Dorr指数：髋关节置换术中的股骨近端髓腔粗细测量法

Dorr指数：髋关节置换术中的股骨近端髓腔粗细测量法

作者：Jacob Wilkerson, Navin D Fernando.

作者单位: J. Wilkerson, N. D. Fernando, University of Washington, Seattle, WA, USA.

译者：陶可（北京大学人民医院骨关节科）

历史

全髋关节置换术(THA)仍然是患有严重退行性髋骨关节炎和其他髋部疼痛病症（例如股骨头坏死）的患者最常用和临床上最成功的手术之一。自从Themistocles Glick教授于1891年描述了第一个全髋关节置换术(THA)的使用以来，假体的设计和理念已经发生了演变；他的象牙植入物被用来替代结核病患者的股骨头。John Charnley爵士被广泛认为是现代全髋关节置换术(THA)之父。他主张使用丙烯酸骨水泥来固定髋臼和股骨组件，并结合小直径股骨头以尽量减少磨损（“低摩擦髋关节置换术”）。

在Dorr分类之前，Noble等测量了股骨髓腔粗细直径指数，将近端股骨几何形状分为烟囱管道形(stovepipe)、正常形状(normal)和香槟杯托形(champagne flute)。股骨髓腔粗细直径指数测量为距小转子近端20 mm的近端股骨皮质内宽度与股骨干峡部皮质内宽度的比率。比率小于3的股骨被归类为“烟囱管道形”，比率为3到4.7的股骨被归类为“正常”，比率为4.7到6.5的股骨被归类为“香槟杯托形”。Dorr等扩展了这些发现，以研究与股骨近端形态差异相关的生物力学与组织学特性。

对早期骨水泥股骨设计的长期随访表明，最常见的翻修原因是无菌性松动。此外，骨水泥股骨固定翻修术的失败率高于初次全髋关节置换术(THA)。“骨水泥病”作为晚期失败的潜在原因促使人们对替代固定形式进行研究。特别是在北美，随着机械工程的进步促进了初始压配固定后的骨整合，非骨水泥假体的使用在20世纪80年代开始得到更广泛的应用。在这种情况下，需要一个分类系统来帮助确定哪些患者适合非骨水泥固定，其成功在某种程度上取决于股骨皮质骨的质量。

目的

早期的非骨水泥植入物的植入具有挑战性，第一代假体的支持者建议将其使用限制于股骨皮质骨坚固的患者。在这种背景下，Dorr等描述了一种分类系统，用于评估接受全髋关节置换术的患者平片上股骨的质量。即使在今天，对于股骨质量较差的患者是否应该使用非骨水泥假体仍存在争议，因此，Dorr等最初制定的标准。在某种程度上至今仍在使用。

与大多数骨科分类系统一样，股骨质量的Dorr分类系统可用于接受全髋关节置换术(THA)的患者的四个主要目的：临床决策、临床医生之间的沟通、确定重建的预后在多大程度上取决于骨质量、和临床研究。Dorr等描述的外科医生了解股骨距-股骨管腔比率也很重要，可用于模板（术前测量）以降低全髋关节置换术(THA)术中骨折的风险。

描述

Dorr分类根据放射学、生物力学和组织学数据评估股骨近端的质量（图1）。该研究基于52名接受初次全髋关节置换术(THA)的患者，描述了三种类型的股骨近端几何形状。在侧位X线片上尤其可以看出股骨类型的差异。

A型表示在正位和侧位X线片上看到厚且明显的皮质，形成狭窄的股骨管腔和股骨近端的“漏斗形”。侧位X线片显示厚厚的弯曲后方皮质。在最初的研究中，这种类型更常见于年轻、体重较重的男性患者。

Dorr A型股骨（“香槟形”）通常容纳扁平、锥形、近端多孔涂层柄（即“单楔形”或“刀片”），股骨柄的长度以及特定植入物的几何形状必须予以考虑。扁平、锥形、近端安装的股骨柄通常实现三点固定：靠近股骨干骺端的两个点，因为植入物的近端接合股骨近端的外侧肩部和内侧股骨距，第三个点靠近股骨干远端。

在某些Dorr A型股骨中，股骨干直径可能过于狭窄，导致植入物在最大限度地适合干骺端之前接合或“卡住”远端。这可能会产生一定程度的轴向稳定性，但通常会导致股骨植入物尺寸过小并且无法在干骺端内实现旋转稳定性。远端被卡住的股骨柄也可能过于挤压。

无论机械稳定性如何，都可能导致(术后)双下肢长度差异或需要减少股骨头或颈部长度以实现平横。尽管Dorr A型股骨患者通常具有较厚的皮质密度，但锥形磨锉的过度撞击可能会导致股骨干部分区域发生骨折。

Dorr B型股骨表明内侧和后皮质骨质流失，导致骨干管变宽，这种情况在男性中比女性更常见。侧位X光片上的B型股骨后脊受到侵蚀，皮质变平，并且破骨细胞活性活跃导致近端“鼠咬状改变”，以致于后脊的远端可能不存在。Dorr B型股骨通常适合大多数股骨柄设计，包括骨水泥型和非骨水泥型。然而，扁平、锥形的股骨柄很大程度上取决于近端皮质骨的质量和三维解剖结构，即使实现了轴向稳定性并且填充了中外侧皮质宽度，如果松质骨的质量较差，旋转稳定性也可能不足或因磨锉不准确而出现缺陷。因此，可以考虑使用骨干或完全骨干连接柄（或骨水泥柄）[25]。

Dorr C型表示内侧和后皮质大量丧失（后脊丧失），皮质的骨清晰度降低（“模糊”外观）。Dorr C型股骨近端被描述为具有“瘦腿”外观。它们的股骨近端髓腔管径较宽，多见于较瘦、老年和女性患者（图1）。Dorr C型股骨（“瘦腿型”）的几何形状通常有利于使用骨水泥柄。尽管在多项研究中，使用扁平、锥形干骨干和骨干柄在Dorr C型股骨中取得了临床成功，但对这些类型植入物的依赖可能会增加并发症的风险。Dorr等的原始研究在组织学上证实了Dorr C型股骨解剖结构通常与潜在的骨质减少相关。因此，使用锥形柄实现机械稳定性所需的力可能导致股骨骨折，通常发生在股骨距水平处。无论是扩髓还是最终假体定位，骨干连接柄都可能导致骨干断裂。其次，使用非骨水泥柄实现机械支撑所需的骨骼完整性可能会导致手术时或术后早期下沉时的轴向或旋转不稳定。使用水泥来实现立即机械交错通常会否定这种考虑。

每种类型均使用定量指标进行分析：皮质指数和股骨髓腔管径与距骨峡部比率（骨距比）。皮质指数定义为：小转子中点以远10 cm处，股骨骨干直径与髓内管直径之差与股骨骨干直径的比值，反映骨皮质厚度（图2）。股骨髓腔管径与股骨距峡部比率是在正位X线片上计算的，即股骨髓腔管径峡部除以股骨距处髓腔内管径，远端髓腔内管径扩大将具有较高的测量比率（图3）。

Dorr A型骨的皮质指数(0.58 ± 0.01)高于Dorr B型骨(0.50 ± 0.0)，Dorr B型骨的皮质指数高于Dorr C型骨(0.42 ± 1 0.01)，所有指标均具有统计学意义。

Dorr C型骨的骨距比(0.64 ± 0.02)也高于Dorr A型骨(0.57 ± 0.02)，但Dorr B型骨(0.59 ± 0.02)与Dorr A型或Dorr C型骨之间没有差异。比率是术前模板的一个重要方面，以避免术中骨折。在Dorr A型骨中，与干骺端相比，股骨管径较小，因此填充干骺端的模板可能会导致内侧股骨距或小转子骨折。此外，Dorr A型骨中厚的后脊可能会使骨干中的股骨柄向前移位，迫使股骨头进入后位置。这会使股骨柄翻转并影响稳定性。在Dorr C型骨中，干骺端可能小于骨干，因此填充骨干的模板可能会导致内侧距骨折。

Dorr等测量每个患者的血清钙（通过原子吸收分光光度法测量）、甲状旁腺激素（通过放射免疫测定法）和维生素D水平（通过液相色谱法），并发现这些值在正常范围内，并且三种Dorr类型之间没有统计差异。

对每种类型股骨的术中骨活检结果进行组织学评估，确定Dorr C型股骨近端在结构和细胞水平上均存在缺陷。从结构上看，Dorr A型骨的皮质骨比Dorr B型和Dorr C型骨厚，Dorr B型骨比C型骨厚。Dorr C型骨的类骨体积、类骨表面、骨的平均形成周期、成骨细胞表面、破骨细胞表面以及成骨细胞和破骨细胞的数量均大于Dorr A型和Dorr B型骨。Dorr A型骨和Dorr B型骨之间的这些参数没有差异。Dorr B型骨的皮质孔隙率高于Dorr A 型和Dorr C型骨，但在该参数方面，Dorr A型和Dorr C型骨之间没有检测到差异。

验证

Dorr分类用于骨科和非骨科专业，以评估股骨近端的形态。在最初的研究中，两名观察者对52名患者的正位和侧位X线片进行了两次检查以进行分类。第一次读数时观察者间差异小于20%，第二次读数时观察者间差异小于5%。自那时起，多项研究评估了Dorr分类的有效性，但结果各不相同。

Mazhar等评估了两名高级骨科住院医师、两名骨科医生和两名接受过关节置换术专科培训的外科医生的Dorr分类的观察者间和观察者内可靠性。在个体对间隔6周的50张正位髋关节X线片进行第一次和第二次审查后，计算观察者内部的可靠性，并在经验水平组内和经验水平组之间评估观察者间的可靠性。作者使用Cohen的kappa值来计算可靠性；Cohen的kappa范围从-1到1，其中0反映随机的一致性机会，1反映完全一致性。在Mazhar等的研究中，住院医师的平均总kappa值（观察者内和观察者内）为0.576，骨科医生为0.553，接受过专科培训的外科医生为0.484；这些kappa值太低，无法支持采用Dorr分类，并且在该研究中，作者发现经验并没有大幅提高可靠性。然而，Mazhar等仅审查了正位X线片。

然而，其他研究发现其可靠性更高，尤其是在经验丰富的医生中。2018年，Nakaya等评估了经验水平（三名初级和三名高级关节成形术外科医生）之间Dorr分类的再现性以及定量指标对观察者可靠性的影响。初级髋关节外科医生的检查员内部重复性为0.36、0.62和0.65，高级髋关节外科医生的内部重复性为0.7、0.86和0.87。与此同时，初级髋关节外科医生的检查者间重复性为0.32，专家髋外科医生为0.52。他们的发现表明，观察者间和观察者内的可靠性与临床经验水平呈正相关，尽管观察者间的可靠性仍然是一个严重的问题，即使在更有经验的医生中也是如此。当观察者还使用皮质指数作为辅助测量时（股骨骨干直径与髓内管直径之差与中小转子远端10cm处股骨骨干直径的比值）（图2），Dorr分类的可靠性显着提高，初级和高级髋关节外科医生的检查者内部重复性分别为0.89和0.86。基于此，我们强烈建议使用Dorr分类的外科医生将其与仔细计算的皮质指数结合使用（图22）。

在骨科手术之外，Sah等发现Dorr C型骨患者的T评分低于A型骨患者，而Singh指数和管距比与T评分无关。这表明Dorr分类可以指示患者的骨质量。然而，之前的一项研究表明，平片并不是评估患者骨质量最可靠的方法。在Sah等的研究中，观察者内部可靠性为92%，鉴于早期研究报告的观察者内部可靠性指标要低得多，这在某种程度上令人放心。我们相信Sah等报告的观察者内部可靠性更高。可能是因为他们使用正位X线和侧位X线片进行评估，这与Mazhar等的研究相反。

局限性

Dorr分类最重要的限制是评估它的研究之间的可靠性不一致。Kappa值约为0.5或更小，不支持分类系统的广泛使用；然而，两项研究发现Kappa值和一致性百分比具有更好的可靠性。

正如我们之前提到的，年龄很容易足够高以推荐使用该分类。一般来说，可靠性较高的研究拥有更有经验的医生，并使用皮质指数等定量指标作为辅助措施。供读者根据Dorr等对近端股骨形态进行分类。我们建议除了定性骨评估之外还使用皮质指数，并与经验丰富的外科医生讨论分类以提高可靠性。

尽管早期的非骨水泥假体很难植入，并且有导致皮质骨质量较差的患者发生股骨骨折的风险，因此Dorr分类对于植入物选择的决策至关重要，但最近的研究发现，现代非骨水泥假体通常是可靠的，即使对于股骨皮质骨质量较差（Dorr C型）的患者也是如此（表1）。这可能会让人质疑，Dorr分类是否能像以前那样为当代组件时代的临床决策提供有价值的贡献。无论如何，无法始终保证非骨水泥植入物的可靠机械固定，并且使用Dorr方法对股骨几何形状进行严格评估可能有助于识别可能受益于骨水泥技术的患者。

结论

尽管已发现Dorr分类在检查者间和检查者内部的可靠性不一致，但皮质指数的使用似乎提高了其可重复性。我们建议使用Dorr分类并注意侧位X线片以进行类型分类和皮质指数的计算。尽管Dorr C型骨曾经被认为排除了无骨水泥固定的使用，但现代股骨柄设计的研究已经证明了这种技术的持久固定。然而，外科医生还必须考虑到，Dorr C型患者往往年龄较大且不爱活动，术中使用非骨水泥THA造成骨折的后果可能会导致二次手术。此外，其中几项研究证明了非骨水泥植入物对较差股骨的疗效，患者数量相对较少，并且手术是由经验丰富的外科医生进行的。正如Leopold所说，新程序或技术的一些长期危险可能要到几年后才会被发现，并且需要非常大的样本量才能准确检测。我们相信，Dorr分类在患者选择方面仍然有用，特别是对于小手术量的外科医生来说，他们可能会考虑使用骨水泥技术来减少髋关节置换术期间的早期机械松动或股骨骨折。我们强烈强调术前模板的重要性，以确保股骨柄适合患者股管的几何形状，从而降低接受全髋关节置换术的患者发生医源性骨折的风险。应进行进一步的研究，以确定对患者骨形态的可靠且有用的评估，以降低THA期间发生术中骨折等并发症的风险。

Fig. 1 This figure shows the Dorr classification.

图1 该图显示了Dorr分类。

Fig. 2 This image shows the cortical thickness index. In this example, the cortical index is 0.5 ([A-B/A] = 50-25/50).

图2 显示了皮质厚度指数。在此示例中，皮质指数为0.5 ([A-B/A] = 50-25/50)。

Fig. 3 This image shows the calcar-to-canal ratio. In this example, the calcar-to-canal ratio would be 50% (B/A= 25/50).

图3 显示了股骨距与股骨管径的比例。在此示例中，股骨距与股骨管径的比率为50% (B/A= 25/50)。

Classifications in Brief: The Dorr Classification of Femoral Bone.

History

Total hip arthroplasty remains one of the most commonly performed and clinically successful procedures available to patients with severe degenerative arthritis and other painful conditions of the hip, such as osteonecrosis [17]. Implant design and philosophy have evolved since the use of the first THA, which was described by Professor Themistocles Glick in 1891; his ivory implant was used to replace the femoral heads of patients with tuberculosis [7]. Sir John Charnley [2] is widely considered the father of modern THA. He advocated for the use of acrylic bone cement to allow for fixation of the acetabular and femoral components, in conjunction with a small-diameter femoral head to minimize wear (“the low-friction arthroplasty”).

Before Dorr’s classification [6], Noble et al. [24] measured the canal flare index to divide the proximal femoral geometry among the stovepipe, normal, and champagne flute shapes. The canal flare index was measured as the ratio of the intracortical width of the proximal femur 20 mm proximal to the lesser trochanter to the intracortical width of the canal isthmus. Femurs with ratios of less than 3 were categorized as “stovepipe,” those with ratios of 3 to 4.7 as “normal,” and those with ratios of 4.7 to 6.5 as “champagne-fluted.” Dorr et al. [6] expanded on these findings to investigate the biochemical and histologic properties associated with differences in the morphology of the proximal femur.

Long-term follow-up of early cemented femoral designs suggested that the most-common cause of revision was aseptic loosening [14, 26]. Furthermore, revision arthroplasty with cemented femoral fixation demonstrated higher rates of failure than did primary THA [15]. “Cement disease” as a potential cause of late failure spurred investigation in alternative forms of fixation [12]. In North America in particular, the use of uncemented implants began to see wider use in the 1980s as advances in mechanical engineering facilitated osteointegration after initial press-fit fixation. In this context, a classification system was needed to help determine which patients were good candidates for uncemented fixation, the success of which was felt to depend to some degree on the quality of femoral cortical bone.

Purpose

Early cementless implants were challenging to implant, and proponents of those first-generation devices recommended limiting their use to patients with robust femoral cortical bone [13, 19]. In this context, Dorr et al. [6] described a classification system to evaluate the quality of the femur on plain radiographs in patients who undergo THA. There is debate even today about whether cementless devices should be used in patients whose femoral bone quality is poor [1, 4], and for that reason, the criteria initially developed by Dorr et al. [6] to some extent remain in use today.

As with most orthopaedic classification systems, the Dorr classification system of femoral bone quality can be used for four main purposes in patients undergoing THA: clinical decision-making, communication among providers, determining to what degree the prognosis of reconstructions may depend on bone quality, and research. It is also critical that surgeons understand the calcar-canal ratio, described in Dorr et al. [6], which can be used in templating to decrease risk of intraoperative fracture in THA.

Description

The Dorr classification evaluates the quality of the proximal femur according to radiographic, biochemical, and histologic data (Fig. ​(Fig.1).1). The study described three types of proximal femoral geometry based on 52 consecutive patients undergoing primary THA [6]. The differences in bone type can especially be appreciated on a lateral radiograph. Type A indicates thick and distinct cortices seen on AP and lateral radiographs, creating a narrow diaphyseal canal and “funnel shape” of the proximal femur. The lateral radiograph shows a thick curved posterior cortex (fin). In the original study, this type was more frequently found in younger, heavier, and male patients. Dorr Type A femurs (“champagne flute”) typically accommodate a flat, tapered, proximally porous coated stem (that is, a “single wedge” or “blade”), although the length of the stem as well as the specific implant’s geometry must be considered. Flat, tapered, proximally fitting stems typically achieve three points of fixation: two points near the metaphysis as the proximal aspect of the implant engages the lateral shoulder and medial calcar, and a third point near the distal aspect of the stem in the diaphysis [16]. In some Dorr Type A femurs, the meta-diaphyseal diameter can be excessively narrow, causing the implant to engage or get “caught up” distally before maximizing their fit in the metaphysis [3]. The may result in some degree of axial stability, but often results in a femoral implant that is undersized and fails to achieve rotational stability within the metaphysis. Stems that are caught up distally also may be excessively proud regardless of mechanical stability, resulting in the potential for leg length discrepancy or the need for reduced head or neck lengths to achieve equality. This may result in a leg-length discrepancy or the need for reduced head or neck lengths to achieve equality. Although patients with Dorr Type A femoral bone often have thick cortical densities, excessive impaction of tapered broaches may result in fracture in the metadiaphyseal region [27].

Type B indicates bone loss from the medial and posterior cortices resulting in a wider diaphyseal canal, which was found to be more prevalent in men than in women. Type B femurs on a lateral radiograph have erosion of the posterior fin with flattening of the cortex and proximal “rat bites” from active osteoclast activity. The distal end of the posterior fin may be absent. Dorr Type B femurs will typically accommodate most stem designs, both cemented and uncemented. However, flat, tapered stems largely depend on the quality of the proximal cortical bone and three-dimensional anatomy, and even if axial stability is achieved and the mediolateral cortical width is filled, rotational stability may be inadequate if the quality of cancellous bone is poor or becomes deficient because of inaccurate broaching. As such, a metadiaphyseal or fully diaphyseal engaging stem (or cemented stem) might be considered [25].

Type C indicates substantial loss of the medial and posterior cortices (loss of the posterior fin) with decreased bony definition of the cortices (a “fuzzy” appearance). Type C proximal femurs were described as having a “stovepipe” appearance. They had a wide canal diameter and were more often found in thinner, elderly, and female patients (Fig. ​(Fig.1).1). Dorr C Type femurs (“stovepipe”) have a geometry that often favors the use of a cemented stem. Although the use of flat, tapered metadiaphyseal and diaphyseal stems has been described with clinical success in Dorr Type C femurs in several studies [5, 22, 28], reliance on these styles of implant may be associated with an increased risk of complications [8, 30]. Dorr Type C femoral anatomy is typically associated with underlying osteopenia, as confirmed histologically in Dorr et al.’s original study [6]. The force necessary to achieve mechanical stability with a tapered broach thus may result in femoral fracture, typically at the level of the calcar. A diaphyseal-engaging stem may result in fracture at the diaphysis, either with reaming or final implant positioning. Second, the integrity of bone necessary to achieve mechanical support with an uncemented stem may result in axial or rotational instability at the time of surgery or early postoperative subsidence. The use of cement to allow for immediate mechanical interdigitation typically negates this consideration [10].

Each type was analyzed using quantitative indices: the cortical index and the canal-to-calcar isthmus ratio. The cortical index was defined as the ratio of the difference between the femoral diaphyseal diameter and intramedullary canal diameter over the femoral diaphyseal diameter at a point 10 cm distal to the mid-lesser trochanter as a reflection of the cortical thickness (Fig. ​(Fig.2).2). The canal-to-calcar isthmus ratio was calculated on an AP radiograph as a fraction of the intramedullary canal’s isthmus over the diameter of the intramedullary canal at the calcar. Widened distal intramedullary canals will have higher ratios for this measurement (Fig. ​(Fig.3).3). Cortical indices were higher in Type A bone (0.58 ± 0.01) than in Type B bone (0.50 ± 0.0) and higher in Type B bone than in Type C bone (0.42 ± 1 0.01), with all measures being statistically significant. Type C bone also had higher canal-to-calcar ratios (0.64 ± 0.02) than Type A bone did (0.57 ± 0.02), but no difference was identified between Type B (0.59 ± 0.02) and Types A or C. Calcar-canal ratios are an important aspect of preoperative templating to avoid intraoperative fracture. In Type A bone, the canal is small compared with the metaphysis, so templating to fill the metaphysis may result in fracture of the medial calcar or lesser trochanter. Additionally, the thick posterior fin in Type A bone may displace the stem anteriorly in the diaphysis, forcing the femoral head into a posterior position. This can retrovert the stem and impact stability. In Type C bone, the metaphysis might be smaller than the diaphysis, so templating to fill the diaphysis may result in fracture of the medial calcar.

Dorr et al. [6] measured serum calcium (measured by atomic absorption spectrophotometry), parathyroid hormone (by radioimmunoassay), and vitamin D levels (by liquid chromatography) in each patient and found these values to be within normal limits and not statistically different among the three Dorr types.

A histologic assessment of intraoperative bone biopsy results from each type of bone determined that Type C proximal femurs had deficiencies at both the structural and cellular level. Structurally, Type A bone had thicker cortical bone than Types B and C bone, and Type B bone was thicker than Type C bone. Osteoid volume, osteoid surface, the mean formation period of osteons, osteoblast surface, osteoclast surface, and numbers of osteoblasts and osteoclasts were all greater in Type C bone than in Types A and B bone. There were no differences in these parameters between Types A and B bone. Type B bone had greater cortical porosity than Types A and C bone, but no differences were detected between Types A and C for this parameter.

Validation

The Dorr classification is used in both orthopaedic and non-orthopaedic specialties to assess the morphology of the proximal femur. In the original study, AP and lateral radiographs from 52 patients were examined by two observers twice for classification. The interobserver variation was less than 20% at the first reading and less than 5% at the second reading [6]. Multiple studies have assessed the validity of the Dorr classification since then, with varied results [20, 23, 29].

Mazhar et al. [20] evaluated the interobserver and intraobserver reliability of the Dorr classification among two senior orthopaedic residents, two orthopaedic surgeons, and two arthroplasty fellowship-trained surgeons. The intraobserver reliability was calculated after individuals performed first and second reviews of 50 AP hip radiographs 6 weeks apart, and interobserver reliability was assessed within and between experience level groups. The authors used Cohen’s kappa value to calculate reliability; Cohen’s kappa ranged from -1 to 1, with 0 reflecting a random chance of agreement and 1 reflecting perfect agreement [21]. In Mazhar et al.’s study [20], the mean total kappa value (intraobserver and intraobserver) for residents was 0.576, 0.553 for orthopaedic surgeons, and 0.484 for fellowship-trained surgeons; these kappa values are too low to support adoption of the Dorr classification, and in that study, the authors found that experience did not improve reliability by very much. However, Mazhar et al. [20] only reviewed AP radiographs.

However, other studies have found greater reliability, particularly among more-experienced users. In 2018, Nakaya et al. [23] assessed the reproducibility of the Dorr classification between experience levels (three junior and three senior arthroplasty surgeons) and the effect of quantitative indices on observer reliability. The intraexaminer reproducibility was 0.36, 0.62, and 0.65 for junior hip surgeons and 0.7, 0.86, and 0.87 for senior hip surgeons. Meanwhile, the interexaminer reproducibility was 0.32 for junior hip surgeons and 0.52 for expert hip surgeons. Their finding suggested that interobserver and intraobserver reliability positively correlated with levels of clinical experience, although interobserver reliability remained a serious concern, even among more-experienced users. When observers also used cortical indices as an assistive measure (the ratio of the difference between the femoral diaphyseal diameter and intramedullary canal diameter over the femoral diaphyseal diameter at a point 10 cm distal to the mid-lesser trochanter) (Fig. ​(Fig.2),2), the reliability of the Dorr classification improved substantially, with an intraexaminer reproducibility of 0.89 and 0.86 for junior and senior hip surgeons, respectively [23]. Based on this, we strongly recommend that surgeons using the Dorr classification employ it in conjunction with carefully calculated cortical indices (Fig. ​(Fig.22).

Outside orthopaedic surgery, Sah et al. [29] found that patients with Type C bone had lower T scores than those with Type A bone did, in contrast to the Singh index and canal-to-calcar ratio, which were not associated with T scores. This demonstrated that the Dorr classification may indicate a patient’s bone quality. However, a prior study showed that plain radiographs are not the most-reliable was to assess patient bone quality [11]. In the study by Sah et al. [29], intraobserver reliability was 92% and is somewhat reassuring in light of an earlier study that reported much lower intraobserver reliability metrics [20]. We believe the higher intraobserver reliability reported by Sah et al. [29] may be because they used AP and lateral radiographs for evaluation, as opposed to the study by Mazhar et al. [20].

Limitations

The most-important limitation of the Dorr classification has been its inconsistent reliability across the studies that have evaluated it [20]. Kappa values of approximately 0.5 or less do not support the wide use of a classification system; however, two studies have found much better reliability [23, 29], with kappa values and agreement percentages easily high enough to recommend the classification’s use, as we noted earlier. In general, the studies that showed higher reliability had more-experienced reviewers and used quantitative indices such as the cortical index as an assistive measure. For readers classifying proximal femoral morphology according to Dorr et al. [6], we recommend that cortical indices be used in addition to qualitative bone assessments, and that classifications are discussed with experienced surgeons to improve reliability.

Although very early uncemented components were difficult to implant and risked causing femoral fractures in patients with poorer cortical bone quality [13, 19], making the Dorr classification essential for decision-making vis-à-vis implant selection, most recent studies have found that modern uncemented components are generally reliable, even in patients with poor (Dorr Type C) femoral cortical bone quality (Table ​(Table1)1) [5, 9, 22, 28]. This may call into question whether the Dorr classification offers as valuable a contribution to clinical decision-making in the era of contemporary components as it once did. Regardless, reliable mechanical fixation with uncemented implants cannot always be assured, and a critical evaluation of femoral geometry using Dorr’s method may help identify patients who may benefit from a cemented techique.

表1. 支持Dorr C型骨非骨水泥固定的研究

Table 1. Studies in support of uncemented fixation in Dorr C Type bone

Conclusions

Although the Dorr classification has been found to have inconsistent interexaminer and intraexaminer reliability, use of the cortical index appears to improve its reproducibility. We recommend that the Dorr classification be used with attention to lateral radiographs for classification into type and calculation of cortical indices. Although Dorr Type C bone once was thought to preclude the use of cementless fixation, studies of modern femoral stem designs have demonstrated durable fixation with this technique [5, 9, 22, 28]. Surgeons must also consider, however, that patients with Type C bone are often elderly and inactive, and the consequences of intraoperative fracture using cementless THA may result in a second surgery. Furthermore, several of these studies [5, 9, 22] demonstrating efficacy of cementless implants in poor femoral bone have had relatively few patients and the procedures were performed by experienced surgeons. As stated by Leopold [18], some of the long-term dangers of newer procedures or techniques may not be discovered until years later and would require very large sample sizes to accurately detect. We believe the Dorr classification remains useful in patient selection, particularly for lower-volume surgeons who may consider cemented techniques to decrease early mechanical loosening or femoral fractures during hip arthroplasty. We strongly emphasize the importance of preoperative templating to ensure a stem will fit the geometry of a patient’s femoral canal to decrease the risk of iatrogenic fractures in patients who undergo THA. Further investigations should be performed to identify reliable and useful assessments of a patient’s bone morphology to decrease the risk of complications such as intraoperative fracture during THA.

文献出处：Jacob Wilkerson, Navin D Fernando. Classifications in Brief: The Dorr Classification of Femoral Bone. Clin Orthop Relat Res. 2020 Aug;478(8):1939-1944. doi: 10.1097/CORR.0000000000001295.