Total hip arthroplasty (THA) is a well developed technique to which the spatial orientation of acetabular component is crucial. Since the idea of "safe zone" being proposed, such idea has long been obeyed by hip surgeons but has also been challenged in recent years. This is because post-operative instability could happen even if acetabular components are placed within "safe zone" . The latest researches have demonstrated that sagittal spinal balance and spino-pelvic mobility can affect the spatial orientation of acetabular components. Factors including spinal degenerative changes, long lumbosacral changes and spinal ankyloses can lead to sagittal spinal imbalance and/or influence spino-pelvic mobility, which subsequently affect pelvic retroversion. Proper pelvic retroversion is a way to compensate for sagittal spinal imbalance and is beneficial to post-operative stability. It is necessary for hip surgeons to rethink "safe zone" before performing THA and understand spinal balance as well as spinopelvic mobility. The goal is to reduce the rate of dislocation. This review started by introducing the related spinopelvic parameters frequently seen in papers published recently and the definitions of acetabular cup orientations. After the spinal sagittal balance and its compensatory mechanisms session, discussed its clinical relevance, as well as the significance of spinal mobility, in spinopelvic motion under three different postures.

Objective:To investigate the effect and safety of the hi-channel in one-stage of minimally invasive pereutaneous nephrolithotomy (mPCNL) in management of complicated renal calculi, compared with single chan-nel in two-stage of mPCNL. Methods: 57 patients underwent mPCNL in treatment of complicated renal calculi were retrospectively reviewed. 31 eases in group A underwent bi-channel in one-stage of mPCNL;26 eases in group B underwent single channel in two-stage of mPCNL. Results= The mean bleeding in the group A was 146. 4 m1(75-262.5 ml), compared with the group B 154.3 ml(75-300 ml), there was no statistically difference between the two groups (P>0.05). The mean operation time in the group A was 88. 4 rain(65-136 min), compared with the group B 123.1 min(70-180 min), there was statistically difference between them(P<0.05). Compared of the clearance rate of stone in the group A 83.9 % (26/31) and B 57.8% (15/26), there was statistically difference be-tween them (P<0.05). Conclusions:According the treatment of complicated renal calculi, the bi-ehannel in one-stage of mPCNL has shorter operation time, higher clearanee rate of stone, compared with single channel in two-stage of mPCNL. The patients need less expenses and shorter time staying in hospital. It is an ideal method.