Procter P, Bennani P, Brown C J, Arnoldi J, Pioletti D P, Larsson S
Stryker Osteosynthesis, Selzach, Switzerland; School of Engineering and Design, Brunel University, Uxbridge, UK.
School of Engineering and Design, Brunel University, Uxbridge, UK.
Clin Biomech (Bristol). 2015 Jun;30(5):500-6. doi: 10.1016/j.clinbiomech.2015.03.003. Epub 2015 Mar 7.
Orthopaedic surgeons often face clinical situations where improved screw holding power in cancellous bone is needed. Injectable calcium phosphate cements are one option to enhance fixation.
Paired screw pullout tests were undertaken in which human cadaver bone was augmented with calcium phosphate cement. A finite element model was used to investigate sensitivity to screw positional placement.
Statistical analysis of the data concluded that the pullout strength was generally increased by cement augmentation in the in vitro human cadaver tests. However, when comparing the individual paired samples there were surprising results with lower strength than anticipated after augmentation, in apparent contradiction to the generally expected conclusion. Investigation using the finite element model showed that these strength reductions could be accounted for by small screw positional changes. A change of 0.5mm might result in predicted pullout force changes of up to 28%.
Small changes in screw position might lead to significant changes in pullout strength sufficient to explain the lower than expected individual pullout values in augmented cancellous bone. Consequently whilst the addition of cement at a position of low strength would increase the pullout strength at that point, it might not reach the pullout strength of the un-augmented paired test site. However, the overall effect of cement augmentation produces a significant improvement at whatever point in the bone the screw is placed. The use of polymeric bone-substitute materials for tests may not reveal the natural variation encountered in tests using real bone structures.
骨科医生经常面临需要提高松质骨中螺钉把持力的临床情况。可注射磷酸钙骨水泥是增强固定的一种选择。
进行了配对螺钉拔出试验，其中用磷酸钙骨水泥增强人尸体骨。使用有限元模型研究对螺钉位置放置的敏感性。
对数据的统计分析得出，在体外人尸体试验中，骨水泥增强通常会提高拔出强度。然而，在比较单个配对样本时，出现了令人惊讶的结果，增强后强度低于预期，这显然与普遍预期的结论相矛盾。使用有限元模型进行的研究表明，这些强度降低可以由螺钉位置的微小变化来解释。0.5毫米的变化可能导致预测拔出力变化高达28%。
螺钉位置的微小变化可能导致拔出强度的显著变化，足以解释增强松质骨中单个拔出值低于预期的情况。因此，虽然在低强度位置添加骨水泥会增加该点的拔出强度，但它可能达不到未增强配对试验部位的拔出强度。然而，无论螺钉置于骨内何处，骨水泥增强的总体效果都会产生显著改善。使用聚合骨替代材料进行试验可能无法揭示使用真实骨结构进行试验时遇到的自然变化。
