Ohkawa Yutaka, Tokunaga Kunihiko, Endo Naoto
Division of Orthopedic Surgery, Department of Regenerative and Transplant Medicine, Niigata University Graduate School of Medical and Dental Sciences, 1-757 Asahimachi-dori, Chuo-ku, Niigata 951-8510, Japan.
J Orthop Sci. 2008 Nov;13(6):533-42. doi: 10.1007/s00776-008-1275-x. Epub 2008 Dec 17.
As hydroxyapatite (HA) has good osteoconductive properties, HA is used as coating material for the implants in cementless arthroplasty. However, its effect is not sufficient for osteoporotic bone. Parathyroid hormone (PTH) is known to have anabolic effects on bone formation. Intermittent administration of PTH increases both cancellous and cortical bone mass. The aim of this study was to confirm the effect of the fixation strength of HA-coated implants in the osteoporotic condition with a mechanical test and a bone histomorphometric method.
Female Sprague-Dawley rats were used for this study. Four weeks after ovariectomy (OVX) or sham surgery, HA-coated titanium rods were inserted into the distal femoral canal (Sham+HA group and OVX+HA group). PTH was administered immediately after the implantation of the HAcoated rods (OVX+HA+P group). We measured the shear strength at the bone-implant interface by a push-out test and the newly formed bone volume on the implant (BV.Im) by bone histomorphometry at 2 and 4 weeks after implantation.
The bone-implant shear strength in the OVX+HA group was significantly lower than that in the Sham+HA group at 2 weeks after implantation of the rods. In the OVX+HA+P group, the strength was significantly higher than that in the other groups. Similarly, at 4 weeks, statistically significant differences were confirmed in the bone-implant shear strength among the Sham+HA group, the OVX+HA group, and the OVX+HA+P group. BV.Im in the OVX+HA group was significantly lower than that in the Sham+HA group at 2 weeks after implantation. BV.Im was significantly higher in the OVX+HA+P group than that in the OVX+HA group. However, there was no difference in BV.Im between the Sham+HA group and the OVX+HA+P group. At 4 weeks after implantation, BV.Im was significantly lower in the OVX+HA group than that in the other groups, but no difference was found between the Sham+HA group and the OVX+HA+P group.
Intermittent administration of PTH has an effect to increase new bone formation on the surface of HA-coated implants in the osteoporotic condition. This finding suggests that PTH administration is useful to improve the initial fixation of HA-coated implants even in osteoporotic patients.
由于羟基磷灰石（HA）具有良好的骨传导特性，因此在非骨水泥关节置换术中用作植入物的涂层材料。然而，其对骨质疏松骨的效果并不充分。已知甲状旁腺激素（PTH）对骨形成具有合成代谢作用。间歇性给予PTH可增加松质骨和皮质骨的骨量。本研究的目的是通过力学测试和骨组织形态计量学方法，确认HA涂层植入物在骨质疏松条件下的固定强度效果。
本研究使用雌性Sprague-Dawley大鼠。卵巢切除（OVX）或假手术后四周，将HA涂层钛棒插入股骨干骺端（假手术+HA组和OVX+HA组）。在植入HA涂层棒后立即给予PTH（OVX+HA+P组）。在植入后2周和4周，通过推出试验测量骨-植入物界面的剪切强度，并通过骨组织形态计量学测量植入物上的新形成骨体积（BV.Im）。
在植入棒后2周，OVX+HA组的骨-植入物剪切强度显著低于假手术+HA组。在OVX+HA+P组中，强度显著高于其他组。同样，在4周时，假手术+HA组、OVX+HA组和OVX+HA+P组之间的骨-植入物剪切强度存在统计学显著差异。植入后2周，OVX+HA组的BV.Im显著低于假手术+HA组。OVX+HA+P组的BV.Im显著高于OVX+HA组。然而，假手术+HA组和OVX+HA+P组之间的BV.Im没有差异。植入后4周，OVX+HA组的BV.Im显著低于其他组，但假手术+HA组和OVX+HA+P组之间没有差异。
间歇性给予PTH可增加骨质疏松条件下HA涂层植入物表面的新骨形成。这一发现表明，即使在骨质疏松患者中，给予PTH也有助于改善HA涂层植入物的初始固定。
