AAOS:提高髋臼假体定位的准确性（1）

原文标题：Improving the Accuracy of Acetabular Component Orientation: Avoiding Malpositioning

1、Causes and Impacts of Poor Acetabular Component Positioning 髋臼假体位置不佳的原因与影响
        Many factors such as poor visualization, greater patient size, inaccuracies of mechanical guides, and changes in patient positioning during surgery can negatively impact acetabular component positioning. Improper orientation contributes to an increased dislocation rate, limb-length discrepancy,component impingement, bearing surface wear, and revision surgery. Acetabular malpositioning also contributes to altered hip biomechanics, pelvic osteolysis, and acetabular component migration. Despite the established definitions of acetabular safe zones, a recent analysis of United States Medicare total hip arthroplasty data revealed dislocation rates during the first six postoperative months to be 3.9% for primary arthroplasty and 14.4% for revision arthroplasty. A recent report cited instability and dislocation as accounting for 22.5% of revision cases。
       导致髋臼假体位置不佳的原因有很多，如显露不充分，患者体型较大，导向器不准确，以及术中患者体位发生变化等。定位不良会增加脱位率，导致肢体长度差异，假体撞击，界面磨损，甚至需要进行翻修手术。髋臼的位置异常也会改变髋关节的生物力学、导致骨盆骨质溶解和髋臼假体移位。虽然有髋臼安全区的概念，但此前一项基于美国医保体系全髋关节置换的研究显示，初次置换术后6个月内脱位率为3.9%，翻修手术为14.4%。而最近的一项研究显示翻修手术脱位和不稳的比率高达22.5%。

2、Larger Femoral Heads and Alternative Bearings 大直径股骨头与摩擦界面材料改进
      The use of larger femoral head sizes in primary total hip arthroplasty has increased dramatically in recent years with the introduction of alternative bearings and has reduced the short-term dislocation rate by almost one-half from 1998 to 2007 (from 4.21% to 2.14%).Dislocation rates have been lowered by increasing the femoral head-neck ratio, decreasing component impingement, increasing the range of hip motion until impingement, and increasing the jump distance when component impingement does occur.Nevertheless, larger femoral heads are not a substitute for proper component placement and precise component orientation; inaccurate component positioning may be associated with alteration in soft-tissue tension and hip biomechanics leading to abnormal gait, trochanteric bursitis, and increased discomfort during walking. All total hip arthroplasty bearing couplings are intolerant of component malpositioning or variation in component positioning; specifically, they are intolerant of excessive lateral opening and anteversion —and implant survivorship and complications are directly related to component positioning.
            从1998年至2007年，在初次全髋关节置换术中应用大直径股骨头和特殊的磨擦界面材料使得短期脱位率下降了将近一半（从4.21%降至2.14%）。通过增加股骨头颈比，减少假体撞击，增加髋关节无撞击的活动范围，增加髋关节撞击时所需“跳跃距离”，可有效降低脱位率。然而，大直径股骨头并不能取代假体精确的置入定位，假体定位偏移可能会改变软组织的张力和髋关节的生物力学，导致步态异常、大转子滑囊炎，并会增加行走时的不适感。全髋关节置换术中各种磨擦界面材料都不能耐受假体位置异常或者假体位置的变化。尤其无法耐受过度的外展和前倾，假体位置与内置物的生存率以及并发症直接相关。

3、Importance of Acetabular Component Positioning 髋臼假体定位的重要性
           Kurtz et al. forecast that the number of primary and revision hip arthroplasties will significantly increase over the next two decades. Annual demand is expected to rise to 570,000 primary and 97,000 revision total hip arthroplasty procedures by 2030. In a recent study of more than 50,000 total hip arthroplasty revisions, the most common cause of revision was instability and/or dislocation (22.5%), and the average cost per revision was in excess of $54,000. Improvement in acetabular component orientation will improve outcomes and reduce healthcare costs。
           Kurtz等曾预测，初次和翻修的髋关节置换在未来20年将会明显增加。在美国，到2030年，预计每年的需求量，初次置换将达57万例，翻修将达9.7万例。在最近的一项研究中，纳入了5万余例全髋关节置换的翻修病例，最常见的翻修原因为不稳和脱位（22.5%），翻修手术的平均费用超过5.4万美元。改善髋臼假体的位置有利于提高临床疗效，减少医疗卫生支出。

4、Use of ‘‘Safe Zones’’ for AcetabularComponent Placement  将髋臼假体安装在“安全区”
          The optimal orientation of the acetabular component remains controversial. Over the last three decades, the Lewinnek ‘‘safe zone’’ has become used as a standardized range for acetabular component placement in an attempt to reduce the risk of instability. The study by Lewinnek et al. helped orthopaedic surgeons to appreciate that outliers in acetabular component orientation are at higher risk for dislocation.However,the resulting concept of safe zone placement is derived from only nine cases of dislocation, and six of these involved revision total hip arthroplasty. Only a single case involved treatment of primary osteoarthritis, which is the most common indication for total hip arthroplasty for surgeons regardless of their arthroplasty experience. Three of the dislocations that did occur involved acetabular components within the safe zone.Additionally, only 113 of 291 patients without dislocation had radiographs of sufficient quality to determine acetabular inclination and anteversion。
          关于髋臼假体理想的位置仍然存在争议。在过去的三十多年中，Lewinnek的“安全区”一直被当作髋臼假体安装的标准范围，以试图降低不稳定的风险。Lewinnek等的这项研究有助于骨科医生明确髋臼假体存在较高脱位风险的异常位置。然而，假体安装安全区的概念，作为这一研究的结果，仅仅基于9例脱位，以及6例因此而行全髋关节翻修术的病例。并且只有1例的原发病是骨性关节炎，而骨关节炎是全髋关节置换术最常见的适应证，无论外科医生关节置换的经验如何。脱位的病例中有3例髋臼假体安装在”安全区“内。此外，291例没有脱位的患者中只有113例影像学质量符合要求。
           The question thus remains: Are conventional methods that aim to orient the acetabular component within the safe zone (defined by multiple authors) the best and most accurate techniques available for minimizing the risk of dislocation? For example, a component whose position is acceptable according to Lewinnek’s standard may be malpositioned according to the patient’s native anatomy. Three-dimensional surface models of the normal hemipelvis derived from volumetric data have revealed that the orientation of native acetabuli did not match the safe zone for acetabular component placement described by Lewinnek. The acetabular anteversion angle measured 19.9  ± 6  (range, 7  to 42 ) and was significantly larger in women (21.3 ± 7.1 ) compared with men (18.5  ± 5.8). Maruyama et al. concluded that this anatomic difference of-fered a possible explanation for the fact that the dislocation rate is higher in women。In addition to this concern, variability in acetabular component orientation has both an intersurgeon and an intrasurgeon component. The rate of malpositioning of acetabular cups has been reported to be 62% to 78% during arthroplasty with use of conventional techniques. The use of presurgical templating, based on radiographs and/or com-puted tomography (CT) scans, combined with intraoperative measurements is subject to inconsistencies and may be time-consuming; also, the patient positioning during preoperative imaging may introduce errors in templating calculations.Current methods for determining acetabular orientation include preoperative imaging (e.g., CT scans), intraoperative imaging (e.g., radiographs and fluoroscopy), and intra-operative anatomic tests. Regardless of how the safe zone is defined, orienting the acetabular component within this zone does not prevent dislocation (Figs. 1 and 2). Surgical techniques based on anatomic landmarks and on patient-specific morphology are evolving and may play a role in improving the accuracy of acetabular component orientation。
          这样，就留下了一个问题：为了使脱位的风险降至最低，将髋臼假体安装在安全区的常规方法（很多学者都赞同）是最好最准确的方法吗？比如，按照Lewinnek的标准，假体的位置尚可接受，而按照患者本来的解剖则可能判定为错位。有研究建立正常半骨盆的三维空间模型，通过容积数据分析，结果显示髋臼的解剖定位与Lewinnek所述安装髋臼假体的安全区并不匹配。经测量，髋臼前倾角为19.9° ± 6°（7°-42°），女性（21.3° ± 7.1°）明显大于男性（18.5° ± 5.8°）。Maruyama等推断，这种解剖差异为女性脱位率较高提供了一种可能的解释。除了上文考虑的因素外，髋臼假体位置的差异还受不同术者以及同一术者不同手术时间的影响。有研究报道，按照常规的方法进行关节置换，髋臼杯错位的发生率为62%-78%。基于X线和CT影像应用术前模板，结合术中的测量容易出现不一致，并且也比较费时。此外，术前进行影像学检查时患者的体位也可能导致模板测算的偏差。目前确定髋臼位置的方法包括术前影像（如CT扫描）、术中影像（如X线片和X线透视）以及术中的解剖定位。不管怎么定义安全区，将髋臼假体安装在这一区域内并不能避免脱位（图1和2）。目前主张在手术中参照解剖标志和患者特异性的形态，这对于提高髋臼假体定位的准确性具有重要意义。

5、Use of ‘‘Patient-Specific Morphology’’ to Establish a ‘‘Patient-Specific Target Zone’’ for Acetabular Component Placement 应用“患者特异性的形态”建立“患者特异性的目标区域”安装髋臼假体
          In total hip arthroplasty, use of patient-specific morphology refers to the practice of allowing the form and structure of the individual hip joint to guide surgical reconstruction and component placement; unlike safe zones, patient-specific morphology does not rely on averages. Although disease, severe dysplasia, or acetabular fracture may pose difficulties in some patients’ hips, certain structures may still often be used as guideposts for optimizing orientation, alignment, and stability.Patel et al. found decreased impingement and instability if the socket was aligned with landmarks or soft-tissue structures that are parallel to the rim of the native acetabulum. Cup placement in the original (natural) abduction and anteversion allowed nor-mal joint motion.At present, three options are available when selecting anatomic landmarks as guides for acetabular component placement: osseous landmarks, soft-tissue landmarks, or a combination of both. The four common methods involving patient-specific morphology all differ slightly in the anatomic landmark that is used: the method of Archbold et al. uses the transverse acetabular ligament,thatofSotereanosetal.uses the osseous landmarks encircling the acetabulum,that of McCollum and Gray uses the sciatic notch,andthat of Maruyama et al. uses the acetabular notch angle.All of these methods take advantage of patient-specific morphology to identify a patient-specific target zone to aid in the creation of a hip arthroplasty that minimizes impingement and implant wear.
             在进行全髋关节置换时，应用患者特异性的形态是指通过个体髋关节的形状和结构指导手术者重建和安装假体。与“安全区”不同，患者特异性的形态不依赖于平均数。虽然有些患者的髋关节由于某些病变、严重的发育不良或髋臼骨折等会增加处理的难度，但有些结构仍可以作为参照，有助于获得良好的定位、力线和稳定性。Patel等发现如果臼杯平行原始髋臼的边缘，与相关的骨性标志或软组织结构对齐，便可减少撞击和不稳。臼杯放置在原始的外展角和前倾角上，可使关节获得正常的活动度。目前在安装髋臼假体寻找解剖标志时，可以参照三个方面的信息：骨性标志、软组织标志以及两者相结合。关于“患者特异性的形态”主要有四种方法，各自在解剖标志上都有一些细微的差别：Archbold等的方法应用髋臼横韧带，Sotereanos等应用髋臼周围的骨性标志，McCollum和Gray应用坐骨大切迹，Maruyama等参照髋臼切迹角。所有这些方法都利用患者特异性的形态确定其特异性的目标区域，从而使髋关节置换术后撞击和内置物磨损降至最小。
髋臼横韧带Transverse Acetabular Ligament
            Archbold et al. described the use of the transverse acetabular ligament as a reference landmark for determining a patient’s native acetabular anteversion and then customizing the position of the cup so that the face of the acetabular componentis parallel to this ligament. The surgeon can also assess the depth and height of the acetabular component relative to the ligament. Using this ligament as an anatomic landmark to guide placement of the cup first requires complete exposure of the acetabulum and clear visualization of the ligament. The socket is then prepared by orienting the face of the acetabular reamers parallel to the ligament until the final reamer sits almost flush with, and just inside, the ligament. The goal is to customize the position of the acetabular component to match the individual patient’s natural anteversion and ab-duction as defined by the ligament and the residual labrum. This ideally optimizes the cupposition to restore the hip center of rotation and maximizes the possibility of center-ing the functional range of motion in the middle of the cup(Fig. 3). The position of the reamer or the acetabular compo-nent relative to the ligament provides the surgeon with real-time information about the depth, height, and anteversion of the socket (Fig. 4). If there is a gap between the ligament and the inferior margin of the cup, the cup is too high. If the socket is too deep, there will be space between the inferior edge of the cup and the inner margin of the ligament; this can be corrected with a lateralized liner. The residual acetabular labrum serves as a guide for determining the acetabular abduction.This surgical technique does not require any external guides, and the cup placement is independent of the patient’s position on the operating table. In a series of 1000 primary total hip arthroplasties performed with use of this technique, Archbold et al. reported a 0.6% dislocation rate with relatively small head sizes (28 mm) and without facechanging liners.
          Archbold等提出应用髋臼横韧带作为参照标志来判断患者本来的髋臼前倾角，使髋臼假体平行韧带，个体化地确定臼杯的位置。术者也可以通过髋臼假体与横韧带的相对位置来评价臼杯深度和高度。应用这一韧带作为解剖标志指导臼杯的安装，首先需要充分显露髋臼，能够清楚地直视韧带。然后平行韧带用髋臼锉确定方向依次打磨髋臼，直至髋臼锉差不多与横韧带相吻合，恰位于韧带内。目的是通过韧带和残留的盂唇，确定髋臼杯的位置，使其与患者个体原始的前倾角和外展角相匹配。这种理想的臼杯位置可以很好地恢复髋关节的旋转中心，并可最大限度地将功能活动范围控制在臼杯的中部（图3）。该手术方法不需要任何外在的导向器，臼杯的安装不受手术床上患者体位的影响。Archbold等在一组1000例初次全髋关节置换的病例中应用这一方法，采用直径相对较小的股骨头，没有使用改变髋臼方向的衬垫，据报道总的脱位率仅0.6%。
图3 应用横韧带确定臼杯的理想位置。A，360°固定窗显露髋臼，髋臼唇和髋臼横韧带都充分暴露；B，髋臼横韧带恰好包住髋臼锉的边缘（提示位于髋臼进口平面的功能位置上）；C和D，参照髋臼横韧带和髋臼唇最终将髋臼假体安装在理想的位置上。

图4：髋臼锉或髋臼假体相对于横韧带的位置，可为术者提供实时的信息，以判断髋臼杯的深度、高度和前倾角（图4）。如果韧带与臼杯下缘之间存在间隙，提示臼杯的位置过高。如果臼杯过深，臼杯下缘与韧带内缘之间会出现一定的间距，此时可以用外移衬垫（lateralized liner）进行矫正。而残留的髋臼上唇可以作为参照，确定髋臼的外展角。图4 髋臼锉相对髋臼横韧带的相对位置可实时地反映髋臼假体的位置。如图所示：a，髋臼假体的位置太高；b，太深；c，正确的高度、深度和前倾；d，高度深度均适当，但过度前倾；e，高度深度均合适，但存在后倾。