Barr Jennifer S, White Jedediah K, Punt Stephanie E W, Conrad Ernest U, Ching Randal P
Orthopedics. 2015 May;38(5):e417-22. doi: 10.3928/01477447-20150504-60.
The effect of simulated early weight bearing on both micromotion and pullout strength of uncemented distal femoral stems was evaluated in this study. The effect of stem endosteal contact and bone quality on implant pullout strength was also analyzed. A randomized matched-pair study was performed using 8 bilateral pairs of fresh human cadaveric femoral specimens. Each specimen pair was dual-energy x-ray absorptiometry scanned, uniformly implanted, fluoroscopically imaged, and randomly assigned to the cycled or uncycled group. The cycled group received 5000 cycles of axial compressive loading (to 700 N) and the contralateral side was not cycled. Micromotion was monitored during cycling and compared with a failure threshold (150 µm), and all implants underwent direct axial distraction (pullout) testing. During cycling, minimal micromotion was observed with an asymptotic decrease in differential motion between the first and last 50 cycles. Both cycled and uncycled groups demonstrated no statistical difference in average pullout force (4888±2124 N vs 4367±1154 N; P=.43). The percentage of cortical contact for each implant was determined from panoramic fluoroscopy images using digital image analysis software. Contact area for the distal third of the stem showed the highest correlation with pullout force and with predicting pullout force. Bone quality did not correlate with pullout force (r(2)=0.367) or stem contact area (r(2)=0.394). In sum, press-fit uncemented femoral stems did not loosen or demonstrate decreased pullout strength with early weight bearing simulated by cyclical axial compressive loading.
本研究评估了模拟早期负重对非骨水泥型股骨远端假体微动及拔出强度的影响。还分析了假体与骨内膜接触及骨质量对植入物拔出强度的影响。采用8对新鲜人尸体股骨标本进行随机配对研究。对每对标本进行双能X线吸收测定扫描、均匀植入、荧光透视成像，并随机分为循环组或非循环组。循环组接受5000次轴向压缩载荷循环（至700 N），对侧不进行循环。在循环过程中监测微动情况，并与失效阈值（150 µm）进行比较，所有植入物均进行直接轴向牵拉（拔出）测试。在循环过程中，观察到微动极小，且前50个循环与最后50个循环之间的差异运动呈渐近性下降。循环组和非循环组在平均拔出力方面无统计学差异（4888±2124 N对4367±1154 N；P = 0.43）。使用数字图像分析软件从全景荧光透视图像中确定每个植入物的皮质接触百分比。假体远端三分之一的接触面积与拔出力及预测拔出力的相关性最高。骨质量与拔出力（r(2)=0.367）或假体接触面积（r(2)=0.394）均无相关性。总之，通过周期性轴向压缩载荷模拟早期负重时，压配式非骨水泥型股骨假体未出现松动或拔出强度降低的情况。
