Abstract：
BACKGROUND: Research on hip instability has focused on establishing \"safe\" ranges of combined component position in supine posture or functional placement of the acetabular component based on the hip-spine relationship. A new angle, the polar axis angle (PAA), of the total hip arthroplasty (THA) components describes the concentricity of both components and can be evaluated in functional positions that confer a greater risk of instability (ie, sitting). The goal of this study was to compare the PAA in functional positions between patients who experienced a postoperative dislocation and a matched control group who did not have a dislocation.
METHODS: An institutional database was searched for patients experiencing a dislocation after primary THA. Patients who had postoperative full-length standing and lateral-seatedradiographs were included in the dislocator group. A control group of nondislocator patients was matched 2:1 by age, body mass index, sex, and hip-spine classification. Radiographic measurements of the neck angle, acetabular ante-inclination, and PAA were performed by 2 separate blinded, trained reviewers.
RESULTS: The lateral-seated neck angle and lateral-seated PAA measurements were significantly lower in the dislocator groups (n = 37) than the control group (n = 74) (23 versus 33 degrees, P < .001; 74 versus 83 degrees, P = .012, respectively). Significant differences were also observed in changes in the polar axes and neck angles between standing and seated positions (P < .001 and P < .001, respectively). When comparing patients who have mobile spines versus stiff spines within the dislocator group, there were no differences in the acetabular, neck, or PAAs. The effect of neck angle on the PAA showed a linear trend across cohorts.
CONCLUSIONS: Patients who experience postoperative instability have a significantly lower PAA on lateral-seated radiographs when matched for age, sex, body mass index, and hip-spine classification. In addition, the lower seated PAA is driven more strongly by decreased functional femoral anteversion, which emphasizes the role of functional femoral version on stability in THA.
METHODS: An institutional database was searched for patients experiencing a dislocation after primary THA. Patients who had postoperative full-length standing and lateral-seatedradiographs were included in the dislocator group. A control group of nondislocator patients was matched 2:1 by age, body mass index, sex, and hip-spine classification. Radiographic measurements of the neck angle, acetabular ante-inclination, and PAA were performed by 2 separate blinded, trained reviewers.
RESULTS: The lateral-seated neck angle and lateral-seated PAA measurements were significantly lower in the dislocator groups (n = 37) than the control group (n = 74) (23 versus 33 degrees, P < .001; 74 versus 83 degrees, P = .012, respectively). Significant differences were also observed in changes in the polar axes and neck angles between standing and seated positions (P < .001 and P < .001, respectively). When comparing patients who have mobile spines versus stiff spines within the dislocator group, there were no differences in the acetabular, neck, or PAAs. The effect of neck angle on the PAA showed a linear trend across cohorts.
CONCLUSIONS: Patients who experience postoperative instability have a significantly lower PAA on lateral-seated radiographs when matched for age, sex, body mass index, and hip-spine classification. In addition, the lower seated PAA is driven more strongly by decreased functional femoral anteversion, which emphasizes the role of functional femoral version on stability in THA.
摘要：
背景：关于髋关节不稳定的研究集中在建立仰卧位或基于髋骨-脊柱关系的髋臼组件功能放置的组合组件位置的“安全”范围。一个新的角度，极轴角(PAA)，全髋关节置换术（THA）组件的同心度描述了这两个组件的同心度，并且可以在赋予更大的不稳定风险的功能位置进行评估（即，sitting).这项研究的目的是比较术后脱位患者的功能位置的极轴角度，和一个没有脱臼的对照组。
方法：在机构数据库中搜索原发性THA后出现脱位的患者。术后进行全长站立和坐位侧位X线片的患者被纳入脱位组。对照组的非脱位患者按年龄2：1匹配，体重指数（BMI），性别,和髋部脊柱分类。颈部角度的射线照相测量，髋臼前倾,和极轴角(PAA)由两个单独的盲法执行，训练有素的审稿人.
结果：与对照组（n=74）相比，脱位组（n=37）的侧位颈角度和侧位极轴角度测量值显着降低（23对33度，P<0.001；74对83度，分别为P=0.012)。在站立和坐姿之间的极轴和颈部角度的变化也观察到显着差异（分别为P<0.001和P<0.001）。当比较脱体组中有活动棘和僵硬棘的患者时，髋臼没有差异,脖子,或极轴角度。颈部角度对极轴角度的影响在队列中显示出线性趋势。
结论：出现术后不稳定的患者，当与年龄相匹配时，侧位X线片的极轴角明显较低，性别,BMI,和髋部脊柱分类。此外,较低的坐位极轴角度由减少的功能性股骨前倾驱动，强调了功能性股骨版本对THA稳定性的作用。
方法：在机构数据库中搜索原发性THA后出现脱位的患者。术后进行全长站立和坐位侧位X线片的患者被纳入脱位组。对照组的非脱位患者按年龄2：1匹配，体重指数（BMI），性别,和髋部脊柱分类。颈部角度的射线照相测量，髋臼前倾,和极轴角(PAA)由两个单独的盲法执行，训练有素的审稿人.
结果：与对照组（n=74）相比，脱位组（n=37）的侧位颈角度和侧位极轴角度测量值显着降低（23对33度，P<0.001；74对83度，分别为P=0.012)。在站立和坐姿之间的极轴和颈部角度的变化也观察到显着差异（分别为P<0.001和P<0.001）。当比较脱体组中有活动棘和僵硬棘的患者时，髋臼没有差异,脖子,或极轴角度。颈部角度对极轴角度的影响在队列中显示出线性趋势。
结论：出现术后不稳定的患者，当与年龄相匹配时，侧位X线片的极轴角明显较低，性别,BMI,和髋部脊柱分类。此外,较低的坐位极轴角度由减少的功能性股骨前倾驱动，强调了功能性股骨版本对THA稳定性的作用。
