临界髋关节发育不良Borderline DDH (5)：MRI上的股骨骨骺髋臼顶指数（FEAR）测量

临界髋关节发育不良Borderline DDH (5)：MRI上的股骨骨骺髋臼顶指数（FEAR）测量是否预测临界髋关节发育不良的不稳定性？

作者：Cécile Batailler, Jan Weidner, Michael Wyatt, Dominik Pfluger, Martin Beck

作者单位: CHU Lyon Croix-Rousse, Hospices Civils de Lyon, Lyon, France.

译者：陶可（北京大学人民医院骨关节科）

摘要

目的：临界髋关节发育不良型既可以表现为稳定，也可以表现为不稳定，这使得手术决策具有挑战性。虽然不稳定髋关节最好通过髋臼重新定位来治疗，但稳定的髋关节可以通过关节镜治疗。几个成像参数可以帮助确定适当的治疗方法，包括在普通X线片上测量的股骨-骨骺髋臼顶(FEAR)指数。本研究的目的是评估MRI上FEAR指数与其放射学测量相比的可靠性和敏感性。

患者和方法：定义了在MRI上测量FEAR指数的技术并验证了其可靠性。一项回顾性研究评估了三组20名患者：一组不稳定的“临界发育不良型髋关节”，其外侧中心边缘角(LCEA)小于25°，通过髋臼周围截骨术成功治疗；一组稳定的“临界发育不良型髋关节”，其LCEA小于25°，通过撞击手术成功治疗；另一组无症状对照组，其LCEA在25°至35°之间。在标准X线片和MRI上均进行了以下测量：LCEA、髋臼指数、股骨前倾角和FEAR指数。

结果：FEAR指数在MRI和X线片上均表现出极好的观察者内和观察者间可靠性。X线片上的FEAR指数比MRI上的更可靠。与不稳定临界组（平均7.9°（标准差6.8°））相比，稳定临界组的MRI上的FEAR指数较低。在FEAR指数截止值为2°的情况下，使用放射学FEAR指数可以正确识别90%的患者为稳定或不稳定，而使用MRI上的FEAR指数则为82.5%。与MRI相比，FEAR指数在普通X线片上更能预测不稳定性。

结论：MRI上测量的FEAR指数比X线片上测量的FEAR指数更不可靠，灵敏度也更低。放射学FEAR指数的2°临界值预测髋关节稳定性的概率为90%。

讨论

本研究的主要结果是，在普通骨盆X线片上测量FEAR指数比在MRI上具有更高的灵敏度和可靠性。

当LCEA在20°和25°之间时，区分稳定和不稳定髋关节可能具有挑战性。决定采用哪种手术治疗主要取决于髋关节的稳定性或不稳定性。通过新的影像学征象来改善诊断不仅有意义，而且必不可少。

随着关节镜实践的进步，在同侧关节镜髋关节手术失败后，随后接受PAO截骨以矫正症状性髋关节发育不良的患者比例从2008年到2015年增加了1.92倍。临界髋关节发育不良患者的手术选择包括关节镜盂唇修复和关节囊闭合/折叠，有时还伴有凸轮切除术，或伴有或不伴有盂唇修复/凸轮切除术的PAO截骨术。治疗方案的选择受到多种因素的影响，包括患者年龄、患者偏好，尤其是外科医生是否认为髋关节不稳定。在骨性结构覆盖不足的情况下，进行髋关节镜检查的风险是因不稳定、髋关节脱位或关节炎进展而导致的持续疼痛。这必须与PAO截骨并发症的风险相平衡，即使是由经验丰富的外科医生进行手术，轻度发育不良患者的临床改善效果也会较低。有报道称，临界髋关节的保髋手术失败，因为确定不稳定或稳定的髋关节可能很困难，并可能导致治疗不当。如果在髋关节发育不良的同时发现潜在的FAI，那么不适当的撞击手术，不注意发育不良，可能会增加不稳定的症状。需要制定严格的患者选择标准，才能考虑对临界髋关节发育不良进行髋关节镜检查。最近的一项研究回顾了1368例髋臼发育不良髋关节镜检查，发现在某些明确和选定的临界髋关节发育不良病例中，可以考虑单独使用髋关节镜检查，但必须仔细注意保存盂唇和关节囊。然而，许多研究表明，如果发育不良为中度或重度，且患者选择不太严格，则临床结果不佳，并且存在医源性不稳定的风险。

髋关节的稳定性通常使用LCEA进行评估；然而，仅凭这种测量不足以评估临界髋关节，需要使用其他评估参数。一些放射学或MRI参数直接由股骨头移位引起，因此高度提示髋关节不稳定，例如髂坐线距离增加、Shenton线断裂或后下关节间隙存在钆（髋关节造影检查）。不稳定髋关节可能存在其他放射学或MRI征象，但预测性较差，例如LCEA介于20°和25°之间、AI大于10°、髋外翻、股骨前倾或盂唇体积增大。其他参数可评估髋关节发育不良的严重程度，尤其是全髋关节置换术的实施。Wyatt等描述的放射学FEAR指数表示髋关节生长过程中股骨近端骨骺板的合力。该指数反映了髋关节在生长过程中的功能行为（稳定或不稳定）。Wyatt等报道称，如果患者出现髋关节疼痛和临界发育不良（定义为LCEA20°至25°），则放射学FEAR指数小于5°表示髋关节稳定的可能性为80%。FEAR指数的可靠性非常好，至少与LCEA或AI的可靠性一样好。FEAR指数优于LCEA的原因可能是难以定义髋臼源边缘，正如已经提到的。在本研究中，放射学FEAR指数的截止值为2°可预测稳定性，90%的患者被正确判断为稳定或不稳定。随着这种测量方法在临界髋关节发育不良的X线片上的应用越来越广泛，正常值和截止值的定义也越来越明确。

有时，FEAR指数很难在X线片上测量。事实上，骨骺瘢痕的界限有时很难确定，并可能导致测量误差。因此，我们评估了FEAR指数的可靠性，并由两名独立观察员进行评估。在我们的研究和Wyatt等的研究中，X线片和MRI FEAR指数表现出极好的观察者间和观察者内可靠性，并且被证明优于AI或LCEA。FEAR指数的假阳性或阴性率主要是由于在某些情况下难以进行测量。MRI是一种非常准确的检查，尤其是带有放射状切口的MR关节造影，这是目前评估原生髋关节关节内病变的最佳术前成像研究。骨骺瘢痕在MRI上很容易被看到，这似乎是提高该参数灵敏度的有希望的途径。然而，我们的研究表明，MRI的可靠性和灵敏度低于普通的放射学测量。可以提出几种解释。在X线片上，骺板瘢痕代表每个额叶切片的不同骺板瘢痕的平均值，因此也代表生长过程中作用于整个股骨头的力量平衡的平均值。对于MRI上的FEAR指数，为了获得一个简单可靠的指数，我们选择仅在一个图像切片上测量FEAR指数。增加测量次数会增加出错的风险。与静态X线片相比，3D MRI重建的准确性会降低。然而，根据所选的额叶切片，骺板瘢痕的形状在各个切片之间可能有所不同，并且骺板瘢痕的方向可能会发生几度的变化。髋臼也可能出现同样的问题，因为它可能会根据与髋臼窝的距离而发生显著变化。此外，Wyatt等指出，FEAR指数代表髋关节的力量平衡。仅使用股骨头中部骨骺瘢痕的轴线主要考虑股骨头上部和顶部之间施加的力量。如果患者因不稳定而出现股骨头轻微半脱位，则矢状图上位于髋臼12点钟位置的切片与位于股骨头12点钟位置的切片不同（图4）。因此，骨骺瘢痕中央部分的测量可能不正确。股骨旋转或外展可能引起的变化与X线片相同。

我们的研究有一些局限性。首先，纳入的患者数量很少，无法匹配某些参数（LCEA、性别）。尽管如此，有症状的临界髋关节患者并不常见，需要进行完整的影像学检查才能比较X线片和MRI。不稳定是由多种因素和手术后症状的发展决定的。因此，该诊断是根据参数关联进行的，并构成了不稳定性的功能定义。这项研究是回顾性的，因此我们可以显示关联但不能做出预测。此外，没有评估某些参数，例如全身韧带松弛、肌肉调节或体重指数。两年的随访似乎太短了。然而，当康复没有进展时，通常会在3到6个月内怀疑结果不佳。相反，1到1年半后，髋关节通常在功能和疼痛方面达到稳定状态。因此，两年的限制似乎是合理的，尽管可能更倾向于更长的随访时间。

总之，MRI上测量的FEAR指数不如X线片上测量的FEAR指数可靠。此外，与MRI相比，FEA 指数是X线片上不稳定性的更好的预测指标。放射学FEAR指数的2°截止值预测髋关节稳定性的概率为90%。放射学FEAR指数是辅助复杂髋关节不稳定诊断的可靠参数。需要前瞻性评估该测量值以预测渐进性不稳定。

Fig 1 a) Anteroposterior pelvic radiograph and b) hip MRI in frontal and sagittal views with a positive Femoro-Epiphyseal Acetabular Roof (FEAR) index (angle between the physeal scar and the sclerosis of the sourcil) for a patient with a borderline dysplastic hip (lateral centre-edge angle = 17.2°, acetabular index = 12.6°) treated with periacetabular osteotomy.

图1 a)前后位骨盆X线片和b)髋关节正位和矢状位MRI，股骨-骨骺髋臼顶(FEAR)指数（骨骺瘢痕与髋臼硬化之间的角度）为阳性，适用于接受髋臼周围截骨术治疗的临界髋关节发育不良患者（外侧中心边缘角 = 17.2°，髋臼指数 = 12.6°）。

Fig 2 a) Anteroposterior pelvic radiograph and b) hip MRI in frontal and sagittal views with a negative Femoro-Epiphyseal Acetabular Roof (FEAR) index (angle between the physeal scar and the sclerosis of the sourcil) for a patient with a borderline dysplastic hip (lateral centre-edge angle = 24°, acetabular index = 9°) treated with impingement surgery.

图2 a)前后位骨盆X线片和b)髋关节正面和矢状面MRI，股骨-骨骺髋臼顶(FEAR)指数（骨骺瘢痕与髋臼硬化之间的角度）为阴性，适用于接受撞击手术治疗的临界髋关节发育不良患者（外侧中心边缘角 = 24°，髋臼指数 = 9°）。

Fig 3 Boxplots of a) the radiological Femoro-Epiphyseal Acetabular Roof (FEAR) index and b) the FEAR index on MRI, comparing all three groups. The boxplots are constituted of several data. The median (middle quartile) marks the mid-point of the data and is shown by the line that divides the box into two parts. The middle box represents the middle 50% of scores for the group, delineated by the lower and the upper quartiles. The upper and lower whiskers represent the highest and lowest value excluding outliers. The triangular plot points are the outliers or the extremes.

图3 箱线图，a)放射学股骨-骨骺髋臼顶(FEAR)指数和b) MRI上的FEAR指数，比较所有三组。箱线图由多个数据组成。中位数（中间四分位数）标记数据的中点，由将箱子分成两部分的线表示。中间框代表该组中间50%的分数，由下四分位数和上四分位数划定。上下顶部代表不包括异常值的最高值和最低值。三角形图点是异常值或极值。

Fig 4 MRI in sagittal and frontal view of a borderline dysplastic hip. The frontal slide is located at 12 o’clock on the acetabulum on the sagittal view. This did not correspond to the 12 o’clock position of the femoral head, due to small subluxation of the femoral head.

图4 临界髋关节发育不良的矢状位和正位MRI。正面滑动位于矢状位上髋臼的12点钟位置。由于股骨头有轻微的半脱位，这与股骨头的12点钟位置不符。

Femoral osteotomy for osteonecrosis of the femoral head

Abstract

Aims: A borderline dysplastic hip can behave as either stable or unstable and this makes surgical decision making challenging. While an unstable hip may be best treated by acetabular reorientation, stable hips can be treated arthroscopically. Several imaging parameters can help to identify the appropriate treatment, including the Femoro-Epiphyseal Acetabular Roof (FEAR) index, measured on plain radiographs. The aim of this study was to assess the reliability and the sensitivity of FEAR index on MRI compared with its radiological measurement.

Patients and methods: The technique of measuring the FEAR index on MRI was defined and its reliability validated. A retrospective study assessed three groups of 20 patients: an unstable group of ‘borderline dysplastic hips‘ with lateral centre edge angle (LCEA) less than 25° treated successfully by periacetabular osteotomy; a stable group of ‘borderline dysplastic hips‘ with LCEA less than 25° treated successfully by impingement surgery; and an asymptomatic control group with LCEA between 25° and 35°. The following measurements were performed on both standardized radiographs and on MRI: LCEA, acetabular index, femoral anteversion, and FEAR index.

Results: The FEAR index showed excellent intraobserver and interobserver reliability on both MRI and radiographs. The FEAR index was more reliable on radiographs than on MRI. The FEAR index on MRI was lower in the stable borderline group (mean -4.2° (sd 9.1°)) compared with the unstable borderline group (mean 7.9° (sd 6.8°)). With a FEAR index cut-off value of 2°, 90% of patients were correctly identified as stable or unstable using the radiological FEAR index, compared with 82.5% using the FEAR index on MRI. The FEAR index was a better predictor of instability on plain radiographs than on MRI.

Conclusion: The FEAR index measured on MRI is less reliable and less sensitive than the FEAR index measured on radiographs. The cut-off value of 2° for radiological FEAR index predicted hip stability with 90% probability. Cite this article: Bone Joint J 2019;101-B:1578-1584.

Discussion

The main result of this study is that the FEAR index is measured with greater sensitivity and reliability on plain pelvic radiographs than on MRI. Differentiating a stable versus unstable hip can be challenging when the LCEA is between 20° and 25°. Deciding upon a particular surgical treatment depends principally on the stability or instability of the hip.5-7 Improving the diagnosis by new imaging signs is not only interesting but is also essential.

As arthroscopy practice has advanced, the proportion of patients undergoing a subsequent PAO for the correction of symptomatic acetabular dysplasia following a failed ipsilateral arthroscopic hip procedure, has increased by 1.92-fold from 2008 to 2015.8 Surgical options for patients with a borderline dysplastic hip include arthroscopic labral repair with capsular closure/plication, and sometimes with cam resection, or PAO with or without concomitant labral repair/cam resection. The treatment chosen is influenced by multiple factors including patient age, patient preference, and especially whether the surgeon believes the hip is unstable or not.10 The risk of hip arthroscopy in the setting of inadequate bone coverage is persistent pain due to instability, hip dislocation, or arthritic progression of the joint.18 This must be balanced with the risk of complications with PAO, even when performed by experienced surgeons, and lower incremental clinical improvement in patients with mild dysplasia. There are report cases of failure of hip preservation surgery on borderline hips, because determination of an unstable or stable hip can be difficult and may lead to incorrect treatment.8,19-21 If potential FAI is found concurrently with hip dysplasia then inappropriate impingement surgery, without attention to the dysplasia, can increase the symptoms from instability. Stringent criteria for patient selection are needed to consider hip arthroscopy for borderline dysplastic hips.22,23 A recent review, on 1368 hip arthroscopies on acetabular dysplasia, found that the isolated use of hip arthroscopy may be considered in some defined and selected cases of borderline acetabular dysplasia, when careful attention is paid to labral and capsular preservation.24 However, many studies have described poor clinical outcomes and the risk of iatrogenic instability, if the dysplasia is moderate or severe, and if the patient selection is not very restricted.24

Stability of the hip is classically assessed by using the LCEA;18 nevertheless, this measurement alone is insufficient for borderline hip and the use of other assessment parameters is required. Some radiological or MRI parameters are directly due to femoral head migration and are therefore highly indicative of hip instability, such as an increase of the distance from the ilioischial line, a break in Shenton’s line, or the presence of Gadolinium in the posteroinferior joint space.24 Other radiological or MRI signs can be present in unstable hip but are less predictive, such as LCEA between 20° and 25°, AI greater than 10°, coxa valga, femoral anteversion, or increased labral volume. Other parameters assess the severity of hip dysplasia, in particular for the implementation of total hip arthroplasty.25 The radiological FEAR index, described by Wyatt et al,13 represents the resultant of the forces across the proximal femoral physis during hip growth. This index reflects the functional behaviour (stable or unstable) of the hip during growth. Wyatt et al13 reported that if a patient presents with hip pain and borderline dysplasia (defined as a LCEA 20° to 25°), a radiological FEAR index less than 5° indicates an 80% probability that the hip is stable. The reliability of the FEAR index was excellent and at least as good as the reliability of LCEA or AI. The superiority of the FEAR index compared with LCEA may be because of difficulty in defining the edge of the acetabular sourcil, as has been alluded to.26 In this study, a cut-off value of 2° for radiological FEAR index predicts stability, with 90% of patients correctly identified as stable or unstable. With the wider use of this measurement on radiographs for borderline dysplastic hip, normal and cut-off values are becoming better defined.

Occasionally, the FEAR index is difficult to measure on radiographs. Indeed, the limits of the physeal scar are sometimes hard to determine and can lead to measurements errors. Accordingly, we assessed the reliability of the FEAR index was assessed with two independent observers. The radiographic and MRI FEAR indices showed excellent inter- and intraobserver reliability in our study and in the study by Wyatt et al,13 and was shown to be superior to the AI or LCEA. The false positive or negative rates of the FEAR index are mainly due to the difficulty in taking measurements in some cases. The MRI is a very accurate investigation, particularly the MR arthrogram with radial cuts, which is presently the best available preoperative imaging study to evaluate intra-articular lesions of native hip.27-30 The physeal scar is easily visualized on MRI and it seemed a promising route to improve the sensitivity of this parameter. Nevertheless, our study has demonstrated that MRI is less reliable and less sensitive than plain radiological measurement. Several explanations can be proposed. On radiographs, the physeal scar represents a mean of different physeal scars of each frontal slice, and thus a mean of the balance of forces acting on the whole femoral head during growth. For the FEAR index on MRI, in order to obtain an easy and reliable index, we have chosen to measure the FEAR index on only one image slice. Increasing the number of measurements increases the risk of errors. MRI reconstruction in 3D loses accuracy compared with a static radiograph. However, according to the chosen frontal slice, the shape of the physeal scar can vary between slices and the orientation of the physeal scar can change by several degrees. The same problem can arise for the acetabular sourcil, which can change markedly according to the distance to the acetabular fossa. Additionally, Wyatt et al13 stated that the FEAR index represents the balance of forces on the hip. Using only the axis of the physeal scar in the middle of the femoral head mainly considers the forces exerted between the superior part of the femoral head and the superior part of the roof. If the patient has a small subluxation of the femoral head due to instability, the slice located at 12 o’clock on the acetabulum on the sagittal view is not the same as the slide located at 12 o’clock on the femoral head (Fig. 4). Thus, the measure of the central part of the physeal scar can be incorrect. The variations potentially induced by the femoral rotation or abduction are the same as with radiographs.

Our study has some limitations. First, the number of patients included was low, without possible matching of some parameters (LCEA, sex). Nevertheless, patients with symptomatic borderline hips are uncommon and complete imaging examinations were necessary to compare radiographs and MRI. The instability was determined by several factors and by the evolution of symptoms after the surgery. Thus, this diagnosis was performed on an association of parameters and constitute a functional definition of instability. This study was retrospective, and thus allows us to show associations but not to make predictions. Moreover, some parameters were not assessed, such as the generalized ligamentous laxity, muscular conditioning, or body mass index. The follow-up of two years may seem too short. However, a poor result usually is suspected within three to six months, when rehabilitation is not progressing. In contrast, after one to 1.5 years the hip has usually reached a steady state concerning function and pain. Therefore, a two-year limit seems rational, although a longer follow-up might be preferred.

In conclusion, the FEAR index measured on MRI is less reliable than the FEAR index measured on plain radiographs. Moreover, the FEAR index is a better predictor of instability on plain radiographs compared with MRI. The cut-off value of 2° for the radiological FEAR index predicted hip stability with 90% probability. This radiological FEAR index constitutes a reliable parameter to aid the complex diagnosis of hip instability. This measurement needs to be assessed prospectively for the prediction of progressive instability.

文献出处：Cécile Batailler, Jan Weidner, Michael Wyatt, Dominik Pfluger, Martin Beck. Is the Femoro-Epiphyseal Acetabular Roof (FEAR) index on MRI a relevant predictive factor of instability in a borderline dysplastic hip? Bone Joint J. 2019 Dec;101-B(12):1578-1584. doi: 10.1302/0301-620X.101B12.BJJ-2019-0502.R1.