Background: Several factors lead to cup malalignment including preoperative pelvic tilt, inaccurate pelvic position on the operating table, pelvic movement during the operation and alignment change after screw fixation of the cup. There are few studies about the deviation of cup alignment from target angle during press-fit insertion, which may be the other cause of cup malalignment. The purpose of this study was to evaluate the deviation of cup alignment from target angle during press-fit insertion by using imageless navigation and to define any influential factors, including gender, age and side of operation.

Methods: Between February 2016 and March 2017, patients undergoing total hip arthroplasty (THA) with imageless navigation were included in the present single-center study. Cup inclination angle was set at 40 degrees in all cases but the anteversion angle varied depending on the stem anteversion in each case using a combined anteversion technique. The final cup was aligned at target angles in both inclination and anteversion, the tracker was detached from the insertion handle and the surgeon inserted the cup until it was seated completely. The tracker was attached again to display both inclination and anteversion angles and these angles were recorded. Deviated Inclination Angles (DIA) and Deviated Anteversion Angles (DAA) in each case were calculated.

Results: There were 124 cases in the present study. The mean age of the patients was 60.2 years (25–93). There were equal numbers of right-sided and left-sided operations, 62 cases each. There were 114 cases (91.9%) with DIA. The mean DIA was 2.65^° (0^°–8^°, SD 1.66). The DIA decreased in 107 cases (86.3%) with 12 cases (9.7%) showing a decrease of 5^° or more. The DIA increased in 7 cases (5.6%) with 2 cases (1.6%) showing an increase of 5^° or more. There were 103 cases (83.1%) with DAA. The mean DAA was 2.3^° (0^°–14^°, SD 2.3). The DAA increased in 78 cases (62.9%) with 11 cases (8.3%) increasing by 5^° or more. The DAA decreased in 25 cases (20.2%) with 4 cases (3.2%) decreasing by 5^° or more. The DIA was significantly higher in males than in females (p = .012). There was significant correlation between DAA and patient’s age (p = .037). There was no significant difference between DIA or DAA and side of operation.

Conclusion: Changes in cup orientation were observed in most cases during cup insertion with hammer blows detected by imageless navigation. Deviation of cup alignment from target angle during press-fit insertion was a possible cause of cup malalignment, male gender and patient’s age were influential factors.

背景：导致杯错位的几种因素包括术前骨盆倾斜，手术台上骨盆位置不正确，手术期间骨盆运动以及螺钉固定杯后对准发生变化。关于压配合插入期间杯对准与目标角度的偏差的研究很少，这可能是杯对准不良的另一原因。这项研究的目的是通过使用无图像导航来评估压入配合过程中杯对准与目标角度的偏差，并定义任何影响因素，包括性别，年龄和手术方式。

方法：在2016年2月至2017年3月之间，本单中心研究包括接受无图像导航的全髋关节置换术（THA）的患者。杯倾角在所有情况下均设置为40度，但使用组合前倾技术，前倾角根据每种情况下的茎前倾而变化。最终的杯子在倾斜和前倾时均以目标角度对齐，将跟踪器从插入手柄上拆下，外科医生将杯子插入，直到其完全就位。再次连接跟踪器，以显示倾斜角度和前倾角度，并记录这些角度。计算每种情况下的偏斜角（DIA）和偏斜角（DAA）。

结果：本研究共124例。患者的平均年龄为60.2岁（25-93）。左侧和右侧手术的次数相等，每例62例。DIA有114例（91.9％）。平均DIA为2.65 ^°（0 ^° –8 ^°，SD 1.66）。DIA下降107例（86.3％），其中12例（9.7％）下降5 ^°或更多。DIA升高7例（5.6％），其中2例（1.6％）升高5 ^°或更多。DAA患者103例（83.1％）。平均DAA为2.3 ^°（0 ^° –14 ^°，SD 2.3）。DAA增加78例（62.9％），其中11例（8.3％）增加5 ^°或者更多。DAA下降25例（20.2％），其中4例（3.2％）下降5 ^°或更多。男性的DIA显着高于女性（p  = .012）。DAA与患者年龄之间存在显着相关性（p  = .037）。DIA或DAA与手术侧之间无显着差异。

结论：在大多数情况下，在插入杯子的过程中观察到杯子方向的变化，并且通过无图像导航检测到锤击。压入配合过程中杯对准偏离目标角度可能是杯对准不良的可能原因，男性和患者年龄是影响因素。