Is Dislocation Risk due to Posterior Pelvic Tilt Reduced With Direct Anterior Approach Total Hip Arthroplasty?

BackgroundPelvic tilt affects acetabular anteversion, and thus total hip arthroplasty (THA) dislocation risk. The pubic symphysis-sacrococcygeal distance (PSCD) is an indicator of pelvic tilt, and a PSCD < 0 mm (ie, excessive posterior pelvic tilt) is associated with a 3.7-fold increase in postoperative dislocation rate. However, it is not known if the direct anterior (DA) approach might reduce this dislocation rate, specifically in high-risk populations such as negative PSCD.MethodsStanding anteroposterior radiographs were reviewed for 510 consecutive DA THAs to determine PSCD. Patients were separated into 2 groups: (1) PSCD > 0 mm (PSCD[+]) and (2) PSCD < 0 mm (PSCD[−]). Incidence of dislocation was determined. We recorded if patients had spinal deformity or lumbar fusion. Continuous variables were analyzed using Student’s t-test, categorical variables were analyzed using Fisher’s exact test, and a sample size calculation was performed.ResultsThree hundred fifty-eight hips (70.2%) were PSCD[+], while 152 hips (29.8%) were PSCD[−]. Three dislocations (3/510 hips, 0.6%) occurred. Two dislocators were in the PSCD[−] group (2/152 hips, 1.3%) and 1 dislocator was in the PSCD[+] group (1/358 hips, 0.3%) (P = .21). Twenty-four patients had degenerative scoliosis (24/510, 4.7%), of which 1 had a dislocation (1/24, 4.2%); 2 dislocations occurred in nonscoliosis patients (2/486, 0.4%) (P = .134). Twenty-seven patients had lumbar spinal fusion (27/510, 5.3%), of which there were no dislocations (0/27, 0.0%); all dislocations were in nonfusion patients (3/483, 0.6%) (P = 1.0).ConclusionWe demonstrate no increased risk for THA dislocation in patients with a PSCD < 0 mm who have undergone a DA approach. These data would suggest a protective effect of the DA approach against dislocation, even in historically high-risk populations.     

Preoperative Posterior Tilt Increases the Risk of Later Conversion to Arthroplasty After Osteosynthesis for Femoral Neck Fracture

BackgroundFemoral neck fractures (FNFs) are one of the most common injuries in the elderly. Treatment is either internal fixation or primary arthroplasty. The main aim of this study is to assess the risk factors associated with fixation failure leading to further arthroplasty in FNFs treated with cannulated screws.MethodsData on internal fixations of FNFs performed at Turku University Hospital between January 1, 2012 and December 31, 2017 were collected retrospectively from the patient database. Radiographical measurements were performed for preoperative displacement and posterior tilt, postoperative displacement, reduction quality, and implant shaft angle.ResultsAltogether 301 cases were included in the study. The overall reoperation rate was 25% and conversion to arthroplasty was performed in 16% of cases. In the multiple variant analysis, adjusted for age and gender, nondisplaced fractures with a 0°-20° preoperative posterior tilt had a significantly lower risk of later conversion to arthroplasty than did nondisplaced fractures with a ≤0° or ≥20° posterior tilt (odds ratio [OR] 4.0, 95% confidence interval [Cl] 1.8-8.6, P = .0005) and displaced fractures (OR 7.2, 95% CI 3.0-17.4, P < .0001). No statistically significant association was found between preoperatively nondisplaced fractures with a <0° or ≥20° posterior tilt and displaced fractures (OR 0.6, 95% Cl 0.2-1.3, P = .2).ConclusionDisplaced fractures and fractures with a preoperative posterior tilt of <0° or ≥20° have a considerably increased risk of reoperation and conversion to arthroplasty. Primary arthroplasty should be considered as treatment for displaced FNFs and fractures with >20° or <0° posterior tilt, especially in fragile patients, to avoid further operations.     

Receptive fields of units in the visual cortex of the cat in the presence and absence of bodily tilt

Summary The receptive fields of units in the visual cortex of anaesthetised cats were studied using spots or slits of light. Some fields were found to be stable when they were repeatedly plotted with the cat maintained in the horizontal position: other fields were not stable and the sharpness of spatial tuning varied though the orientation of the axis did not shift. When the cat was tilted the field axis of the majority of cells followed the tilt. In 14 cells, however, changes occurred in the receptive field which were not observed when the animal remained in the horizontal plane. These changes included drifts of the field axis in a direction which, with one exception, was opposite to the tilt, and alterations in the spatial extent of the field. On returning the animal to horizontal the axis of 4 fields drifted past the original orientation. These effects were not eliminated by either bilateral destruction of the labyrinth or high cervical transection of the spinal cord. The time of onset of the tilt effects varied from cell to cell: some of this variability is probably an effect of anaesthesia.The findings are consistent with the view that the receptive field of certain cells in the visual cortex are capable of being modified, one of the modifying influences being the orientation of the body in space.This work was supported by grants from the Science Research Council to G. Horn and from the U.S. Public Health Service to G. Stechler (Grant MH 16215) and R.M. Hill (Grant NB 05653).     

Can imaginary head tilt shorten postrotatory nystagmus?

In healthy subjects, head tilt upon cessation of a constant-velocity yaw head rotation shortens the duration of postrotatory nystagmus. The presumed mechanism for this effect is that the velocity storage of horizontal semicircular canal inputs is being discharged by otolith organ inputs which signal a constant yaw head position when the head longitudinal axis is no longer earth-vertical. In the present study, normal subjects were rotated head upright in the dark on a vertical-axis rotational chair at 60°/s for 75 s and were required to perform a specific task as soon as the chair stopped. Horizontal position of the right eye was recorded with an infra-red video camera. The average eye velocity (AEV) was measured over a 30-s interval following chair acceleration/deceleration. The ratios (postrotatory AEV/perrotatory AEV) were 1.1 (SD 0.112) when subjects (N=10) kept their head erect, 0.414 (SD 0.083) when subjects tilted their head forward, 1.003 (SD 0.108) when subjects imagined watching a TV show, 1.012 (SD 0.074) when subjects imagined looking at a painting on a wall, and 0.995 (SD 0.074) when subjects imagined floating in a prone position on a lake. Thus, while actual head tilt reduced postrotatory nystagmus, the imagination tasks did not have a statistically significant effect on postrotatory nystagmus. Therefore, velocity storage does not appear to be under the influence of cortical neural signals when subjects imagine that they are floating in a prone orientation. Electronic Publication     

Atrioventricular dissociation as a cause of syncope determined by head-up tilt test

This report describes a patient with syncopal attacks in a sitting position on a reclining seat, in whom atrioventricular dissociation due to accelerated ventricular rhythm was determined to be the cause by recording of the electrocardiogram, blood pressure, and mitral and aortic Doppler flow during a 60 degree head-up tilt test.     

Regulation of subcutaneous blood flow during head-up tilt (45°) in normals

Local and remote regulation of subcutaneous blood flow in the forearm and leg was studied during head-up tilt (45°) in 6 young healthy male subjects. Relative blood flow was estimated by the local ¹³³Xe washout technique. Lowering of a leg lead to a 51 % decrease in its subcutaneous blood flow due to a veno-arteriolar reflex elicited by the increase in venous transmural pressure. During head-up tilt subcutaneous blood flow in the arm remaining at heart level decreased by 27%, in the leg blood flow decreased by 50%. Following proximal nervous blockade, head-up tilt did not induce vasoconstriction in forearm at heart level, but blood flow in distal leg decreased by 45%. Thus there was no difference in the vasoconstrictor response in the leg to head-up tilt or lowering of the labelled area by 40 crn. Since head-up tilt caused neurogenically mediated vasoconstriction in subcutaneous tissue, subcutaneous blood flow in the extremities seems to be regulated by remote (baroreceptor) as well as local sympathetic reflex mechanisms (veno-arteriolar reflex).     

倾斜试验加硝酸异山梨醇酯舌下含化在不明原因晕厥诊断中的价值

目的：探讨倾斜试验和硝酸异山梨醇酯舌下含化倾斜试验在不明原因晕厥诊断中的价值。方法：６８例不明原因晕厥者随机均分为直立倾斜试验（ＴＴＴ）组及硝酸异山梨醇酯舌下含化倾斜试验（ＩＤ＋ＢＴＴＴ）组。结果：ＴＴＴ组总阳性率为７３．５％,ＩＤ＋ＢＴＴＴ组为６０．６５％,两组阳性率无统计学差异（ｘ＾２＋１．２６８,Ｐ〉０．０５）,特异性亦无显著性差异（９２．９％与９３．３％,Ｐ〉０．０５０。ＩＤ＋ＢＴＴＴ组诱     

直立倾斜试验后自主神经功能恢复特点初探

目的通过倾斜试验前后心率变异的变化探讨倾斜试验以及倾斜试验过程中应用异丙肾上腺素（isoproterenol）对自主神经有无较持续的影响及试验的安全性。方法对64例有晕厥史或晕厥前兆患者进行倾斜试验,分为基础倾斜试验（basic tilt table test,BTTT）阳性组5例和阴性组59例,异丙基肾上腺素倾斜试验（isoproterenol tilt table test,ITTT）阳性组31例和阴性组18例。选择倾斜试验前5min及倾斜试验结束后1h5min进行心率变异频域法分析,提取tatol、ulf、vlf、lf、hf、lf/hf6项参数。结果全部病例倾斜试验前后6项参数对比,除vlf外（p=0.011）,其余各项无显著性差异,p〉0.1。BTTT阳性组倾斜试验前后对比,无显著性差异,p〉0.08;BTTT阴性组倾斜试验前后对比,除vlf外（p=0.03）,其余各项无显著性差异,p〉0.1。ITTT阳性组倾斜试验前后对比,无显著性差异,p〉0.1;ITTT阴性组倾斜试验前后对比,除hf外（p=0.013）,其余各项无显著性差异,p〉0.1。BTTT阳性组与阴性组对比,无显著性差异,p〉0.4。ITTT阳性组与阴性组对比,无显著性差异,p〉0.1。结论提示倾斜试验前与倾斜试验结束后1h时,心率变异分析除个别参数外,无显著性差异和规律性变化。倾斜试验结束后1h,自主神经的活动已基本恢复到原来状态。倾斜试验以及倾斜试验过程中应用药物（isoproterenol）对自主神经的影响是暂时的,检查后的安全性较好,对检查程序、病人检查后的留观时间有指导意义。     

倾斜试验中晕厥患者自主神经功能的变化

目的　运用频谱法研究直立倾斜试验中血管性晕厥的发生机制。方法　对 2 7例不明原因晕厥患者行直立倾斜试验 ,运用频谱法计算低频 (LF)、高频 (HF)及LF/HF的变化。结果　 15例发生晕厥或先兆晕厥 (阳性组 ) ,12例未出现症状 (阴性组 ) ,倾斜前两组LF、HF和LF/HF差异无显著性 ;阴性组倾斜后即刻HF明显下降 ,LF/HF显著升高 ,平卧后恢复到倾斜前水平 ,阳性组晕厥或先兆晕厥发作时 ,HF突然升高 (10 4 7± 4 0 4→ 32 95± 10 4 8) ,明显高于倾斜前 (2 3 4 4± 4 2 0→32 95± 10 4 8,P <0 0 5 ) ,LF/HF显著下降 (3 2 8± 0 39→ 1 0 7± 0 31,P <0 0 1) ,试验终止平卧后 ,HF和LF/HF恢复 ,两组LF在倾斜前后不同阶段均无明显变化。结论　在平卧、静息状态下 ,阳性患者和阴性患者的自主神经功能差异无显著性 ,倾斜后阳性患者迷走神经兴奋性在抑制过程中突然过度增强 ,导致晕厥或先兆晕厥发生。