然而，已有报道称椎弓根螺钉会松动，尤其是在对机械要求较高的结构中或在骨密度较低的椎体中。
对6只成年猪以系统变化的单盲方式植入4种类型的钛单轴椎弓根螺钉（无涂层、仅HA涂层、仅TPS涂层和HA-TPS复合涂层）。在3个月的存活期后，将脊柱整块取出，并在相邻椎体中植入“零时”对照螺钉。用收获后的计算机断层扫描评估螺钉置入情况和骨密度，并用扭转螺钉拔出分析（60枚螺钉）和非脱钙组织学分析（16枚螺钉）评估组织-植入物界面的强度。
术后3个月时，所有3种涂层螺钉的峰值扭矩均增加（固定增强），无涂层螺钉的峰值扭矩显著降低（P < 0.001）。虽然3种螺钉涂层之间的3个月峰值扭矩在统计学上无差异，但10枚仅TPS涂层的螺钉中有4枚的峰值扭矩几乎为0（<0.1 N·m），而10枚仅HA涂层的螺钉中只有1枚，10枚HA-TPS复合涂层的螺钉中则为0枚。组织学分析证实了生物力学研究结果，即仅HA涂层和HA-TPS复合涂层螺钉的骨整合得到改善。
在这个非融合模型中，促进机械互锁的椎弓根螺钉涂层（TPS）或直接成骨细胞结合（HA）可增强螺钉固定。然而，更多非HA涂层的螺钉被认为是“松动的”，其拔出峰值扭矩几乎为零且有纤维包裹。HA骨整合增加可能会降低螺钉松动的发生率，并改善非融合手术中椎弓根脊柱内固定的效果。
